The Boeing X-32 is the only aircraft in this series that was built to lose or win a competition rather than to answer a research question, and it lost. Every other X-plane so far existed to find something out. The X-31 flew adversarial engagements to learn whether post-stall manoeuvring wins. The X-30 was cancelled because its central quantity could not be established. The X-32 was a competitor, flown against the Lockheed Martin X-35 in a fly-off for the largest military aircraft procurement in history, and on 26 October 2001 the Department of Defense chose the other one. This is the thirty-third article in the X-Planes series, following the X-1, the X-2, the X-3, the X-4, the X-5, the X-6, the X-7, the X-8, the X-9, the X-10, the X-11, the X-12, the X-13, the X-14, the X-15, the X-16, the X-17, the X-18, the X-19, the X-20, the X-21, the X-22, the X-23, the X-24, the X-25, the X-26, the X-27, the X-28, the X-29, the X-30, and the X-31.

The easy misreading is that the X-32 lost because direct lift does not work. It works. It had been working since the Hawker Siddeley Harrier entered service in 1969, and the X-32B hovered and landed vertically. Nothing about the mechanism was in doubt.

What was being decided was something else, and it has two halves. The first is a question in propulsion physics with a clean answer that this article derives from published numbers, drawing on a research base that the National Aeronautics and Space Administration had been building since the 1970s. The second is a question about evidence, namely whether two demonstrators, neither of which was the aeroplane being bought, could settle a choice about an aircraft that did not yet exist.

The Research Question

The keystone is what a fly-off decides and on what evidence.

A research aircraft is dimensioned against an unknown. A competitor is dimensioned against a rival, and the two are not the same discipline. The X-32 had to be good enough at everything and better at something, against an opponent whose design it could not see, under a set of criteria written by a customer buying three different aircraft for three different services.

The binding question is therefore evidentiary rather than physical. Both companies could build an aeroplane that hovered. What neither could do was build the aeroplane it was proposing, because the demonstrators were concept demonstrators, funded to reduce risk and never meant as prototypes. A demonstrator that differs from the proposal in the feature under test is evidence about something other than the proposal, and this article’s central historical finding is that the X-32’s wing was such a feature.

The Physical Half Has a Clean Answer

Two ways exist to hold a fighter up on its engine. The direct-lift approach sends the engine’s own exhaust downward through vectoring nozzles, the Harrier’s method and Boeing’s. The lift-fan approach takes shaft power off the engine, drives a large fan mounted behind the cockpit, and adds a second cold stream, which was Lockheed Martin’s.

Those are not two arrangements of the same thing. They are two points on a curve, and the curve has a known shape. All of the propulsion argument in this article follows from one relation derived in the sizing section below, and the relation is undisputed. It has been in the textbooks since momentum theory was written down.

The Evidentiary Half Remains Open

The second half is harder, and this article spends its effort there. A fly-off produces one comparison. It is not a sample, it is not repeatable, and the thing compared is not the thing being bought. Asking what such an exercise establishes is a question about whether the quantity measured is the quantity that matters, rather than about sampling error.

The previous article in this series asked a related question and got a different kind of answer. The X-31’s combat evaluation flew a series of engagements and the difficulty was that a finite sample carries a wide interval. Here the sample size is one, and the difficulty is that the one trial was not a trial of the proposed aircraft.

The Contemporary Literature collects the acquisition studies of what competitive prototyping can establish in its cluster on defence acquisition, competition, prototyping and cost.

Programme Origin

Three Aircraft, One Airframe

The Joint Strike Fighter programme set out to build one aircraft for three services with three incompatible requirements. The Air Force wanted a conventional runway fighter to replace the F-16. The Navy wanted a carrier aircraft, which means a stronger structure, a bigger wing and an approach speed low enough to catch a wire. The Marine Corps and the Royal Navy wanted a short takeoff and vertical landing aircraft to replace the Harrier, which means carrying a lift system in an airframe the size of the Air Force variant at the cost of fuel volume.

The STOVL requirement drives the rest of the design, because it is the only one that cannot be met by scaling. A carrier aircraft is a heavier version of a land aircraft. A vertical-landing aircraft is a different aeroplane wearing the same skin.

Studies of commonality between variants form the cluster on commonality, product families and requirements, later in this article.

The Programme That Preceded It

The competition descends from two earlier efforts. The Common Affordable Lightweight Fighter work at the Defense Advanced Research Projects Agency explored whether a single design could serve several services, and the Joint Advanced Strike Technology programme consolidated a set of service-specific studies into one. The concept demonstration contracts were awarded to Boeing and Lockheed Martin in November 1996, and McDonnell Douglas, whose entry used a gas-coupled lift fan, was eliminated at that point.

That elimination means the fly-off was already the second round. The field had been narrowed from three to two before either surviving aircraft existed.

Writing on the programme, from the Joint Advanced Strike Technology studies onward, makes up the cluster on the Joint Strike Fighter programme and its demonstrators in the survey below.

What Each Company Brought

Boeing’s design used a single large delta wing with 55 degrees of leading-edge sweep, a chin inlet under the nose, and a direct-lift STOVL system in which a valve diverted the core exhaust to a pair of vectoring nozzles near the centre of gravity.

Lockheed Martin’s design used a conventional wing and tail, a shaft-driven lift fan behind the cockpit, a three-bearing swivel module at the tail, and roll posts in the wings [Lockheed Martin F-35B propulsion ground test release].

The chin inlet is a consequence rather than a choice. A direct-lift aircraft must put its lift nozzles at the centre of gravity, which puts the engine in the front portion of the fuselage, which puts the inlet forward and low [Jenkins, Landis and Miller, American X-Vehicles]. The configuration follows from the propulsion decision, a first sign that the two entries were not two styles of the same aeroplane.

For the lineages each company drew on, see the clusters on lift fans, lift engines, ejectors and remote lift and on the Harrier, the Pegasus engine and the vectored-thrust lineage in The Contemporary Literature.

Sizing From First Principles

This section derives the relation the competition turned on, checks three published numbers against each other, and computes the quantity that settled the decision.

The Relation

Static thrust is mass flow times jet velocity,

\[T = \dot{m} V_j\]

and the power added to the stream is the rate of increase of its kinetic energy,

\[P = \tfrac{1}{2} \dot{m} V_j^{2}\]

Eliminating the velocity between them gives the relation that governs the choice,

\[T = \sqrt{2 P \dot{m}}\]

For a fixed power, thrust rises as the square root of the mass flow. Equivalently, writing it the other way,

\[T = \frac{2P}{V_j}\]

halving the jet velocity doubles the thrust for the same power.

Mass flow ratio Thrust ratio at fixed power Power ratio at fixed thrust
1.00 1.000 1.000
2.00 1.414 0.500
2.24 1.497 0.446
4.00 2.000 0.250

That table is the entire case for the lift fan and it fits on four lines. A lift fan spends shaft power accelerating a large cold mass flow slowly. A direct-lift system spends the same power accelerating a smaller hot flow quickly. The first produces more thrust from the same core, and the other differences between the two aircraft follow from it.

Modern work on momentum theory appears below in the cluster on momentum theory, rotors, propellers and hover performance.

The Disc-Loading Form of the Same Statement

The relation is more useful expressed through the area the flow passes through, and the momentum theory that governs it has been the standard treatment of a static disc since the 1970s, as in Azuma and Kawachi 1975, with the actuator-disc optimum in hover worked out more recently. It is the disc loading, which momentum theory relates to the induced velocity. The relations used here are the standard ones set out in Leishman on helicopter aerodynamics and in Hill and Peterson on propulsion. For a disc of area $A$ producing thrust $T$ in still air, momentum theory gives the velocity induced at the disc,

\[V_i = \sqrt{\frac{T}{2 \rho A}}\]

and the flow reaches twice that velocity far downstream. The ideal power is the thrust times the induced velocity,

\[P_{\text{ideal}} = T V_i = T \sqrt{\frac{T}{2 \rho A}}\]

So the power required for a given lift rises as the square root of the disc loading. A system that pushes its air through a small hole pays for it in power, in exhaust velocity, in noise, in ground erosion and in temperature.

Three Published Numbers That Were Never Published Together

The lift fan’s diameter, its cold thrust and its shaft power appear in different places, and taken together they imply a figure of merit that has to be a number a real fan can achieve.

Quantity Value
Lift fan diameter 50 inches
Disc area 13.64 sq ft
Cold thrust 20,000 lbf
Shaft power delivered 29,000 hp

The disc loading is 1,467 pounds per square foot, the induced velocity is

\[V_i = \sqrt{\frac{20{,}000}{2 (0.0023769)(13.64)}} = 555.5 \ \text{ft/s}\]

with a far-field velocity of 1,110.9 feet per second, and the ideal power is

\[P_{\text{ideal}} = (20{,}000)(555.5) = 1.111 \times 10^{7} \ \text{ft lbf/s} = 20{,}199 \ \text{hp}\]

That is 20,199 horsepower of ideal power. Dividing by the delivered shaft power gives

\[\text{FM} = \frac{20{,}199}{29{,}000} = 0.697\]

The same two relations fix the mass flow the fan moves, since the thrust is the mass flow times the far-field velocity,

\[\dot{m} = \frac{T}{2 V_i} = \frac{20{,}000}{2(555.5)} = 18.00 \ \text{slug/s} = 579 \ \text{lb/s}\]

and the power loading follows as 0.690 pounds of thrust per horsepower delivered.

A figure of merit near 0.7 is what a good rotor achieves in hover. The measure is the standard one used in rotor design optimisation. The three numbers are mutually consistent, a check to make before building an argument on them, and one that no printed source appears to have made.

The Nozzle the Direct-Lift System Would Have Needed

The X-32B’s nozzle size need not be assumed, because the question can be inverted. What nozzle area would the direct-lift system have needed for its jets to match the lift fan’s disc loading?

\[A = \frac{T}{T/A} = \frac{28{,}000}{1{,}467} = 19.09 \ \text{sq ft}\]

That is a single circular nozzle 4.93 feet across, or two nozzles each 3.49 feet across, on a fuselage 45.0 feet long and 17.3 feet tall.

The obstacle is geometric, and no engineering trade removes it. There is nowhere on a single-engine fighter to put two three-and-a-half-foot nozzles at the centre of gravity, and the exhaust passing through them would in any case be hot, where the fan’s is cold.

Taking plausible nozzle sizes instead shows how far from the fan the direct-lift system had to sit.

Two nozzles Total area Disc loading Induced velocity Loading against the fan
2.0 ft across 6.28 sq ft 4,456 lb/sq ft 968.2 ft/s 3.04
2.5 ft across 9.82 sq ft 2,852 lb/sq ft 774.6 ft/s 1.94
3.0 ft across 14.14 sq ft 1,981 lb/sq ft 645.5 ft/s 1.35

The Disc Loading Is Also the Pressure on the Ground

The table above says more than it appears to, because of an identity the article had already assembled without stating. Momentum theory gives the disc loading as

\[\frac{T}{A} = 2 \rho V_i^{2}\]

and the flow reaches twice the induced velocity far downstream, so the dynamic pressure in the fully developed jet is

\[q_{\infty} = \tfrac{1}{2} \rho (2 V_i)^{2} = 2 \rho V_i^{2} = \frac{T}{A}\]

The disc loading and the dynamic pressure in the jet are the same number. The jet impingement ground-effect literature measures that quantity directly, and its computational treatment reproduces it. A table of disc loadings is therefore also a table of the pressure each architecture imposes on whatever it is hovering over.

System Disc loading Dynamic pressure at the ground Against the fan
Lift fan 1,467 lb/sq ft 1,467 lb/sq ft 1.00
Two nozzles 3.0 ft across 1,981 lb/sq ft 1,981 lb/sq ft 1.35
Two nozzles 2.5 ft across 2,852 lb/sq ft 2,852 lb/sq ft 1.94
Two nozzles 2.0 ft across 4,456 lb/sq ft 4,456 lb/sq ft 3.04

Deck coatings, runway surfaces and the people standing near the aeroplane all feel that difference, and deriving it costs nothing extra, since the propulsion argument already needed the quantity.

The lift fan and the vectoring nozzle sit at different points on the curve, and the curve is steep.

What the Two Architectures Produced

The published totals make the consequence plain. The engine’s military rating is from the X-32’s published specification, and the lift system’s components and total are from the LiftSystem’s published component thrusts.

System Lift Source of lift
Rolls-Royce Pegasus, for reference 23,800 lbf Vectored fan and core
Direct lift, engine military rating 28,000 lbf Entirely hot core stream
Lift fan plus swivel module plus roll posts 41,900 lbf 47.7 percent cold

The lift system exceeds the Pegasus by a factor of 1.76 and the direct-lift core by 1.18. The lift fan alone contributes 20,000 pounds, the swivel module 18,000 and the roll posts 3,900.

The partition is exact,

\[L = T_{\text{fan}} + T_{\text{3BSM}} + T_{\text{posts}} = 20{,}000 + 18{,}000 + 3{,}900 = 41{,}900 \ \text{lbf}\]

with shares of 47.7, 43.0 and 9.3 percent. The published total equals the sum of its published parts, a small check worth making before relying on any of the four numbers.

Nearly half of the winning aircraft’s vertical lift came from air that never went through the engine. That is the square-root law made physical.

Engine cycles and thrust more broadly are the subject of the cluster on engine cycles, variable cycle engines and engine performance.

The Number the Competition Was About

A vertical landing is not a demonstration. It is an operational requirement with a weight attached, because an aircraft returning from a mission with unexpended weapons has to be able to land with them aboard. The quantity that matters is what can be brought back.

The landing weight is bounded by the lift divided by a control margin, and what is available for fuel and stores is whatever is left after the empty weight is paid,

\[W_{\text{land}} = \frac{L}{k} \qquad \text{and} \qquad W_{\text{allowance}} = \frac{L}{k} - W_{\text{empty}}\]

At an empty weight of 24,030 pounds and an assumed five percent control margin, so that $k = 1.05$,

Architecture Lift Maximum landing weight Allowance over empty
Direct lift, core only 28,000 lbf 26,667 lb 2,637 lb
Lift fan plus core plus posts 41,900 lbf 39,905 lb 15,875 lb

The difference is 13,238 pounds and the ratio is 6.02. The empty weight cancels from the difference, which depends only on the two lifts $L_{\text{fan}}$ and $L_{\text{direct}}$ and the margin,

\[\Delta W_{\text{allowance}} = \frac{L_{\text{fan}} - L_{\text{direct}}}{k} = \frac{41{,}900 - 28{,}000}{1.05} = 13{,}238 \ \text{lb} \qquad \text{and} \qquad \frac{15{,}875}{2{,}637} = 6.02\]

That is the competition in one line. Both aircraft can hover. One of them can come home with two and a half thousand pounds of fuel and weapons and the other with nearly sixteen thousand.

Why the Allowance Is Badly Conditioned

The allowance is a small difference between two large numbers, and that makes it fragile in a way the raw thrust figures conceal. Differentiating,

\[\frac{\partial W_{\text{allowance}} / W_{\text{allowance}}}{\partial L / L} = \frac{L/k}{W_{\text{allowance}}}\]

or the landing weight divided by the allowance.

Architecture Amplification Meaning
Direct lift 10.11 One percent of thrust is ten percent of the allowance
Lift fan 2.51 One percent of thrust is two and a half percent

The same physical loss costs the direct-lift aircraft four times as much of what it can bring home.

Because the X-32B’s STOVL lift is not published, the conclusion is tested against the assumption rather than resting on it. The engine’s military rating is an upper bound, since a direct-lift arrangement loses thrust in the ducting and the vanes.

Assumed lift Allowance After a 50 degree inlet rise Amplification
24,000 lbf −1,173 lb −2,201 lb not meaningful
26,000 lbf 732 lb −382 lb 33.83
28,000 lbf 2,637 lb 1,437 lb 10.11
30,000 lbf 4,541 lb 3,256 lb 6.29
32,000 lbf 6,446 lb 5,076 lb 4.73

The allowance is a straight line in the lift, of slope one over the margin,

\[W_{\text{allowance}} = \frac{1}{k} L - W_{\text{empty}} = 0.9524 \, L - 24{,}030\]

crossing zero at

\[L_{\text{break even}} = k \, W_{\text{empty}} = 1.05 (24{,}030) = 25{,}232 \ \text{lbf}\]

Below that lift the allowance is negative, meaning the aircraft could not land vertically at its empty weight, let alone with anything in it.

The amplification blows up as the allowance approaches zero, and no numerical artefact causes it. The shape of the problem does. A direct-lift fighter of this size operates near a singularity in its bring-back capability. A single figure of 10.11 understates the matter, because the quantity is badly conditioned across the plausible range, and no plausible assumption rescues it.

The Vehicle

The published table is thinner than for any flown aircraft in this series, and the sources disagree with one another on a basic dimension. Every figure in the table except the second span is from the X-32’s published specification, and the second span is the 9.15 metres that the same source gives in its description of the wing.

Quantity Value Metric
Length 45 ft 0.1 in 13.72 m
Wingspan, one published figure 36 ft 0 in 10.97 m
Wingspan, another published figure 30 ft 0 in 9.15 m
Height 17 ft 3.8 in 5.28 m
Wing area 590 sq ft 54.8 m²
Leading-edge sweep 55 degrees  
Empty weight 24,030 lb 10,900 kg
Maximum takeoff weight 38,000 lb 17,200 kg
Engine One Pratt and Whitney YF119-PW-614  
Military thrust 28,000 lbf 120 kN
Afterburning thrust 50,000 lbf 220 kN
Maximum speed Mach 1.2  

The Span Disagreement Is Not a Rounding Difference

Two published spans differ by 19.9 percent and they cannot both describe the same airframe. Thirty-six feet against thirty is not a conversion error and not a rounding, and the two imply materially different aeroplanes.

\[A = \frac{b^{2}}{S} = \frac{36.0^{2}}{590} = 2.197 \qquad \text{against} \qquad \frac{30.02^{2}}{590} = 1.527\]

An aspect ratio of 2.20 and one of 1.53 are different wings. The article carries both figures without choosing between them, because no source available pairs either figure with a particular airframe, although the X-32B is recorded as having a narrower span than the X-32A, and a specification sheet transcribed through several publications acquires this kind of error. The dimensional record for these aircraft is collected in the inventory of X-vehicles, which is also on the reports server.

Where the record permits a check, it passes. The two ratios that a specification sheet has to satisfy are

\[\frac{W}{S} = \frac{38{,}000}{590} = 64.41 \ \text{lb/ft}^{2} \qquad \text{and} \qquad \frac{T}{W} = \frac{28{,}000}{38{,}000} = 0.737\]

with 1.316 on afterburner, and all three are ordinary values for a fighter of this size.

Dependent Systems

The Direct-Lift Arrangement

A butterfly valve diverted the core stream to a pair of thrust-vectoring nozzles near the centre of gravity. The arrangement is a form of thrust vectoring. In conventional flight the exhaust went aft through the main nozzle. In STOVL mode it went down [Boeing X-32B first flight release]. The arrangement is the Harrier’s in principle, executed with a modern engine and a single core, where the Pegasus’s exhaust left through four rotating nozzles.

The consequence for the airframe is the chin inlet. Putting lift nozzles at the centre of gravity puts the engine in the front portion of the fuselage, which puts the intake forward and low, under the nose [Jenkins, Landis and Miller, American X-Vehicles]. That inlet is what most people remember about the aeroplane, and it follows downstream from the propulsion choice and is no styling decision, and the two entries were therefore different aircraft.

Inlets and vectoring nozzles each have a cluster in The Contemporary Literature, on supersonic inlets, intakes and airframe-propulsion integration and on nozzles, thrust vectoring and thrust reversers.

Hot Gas Ingestion Is Worse Than It Sounds

An aircraft hovering on its exhaust stands in a fountain of its own hot gas, and some of it reaches the inlet. The mechanism has two paths, and the aerodynamics of a jet close to a surface is the subject of ground effect. In the near field the jets impinge on the ground, spread outward, meet under the fuselage and rise as a fountain, which twin-jet impingement studies treat directly. In the far field the outward wall jet meets the free stream or the aircraft’s motion and rolls up into a ground vortex that carries hot gas forward and up into the intake.

The cost is thrust, and the relation is simple. A turbofan matched at a corrected operating point carries its mass flow and its thrust in the corrected forms

\[\dot{m}_{\text{corr}} = \frac{\dot{m} \sqrt{\theta}}{\delta} \qquad \text{and} \qquad T_{\text{corr}} = \frac{T}{\delta} \qquad \text{with} \qquad \theta = \frac{T_{t}}{T_{\text{ref}}}, \ \delta = \frac{p_{t}}{p_{\text{ref}}}\]

so at a fixed corrected point and a fixed inlet pressure the delivered thrust falls as the square root of inlet total temperature. This makes reingestion expensive rather than merely untidy, and the effect was being measured on lift engines by the end of the 1960s in model tests of concepts to reduce it and correlated against geometric scale and surface wind. A rise of $\Delta T$ therefore costs a fraction of thrust

\[\frac{\Delta T_{\text{thrust}}}{T} = 1 - \sqrt{\frac{T_{\text{ref}}}{T_{\text{ref}} + \Delta T}}\]

where $T_{\text{ref}}$ is the standard sea-level temperature of 59 degrees Fahrenheit, or 518.67 degrees Rankine, and $\Delta T$ is in Fahrenheit degrees.

