First Published in Australian Aviation, April and May, 1991, Issues
(c)1991, 1997, Carlo Kopp

At the time of writing the Northrop/MDC YF-23A and Lockheed/B/GD YF-22A had both completed their respective demonstration/validation flight test programs . While the USAF have not revealed much about the internals and performance of the aircraft, their airframe geometry and known powerplant parameters reveal much of their design philosophy and performance. Both aircraft reflect their prime contractors' respective philosophies of stealth aircraft design as much as they reflect their common mission profile.

Principal airframe/propulsion design objectives were sustained supersonic cruise on dry thrust, high energy manoeuvrability, superior combat radius to the F-15 with all weapons and fuel carried internally and low signatures.

Both ATF prototypes are approximately 10% larger than the F-15 and both carry approximately twice the internal fuel of an F-15C, while both have about 50% more wing area at about 30% greater combat weight. As such both aircraft clearly illustrate the long range air superiority mission which was originally envisaged for the aircraft, penetrating deep into Soviet airspace to destroy air defence aircraft and to disrupt Soviet offensive air operations. The decline of the Soviet empire during the last 18 months has understandably led to many US politicians calling for the scrapping of the ATF program, in view of the 'diminished threat'. This myopic posture needless to say wholly disregards the fact, that the USSR itself is quite unstable and could well slip back into hardline Stalinism, and also ignores the reality that the USSR will sell the Flanker and Fulcrum to any party who can pay for it. It is likely that that these capable teen series class aircraft will become as common in the Third World as the ubiquitous Fishbed. The mere perception that a capability matching that of the frontline Western aircraft is present will be destabilising - the instance of Iraq with its Fulcrums and Fencers is a case study, their tactical and technical incompetence clearly underscoring this sad phenomenon.

The reality is that capabilities are a good measure of intent, it is unrealistic at the least to assume that any nation will expend vast sums of money to acquire specific weapons systems without seeing how that expenditure will further its interests. Long range air superiority aircraft such as the Flanker serve a clearly defined role, offensive strategic air war.

How the ATF performs this role is best judged by a closer look at the design philosophy of the airframe, propulsion and weapon system.

Airframe Design

The ATF airframes represent another quantum leap in air superiority airframe design, as great as that represented by the teen series fighters. Two new and key capabilities were integrated in the ATF program, low observability (ie stealth) and supersonic cruise.

The objective of low observables is to reduce the performance of hostile radar and infrared surveillance, tracking and guidance systems. Existing airframes perform poorly in this respect, and thus only a new airframe design can address the problem.

Supersonic cruise serves several purposes, providing for fast and deep penetration into hostile airspace, while offering the supersonic cruise fighter a major energy advantage over subsonic/transonic dogfighters which it can both outmanoeuvre and outlast in a supersonic engagement. The high corner speed of such aircraft also provides a major manoeuvring advantage when evading SAMs at altitude, enhancing survivability on deep penetration missions. Supercruise required major advances in propulsion technology and nontrivial concessions in airframe design.

Low observability in the ATF designs is achieved by a range of measures, how these are applied clearly illustrates the heritage of the respective designs.

The Lockheed/B/GD YF-22 employs planform shaping and faceting with blended facet boundaries, the latter a necessary concession to high performance aerodynamics. This is apparent in the shape of the nose, the fuselage sides about the inlets and engines, and the upper forward fuselage. Lockheed/B/GD used serrated edges extensively, as with the F-117A, to control the returns from panel boundaries, this is very visible on the undercarriage and weapon bay doors.

The planform results in a multiple lobe design, as the boundaries of the major surfaces are not parallel with respect to each other. Planform return lobe structure is defined by the radiation pattern lobes resulting from surface wave reflections which occur at the leading and trailing edges of the airframe's major surfaces. The objective of lobing is to concentrate this unavoidable radar return into specific directions so as to minimise frontal/aft/beam aspect return and maximise scintillation in the direction of the lobe. Scintillation is a measure of how rapidly the size of the return varies with angle, the greater this variation, the more difficult a target is to track. The lower the number of lobes and the narrower the lobes, the lower the probability of detecting any return.

