Title: ATF: YF-22A and YF-23A - A Technical Comparison By: Carlo Kopp Date: November 1st, 1997 4154 Flashback:Orig. Multipage Version Hard Copy:Printer Friendly
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
28th July, 1986 - Request for Proposals issued by
USAF
31st October, 1986 - Team Selections for 50 month
Demonstration/Validation program, both to build two
prototypes. 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
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.
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 ?