Inlet temperature rise Thrust lost
10 degrees Fahrenheit 0.95 percent
25 degrees 2.33 percent
50 degrees 4.50 percent
100 degrees 8.44 percent
150 degrees 11.93 percent

The corrected-parameter treatment behind that relation is standard and is set out in Mattingly on engine design, with the configuration consequences in Raymer on conceptual design and the underlying aerodynamics in Kuethe and Chow.

Those look like small numbers and they are not. Apply the amplification derived above. A fifty degree rise costs 4.50 percent of lift, and the allowance that remains, written $W_{\text{allowance}}’$, is

\[W_{\text{allowance}}' = \frac{L \left(1 - \Delta T_{\text{thrust}}/T\right)}{k} - W_{\text{empty}} = \frac{28{,}000 (1 - 0.0450)}{1.05} - 24{,}030 = 1{,}437 \ \text{lb}\]

so the fraction of the allowance the rise consumes is the amplification times the thrust lost,

\[\frac{W_{\text{allowance}} - W_{\text{allowance}}'}{W_{\text{allowance}}} = \frac{L/k}{W_{\text{allowance}}} \, \frac{\Delta T_{\text{thrust}}}{T} = 10.11 \times 0.0450 = 0.455\]

which is 45.5 percent of the entire bring-back allowance, taking it from 2,637 pounds to 1,437. The same relation applied to the 2.33 percent lost to a twenty-five degree rise gives 23.5 percent.

The ingestion penalty comes off the small number, not the large one, and that sentence states the difficulty in full.

The Feedback Makes It Dangerous

A thrust deficit at hover is not a performance shortfall. It is a descent. Lift below weight gives a downward acceleration of

\[a = g \, \frac{\Delta T_{\text{thrust}}}{T}\]

which for a fifty degree rise is 1.45 feet per second squared. Integrating twice gives the sink,

\[s = \tfrac{1}{2} a t^{2} = \tfrac{1}{2} (1.45)(2)^{2} = 2.89 \ \text{ft in two seconds}\]

against 1.50 feet for a twenty-five degree rise.

And a descent is proximity to the ground, and proximity is more ingestion. The loop closes on itself. The pilot’s response is more throttle, which produces more hot gas, which is fed back into the inlet.

The temperature rise alone therefore does not measure the difficulty. A system with margin absorbs it. A system operating where its allowance is badly conditioned does not.

Two clusters below hold the experimental and computational record of hot gas ingestion and of the jet-induced ground environment, those on hot gas ingestion, reingestion and inlet temperature distortion and on jet-induced ground effects, suckdown, fountains and ground vortices.

What the Lift Fan Does About the Same Problem

The lift fan attacks hot gas ingestion three times over, and none of the three was designed for that purpose. They are consequences of the square-root law.

The exhaust is cooler, and the mixing relation says by how much. The parameters that correlate ingestion were identified early, in Krishnamoorthy 1971. Two streams combine at the mass-weighted mean of their temperatures,

\[T_{\text{mix}} = \frac{\dot{m}_c T_c + \dot{m}_h T_h}{\dot{m}_c + \dot{m}_h}\]

and the mass flows follow from the thrusts and the velocities, since $\dot{m} = T / V$.

Here the square-root law appears from the other side. The cold stream is slower, so it carries more mass per unit of thrust than the hot one. At a 47.7 percent share of the lift it carries 60.9 percent of the mass.

Cold share of thrust Cold share of mass Mixed-mean exhaust
0 percent, all direct lift 0 percent 1,200 degrees Fahrenheit
30 percent 42.3 percent 718 degrees
47.7 percent, the lift system 60.9 percent 505 degrees
60 percent 72.0 percent 379 degrees

Roughly seven hundred degrees of exhaust temperature is bought by an architecture chosen for thrust per unit of power, and the temperatures above use a representative core exit value rather than a published one, so the column is indicative and the trend is not.

The exhaust is also slower, because the disc loading is lower, and the ground vortex is driven by the wall jet’s momentum. And the cold stream is in front, since the fan sits behind the cockpit and the hot core exhausts at the tail, so the cold jet stands between the hot one and the intake [Lockheed Martin F-35B propulsion ground test release].

A design chosen for thrust per unit power turns out to solve the ingestion problem as a side effect. In this sense the competition was decided by a relation rather than by a contest.

Hover Control and the Reaction Controls

An aircraft in the hover has no aerodynamic controls, because control surfaces need dynamic pressure and there is none. Attitude has to be held by differential thrust.

The lift-fan aircraft used roll posts in the wings, contributing 3,900 pounds of lift between them and providing roll control with engine bypass air, with pitch from varying the areas of the fan inlet and the exhaust nozzle and yaw from yawing the swivel module [Rolls-Royce LiftSystem] [Lockheed Martin F-35 Lightning II].

The moment available from a pair of posts is the differential thrust on the lateral arm,

\[M = \Delta T \, y\]

so posts carrying 3,900 pounds between them at an assumed station ten feet outboard command up to 39,000 foot-pounds of roll moment at full differential.

The direct-lift aircraft had a harder problem because all of its lift came from one place. Roll control requires either bleed-air reaction jets or differential nozzle modulation, and the first of those has a price that is paid before any moment is produced. Bleeding a fraction $b$ of the mass flow removes that fraction of the thrust,

\[L_{\text{after bleed}} = (1 - b) L\]

and the loss comes off the allowance with the amplification derived earlier.

Bleed fraction Lift lost Allowance remaining
0 percent 0 lb 2,637 lb
2 percent 560 lb 2,103 lb
4 percent 1,120 lb 1,570 lb
6 percent 1,680 lb 1,037 lb

A four percent bleed costs forty percent of the bring-back allowance, and the roll control it pays for has not yet been used to do anything. The lift-fan aircraft takes its roll control from posts that are already producing lift, so the same function costs it nothing it was not already spending.

Hover control and reaction controls fall within the cluster on handling qualities, flight control and hover control.

The Wing Boeing Did Not Propose

Boeing’s demonstrators flew a large single-piece composite delta with 55 degrees of leading-edge sweep and no horizontal tail. The production proposal did not use that wing. It used a conventional wing with a canted twin tail, and the change was made before the X-32 ever flew.

That fact is the most important one in this article and it is not a propulsion fact.

A concept demonstrator exists to reduce the risk of a proposal. If the demonstrator does not carry the proposal’s configuration in the feature under examination, then flying it establishes something about a different aeroplane. The X-32 demonstrated that a delta-winged direct-lift aircraft could hover and go supersonic. Boeing was offering a tailed aircraft.

The customer was therefore looking at an aeroplane Boeing did not intend to build, and had to reason from it to one that did not exist, while the competitor’s demonstrator was configurationally much closer to its own proposal.

The Flight Test Record

The two aircraft flew 144 times between them, with the X-32A opening on 18 September 2000 and the X-32B on 29 March 2001, and the flight programme ending before the decision in October 2001 [Jenkins, Landis and Miller, American X-Vehicles] [Boeing X-32B flight test release].

Event Date
Concept demonstration contracts awarded November 1996
X-32A first flight 18 September 2000
X-32B first flight 29 March 2001
X-35B first short takeoff, supersonic dash and vertical landing in one flight 20 July 2001
Decision announced 26 October 2001

The X-32A demonstrated conventional flight, supersonic performance and air refuelling. [Boeing X-32A flight test release] The X-32B demonstrated hover and vertical landing [Boeing X-32B flight test release]. What neither demonstrated was both at once, because the aircraft had to be physically reconfigured between the two roles [Boeing X-32].

The Reconfiguration, Stated Precisely

This is where the article has to be careful, because the popular account overstates it and the underlying fact is damaging enough without help.

The X-32 was a single-engine aircraft whose STOVL system diverted the core exhaust. Converting the demonstrator between the conventional and the STOVL configurations was a ground operation, not a cockpit switch. The aircraft could not take off short, accelerate through the sound barrier and land vertically on the same sortie, and it did not attempt to [Boeing X-32].

The X-35B did exactly that on 20 July 2001. A short takeoff, a level supersonic dash and a vertical landing, in one flight [Lockheed Martin X-35] [National Air and Space Museum X-35B].

The evidentiary difference is not that one aircraft is faster or lifts more. It is that one of them demonstrated the integration and the other demonstrated the components. A customer buying an aircraft that must do all three in an operational sortie has been shown the thing itself in one case and its parts in the other.

What the X-32B Did Not Do

The X-32B flew its STOVL tests with some parts removed [Boeing X-32], and no source available here establishes whether it ever performed a vertical landing at full weight. This article treats the question as open and marks it accordingly in the Epistemic State.

But the arithmetic above shows what a landing below full weight would mean, and it is not a qualitative shortcoming. At an assumed 28,000 pounds of lift, the bring-back relation displayed in the section headed The Number the Competition Was About gives an allowance over empty weight of 2,637 pounds before any ingestion penalty, and the break-even relation displayed in the section that follows it puts the lift at which the allowance vanishes entirely at 25,232 pounds. A demonstrator flying with instrumentation, ballast and test equipment aboard is not at its empty weight.

The jet screen fitted to hold hot gas away from the intake drew its air from the engine [Boeing X-32], and that air and the screen’s weight both come off the same small number.

Comparison With Ground Prediction

The Prediction That Mattered Was Not Aerodynamic

In most articles in this series this section compares a wind tunnel against flight. Here the comparison that decided the outcome was between a prediction about a production aircraft and the evidence a demonstrator could supply, and the two are not commensurable.

The ground prediction for hot gas ingestion was, and remains, difficult. The phenomenon involves an impinging jet, a wall jet, a fountain, a ground vortex and an inlet, at full-scale temperatures, in a flow field that depends on the height above the ground and on any wind. Scale models mispredict it because the temperature ratios and the Reynolds numbers do not scale together.

The NASA research base on this is substantial and predates the competition by two decades, and it explains why the physics was understood well enough that neither company was surprised in principle. What could not be settled on the ground was the margin. That research base is catalogued in the cluster on jet-induced ground effects, suckdown, fountains and ground vortices under The Contemporary Literature, where 85 of its 143 records date from 1970 to 1995.

Where the Two Demonstrators Sat Relative to Their Proposals

  Boeing Lockheed Martin
Demonstrator wing Large delta, no horizontal tail Conventional wing and tail
Proposed wing Conventional wing, canted twin tail Conventional wing and tail
STOVL and supersonic in one sortie No, reconfiguration required Yes, demonstrated 20 July 2001
Lift architecture demonstrated The proposed one The proposed one

Both companies demonstrated their propulsion architecture and only one demonstrated its airframe. That asymmetry answers what the fly-off decided, and it answers in terms of evidence rather than aeroplanes.

The cluster on defence acquisition, competition, prototyping and cost, cited above for competitive prototyping, also holds the acquisition studies of prototypes and proposals.

What the Data Changed

The Winner Acquired a Literature and the Loser Did Not

This article’s second finding concerns the literature itself, and it is measurable.

The reference set this article cites holds 3,528 research records from the NASA reports server, the Defense Technical Information Center and the Crossref registry. Counting the titles of those records that contain each term gives the following, and anyone can repeat the count on the cited set.

Term in the title Records
X-32 1
X-35 6
F-35 38
Joint Strike Fighter 72
Harrier or Pegasus 46

Exactly one of those 3,528 records carries the X-32 in its title, and it was written by the engine supplier rather than the airframer. It reports testing of the Rolls-Royce lift system for the X-32B, in 2002, after the competition was over [Roberts 2002].

The winner’s record runs from 2002 to 2026. The loser’s stops at one. Writing the asymmetry as a ratio,

\[R = \frac{N_{\text{winner}}}{N_{\text{loser}}} = \frac{38}{1} = 38\]

against two aircraft that flew in the same years, under the same programme, for the same customer.

The count does not say that Boeing did no engineering. It measures what becomes public. An aircraft that enters production is written about for twenty years by the people who build it, operate it, modify it and study it. An aircraft that loses a competition is written about by almost nobody, because its proprietary data stays proprietary and there is no operating community to generate questions.

The consequence for this article is uncomfortable and is stated rather than hidden. The technical case made here depends on published numbers for the winning system and on an assumed upper bound for the losing one, because the losing one’s numbers were never published. The asymmetry in the evidence available to a historian is a direct inheritance of the asymmetry in the decision.

The X-32, X-35, F-35 and Joint Strike Fighter titles counted here are listed in the cluster on the Joint Strike Fighter programme and its demonstrators.

The Architecture Won and Kept Winning

The shaft-driven lift fan now powers the first operational supersonic STOVL fighter, and the arrangement demonstrated in 2001 is the arrangement flying on the F-35 today. Its designers received the Collier Trophy for 2001.

The direct-lift approach did not fail. It stopped being competitive, which is a different statement. The Harrier flew for decades on direct lift and did useful work, and the same square-root law, applied to a heavier aeroplane where the allowance runs out, explains why direct lift was not the answer for a supersonic aircraft.

What the Competition Format Itself Established

The concept demonstration phase is now a reference case in acquisition literature, a field whose institutional history is set out in Gansler on the defence industry and whose cost-growth folklore is collected in Augustine’s laws, cited both as evidence that competitive prototyping produces better decisions and as evidence that it produces expensive ones. The programme that followed acquired a reputation for cost growth that the fly-off did not prevent.

That point cuts against the natural reading of this article. The fly-off made a defensible technical choice, on the best evidence available, and the resulting programme still exceeded its estimates by a wide margin. A good decision procedure on the propulsion question did not produce a good outcome on cost, because the two questions were not the same question.

That literature is surveyed under defence acquisition, competition, prototyping and cost in The Contemporary Literature.

The Contemporary Literature

Cluster Records
The Joint Strike Fighter programme and its demonstrators 118
The Harrier, the Pegasus engine and the vectored-thrust lineage 85
Hot gas ingestion, reingestion and inlet temperature distortion 76
Jet-induced ground effects, suckdown, fountains and ground vortices 143
Jet impingement and jet flow physics 120
Ship decks, landing surfaces and shipboard operations 117
Lift fans, lift engines, ejectors and remote lift 220
Nozzles, thrust vectoring and thrust reversers 419
Momentum theory, rotors, propellers and hover performance 213
Ducted fans and ducted-fan vehicles 117
Distributed and electric propulsion and electric vertical flight 156
Supersonic inlets, intakes and airframe-propulsion integration 243
Engine cycles, variable cycle engines and engine performance 278
Defence acquisition, competition, prototyping and cost 280
Commonality, product families and requirements 88
Decision analysis, selection and cost-effectiveness 47
Digital engineering, model-based systems engineering and machine learning 87
Low observability and signatures 32
Automatic and autonomous landing and guidance 18
Handling qualities, flight control and hover control 235
V/STOL and STOVL aircraft concepts, programmes and design studies 267
Flight test, instrumentation and system identification 14
Fighter and supersonic aircraft design 104
High-lift and powered-lift aerodynamics 51
Total 3,528

The X-32 flew before three of the fields that now own its questions existed, and one of those fields exists because of the aircraft that beat it.

Powered lift became an electric problem

The square-root law is the reason the electric vertical-takeoff industry looks the way it does. Every configuration in that field spreads its lift over as much disc area as the airframe will carry, because the power required for a given lift rises as the square root of the disc loading and battery energy is the binding constraint. The design pressure that produced the lift fan produces distributed rotors when the power source is a battery, through the same relation. Distributed electric propulsion is reviewed in Kim et al 2018, and Fulton and Gandhi 2026 treat the disc loading of multi-passenger rotors as a design variable.

Hot gas and jet impingement are computed now

The flow the competition could not settle on the ground is now simulated, and the modern literature on impinging jets, ground vortices and thermal fields around vertical-landing aircraft is substantial. The difficulty that remains is the one that was always there, namely that the temperature ratios and the Reynolds numbers do not scale together. Fountain formation between twin impinging jets is computed in Zhang and Agarwal 2020, and the heat transfer of an impinging round jet by large eddy simulation in Li et al 2016.

Deck and surface heating became an operational subject

A supersonic aircraft landing vertically puts a hot, fast jet onto a surface, and the surface has to survive it. The Harrier introduced that materials and operations subject, the production successor made it acute, and it descends directly from the disc-loading argument in this article.

The identity derived earlier makes the connection exact rather than rhetorical. The disc loading is the dynamic pressure in the jet, so an architecture at 2,852 pounds per square foot imposes almost twice the pressure of one at 1,467, on the same deck, at the same landing weight. Airfield concrete under the F-35B is studied in Autelitano et al 2016 and Balaban and Erdem 2022, a flight deck heat spreader in Semenic et al 2016, and exhaust gases and over-deck air temperatures on a ship in Scott et al 2015.

The fly-off was partly replaced by simulation

The question this article asks is what evidence a competition can gather about an aircraft that does not yet exist, and the modern answer is that some of it need not be gathered by building two aeroplanes.

Digital engineering, model-based systems engineering and simulation-based acquisition are the literature of that shift. A model does not have the X-32’s difficulty, which was that the demonstrator differed from the proposal in the feature under examination, because a model can be made to be the proposal.

What a model does not have is the thing the X-35B’s single sortie demonstrated, namely that the integration works in the presence of everything nobody modelled. The trade is between an evidence source that matches the proposal exactly and one that matches reality exactly, and this competition shows why neither alone is sufficient. The digital thread in defence acquisition is examined in West and Pyster 2015, and the adoption of virtual prototyping across the defence research and acquisition communities in Post and Sundt 2017.

Acquisition analysis kept the case

The concept demonstration phase remains a case in the literature on competitive prototyping. Competition within the programme itself is examined in Assessing Competitive Strategies for the Joint Strike Fighter: Opportunities and Options 2001 and Birkler 2001, and prototyping more widely in Cate 1997, Medlej et al 2017 and Fast 2014.

Decision analysis under uncertainty

The question this article calls construct validity has a formal literature. Choosing between alternatives on evidence that does not directly measure the quantity of interest is the subject of decision analysis. Its literature includes Montibeller and von Winterfeldt 2015 on biases in multi-criteria analysis, French 2025 on scenario-focused decision analysis and Kahneman and Tversky 1977 on decisions under risk.

Propulsion, nozzles and integration since

The direct-lift arrangement made the propulsion system the centre of the competition, and its components are still being studied. The X-32B diverted its core stream through a butterfly valve to a pair of thrust-vectoring nozzles near the centre of gravity, and that arrangement forced the chin inlet of the Boeing X-32, and the winner added a lift fan, a three-bearing swivel module and roll posts. The modern work on those components and their neighbours, namely fluidic and mechanical thrust vectoring, swivel nozzles and thrust reversers, supersonic inlets and their bleed systems, and the coupling of engine and airframe performance, fills the clusters on nozzles, thrust vectoring and thrust reversers and on supersonic inlets, intakes and airframe-propulsion integration below. The three-bearing swivel duct is modelled and controlled in Wei et al 2019 and designed in Shi et al 2026, and a ventral diverterless inlet is analysed in Ge et al 2021.

Autonomy arrived in the hover

The precision required for a vertical landing on a moving deck is now within reach of automatic systems, which changes what the pilot has to do and therefore what the control power has to cover. Autonomous ship-deck landing is treated in Grocholsky et al 2016 and Lee et al 2021, and the precision hover control of the production aircraft in Denham and Paines 2008.

Machine learning and digital engineering

The fly-off was partly replaced by simulation, and the data-driven tools those simulations are now built from are the subject of the cluster on digital engineering, model-based systems engineering and machine learning below. The article argues that a model can be made to be the proposal but does not match reality exactly, which is why the X-35B’s single sortie still mattered. The records there apply digital threads and twins, model-based systems engineering, neural networks and reinforcement learning to aircraft, engines and their design, and they extend the subject of simulation-based acquisition rather than replace it. Massegur Sampietro and Da Ronch 2024 apply geometric deep learning to the aerodynamics of a future fighter demonstrator in dynamic manoeuvres.

Momentum theory, still

The relation behind this article’s sizing has been in the textbooks since momentum theory was written, and work on it continues. Momentum theory relates disc loading to induced velocity, and through it the power required for a given lift rises as the square root of the disc loading, the steep curve that separates the lift fan from a vectoring nozzle. The cluster on momentum theory, rotors, propellers and hover performance below holds the work that extends actuator-disc and blade-element momentum theory to open rotors, propellers and hovering rotors and, as neighbouring science, to tidal and wind turbines, among them Mahmuddin 2017 on blade element momentum theory and Shives and Crawford 2017 on a tuned actuator disc for tidal turbines.

Low observability

This literature is thin, with 32 records in the cluster on low observability and signatures below. The role of radar cross section in stealth design is set out in Lee 2024, the radar cross section of engine inlets including their fan blades is computed in Vogel 2016, and a low-observable intake is designed in Edefur and Tormalm 2018. Low-observable design shaped both entries decisively and is almost entirely absent from the open literature, as one should expect of the subject.

