ParaNet BBS/atf
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ParaNet BBS/atf
| File Name: | atf.txt |
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| Author: | Unknown |
| Date: | Unknown |
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| BBS Main Page: | ParaNet Main Page |
| Key Words: | ParaNet, UFO, Ufology |
(463) Tue 2 Jun 92 5:18p Rcvd: Tue 2 Jun 5:28p
By: Uucp, ParaNet(sm) Information Servi (104/422)
To: Michael Corbin
Re: ATF
St: Pvt Rcvd
------------------------------------------------------------------------------
@MSGID: 1:104/422@Fidonet 4d115a95
From scicom!csn.org!mcorbin
From: mcorbin@csn.org (Michael Corbin)
To: scicom!mcorbin
Date: Tue, 2 Jun 1992 16:22:15 -0600
Reprinted with permission from Aerospace Publications, Canberra,
Australia, material not for inclusion in any other work or for
reprinting in any other publication.
(C) AEROSPACE PUBLICATIONS PTY LTD 1991
For reprints, photocopies, back issues, subscriptions, please
snailmail or fax to :
AEROSPACE PUBLICATIONS PTY LTD
P.O. Box 3105, WESTON CREEK, ACT 2611, AUSTRALIA
Ph:+616-288-1677 Fax:+616-288-2021
As published in April 1991 issue of the AUSTRALIAN AVIATION journal.
[Author's Note: this is the review of the background history
behind the project, Part 2 contains a detailed technical re-
view of the YF-22 and YF-23. I will be adding in some addi-
tional (unpublished) comment on why the USAF made the deci-
sion it did in the third installment]
ADVANCED TACTICAL FIGHTER
Part 1: The Evolutionary Path
The rollout and first flights last year of the YF-22A and
YF-23A Advanced Tactical Fighter (ATF) demonstrator aircraft
represents another quantum leap in the evolution of air su-
periority aircraft design.
Unlike earlier designs, the ATF is a careful blend of ad-
vanced aerodynamics, propulsion and electronics and involves
a degree of system integration never before attempted in a
tactical aircraft. The reason for this unprecedented effort
is quite clear - the Russians have finally deployed their
equivalent to the teen series fighters (see May, June 1990
AA), the Flanker and Fulcrum, and have thus very rapidly
closed the technological gap which offered such favourable
exchange rates for so long. It is worth noting that the teen
series fighters held the high ground for well over a decade
which is within itself no mean feat, if we observe the his-
tory of fighter development.
It is by turning back to the last two decades of that histo-
ry that we can fully understand the evolution in tactical
thinking that spawned the design concepts now embodied in
the ATF. It was in fact about twenty two years ago that a
pivotal point in the development of air combat tactics was
reached, and a new outlook developed on the issue of air
combat performance parameters. The setting for this situa-
tion was more than well publicised, as the USAF hammered the
Third World infrastructure of North Vietnam with weapons
designed to destroy industrialised economies. TAC flew daily
raids with fast big and well armed F-105D Thuds and F-4C/D
Phantoms. The Thud was initially designed for tactical nu-
clear strikes and thus sacrificed manoeurving ability for
speed at low level, as such it had no serious competitors in
its class. Vietnam saw the Thuds loaded up with 500 lb and
750 lb iron bombs flying low level dive bombing raids on a
range of targets, the Thuds carried only an internal 20 mm
gatling for self defence.
The Phantom in its C and D incarnations was a minimal modif-
ication of the US Navy's established F-4B fleet defence in-
terceptor, the F-4 had a useful bomb carrying ability but
significantly served as the USAF's principal air superiority
aircraft. It was armed with semi-active radar guided AIM-
7D/E missiles, heatseeking AIM-9B and AIM-4D missiles and in
some instances, 20 mm gatling centreline gunpods. Their op-
position was a mixed bag of second hand MiG-17F, MiG-19S/F-6
and MiG-21F aircraft, armed with 23 mm and 30 mm guns and in
some instances, AA-2 Atoll heatseeking missiles. The air-
craft were flown by Vietnamese, Russian, Czech, Polish and
East German pilots, the latter not publicised for obvious
propaganda reasons. The USAF did not fare very well,
achieving an air-air kill ratio of 2.18:1 in the period
between 1965 and 1968. The reasons were manifold, as inade-
quacies in missile performance, weapon systems and tactics
combined with absurd rules of engagement (ROE) offered every
imaginable advantage to the Communists, who did not hesitate
to exploit them. What had become very apparent was that the
performance characteristics of the aircraft and weapons used
were ill matched for the kind of engagements which were en-
tered. The MiGs were light VFR only fighters with simple
gyro stabilised gunsights and no fire control worth mention-
ing, the 17 and 19 being both optimised for climb perfor-
mance at high subsonic speeds. This gave them good turning
ability and respectable subsonic acceleration which combined
well to provide the basic elements of good gunfighting air
combat performance.
