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Encyclopedia of Aerospace Engineering, Online © 2010 John Wiley & Sons, Ltd.This article is © 2010 John Wiley & Sons, Ltd.This article was published in the Encyclopedia of Aerospace Engineering in 2010 by John Wiley & Sons, Ltd.

Tactical Aircraft Aerodynamic Integration

Jeffrey W. Hamstra and Brent N. McCallumLockheed Martin Aeronautics Company, Fort Worth, TX, USA

1 Introduction 1

2 Classic Tactical Aircraft Aerodynamic Integration 1

3 System Engineering Requirements 5

4 Advanced Integration Technologies 7

5 Evolving Development Techniques 10

6 Modern Tactical Aircraft Case Studies: F-22 andF-35 10

7 Summary 13

Symbols/Notation 13

References 13

Further Reading 14

1 INTRODUCTION

Tactical aircraft propulsion aerodynamic integration isdefined as the integration of jet engine air inlet and exhaustsystems, as opposed to the physical/functional integration ofthe engine itself. For tactical aircraft (also known as combator fighter/attack aircraft), aerodynamic integration demandsvery close coordination between the air system contractor(ASC) and propulsion system contractor (PSC).

Propulsion aerodynamic integration state-of-the-art hasevolved significantly since design of legacy transonic air-craft currently in the military force structure, exemplifiedin the United States by the F-14, F-15, F-16, and F-18.

New air system-level requirements derived from a systemsengineering approach, in particular, survivability and afford-ability, must now be considered on at least an equal basis astraditional aero-performance parameters such as installationlosses, net thrust, operability, maneuverability, and maxi-mum design speed. To satisfy evolving requirements in amulti-disciplinary design environment, new inlet and exhausttechnologies have emerged, including stealth-complianthighly integrated shaping and multi-axis thrust vectoring.Further technology advancements, including structural inte-gration and active flow control, are currently in development.These technologies have been enabled in part by the growth incomputational power available to both design and test com-munities. Emerging combat air systems such as the F-22 andF-35 characterize the advanced inlet/exhaust designs drivenby these new requirements, technologies, and developmenttechniques.

This section addresses aerodynamic integration of tacti-cal aircraft jet engine inlet and nozzle systems from an airvehicle system-level viewpoint. For more fundamental infor-mation on jet propulsion inlet and exhaust systems, referto Gas Turbine Engines: Inlets, Gas Turbine Engines: Noz-zles, Choosing and Sizing the Propulsion System, and BasicPrinciples: Gas Turbine Compatibility.

2 CLASSIC TACTICAL AIRCRAFTAERODYNAMIC INTEGRATION

Tactical aircraft are generally defined as those military air-craft employing weapons directly in support of ground troops,and include fighters and attack aircraft. Their performancerequirements are characterized by high subsonic cruise speed,supersonic dash, air-to-air combat (which requires high

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2 Propulsion Integration

Figure 1. F-15 Propulsion aerodynamic integration features. Left part of this figure is reproduced by permission of Mike Freer – Touchdown-Aviation. Right part of this figure is reproduced by permission of Lee Jangsev-Korea Air Photos.

maneuverability), survivability (i.e., stealth), moderate range(1000 to 2000 km), and a wide range of payload. With theexception of hypersonic vehicles, tactical aircraft propul-sion system aerodynamic integration requirements are moredemanding than for any other class of aircraft.

For legacy systems such as the F-14, F-15, F-16, andF-18, inlet and exhaust integration were driven primarilyby aeroperformance requirements, with weight an impor-tant but secondary consideration. These aircraft feature eithertwo-dimensional (F-14 or F-15) or conformal (F-16 andF-18) inlets, and axisymmetric, non-vectoring engine-mounted exhaust systems. Engine inlet and nozzle designs ofthis era were based on geometry that could be analyzed withsimple textbook equations and empirical design guidelines.Example design guidelines are provided in Crosthwait (1967)for inlets and Gamble, Terrell and DeFrancesco (2004) fornozzles, and a thorough historical perspective for inlet design

is provided by Sobester (2007). Huenecke (1987) gives anoverview of both inlet and nozzle integration for the F-15and F-16. Figures 1 and 2 illustrate key propulsion integrationfeatures for these two aircraft.

Propulsion integration has more recently evolved to a bal-ancing of aerodynamic and survivability needs based on airsystem-level performance requirements. In the case of the USF-117 Stealth Fighter, survivability was the primary designdriver and propulsion aerodynamics was secondary. Surviv-ability characteristics, which include alignment of inlet andnozzle edges with vehicle planform edges, 2-D nozzles, ductshaping, and full obscuration of the engine, complicate thepropulsion system aerodynamic integration. Recently, sys-tems engineering derived requirements, including weightand life cycle cost (LCC), have played a primary role in amulti-disciplinary design environment for inlet and exhaustintegration.

Figure 2. F-16 Propulsion aerodynamic integration features.

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Tactical Aircraft Aerodynamic Integration 3

2.1 Inlet integration

Tactical aircraft typically spend most of their life at subsonicconditions. For instance, based on historical usage data, theF-16 exceeds Mach 1 less than 1% percent of flight time.Subsonic inlet aerodynamic design is driven primarily byduct losses, form and spillage drag, and cowl lip separationat static or takeoff conditions. The requirement for super-sonic dash, even though it may rarely occur, can increasedesign complexity substantially, and therefore must be con-sidered in the propulsion aerodynamic integration. AboveMach 1.4, shock losses and spillage drag begin to domi-nate the inlet performance. Fixed-geometry inlets, as withthe F-16 and F-18, can have adequate pressure recovery atthe aerodynamic interface plane (AIP, the analytical inter-face between the inlet and engine) and low enough spillagedrag to achieve limited supersonic flight conditions. HigherMach or extended supersonic requirements may lead to vari-able geometry multi-ramp inlets, such as the 2-D F-14 andF-15 inlets or the conical F-111 translating 1/4 cone inlet.These variable geometry and multi-ramp designs are mechan-ically scheduled to reduce shock losses (thereby improvingpressure recovery) and spillage drag across a large rangeof supersonic flight conditions. Variable geometry can alsobe used to improve inlet performance at maneuver condi-tions. Cawthon, Truax and Steenken (1973) provide a generalapproach for optimizing an inlet design with these consider-ations, and Imfeld (1974) provides a specific example for theF-15 inlet.