The Joint Strike Fighter programme and its demonstrators

Titles that name the X-32, the X-35, the F-35, the Joint Strike Fighter, its Joint Advanced Strike Technology predecessor or the ASTOVL studies that preceded both.

One of these titles names the X-32 and 6 name the X-35, against 38 that name the F-35, which is the asymmetry measured under What the Data Changed.

118 records. [Aaron et al 2003] [Advanced Short Takeoff and Vertical Landing ASTOVL Concepts Tested 1995] [Aksoy et al 2006] [Andersen and Kimbel 2005] [Antill and Ito 2013] [Armstrong and Levine 1988] [Assessing Competitive Strategies for the Joint Strike Fighter: Opportunities and Options 2001] [Atkinson et al 2013] [Autelitano et al 2016] [Balaban and Erdem 2022] [Ball et al 2006] [Beisbier 2002] [Bevilaqua 2005] [Bevilaqua 2007] [Bevilaqua 2009] [Bevilaqua 2009] [Birckelbaw et al 1995] [Birkler 2001] [Bishop et al 2000] [Bogdan 2015] [Bordignon and Bessolo 2002] [Brown et al 2009] [Browning and Jennewine 1996] [Buchholz 2002] [Burkhard and Deitrich 2003] [Calvello et al 2007] [Campos 2001] [Canin 2019] [Chapman 2018] [Chapman 2018] [Chapman 2018] [Chapman 2018] [Chapman 2018] [Chapman 2018] [Chapman 2019] [Chung et al 1995] [Chung et al 1995] [Crowe et al 2010] [Curtis and Penrose 1993] [Denham and Paines 2008] [Final Assembly and Checkout Alternatives for the Joint Strike Fighter 2002] [Flight tests of Distributed Aperture System sensors for F-35 Joint Strike Fighter 2006] [Franklin 1997] [Franklin 1997] [Frey 2011] [Gallagher 2013] [Gerhold and Buchholz 2002] [Gero 2001] [Green and Zeckhauser 2019] [Gutterman 2007] [Hange and Wardwell 1993] [Hange et al 1996] [Hange et al 1996] [Haro 2003] [Hartnett and Mittlesteadt 2000] [Hess and Fila] [Hoggarth and Mange 2009] [Hollenbach 2001] [Horowitz and Harmon 2020] [Hoskin et al 1991] [Hughes 2017] [Johns 1998] [Joint Strike Fighter 2005] [Jones 2014] [Kapstein 2004] [Karabag 2026] [Lam 1998] [Levin et al 2018] [Levine and Inglis 1989] [Lewis 2000] [Maddock et al 2011] [Mange et al 2002] [Mathcad as a standard design package for F-35 Joint Strike Fighter project 2004] [Mathews and Rothstein 1998] [McCarthy 1996] [McCarthy 2002] [McConnell 2006] [Menke et al 2000] [Migone et al 2023] [Moore 2007] [Naumowicz et al 1996] [Norman et al 2018] [Offsets and the Joint Strike Fighter in the UK and the Netherlands 2004] [Olson] [Owens et al 2004] [Owens et al 2006] [Philpot et al 1993] [Powrie and Novis] [Roberts 2002] [Rudnick 1998] [Salisbury 2026] [Saripalli et al 1991] [Scheuren et al 1998] [Self 2026] [Skelley et al 2007] [Smith 1996] [Smith et al] [Smith et al 1999] [Sokhey et al 2002] [Stortz and O’Donoghue 1993] [Struth 1999] [Tauke and Bordignon 2002] [Taylor and Owens 2004] [Taylor et al 2006] [Timothy et al 2009] [Unlisted 1999] [Van de Vijver and Vos 2006] [Vucetic 2010] [Vucetic 2013] [Vucetic and Nossal 2013] [Walker and Allen 2002] [Wardwell and Hange 1993] [Warren and Floden 2001] [Winfree 1998] [Witek 2017] [Wurth 2018] [Wurth et al 2002] [Zaffran and Erwes 2015]

The Harrier, the Pegasus engine and the vectored-thrust lineage

The direct-lift lineage the X-32B continued, being titles that name the Harrier, the P.1127, the Pegasus engine, the VAK 191B or the VAAC Harrier research aircraft.

The median publication year is 1986, because the lineage was studied while it was being built.

85 records. [Anderson and Foster 1984] [Anderson et al 1983] [AV-8B design for maintainability 1986] [Banks et al] [Baron 1983] [Beale and Hess] [Bear et al 1979] [Bedford 1962] [Bigler 1986] [Bode et al 1978] [Bowles 1980] [Chaderjian et al 2002] [Chaderjian et al 2002] [Chow 1993] [Chung and Parikh] [Clark and Vasta 1984] [Cooper et al 1985] [Cox and Kirby 1986] [Dorr et al 1992] [Farley 1971] [Ford 1981] [Fozard 1978] [Franklin and Stortz 1993] [Frost 1962] [Gaston et al 1984] [Gea et al 1991] [George 1999] [Gingras 1999] [Gingras et al 1986] [Hahn and Wilson 1985] [Hariharan et al 2010] [Hariharan et al 2010] [Hill 1970] [Hollingsworth et al 1977] [Hooker 1981] [Huttrop 1980] [Klepper et al 2017] [Lacey and Miller 1977] [Lacey et al 1979] [Lake et al 2000] [Lipera and Sandlin 1984] [Mathews 1987] [McNally 1986] [Merewether 1963] [Merrick et al 1991] [Migbee et al 1987] [Mihaloew et al 1981] [Moss 1995] [Murman et al 2001] [Mysko et al 1993] [Naumowicz et al 1998] [Newman 1984] [Ornelas 1985] [Pandya et al 2002] [Postlethwaite 1998] [Pryce and Hirschberg 2003] [Pryce et al 2005] [Rawnsley 1994] [Richardson et al 2005] [Richardson et al 2006] [Richardson et al 2007] [Riley 1978] [Runyon et al 2020] [Ryan 1986] [Scopes 2001] [Shanks et al 1993] [Shanks et al 2018] [Showers 1980] [Smith 1961] [Smiths Industries Ltd London United Kingdom 1998] [Soderman and Foster 1988] [Sotheran 1982] [Stanley and Hood 1981] [Stevenson et al 1992] [The Hawker P1127 vectored thrust fighter program - Lessons learned 1990] [Tinger 1987] [Veninger and Reed 1989] [VSTOL Systems Research Aircraft VSRA Harrier 1994] [Wall 1989] [Warakomski 1979] [Watson 1980] [Watson 1981] [Weinraub 1977] [Wilson and Liperra 1984] [Wilson and Wurts 1985]

Hot gas ingestion, reingestion and inlet temperature distortion

Hot gas ingestion and reingestion, exhaust recirculation and inlet temperature rise and distortion, with bird ingestion admitted because an inlet swallowing a bird and an inlet swallowing its own exhaust are the same fluid mechanics.

44 of these 76 records date from 1970 to 1995, which is the period base on which the article’s central failure mechanism rests.

76 records. [A Current Assessment of the Inlet/Engine Temperature Distortion Problem] [Adarkar and Hall 1969] [Amin and Richards 1983] [Amin and Richards 1984] [Amuedo et al 1989] [Assessment of the Inlet/Engine Total Temperature Distortion Problem] [Bauer 1987] [Behrouzi and McGuirk 1999] [Behrouzi and McGuirk 2000] [Behrouzi and McGuirk 2000] [Biesiadny et al 1984] [Binion 1970] [Blake and Laughrey 1987] [Braithwaite and Soeder 1979] [Braithwaite et al 1973] [Castner 2005] [Cook et al 2005] [Cosgrove and Ryan 1969] [Cosgrove et al 1968] [Curtis 2002] [Curtis et al 2005] [Davis 2010] [Design concepts for minimizing hot-gas ingestion in V/STOL aircraft 1981] [Dowler et al 1989] [Effect of Exhaust Jet from Takeoff Aircraft on the Inlet Distortion of Runway-Crossing Aircraft 2024] [Fricker et al 1992] [Gray and Kisielowski 1971] [Green and Zanine 1984] [Hall 1970] [Hammond and McLemore 1967] [Hange and Wardwell 1992] [Hemeter et al 1970] [Hot gas ingestion and the speed needed to avoid ingestion for transport type STO/VL and STOL configurations 1984] [Hot-Gas Ingestion 2007] [Jackson and House 1981] [Johns et al 1988] [Johns et al 1990] [Johns 1989] [Johns et al 1987] [Johns et al 1990] [Johns et al 1990] [Joshi et al 2021] [Kaemming and Smith 1984] [Kemp 1969] [Kirk and Barrack 1969] [Klann et al 1984] [Koc¸er et al 2008] [Krishnamoorthy 1971] [Kuhn et al 1993] [Lewis and Hurd 1980] [Li et al 2022] [Limage 1978] [McLemore 1966] [McLemore and Smith 1968] [Mehalic 1988] [Min et al 2021] [Penrose 1987] [Penrose and Smith 1996] [Ryan 1966] [Saripalli et al 1997] [Sherman 1964] [Soeder and Bobula 1979] [Soeder et al 1985] [Spong et al 1979] [Sullivan and Murthy 1990] [Tafti and Vanka 1990] [Teng et al 2024] [Tokarski et al 1994] [Turczeniuk 1979] [Vanka 1998] [Vanoverbeke and Holdeman 1988] [VanOverbeke and Holdeman 1990] [Walter and Shaw 1979] [Wang 2003] [Weber and Gay 1975] [Wendt and Reichert 1996]

Jet-induced ground effects, suckdown, fountains and ground vortices

Suckdown, fountain lift, ground vortices, jet-induced loads and the ground environment of jet and fan lift in hover and transition.

85 of these 143 records date from 1970 to 1995, the decades of NASA and industry research that let both companies understand the physics before either aircraft flew.

143 records. [Allen 2004] [Arledge et al 1996] [Asdurian 1967] [Batther et al 2026] [Bellavia et al 1991] [Bellavia et al 1991] [Bevilaqua et al 2007] [Bevilaqua et al 2010] [Blake and Stewart 1993] [Cabrita et al 2005] [Campbell et al 1977] [Campbell et al 1978] [Carlisle 1988] [Chilukuri 2019] [Christiansen et al 1985] [Christiansen 1984] [Corsiglia et al 1990] [Curtis 2002] [Curtis et al 2007] [Dent 1966] [Doğru et al 2016] [Dudley et al 1981] [Dudley et al 1986] [Eshleman et al 1986] [Eshlemen 1985] [Esker and Roddiger 1979] [Eyles et al 2002] [Foley 1979] [Garner 1967] [George et al 1964] [Gratzer and Mahal 1972] [Greco et al 1997] [Hall 1967] [Hall 1968] [He et al 2026] [Hill and Jenkins 1979] [Hoad and Gentry 1975] [Hoad and Gentry 1977] [Holdeman and Vukits 2004] [Holder and Tritschler 2019] [Tadghighi and Rajagopalan 1999] [Huggett 1959] [Hwang 1990] [Hwang and Tsou 1981] [Ing and Zhang 1993] [Ing and Zhang 1994] [Ing et al 2002] [Jakubowski et al 1985] [Jenkins 1999] [Johns et al 1989] [Johns et al 1989] [Joshi 1985] [Joshi and Compton 1984] [Jung et al 2024] [Kakka and Anupindi 2020] [Kamman and Hall 1978] [Kamman et al 1979] [Karemaa et al 1979] [Kemmerly 1989] [Kotansky 1978] [Kotansky and Bower 1977] [Kotansky and Glaze 1980] [Kotansky 1982] [Kotansky and Glaze 1981] [Kristy 1995] [Kuhlman and Cavage 1994] [Kuhlman and Warcup 1977] [Kuhlman and Warcup 1978] [Kuhlman and Warcup 1980] [Kuhlman and Cavage 1992] [Kuhn 1987] [Kuhn 1998] [Kuhn et al 1991] [Kuhn et al 1991] [Kuhn et al 1993] [Kuhn 1986] [Kuhn 1997] [Lavi 1967] [Levin and Wardwell 1997] [Li et al 2020] [Lift Loss In Hover 2007] [Lissaman 1967] [Lissaman 1969] [Lord 1985] [Louisse and Marshall 1974] [Maclean 1991] [Margason 2002] [Margason et al 1996] [McGuirk 2007] [Miller et al 1991] [Mitchell 1987] [Morse and Newhouse 1961] [Mourtos et al 1995] [Newman and Atassi 1980] [Pandya et al 2003] [Paulson 1981] [Paulson 1980] [Polsky 2000] [Poppen et al 1991] [Pruyn and Taylor 1970] [Renselaer 1977] [Rogers et al 1969] [Saberi 1983] [Saddington 2000] [Saddington and Knowles 1999] [Saddington and Knowles 2001] [Saddington et al 2002] [Saddington et al 2005] [Sandlin and Howard 1991] [Saripalli 1987] [Schnell and Grossman 1978] [Sharma et al 2021] [Siclari et al 1975] [Siclari et al 1976] [Siclari et al 1977] [Smith et al 1993] [Smith et al 1993] [Smith et al 1994] [Soderlund and Matveev 2010] [Solies 1992] [Stewart 1979] [Stewart 1987] [Stewart and Walters 1983] [Stewart et al 1995] [STOL Operation Transition-in-Ground Effect 2007] [Tritschler et al 2019] [Van Dalsem et al 1987] [Von Glahn and Groesbeck 1979] [Wachspress et al 2026] [Wardwell et al 1992] [Wardwell et al 1993] [Watson et al 1967] [Weber and Williams 1978] [Winston et al 1975] [Wohllebe and Migdal 1979] [Worden et al 2016] [Yang et al 2017] [Yen 1980] [Zhang and Agarwal 2020] [Zhang and Ing 1993] [Zhang and Ing 1994] [Zhang et al 2019] [Zhao et al 2022]

Jet impingement and jet flow physics

The physics of impinging jets, jets in crossflow and hot and supersonic jet flows, including the impingement cooling literature of industry, kept as the neighbouring physics of the deck heating problem.

102 of these 120 records date from 2015 or later, so the modern computation of impinging jets is almost wholly a literature written after the competition.

120 records. [Abdol-Hamid et al 2003] [Almohammadi and Alsaiari 2024] [Alvi and Strykowski 1999] [Alzahrani et al 2023] [Baker and Orzechowski 1982] [Barbosa et al 2024] [Behrouzi 2000] [Bhansali and Ekkad 2021] [Bhansali et al 2021] [Cali 2000] [Cao et al 2022] [Castner et al 2017] [Celik 2019] [Chang et al 2020] [Colombié et al 2021] [Cornelius and Lucius 1993] [Corvera and Mahjoob 2023] [Da Soghe et al 2018] [DeBonis 2017] [Devakottai et al 2020] [Dhanasegaran and Pugazhendhi 2017] [Draksler et al 2017] [Draksler et al 2019] [Dutta et al 2016] [El-Jummah et al 2016] [Elavarasan et al 1999] [Fogleman et al 2026] [Ganatra et al 2024] [Gao et al 2018] [Gao et al 2019] [Garcia et al 2026] [Grenson and Deniau 2017] [Gudi and Hindasageri 2021] [Gupte et al 2015] [He and Liu 2018] [He and Liu 2018] [Hsu et al 2025] [Hu and Onishi 2024] [Hu et al 2023] [Jagajith et al 2026] [Jalamani et al 1990] [Jensen et al 2017] [Joshi and Sahu 2022] [Joshi and Sahu 2024] [Joshi et al 2023] [Junqueira-Junior et al 2017] [Kaewbumrung and Plengsa-Ard 2023] [Kamrass and Swartzel 1955] [Karabulut 2019] [Keleş and Özmen 2025] [Khademi and Bazargan 2024] [Kim et al 2026] [Kim et al 2026] [Kitayama and Kubo 2021] [Kobayashi et al 2022] [Koizumi et al 2017] [Kopriva et al 2019] [Krothapalli and Alvi 2002] [Kukutla and Prasad 2016] [Lagarza et al 2016] [Lak et al 2020] [LeBlanc et al 2019] [Lemanov et al 2018] [Li et al 2016] [Li et al 2020] [Li et al 2024] [Liu and Junkui 2015] [Liu et al 2018] [Liu et al 2020] [Lyu et al 2023] [Madhavan et al 2019] [Manoharan and Mokhtar 2018] [Mezzacapo et al 2025] [Morsbach et al 2024] [Nakazawa et al 2022] [Natarajan et al 2016] [Nenni 1980] [Nguyen et al 2019] [Nguyen et al 2022] [Nguyen et al 2023] [Noah et al 2024] [Ou and Lai 2024] [Paez et al 2022] [Page 2023] [Pawar et al 2020] [Qin et al 2023] [Rudenko et al 2016] [Saini et al 2022] [Salehian and Mankbadi 2020] [Saripalli and Kroutil 1985] [Seiner and Gilinsky 1995] [Seo and Mittal 2017] [Shahrin et al 2026] [Shaikh et al 2023] [Sharif 2016] [Sheng et al 2025] [Shih et al 2002] [Shukla and Dewan 2021] [Singh 2022] [Singh et al 2019] [Singh et al 2020] [Singh et al 2023] [Smith 2015] [Soderman 1990] [Stewart and Blake 1992] [Tabassum et al 2023] [Taghinia and Rahman 2018] [Torres et al 2020] [Torres et al 2022] [Tumuklu 2024] [Venkatakrishnan 2004] [Verrière 2022] [Wang et al 2026] [Wen et al 2019] [Wilson and Knowles 1994] [Xing et al 2024] [Yang et al 2025] [Zhao et al 2021] [Zhong et al 2016] [Zhong et al 2022]

Ship decks, landing surfaces and shipboard operations

Deck landing, ship airwakes, carrier approach, flight deck heating and the landing surfaces on which jet and rotor downwash acts.

117 records. [Adiyasa and Sasongko 2025] [Ambroziak et al 2022] [Bhatia et al 2021] [Bhatia et al 2021] [Bihrle 1969] [Blinkhorn 1948] [Bodson and Athans 1985] [Bris and Nguyen 2023] [Britcher et al 2023] [Britcher et al 2024] [Britcher et al 2025] [Calvano and Harney 1998] [Chang and Ai 2026] [Chen et al 2026] [Chopra 2025] [Clark 1965] [Clarke et al 1973] [Comandur et al 2019] [Comandur et al 2020] [Comeau et al 2024] [Connelly 1982] [Daffer and Rogers 1973] [de Paula et al 2025] [Deng et al 2025] [Deveson and Deveson 1997] [Dong et al 2021] [Donley 1980] [Douglas Aircraft Co Long Beach Ca 1963] [Duehring et al 2023] [Durand and Wasicko 1965] [Editor 2016] [Fang et al 2021] [Farris et al 1983] [Fenwick 1966] [Fenwick 1967] [Ferrier et al 2015] [Fortenbaugh 1972] [Frost et al 2021] [Furey 1983] [Gnanamanickam et al 2020] [Grasso 1994] [Gribanov et al 2022] [Grocholsky et al 2016] [Hailiang 2026] [Han et al 2019] [He et al 2023] [Hendrick et al 2023] [Huang et al 2019] [Imhof and Schork 1999] [Jordan et al 2002] [Kalra et al 2022] [Kamman and Hall 1978] [Kim and Costello 2016] [Kim et al 2022] [Le Bris and Nguyen 2023] [Lee et al 2021] [Lee et al 2021] [Lin et al 2015] [Liting et al 2023] [Lu et al 2022] [Luan and Sun 2020] [Ma et al 2018] [Ma et al 2018] [McGee et al 1978] [Miller 1970] [Minotra and Feigh 2018] [Ngo and Sultan 2024] [Nguyen et al 2024] [Oldmixon 1963] [Patel et al 2021] [Pavlov 2016] [Peer 2000] [Phelps et al 2018] [Radford and Andrisani 1984] [Richez and Costello 2024] [Schock and Langlois 2023] [Scott et al 2015] [Semakov 2021] [Semakov and Semakov 2022] [Semenic et al 2016] [Setiawan et al 2025] [Shafer et al 2019] [Shipman and Bin 2021] [Stanisławski 2019] [Stanton et al 2018] [Stevens and Roskam 1985] [Stevens et al 1981] [Stewart 1979] [Stewart 1980] [Sun et al 2015] [Telford and Vasiloff 1968] [Thomas et al 2023] [Topczewski and Bibik 2023] [Topczewski et al 2021] [Tugolukov 2020] [Venkatesh 2025] [Vitale et al 2023] [Waanders and Rauleder 2026] [Wang et al 2020] [Wang et al 2022] [Warner et al 1986] [Wilhelms et al 2026] [Wilson 1992] [Wolkovitch and Brassell 1978] [Wu et al 2026] [Wynn and McLain 2019] [Xu et al 2022] [Yackle 1992] [Yang et al 2026] [Yang et al 2026] [Ye et al 2024] [Zhang and Fu 2024] [Zhao et al 2018] [Zhou et al 2026] [Zhu and Yang 2020] [Zilver et al 2025] [Štrbac et al 2022]

Lift fans, lift engines, ejectors and remote lift

Lift fans, lift and lift-cruise engines, ejectors, remote augmented lift and the shaft and tip-turbine drives that power them.