The Northrop/MDC YF-23 employs planform shaping with extensive blending, the latter technique used to advantage with the large B-2A. Blending has the major strength of not compromising high speed aerodynamics, the blended airframe offering very low drag by avoiding vortices which may be produced by a faceted geometry. In addition to RCS reduction through shaping, the YF-23 also employs carefully shaped exhausts to conceal the engine hot end, yet another technique developed during the B-2A program.

The unusual 'diamond' planform of the YF-23 is a 2 major lobe design, as all major edges fall into groups of two parallels.

The result of the low observables techniques employed with these aircraft is a major reduction in aircraft detectability by radar, and in the YF-23, also detectability by Infra-Red Search & Track (IRS&T) systems. This will radically shrink the usable envelope of hostile radar guided weapons and in the instance of the YF-23, also heatseeking weapons.

Lockheed/B/GD chose a somewhat conservative hybrid planform airframe layout, reminiscent of the F-15 and F/A-18, with closely spaced engines, long inlet tunnels, outward canted vertical tails and rudimentary strakes over the inlet boxes to promote vortex lift over the outboard wing sections at high AoA. The characteristics of this general layout are well understood, the forward sloped inlets providing good airflow characteristics at high AoA and the conventional tail providing good controllability under such conditions, apparently earlier attempts at using a V-tail did not yield the desired results. The close spacing of the engines reduces inertia in the roll axis, but may penalise survivability. Weapon bays are located on the sides of the inlet boxes and a single central bay is located beneath the centresection, all located well aft of the inlet to preclude ingestion problems. Typically AIM-9s fit in the inlet bays and AIM-120s in the split central bay.

The single piece canopy cockpit is well elevated to maximise the pilot's situational awareness.

Northrop/MDC chose a far more radical airframe layout, driven by the objectives of stealthiness and supercruise. The extensively blended fuselage has rudimentary chines which smoothly blend into the wing leading edge, the blending allowing good area ruling and low supersonic drag. The low wing aspect ratio is used to optimise supercruise performance. The ventral trapezoidal inlets feed the engines via stealthy S-bends, and the rear boattail and submerged dorsal exhausts were specifically aimed at low drag and infrared signature. The YF-23 employs an unconventional V-tail with a planform consistent with the airframe lobing strategy. The large centresection area will provide substantial body lift at high AoA thus improving turn performance, a technique used in the F-14 and Flanker. While the widely spaced engines result in some roll rate penalty, they are sufficiently separated to avoid fratricide in the event of turbine breakup. Two tandem weapon bays are employed, the aft bay is reported to be very large and contains pairs of staggered AIM-120s, the forward bay carrying AIM-9s.

The YF-23 employs a two piece canopy, the cockpit is like it's competitor's well elevated for good visibility.

The exhausts of the two aircraft differ radically. Lockheed/B/GD had chosen a layout aimed at maximising lower speed manoeuvrability via the use of thrust vectoring, even though this was not a mandatory USAF requirement. Two dimensional thrust vectoring nozzles provide vectoring to enhance response in pitch. Northrop/MDC on the other hand rated stealth and drag so important, that they employed a serrated planform beavertail with B-2-like submerged ventral exhaust troughs. This approach reduces both depressed tail aspect infrared emissions and tail aspect radar cross-section, but precludes any vectoring.

Both prototypes are reported to employ relaxed static stability, with multiply redundant digital fly-by-wire control systems.

The navalised ATF derivative planned to replace the Grumman F-14 as the USN's principal air superiority fighter has yet to materialise. Lockheed/B/GD have proposed a variable geometry wing derivative of the TAC design, in order to accommodate the Navy carrier recovery an launch requirements, ie low speed on approach and high lift at low speed on catapult launch. At the time of writing no information was available on the Northrop/MDC proposal.

Propulsion

The unique and new supersonic cruise mission profile of the ATF has had a major impact upon the powerplants to be used for the aircraft. The higher combat weight of the aircraft in comparison with the F-15 imposed a need for greater installed afterburning thrust, in the 35,000 lb class per engine, to maintain the preferred 1.4:1 class combat thrust/weight ratio, while the supercruise profile imposed the need for high dry thrust particularly within the supersonic part of the envelope. The latter requirement was particularly painful, as it forced a move to higher temperatures within the engine, particularly the turbine.

