Article 8523 of rec.aviation.military:
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From: jfb@usgp1.ih.att.com (Joe Baugher)
Subject: Lockheed YF-12A
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Summary:  Mach 3+ interceptor
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The Lockheed YF-12A Mach 3 interceptor of the mid-1960s had its origin 
in the top-secret A-12 spyplane which had been designed by Lockheed at 
Central Intelligence Agency request as a successor to the U-2 
spyplane.  

The basic U-2 concept dated back to 1954, and as early as 1957 the CIA 
had concluded that the high-flying U-2 might soon be vulnerable to 
missiles and would have to be replaced with something more advanced if 
reconnaissance missions over Soviet territory were to continue 
unmolested.  The CIA wanted an aircraft with a maximum cruising speed 
of over Mach 3 which could operate at altitudes exceeding 80,000 feet, 
which should render the aircraft immune from interception by any known 
threat.  

After some preliminary studies, both Convair and Lockheed were given 
funds to carry out detailed design studies.  Even before this study 
had gotten underway, the Lockheed Skunk Works team (headed by the 
famous engineer Clarence R. "Kelly" Johnson) had already been trying 
to interest the government in a U-2 replacement, and had been 
experimenting with advanced propulsion concepts involving a turbojet 
powered by a liquid hydrogen/liquid oxygen mixture, but these ideas 
were abandoned as being impractical at an early stage in the process.  

On August 29, 1959, Lockheed was declared the winner of the contest 
and was awarded a limited development contract for design, wind-tunnel 
testing, and the construction of a mockup.  The project came to be 
known under the deliberately deceptive codename *OXCART*.  The 
designation A-12 became associated with the project, which is sort of 
odd, since such a designation was not consistent with either the 
official USAF or the internal Lockheed company designation scheme.  In 
some documents, the various Skunk Works proposals that were at various 
times being given consideration during the initial design phase bore 
the in-house design numbers of A-1 through A-12, and the A-12 
designation was supposedly chosen because the 12th design was the one 
that was eventually produced.  However, Lockheed's designer Clarence 
L. ("Kelly") Johnson seems to have referred to the aircraft as A-11 
rather than A-12.  To make things even more confusing, the designation 
A-11 was used by President Lyndon Johnson when he officially revealed 
the existence of the project in February of 1964, but this may have 
have simply been a slip of the tongue on Lyndon's part.  It is 
possible that the CIA came up with the A-12 designation itself.  The 
OXCART document claims that the aircraft WAS originally designated 
A-11, but was later redesignated A-12 as a result of changes that had 
been introduced to make the aircraft capable of achieving a lower 
radar cross section, with the designation A-11 later becoming 
associated with the YF-12A interceptor version.  

On September 3, 1959, the CIA authorized Lockheed to proceed with 
antiradar studies, aerodynamic structural tests, and engineering 
designs, and on 30 January 1960 the Agency gave the green light to 
produce 12 aircraft.  Serial numbers were 60-6924/6935 .  Later, three 
more single-seaters (60-6937/6939) and nine two-seaters 
(60-6940/60-6948) were ordered.  

The Pratt and Whitney Division of United Aircraft Corporation was 
chosen to develop the propulsion system.  Their J58 engine, which was 
to be used in the A-12, had been sponsored originally by the US Navy 
for its own purposes, and was to be capable of a speed of Mach 3.0.  
Navy interest in the development was diminishing, however, and the 
Secretary of Defense had decided to withdraw from the program at the 
end of 1959.  The CIA revised interest in the J58, and requested that 
the engine be further developed and optimized for a speed of Mach 3.2.  
The new contract called for initial assembly of three advanced 
experimental engines for durability and reliability testing, and 
provision of three engines for experimental flight testing in early 
1961.  

The A-12 was to be built almost entirely of heat-resistant titanium 
alloys, chosen because of their relatively light weight and great 
strength.  However, titanium is relatively costly and is a very hard 
metal which is very difficult to mill and machine.  Consequently, its 
use as as an important aircraft component required the development of 
entirely new technologies.  The Titanium Metals Corporation was chosen 
as the primary contractor for the metal.  Quality control is 
especially difficult during titanium alloy manufacture--even the most 
minute of impurities can render the batch into a useless brittle metal 
which shatters under the weakest of stresses.  Of the early deliveries 
from Titanium Metals Corporation, some 80 percent had to be rejected 
as being flawed, and it was not until 1961 that quality became 
consistently satisfactory.  