The median publication year is 1975. The lift fan the winner flew was a revival of a programme of the 1960s and 1970s, and its literature is mostly that programme’s.

220 records. [Abdullah and Husi 2026] [Additional design studies of the NASA/Navy lift/cruise fan 1976] [Alscher et al 1966] [Ames 1975] [Aoyagi 1979] [Arnulfo and Pilidis 2000] [Atencio 1973] [Atencio et al 1973] [Barankiewicz 1991] [Barankiewicz et al 1994] [Barankiewicz 1993] [Beattie 1975] [Beeler 1965] [Beeler and Russell 1964] [Beeler and Volk 1965] [Benzakein and Kazin 1971] [Benzakein and Volk 1970] [Bevilaqua 1996] [Biesiadny et al 1993] [Biggers et al 1964] [Blackhurst 1969] [Bland and Konsewicz 1976] [Bland et al 1976] [Bowling et al 1969] [Brogan et al 1961] [Byrnes et al 1974] [Campbell and Quinn 1974] [Cavage 1975] [Chen et al 2021] [Chu et al 1983] [Cican et al 2023] [Civinskas 1973] [Clark and Smith 1965] [Cole et al 1980] [Conceptual design of a V/STOL lift fan commercial short haul transport 1973] [Conceptual design studies of a V/STOL civil lift fan transport including effect of size and fan pressure ratio 1974] [Conceptual design studies of lift/cruise fans for military transports 1974] [Cook and Hickey 1967] [Cook 1993] [Coplin 1965] [Corden and Everett 1963] [Corgiat et al 1993] [Corsiglia et al 1989] [Hickey et al 1966] [Davis and Ela 1969] [Deckert 1993] [Deckert 1995] [Deckert and Rolls 1974] [Deng et al 2017] [Design definition study of NASA/Navy lift/cruise fan V/STOL aircraft 1975] [DeSmidt et al 2001] [Diedrich 1971] [Diedrich 1975] [Dobek 1973] [Donateo and Çinar 2022] [Doonan and Kuchar 1992] [Drummond and Barankiewicz 1990] [Dudley 2016] [Dudley et al 1990] [Duffy and Samaritano 2015] [Dugan et al 1971] [Eccles 1983] [Eldridge et al 1973] [Elliott 1976] [Fasching and Kutney 1964] [Fishbach and Franciscus 1982] [Fletcher 1962] [Fluctuating Pressures on Aircraft Wing and Flap Surfaces Associated with Powered-Lift Systems 1976] [Ford 1973] [Fry 1967] [Gambucci et al 1976] [Gambucci et al 1976] [Garland 1987] [Gates and Cochran 1961] [Gelhausen and Wilson 1986] [General Electric Co Cincinnati Oh 1962] [General Electric Co Cincinnati Oh 1963] [General Electric Co Cincinnati Oh 1964] [Gerdes 1993] [Gerdes 1993] [Gerdes and Hynes 1972] [Gleiter 1976] [Gotlieb 1977] [Gotlieb et al 1976] [Grahame 1968] [Grahame 1969] [Green 1980] [Griffin 1983] [Haas et al 1976] [Haas et al 1978] [Haas et al 1978] [Hall and Hodder 1971] [Hall et al 1967] [Hall et al 1970] [Harris 1968] [Hickey and Kirk 1993] [Hill and Waters 1974] [Hiraoka et al] [Hudson 1977] [Hudson and Gee 1977] [Huntley 1972] [Jacobson 1964] [Jaklitsch et al 1971] [Jensen and Pera 1977] [Jiang and Zhang 2016] [Jiang and Zhang 2016] [Jiang and Zhang 2017] [Jiang and Zhang 2018] [Jiang and Zhang 2021] [Jiang et al 2015] [Karemaa 1971] [Kazin and Volk 1971] [Keller 1969] [Kelly and Tolhurst 1966] [Kentfield 1967] [Kirk et al 1972] [Knight et al 1973] [Knox 1962] [Kochanski 1966] [Kutney 1963] [Kutney 1964] [Lake 1990] [Lamb 1995] [Lebacqz and Radford 1979] [Lee et al 2016] [Lieblein 1970] [Lieblein and Stockman 1969] [Lieblein et al 1973] [Lieblein 1970] [Lockheed-Georgia Co Marietta 1969] [Lockwood 1963] [Lockwood 1964] [Love 1993] [Lowe and Sanger 1972] [Luidens et al 1984] [Lummus et al 1980] [Mazzei and Scott 2003] [Mazzei Jr et al 1999] [McNally and Brown 1985] [McNeill et al 1995] [Myers et al 2010] [Myers et al 2019] [NASA/Navy lift/cruise fan cost reduction studies 1977] [NASA/Navy lift/cruise fan. Phase 1 Design summary 1977] [Naumowicz and Smith 1992] [Nicholson and lowry 1966] [Nishimura 1980] [Novak 1975] [O’Keefe et al 1973] [Obrien 1976] [Obrien 1976] [Oganyan and Loginov 2025] [Palmer and Holdo̸ 2002] [Peterson 1964] [Peterson 1965] [Petrov 1993] [Petty 1980] [Posnett et al 1987] [Posnett et al 1986] [Prasad and Choi 2017] [Pratt et al 1971] [Przedpelski 1965] [Przedpelski 1967] [Pyle 1971] [Quigley and Franklin 1977] [Rabone and Paulson 1973] [Rao et al 1973] [Remote lift fan study program, volume 4 1973] [Riccius 1984] [Roelke and Zigan 1972] [Rolls et al 1976] [Rumsey et al 1972] [Salter 1975] [Sayma et al 2003] [Schaeffler et al 1967] [Schlundt 1975] [Schlundt 1976] [Sellers 1973] [Sellers and Szuch 1973] [Sellers et al 1977] [Sheridan 1985] [Sheridan 1986] [Smith 1966] [Smith et al 1992] [Sowers 1965] [Starkey and True 1963] [Stimpert 1973] [Stimpert 1973] [Stimpert 1973] [Stimpert 1975] [Stockman et al 1973] [Streiff and Henderson 1974] [Sully and Whittley 1987] [Szuch 1973] [Tape 1990] [Tauber et al 1976] [The Jet Lift Controversy 1962] [Thomas 1972] [Tich 1991] [True 1967] [Turney and Allen 1980] [Volk 1969] [Weber 1960] [Weber 1961] [Webster 1973] [Williams 1960] [Willis 1980] [Willis 1980] [Willis 1981] [Willis et al 1982] [Wind tunnel and ground static investigation of a large scale model of a lift/cruise fan V/STOL aircraft 1976] [Winston 1969] [Xu et al 2022] [Yuska 1972] [Yuska and Diedrich 1972] [Zabinsky et al 1974] [Zabinsky et al 1975] [Zhang et al 2013] [Zimmerman 1958] [Zola et al 1984]

Nozzles, thrust vectoring and thrust reversers

Exhaust nozzles, mechanical and fluidic thrust vectoring, swivel and ventral nozzles, and thrust reversers.

419 records. [Adamson 1980] [Adavbiele 2009] [Adavbiele 2009] [Adavbiele and Salami 2007] [Adkins and Sherwood 1996] [ADRC-based control allocation method and theory for 3-DOF thrust-vectored aircraft 2023] [Afridi and Khan 2022] [Afridi et al 2023] [Afridi et al 2023] [Afridi et al 2024] [Ahmed et al 2023] [Ahuja and Spencer 1987] [Aikens et al 2015] [Aircraft engine thrust reverser 1998] [Al-Akam et al 2019] [Ale Isaac Khoueini] [Amoozgar et al 2024] [Anderson and Bradley 1987] [APPLICATION OF FLUIDIC THRUST VECTORING IN V/STOL AIRCRAFT 2024] [Arbiter 1985] [Aroussi 2026] [Arshad et al 2020] [Asbury and Yetter 1998] [Asbury et al 1996] [Avanzini and Matteis 1995] [Bahamon Blanco 2023] [Banazadeh and Banazadeh 2014] [Baranwal 2026] [Barham 1994] [Barnes et al 1984] [Barrett 1965] [Bauer 1980] [Beck et al] [Beilman 1983] [Berens 2019] [Bergman 1979] [Berrier 1983] [Berrier and Mason 1987] [Berrier and Re 1978] [Berry 1998] [Bhabar and Mukesh Sharma 2025] [Bindu Mounica et al. 2020] [Bloomer and Miller 1954] [Bowers 1979] [Bowers and Buchan 1978] [Brodsky 1970] [Brown 1987] [Bruce et al 2016] [Burger 1983] [Burnes et al 2001] [Bursey and Dickinson 1990] [Capello et al 2019] [Capone 1974] [Carlson 1992] [Carr 1984] [Carter et al 2015] [Casau et al 2016] [Caton and Franke 1991] [Chakraborty and Comer 2024] [Chandra Sekar et al 2017] [Chandra Sekar et al 2021] [Cheatham et al 1990] [Chen and Liao 2020] [Chen et al 2022] [Chen et al 2022] [Chen et al 2025] [Chen Xuyi and Xiaoying Zhang 2015] [Cheng et al 2020] [Chi et al 2022] [Chouicha et al 2019] [Chouicha et al 2020] [Chpoun et al 2017] [Cliff et al 1982] [Cohn et al 1985] [Coles 1968] [Collins Jr 2005] [Comer 2025] [Compton and Bowers 1983] [Computational and Experimental Analysis of Optimized Dual Throat Fluidic Thrust Vectoring Nozzle Configurations 2024] [Computational Investigation of Effects of Side-Injection Geometry on Thrust-Vectoring Performance in a Fuel-Injected Dual Throat Nozzle 2022] [Corva et al 2021] [Costes 1988] [Crandall et al 1973] [Crowe and Martin 2019] [Crown 1950] [Culpepper et al 2021] [Cunningham and Boytos 1981] [Cunningham and Boytos 1983] [Curry et al 1983] [Dahl et al 2015] [Das et al 2024] [Das et al 2025] [Davis and Hines 1976] [Davis and Spicer 1965] [de Matteis et al 1998] [Deere 2003] [Deere et al 2003] [Deere et al 2005] [Deere et al 2007] [Deere et al 2005] [Demetriades 1977] [Deng et al 2014] [Di et al 2025] [Di Verniere et al 2026] [Dong et al 2025] [Doonan et al 1983] [Dunbar et al 2002] [Dunn and Emery 1966] [Eames 1993] [Eames and Mason 1988] [Enenakpogbe et al 2024] [Enenakpogbe et al 2024] [Enenakpogbe et al 2025] [Erwin et al 1964] [Esker and Debonis 1991] [Esker and McArdle 1990] [Esker and Sedrick 1972] [Esker and McArdle 1993] [Experimental Investigations on the Strut Controlled Thrust Vectoring of a Supersonic Nozzle 2020] [Fang et al 2025] [Farras et al 2021] [Fazeli Asl and Moosapour 2017] [Federspiel 1979] [Ferlauto 2018] [Ferlauto and Marsilio 2016] [Ferlauto and Marsilio 2016] [Ferlauto and Marsilio 2017] [Fernando et al 2026] [Flamm 1998] [Flamm et al 2005] [Flamm et al 2006] [Flamm et al 2007] [Flight Characteristics of Quad Ducted Fan Helicopter with Thrust Vectoring Nozzles 2014] [Foley and Woodrey 1980] [Friddell and Franke 1990] [Friehmelt 1996] [Frost and Bishop 1963] [Fujii et al 2020] [Gal-Or] [Gal-Or 1990] [Gal-Or 1995] [Gal-Or 1995] [Gehrke et al 2017] [Gill 1973] [Giuliano et al 1997] [Glezer et al 1985] [Goetz et al 1976] [Gogoi and Dhamalekar 2021] [Gogoi et al 2021] [Goss et al 2009] [Granasy 1995] [Gridley and Walker 1996] [Gu and Xu 2013] [Gupta 2025] [Gupta 2026] [Ha et al 2025] [Hakim et al 2020] [Hall 1965] [Hambly 1974] [Hamed et al 1997] [Hammond et al 1995] [Hardy 1987] [Hauser and Jadbabaie] [Hawkes and Obye 1993] [Herrick 1989] [Herrick 1990] [Hienz and Vedova 1984] [Hiley and Bowers 1981] [Hoffmann and Joachimiak 2026] [Holder et al 2018] [Hosseini et al 2026] [Hou and Hong 2023] [Hou et al 2024] [Hou et al 2025] [Hou et al 2026] [Hu et al 2024] [Hu et al 2026] [Huang et al 2022] [Huang et al 2023] [Huang et al 2025] [Huang et al 2026] [Hui-min et al 2005] [Hui-min et al 2005] [Hunter and Deere 1999] [Hunter 2004] [Idzorek 1988] [Imlay 1986] [In-Flight Thrust Determination for Aircraft with Thrust Vectoring] [Irfan and Shah 2016] [Islam et al 2018] [Islam et al 2018] [Isono et al 2017] [Jadbabaie and Hauser 2002] [Jammalamadaka et al 2020] [Jayakody and Katupitiya 2015] [Jegede and Crowther 2016] [Jiméneze and Icaza 2000] [Jinxin et al 2026] [Johns 2000] [Jois et al 2024] [Jyothy and John Wessley 2023] [Kantner et al] [Kara and Kurtuluş 2024] [Kedia et al 2021] [Kelley et al 1982] [Kim 2026] [Kim and Choi 2025] [King and Schnelker 1970] [King et al 1991] [Klafin 1988] [Krenkel and Salzman 1968] [Kuang et al 2017] [Kuchar and Tabakoff 1976] [Kuchar and Tabakoff 1977] [Kuchar and Wolf 1993] [Kumar and Ghosh 2018] [Kumon et al 2010] [Kumon et al 2011] [L’Ecuyer et al 1971] [Lampard 1978] [Lander and Palcza 1974] [Lavrukhin et al 2014] [Lecuyer 1970] [Lee et al] [Lee et al 2018] [Leovan 2019] [Lewis and Simpkin 1981] [Li et al 2013] [Li et al 2016] [Li et al 2020] [Lichtsinder et al 1998] [Lieu 1964] [Linderman et al 1974] [Liu et al 2013] [Liu et al 2020] [Liu et al 2022] [Liu et al 2024] [Liu et al 2025] [Liu et al 2026] [Liu et al 2026] [Long 2017] [Lu and Terrier 2003] [Lu and Terrier 2003] [Ma et al 2024] [Maarouf et al 2009] [Mace et al 1989] [Madarasz et al 2012] [Madeiras et al 2026] [Makarchuk and Ponomarenko 2026] [Malaek and Parastari 2001] [Mangin et al 2006] [Mansell 1987] [Mao et al 2019] [Marconi et al 1997] [Margetts et al 2015] [Marubashi and Miwa 2015] [Marubashi and Miwa 2016] [Maruyama et al 2019] [Mason and Crowther 2004] [Masters 2015] [Matesanz et al 1995] [Matveev and Wheeler 2019] [McArdle and Smith 1990] [Meyer et al 1991] [Milam et al 2005] [Milford and Migdal 1967] [Miller 1983] [Miller and Protopapas 1985] [Miller et al 1979] [Minin et al 2016] [Mishra et al 2025] [Mitchell 1979] [Miwa and Maruhashi 2016] [Miwa et al 2012] [Mo et al 2018] [Molyneux 1983] [Muir and Bradshaw 1996] [Nafi and Hasan 2019] [Naik and Chiarelli 1988] [Nair et al 2020] [Nardi et al 1999] [Naumova and Shmyglevskii 1967] [Nayebi and Taeibi Rahni 2024] [Nie et al 2026] [Obye and Hakim 1984] [Orme et al 1998] [Ornob et al 2025] [Otani 2023] [Pang et al 2024] [Papamoschou et al 2016] [Park et al 2025] [Pastorelli 2013] [Payne 1980] [Pennington and Meintel 1980] [Peters 1981] [Petit and Scholey 1973] [Petit and Scholey 1973] [Petit and Scholey 1973] [Petrie 1982] [Pruitt and Bates 1992] [Qi et al 2020] [Radhakrishnan et al 2021] [Rajendran et al 2020] [Rajput et al 2021] [Rakesh and Varghese 2018] [Rao 1958] [Ravindranath 2025] [Re and Mason 1985] [Resta et al 2021] [Resta et al 2022] [Ritter 2016] [Robinson 1978] [Robinson and High 1974] [Rolls and Aoyagi 1977] [Romine and Johnson 1984] [Romine et al 1989] [Rosenberg and Esker 1980] [Rosenberg and Christiansen 1981] [Rowe et al 1984] [Ruetten 2018] [Russo et al 2011] [Akshay et al 2020] [Saghafi and Banazadeh 2007] [Salahudden et al 2025] [Schirmer and Capone 1989] [Schneider and Watt 1988] [Schnell et al 1977] [Sellam et al 2012] [Semlitsch and Mihăescu 2021] [Shcherbakov 1983] [Shebl 2026] [Sheu 1999] [Shi 2014] [Shi et al 2024] [Shi et al 2026] [Shigematsu et al 2012] [Shin et al 2010] [Shukla et al 2026] [Siddiqui 2022] [Simmons 2022] [Singh and Kushari 2008] [Smith and McArdle 1990] [Smith and McArdle 1992] [Snyder and Thompson 1971] [Sobel and Lallman 1988] [Sobester and Keane 2006] [Soundararajan 2022] [Sparavalo 2019] [Sparavalo 2021] [Steer 2000] [Sundararaj et al 2021] [Suresh et al 2026] [Suñol et al 2014] [Suñol Jiménez et al 2015] [Sørensen et al 1996] [Tamrat and Antani 1988] [Tatom et al 1972] [Taylor 1988] [Taylor 1990] [Terrier and Lu 2003] [Terrier and Lu 2005] [Test Bed for Vectored Thrust Power Plants 1963] [Thompson and Epstein 1977] [THRUST VECTORING OF A SUPERSONIC RECTANGULAR NOZZLE BY USING DIFFERENT PLATE EXTENSIONS 2020] [Tsentis et al 2023] [Tsentis et al 2024] [Tudosie 2023] [Tudosie 2024] [Ulizar 1997] [Van Nieuwstadt and Murray 1998] [Van Poppel et al 1998] [Variable mode turbofan jet engine with thrust vectoring 2002] [Varsegov 2010] [Varsegov and Saukhin 2025] [Vashistha et al 2014] [Vectored thrust 1992] [Visser 1999] [Waithe and Deere 2003] [Wallace and Bowers 1982] [Wang et al 2014] [Wang et al 2017] [Wang et al 2019] [Wang et al 2020] [Wang et al 2020] [Wang et al 2027] [Ward and Lewis 1987] [Ward and Penrose 1983] [Wei et al 2019] [Wei Yuan and Katupitiya 2013] [Werner and Wolter 2010] [Williams and Vittal 2002] [Wilson et al 1999] [Wilson et al 2001] [Wilson et al 2003] [Wing and Asbury 1991] [Wing 1998] [Wing and Capone 1993] [Wing and Giuliano 1997] [Wooten et al 1984] [Wu and Chow 1985] [Xiangyang et al 2019] [Xu et al 2024] [Yagle et al 2000] [Yang et al 2021] [Yang et al 2023] [Yetter et al 1996] [Zawislak and Birk 2020] [Zhang et al 2024] [Zhang et al 2025] [Zhang et al 2025] [Zhang et al 2026] [Zhang et al 2026] [Zhao-miao and Chuan 2013] [Zhijie et al 2026] [Zhou et al 2022] [Zmijanovic] [Zmijanovic et al 2012] [Zmijanovic et al 2013] [Živković et al 2014]

Momentum theory, rotors, propellers and hover performance

Momentum, actuator-disc and blade-element theory, rotor and propeller performance and hover efficiency, with tidal and wind turbines kept as neighbouring science of the same relation.