The two bidders for the ATF powerplant are Pratt & Whitney and General Electric with their YF119 and YF120 designs respectively. The P&W YF119 is the lower risk of the two designs, an advanced low bypass ratio turbofan. The GE YF120 is more radical, as it is a variable cycle engine capable of adjusting its bypass ratio to the optimum for a given flight regime.

GE's involvement with variable cycle engines dates back a decade, with a major technology demonstration program built around a substantially redesigned YJ101 (former YF-17) powerplant. This was followed by work on an F404 derivative, this providing the foundation for GE's variable cycle technology. The core of the YF120 was derived from work done during the government sponsored ATEGG (Advanced Technology Engine Gas Generator) and JTDE (Joint Technology Demonstrator Engine) programs. Subsequently early development XF120 engines underwent testing at the USAF Systems Commands AEDC facility. Ground test prototype YF120s have been under test since late 1989.

Internal details of the YF120 are, not surprisingly, classified. The engine is known to be a two shaft design with a minimum number of rotating stages, a fan which has been speculated to be a single stage design and a compressor using integrated bladed rotors. In common with earlier GE VCEs, the YF120 uses VABI (Variable Area Bypass Injector) technology to alter engine bypass ratio. The YF120 is reported to use aerodynamically actuated VABIs, in which respect it differs from earlier designs which used mechanical actuation. Typical VABI technology used in earlier GE designs saw the use of sliding sleeves which would reduce the cross section at the fan exit entry to the bypass duct, and at the tailpipe exit from the bypass duct.

This arrangement allows the engine to smoothly optimise its bypass ratio to the flight regime. For maximum afterburning thrust on takeoff or efficient subsonic long range cruise, a high bypass ratio is set. For supersonic cruise a turbojet is approximated, with very low or zero bypass ratio. Turbojets are considered optimal for supersonic flight as their dry thrust drops far more slowly than that of a fan with increasing vehicle airspeed. The ATF flight profiles are sufficiently unconventional to create major difficulties for a fixed bypass ratio engine designer attempting to reconcile the diverse demands of lower speed operation and supersonic cruise.

This must have been the case with P&W, who have bid a fixed bypass ratio turbofan derived from the ATEGG/JTDE programs and the company's existing F100 family of fans.

Published reports indicate the GE engine has demonstrated better supercruise performance than its conventional rival and it is very likely that GE's gamble with a more radical technology will yield the desired payoff. The gain in overall engine performance in comparison with existing teen series fighter powerplants is clearly illustrated by a Lockheed/B/GD flight envelope chart for the YF-22 which shows a military thrust envelope for the YF-22 as greater at all airspeeds and altitudes than the afterburning envelope of the F-15C. In the thrust/drag limited low altitude regime the YF-22 dry envelope is 7% greater than that of the F-15C, given the similar configuration of both airframes and greater wetted area of the YF-22 this suggests dry thrust in excess of 25,000 lb per engine.

Avionics, Cockpit and Weapon System

Avionics is an area where the ATF will offer a radical improvement over existing systems. From the outset avionics were a key aspect of the ATF program. Initial studies were aimed at a distributed architecture designated Pave Pillar, the objective of which was to employ physically separate common computing modules for the aircraft's vital systems. This would provide superior tolerance to battle damage and internal systems failures, while reducing the requirement for unique spares modules. A high level of integration was also sought in the comm/nav systems and electronic warfare systems, under the USAF Icnia (Integrated Communications, Navigation and Identification Avionics) and Inews (Integrated Electronic Warfare System) technology development programs respectively.

A major system level requirement was supportability in the field and very high reliability, the latter a must in view of the complexity of the aircraft. The scale of effort in this area is reflected by a requirement for a combat turnaround of 15 minutes (cf 35 minutes for F-15), a requirement for 9 support personnel/airframe and 6.8 C-141 loads of support equipment, in comparison with the existing 17 for a 24 aircraft TAC squadron.