The Phantoms were IFR supersonic interceptors, with air in-
tercept radar, two man crew, beyond visual range (BVR) radar
guided missiles and tail aspect only heatseeking missiles,
both types optimised for killing high flying bombers. The
missiles lacked the manoeuvre performance to successfully
kill a nimble and small target unless launch conditions were
optimal and the target's manoeuvre options were highly res-
tricted. The Phantom's advantage in transonic acceleration
and climb performance was balanced by high wing loading and
unspectacular turning performance.
The USAF was clearly unhappy about this situation and meas-
ures were sought to improve kill ratios. The demand for a
gun and better turn performance spawned the F-4E with a
stretched fuselage, improved fuel capacity, chin mounted M61
20 mm gatling gun and manoevring slats. The same pressures
also led to a major review of air-air tactics which saw the
adoption of energy manoeuvrability as a fundamental of the
new air comabt manoeuvring doctrine. Conceived by a serving
USAF fighter pilot, Major John Boyd, energy manoeuvrability
revolved about the use of an aircraft's energy state (ie
speed/altitude) to gain a positional advantage in a
manoeurving engagement, thus gaining a firing opportunity.
Because the close-in air-air weapons of the period were guns
and tail aspect heatseekers, the best firing opportunities
resulted from tail aspect shots, this in turn dictated that
an aircraft must possess superior sustained turning, ac-
celeration and climb performance to defeat an opponent.
While the F-4 had the acceleration and climb performance to
kill most current opponents, it was clear that the next gen-
eration of fighters had to possess even greater
thrust/weight ratios and much better sustained turning per-
formance. The latter was simply not achievable by modifica-
tions to existing types which had their origins in the late
fifties and hence were aerodynamically highly optimised to
strike or interception roles.
The USAF initiated its FX program, while the USN discarded
its troubled F-111B bomber turned interceptor in favour of
the new VFX. Both the VFX and FX exploited new propulsion
technology, discarding afterburning turbojets in favour of
afterburning turbofans which offered much better specific
fuel consumption in dry thrust and a higher ratio of after-
burning thrust to dry thrust. Experience in Vietnam clearly
indicated that the endurance/combat radius of the 400 NM
class F-4 was inadequate and hence the VFX and FX were
designed to a 1000 NM class combat radius. Climb and turn
performance dictated low wing loading and good AoA perfor-
mance this in turn shaping the wing and inlet designs.
First to fly was Grumman's VFX, designated the F-14A, a
large twin with swing wings and a pair of TF-30 fans. The
F-14A had a large bubble canopy for good visibility during
dogfights, a Head Up Display (HUD) gunsight, computer con-
trolled automatic wing sweep and glove vane positioning, a
massive AWG-9 pulse Doppler air intercept/fire control radar
system capable of tracking multiple targets in ground
clutter and an internal M-61 gun. It was bigger, more com-
plex and more expensive than the F-4, but it also offered
agility and manoeuvrability without precedent. The first of
the teen series fighters had thus made its mark.
The 20,000 lb class TF30-P414 powerplants fitted to the F-
14A were a stop gap measure which offered a 1:1 class
thrust/weight but not the stunning 1.2+ class thrust/weight
sought by the Navy, that was to occur with the F-14B which
was to be fitted with F401-P-400s, navalised derivatives of
the emerging Pratt&Whitney FX powerplant. For budgetary rea-
sons this never eventuated, the F-14A having to wait until
the nineties for the 30,000 lb class F-110-GE-400 power-
plant.