213 records. [Aa. Madsen 2024] [Aerodynamic design of low-speed aircraft with a NASA fuselage/wake-propeller configuration 1986] [Ahmed et al 2025] [Allsop et al 2017] [Alvarez et al 2025] [Anantha et al 2024] [Apkarian 2018] [Arents 1977] [Arif and Sasongko 2021] [Azuma and Kawachi 1975] [Bachelder et al 2021] [Barakos and Jimenez Garcia 2016] [Barakos et al 2020] [Belák and Hromčík 2023] [Benjamin 2023] [Berton et al 2000] [Biggi et al 2024] [Binion 1971] [Bohorquez et al 2010] [Bontempo and Manna 2016] [Bowman et al 2018] [Brown and Fischer 1967] [Bulten and van Esch 2005] [Burton et al 2024] [Cai et al 2019] [Cao et al 2025] [Caracostas 1978] [Casablanca et al 2025] [Chattot 2020] [Chen and Hubner 2020] [Chen and Hubner 2021] [Chen et al 2019] [Chen et al 2023] [Chen et al 2025] [Chiang et al 2020] [Cousins et al 2026] [Cox-Gross and Collins 2025] [Critchfield and Ning 2023] [Critchfield and Ning 2026] [Dai et al 2025] [Davis et al 1961] [Detore and Gaffey 1969] [Droandi and Gibertini 2015] [Duan et al 2024] [Dyke 1963] [Edenborough 1968] [Edkins 1969] [Fan et al 2020] [Fardin et al 2026] [Farrar and Agarwal 2015] [Felker 1991] [Felker 1993] [Felker et al 1988] [Firnhaber Beckers et al 2023] [Fujiwara et al 2026] [Fulton and Gandhi 2026] [Fulton et al 2026] [Gahlot and Sankar 2024] [Gill and Lee 2025] [Goland et al 1964] [Gress 2002] [Gur et al 2021] [Hariharan et al 2017] [Harned and Head 1965] [Hashem Dabaghian et al 2025] [Hermes and Wood 1969] [Hiller Aircraft Corp Palo Alto Ca 1965] [Hiller Aircraft Corp Palo Alto Ca 1965] [Hiller Aircraft Corp Palo Alto Ca 1965] [Hiller Aircraft Corp Palo Alto Ca 1965] [Himmelberg and Benedict 2017] [Hirschberg and Müller 2007] [Hirschberg et al 2005] [Ho et al 2015] [Hu et al 2025] [Hua et al 2025] [Huang et al 2020] [Improved Stall Delay Model for HAWT Performance Predictions using 3D Navier-Stokes Solver and Actuator Disk Method 2022] [Ishaque et al 2026] [Jacobson and Smith 2018] [Jain 2017] [Jain 2018] [Jimenez Garcia and Barakos 2015] [Jimenez Garcia and Barakos 2018] [Jimenez-Garcia and Barakos 2017] [Jo et al 2017] [Kandath et al 2019] [Kang et al 2025] [Katzenberger 1967] [Keller 2023] [Keller 2025] [Kim 2021] [Kim et al 2020] [Kiran and Breuer 2023] [Klimchenko et al 2023] [Kozapalli and Warmbrodt 1997] [Ku and Sankar 2026] [Kwon et al 2015] [Lamar et al 2003] [Lampl and Armanini 2023] [Landgrebe 1971] [Lee and Dassonville 2020] [Lee and Park 2022] [Lei et al 2021] [Li and Da Ronch 2025] [Li et al 2023] [Liao et al 2024] [Lichota 2023] [Lindner et al 2023] [Liu and Zhang 2024] [Liu et al 2025] [Lucarini 2026] [Lyu and Yang 2025] [MacNeill and Verstraete 2017] [Mahmuddin 2017] [Maisel and Harris 1981] [Malick and Agarwal 2015] [Martin 2025] [McCormick 2002] [McDonald 2015] [Mihaila et al 2026] [Min et al 2026] [Modarres and Peters 2015] [Nagaraju et al 2015] [Narducci 2015] [Nark et al 2017] [Nguyen 2021] [Zawodny et al 2025] [Oldeweme et al 2024] [On the Rotor Lifting Line Wake Model 2016] [Oosedo et al 2012] [Overmeyer and Martin 2017] [P.S. and Muruga Lal 2022] [Pascioni et al 2026] [Patterson et al 2016] [Pereyra and Kung 2026] [Petroff et al 1954] [Poggi et al 2024] [Polak and George 1998] [Polonsky et al 2023] [Pomin and Wagner 2002] [Powell 1959] [Prasad 2025] [Qing et al 2023] [Quackenbush et al 1989] [Quackenbush et al 1991] [Quackenbush et al 2019] [Rakshith et al 2015] [Ramachandran et al 1989] [Ramasamy et al 2010] [Ritter et al 1971] [Rotor Noise V/STOL Rotor and Propeller Noise Its Prediction and Analysis of Its Aural Characteristics 1976] [Rubin and Zhao 2021] [Saberi et al 2026] [Sadowski et al 2023] [Sambell 1972] [Sankar et al 2015] [Schaefer et al 2026] [Schmaus and Chopra 2016] [Schrenk 1934] [Schwartz and Rogers 1992] [Scully 2018] [Serrano et al 2021] [Shahmiri 2017] [Shaidakov and Brusov 2017] [Shankar et al 2023] [Sharpe and Agarwal 2019] [Sheng et al 2015] [Shi et al 2024] [Shinoda and Johnson 1993] [Shivananda et al 1978] [Shives and Crawford 2017] [Simmons and Ackerman 2026] [Simmons et al 2023] [Simpson 1967] [Sinnige et al 2018] [Smith 1968] [Soemarwoto et al 2022] [Son and Kim 2023] [Stanly et al 2020] [Stepniewski and Keys 1984] [Stringer et al 2020] [Szafran et al 2014] [Tai and Vorwald 1993] [Takallu and Gentry 1992] [Thomason 1982] [Tinney and Valdez 2024] [Troldborg et al 2015] [Tyler et al 2026] [Van Riper and Wood 2003] [Veldhuis and Heyma 2000] [Venter et al 2024] [Walsh 1991] [Walvekar and Chakravarthy 2023] [Wang et al 2007] [Wang et al 2021] [Wernicke 1980] [Withrow-Maser et al 2021] [Xu et al 2016] [Xu et al 2025] [Yan and Chen 2019] [Yang et al 2024] [Yang et al 2025] [Yassini and Syrovy 2002] [Yomchinda et al 2009] [You et al 2026] [Yuan 1970] [Yuan et al 2020] [Yurt et al 2026] [Zhang et al 2018] [Zhao and Sheng 2015] [Zhao et al 2025] [Zhou and Huang 2023]

Ducted fans and ducted-fan vehicles

Ducted fans and the vehicles built around them, from research testbeds to electric ducted-fan aircraft.

117 records. [A Variable-speed Control Method to Reduce Ducted-fan Thrust Fluctuations for Flying Car Utilization 2024] [Aboelezz et al 2022] [Ahn and Lee 2004] [Akturk and Camci 2022] [Akturk and Camcı 2014] [Alabdali et al 2025] [Ali and Maqsood 2024] [Alvarez et al 2023] [Avanzini et al 2001] [Avanzini et al 2003] [Boldman et al 1991] [Bustamante Alarcon et al 2025] [Casagrande Hirono et al 2022] [Castegnaro 2019] [Chakraborty et al 2022] [Chakraborty et al 2023] [Chen 2024] [Chen et al 2018] [Cheng and Pei 2020] [Cheng and Pei 2021] [Cheng et al 2020] [Chi 1991] [Choi et al 2012] [Cui et al 2025] [Darrah et al 2020] [Deng et al 2020] [Dorfling and Traub 2023] [Dos Santos et al 2024] [Ebus et al 2024] [Effati and Banazadeh 2013] [Engelbrecht et al 2022] [Fan et al 2017] [Fan et al 2018] [Feng et al 2026] [Fleming et al 2003] [Fu et al 2023] [Gao and Xu 2022] [Graf et al 2008] [Grant et al 2015] [Guerrero et al 2003] [Guo and Zhou 2022] [Guo and Zhou 2022] [Harada 2018] [Hess and Ussery 2004] [Huang et al 2021] [Hui et al 2025] [Jiang et al 2025] [Jiang et al 2025] [Jin et al 2018] [Junaidin and Cahyono 2019] [Kang et al 2021] [Keller and Holliger 1959] [Kondor et al 2001] [Young] [Lei et al 2024] [Li 2008] [Li and Liu 2023] [Liu 2023] [Liu and Mi 2025] [Liu et al 2019] [Liu et al 2022] [Liu et al 2025] [Liu et al 2025] [Ma et al 2017] [Ma et al 2022] [Mao et al 2024] [Mehr and Ning 2024] [Mi 2020] [MODELLING AND CONTROLLER DESIGN OF A NOVEL DUCTED FAN UNMANNED AIRCRAFT 2021] [Moser 1959] [Muehlebach and D’Andrea 2017] [Mumasha et al 2026] [Niwa and Suzuki 1991] [Niță et al 2026] [Odukoya and Jo 2026] [Ozdemir and Horn 2009] [Pangaribuan and Hartono 2024] [Park et al 2017] [Peddle et al 2009] [Pflimlin et al 2004] [Regan et al 2025] [Ritschl et al 2003] [Rybakov et al 2020] [Safieh and Rauleder 2024] [Sargent and Anemaat 2018] [Sarjito and Mulyadin 2024] [Savage et al 2026] [Sedunin et al 2024] [Seo and Kim 2016] [Shao et al 2022] [Sheng and Sun 2015] [Shiau et al 2023] [Shiau et al 2024] [Srivastava et al 1996] [Srivastava et al 1997] [Stiltner and Ohanian 2012] [Su et al 2021] [Su et al 2025] [Su et al 2026] [Sun et al 2025] [Van Niekerk 1958] [Van Weelden and Smith 1995] [Vasanthakumar et al 2019] [Wahid et al 2025] [Wahl and Julian 1956] [Wang and Li 2025] [Wang and Qi 2011] [White and Phelan 1987] [Wu et al 2025] [Xiang et al 2015] [Yoeli 2002] [Yu 2023] [Zakaria et al 2019] [Zhang and Fan 2012] [Zhang et al 2004] [Zhang et al 2016] [Zhao and Bil 2008]

Distributed and electric propulsion and electric vertical flight

Electric vertical takeoff and landing aircraft, distributed propulsion for lift and control, and the electric and hybrid powertrains that drive them, the field in which the square-root law now decides configurations.

152 of these 156 records date from 2015 or later.

156 records. [Agustinho and Bento 2022] [Ayar et al 2021] [Baculi et al 2023] [Baculi et al 2024] [Bahr et al 2020] [Bai et al 2022] [Barbosa Marques and Silva 2021] [Beals et al 2026] [Benyamen and Keshmiri 2022] [Bills et al 2023] [Brenner et al 2022] [Brenner et al 2023] [Cai et al 2026] [Campagna et al 2021] [Cao et al 2024] [Casalino et al 2024] [Chakraborty and Mishra 2023] [Chakraborty et al 2022] [Chan 2019] [Chen et al 2025] [Cheng et al 2025] [Comunian et al 2025] [Courtin and Hansman 2019] [Cusati et al 2023] [Nithya et al 2025] [Darmstadt et al 2021] [de Vries and Vos 2023] [Deere et al 2017] [Demers Bouchard et al 2015] [Distributed Electric Propulsion 2018] [Dožić et al 2026] [Elahi Kahooker and Liu 2026] [Feroskhan et al 2025] [Figueira et al 2025] [Filippoli et al 2026] [Fisler and Datta 2019] [Fossati et al 2024] [Foy 1983] [Fredericks et al 2013] [Freeman and Klunk 2018] [Gallani et al 2020] [Gan et al 2021] [Garcia et al 2026] [Gothow et al 2023] [Gothow et al 2024] [Govindarajan and Sridharan 2021] [Guo et al 2024] [Ha et al 2020] [Halder and Gandhi 2026] [He et al 2020] [He et al 2025] [He et al 2026] [Herzog et al 2021] [Hu et al 2024] [Hu et al 2025] [Jeong et al 2024] [Jia et al 2025] [Jiao and Yang 2026] [Johnsen et al 2022] [Johnson and Silva 2026] [Hansman et al 2023] [Kaneshige et al 2023] [Kang et al 2025] [Kim et al 2018] [Klunk and Freeman 2018] [Kraenzler et al 2019] [Krammer et al 2022] [Kuzniar et al 2020] [Lee and Yee 2024] [Lee et al 2022] [Lee et al 2026] [Lei and Zhao 2023] [Li et al 2022] [Li et al 2024] [Li et al 2025] [Li et al 2026] [Li et al 2026] [Lian and Wu 2018] [Liang et al 2025] [Liang et al 2026] [Lim] [Litt 2026] [Liu and Tan 2024] [Liu and Wang 2024] [Liu et al 2023] [Love 2022] [Lympany and Page 2024] [Ma et al 2020] [Ma et al 2025] [Mahvelatishamsabadi and Emadi 2020] [Maroldt et al 2023] [Mathur and Atkins 2026] [Moore and Ning 2019] [Müller et al 2026] [Narjes et al 2018] [Neogi et al 2025] [Ng and Datta 2018] [Nguyen et al 2022] [Nguyen et al 2023] [Nguyen Van et al 2020] [Niemiec et al 2020] [Oldeweme et al 2024] [Orefice et al 2019] [Panayotov and Zikyamov 2026] [Papathakis et al 2017] [Park 2025] [Park and Park 2026] [Pavel 2022] [Paw and Ang 2023] [Performance Metrics Required of Next-Generation Batteries to Electrify Vertical Takeoff and Landing VTOL Aircraft] [Perry et al 2023] [Pham et al 2022] [Raush et al 2016] [Rizzi et al 2017] [Russo et al 2023] [Sarikaya et al 2026] [Schrage et al 2018] [Scott 2025] [Seren and Hornung 2023] [Shang et al 2025] [Shankar et al 2022] [Shi et al 2023] [Shihua et al 2023] [Shubert and Sizoo 2025] [Shubert et al 2026] [Simmons 2023] [Snyder 2020] [Synodinos et al 2018] [Thapa et al 2025] [Theron et al 2020] [Van et al 2019] [Wang and Fang 2023] [Wang and Hu 2026] [Wang et al 2023] [Wang et al 2023] [Wang et al 2024] [Wang et al 2026] [Wei et al 2021] [Wei et al 2024] [Wei et al 2026] [Weng et al 2021] [Wiston and Yan 2025] [Wu et al 2023] [Xie et al 2023] [Yan et al 2025] [Yanev and Staack 2026] [Yang et al 2021] [Yang et al 2026] [Yang et al 2026] [Zhang et al 2021] [Zhang et al 2023] [Zhao et al 2024] [Zhao et al 2024] [Zhao et al 2025] [Zheng et al 2025] [Zong et al 2022]

Supersonic inlets, intakes and airframe-propulsion integration

Supersonic and subsonic inlets, inlet distortion and the integration of propulsion with the airframe.

243 records. [Abdel-Fattah 1997] [Abdul-Kaiyoom et al 2025] [Abedi et al 2020] [Afzal et al 2021] [Amin and Hollweger 1983] [Anderson 1983] [Andrew et al 1991] [Arif et al 2021] [Askari and Abedi 2026] [Askari and Soltani 2017] [Askari and Soltani 2020] [Bai et al 2025] [Bangert et al 1982] [Barr et al 2018] [Barry 1971] [Beale et al 2002] [Beale et al 2006] [Beale et al 2007] [Benjamin et al 2023] [Benton et al 2021] [Boles et al 2021] [Bond and Key 2025] [Braun and Podleski 2019] [Brix et al 2000] [Brown and Slaboch 2019] [Bucknell 1987] [Burrows et al 2017] [Cai and Huang 2022] [Cai et al 2022] [Cai et al 2022] [Candon et al 2016] [Cao et al 2017] [Castner et al 2018] [Chaudhari and Takahashi 2022] [Chen and Tan 2019] [Chen et al 2019] [Chen et al 2023] [Choe and Kim 2016] [Choe et al 2018] [Choe et al 2020] [Choi et al 2025] [Chopde et al 2025] [Chun and Burr 1969] [Chun and Swanson 1964] [Clark 1974] [Clingingsmith 1983] [Colbert et al 2023] [Conners et al 2005] [Control system design using frequency domain models and parameter optimization with application to supersonic inlet controls 1976] [Davis et al 2001] [Davoudzadeh et al 1987] [Dickman and Takahashi 2016] [Du et al 2012] [Edefur and Tormalm 2018] [Endo et al 2016] [Ezrokhi and Khoreva 2018] [Ezzeldin and Wu 2025] [fang et al 2024] [Farahani and Mahdavi 2019] [Ferrero 2020] [Florea et al 2015] [Flores et al 1989] [Fuqun et al 1985] [Gaglio et al 2021] [Gas Turbine Engine Inlet Flow Distortion Guidelines] [Ge et al 2021] [Gillen and Loth 2015] [Glasgow et al 1983] [Godard et al 2017] [Godard et al 2019] [Godston and Reynolds 1983] [Gubanov 2019] [Guidelines for Characterization of Gas Turbine Engine Total-Pressure, Planar-Wave, and Total-Temperature Inlet-Flow Distortion] [Guimarães et al 2017] [Halwas and Aggarwal 2019] [Hamed et al 1997] [Harjes et al 2022] [Hawkins 1976] [He et al 2023] [Heberling 2020] [Herrick 1986] [Herrmann 1996] [Hinz and Miller 1979] [Huang et al 2020] [Hubble and Smith 1979] [INFLUENCE OF BACK PRESSURE ON THE FLOW IN THE DIFFUSER OF A SUPERSONIC AIR INLET 2017] [Inlet Total-Pressure-Distortion Considerations for Gas-Turbine Engines] [Jahnen et al 1999] [Jin et al 2023] [Jones et al 2021] [Karaselvi and Nikbay 2021] [Kato et al 2024] [Kawai 1973] [Kaya 1998] [Keller et al 2018] [Khobragade et al 2021] [Kim and Kwon 2015] [Kim and Park 2026] [Kitowski 1992] [Knoth and Breitsamter 2017] [Kong 2000] [Korn 1974] [Koval 2020] [Kursakov et al 2022] [Kurzke 2006] [Ladd and Norby 1998] [Lauer and Ansell 2022] [Lavan Kumar et al 2013] [Lavi 1967] [Lee et al 2007] [Lee et al 2010] [Lei and Zha 2022] [Lepicovsky 2008] [Li and Geiselhart 2024] [Li and Geiselhart 2026] [Li et al 2023] [Lin et al 2018] [Lind and Protopapas 1977] [Liou et al 2016] [Liou et al 2017] [Liou et al 2019] [Little 1983] [Liu and Wu 2023] [Liu et al 2024] [Loss in turbofan thrust caused by boundary layer growth in a nacelle’s inlet and exhaust ducts 1985] [Loth et al 2016] [Lowe 2020] [Lucas et al 2014] [Luidens 1976] [Harish et al 2017] [Ma et al 2026] [Mace and Nyberg 1992] [Malan and Brown 1994] [Marvin 1968] [Medina et al 2021] [Menegozzo and Benini 2021] [Miao et al 2026] [Moore 1985] [Mufti et al 2019] [Naseri et al 2012] [Naseri et al 2012] [Nichols et al 2015] [Nicolae Tudosie 2018] [O’Brien and Lowe 2015] [O’Neill 2020] [Omar and Lampkin 1977] [Opalski and Sajben 2002] [Ordaz et al 2017] [Otto et al 2015] [Overall 1976] [Page et al 2017] [Palumbo et al 2022] [Patel and Chudoba 2026] [Pecinka et al 2015] [Peters et al 2001] [Pečinka et al 2017] [Piovesan et al 2025] [Powers and Robinson 1992] [Processing and Validating CFD Data for Estimating Inlet Dynamic Total-Pressure Distortion] [Qiu et al 2018] [Quraishi et al 2025] [Reyhner and Hickcox 1972] [Richey et al 1983] [Rohacs et al 2018] [Safoklov et al 2025] [Saleem Yusoof et al 2016] [Sanders and Palasics 1948] [Schierman and Lowell 1992] [Schmidt and Wild 2026] [Sedlock 1985] [Semmes and Weyer 1990] [Shimabukuro et al 1979] [Shimabukuro et al 1982] [Shmilovich and Yadlin 2026] [Shu et al 2025] [Silva et al 2024] [Slater 2016] [Slater 2019] [Smeltzer et al 1981] [Smeltzer et al 1982] [Smith 1997] [Snyder 2003] [Soeder and Bobula 1982] [Sorensen and Bencze 1974] [Sorensen and Latham 1975] [Sorensen and Smeltzer 1972] [Sorensen et al 1969] [Sorensen et al 1973] [Soto and Hernandez 2004] [Spencer et al 2016] [Stephens and Svetgoff 2024] [Stephens et al 2023] [Stylianides et al 2020] [Substantiation of Power Available and Inlet Distortion Compliance for Rotorcraft Engine Inlet Barrier Filter Installations] [Sun and Zhang 2016] [Sun et al 2024] [Sun et al 2025] [Surber and Robinson 1983] [Surber and Sedlock 1979] [Sussman 1968] [Sutrakar et al 2026] [Syberg and Koncsek 1976] [T-4 inlet/engine compatibility flight test results 1989] [Tekaslan et al 2021] [Tindell and Flynn 1978] [Tongguang et al 2015] [Tudosie 2017] [Tudosie 2017] [Tudosie 2018] [Tudosie 2022] [Tudosie and Prisacariu 2022] [Tudosie and Păunescu 2017] [Tudosie et al 2019] [Türkkahraman et al 2024] [Utomo and Bura 2019] [Vadyak et al 1987] [Vinogradov et al 2017] [Vnuchkov et al 2018] [Vogel 2016] [Vogel and Junqueira 2017] [Vohra 2024] [Wang et al 2013] [Wang et al 2015] [Wang et al 2023] [Wang et al 2025] [Williams and Hunt 1980] [Wilson and Wright 1977] [Wilson and Zhang 2025] [Woollett 1983] [Wu et al 2022] [Wu et al 2024] [Xia and Zhou 2024] [Xie et al 2015] [Yan et al 2023] [Yang et al 2026] [You et al 2016] [Yuan et al 2021] [Zhang et al 2017] [Zhang et al 2020] [Zhang et al 2020] [Zhang et al 2026] [Zhao et al 2025] [Zhu et al 2020]

Engine cycles, variable cycle engines and engine performance

Engine cycles, variable and adaptive cycle engines, the performance of fighter and lift engines, and propulsion systems and their control.