2.1.1 Inlet sizing

Inlet size is another key design parameter that affects cowl liplosses, duct losses, and form and spillage drag. Generally, theinlet minimum flow area (known as the “throat”) is usuallysized for a Mach number of 0.65 to 0.75 at the maximuminlet airflow condition. While larger throat area is desired tominimize pressure loss and distortion, and to provide airflowgrowth margin, smaller throat area leads to designs that arephysically smaller and easier to integrate with lower drag andlower weight. While the original F-16 inlet was designed fora throat Mach number of 0.72, subsequent aircraft versionsincorporated a higher airflow engine, and a growth inlet wassized for near critical operation (M = 1) at maximum engineairflow (see Hagseth, 1987). Trade studies are required tooptimize inlet size and balance pressure losses, spillage drag,consideration for distortion and engine/inlet compatibility,and physical integration. Additional discussion of inlet sizingis provided in Gas Turbine Engines: Inlets.

2.1.2 Boundary layer control

Legacy tactical aircraft inlets incorporate a boundary layerdiverter as identified on the F-15 in Figure 1. The bound-ary layer diverter offsets the inlet from the fuselage andprovides a passage for the forebody boundary layer tospill between the inlet and forebody. The diverter pre-vents the low energy boundary layer from entering theinlet and degrading aeroperformance, and, during super-sonic flight, it isolates the inlet shock from the boundarylayer to improve aerodynamic stability. Tactical aircraft inletsmay also contain variable bleed and bypass systems. Thebleed system prevents significant boundary layer buildup oncompression ramps to improve aerodynamic stability andaeroperformance. Bypass systems may be necessary to matchinlet airflow to engine demanded airflow. At high super-sonic speeds, engine demanded airflow decreases to preventexceeding engine internal aerodynamic and/or material tem-perature limitations. However, inlet characteristic airflowmay be significantly greater than the demanded airflow. Abypass system provides a means to spill the excess airflowefficiently without impacting the inlet aerodynamic stability.Bleed and bypass systems typically exhaust the air on theupper surface of the vehicle in a location with a favorablelocal pressure. On occasion, diverter, bleed, or bypass air-flow is utilized as a secondary air source for heat exchangers,ejector nozzles, or other such functions.

2.1.3 Cowl integration

Tactical aircraft inlet cowl edges are often characterized by arelatively sharp profile to minimize supersonic drag. In somecases the edges may also be swept. While sharp edges aredesired for supersonic flight, they create additional perfor-mance penalties at static or low-speed conditions. Typically,a vortex will form and be ingested along the cowl lip at highengine airflow and static conditions. The vortex strength is afunction of inlet sizing, lip cross-section shape, and lip sweep.These design parameters can be adjusted to mitigate the vor-tex, but this may also affect other considerations such asspillage drag. Other approaches to mitigate lip vortex effectsinclude tailoring the engine control system to tolerate staticdistortion characteristics or the use of actuated or blow-inauxiliary inlets, which can be very useful in reducing inletdistortion and increasing pressure recovery.

2.1.4 Inlet duct integration

The internal subsonic duct length of an inlet is derived frominlet and engine relative placement, and the overall internalarrangement of the aircraft. Duct lengths are characterized

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by L/D (length to engine face diameter ratio) and typicallyrange from 4 to 7. Long, straight ducts of gradual cross sec-tional shape and area change provide the best balance ofaero-performance parameters. However, to navigate aroundother systems such as the landing gear, crew station, internalweapons bays, and fuel tanks, the duct may be serpentine innature, with substantial offset in the vertical and/or horizontalplanes. Rapid turning can introduce adverse pressure gradi-ents, pressure recovery loss, or spatial distortion increase dueto boundary layer growth or flow separation.

2.1.5 Inlet maneuverability

Maneuverability is driven by air-to-air combat resulting inextreme attitudes, which introduces severe pressure recov-ery and spatial distortion challenges for the inlet system.A typical tactical aircraft may maneuver up to 30◦ (andmore in some cases) angle-of-attack and 15◦ angle-of-sideslipat subsonic conditions. As speed increases, the maneuverrequirements will decrease but could be up to 20◦ angle-of-attack and 5◦ angle-of-sideslip even at supersonic speeds.Since these conditions are transient, distortion effects are usu-ally the first consideration for engine/inlet compatibility, andrecovery effects on thrust are secondary. Extensive guide-lines for inlet and forebody integration for maneuverabilityconsiderations were developed during the 1970s and can befound in Cawthon, Truax and Steenken (1973).

In some cases, such as the F-16 or Eurofighter Typhoon(see Philpot, 2000), the inlet is located below the forebody,which provides favorable local flow conditions at high angle-of-attack. However, this under-fuselage location may notprovide beneficial local flow conditions at angle-of-sideslip.In other cases, such as the F-14 and F-15, the inlets are locatedon the side of the fuselage. The side-mounted inlets provideshielding at angle-of-sideslip for the windward inlet but notthe leeward inlet. In addition, the side-mounted integrationmay not provide any benefits at high angle-of-attack. TheF-18 blends these techniques by utilizing side-mounted inletsshielded by a wing leading edge strake. Other approaches mayalso be employed to address maneuver effects such as cowllip shaping or tailoring the engine control system to toleratemaneuvering distortion characteristics.

2.1.6 Structural design impacts on aerodynamicdesign

Structural integration and manufacturing must also be con-sidered in the inlet aerodynamic design, since aerodynamicsurfaces may be constrained by structural design limitations.A good example is provided by Hagseth (1987) for theincreased airflow inlet for the F-16. The F-16 was originally

designed for the Pratt & Whitney F100 engine, but with theintroduction of the General Electric F110 engine and laterversions of the F100 engine, the inlet was re-designed toprovide increased airflow capacity. The F-16s modular inletstructure facilitated the re-design without impact to the over-all airframe structure, but this also imposed constraints onthe inlet aerodynamic surfaces. Additionally, inlet structurehas been classically composed of machined aluminum bulk-heads with formed sheet metal skins requiring labor-intensiveinstallation of thousands of fasteners. Aluminum skins wereeventually replaced with composite skins for weight consid-erations or to improve aerodynamic design flexibility.

2.2 Nozzle & exhaust integration

Tactical aircraft exhaust integration is a partnership betweenpropulsion system and air system contractors. The exhaustnozzle is typically designed and manufactured by the PSC,and furnished as engine-mounted hardware. Nevertheless,since exhaust nozzle design and aftbody integration areimportant factors in propulsion system performance and aero-dynamic drag, the air vehicle manufacturer has a large role inspecifying the nozzle shape, size, and functionality. It is theair vehicle manufacturer’s responsibility to ensure the nozzleand aftbody are integrated with minimum drag.