The YF-23 avionic system is built around a core integrated system using Unisys 32 bit GPPE (General Purpose Processing Element) modules. The original 3 CPU 1750 architecture mission computer arrangement was discarded as the support hardware requirements were excessive, and the computational power inferior.

Signal processing is done with a single dedicated processor, sliced between two large physically separated 75 card racks, with redundant functional modules spread between the racks to enhance survivability.

The YF-22 avionic system is built around Hughes CIP (Common Integrated Processor) modules. Lockheed/B/GD have apparently opted for unconventional liquid cooling of the processor modules to reduce hardware operating temperatures.

Weapon system software is to be implemented in US DoD standard ADA language, it is not clear whether the production code will be to current ADA or revised ADA 9X standard.

The Inews electronic warfare systems are being developed by two contractor teams, TRW/Westinghouse/Tracor/Perkin Elmer for the YF-23 and Sanders/GE/Motorola/HRB for the YF-22.

The sensor suite will be dominated by an active phased array radar. The radar will employ electronic antenna scan exploiting over 1,000 transmit/receive/phase-shifter elements, each of which is a wholly self contained module. This arrangement results in a highly robust design which doesn't require mechanical pointing, as main lobe shape and direction are controlled electronically, and which gracefully degrades in performance as modules fail. The use of electronic beam shaping/pointing provides major advantages as this class of radar may timeshare its antenna between modes, optimise lobe shapes to modes, tolerate violent manoeuvring and also selectively direct nulls at troublesome jammers as a potent ECCM. Both contenders would employ a Westinghouse/TI radar design, initially flown in 1989 and derived from the URR (Ultra Reliable Radar) program.

This radar is the most radical step in fighter air intercept radar design since the first pulse Doppler sets were introduced in the early seventies, and offers diverse upgrade paths through software changes in the beam control subsystem and the signal processing subsystem.

The radar is to later be supplemented by an EOSS (Electro-Optical Sensor Suite) which is essentially an advanced IRS&T set. Both contenders are to employ a Martin Marietta/GE system using focal plane array (FPA - see earlier TE) technology. The advantage in a FPA design is higher sensitivity and the absence of moving parts, scanning being accomplished electronically. At the time of writing it was unclear as to whether a cheaper mid-infrared PtSi or InSb design would be adopted, or whether a long-infrared HgCdTe design would be employed. While the latter can detect airframe skin friction, it is more demanding in cooling and signal processing. The difficult requirement is to detect and track targets against an IR background at low level, at altitude the background environment is easier to deal with. At the time of writing the EOSS was deferred as it was considered too immature for a low risk production design.

The cockpits of both the YF-22 and YF-23 will be conventional 'glass' arrangements, although Lockheed/B/GD have opted for LCD technology in preference to CRT displays. The YF-22 uses no less than 6 LCDs, typically providing 512x512 pixel resolution with 4,096 colours. An advanced HUD will be employed, as will the USAF's new G-suit technology currently being introduced on the F-15. Both contenders are reported to use conventional control layouts, the sidestick controller not being used.

Flight testing of both avionic suites has taken place on dedicated testbed aircraft, Boeing using a 757 and Northrop/MDC a well reworked BAC-111.

The ATF will be armed primarily with the AIM-120 Amraam ARH BVR missile, supplemented by a short range all aspect heatseeker, the AIM-9M at this time. A design requirement is the carriage of four Amraams, these must be ejected from internal bays at launch. An internal gun will be employed, although it appears that the gun is absent on all prototypes.

Performance

It is clear from published accounts that the ATF is an enormous step forward in aerodynamic and low observables performance in comparison with the teen series fighters and their Soviet counterparts. Both competitors have repeatedly supercruised on dry thrust with speeds of 1.58 Mach reported for both airframes with YF-120 powerplants. In addition the YF-23 attained 1.8 Mach in afterburner and reports indicate that the final maximum speed figures have been classified by the USAF.

Both airframes offer 1.4:1 class combat thrust/weight ratio performance and combat wing loadings well below 60 lb/sqft, therefore the energy manoeuvrability performance will equal if not exceed that of the F-15. Controllability at high AoA has been reported as excellent for both types, in the absence of hard data it is therefore difficult to estimate whether Lockheed/B/GD's claimed advantage in manoeuvrability will be decisive.