The USAF's FX subsequently flew in 1972, taking advantage of
the 25,000 lb class F100-PW-100 powerplants and optimised
for energy manoeuvrability. Like the F-14 it had a large
bubble canopy, HUD, powerful pulse Doppler fire control ra-
dar, low wing loading and internal gun. Because it was
smaller and lighter than the F-14A, it offered a stunning
1.4:1 class thrust/weight ratio and thus set the standard
for air combat fighters (see AA Sept/Nov 84).
By the mid seventies the F-14A and F-15A entered service and
quickly established their superiority over existing air-
craft. Cost of ownership had however proven to be a major
issue as both aircraft cost much more to buy and even more
to maintain, given their more complex powerplants and avion-
ic systems. Under pressure from legislators, the USAF ini-
tiated the Light Weight Fighter (LWF) program to supplement
the F-15 with a smaller and much cheaper VFR dogfighter, an
aircraft armed with guns and heatseeking missiles and
equipped with a small pulse Doppler radar optimised for dog-
fighting alone.
Northrop bid their YF-17, a derivative of their P-530
lightwieght fighter, while General Dynamics bid their YF-16,
derived from a fly-by-wire relaxed static stability technol-
ogy demonstrator. The YF-17 Cobra was a small twin with two
'leaky turbojet' YJ101-GE-100 powerplants and a hybrid plan-
form comprised of massive Leading Edge Extension (LEX)
strakes and a moderately swept wing. The YF-16 was fitted
with a single F100 common to the F-15 and employed extensive
wing/body blending, also using strakes and a moderately
swept wing. The YF-16 was the first aircraft ever built to
be statically unstable and relied upon a triple redundant
analogue computer system to remain flyable.
The LWF flyoff was won by the YF-16 due in no small measure
to its powerplant commonality with the F-15, and to its
smaller size and somewhat better thrust/weight ratio perfor-
mance. Subsequently selected as the standard NATO air su-
periority fighter, the F-16 is today one of the mainstays of
Western air power.
Like the USAF the Navy came under increasing budgetary pres-
sure from legislators, who quickly quashed the Navy's plans
for a fleet of supercarriers equipped with a force of air
superiority F-14Bs and strike F-14Cs, the latter a strike
fighter derivative of the F-14B intended to replace the un-
derpowered A-6 bomber. The Navy were directed to select one
of the two USAF LWF contenders under the Naval Air Combat
Fighter (NACF) program, the intention being being to replace
the ageing A-4, A-7 and F-4 fleets with a single dual role
lightweight fighter bomber. Many in the US Navy opposed this
move, which largely defeated the Navy's strategy of acquir-
ing a 1000 NM radius air superiority/strike force.
The Navy eventually selected the F/A-18A, a substantial
redesign of the YF-17 airframe with greater internal fuel
capacity, bigger 16,000 lb class F404 engines and BVR mis-
sile capability, absent on the smaller F-16. The F/A-18A was
designed to rigid reliability and maintainability specifica-
tions, which substatially increased the cost of the air-
craft, which by then had acquired a very sophisticated suite
of avionic systems, imposed largely by the need for one air-
frame to fulfill two diverse roles. Another side effect of
this program was the 'detuning' of the F404 powerplant's
performance to improve reliability and lifetime.
The F/A-18A also employed fly-by-wire, but employed a so-
phisticated quadruplex digital system where software changes
could be employed to 'tweak' handling characteristics. The
avionic system was built around multiply redundant serial
Mil-Std-1553B databusses and employed dual redundant digital
computers.
With the entry into service of the F/A-18A the US services
completed their reequipping with teen series fighters, even-
tually building up a force of several thousand aircraft of
these four basic types.
The basic philosophy of high thrust/weight ratio and sus-
tained turning performance in transonic dogfights shaped
these aircraft aerodynamically and hence imposed fundamental
constraints to the other performance characteristics of this
family of aircraft.