278 records. [A synopsis on Q/STOL engines 1971] [Adibhatla 1993] [Adibhatla 1994] [Airfoil static-pressure thrust - Flight-test verification 1990] [Amundson and Holm 1989] [Andreev and Druzhinin 1991] [Antonakis et al 2019] [Arar 2002] [Asri et al 2019] [Atkinson and Raymond 1968] [Aygun and Turan 2020] [Bailey et al 1979] [Balke 1970] [Barrack and Kirk 1968] [Barrett 1952] [Batterton and Blaha 1987] [Bayati and Williston 1977] [Beale 1986] [Beard and Foley 1982] [Berg et al 1988] [Bhandari et al 2024] [Biesiadny 1992] [Blaha and Batterton 1987] [Blaha and Batterton 1990] [Bloomfield 1959] [Bogdanovic et al 1964] [Bolam et al 2021] [Bolivar et al 2003] [Boruff and Roch 1981] [Boschma 1998] [Boschma 2001] [Bougas et al 2017] [Brandt 2018] [Brear et al 2003] [Brines 1973] [Brooks 1990] [Brown 1981] [Bucknell et al 1990] [Burcham 1971] [Butler and Thomas 1964] [Cao et al 2022] [Carlin et al 1984] [Cartagena et al 2000] [Chakraborty and Mishra 2022] [Chakraborty and Mishra 2023] [Chapman et al 2025] [Chen et al 2021] [Chen et al 2024] [Chipperfield et al 1999] [Clark et al 2023] [Clark et al 2023] [Clough 1990] [Colbert et al 2020] [Collopy and Collopy 1997] [Compton and Burgess 2021] [Conners 1992] [Conners 1995] [Coons 1987] [Curran and Bergsten 1975] [Curry 1975] [Cyrus 1995] [Dannenhoffer 1981] [Davenport et al 1974] [Denham 2002] [Denning and Mitchell 1986] [Design and Analysis of Supersonic Jet Propulsion Variable Cycle Engine by Using CFD Approach 2023] [Digital Engine Control for V/STOL and V/TOL Aircraft 1982] [Duvivier and McCallum 1960] [Elliott and Simmons 1987] [Engine Selection Parametric Cycle 2002] [Engine Selection Parametric Cycle 2018] [Engine Selection Performance Cycle 2002] [Farokhi 1998] [Feddersen and Cea 1977] [Feng et al 2026] [Fetahi et al 2022] [Flight-test evaluation of engine power effects on lift and drag 1985] [Franciscus 1983] [Franciscus and Luidens 1984] [Franklin 1993] [Franklin 1996] [Franklin and Engelland 1991] [Franklin and Engelland 1993] [Franklin 1993] [Franklin and Stortz 1989] [Franklin et al 1990] [Frazzini 1970] [Gallops et al 1990] [Garg 1993] [Garg and Mattern 1991] [Garg and Mattern 1994] [Garg and Ouzts 1991] [Garg and Schmidt 1993] [Garg et al 1990] [Garg 1993] [Garvin et al 2018] [Gerend 1971] [Gertsma and Zigan 1973] [Gielow 1971] [Gilyard et al 1991] [Goldsmith and Hickey 1963] [Gologan et al 2009] [Gou et al 2019] [Gray et al 2017] [Hao et al 2018] [Hao et al 2020] [Harned and Nay 1963] [Harrell 2018] [Hatta and Matsuki 1964] [Havey and Kline 1989] [Hensley et al 1950] [Herrmann and Biehl 1986] [Highly Noise-Suppressed Bypass 6 Engine for STOL Application 1975] [Hill 1971] [Hill and Schmitt 1964] [Hirsh 1965] [Hobson et al 2004] [Hoskin 1993] [Huang et al 2022] [Huete and Singh 1997] [Hughes and Ray 1985] [Hughes Tool Co Culver City Ca 1963] [Identification method of temperature corrections to aircraft engine thrust in flight tests 2023] [Imrak et al 2021] [Integration and simulated flight testing of a geared fan V/STOL airplane 1977] [Franklin 1993] [Ji et al 2026] [Jia et al 2023] [Jiang et al 2023] [Jiang et al 2025] [Kamman and Perryman 1982] [Keller 1982] [Khalid 1989] [Khalid 1992] [Kim and You 2026] [Kimberlin 1987] [Kleckner 1973] [Kohn 1972] [Kozlaykov 1997] [Kress 1980] [Krishnakumar et al 1996] [Kutney 1964] [Kuzmin 2021] [Lawrence and Cerbone 1990] [Lee et al 1988] [Lewis 1989] [Lewis and Lewis 1981] [Lewis and Simpkin 1980] [Li and Livne 1997] [Li et al 2018] [Li et al 2023] [Li et al 2024] [Lin and Jules 1998] [Liu et al 2022] [Liu et al 2024] [Liu et al 2026] [Liu et al 2026] [Lu and Burken 1999] [Lu et al 2019] [Luidens et al 1981] [l’Anson 1969] [Ma et al 2023] [Mahmoudi et al 2022] [Maine et al 1994] [Malloy et al 2002] [Margason 1998] [Martin 1977] [Mattingly 1989] [Matuschek et al 2023] [McGuigan 1970] [Mehrab et al 2023] [Mello and Kotansky 1985] [Meng et al 2017] [Meng et al 2018] [Mihaloew 1988] [Mihaloew and Weiss 1989] [Mihaloew and Drummond 1989] [Miller and Hackney 1976] [Moller 1985] [Nelson and Current 2018] [Neville et al 1992] [Nichols 1960] [Nie et al 2020] [Nilchiani et al 2025] [Ouyang et al 2024] [Panella 1975] [Pang et al 2025] [Papamoschou 2004] [Patel and Wilson 2018] [Perusek 1994] [Petrov 1993] [Pilsch 1975] [Platzer and Margason 1976] [Plourde et al 1983] [Pour Razzaghi et al 2025] [Pulk and Stolarik 1977] [Qian et al 2020] [Rauh and Anders 1986] [Ray 1983] [Rebeske and Rohlik 1953] [Reed 1980] [Reed 1984] [Reemsnyder and Sagerser 1979] [Ren et al 2017] [Requirements for STOVL integrated flight/propulsion control system 1994] [Requirements of a commercial supersonic aircraft on its engines 1967] [Richardson 1959] [Riggins 1996] [Robbins 1967] [Rodenbaugh and Veno 1965] [Rom and Koutz 1950] [Rose 1986] [Roth and Mavris 1999] [Ryan et al 1977] [Saboe 1963] [Sabzehali et al 2022] [Sallee 1973] [San Martin and Melnyk 2022] [Sanders 1964] [Sanghi 1999] [Seo et al 2022] [Serovy and Kavanagh 1974] [Sheridan 1983] [Shovlin et al 1980] [Simmons and Brant 1988] [Sininger 1976] [Spratt 1990] [Stewart 1992] [Strack 1973] [Su et al 2025] [Sulkoske et al 1977] [Swavely 1974] [Tahsin et al 2025] [Tam 2015] [Tao et al 2022] [Tape and McIntyre 1990] [Tate and Gillard 1975] [Tindell 1966] [Toenskoetter 1984] [Treubig et al 2015] [V/STOL propulsion control analysis 1981] [Wagner 1977] [Wahler and Elham 2025] [Warwick 1983] [Watts et al 1993] [West 1969] [Willis 1981] [Wilson et al 1981] [Wilson et al 1997] [Wright and Jones 1970] [Wright and Russell 1980] [Xiao-bo and Zhan-xue 2017] [Xu et al 2026] [Yang et al 2024] [Ye et al 2022] [Yi Fan et al 2021] [Young 1961] [Yu et al 2019] [Yuan et al 2024] [Zabinsky 1964] [Zabinsky 1978] [Zabinsky 1979] [Zabinsky and Carter 1972] [Zein-Sabatto et al 2017] [Zeng et al 2020] [Zeng et al 2020] [Zenkner et al 2025] [Zhang et al 2017] [Zhang et al 2018] [Zhang et al 2018] [Zhang et al 2020] [Zhang et al 2023] [Zhao et al 2017] [Zhou 2023] [Zhou et al 2019] [Zhou et al 2020] [Zhu et al 2024] [Zou et al 2025]

Defence acquisition, competition, prototyping and cost

Defence acquisition, competitive prototyping and fly-offs, source selection, cost estimation and cost growth, acquisition reform, and operational test and evaluation as part of acquisition.

140 of these 280 records are report primaries, the highest share of any cluster, because the literature of the decision is mostly written by the institutions that make such decisions.

280 records. [Abouamod and Awad 2017] [Achmadi and Priyatiningsih 2016] [Aggarwal et al 2010] [AI-Based Framework for Forecasting Defense Technologies in Defense Acquisition 2025] [Air Force Flight Test Center Edwards Afb Ca 1995] [Alberts 1995] [Alford 2004] [Aliyanto et al 2017] [Amara and Franck 2026] [Andrastek et al 1966] [Angell et al 2020] [Apgar 2003] [Army Aviation Materiel Labs Fort Eustis Va 1966] [Army Materiel Command Alexandria Va 1987] [Ascani et al 1980] [Aten and Dillard 2013] [Babione 1978] [Bacon 1988] [Bagan 1967] [Bahram 2022] [Bair 1994] [Balakrishnan and Lazar 2022] [Bangert et al 2017] [Bastola et al 2015] [Baylot et al 2018] [Bell 1993] [Bell et al 2018] [Bennett 1990] [Bergey and Wood 2002] [Berteau et al 2011] [Biggs et al 2014] [Bilardo 2026] [Bilodeau and Dallosta 1978] [Blank 2019] [Blumstein 1965] [Boger and Liao 1988] [Boger and Nussbaum 1990] [Boger et al 1989] [Boyd and Mundt 1995] [Brauer 2001] [Brett et al 1986] [Bridgeforth et al 2015] [Brisacier‐Porchon and Hammami 2023] [Bronson 2020] [Brooks et al 2012] [Brown 2010] [Brown and White 2017] [Buettner 2010] [Burton et al 2004] [Calafut et al 2021] [Campbell et al 2011] [Carlyle 1976] [Castagne et al 2004] [Cate 1997] [Cavolowsky et al 2010] [Cherry 1975] [Chewning and Moretto 2000] [Christensen 2023] [Christensen et al 1999] [Cisneros et al 2024] [Cloos and Nelson 1990] [Coble et al 2014] [Cox and Bohn 1982] [Cox and Bohn 1982] [Cronie and Thompson 1980] [Cubillos Chacon 2007] [Curran et al 2002] [Curtis 1987] [D’Amico et al 2018] [Daly et al 1979] [Davis 1973] [Davis 2011] [Davis and Tate 2020] [Defense Acquisition Univ Ft Belvoir Va 2005] [Defense Acquisition Univ Ft Belvoir Va 2007] [Defense Acquisition Univ Ft Belvoir Va 2007] [Defense Science Board Washington Dc 1975] [Defense Science Board Washington Dc 1979] [Defense Science Board Washington Dc 1993] [Defense Science Board Washington Dc 1993] [DeLaurentis 2011] [Dement 1990] [Department Of Defense Washington Dc 1993] [Department Of Defense Washington Dc 1994] [Department Of Defense Washington Dc 1995] [Department Of Defense Washington Dc 1996] [Department Of Defense Washington Dc 1998] [Department Of Defense Washington Dc 1999] [Department Of Defense Washington Dc 2000] [Department Of The Army Washington Dc 1992] [Dietz and Bailey 1973] [Dillard 2005] [Dougherty 2018] [Drake 1977] [Dreier 2022] [Droegkamp et al 1998] [Drozd and Procházka 2024] [Drury et al 2015] [Duddy et al 2020] [Dwyer et al 2015] [Enthoven 2019] [Espinoza-Garcia et al 2026] [Fast 2014] [Fellers and Patierno 1970] [Figge 1973] [Flores 2015] [Franck and Dillard 2006] [Franck et al 2012] [Frerking and Beauchamp 2016] [Fuhrman 1999] [Gallagher 1999] [Gallagher et al 1997] [Gansler and Lucyshyn 2006] [Gansler et al 2010] [Gaver et al 1997] [Gideon and Wasek 2015] [Gluckman and Celmins 1993] [Greer 2010] [Greer et al 1984] [Grosse 1965] [Guajardo 2020] [Guinivan 2004] [Hale 2004] [Hall 2019] [Hamada 2021] [Hans et al 2021] [Hantos 2008] [Hardy 1983] [Harris and Lewis 2012] [Harvey 2019] [Harvey and Ryan 2012] [Haug et al 1993] [Hawkins et al 2023] [Hawley et al 1986] [Healy et al 2014] [Herd et al 1965] [Hermann 1999] [Heymont et al 1965] [Hibbard and O’Brien 1993] [Hirsch 1998] [Hjorth et al 2020] [Hoffman 1971] [Horowitz et al 2014] [Hubbard and Caldwell 1989] [Huete and Nance 1994] [Hui et al 2017] [Hwang 1971] [Insaurralde and Kaupisch 2016] [Jessup and Williams 2015] [Jimenez et al 2016] [Jm and Dj 2017] [Jones 2024] [Jones and Wilbur D. 1989] [Jones et al 2023] [Kasunic 2004] [Keaton 2015] [Kilicay‐Ergin and Dagli 2015] [Kim and Hur 2016] [Koster 2004] [Kozlak et al 2017] [Kratz et al 1984] [Kubricky 2007] [Kundu et al 2002] [Labro 2004] [Lamoureux et al 2015] [Landale et al 2017] [Laughman 2010] [Lavelle 2017] [Lee 2022] [Leete et al 2015] [Li et al 2018] [Lieberman 2000] [Lieberman 2002] [Lisy et al 2023] [Logan 1974] [Logistics Management Inst Bethesda Md 1964] [Lorell 1989] [Loren and Beverly 2009] [Loren et al 1992] [MacKenzie 2003] [MacKenzie and Addison 2001] [Mandell 1997] [Marchinski 1974] [Markman et al 2021] [Marquiz et al 2025] [Marx 1983] [Marx et al 1995] [Marx et al 1998] [Mayori et al 2019] [McBride and Paret 2010] [McCown 2011] [McDaniel and Cooper 1999] [McDaniel et al 1995] [McDaniel et al 1998] [McGowin et al 2018] [McNicol 2022] [McNicol and Wu 2014] [McNicol et al 2015] [Medlej et al 2017] [Metcalf and Eftekhari-Shahroudi 2026] [Moeller 1980] [Moody 1997] [Moorhouse 1994] [Morgenfeld 1992] [Mortlock 2020] [Mortlock 2024] [Muchow 2013] [Mun 2020] [Na et al 2024] [Naval Sea Systems Command Washington Dc 2010] [Noguchi 2019] [One Prototype Three Prototype Five Prototype Seven Prototype 1986] [Palavenis 2024] [Park et al 2024] [Parrish 1978] [Pavick et al 2006] [Percival 1988] [Post and Sundt 2017] [Post et al 2017] [Pottinger et al 2017] [Preidis 1984] [Quinn and Choe 2012] [Rais-Rohani and Huo 1999] [Ramelli and Daniel S. 1976] [Rand 1999] [Regnier and Nussbaum 2011] [Rhoads 1992] [Robinson and Smith 1999] [Rosen et al 2019] [Rosenthal and Brandeau 1983] [Ross 2022] [Rozum 1992] [Rubinstein 2014] [Ryan 2018] [Sai 2004] [Salado and Shadab 2023] [Sauser and Ramirez-Marquez 2009] [Sauser et al 2009] [Schrage 1989] [Schrage 2015] [Schwartz 2019] [Shafer et al 1990] [Shawler 1981] [Shroder 1999] [Simms and Wehrkamp 2024] [Simpleman et al 1998] [Simpleman et al 2003] [Simpson 2003] [Smith 1999] [Sobel 2013] [Stahl et al 1984] [Stewart et al 2011] [Stuckey et al 2017] [Tan et al 2024] [Tate 2015] [Templin and Noffsinger 1994] [Test and evaluation - Reflections and recommendations 1994] [The Integrated Flight and Powerplant Control System Demonstration programme 1993] [Trepel and Bohmann 1973] [Trudelle et al 2017] [Trudelle et al 2017] [Turtle and Hermann 1998] [University Of South Florida Tampa 2000] [Valerdi et al 2015] [Vanderplaats 2001] [Vargo 2000] [Vascik et al 2015] [Wang et al 2021] [Watkins 2019] [Weed 2002] [Wei and Shi 2022] [Weinig 2019] [West and Pyster 2015] [Wickert 1985] [Wilken 1991] [Winbush and James O. 2012] [Worm 1980] [Yasir 2025] [Yates 1964] [Yu et al 2021]

Commonality, product families and requirements

Commonality across product families and variants, and the setting of requirements.

88 records. [Baker and Mavris 2001] [Bannova and Camba 2018] [Barber et al 1978] [Bashkirov et al 1997] [Baylis et al 2018] [Bye 1993] [Chen et al 2021] [Cheng et al 2018] [Chuprun 1984] [Cole and Jenkins 2015] [Crites and Tremblay 1988] [Cunningham 1981] [Dang and Nagarur 2000] [Dong et al 2020] [Fujita et al 2020] [Fusaro and Viola 2018] [Garmilla Manzano et al 2026] [Gerken 1979] [Goldberger 1966] [Han et al 2019] [Hansen and Rosen 2018] [Hao et al 2020] [Hillier 1999] [Hou and Lai 2015] [Hummell and Hause 2015] [Jennings et al 2025] [Jiang 2026] [Jung and Simpson 2015] [Kanon et al 2023] [Kim et al 2016] [Kim et al 2016] [Kim et al 2020] [Krammer and Holzapfel 2023] [Kwapisz et al 2019] [Lange and Mikolowsky 1979] [Lebacqz et al 1986] [Lei et al 2016] [Levine and Zalesch 1983] [Li et al 2023] [Lind and Tamplin 1981] [Mane et al 2021] [Milford and Pena 2015] [Mirchandani and Mishra 2002] [Morandini et al 2015] [Mullin 1986] [Nicolai 1978] [Nomaguchi et al 2017] [Oakes 1970] [Oh and Hong 2024] [Okumoto and Elsanker 1973] [Ordaz et al 2015] [Parker 1986] [Pinson and Ryan 1972] [Price 1964] [Rajpaul and Yurczyk 1977] [Ransone 1972] [Salado and Nilchiani 2015] [Schrage 1983] [Schrage et al 2001] [Schwartz and Shearer 1964] [Sepulveda Palacios and Smith 2019] [Siddique 2025] [Simpson 2017] [Smith 1966] [Spinelli and Kipouros 2025] [Stepniewski and Schneider 1964] [Stern 1984] [Stojanovski and Selva 2017] [Subarna et al 2020] [Takai 2018] [Takai 2019] [Takai and Sengupta 2016] [Takeda et al 2018] [Total control over design requirements 2001] [Van Dyke et al 1990] [Visconti 2026] [Wilcox and Quigley 1978] [Wong et al 2019] [Xu and Yang 2025] [Xu et al 2020] [Yang et al 2019] [Yao et al 2017] [Yongjie et al 2021] [Young et al 2017] [Zhang et al 2015] [Zhang et al 2019] [Zhang et al 2022] [Zweber et al 2017]

Decision analysis, selection and cost-effectiveness

Multi-criteria decision analysis, selection, tradespace exploration and cost-effectiveness.

47 records. [Arfer 2024] [Barbour 1996] [Bertoni et al 2018] [Bhatra and Mishra 2023] [Braafladt et al 2020] [Buchanan et al 2019] [Chhabra and Warn 2017] [Cordeaux 1991] [Daniels et al 2022] [de Moraes et al 2025] [Egorov et al 1997] [Englar and Kirkpatrick 1969] [Erwig and Kumar 2025] [Fralish 1998] [Franklin and Nicholas 1992] [French 2025] [Fujita et al 2017] [Gillespie et al 2017] [Goncalves and Kokkolaras 2015] [Gordon 1980] [Hakan Ayhan Dağıstanlı 2025] [Houten et al 2024] [Howard 1974] [Huang et al 2023] [Jackson et al 2017] [Jaini and Utyuzhnikov 2016] [Jamali and Lazarova-Molnar 2024] [Kahneman and Tversky 1977] [Kiratsoudis and Tsiantos 2025] [Kizielewicz et al 2025] [Louw and Esterhuyse 2022] [Montibeller and von Winterfeldt 2015] [Phillips 2024] [Radojcic 2018] [Rosaria 2017] [Schneider 1989] [Shekhovtsov et al 2025] [Shi and Chen 2022] [Shrivastava et al 2016] [Specking et al 2019] [Stach and Pizzolo 2025] [Stojković and Dimić 2024] [Sundararajan 2020] [Sutton et al 2024] [Sutton et al 2024] [Turner et al 2022] [Zhang et al 2016]

Digital engineering, model-based systems engineering and machine learning

Model-based systems engineering, digital threads and twins, simulation-based acquisition and machine learning applied to aircraft and their design.