Tactical radius and cruise speed are also critical parameters for the mission, in both areas the ATF is well ahead of the teen series fighters. Again in the absence of hard figures it is difficult to establish whether Northrop/MDC's greater speed and radius performance are a decisive advantage. Certainly the ATF's 25,000 lb class fuel capacity must offer a major gain in radius in comparison with the 13,000 lb class F-15, how much more will depend on the flight profile. Reports suggest the YF-22 consumes 30% less fuel in supercruise than an F-15 in afterburner, suggesting an SFC of about 1.5 lb/lbt/hr which is about twice the dry SFC of an F100-PW-100. Therefore on a purely supercruise mission profile the additional fuel may not offer a gain in radius, however a mixed subsonic/supercruise profile almost certainly would, the gain inversely proportional to the ratio of time spent in supercruise vs subsonic cruise. Both airframes are designed for boom refuelling.

The combined effects of the airframe and powerplant designs will see a shift toward supersonic engagements, where current generation aircraft optimised for transonic/subsonic manoeuvring with afterburner cannot measure up. The current generation fighter will suffer shortfalls in persistence due increased fuel flow and sustained manoeuvring performance due aerodynamics optimised for turning at lower speeds.

Low observables performance is an area where Northrop/MDC will almost certainly win out over Lockheed/B/GD, due to the effort expended on the design of the rear fuselage exhaust area and due to the use of blending and lobing techniques which offer far lower numbers of airframe discontinuities. Any discontinuity promotes surface wave scattering, therefore the smoother the design the lesser the scattered return. As the RCS figures are classified, it is not clear how great a performance margin exists. Tail aspect radar and infrared performance must be superior in the Northrop/MDC design simply as a result of the geometry used.

Lockheed/B/GD compromised low observables performance to achieve greater agility, whereas Northrop/MDC focussed on stealth, speed and radius performance. The USAF's decision will clearly illustrate which of these parameters are considered of greater value in the projected strategic air war of the future.

The Perspective View

To the Australian observer the ATF underscores the revolution under way in tactical air warfare, with stealthiness, radius and agility growing significantly against the existing generation of aircraft. The ATF will be substantially more expensive than smaller multirole fighters such as the F/A-18A, but also offers vastly superior performance in the long range air superiority mission.

(Editor's Note: since the time we published this item in 1991, the outcome predicted in this article has indeed come to pass, with the PRC and India about to deploy large numbers of advanced Flankers, and even Malaysia deploying the potent MiG-29SE with the deadly Archer missile. The issues surrounding the RAAF's Hornet replacement will be covered in some detail in August, September and October, 1997, issues. In hindsight, we correctly anticipated current events, the early replacement of the Hornet now a distinct possibility)

In the current regional air defence environment the F/A-18A has no serious rival. This could however change with a regional acquisition of the Fulcrum and Flanker. While the Fulcrum could be readily tackled in BVR and visual engagements, the larger Flanker would present a serious problem particularly in extended range BVR engagements due to its superior radius and radar performance. Well flown Flankers could present a serious problem for the RAAF as they have greater persistence, superb manoeuvring performance and a larger envelope for firing radar guided missiles.

As the Gulf war demonstrated, modern radar guided missiles are far more lethal than their Vietnam era predecessors and the initial pre-merge phase of an engagement has thus become far more dangerous. Closing fighters now have the option of a head-on BVR missile shot, a situation where radar and RCS performance are critical. Evading an inbound missile can severely disadvantage the defending fighter in terms of geometry and energy state, this in turn penalises it once the merge occurs and a turning dogfight is initiated. A Flanker with its powerful radar and BVR missiles has thus a major advantage over an F/A-18A, which can only employ its manoeuvrability and weapon system to an advantage once a turning engagement has been entered. In a close in turning fight it has the advantage of smaller size and better dogfighting radar modes, but will suffer an energy disadvantage if the Flanker is flying at a lower fuel state. Similarly the Flanker will have an advantage in persistance, given fuel state.