Evolution did not stand still however, and the early
eighties saw the deployment of one of the most significant
air combat weapons of its time - the all aspect heatseeking
Lima model of the established AIM-9 Sidewinder missile. The
AIM-9L did not require a tail chase position to lock on to a
tailpipe, it was quite happy to lock on from any angle in-
cluding 12 o'clock ie head-on. Soon after deployment the
AIM-9L proved that much of the air combat tactics textbook
had been obsoleted, in that instantaneous turning perfor-
mance became far more important than sustained turning per-
formance. The ability to point the nose at an opponent
quickly and loose off a missile became far more important
than the ability to follow through multiple turning
manoeuvres to acquire a tail aspect gun/heatseeker firing
position. While a tail aspect position did improve the kill
probability of the missile by reducing the target's evasive
manoeuvre options, the AIM-9L's all aspect performance was
still superb, as learned the hard way by the Argentine and
Syrian air forces in 1982.
Clearly the day of the classical dogfight was almost over,
in that the first aircraft to acquire its opponent would be
first to fire and most likely to win the engagement. Only if
the first firing opportunity were to fail and the combatants
were to pass each other and then engage in a turning dog-
fight, was there a major requirement for sustained turning
performance. Yet again, however, the all aspect capability
of the AIM-9L would convert fleeting nose on target oppor-
tunities into real firing opportunities.
The first aircraft to take advantage of this situation was
the Navy F/A-18A, which had its flight control software
tweaked up to optimise instantaneous turn performance, this
combined with its sophisticated HUD and fire control radar
dispelled any doubts of the aircraft's lethality, given ear-
lier criticism of its low (ie 1.1:1 !) combat thrust/weight
ratio. Acceleration and climb performance, and low energy
bleed in manoeuvring at transonic speeds were the key param-
eters in this class of engagement.
A new philosophy for air combat tactics was thus developed
by the USAF, who envisaged long range medium to high alti-
tude penetration of hostile airspace by supersonic cruise
capable fighters with all aspect fire and forget missile ar-
mament. A key element in the new strategy was the AIM-120
Amraam missile (AA Sept 86), an active radar guided intelli-
gent fire and forget BVR missile, designed to replace the
established semi-active radar guided AIM-7. Coupled with a
suitable fire control radar the AIM-120 allows a single
fighter to salvo up to eight rounds at eight separate in-
bound targets within the acquisition geometry of the fire
control radar.
Manoeuvring at sustained supersonic speeds, the new look air
superiority fighter could outmanoeuvre SAMs and most AAMs,
while always retaining an energy advantage over the
subsonic/transonic speed range optimised teen series turning
dogfighter. The aerodynamic and propulsion design comprom-
ises which supported sustained turning performance at high
subsonic and transonic speeds seldom improved the ability of
the aircraft to sustain high energy manoeuvres at Mach 1.5
class speeds, where much of the wing was enveloped in the
shock cone produced by the nose of the aircraft.
The philosophy of first-look first-shoot reflected in the
need for superior sensor capability and low observability ie
Stealth. The former and latter requirements result in the
need for a frequency/spatially agile radar and high perfor-
mance InfraRed Search & Track (IRST), while the latter re-
quirement imposes the need for all of the tricks of the
Stealth trade, ie shaping, skinning and detailing.
The first aircraft to fly which embodied some of the new
technology was the ill-fated F-16XL. A radical redesign of
the F-16A, the XL was a supersonic cruise demonstrator with
a cranked arrow delta wing optimised for that flight regime.
The aircraft was, on the strength of published reports, a
major technical success, with two demonstrators eventually
flying. The highly swept inboard wing section of this air-
craft produced substantial vortex lift at supersonic speeds,
while also improving instantaneous turn rate and extending
the 9G manoeuvre envelope well above Mach 1. An additional
benefit of the new configuration was a substantial increase
in internal fuel capacity, providing a 120% improvement in
combat radius performance.
The F-16XL suffered the fate of many pioneering aircraft be-
fore their time, its F-16E dual role strike fighter deriva-
tive lost out in a flyoff against MDC's bigger and more ca-
pable F-15E Strike Eagle, thus ending all prospects for its
eventual production. Many observers attributed its demise to
a political strategy played by the USAF, to prevent an older
generation airframe derivative from being used by legisla-
tors as an excuse to kill off or postpone the ATF program.
Equipped with Amraam, higher thrust engines and new radar,
the F-16XL could cover a large part of the role envisaged
for the ATF at substantially lower unit and program costs.
As an older generation airframe however its infrared and ra-
dar signatures are substantial and this would greatly reduce
its effectiveness (although trivia of this nature hardly
ever bother astute decisionmakers such as politicians...).