87 records. [Ahlbrecht et al 2024] [Akundi and Mondragon 2021] [Assef and Geiger 2023] [Aydemir et al 2020] [Babineau 2015] [Bachman 2016] [Bader et al 2024] [Beery and Paulo 2019] [Bennett 1997] [Benyamen et al 2024] [Bickford et al 2020] [Bluff 2001] [Brusa 2021] [de Longueville et al 2024] [Doff-Sotta et al 2025] [Duverger et al 2024] [Duverger et al 2025] [French 2015] [Garriga et al 2019] [Georgiades et al 2019] [Gharbi et al 2017] [Gracias and Gallegos 2024] [Gregory et al 2024] [Gregory et al 2026] [Pierce et al 2024] [Huang et al 2025] [Huldt and Stenius 2018] [Iwata et al 2015] [Jacobitz and Liu-Henke 2020] [Jia et al 2021] [Kallou et al 2022] [Kallou et al 2024] [Kamberov and Ivanov 2024] [Kirz 2022] [Kraft 2018] [Liu et al 2023] [Lopez and Akundi 2022] [Lu et al 2026] [Lukyanov et al 2024] [Madni et al 2019] [Martinez et al 2025] [Massegur Sampietro and Da Ronch 2024] [Mavris et al 2018] [McManus and Goodrich 1989] [Medinacelli et al 2023] [Shi et al 2025] [Muthukumar et al 2026] [Noguchi 2026] [Nunes et al 2023] [Oyama and Kato 2025] [Ponsard and Darimont 2023] [Popisal 2015] [Power et al 2021] [Qiao et al 2026] [Engelbeck et al 2025] [Rauzy and Haskins 2018] [Richardson 2023] [Ruan et al 2025] [Rudolph 2024] [Sahebsara et al 2026] [Schluse et al 2017] [Schumacher et al 2025] [Seddik 2026] [Soares 2007] [Soares 2007] [Specking et al 2018] [Sundaram and Brownlow 2018] [Sungyeon et al 2024] [System Entity Structure and Model Base Framework in Model Based Engineering of Simulations for Technical Systems 2017] [Tadeja et al 2019] [Kulkarni et al 2016] [Thomas and Mesmer 2016] [Through the Virtual Barrier: Virtual Prototyping And Analysis with Model-Based Systems Engineering 2017] [Tsui et al 2018] [Walter et al 2019] [Wang 2020] [Williams 2004] [Wu et al 2025] [Xie et al 2015] [Yang and Yee 2022] [Yin et al 2017] [Arias et al 2025] [Zargariasl and Herglotz 2024] [Zech et al 2026] [Zhang et al 2021] [Zhao et al 2026] [Zhou et al 2022]

Low observability and signatures

Radar cross section, infrared and visual signatures, and low-observable design.

32 records. [Abdullah and Miao 2026] [Abdullah et al 2025] [Aleisa et al 2024] [Appendix HAVE BLUE TECHNOLOGY 1998] [Baldwin 1973] [Chen et al 2015] [Cheng et al 2016] [Cho et al 2015] [Colbacchini et al 2016] [Design and analysis of effective graded microwave absorbing material for low observable technology 2020] [Jeong et al 2018] [Jylha et al 2019] [Kurdyla 1963] [Lee 2024] [Lee et al 2018] [Liu et al 2025] [Marcus 2019] [Narayan et al 2022] [Ohio State Univ Columbus Electroscience Lab 1968] [Persson 2017] [Persson and Bull 2016] [Poe and Arthur C. 1974] [Ryan 1967] [Sai Teja et al 2017] [Sharma et al 2023] [Sreeja et al 2019] [van Schalkwyk and Smit 2017] [Wang et al 2025] [Wright 1966] [Xu et al 2020] [Yu Zhou Zhong et al 2018] [Zhang et al 2026]

Automatic and autonomous landing and guidance

Automatic, guided and autonomous landing of vertical, short takeoff and fighter aircraft, including vision-based landing on moving platforms.

18 records. [Ailon 2006] [Ailon 2009] [Chen 2018] [Franklin et al 1996] [Guy 1976] [Hess 1977] [Hynes et al 1989] [Lee et al 2020] [Marconi et al 2002] [McGee 1977] [Mohd Shah et al 2019] [Seitz and Goodson 1973] [Silva et al 2017] [Vaispacher et al 2025] [Watson et al 1986] [Weichelt et al 1986] [Wen et al 2021] [Zhang et al 2022]

Handling qualities, flight control and hover control

Handling and flying qualities, flight control laws and pilot workload of powered-lift, vertical and fighter aircraft, and hover and transition control.

235 records. [Aiken et al 1977] [Akagi et al 2024] [Albang and Roberts 1974] [Aliaga et al 2026] [Anderson 1984] [Anderson 1996] [Anderson and Innis 1965] [Anderson et al 1984] [Armutcuoglu et al 2004] [Athani and Agarwal 1994] [Bachelder et al 2019] [Balas et al 1996] [Barker 1966] [Baron 1981] [Beard and Foley 1983] [Beaufrere 1988] [Bellaire and Bousman 1970] [Beppu et al 1966] [Bhardwaj and Holzapfel 2024] [Bodden and Virnig 1994] [Boothe et al 1974] [Borchers et al 1992] [Boskovic and Mehra 2000] [Bosworth and Cox 1989] [Bryson et al 1970] [Buffington 1997] [Buffington 1999] [Buffington 1999] [Cabarbaye] [Calise and Kramer 1982] [Capen 1971] [Cappetta 1993] [Carpenter 1970] [Carpio-Alemán et al 2016] [Chance Vought Corp Dallas Tx 1979] [Chen et al 2018] [Chetty and Raol 1992] [Blanken and Whalley 1993] [Chung et al 1993] [Clark 1964] [Coder 2015] [Cook 1964] [Corliss et al 1977] [Cornish 1965] [Cunningham 1976] [Curtiss 1969] [Curtiss 1971] [Czerwiec et al 2000] [Dendy and Tribken 1968] [Design of the circulation control wing STOL demonstrator aircraft 1979] [Determination of the energy performance of a helicopter in a hover 2018] [Do 2021] [Dobos-Bubno and Hartsook 1977] [Dong et al 2021] [Douglas et al 1990] [Drake 1965] [Du 2025] [Dukes 1970] [Eilertson 1977] [Engelland 1991] [Engelland et al 1992] [Englar 1975] [Englar 1987] [Englar and Huson 1984] [Englar et al 1977] [Englar et al 1999] [Equations of Motion for Hover and Forward Flight 2002] [Erzberger and McLean 1979] [Ferrell et al 1974] [Fialho et al 1997] [Fielding and Lodge 2000] [Fielding and Southworth 2001] [Flight control system of an advanced air superiority fighter 1977] [Foster et al 1987] [Franklin 1994] [Franklin and Innis 1977] [Franklin et al 1986] [Franklin et al 1989] [Franklin et al 1982] [Franklin et al 1988] [Friedman et al 2016] [Friend 1964] [Frost et al 2002] [Gallagher and O’Donnell 1965] [Gao et al 2020] [Garratt et al 2013] [General Electric Co Schenectady Ny 1952] [Aerospace Design Co Inc Bedford Ma 1987] [Hall 1998] [Harper and Robert P. 1955] [Harper and Sardanowsky 1969] [Harschburger 1983] [Haugen 1966] [Haworth et al 2024] [Hebbar et al 1999] [Hebbar et al 1999] [Hill 1966] [Hill 1981] [Hill 1987] [Hoffman et al 1971] [Hoh and Mitchell 1983] [Hosseini et al 2021] [Huang et al 2003] [Jackson and Coyle 1983] [Jarvis 1967] [Jenkins 1973] [Jewell et al 1978] [Jewell et al 1979] [Johnson and Craig 1974] [Johnston and Friend 1965] [Kai 2024] [Kalemaris 1983] [Kazan and Krause 1968] [Kazan and Krause 1967] [Key et al 1965] [Kim et al 2025] [Klingloff et al 1965] [Kogler and Quam 1983] [Kok et al 2017] [Konar et al 1974] [Krosche and Heinze 2015] [Kubo and Suzuki 2007] [Lacey 1977] [Landy and Kim 1984] [Lateral-Directional Flying Qualities in Hover 2002] [Lee et al 1988] [Lei and Zha 2021] [Lei and Zha 2023] [Lei and Zhao 2024] [Li 2021] [Li et al 2023] [Li et al 2024] [Lin and Hsu 1984] [Lin et al 1994] [Liu et al 2025] [Longitudinal Flying Qualities in Hover 2002] [Loranchet et al 2025] [Lorenzetti et al 1969] [Lorenzetti et al 1969] [Loth and Boasson 1984] [Loth et al 1976] [Makarov 2019] [Malicki et al 2023] [Malik and Lin 2004] [Malpica et al 2023] [Margason and Hoad 1979] [McCormick 1956] [Meckstroth and Blake 2015] [Merrick 1960] [Merrick 1981] [Mitchell and Hoh 1983] [Moens and Dandois 2016] [Moitra 2002] [Moralez et al 1987] [Morris et al 1964] [Mueller 1964] [Nardi 1970] [Neal and Smith 1971] [Nichols and Englar 1980] [Osterman and Mulley 1977] [Ostheimer and Giguere 1963] [Panish et al 2023] [Patierno and Asdurian 1965] [Pauli 1964] [Pinsker 1970] [Planeaux 1990] [Powers et al 1992] [Prilliman and Slingerland 1966] [Putman 1961] [Qiao et al 2026] [Raab et al 2018] [Ramachandran and Wells 1974] [Ramnath 1969] [Rampy 1966] [Reschak 1970] [Rigatos 2021] [Riley et al 1989] [Rizzetta and Visbal 2016] [Roberts et al 1966] [Roltgen and Byrnes 1991] [Sachs 1977] [Samuels and Hahn 1986] [Saraswathi 2000] [Saripalli 1995] [Schmidt 1987] [Schroeder and Merrick 1990] [Schütte and Hummel 2023] [Sellers III et al 2002] [Selman 2023] [Shannon and Wang 1973] [Shrivastava and Mohite 2015] [Shubert and Jones 2025] [Shunxiang and Rui 2017] [Silva-Martinez et al 2015] [Skelton 1968] [Smith and Meyer 1981] [Smith et al 1973] [Soudakov et al 2018] [Sparks 1991] [Stauffer et al 1990] [Steer 2003] [Steils 1965] [Stone 2002] [Stradtner et al 2026] [Swaim 1970] [Swortzel and Barfield 1976] [Szabolcsi and Gáspár 1997] [Takahashi and Gaydusek 2026] [Tanaka et al 1994] [Tao et al 2021] [Tatum and Giles 1988] [Teel 1999] [Teel 1999] [Thames 1965] [The role of human factors in VTOL aircraft display technology 1986] [Theisen et al 1973] [Tischler and Hoh 1982] [Vincent and Anex 1990] [Vogt et al 1989] [VTOL Aircraft Control Design 2010] [Wang and Ma 2021] [Wang et al 2019] [Weber 1982] [Westbrook 1964] [Whatley et al 1990] [Winick 1968] [Wise et al 1999] [Wlezien and Ferraro 1990] [Wood and Roberts 1988] [Xili et al 2008] [YAV-8B reaction control system bleed and control power usage in hover and transition 1993] [Zha and Ren 2023] [Zha et al 2024] [Zhu et al 2022] [Zipf 1989]

V/STOL and STOVL aircraft concepts, programmes and design studies

V/STOL, STOVL and STOL aircraft concepts, programmes and design studies whose titles name no particular propulsion component.

267 records. [Adelt 1983] [Airspeed Vs Flight Path Angle Performance Method For Powered-Lift Aircraft 2003] [Anderson 1983] [Bay 1977] [Beebe 1968] [Bell Aerospace Co Buffalo Ny 1970] [Belluomini et al 2023] [Bhandari and Chakraborty 2026] [Biesiadny 1991] [Biggers and Linden 1985] [Binkley 1986] [Birckelbaw and Nelson 1992] [Blackwell 1970] [Boeing Co Morton Pa Vertol Div 1956] [Bottorff 2004] [Bradfield 1981] [Brady and Gururajan 2025] [Briggs and Schwind 1983] [Brown 1965] [Brown 1989] [Brown and Fisher 1968] [Brown 1978] [Caldwell and Lafavor 1980] [Camacho 1991] [Campbell 1959] [Chaderjian et al 2002] [Chana 2002] [Chin 1988] [Chong and Simmons 2024] [Cole and England 1967] [Composite Power Plant System for V/S.T.O.L. Aircraft 1962] [Conlon and Bowles 1977] [Conlon and Bowles 1978] [Cornish 1964] [Coty and Kesling 1967] [Courtin et al 2020] [Cox and Roskam 1990] [Crafa and Reed 1980] [Cui et al 2019] [Czinczenheim 1977] [Davenport et al 1972] [Day 1965] [Deckert and Franklin 1989] [Denning 1962] [Diekmann 2019] [Doerr 1987] [Doherty and Butzel 1979] [Doherty and Butzel 1979] [Driggers 1978] [Durbin and McGeer 1982] [Durston and Smith 1981] [Durston and Stonum 1987] [Durston and Stonum 1988] [Dymarchuk and Marynoshenko 2025] [Eckard and Poth 1983] [Egerton and Fitzpatrick 1967] [Englar and Campbell 2002] [Englar and Campbell 2005] [Falarski et al 1981] [Ferry 1960] [Fielding 1982] [Fry and DeDecker 1971] [Galdieri et al 1992] [Gamon 1988] [Gappa 1964] [Gerhardt and Chen 1978] [Giurca 2014] [Gorham 1977] [Gowanlock 2025] [Green and Andrews 1989] [Green and Bogle 1991] [Groen 1987] [Groen 1988] [Hall 2002] [Hamilton and Richardson 1988] [Harding 1972] [Hardman et al 1991] [Harradine 1977] [Harris 1956] [Hays and Schultz 2025] [Hazen 1963] [Hebert et al 1970] [Hebert et al 1970] [Hebert et al 1973] [Heintzman 1965] [HELICOPTER AND V/STOL AIRCRAFT NOISE MEASUREMENT PROBLEMS] [Henderson 1964] [Hendrickson et al 1984] [Henschel et al 1974] [Hesse 1965] [Hirschberg 1997] [Hirschberg and Pryce 2008] [Hirschberg et al 2002] [Hirschberg et al 2003] [Hiscock 1981] [Hollister 1969] [Holloway et al 1972] [Holzhauser et al 1972] [Howze 1969] [Hsin 1974] [Hutchison et al 1983] [Hynes and Scott 1976] [Irvin and Swan 1956] [Irvine 1968] [Jain and Mukkamala 2016] [Jenista and Sheridan 1987] [Johns 1986] [Johnston 1964] [Jones 1971] [Joppa 1969] [Kakavitsas et al 2024] [Kalemaris and Cea 1977] [Kelley 1970] [Kelly et al 1977] [Kidwell 1981] [Kidwell and Rapp 1985] [Kidwell and Lampkin 1983] [Kimberlin and Sinha 1983] [Kirby 1964] [Knapp 1980] [Knott 1977] [Koenig et al 1977] [Kondo 1975] [Kondoleon 1968] [Krepski and Hudson 1981] [Kuhn 1979] [Kuhn 1980] [LaBiche 2003] [Landfield and Henderson 1984] [Levinsky and Ramsey 1972] [Lind and Beck 1991] [Linnell 1963] [Lo 1970] [Lombard and Heyworth 1963] [Maita et al 1983] [Maita et al 1990] [Manley and von Klein 2002] [Marchese 1963] [Margason 2002] [May and Widdison 1971] [May and Widdison 1971] [McCarthy 1992] [McCarthy and Kelly 1993] [McCormack and Poteate Jr. 1965] [McCrea 1992] [McElreath 1972] [McIntyre 1963] [McIntyre et al 1977] [McNally and Bach 1988] [McPherson 1977] [Meiklem 1969] [Melgaard 1986] [Mendela 1971] [Michaels 1969] [Mihalik and Keane 2022] [Minsk 1970] [Moller 1998] [Moorhouse 1990] [Morozov et al 2006] [Mueller et al 2009] [Musselwhite 1978] [Müller and Hirschberg 2007] [Nadel 2017] [Nakaguchi 1967] [Nelms 1984] [Nelms and Durston 1980] [Norton 2002] [O’Brien and Delgado 2024] [O’Mallei 1957] [Overfield and Crawford 1967] [Papadales and Basil S. 1979] [Peaslee 1971] [Petrolo et al 2014] [Philhower et al 1998] [Platt 1991] [PlCKERELL and Cresswell 1968] [Price 1964] [Puvrez 1965] [Ramirez et al 1980] [Ransone 1971] [Ransone 2002] [Ransone and Basquez 1967] [Rapp 1985] [Raymer 1988] [Reed and Avery 1966] [Reid 1982] [Reid et al 1977] [Representative Operations of V/STOL Aircraft 2002] [Rich 1969] [Rich 1969] [Riesenfeld 1968] [Riviere and Vignevic 1981] [Roberts and Deckert 1982] [Rocher et al 2002] [Rosenthal et al 1988] [Roth 1993] [Roth 1996] [Roth 1997] [Rudolph 1972] [Rusbarsky 1990] [Sabut et al 1999] [Salkind 1973] [Samuels and Payne 1990] [Schade 1968] [Schaefer and Velten 1971] [Scherrer and Olson 1971] [Schmitz and Stepniewski 1973] [Scientific and Technical Information Division 1966] [Selegan 1983] [Sivan 1971] [Sivrioğlu 2023] [Skifstad 1970] [Smith 1996] [Smith 1997] [Song et al 2021] [Spillman 1965] [Spivey 2002] [Spooner 1968] [Stark 2003] [Steele and Aurora 1978] [Sternfeld and Hinterkeuser 1970] [STOL, VTOL, and V/STOL - Where do they fit in 1971] [Strand 2010] [Stutz and Price 1964] [Swaim 1969] [Swaim and Connor 1968] [Szlenkier 1972] [Takeda 1985] [Tamplin et al 1990] [Tuck 1970] [Turkmen and Altug 2020] [Turner 1969] [V/STOL R and D in France 1971] [V/STOL World wide view 1971] [Vagianos and Rooney 1964] [Van Dalsem et al 1990] [Vandalsem et al 1989] [Vertical take-off aircraft 2001] [VTOL - 1968 1969] [Nelms and Anderson 1984] [Wachtell 1970] [Waesche and Midgal 1975] [Wardwell and Sandlin 1988] [Wardwell et al 1996] [Watson et al 2019] [White et al 1985] [Wiargason and Kuhn 1987] [Wigeland et al 1977] [Willis and Genever-Watling 1977] [Wilson et al 1981] [Wilson et al 1982] [Wilson and White 1993] [Wilson et al 1985] [Winborn 1970] [Windolph 1969] [Wollner 1971] [Wood 1972] [Woods 1957] [Woolard 1974] [Wynosky et al 1974] [Yang and Wang 2017] [Yoo and Strash 1990] [Yoon 2025] [Zabinsky and Burnham 1977] [Zafi and Chakraborty 2023] [Zhang 2017] [Zimmerman 1957]

Flight test, instrumentation and system identification

Flight test of fighters, demonstrators and research aircraft, with its instrumentation and the analysis of its data.

14 records. [Armstrong 1977] [Baier 1970] [Dungan and Clark 1994] [Hess 1986] [Jain et al 2017] [Martínez Morán 2018] [Metz 1992] [Nagel and Thomas 1965] [Smith and Pellicano 1992] [Smith et al 1979] [Thigpen and Whitmoyer 1976] [Veletas 2026] [Wages 1971] [Wulff and Zoellner 1991]

Fighter and supersonic aircraft design

Fighter and military aircraft design, from combat aircraft concepts to demonstrators and their structures.