2.2.1 Axisymmetric convergent-divergent nozzles

Most classic tactical aircraft exhausts systems are axisym-metric for structural efficiency with variable geometry forafterburning. The exhaust nozzle contains a convergent-divergent (CD) internal flow path of overlapping flaps toachieve variable throat and exit areas. Overlapping externalflaps provide a fairing between the nozzle exit and the airvehicle aftbody. In addition, the exhaust system for tacticalaircraft is typically designed to allow afterburning, whichrequires a large variation in the minimum nozzle flow area(the “throat area”, or A8) for operability. In non-afterburningmode (known as “dry power”) the throat area is sized to main-tain stable, efficient engine operation. In afterburning, thethroat area must be substantially increased to compensate fordecreased flow density. Nozzle exit area, A9, is also variedwith afterburning to optimize installed performance. In mostcases, A9 and A8 are mechanically linked and scheduled withpower setting according to an A9/A8 ratio.

2.2.2 Nozzle jet-induced drag

Aftbody and exhaust integration are critical to maintaininglow drag. There is a trade between nozzle length and aftbody

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boattail angles and the resulting drag and weight. Findingthe optimum length and external shape is important to netpropulsion performance. For example, Catt, Welterlen andReno (1993) demonstrated that exhaust nozzle shaping andlength for the F-16 axisymmetric nozzle are critical to mini-mizing drag and jet effects, and Schnell (1974) demonstratedaircraft minimum drag reductions through nozzle shaping forthe F-14. Additionally, the aftbody is typically not axisym-metric, and integration of an axisymmetric exhaust may resultin large aftbody boattail angles and base regions, which intro-duce drag. This is evident in twin engine configurations suchas the F-15 where a base region is required between the twoclosely spaced nozzles. These base regions can be used asan exit for secondary flow systems, since they typically fea-ture low local pressure. For example, the F-16 base regions oneither side of the exhaust are used for nacelle ventilation exits.

Other integration approaches include 2-D or more highlyintegrated exhausts for survivability as with the high aspectratio F-117 exhaust (a non-afterburning design). Such con-formal exhausts can provide a better integration with lowerdrag or survivability benefits, but they are less efficient struc-turally, and therefore heavier, than axisymmetric designs.These types of exhausts are typically avoided due to com-plexity and weight.

2.2.3 Thrust vectoring

The exhaust system can be used to enhance air vehiclemaneuverability through the use of thrust vectoring (TV) –deflection of the exhaust jet relative to the airframe to producea non-axial thrust component and a net control moment onthe aircraft. TV typically requires mechanical variation of theexhaust system to accomplish either single axis (pitch or yaw)vectoring, or a combination of both pitch and yaw, knownas multi-axis thrust vectoring (MATV). Thrust vectoringschemes have been pursued for many years, with numer-ous concepts proposed, investigated, and brought throughvarious stages of development. Several MATV approachesusing axisymmetric nozzles have been demonstrated throughflight test maturity, including the F-18 High-Alpha ResearchVehicle (Asbury and Capone, 1995) and the F-16 Multi-AxisThrust Vectoring configuration (Small and Bonnema, 1994).Regardless of the approach, TV has been demonstrated to pro-vide substantial benefits in maneuverability. However, due toweight, complexity, the application-specific desire for closeair combat maneuvering, and the potential redundancy of TVwith aerodynamic control services, thrust vectoring has notbeen implemented in production for legacy US tactical sys-tems. The recently developed F-22 proves an exception tothis rule, however, as it employs 2-D nozzles with pitch axisvectoring (discussed in more detail in Section 6.1.2).

2.2.4 Ejector nozzles

Integrated ejector capability is another example of an exhaustnozzle feature for which very close coordination is requiredbetween PSC and ASC. Ejector nozzles (in which a sec-ondary flow is “pumped” by the primary jet flow) are typicallyused for exhaust system cooling, pumping secondary flow,or airflow matching. For example, the TF30 engine for theF-111 employed an ejector nozzle with air supplied from thefreestream for aerodynamic area control.

During the 1990s, several efforts were undertaken todemonstrate the viability of an ejector system for cooling theF-16 nozzle to improve nozzle flap durability and thus reducesupport cost and logistics footprint. In these efforts, both Pratt& Whitney F100 and General Electric F110 engines weremodified to incorporate an ejector slot on the internal flapsslightly downstream of the nozzle throat. Ejector cooling flowwas supplied by an external secondary air inlet supplying thenacelle ventilation system. A major challenge with ejectordesign is matching the supply air pressure to the ejector slotpressure to provide adequate airflow pumping over a widerange of flight conditions. While each F-16 design workedas planned, the benefits of nozzle cooling were not shown tooutweigh the added weight and complexity of the system, andit was never adapted for a production version of the aircraft.

3 SYSTEM ENGINEERINGREQUIREMENTS

Recent practice in the United States has moved to aperformance-based specification (PBS) approach in whichkey performance parameters (KPPs) are specified at the airsystem level. This approach allows for much greater interpre-tation by the air system contractor as to how the air vehicleis configured, and how systems are balanced to providean overall optimization. Systems engineering requirementsallocation techniques have thus become critical to correctlydecompose KPP requirements to the system, subsystem,and component level. In this section, some of the moreimportant requirements related to tactical aircraft propul-sion aerodynamic integration are discussed. Of particularnote, survivability and affordability have emerged as leadingdesign drivers.

3.1 Classic aeroperformance: Net installed thrust,TSFC and operability

While inlet and nozzle aerodynamic performance met-rics such as inlet pressure recovery and nozzle thrust

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coefficient remain as important measures of component per-formance, the concept of net installed propulsive thrust(Fnet) is more useful in judging the overall performanceof the installed propulsion system and in allocating per-formance requirements to lower-level components. Fnetincludes consideration of uninstalled engine thrust, freestream momentum (known as “ram drag”), inlet pressurerecovery, inlet spillage and/or bypass drag, inlet bound-ary layer control drag, nozzle internal performance, nozzlejet-induced aftbody drag, and the associated secondary airsystem drag components. Fnet also often accounts for a nom-inal level of power take-off from the engine, be it in termsof compressor bleed or mechanical horsepower extraction.It must also be noted that the propulsion system integrationwill have an impact on overall non-throttle dependant air-craft drag, Cdmin . This dependency becomes more entwinedas design of inlets and nozzles become more integrated; thus,it is critical early in the development process to identify arigorous aero/propulsion bookkeeping scheme. Likewise, aspropulsion and power/thermal management systems becomeincreasingly integrated, similar bookkeeping issues areintroduced.

Net installed thrust has a first-order impact on airvehicle-level performance metrics such as acceleration time,maximum speed, and specific excess power. In achievingthe highest performance levels, the ratio of Fnet to aircraftweight will exceed 1.0. To optimize Fnet, it is critical toachieve an efficient inlet and nozzle aerodynamic integra-tion, since installation losses can reduce uninstalled enginegross thrust on the order of 30–50% or more. Thrust specificfuel consumption (TSFC), defined as the ratio of fuel flowrate to net installed thrust, is likewise of first-order impact onair vehicle-level performance metrics such as range. Addi-tional discussion on these parameters can be found in BasicPrinciples: Thrust, Drag and Induced Forces.