The ATF program had its origins in numerous USAF air combat
studies carried out in the late seventies and early
eighties, when intelligence information revealed the So-
viets' early flight testing of the Fulcrum and Flanker. From
the observed geometry of the airframes it was clear that
both types would have the vortex lift performance to chal-
lenge the teen series aircraft in turning dogfights, by the
same token both Soviet fighters would be handicapped by
their geometry in both supersonic manoeuvre and low observa-
bility performance.
The ATF was to be the successor to the F-15, a long range
air superiority fighter with the performance to kill any
other tactical aircraft and the operating radius to threaten
targets deep inside the USSR while flying from bases in
Western Europe. This was to be achieved by the use of a
highly integrated airframe/systems/propulsion design ex-
ploiting advanced aerodynamics, engines and stealth technol-
ogy, the latter to delay an opponent's initial firing oppor-
tunity for as long as possible, and thus capitalise on the
large Radar Cross section (RCS) of the Fulcrum and Flanker.
Subsequent to studies, an RFP was issued in July 1986, and
two contractor teams, Northrop/McDonnell-Douglas and
Lockheed/Boeing/General Dynamics were selected in October
1986 for the initial 50 month demonstration/validation phase
flyoff. The rollout of the prototypes was initially
scheduled for mid 1989, but ongoing slippages have delayed
this until the middle of last year.
Part 2 provides a technical comparison of the YF-22A and
YF-23A prototypes
Picture Caption # 1 (F-4B Phantom)
MDC F-4B Phantom II. The F-4 was the mainstay of the USN's
and USAF's tactical fighter force in the SouthEast Asian
conflict. The Phantom offered superb acceleration and climb
performance for its day, while carrying an impressive air-
air payload of 4 heatseeking AIM-9D and 4 semi-active radar
AIM-7E missiles. In engagements with the smaller and nimbler
NVAF MiGs the F-4 was hampered by poor missile performance
and reliability, inadequate radar lookdown performance and
the absence of a gun for close in engagements.
Picture Caption # 2 (F-14A Tomcat)
Grumman F-14A Tomcat. Grumman's large F-14 fighter was the
first of the teen series aircraft to fly and deploy. It was
equipped with a pair of 20,000 lb class TF-30 afterburning
fans and a computer controlled variable geometry wing to
provide superb turning and acceleration performance, while
its massive pulse Doppler AWG-9 fire control radar and Head
Up display allowed the targeting of 100 NM class AIM-54
Phoenix missiles, AIM-7 Sparrow, AIM-9 Sidewinder missiles
and an internal M-61A1 20 mm gun. It has remained a formid-
able dogfighter to this day.
Picture Caption # 3 (F-15A Eagle)
MDC F-15A Eagle. The F-15A was designed, like the F-14A, for
high thrust/weight ratio to provide superlative accelera-
tion, climb and turn performance. Like the F-14, it is
equipped with a high power long range lookdown/shootdown
pulse Doppler radar. Armed with a mix of AIM-7 and AIM-9
missiles and an internal M-61 gun, the F-15 has repeatedly
demonstrated its capability in the Middle East. The most re-
cent subtype, the dual role strike fighter F-15E, is struc-
turally strengthened for 9G manoeuvres.
Picture Caption # 4 (F-16A Falcon)
Dubbed the 'Electric Jet', GD's F-16 was the first tactical
aircraft to employed relaxed static stability and fly-by-
wire control. Initially acquired as a low cost VFR dog-
fighter armed with an internal M-61 gun and heatseeking
AIM-9 missiles, the later F-16C is a truly multirole tacti-
cal aircraft, with wide angle holographic HUD, and provision
for Lantirn terrain following radar/FLIR pods and the AIM-
120 Amraam BVR missile.
Picture Caption # 5 (F-16XL )
The F-16XL was a supercruise technology demonstrator derived
from the basic F-16 airframe/powerplant. The cranked arrow
delta wing allowed the aircraft to cruise supersonically on
dry thrust, improved the manoeuvre envelope substantially
while providing enough additional internal fuel capacity to
increase the combat radius by 120%. Sadly it never entered
production, losing to the F-15E in a competitive flyoff for
the Dual Role Fighter program. As a teen series airframe
lacking stealth capability, it cannot compete with the newer
ATF aircraft.