The ATF with its low frontal RCS has a distinct advantage over any current opponent in any such engagement, allowing it to ruin its opponent's entry into the engagement, and then apply its supersonic agility and persistence to force the engagement on its terms. The reduced RCS and in the YF-23 IR signature, will also reduce the usable radius of its opponent's weapons, while allowing the ATF to disengage more readily, itself not suffering any penalties in missile guidance effectiveness.

Were the RAAF confronted with the Flanker, it would have little option other than to consider a two tier force employing the ATF as the long range air superiority element. This in turn however raises questions about whether our political leadership would be prepared to acquire such aircraft, even in limited numbers, given the expense and perceived specialised role. Numbers are a major issue in this context, a very small number of top tier aircraft may not yield the desired effect but will incur the fixed overheads resulting from supporting the type. A large number would be costly, and this would result in interservice political problems.

Hopefully this question will not need to be considered during the projected lifetime of the F/A-18A force, allowing the RAAF to look at cheaper second tier follow-on fighters employing the technology advances currently seen in the ATF.

The USAF at the time of writing envisaged about 500 ATFs to replace the frontline elements of the F-15C force, a reduced requirement against the original 750 airframes, with an additional 450 Navy airframes. The size of the production run would have a major impact on unit costs, given the substantial R&D overhead. Political debate on the usefulness of the aircraft has been heated, as many US politicians consider it to be a specialised asset targeted at defeating Soviet air power in a NATO theatre conflict. While this is clearly not the case, laymen of such calibre seldom allow facts to interfere with their righteous crusades.

The reality is that both the Fulcrum and Flanker if flown by competent pilots and applied appropriately, could successfully contest teen series fighters. The sheer incompetence of the Iraqi air force in the Gulf should not colour perceptions of the worth of the Fulcrum and Flanker. They are serious players and the high production rate of the Fulcrum reflects its status as one of the USSR's hottest exports, almost certainly supplanting the Fishbed as the Third World's premier tactical aircraft.

With shrinking budgets the US will be stretched to meet its commitments and this will reflect in lesser numbers of tactical aircraft available for bushfire conflicts such as the Gulf campaign. Both TAC and the Navy will require a new air superiority fighter by the turn of the century, simply due to airframe fatigue. Both the F-14 and F-15 are in the process of production windup and shutdown.

The question of course remains, will sanity win out ? The ATFs are both quite clearly good implementations of this class of aircraft, unlike the stillborn A-12 which was killed off earlier this year as it could not meet its design specification. US observers repeatedly commented early this year that the A-12 was in a more secure position politically than the ATF as the Navy's A-6E force is now block obsolescent and almost out of life. The F-14 and F-15 have at least a decade of useful life left in them.

Alternatives proposed to the ATF vary from F-15s reengined with ATF powerplants to the revival of the F-16XL, although the latter would require a major redesign to provide some measure of stealthiness.

The most reasonable outcome would be low rate production of the ATF to be later supplemented by a smaller fighter, in the same fashion as the F-15/F-16 programs developed. Whether this eventually occurs remains to be seen, and thus the ultimate fate of the superb ATF contenders is unclear.

Reference Data

Table 1. Performance Comparison - YF-22A, YF-23A, F-15C, F/A-18A

Definitions:

• MTOW - Maximum TakeOff Weight
• Combat Weight - 50% internal fuel, typical AAM load
• IR AAM - InfraRed, ie heatseeking Air-Air Missile
• BVR AAM - Beyond Visual Range Air-Air Missile, usually radar guided
• Combat Parameter - taken at combat weight, typical weapon load, at altitude
• Missile Weights: AIM-9=200 lb, AIM-7=500 lb, AIM-120=330 lb,

Author's note:

Given the early stage of the ATF development program and the secrecy imposed by the USAF, many figures in this table are estimates. In particular speeds, weights and thrust figures must be treated with caution, as many of these are nominal rather than actual. Note the 2.5M max speed of the F-15 is clean, with a full missile loadout this drops to 1.78M.