The installed propulsion system configuration must alsomaintain engine operability across the entire range of air-craft operation. Inlet distortion (spatial, temperature, planarwave, etc.) and low airflow instabilities are the primary oper-ability concern driven by aerodynamic integration; see BasicPrinciples: Gas Turbine Compatibility.

3.2 Survivability

Incorporation of survivability (also called “stealth” or “LowObservable”) techniques is now recognized as a key require-ment for current and future tactical aircraft designs, withconsideration of radio frequency, infrared, visible, and acous-tic regimes all of some level of emphasis. Survivabilityconsiderations have created a dramatic shift in propulsion

integration techniques as well as overall air vehicle design.While aeroperformance is still the most dominant require-ment for the propulsion system and overall air vehicle,certain fundamental survivability features are evident asstate-of-the-art on many modern military platforms. Thesetechniques include edge alignment, sloped/faceted surfaces,engine obscuration, etc. The F-117 Stealth Fighter and B-2bomber exemplify how the entire air vehicle design can bedominated by survivability considerations, resulting in non-traditional propulsion concepts and air vehicle shaping. Sincespecific design techniques and related performance are tightlyprotected by aircraft and engine manufacturers and theirsponsoring organizations, a thorough discussion is out ofscope of this article. Nevertheless, it can be stated that there isa substantial and unprecedented design challenge incorporat-ing survivability features while retaining high aerodynamicperformance and simultaneously improving affordability.

3.3 Weight

Weight has always been a parameter of high concern inany tactical aircraft design, since it has first-order impacton both vehicle performance and procurement cost. Inletweight is somewhat difficult to quantify, since much of theinlet is highly integrated with the overall airframe. It is typ-ical to look at inlet weight on a “delta from baseline” basisand consider those discrete parts that can be severed (e.g.,dedicated aperture or duct structure, mechanical actuationcomponents, ducting, doors, screens, etc.). Inlet weight isdriven by physical cross-sectional size (as determined fromengine and secondary airflow requirements and the sizingapproach), length (which falls out from the overall integra-tion scheme), mechanical complexity, and structural loads.While steady-state operating pressure and aircraft maneuverloads are important, it is the “hammershock” load that resultsfrom an engine stall that is usually the structural sizing case.

Tactical aircraft engine exhaust systems are usually pro-vided as part of the engine, and as a result, their weight isbookkept and optimized at the engine system level. However,air vehicle system level requirements, including survivability,functionality (i.e., thrust vectoring or ejector cooling), moldline integration and drag reduction, and mechanical controlrange and rates, can have a first-order impact on weight.

3.4 Affordability and life cycle cost

Life cycle cost (LCC) is defined as the summation of devel-opment, acquisition, and operation and support (O&S) costsfor a given system. LCC is a critical element in the concept of

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affordability, which is loosely defined in terms of a capability-to-cost relationship, or more simply, as the cost of obtaininga certain combat capability. In recent years, affordability hasbecome a dominant consideration for tactical aircraft, andthis requirement has flowed to the propulsion system. Aswith weight, it is difficult to separate the LCC contributionfor a propulsion component or subsystem from that of the sys-tem as a whole. Furthermore, while development cost itselfmay represent only a small portion of the total LCC, bothacquisition and O&S costs are to a large extent defined bythe propulsion configuration features selected early in devel-opment. Acquisition cost is a strong function of physicalsize, shape, weight, material selection, mechanical complex-ity, and manufacturing difficulty, all of which are determinedin the design phase. O&S cost for inlet or nozzle componentsis even harder to quantify, but in general trends with mechan-ical complexity and reliability, vulnerability and damagetolerance (including foreign object damage, FOD), materialreparability, etc. Since fuel cost is part of support cost, fuelconsumption characteristics of the propulsion system alsoinfluence LCC. As an example trade, a variable-geometryinlet with mechanical actuation might provide better aerody-namic performance leading to better TSFC and lower fuelcost, but at the same time, it will weigh more, cost more tobuild, and require more maintenance events and hours perevent to keep all its moving parts in repair.

3.5 Noise, emissions andoperational/environmental robustness

Excluding stealth considerations, propulsion noise (jet noiseand engine/fan noise) and CO2 and NOx emissions have notbeen of high concern for tactical aircraft as other parame-ters described herein. Few compromises to either legacy ormodern air vehicle systems were made with these parame-ters in mind. However, as civilian communities become moreinvolved regarding peacetime basing options for fighter air-craft, noise is becoming more important. Also, as a result ofboth rising price of fuel (and thus O&S cost) and the “Green”movement to reduce aircraft emissions, fuel efficiency isbecoming of greater interest to military customers.

Inlet and nozzle systems must also be robust against ahost of operational/environmental considerations. Such con-siderations include bird strike; ice accretion, shedding, andingestion; salt water, aircraft fluids, and other corrosivesubstances/chemical agents; electro-magnetic interference(as applied to electronic control systems); armamentexhaust or other hot gas ingestion; foreign object debrisincluding sand/particulate matter ingestion and resultant ero-sion/fouling potential; extremes of temperature (especially

the impact on actuation fluid systems); maintenance,repair, and overhaul actions (maintainer access, droppedtool impacts, seal degradation); structural loads; vibra-tion/acoustic loads (especially external turbulence), etc.Design response to these requirements is typically based onlegacy techniques and best practice.

4 ADVANCED INTEGRATIONTECHNOLOGIES

During the last 20 years many advanced aerodynamic inte-gration technologies for tactical aircraft application havebeen identified, researched, developed, and demonstrated.Throughout the 1980s, the primary objective was improve-ments in aerodynamic performance and/or functionality(such as thrust vectoring) and stealth capability. As the ColdWar ended and defense acquisition budgets were reduced, theemphasis shifted to decreased weight and life cycle cost whilemaintaining aerodynamic performance and stealth capabil-ity. While many viable advanced technologies have beenmatured over the past two decades, there have been limitedopportunities to integrate those technologies into productionsystems due to the limited number of new or derivative tacti-cal aircraft programs. Although an advanced technology mayclearly improve air vehicle capability and LCC, it also intro-duces additional development risk and cost. Consequently,advanced technologies typically require substantial demon-stration and evaluation to reduce risk prior to introductioninto a production program. Flight demonstration is typicallyviewed as the culmination of a technology development pro-gram (Moorehouse and Hamstra, 2003).