Picture Caption # 6 (F-18A )
Using a hybrid planform wing and digital fly-by-wire, the
MDC F/A-18A was the last of the teen series fighters. It was
the first tactical aircraft to employ a fully digital Mil-
Std-1553B bussed avionic system under the control of redun-
dant digital computers. A multirole derivative of the YF-17
airframe, the later F/A-18 is a fully capable all weather
strike fighter which retains excellent air superiority per-
formance.
Picture Caption # 7 (Flanker)
The Su-27 Flanker is the most capable aircraft in the Rus-
sian inventory and is expected to be a hot seller in the
Third World market. Aerodynamically it reflects the design
philosophy of the teen series aircraft, employing vortex
lift, high thrust/weight ratio and fly-by-wire control.
Equipped with a large pulse Doppler radar, internal 30 mm
gun, BVR and heatseeking missiles, it is a formidable op-
ponent. Recently tested on the V-MF's new CVAN, the Flanker
has the combat radius and performance to contest any teen
series aircraft.
ADVANCED TACTICAL FIGHTER
Part 2: YF-22A and YF-23A - A Technical Comparison
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 perfor-
mance of the aircraft, their airframe geometry and known
powerplant parameters reveal much of their design philosophy
and performance. Both aircraft reflect their prime contrac-
tors' respective philosopies of stealth aircraft design as
much as they reflect their common mission profile.
Principal airframe/propulsion design objectives were sus-
tained supersonic cruise on dry thrust, high energy manoeu-
vrability, 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 il-
lustrate 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 dis-
rupt Soviet offensive air operations. The decline of the So-
viet 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 capabili-
ty 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 in-
tent, it is unrealistic at the least to assume that any na-
tion 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 su-
periority 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 perfor-
mance 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 ad-
dress 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 advan-
tage 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, enhanc-
ing survivability on deep penetration missions. Supercruise
required major advances in propulsion technology and non-
trivial 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 facet-
ing with blended facet boundaries, the latter a necessary
concession to high performance aerodynamics. This is ap-
parent 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 boun-
daries 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 re-
flections 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 exten-
sive 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 ex-
hausts 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 [Auth: Avleak got this one wrong...], as all ma-
jor edges fall into groups of two parallels.
The result of the low observables techniques employed with
these aircraft is a major reduction in aircraft detectabili-
ty 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 surviva-
bility. Weapon bays are located on the sides of the inlet
boxes and a single central bay is located beneath the cen-
tresection, 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 blend-
ing allowing good area ruling and low supersonic drag. The
low wing aspect ratio is used to optimise supercruise per-
formance. 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 in-
frared signature. The YF-23 employs an unconventional V-tail
with a planform consistent with the airframe lobing stra-
tegy. 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 manouvrability via the use of thrust vectoring, even
though this was not a mandatory USAF requirement. Two dimen-
sional 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 sta-
bility, 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 ac-
commodate the Navy carrier recovery an launch requirements,
ie low speed on approach and high lift at low speed on cata-
pult 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 in-
stalled afterburning thrust, in the 35,000 lb class per en-
gine, 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 super-
sonic part of the envelope. The latter requirement was par-
ticularly painful, as it forced a move to higher tempera-
tures 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 tech-
nology. The core of the YF120 was derived from work done
during the government sponsored ATEGG (Advanced Technology
Engine Gas Generator) and JTDE (Joint Technology Demonstra-
tor 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, classi-
fied. 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 us-
ing 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 re-
ported to use aerodynamically actuated VABIs, in which
respect it differs from earlier designs which used mechani-
cal 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. Turbo-
jets are considered optimal for supersonic flight as their
dry thrust drops far more slowly than that of a fan with in-
creasing vehicle airspeed. The ATF flight profiles are suf-
ficiently 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 [Auth: ultimately a
wrong assumption, based to some degree on off-the-record
comments made by parties involved]. The gain in overall en-
gine 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 im-
provement 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 (Integrat-
ed Electronic Warfare System) technology development pro-
grams 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 tur-
naround of 15 minutes (cf 35 minutes for F-15), a require-
ment 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 mis-
sion 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 stan-
dard 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 ex-
ploiting over 1,000 transmit/receive/phase-shifter elements,
each of which is a wholly self contained module. This ar-
rangement results in a highly robust design which doesn't
require mechanical pointing, as main lobe shape and direc-
tion are controlled electronically, and which gracefully de-
grades 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, op-
timise 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 intro-
duced 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 sys-
tem using focal plane array (FPA - see earlier TE) technolo-
gy. 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 fric-
tion, 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 back-
ground environment is easier to deal with. At the time of
writing the EOSS was deferred as it was considered too imma-
ture for a low risk production design.