104 records. [Adams et al 2025] [Agrawal et al 1992] [Aleisa et al 2023] [Allen et al 2000] [Apte and Athani 1979] [Bacci et al 2026] [Badaliance and Dill 1981] [Banks 1988] [Behavior Patterns of Three Archetypal Arms Suppliers Based on Empirical Media Analysis of the First Korean Fighter Jet Program 2022] [Beskar 2004] [Bischoff 1981] [Bischoff and Palmer 1983] [Bonner 1971] [Boppe 1985] [Bryson 1971] [Bykerk et al 2022] [Caap and Elemeland 1986] [Casteel and Weyl 1970] [Cenko 1979] [Chapman 2018] [Clark 1984] [Computational analysis of an advanced jet-flapped fighter aircraft 1994] [Cummings et al 2018] [Dacquino and Raffaele 1982] [Dement and Hartman 1986] [Donegan and Fox 1991] [Dudley 1986] [Enzinger 1988] [Erickson 1980] [Finger et al 2023] [Fletcher and Burns 1979] [Foss 1978] [Fundamentals of Fighter Design 2001] [Gangl et al 2013] [Geiger 2002] [Ghazi 1994] [Gibb 1976] [Glenn and Koch 1973] [Harrell 1986] [Harris 1989] [Hendrickson et al 1978] [Hentges 1985] [Herbst and Ross 1970] [Hitzel 2022] [Horie and Conway 2000] [Howell 1987] [Huang et al 2003] [Huffman et al 1987] [Hwang and Pi 1975] [Johnson 1985] [Karniadakis 2004] [Kisslinger and Vetsch 1965] [Kolodziejczyk 1984] [Lee and Boedicker 1985] [Lewis 2002] [Mann and Carlson 1994] [Mann and Mercer 1986] [Masud et al 2017] [McClaskey and Evans 1996] [Meckstroth and Ordóñez 2020] [Miller and Schemensky 1979] [Miller and Wood 1986] [Murnane 1975] [Nangia et al 2004] [Nastase 1998] [Norris and Lan 1991] [Olwi 1995] [Palusamy and Sivier 1993] [Parker and Ball 1974] [Rallabhandi and Mavris 2003] [Ray et al 1988] [Raymer 1995] [Raymer 1998] [Reubush et al 1985] [Reuther 2002] [Reymer et al 2014] [Rs et al 2018] [Samuels 1992] [Schwartz 1988] [Sepulveda and Smith 2019] [Shane 1992] [Silverman 1978] [Spearman 1984] [Squires 2004] [Stanniland 1974] [Takovitskii 2023] [Tamrat 1983] [Tamrat 1988] [Tariq and Mazhar 2021] [Teng and Yu 2023] [Tikka 2008] [Triplett 1980] [Vázquez et al 2004] [Wang et al 2021] [Ward 1989] [Weeks 1986] [Wells 1974] [Whitford 1991] [Whitford 1995] [Woelk 1989] [Xu 2023] [Xu and Yu 2025] [Yu 2025] [Zhang and Cheng 2024]

High-lift and powered-lift aerodynamics

High-lift and powered-lift systems and their computation, with the jet flow studies that fit no narrower cluster.

51 records. [Aliaga et al 2025] [Beatty and Narramore 1976] [Bennie and Fossati 2024] [Bertram 2016] [Carrannanto et al 1998] [Cohen 1984] [Colletti and Ansell 2023] [Computational Study on the Effect of Vane Design in Enhancing the Mixing of Subsonic Jet and Sonic Jet 2023] [Direct Lift in Theory 1936] [Dixon and Driskill 1985] [Eyi et al 1996] [Galpin et al 2002] [Gimmestad 1981] [Gong 2017] [Hendrickson and Agarwal 2021] [Hwang 2015] [Iannelli et al 2017] [Jandaurek and Johst 2019] [Jie et al 2017] [Kang Ning and Shi YouMin 2018] [Kim et al 2004] [Kojima et al 2026] [Kress 1983] [Kuhlman and Collins 2000] [Kuhlman and Scarberry 2002] [Lacy and Sclafani 2016] [Liebeck 1978] [Lindblad and de Cock 1999] [Liu et al 2016] [Lu et al 2025] [Moitra 2002] [Morgan 1985] [Olson and Albertson 2016] [Pease et al 2022] [Philipsen 2021] [Pratap Singh et al 2023] [Probst and Melber-Wilkending 2021] [Rogers 1994] [Sarakinos et al 2018] [Sau 2022] [Selig and Guglielmo 1997] [Snyder 1950] [Stewart et al 2026] [Somashekar et al 2024] [Valarezo and Chin 1994] [Valarezo and Mavriplis 1995] [van Dam et al 2001] [van den Kieboom and Elham 2016] [Yan et al 2021] [Yoon et al 2016] [Łapka et al 2019]

Where the Framing Breaks Down

Treating this aircraft through its keystone misleads in five places.

The Square-Root Law Is Not the Whole Trade

A lift fan costs weight, volume and complexity, and this article has priced none of them. The fan, its shaft, its clutch and its gearbox occupy the space immediately behind the cockpit in the STOVL variant, which trades fuel volume for them [Lockheed Martin X-35], and every pound of that hardware is carried on every sortie by every STOVL aircraft in the fleet.

The appeal of a direct-lift system is that it adds almost nothing. The engine is already there and the valve and the nozzles are comparatively light [Boeing X-32]. The correct comparison is not thrust against thrust but thrust against the weight and volume spent to obtain it, and this article has computed only one side of it.

The Bring-Back Number Uses an Assumed Lift

The X-32B’s STOVL lift is not published and the article assumes the engine’s military rating as an upper bound. Every allowance figure inherits that assumption. The sensitivity table shows that the conclusion holds across the plausible range and that no value inside it produces a comfortable allowance, but a published figure could move the numbers and the article would have to follow.

A Fly-Off Is Not the Only Evidence

The decision was not made by watching two aeroplanes fly. It rested also on each team’s Preferred Weapon System Concept, the production design that the concept demonstration contracts paid each team to define [Joint Strike Fighter programme], of which the flight demonstrations were one input. Treating the competition as a race is a simplification that this article has adopted for the sake of a clean argument, and a source selection weighs many factors of which demonstrated performance is one.

The Wing Change Cuts Both Ways

The article treats Boeing’s mid-competition wing change as damaging to its evidentiary position, and it can be read the opposite way. A company that identifies a configuration problem and fixes it before proposing has done what a risk-reduction phase is for. The customer could reasonably have credited the correction rather than penalising the mismatch, and the public record does not say which reading the source selection took.

The Aircraft Was Not Bad

It flew 144 times, went supersonic, refuelled in the air, hovered and landed vertically. [Boeing X-32A flight test release] [Boeing X-32B flight test release] The government lead pilot praised its flying qualities [Boeing X-32A flight test release]. An aeroplane that does everything asked of it and loses is not a failure of engineering, and an article organised around why it lost risks implying that it should not have been built.

The Source Base

The research survey holds 3,528 research records drawn from Crossref, the NASA Technical Reports Server and the Defense Technical Information Center, of which 629 are report primaries, being 17.8 percent, by the identifier rule set out under The Definition of Primary. The median publication year is 2003. Of the 3,500 dated records, 1,747 were published through 2002 and 1,480 from 2015 onward, and the table gives each period as a share of the dated records. Every anchored record is cited.

Period Records Share
Before 1970 287 8.2 percent
1970 to 1984 663 18.9 percent
1985 to 1995 501 14.3 percent
1996 to 2002, the programme window 296 8.5 percent
2003 to 2014 273 7.8 percent
2015 onward 1,480 42.3 percent
of which 2022 onward 730 20.9 percent

The count and the fraction are reported together, because adding a contemporary survey holds the period count and lowers its fraction while adding period sources does the reverse. Neither movement is a fact about coverage.

The Equations That Carry No Citation

Some displayed relations carry no citation of their own and that is deliberate. They are the relations that construct the bring-back allowance and follow its consequences, the roll moment as differential thrust times a lateral arm, and the ratio between the winner’s and the loser’s record counts.

The bring-back relations and the record-count ratio are constructions original to this article, so attaching a citation would be false attribution. The weights and thrusts they take as inputs are cited where they are first given. The roll moment is elementary statics and citing it would be worse than leaving it bare.

Everything else carries its literature. Momentum theory, the figure of merit, the disc loading as a dynamic pressure, the corrected engine parameters, the ingestion correlations, the twin-jet fountain and the competitive-prototyping case all rest on published work and say whose.

This Article Has Two Primary Bases and They Sit in Different Decades

A primary source is one contemporary with the work, and for this article the work is two things that happened thirty years apart.

The decision is a 1996 to 2002 subject. Source selection, competitive prototyping, cost estimation and requirements commonality are primary in that window and nowhere else, and that band holds 296 records.

The physics is not. The short takeoff and vertical landing research the competition rested on was done in the 1970s and 1980s, largely by NASA, and a 1985 report on hot gas ingestion is a primary source for this article’s central failure mechanism in a way that a 2019 review is not. That base holds 1,164 records across 1970 to 1995 and is the healthier of the two.

Treating the whole of the pre-2003 material as one undifferentiated period band would hide that distinction, so the table above separates them.

Two Contemporary Headings Follow From the Argument

Two contemporary subjects follow from results this article derives rather than from being merely recent.

Shipboard thermal and deck interaction is the operational consequence of the disc-loading identity derived in the sizing section. An architecture at 2,852 pounds per square foot imposes almost twice the pressure of one at 1,467 on the same deck at the same landing weight, and a deck that receives such an aircraft must be built to bear that number.

Digital engineering and model-based acquisition is what partly replaced the fly-off. A model does not have the X-32’s difficulty, since a model can be made to be the proposal, but a model also does not have what the X-35B’s single sortie demonstrated. The trade is between an evidence source that matches the proposal exactly and one that matches reality exactly, and this competition is the case that shows why neither alone is sufficient.

A Homonym Inside the Discipline

Hot gas ingestion is also a turbomachinery subject, and it uses the identical phrase. Sealing flows between a turbine rotor disc and its stator are an active field whose papers are titled “hot-gas ingestion” exactly as the inlet problem is.

Forty-four cited research titles contain the words “hot gas”, and none concerns a turbine rim. Rim cavities, purge flows and sealing flows in turbines, and combustor dampers, are excluded. Dust, particle and salt ingestion are a different inlet problem and are excluded too, and no cited title names any of them.

That is the most dangerous class of homonym, because it is internal to the discipline. Bird ingestion is deliberately admitted, because an inlet swallowing a bird and an inlet swallowing its own exhaust are the same fluid mechanics.

The Hot Gas Ingestion Literature Is Thin

Sixty-one cited research records, each under its own title, concern the ingestion, reingestion, recirculation or environment of hot or exhaust gas. The open literature on inlet reingestion is genuinely small, because the measurements that matter are full-scale, expensive, and made by manufacturers rather than by research agencies. The article’s central failure mechanism rests on a thin public base and says so.

The Vehicle Cluster Is the Finding

One cited research record carries the X-32 in its title. It comes from the engine supplier and was published after the decision.

That is reported as a finding rather than as a gap, and the article’s own argument depends on saying so, because it is the reason the technical case here rests on the winner’s published numbers and the loser’s inferred bound.

The Literature of the Decision

The keystone of this article is not a physical quantity, so part of its literature is the literature of a decision. Source selection, competitive prototyping, cost growth and requirements commonality are that literature, and they have their own headings because a paper on acquisition strategy is not a paper on aerodynamics.

The keystone word is also the worst homonym. Competition between firms and competition between species are both enormous literatures, and both dwarf the procurement sense. So do dietary ingestion against inlet ingestion, and language acquisition against defence acquisition. Records in those other senses are excluded.

The Definition of Primary

Primacy is a property of the document, and this survey derives it from the identifier. A record is a report primary when its address is on the NASA Technical Reports Server or it carries a digital object identifier under the 10.21236 prefix, which Crossref registers for Defense Technical Information Center reports. The NASA reports on powered lift of the 1970s and 1980s that carry this article’s physics are report primaries under that rule, and so are 140 of the 280 acquisition studies. The rule does not reach the conference and journal papers of the competition years, such as the engine supplier’s report on the X-32B lift system and the X-35B control papers of 2002, so 17.8 percent is a lower bound on how much of the survey is first-hand.

Thin Subjects

Seven subjects that this article’s derivations and conclusions depend on have thin literatures. Each count below is the number of research records in this survey whose title carries at least one of the listed terms, with a hyphen read as a space.

Subject Title terms counted Records
the bring-back allowance in vertical landing bring back, bringback, vertical landing weight, vertical landing thrust 1
disc loading as the variable of the square-root law disc loading, disk loading 13
the fountain between two lifting jets fountain 14
suckdown in hover suckdown, suck down 10
the three-bearing swivel nozzle swivel, three bearing, 3 bearing 10
source selection between competing designs source selection 10
construct validity of a demonstration construct validity 0

The bring-back allowance has one title. It concerns the vertical landing thrust requirements of a STOVL aircraft, so the allowance relations derived above are this article’s own construction, as the subsection on uncited equations says.

Disc loading is named in 13 titles, and 12 of them name a low or a high disc loading. Those titles compare configurations by their disc loading rather than derive the square-root law, which is textbook momentum theory.

The fountain has 14 titles, of which 8 date from before 1995, and suckdown has 10, so the two jet-induced effects the hover argument names are carried by a small and mostly older literature.

The three-bearing swivel nozzle that the winner flew has 10 titles, and 8 of them date from 2014 or later, after the nozzle had flown on the production aircraft.

Source selection has 10 titles and none of them names an aircraft. The account of how the competition was decided therefore rests on the programme’s public record rather than on a published analysis of this source selection.

No title names construct validity. The term is used here in its sense from measurement theory, as set out in construct validity.

What the Survey Admits

A record is admitted only when a person reading its title finds it on this article’s subject. That subject is the short takeoff and vertical landing fighter and the decision between two of them. A title is therefore admitted when it concerns lift propulsion by direct lift, lift fans, lift engines or ejectors, momentum theory and hover performance, jet-induced and ground effects, hot gas ingestion and inlet temperature distortion, nozzles and thrust vectoring, impinging and hot jets, ship decks and landing surfaces, or the design, control and history of vertical and short takeoff aircraft. It is admitted too when it concerns fighter design, inlets and fighter engine cycles, low observability, carrier approach and landing, electric vertical flight and distributed propulsion for lift, or the acquisition, commonality, decision analysis and digital engineering of a competition between prototypes. A title that shares only general aeronautics with that subject is excluded. So are the classes of title that most often do so, namely turbomachinery components and engine health, conventional electric, hybrid, hydrogen and solar aircraft, the flight control and structures of helicopters, the flight control and handling of conventional fixed-wing aircraft, small unmanned aircraft and their autonomy, flight test of unrelated aircraft, generic aerodynamics and unrelated airframe subsystems, hypersonic vehicles, supersonic transports and air cushion vehicles, and decision and digital methods applied to systems other than aircraft. Many words this subject depends on also name something else, and a record that shares only such a word is excluded. Figure of merit also names measures in electronics, optics and thermoelectric materials. Lift also names gas lift in oil wells, heavy lift in shipping and the lift of hydrofoils, and thrust also names the thrust bearings of rotating machinery. Hot gas ingestion also names the sealing flows at turbine rims, inlet temperature distortion also names the hot streaks a combustor sends into a turbine, and reingestion also names a feeding behaviour of rabbits, hares and gophers. Landing pads are also built on the Moon and on Mars, and nozzles are also rocket nozzles, so aerospike, pintle, solid-motor and spacecraft nozzles and reaction controls are excluded. The designations F119 and F135 also number abstracts in medical conference programmes. Propulsion research on ships, underwater vehicles and spacecraft, and acquisition in its data, visual, seismic and corporate senses, share the vocabulary of this subject without its subject, and so does impingement by liquid jets. Correction, erratum, retraction and withdrawal notices, journal front matter and conference indexes are excluded as well, because a survey counts research works, and one document deposited twice is counted once.

Some records of neighbouring science are kept as doubtful. Momentum theory for tidal, wind and hydrokinetic turbines shares the sizing relation, industrial cooling by impinging air jets shares the physics of the hot jet on a deck, and product-family commonality and technology readiness assessment outside aircraft share the management side of the decision. Each is kept, and a reader may weigh it accordingly.

Every research title has been read for relevance, so the off-topic share that remains is a matter of reading judgement. A reading of titles cannot show that a work is relevant in substance, so this is a statement about titles only.

The survey has no residual cluster. Every admitted title belongs to one of the named literatures above. Titles on test and evaluation belong to the acquisition literature, and analyses of takeoff, landing and flight performance belong to flight test, so a title whose only link to the subject is a test, evaluation or simulation vocabulary is excluded.

Epistemic State

Historical fact, from the published record.

  • Two X-32 demonstrators were built by Boeing under a concept demonstration contract awarded in November 1996. The X-32A first flew on 18 September 2000 and the X-32B on 29 March 2001.
  • The two aircraft flew 144 times between them.
  • The X-32B used direct lift, diverting the core exhaust to vectoring nozzles near the centre of gravity, and required ground reconfiguration between the conventional and STOVL arrangements.
  • The X-35B performed a short takeoff, a level supersonic dash and a vertical landing in a single flight on 20 July 2001.
  • The Department of Defense selected the Lockheed Martin entry on 26 October 2001.
  • The Rolls-Royce lift system produces 20,000 pounds from the lift fan, 18,000 from the swivel module and 3,900 from the roll posts, for a published total of 41,900 pounds, with 29,000 shaft horsepower delivered to a fan 50 inches in diameter.
  • Boeing’s production proposal used a conventional wing with a canted twin tail rather than the demonstrators’ delta, and the change was made before the X-32 flew.

Engineering analysis performed for this article and verified independently.

  • Thrust for a given power rises as the square root of mass flow. This is an identity, obtained by eliminating the jet velocity between the thrust and power relations.
  • The lift fan’s published diameter, thrust and shaft power imply a figure of merit of 0.697, a value a real ducted fan can achieve, so the three numbers are mutually consistent.
  • Matching that disc loading with 28,000 pounds of core thrust would need 19.09 square feet of nozzle, a single opening 4.93 feet across, which does not fit on the airframe.
  • A fifty degree Fahrenheit inlet temperature rise costs 4.50 percent of thrust.
  • At an empty weight of 24,030 pounds and a five percent margin, the direct-lift allowance over empty weight is 2,637 pounds against 15,875 for the lift system, a ratio of 6.02.
  • The allowance amplifies a fractional thrust change by 10.11 for direct lift and 2.51 for the lift system, so the same physical loss costs the direct-lift aircraft four times as much.
  • The direct-lift allowance vanishes entirely below 25,232 pounds of lift.
  • One record in the cited set of 3,528 carries the X-32 in its title, against 38 for the F-35.

Inference, where the record supports a conclusion without stating it.

  • The X-32B’s STOVL lift is not published, and this article uses the engine’s military rating as an upper bound. Every allowance figure inherits that assumption, and the sensitivity table is given so the reader can see how much rests on it.
  • The nozzle sizes in the disc-loading table are plausible values rather than published ones, used to bracket the comparison.
  • The attribution of the chin inlet to the propulsion choice is an inference from the geometry of where lift nozzles must sit, and the sources describe the arrangement without drawing that conclusion.

Claims the record does not settle.

  • Whether the X-32B ever landed vertically at full weight is not established. Its STOVL tests were flown with some parts removed, and no source available here states its landing weights.
  • The lift fan’s weight, volume and cost penalty is not computed here. The trade is therefore presented from one side only.
  • The source selection’s reasoning is not public in any detail. The weight it gave to the single-sortie demonstration, to the wing change, or to cost cannot be established.
  • Two published wingspans differ by 19.9 percent. The X-32B is recorded as narrower in span than the X-32A, but no source available here pairs either figure with an airframe.
  • Whether Boeing’s wing change should be read as a weakness in its evidentiary position or as evidence of a working risk-reduction process is a judgement the public record leaves open.

Out of Scope

  • The F-35 programme after 2001, including its cost history, its variants and its service entry.
  • The detailed design of the Rolls-Royce lift system beyond the published thrust and power figures.
  • Low-observable design beyond the thin cluster in The Contemporary Literature, since it shaped both entries decisively but is almost absent from the open literature.
  • The McDonnell Douglas entry eliminated in 1996, which used a gas-coupled lift fan and deserves separate treatment.
  • Carrier suitability and the Navy variant’s structural requirements.
  • The international partnership arrangements that funded part of the programme.

Conclusion

The X-32 lost a competition it was well built to enter, and the physics of why is a single relation that has been in the textbooks for a century.

Thrust for a given power rises as the square root of mass flow. A lift fan spends its power on a large cold stream and a direct-lift system spends the same power on a smaller hot one, so the first produces more lift from the same core. Everything that separated the two aircraft follows from that. The cooler exhaust, the slower wall jet, the cold stream standing between the hot one and the intake, and above all the weight that can be brought home.

That last quantity is the competition in one number. At an empty weight of 24,030 pounds and an assumed five percent control margin, direct lift permits an allowance over empty weight of 2,637 pounds and the lift system permits 15,875. And the small number is badly conditioned, amplifying a one percent thrust loss into a ten percent loss of everything the aircraft can carry home, so a fifty degree ingestion of its own exhaust takes nearly half of it.

But the article ends on the evidentiary argument, because it is sharper than the propulsion one. Boeing flew a delta wing it had already decided not to propose. The customer was therefore shown an aeroplane nobody intended to build and had to reason from it to one that did not exist, while the competitor’s demonstrator flew a short takeoff, a supersonic dash and a vertical landing in a single sortie in the configuration it was offering.

A fly-off decides between the things placed in front of it. When one of those things is not the thing being bought, the fly-off has answered a question adjacent to the one asked.

And the decision determined not only which aircraft was built but which one is known. Among the three thousand five hundred and twenty-eight research records this article cites, the winner appears in thirty-eight titles across two decades and the loser in one, written by its engine supplier, after the result was announced. An aeroplane that flew one hundred and forty-four times, went supersonic, refuelled in the air and landed vertically left almost no public technical trace, and that silence is the last thing the competition decided.

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