Even with adequate risk reduction, any given technologymust justify inclusion into a production system based on meritshown through system-level trades on that specific applica-tion. Some of the technologies discussed in this section havebeen incorporated on production tactical systems; others maydemonstrate benefits for future systems, may have utility forstrategic, mobility, reconnaissance or other systems, or maysimply remain “on the shelf.”

4.1 Inlet technologies

Advanced inlet shaping/integration concepts such as thecaret inlet and diverterless inlet are excellent examples ofapproaches to achieve high aeroperformance with shapingfor survivability. Other inlet technologies of particular noteinclude compact, full-obscuration inlet ducts, inlet flow con-trol, and structurally integrated inlets.

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4.1.1 Caret inlet

The caret inlet technique has been understood as an academicconcept for many years (Seddon and Goldsmith, 1985), butwas not matured to a realistic engineering design until the1980s. The primary trait of caret inlets is a pair of obliquecompression ramps that generate a 2-D flow field and co-planar shock waves at the supersonic design point. Primaryadvantages of the caret inlet are efficient supersonic flowcompression (as with the F-14 or F-15) and swept inlet edgesthat can be aligned with the aircraft planform. The challengewith the caret inlet lies at supersonic, off-design conditionswhere the shocks generated by the two ramps are no longerco-planar, resulting in shear layers and potential distortionand inlet instability. The caret inlet concept was adopted forboth F-22 and F/A-18E/F. Design and development of theF/A-18E/F inlet is discussed in Hall et al. (1993).

4.1.2 Diverterless inlet

Another advanced inlet integration approach investigatedand developed during the 1990s was the “bump” inlet. Thisapproach was of interest due to its potential to allow elimi-nation of boundary layer diverters. Whereas the caret inlet isbased on a 2-D flow field, a bump inlet is derived by stream-line tracing through a three-dimensional flow field (Seddonand Goldsmith, 1985).

Boundary layer diverters have traditionally been cru-cial for most tactical aircraft inlet integration approaches.The diverter serves to improve performance and maintainsupersonic inlet/engine compatibility by preventing bound-ary layer ingestion and physically isolating the inlet shocksfrom the forebody boundary layer. However, diverters mayintroduce undesirable survivability characteristics and inhibitphysical integration of the inlet cowl and forebody, which isdesirable from a weight reduction standpoint.

Various research efforts were undertaken to mature thebump inlet concept into a practical design, including a flighttest effort on an F-16 that lead to incorporation of such an inleton the JSF X-35 concept demonstrator aircraft and productionF-35 aircraft (see Hamstra, McCallum and McFarlan, 2003;and Hehs, 2000). This particular design, known as the divert-erless supersonic inlet, integrated a highly three-dimensionalbump compression surface with a forward-swept cowl. Thiscombination produces a pressure gradient that diverts themajority of the boundary layer and provides a stable interac-tion between the inlet shocks and remaining boundary layer,eliminating the need for both boundary layer diverter andbleed systems. A diverterless inlet concept was also employedon the JSF X-32 demonstrator.

4.1.3 Compact inlet ducts

As tactical aircraft design evolved in the 1990s, compactinlet ducts became another technology of emerging inter-est due to the desire to enable lower cost through lowerinlet length. In this context, “compact” refers to shortinlet ducts (L/D ∼ 4) that achieve full line-of-sight obscu-ration of the engine, which is necessary for survivabilitycompliance. Unfortunately, achieving full obscuration in acompact design requires high rates of duct curvature and flowarea/shape change, all of which traditionally introduce unac-ceptable pressure loss and distortion. However, through theuse of modern design techniques, researchers were able todevelop and validate with wind tunnel experiments compactdesigns that achieved excellent performance (see Philhower,Robinson and Brown, 1998).

4.1.4 Inlet flow control

In the 1990s “flow control” began to emerge as a technol-ogy with many aircraft applications. In the context of jetengine inlet systems, flow control refers to the manipula-tion of large-scale flow phenomena (such as inlet distortion)with relatively small-scale perturbations to the flow enactedin highly-receptive zones within the inlet. Flow control tech-niques may be active or passive and involve open loop orclosed loop controls.

One example of inlet flow control is for reducing adversesecondary flows in “ultra-compact” inlet ducts (full obscura-tion designs of L/D < 4), suggested by Anderson et al. (1999)and continued by Miller, Anderson and others (see Hamstra,Miller and Truax, 2000). These efforts showed that as ductcurvature increases, the secondary flow increases to a pointwhere a vortex will lift off the duct surface, thereby decreas-ing pressure recovery and increasing distortion at the engineface. Studies found that localized placement of microvanesor airjets could control the secondary flow and prevent vortexlift off. Inlet flow control research continues and has maturedthrough full-scale demonstration of a representative advancedinlet coupled to a turbofan engine.

4.1.5 Structurally-integrated inlets and probabilisticloads

Structurally integrated inlets, including unitized, fastener-less structure based on probabilistic design loads, were alsodeveloped to reduce weight and LCC. As mentioned pre-viously, one of the primary design loads for inlet structureis the pressure load (hammershock) due to an engine stall.For legacy fighters such as the F-16, structural sizing wasbased on a “worst case” stack up of conditions that would

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give the highest possible hammershock load. The worst-casehammershock loads occur at high dynamic pressures, super-sonic speeds, and low altitude. However, the vehicle residencetime and probability of a stall at these conditions is very low.For more modern designs, research has shown that a “prob-abilistic” hammershock load is more appropriate (Gridley,Sylvester and Truax, 1999). For the case studied and basedon an acceptable risk of occurrence of 1 in 10 million, thisapproach reduced design loads from 70 to 44 psid, whichresulted in an estimated inlet duct weight reduction of 40%.

Inlet structural design and manufacturing technologiessimilarly evolved to consider structurally integrated conceptsto further reduce weight and LCC. Modular legacy inletsystem components, which were bolted to the airframe orassembled as part of a fuselage section, were replaced withunitized components sharing airframe bulkheads and loads.As mentioned in Section 2.1.6, inlet structure for legacyfighters consisted predominantly of aluminum bulkheads andframes and multi-piece aluminum or composite duct skinsattached with thousands of fasteners. In the most advancedapproaches considered, the multi-piece aluminum and com-posite skins are replaced with single-piece, fiber-placedcomposite ducts. Metal inlet duct bulkheads and frames arereplaced with composite webs with preformed, bonded joints,which reduce/eliminate fasteners and integrate directly withairframe bulkheads. This approach reduced cost substan-tially by eliminating the labor-intensive fastener installation.However, these concepts required expensive tooling for thesingle-piece duct, and repairs could become problematic inthe event of extensive damage to inlet structure.