The cockpits of both the YF-22 and YF-23 will be convention-
al 'glass' arrangments, 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 em-
ployed, 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 controll-
er 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 proto-
types.
Performance
It is clear from published accounts that the ATF is an enor-
mous step forward in aerodynamic and low observables perfor-
mance in comparison with the teen series fighters and their
Soviet counterparts. Both competitors have repeatedly super-
cruised 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 ab-
sence 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 parame-
ters for the mission, in both areas the ATF is well ahead of
the teen series fighters. Again in the absence of hard fig-
ures it is difficult to establish whether Northrop/MDC's
greater speed and radius performance are a decisive advan-
tage. 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 pro-
file. 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 certain-
ly 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 pewerplant 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, there-
fore the smoother the design the lesser the scattered re-
turn. As the RCS figures are classified, it is not clear how
great a performance margin exists. Tail aspect radar and in-
frared 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 con-
sidered of greater value in the projected strategic air war
of the future.
The Perspective View
To the Australian observer the ATF underscores the revolu-
tion under way in tactical air warfare, with stealthiness,
radius and agility growing significantly against the exist-
ing 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 [non Australian readers
please note the RAAF's air superiority fighter is the F/A-
18A].
In the current regional air defence environment the F/A-18A
has no serious rival. This could however change with a re-
gional acquisition of the Fulcrum and Flanker. While the
Fulcrum could be readily tackled in BVR and visual engage-
ments, 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 persistance, 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 [cca 50% of Gulf kills due AIM-7 SARH BVR
AAM]. 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 disad-
vantage the defending fighter in terms of geometry and ener-
gy 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 ad-
vantage 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 gui-
dance effectiveness.
Were the RAAF confronted with the Flanker, it would have
little option other than to consider a two tier force em-
ploying the ATF as the long range air superiority element.
This in turn however raises questions about whether our pol-
itical leadership would be prepared to acquire such air-
craft, even in limited numbers, given the expense and per-
ceived 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 [this situation would be common to a number of
non-US air forces].
Hopefully this question will not need to be considered dur-
ing 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 ad-
ditional 450 Navy airframes. The size of the production run
would have a major impact on unit costs, given the substan-
tial 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 in-
terfere with their righteous crusades [US readers will hope-
fully forgive the author's comment here...].
The reality is that both the Fulcrum and Flanker if flown by
competent pilots and applied appropriately, could success-
fully contest teen series fighters. The sheer incompetence
of the Iraqi air force in the Gulf should not colour percep-
tions 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 tac-
tical 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 pro-
cess 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 [a major factor
in the ATF decision] 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. Wheth-
er this eventually occurs remains to be seen, and thus the
ultimate fate of the superb ATF contenders is unclear.
---------------------------
(AA will review the winning contender as more detailed in-
formation becomes available)
REFERENCES:
Table 1. Performance Comparison - YF-22A, YF-23A, F-15C,
F/A-18A
Table 2. ATF Program Schedules
*** 28th July, 1986 - Request for Proposals issued by USAF
*** 31st October, 1986 - Team Selections for 50 month
Demonstration/Validation program, both to build two proto-
types. A Lockheed/Boeing/General Dynamics team is to compete
with a Northrop/McDonnell Douglas team.
*** Mid 1990 - L/B/GDC YF-22A and N/MDC YF-23A enter Dem/Val
flight test program
*** 30th April, 1991 - USAF to announce selection of pre-
ferred aircraft.
Picture Caption # 1 (A-12 ATA)
The ill fated A-12A Avenger II was to be a stealthy interd-
ictor replacing the A-6E and F-111 family. The US Navy en-
visaged 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 en-
visaged, but no major funding has been allocated at this
time.