Table 2. ATF Program Schedules

Pic 1 (A-12 ATA)

The ill fated A-12A Avenger II was to be a stealthy interdictor replacing the A-6E and F-111 family. The US Navy envisaged the use of the long range ATA in conjunction with the navalised ATF to provide a 1000 NM + power projection capability. The ATA was cancelled earlier this year, as it had become severely overweight and could not meet design performance requirements with a pair of 12,000 lb class F404 engines. The expense of a major redesign with 18,000 lb class F110 engines was substantial and the US DoD killed the program, leaving the Navy with a fleet of obsolescent A-6Es. A short term fix is the adoption of an enlarged strike derivative of the F/A-18, supplemented by strike capable F-14Ds. In the longer term, an AX strike aircraft is envisaged, but no major funding has been allocated at this time.

Pic 2 (YF-22 )

The YF-22 was optimised for agility with some resulting loss in stealthiness. The general layout is similar to the F-15 and F/A-18, but much larger. RCS reduction is achieved largely through planform shaping and faceting, resulting in a multiple lobe design. Thrust vectoring is employed to improve pitch response.

Pic 3 (YF-23 PAV-1)

The YF-23 was optimised for speed, range and stealth at some expense in agility, compared to its rival. The general layout is unique and exploits much of the design technique developed in the B-2A ATB program. RCS is reduced through careful planform shaping and blending, with a unique low drag tail which conceals dorsal exhausts in troughs to reduce both RCS and IR emissions (USAF).

Pic 4 (YF-23 PAV-2)

The ATF is designed for a 1:1 class dry thrust/weight ratio and supersonic dry cruise. This provides it with a major energy advantage over a teen series (or teenski series) opponent, which it can outmanoeuvre and outlast in a supersonic engagement (USAF).

Pic 5 (YF-22 launching AIM-9 missile)

The ATF will carry its missiles internally to minimise RCS. Both the AIM-120 Amraam and AIM-9 are ejected from their bays at launch, so that the increase in RCS due open bays is transient and thus cannot allow tracking. The missiles will be supplemented by an internal gun (USAF/Lockheed/Boeing).

Pic 6 (YF-23 PAV-1)

The ATF has been designed for a minimal frontal RCS to provide a major advantage in the high noon shootout pre-merge phase of an engagement. A conventional opponent cannot shoot until a lock is acquired, and thus is likely to get hit in the face with an Amraam fired by the closing ATF before he can acquire the ATF. Once a turning engagement is entered, the high dry thrust/weight ratio of the ATF will confer a major energy advantage. A measure of this is a Lockheed report which indicates the YF-22 dry envelope is greater than the reheated envelope of the F-15C !

Pic 7 (YF-23 PAV-1 & PAV-2)

The ATF is designed to be long legged, with 25,000 lb class internal fuel capacity supplemented by inflight refuelling. This provides it with phenomenal range in subsonic cruise and excellent persistence in supercruise. In strategic air warfare terms, the ATF can penetrate deep into hostile airspace to defeat defending fighter aircraft and disrupt any attempts at offensive air operations, the ultimate application of Lanchester's laws (USAF).

Author's Commentary Added to 1991 sci.military Internet Newsgroup Posting

Topic:

Why did the USAF make the decision it did and select the Lockheed and Pratt's designs in preference to the Northrop and GE designs ?

The decision criteria for selection were pretty broad and covered performance and ability to meet the design spec, ability to meet manufacturer's internal spec, price, life-cycle-cost and development risk. The USAF have stated that the criterion of industrial base was not important, but informed sources advise me that this was not entirely true and that the USAF looked at the issue very seriously.

On the strength of what has been published about both aircraft and engines, the US taxpayer would have gotten an excellent deal in terms of system performance with either aircraft, they are both top performers. The final comparison appears as such:

1.Performance

Both aircraft apparently met the USAF's performance specs. Northrop were a bit faster, longer ranging and stealthier, whereas Lockheed were a bit more manoeuvrable. It appears that the performance margins between both types were not dramatic.

The GE engine performed somewhat better in the trials than the P&W engine, but the final P&W proposal included an enlarged fan and hence higher thrust for production aircraft, presumably equalising the difference.

2.Price

Apparently Lockheed and P&W were cheaper, by how much does not appear to have been published anywhere (anybody know ?)