4.2 Nozzle technologies

Since the early 1980s, R&D efforts continued to improve theclassic convergent-divergent (CD) axisymmetric nozzle interms of affordability, survivability, and aftbody drag reduc-tion. Engine manufactures have made enough incrementalprogress in these areas such that the engine-mounted axisym-metric CD nozzle remains as the “dominant architecture” forthe most modern tactical aircraft.

At the same time, however, structurally integrated,conformal exhaust systems were investigated to increasesurvivability and reduce weight. “Conformal shaping” in thiscontext refers to exhaust systems that are highly integratedwith the natural shape of the vehicle planform, such as thoseon the F-117 and B-2. Conformal shaping and partially orfully fixed internal and external geometry simplify aftbodyintegration and allow elimination of gaps, seals, and visiblemoving parts, but introduce enormous challenges regardingthroat area and thrust vector control. As an ultimate goal,

nozzle technologists have desired to combine the shaping fea-tures of F-117/B-2 nozzles with the vectoring/afterburningfunctionality of the F-22 but to do so at the cost and weight ofa traditional axisymmetric nozzle. This goal remains elusive.

4.2.1 Advanced vectoring techniques

Requirements for thrust vectoring complicated the task ofdeveloping fixed-geometry exhausts. While pitch/yaw vec-toring was investigated, the primary approach was yawvectoring for control of tailless aircraft. Two successfulapproaches emerged from multiple investigations: the noz-zle throat disc and fluidic injection (or nozzle “flow control”,see Section 4.2.3). The nozzle throat disc (Garret and Zilz,1992) employed a rotating disc at the throat station to skewthe sonic line, thus creating vectored thrust. This approachachieved high levels of vectoring, but, due to the variablegeometry throat, weight was still an issue. The fluidic vector-ing approach (Miller et al., 2000; Miller, Yagle and Hamstra,1999) employed fluidic injectors (using engine bleed) in thenozzle expansion section to either skew the sonic line orcreate a weak oblique shock and thus vectoring, while simul-taneously controlling effective jet throat area. This approachachieved high levels of vectoring and is lighter, since it iscompatible with a physically fixed geometry throat. However,fluidic approaches require a high-pressure airflow source thatmust be powered and controlled, thereby introducing a newset of issues. Many other mechanical and fluidic approachesremain under investigation.

4.2.2 Exhaust structural integration

Structurally integrated exhaust systems have been inves-tigated to reduce weight and LCC through load sharingbetween airframe and exhaust structure. Such load shar-ing is challenging due to non-uniform thermal expansionand high thermal loads. Various approaches, includingengine-mounted, airframe-mounted, and structurally inte-grated nozzles, have been utilized for advanced aircraft withvarying degrees of success. Despite significant advancementin state-of-the-art, structural integration of hot exhaust struc-ture with airframe structure remains a very difficult problem.

4.2.3 Nozzle flow control

Active flow control has been an area of significant investiga-tion, with the desire to provide both throat area (A8) and/orthrust vector control (see Section 4.2.1). Flow control hasalso been shown as applicable to aftbody drag reduction (seeHaid and Gamble, 2004) and jet noise reduction. For nozzle as

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well as inlet systems, a major issue is the penalty introducedfor extracting mechanical, pneumatic, or electrical power todrive the flow control technique. As mentioned in Section 3.1,power extraction results in an adverse impact on net installedpropulsive force, and must therefore be justified at the vehiclesystem level. Active flow control may also involve routing,valving, insulation, software controls, and failure mode con-siderations, all of which must be factored into affordabilityand survivability improvements.

5 EVOLVING DEVELOPMENTTECHNIQUES

In the time period between legacy and modern tactical air-craft, numerous advancements have been made in the designengineer’s ability to produce, analyze, and harness informa-tion describing the physical and performance characteristicsof inlet and nozzle systems. Most of these improvementsresulted from advancements in information technology pow-ered by gains in computer processing hardware and theassociated software and infrastructure. Four specific areas ofadvancement were computer-aided design (CAD), computa-tional fluid dynamics (CFD), computer-aided manufacturing(CAM) and rapid prototyping, and high-speed experimentaldata acquisition and analysis. A detailed perspective on thesetechniques can be found in Raj (1998).

5.1 Computer-aided design

Three-dimensional CAD tools, often coupled with structuralor aerodynamic analysis tools, have provided the ability tocraft complex geometries with little effort, and to store andredesign those items with ease. As an example, modern CADtools allow lofting of engine inlet ducts in 3-D space follow-ing specified centerline, flow area, and cross-sectional shapedistributions. The duct contour can become very sophis-ticated when short, compact full-obscuration designs arerequired. Some of these designs would be difficult if notimpossible to loft without computer methods. Additionally,parametric models allow the designer to quickly explore andmodify designs in minutes instead of hours or days.

5.2 Computational fluid dynamics

Perhaps the most drastic change regarding inlet and nozzledesign involves the use of CFD methods (see CFD). WhileCFD has advanced in terms of solver accuracy, user inter-

face, hardware cost, graphical output, and so on, it has beensolution speed (e.g., turn-around time) that has the most sig-nificant impact. “Speed” in this context implies more thanperformance indices obtained in a laboratory environment.Rather, speed is measured by the solution throughput achiev-able on a day-to-day basis by design engineers with access totypical, non-exotic computing resources – for example, thenumber of solutions of a given size that can be convergedovernight on an individual engineer’s workstation. Variousstudies have shown that this trend follows a “Moore’s Law”-like exponential improvement with time. With improvementsin solution speed and results analysis capability, the aerody-namic designer is able to derive increasingly sophisticatedinsights into the flow field phenomena and harness thatknowledge for design improvements.

5.3 Computer-aided manufacturing

CAM techniques, in particular, numerically controlled (NC)machining, have contributed to development of advancedinlet/nozzle integration schemes by providing improvementsin wind tunnel model mold line accuracy, parts interchange-ability, rendition of sophisticated contours, and so on. Inthe 1990s, rapid prototyping techniques, such as laser stereolithography and direct manufacturing, also became popularas a low-cost, rapid turn-time method for manufacturing windtunnel model parts or even complete models.

6 MODERN TACTICAL AIRCRAFT CASESTUDIES: F-22 AND F-35

The two most recent examples of clean-sheet tactical aircraftdevelopment in the United States, the F-22 and F-35, arediscussed as state-of-the-art case studies. The F/A-18E/F, anevolutionary upgrade to the F/A-18C/D, is also noteworthyand is discussed in detail by Hall et al. (1993). One can seethat with the F-22 and F-35 inlet and nozzle designs, top-levelsystems engineering requirements such as stealth compati-bility, weight, and procurement and support cost had a majorimpact on the overall system design.