Picture Caption # 2 (YF-22 rear aspect)
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 im-
prove pitch response.
Picture Caption # 3 (YF-23 top or aft view)
The YF-23 was optimised for speed, range and stealth at some
expense in agility, compared to its rival. The general lay-
out 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.
Picture Caption # 4
The ATF is designed for a 1:1 class dry thrust/weight ratio
and supersonic dry cruise. This provides it with a major en-
ergy advantage over a teen series (or teenski series) op-
ponent, which it can outmanoeuvre and outlast in a superson-
ic engagement.
Picture Caption # 5/6 (YF120 cutaway + external view)
The GE YF120 variable bypass ratio engine is the key to the
stunning performance of the ATF. With 25,000 lb class dry
and 35,000 lb class reheated thrust, this engine outper-
formed its rival YF119 in both the YF-22 and YF-23 proto-
types. The variable bypass ratio allows the engine to optim-
ise itself for the flight regime, allowing thus efficient
dry cruise at speeds between 1.4 and 1.58 Mach.
Picture Caption # 7 (YF-22 launching 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.
Picture Caption # 8
The ATF has been designed for a minimal frontal RCS to pro-
vide 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 re-
port which indicates the YF-22 dry envelope is greater than
the reheated envelope of the F-15C !
Picture Caption # 10/11 (both refuelling)
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 air-
space to defeat defending fighter aircraft and disrupt any
attempts at offensive air operations, the ultimate applica-
tion of Lanchester's laws.
ADVANCED TACTICAL FIGHTER AIR SUPERIORITY PERFORMANCE COMPARISON TABLE
---------------------------------------
----------------------------------------\
Type YF-22A YF-23A F-15C F/A-18A
ATF ATF Eagle Hornet
---------------------------------------
----------------------------------------\
Regional Users - - USAF, USN,RAAF
JASDF
---------------------------------------
----------------------------------------\
Crew 1 1 1(2-D) 1(2-B)
---------------------------------------
----------------------------------------\
Dimensions [ft]
Span 43.0 43.6 42.8 40.4
Length 64.2 67.4 63.8 56.0
Height 17.7 13.9 18.5 15.3
Wing Area [sq] 830.0 950.0 608.0 400.0
---------------------------------------
----------------------------------------\
Weights [lb]
Basic Empty 34,000 37,000 32,050 23,000
MTOW - - 68,000 37,500
Combat 48,820 51,320 39,800 30,000
---------------------------------------
----------------------------------------\
Int Fuel [lb] 25,000 24,000 13,455 11,000
---------------------------------------
----------------------------------------\
Propulsion
Manufacturer GE or P&W GE or P&W GE GE
Type GE YF120 GE YF120 F110-GE100 F404-GE400
P&W YF119 P&W YF119
Thrust,Dry [lb] ~25,000 ~25,000 18,300 11,000
Thrust,A/B [lb] ~35,000 ~35,000 28,000 16,000
---------------------------------------
----------------------------------------\
Weapon Load (A/A)
Gun M-61A1 M-61A1 M-61A1 M-61A1
IR AAM 4xAIM-9M 4xAIM-9M 4xAIM-9M 2xAIM-9M
BVR AAM (A) 4xAIM-120 4xAIM-120 4xAIM-7M 2xAIM-7M
(B) 4xAIM-120 2xAIM-120
---------------------------------------
----------------------------------------\
Performance
Max.Sp.Alt [Mach] >1.8 >1.8 2.5 (1.78) 1.8
Cruise Sp. Alt [Mach] ~1.58 ~1.58 subsonic subsonic
Combat T/W Dry [-] ~1.02 ~0.97 0.92 0.733
Combat T/W A/B [-] ~1.43 ~1.36 1.41 1.07
Combat Wg Ldg[lb/ft2] 58.8 54 63.2 75.0
Combat Radius [NM] >1000 >1000 ~600 405
Inflight Refuelling boom boom boom probe
---------------------------------------
----------------------------------------\
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.
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 sat 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.
Carlo Kopp
carlo@gaia.gcs.oz.au
Defence Writer
Aerospace Publications
egardless 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 sat 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.
Carlo Kopp carlo@gaia.gcs.oz.au Defence Writer Aerospace Publications