3.Development Risk

Northrop were penalised in a number of areas. Firstly Lockheed did more aggressive flying (played their politics right by doing it very visibly) during the dem/val program and demoed high AoA manoeuvres and missile launches well in excess of nominal dem/val requirements.

Secondly Lockheed built a very conservative airframe design with very conservative materials, ie an F-15/F-18ish almost hybrid planform geometry using a lot of aluminium and titanium alloys, unlike Northrop who opted for cca 50% empty weight in composites, using a very stealthy airframe geometry, never used before in a fighter.

Thirdly Lockheed did not suffer the development pain which Northrop did with their stealthy exhaust ducts. The lining of the YF-23 exhausts is a laminated alloy structure full of tiny cooling holes fed by engine bleed air. It was apparently rather heavy and may have required major design changes to bring it to production. Also the main weapon bays of the YF-23 apparently stacked the Amraams vertically and the USAF were unhappy about the potential for jams in the launcher mechanism preventing the firing of subsequent missiles.

Northrop, true to their tradition, created a showpiece of the state of the art in technology - ie a high performance truly all aspect stealth airframe with better speed/range performance and bigger weapon bays than its rival. The price of innovation was the loss of the contract, as the YF-23 combines a lot of new ideas which have never been used before. Whereas the Lockheed F-22 is clearly an evolutionary development of current aerodynamic/stealth technology, the Northrop YF-23 is very much revolutionary. Therefore risky.

Similarly, the P&W engine was conservative, whereas the GE engine was a radical variable bypass ratio design never used in production before.

4.Industrial Base

MDC and Northrop have ongoing commitments for the C-17, F/A-18 and B-2 respectively, whereas Lockheed and GD don't really have any real military projects left once the P-3 and F-16 are completely closed. Similarly GE will be building F110s and F404s for F-16 and F-18 production to the end of the decade, whereas P&W only have the F100 for which the biggest user, the USAF F-15 force, is unlikely to seek additional purchases.

Therefore, a decision to buy Northrop/GE could have seen both Lockheed and P&W end up shutting down their military airframe/engine businesses around the end of the decade.

Summary

The US taxpayer is getting the cheaper and more predictable product with some penalty in top end performance and long term performance growth potential.

The USAF however had NO choice in this matter as the Administration killed the A-12 Avenger in January due cost overruns resulting from high risk R&D. By killing off the radical but high performance A-12, the Administration set a clear precedent. The A-12 was considered a very secure project politically because its cancellation would mess up Navy deployment plans for the next decade (the A-6Es are very old, basic airframe design 1958) and cause all sorts of problems.

In comparison with the A-12, the ATF was considered politically expendable as it is seen (incorrectly in my opinion) as a dedicated killer of PVO/VVS aircraft, while the F-15s will remain viable for at least another decade.

As a result, the USAF had no choice than to pursue the lowest risk design options regardless of any other criteria. As it turns out, both Lockheed and P&W were desperate enough to submit lower bids and hence the decision could not have really gone the other way. If the USAF chose the F-23 and it got into difficulties say in 1994 due R&D problems, it would almost certainly die the death of the A-12. Politicians generally seem to have little respect for air warfare strategy.

As for the future of the F-23, it may not end up being adopted by the Navy simply because the Navy is having real money problems, ie. buying F-18s instead of its preferred F-14s. Therefore the Navy is unlikely to buy any Naval ATFs until the end of the decade, by which time the Lockheed product will have matured whereas the Northrop one will have been sitting on the shelf.

Alternative roles for the airframe could be theatre strike and reconnaisance, but it is basically too good an airframe for these jobs and hence cheaper options could be found.

Final Observation: politics is always a stronger decision criterion than technology or air warfare strategy.

Further Information:

Lockheed-Martin/Boeing (Lockheed/Boeing/GD) F-22A

Northrop/McDonnell-Douglas YF-23

Artwork and text (C)1997, 1996 Carlo Kopp

Air Doctrine for the 21st Century

Battlefield of the Future

Principles of War for the Battlefield of the Future

F22: First Flight of the Raptor!

Modernizing US Tactical Aviation for Air Dominance

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