6.1 F-22 Advanced tactical fighter

The F-22 is a twin-engine air superiority aircraft featuringa classic wing/body/tail configuration shaped with stealthrequirements in mind. A prototype YF-22 first flew in 1990and the first production version flew in 1997. The F-22 was

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designed to replace the F-15 as the front-line fighter for theUnited States Air Force. The F-22 incorporates twin Pratt &Whitney 35 000 lb (160 kN) thrust class F119-PW-100 twinspool afterburning turbofan engines. With these engines, theF-22 is able to sustain supersonic cruise speeds without theuse of its afterburners. Additional details on the evolutionof the F-22 aircraft and F119 engine can be found in Hehs(1998) and Deskin and Yankel (2002), respectively. Key F-22propulsion integration features are shown in Figure 3.

6.1.1 The F-22 engine inlet

The F-22 inlet system features twin side-mounted inlet aper-tures, each feeding a single engine through a long (L/D ∼ 6),full-obscuration S-duct. The apertures are highly swept forstealth compatibility and utilize a two-dimensional, externalcompression “Caret” design (see Section 4.1.1). Bound-ary layer control is provided with a classic boundary layerdiverter and bleed system. The inlet design provides aninherent angle-of-attack shielding function, enabling fullengine/inlet compatibility across a wide range of operatingconditions. Due to stealth, weight, and mechanical reliability(i.e., maintenance cost) considerations, the F-22 inlet geom-etry is fully fixed, and does not have the variable geometryfeatures of previous air superiority systems such as the F-14and F-15.

F-22 inlet development was aided by significant advance-ments in wind tunnel test data processing, specifically, theability to produce near-real-time analysis of dynamic distor-tion data. Prior to the F-22 timeframe, dynamic distortion datawas recorded during the test but processed and analyzed posttest. With improvements in computer power, by the late 1980shardware was available to acquire and analyze dynamic dataat the test site, allowing engineers the ability to make design

decisions based on this data in near-real time. While CFDanalysis was used on F-22, solution throughput in the late1980s/early 1990s had not yet reached the rate required tobase major decisions on CFD-produced information (in theabsence of supporting test data). The role of CFD was to addinformation to a knowledge base derived primarily from testdata.

6.1.2 The F-22 engine nozzle

Supplied as part of the twin F119 engines, the F-22 noz-zle features a stealth-compliant, 2-D, convergent-divergent,thrust vectoring design. The nozzles are highly tailored to theF-22’s requirement for optimum performance (net installedpropulsive thrust (Fnet)) at minimum weight. In-flight thrustvectoring enables an enormous Mach/angle-or-attack/angle-of-sideslip operating range, which in turn creates a maneuvercompatibility requirement for the engine inlet system. Withthe mechanism in place for thrust vectoring, added capabil-ity for thrust reversing was also studied early in the program,but this feature did not trade favorably with cost and weightimpacts, and thus is not present on the production system.

6.2 F-35 Joint strike fighter

The F-35 is a single-engine tactical aircraft featuring awing-body-tail configuration layout similar to the F-22. Ademonstrator X-35A version flew in October 2000 and thefirst production version flew in 2006. From inception, the air-craft was designed with three specific “variants” in mind tomeet the needs of US and allied Air Force, Navy, and Marinecustomers – Conventional Takeoff and Landing (CTOL),

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Short Takeoff Vertical/Landing (STOVL), and aircraft carriervariant (CV). Each variant is designed to unique require-ments, yet features high commonality with the other variantsto enable overall affordability. The F-35 is thus designed toreplace the F-16, F-18, and AV-8B and numerous other air-craft. Two interchangeable 40 000 lb (180 kN) thrust classafterburning turbofan engines can power the F-35, either theF135 offered by Pratt & Whitney or the F136 offered by theGeneral Electric/Rolls-Royce Fighter Engine Team. CTOLand CV propulsion systems are identical; the STOVL variantincorporates a shaft-driven lift fan in the forward fuselage,a vectoring engine nozzle, and other special systems to pro-vide thrust augmentation and aircraft control necessary forSTOVL operation. Key F-35 propulsion integration featuresare shown in Figure 4.

6.2.1 The F-35 engine inlet

F-35 engine inlet design considerations included stealth com-patibility, cost and weight, transonic cruise and maneuverperformance, and amenability to low-speed performanceenhancement for STOVL operation. The engine inlet sys-tem features twin side-mounted external compression inletapertures and a bifurcated inlet duct. All three variants haveidentical engine inlet systems except for incorporation of atop-mounted auxiliary inlet on the STOVL aircraft. A twinside-mounted inlet arrangement was chosen for compatibil-ity with the overall aircraft configuration, in particular, thecenterline-mounted STOVL lift fan. The inlet aperture uti-lizes a highly 3-D compression surface and forward-swept

cowl to provide both flow compression and boundary layerdiversion functionality. These features allow elimination of adiscrete boundary layer diverter and/or boundary layer bleedsystem, thereby improving stealth compatibility and reduc-ing inlet weight, manufacturing complexity, and cost whilemaintaining required performance (total pressure recoveryand drag) and compatibility (distortion and airflow match-ing) levels (see Section 4.1.2). The primary engine inlet isfully fixed with no moving parts. A very short bifurcatedS-duct fully obscures direct view of the engine.

Advanced CFD techniques played a critical role in devel-opment of the F-35 inlet system. The highly contoureddesign of the inlet compression system cannot be assessedby conventional analytical techniques. Similarly, the com-pact inlet S-duct features complex flow characteristics thatare sensitive to subtle changes in duct area, offset, shape,and inflow distortion pattern, and thus require computationalmeans to model. Advancement in wind tunnel test techniqueswas also required by the F-35. With both lift fan and mainengines supplied by closely coupled inlets, a standard 40-point instrumentation rake was shown to be inadequate torender distortion patterns to necessary resolution, and newinstrumentation designs thus had to be developed.

6.2.2 The F-35 engine nozzle

Key F-35 engine nozzle design considerations includedstealth compatibility, cost and weight, STOVL compatibility,and traditional nozzle performance. As part of the aircraft’sengine interchangeability requirements, both F135 and F136

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engines utilize identical nozzle hardware manufactured byPratt and Whitney. The CTOL and CV nozzles are commonand feature an axisymmetric convergent-divergent designwith a serrated trailing edge; the STOVL nozzle is shapedsimilarly but is shorter in length. The F-35 nozzle does notvector in up-and-away flight as the F-22 nozzle does. Thrustvectoring was evaluated several times during nozzle devel-opment, but for F-35, the performance benefit of this featuredid not trade favorably with cost and weight impacts as it didon F-22.

6.2.3 F-35 STOVL inlet/nozzle systems

In addition to the primary inlet/nozzle systems describedabove, the F-35 STOVL variant incorporates other featuresto enable efficient aerodynamic integration of the STOVLpropulsion system. Specific features include a dedicated liftfan inlet, an auxiliary engine inlet, a variable-area lift fannozzle, and a three bearing swivel duct (3BSD) feature onthe engine. The lift fan inlet is very close-coupled to thewaterline-oriented lift fan face, and significant developmenteffort was required to minimize inlet lip separation through-out the transition from takeoff to conventional flight. Theauxiliary inlet is similarly closely coupled to the engine fanface. The lift fan nozzle is a variable-area vane box designthat provides both exhaust area control and lift fan thrust vec-toring. The 3BSD feature on the engine allows downwardvectoring (to over 90◦) and some side-to-side yaw motion ofthe engine jet exhaust during STOVL operation.

7 SUMMARY

Propulsion aerodynamic integration state-of-the-art hasevolved significantly since design of legacy transonic com-bat aircraft currently in the military force structure. Thesechanges have been driven by a more holistic view oftactical air system development, increased emphasis on sur-vivability and affordability, revolutionary improvements incomputer-based design tools and methods, and incorporationof advanced components and integration technologies.

SYMBOLS/NOTATION

2-D Two-dimensional3-D Three-dimensional3BSD Three-bearing swivel ductASC Air system contractorA8 Nozzle minimum (throat) flow area

A9 Nozzle exhaust plane flow areaAIP Aerodynamic interface planeATF Advanced tactical fighter (F-22)Cfg

Nozzle gross thrust coefficientCdmin Aircraft minimum drag coefficient (non-throttle

dependent)FOD Foreign object debris/foreign object damageFnet Net installed propulsive forceJSF Joint strike fighter (F-35)KM KilometerKPP Key performance parameterLCC Life cycle costL/D Length to diameter ratio (inlet duct)MATV Multi-axis thrust vectoringO&S Operations and supportPBS Performance-based specificationPSC Propulsion system contractorSTOVL Short takeoff and vertical landingTV Thrust vectoringTSFC Thrust-specific fuel consumption

REFERENCES

Anderson, B.H., Miller, D.N., Yagle, P.J. and Truax P.P. (1999) Astudy of MEMS flow control for the management of engine facedistortion in compact inlet systems. FEDSM99-6920.

Asbury, S.C. and Capone, F.J. (1995) Multiaxis Thrust-VectoringCharacteristics of a Model Representative of the F-18 High-Alpha Research Vehicle at Angles of Attack from 0◦ to 70◦. NASATechnical Paper 3531.

Catt, J.A., Welterlen, T.J. and Reno, J.M. (1993) Decreasing F-16nozzle drag using computational fluid dynamics. AIAA Paper93-2572.

Cawthon, J.A., Truax, P.P. and Steenken, W.G. (1973) Supersonicinlet design and airframe-inlet integration program. Air ForceFlight Dynamics Laboratory Technical Report AFFDL-TR-71-124.

Crosthwait, E.L. (1967) Preliminary design methodology for air-induction systems. Air Force Systems Command Technical ReportSEG-TR-67-1.

Deskin, W.J. and Yankel, J.J. (2002) Development of the F-22propulsion system. AIAA Paper 2002-3624.

Gamble, E., Terrell, D. and DeFrancesco, R. (2004) Nozzle selectionand design criteria. AIAA Paper 2004-3923.

Garret, T.M. and Zilz D.E. (1992) Nozzle throat disc for thrustvectoring. United States Patent No. 5,092,524.

Gridley, M., Sylvester, T.G. and Truax, P.P. (1999) Impact of aprobabilistic approach to inlet hammershock design loads. AIAAPaper 99-2114.

Haid, D. and Gamble, E.J. (2004) Nozzle Aftbody Drag ReductionUsing Fluidics. AIAA Paper 2004-3921.

DOI: 10.1002/9780470686652.eae490



Hagseth, P.E. (1987) F-16 Modular common inlet design concept.AIAA Paper 87-1748.

Hall, G.R., Hurwitz, W.M., Tiebens, G.S., Norby, W.P., Singshinsuk,P. and Wilt, C.E. (1993) Development of the F/A-18E/F airinduction system. AIAA Paper 93-2152.

Hamstra, J.W., McCallum, B.N., McFarlan, J.D. and Moorehouse,J.A. (2003) Development, verification, and transition of anadvanced engine inlet concept for combat aircraft application.NATO RTO Paper AVT-100.7.43.

Hamstra, J.W., Miller, D.N., Truax, P.P., Anderson, B.A. and Wendt,B.J. (2000) Active Inlet Flow Control Technology Demonstra-tion. Aeronaut. J., 104(1040), 473–479.

Hehs, E. (1998) F-22 Design Evolution. Code One Magazine,13(2–3).

Hehs. E. (2000) Diverterless supersonic inlet. Code One Magazine,15(3), 8–13.

Huenecke, K. (1987) Modern Combat Aircraft Design, Naval Insti-tute Press, Annapolis, Maryland.

Imfeld, W.F. (1974) The development program for the F-15 inlet.AIAA Paper 74-1061.

Miller, D.N., Yagle, P.J. and Hamstra, J.W. (1999) Fluidic throatskewing for thrust vectoring in fixed geometry nozzles. AIAAPaper 99-0365.

Miller, D.N., Yagle, P.J., Bender, E.E., Ginn, K.B. and Smith, B.R.(2000) Demonstration of fluidic throat skewing for thrust vector-ing in structurally fixed nozzles. ASME Paper 2000-GT-0013.

Moorehouse, J.A. and Hamstra, J.W. (2003) Vehicle PropulsionIntegration Technology Demonstrated By The F-16 FightingFalcon. NATO RTO Paper AVT-100.7.41.

Philhower, J.S., Robinson, D.E. and Brown, R.J. (1998) Devel-opment of a Highly Offset Induction System for a SupersonicSTOVL Fighter. AIAA Paper 98-3417.

Philpot, M. (2000) Future challenges for powerplant aerodynamicintegration in combat aircraft. ICAS Paper 2000-6.11.1.

Raj, P. (1998) Aircraft design in the 21st century: implications fordesign methods. AIAA Paper 98-2895.

Schnell, W.C. (1974) F-14A Installed nozzle performance. AIAAPaper 74-1099.

Seddon, J. and Goldsmith, E.L. (1985) Intake Aerodynamics,American Institute of Aeronautics and Astronautics, EducationalSeries, New York.

Small, L. and Bonnema, K. (1994) F-16 MATV program lessonslearned. AIAA Paper 94-3362.

Sobester, A. (2007) Tradeoffs in jet inlet design: a historical per-spective. J. Aircraft, 44(3).

FURTHER READING

Society of Automotive Engineers (1978) Gas turbine engine inletflow distortion guidelines. Aerospace Recommended Practice1420.

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