Since the airframe would undergo aerodynamic heating during sustained 
supersonic cruise, significant thermal expansion was expected.  In 
order to accommodate for this thermal expansion, a set of chordwise 
corrugations were added to the central portion of the wing, and 
expansion gaps were provided between some panels.  During protracted 
operations above Mach 3 it was estimated that the fuel tanks would 
heat up to about 350 degrees Celsius, so that a special low-volatility 
fuel (known as JP-7) had to be supplied and the tanks themselves had 
to be rendered inert with nitrogen gas to prevent fuel explosions in 
the tank because of the heat.  Special lubricating oil had to be 
developed for operation at 600 degrees F., and contained a diluent in 
order to remain fluid at operation below 40 degrees.  

The wing was of short-span modified delta planform, supplemented by 
long fuselage chines which extended forward all the way to the nose.  
These chines had the beneficial effect of contributing to yaw damping 
at high speeds and also provided additional space for fuel and 
equipment.  The blending of the fuselage, chines, and wings also 
helped to reduce the A-12's radar signature over that of other 
aircraft.  

The engines were housed in long nacelles that were mounted at 
approximately mid-span on each wing.  The nacelles were provided with 
a complex inlet and ejector system, with the inlets contributing as 
much as 60 percent of the total engine thrust at Mach 3.  During 
takeoff, suck-in doors mounted on the side of the engine nacelles open 
up to admit additional air to the engines.  The engines contained 
large conical-shaped inlet spikes which could be pushed forward or 
backwards to adjust for aircraft speed.  During takeoff and low-speed 
flight, the inlet spikes were fully forward, but as speed increased, 
the inlet spikes were pulled to the rear a maximum of 26 inches so 
that the shockwave could be maintained at the inlet throat.  

A vertical tail was mounted above the rear of each engine nacelle.  
The vertical tails were all-moving, and were canted inwards.  Fixed 
fins were mounted underneath each nacelle, and a fin was mounted 
underneath the rear fuselage which could be folded aside for takeoffs 
and landings.  The landing gear was fairly conventional, with the 
three-wheeled main members retracting inwards into bays in the 
fuselage and the nosewheel retracting forward into a bay in the 
forward fuselage.  

A small Skunk Works engineering team worked with engineers from Pratt 
& Whitney and were able to construct the first prototype in only 22 
months.  In December 1961, the first A-12 (article number 121, USAF 
serial number 60-6924) was trucked from Palmdale, California to the 
secret base at Groom Lake, Nevada, so chosen that it would be remote 
from prying eyes.  However, the J58 engine was still not ready, and it 
was decided that a pair of Pratt & Whitney J75 engines would be used 
for the initial test flights.  

Finally, on 26 April 1962, aircraft 121 was ready.  On that day, 
Lockheed test pilot Louis Schalk took it for an unofficial, 
unannounced, maiden flight lasting some 40 minutes.  The first 
official flight took place on April 30, 1962, piloted again by Louis 
Schalk.  The aircraft broke the sound barrier on its second official 
flight, 4 May 1962, reaching Mach 1.1.  

Aircraft No. 122 arrived at Groom Lake on 26 June, and spent three 
months in radar testing before engine installations and final 
assembly.  Aircraft No. 123 arrived in August and flew in October.  
Aircraft No. 124, a two-seated version intended for use in training 
OXCART project pilots, was delivered in November.  It was to be 
powered by the J58 engines, but delivery delays and a desire to begin 
pilot training prompted a decision to install the smaller J75's.  The 
trainer flew initially in January 1963.  The fifth aircraft, No. 125, 
arrived at the area on 17 December.  

On October 27, 1962 a U-2, flown by a Strategic Air Force pilot on a 
SAC-directed mission, was shot down by a surface-to-air missile while 
flying over Cuba in search of Soviet missile sites.  This raised the 
dismaying possibility that continued manned, high-altitude 
surveillance of Cuba might become too dangerous, and the OXCART 
program suddenly assumed greater significance and its achievement of 
operational status became one of the highest national priorities.  

By the end of 1962, speeds of Mach 2.16 and altitudes of 60,000 feet 
had been achieved, still with the the lower-powered J75 turbojets, 
although some flights did take place with just one J58 installed.  
However, by the end of January 1963, ten J58 engines were available, 
and the first flight with two of them installed occurred on 15 
January.  Thenceforth all A-12 aircraft were fitted with their 
intended propulsion system.  

In the meantime, an entirely new mission had appeared for the 
*OXCART*.  In September of 1959, the USAF had cancelled its contracts 
for the North American F-108 Rapier, a Mach 3-capable aircraft that 
had been proposed as the USAF's next-generation interceptor to replace 
the F-106.  The reason given for the cancellation was that the F-108 
was simply too expensive for the USAF, now that the primary Soviet 
threat to the US mainland was its battery of intercontinental range 
ballistic missiles rather than its fleet of long-range bombers.  
Nevertheless, Lockheed thought that the Air Force might still be 
interested in a less-costly F-106 replacement should the Soviet bomber 
fleet ever again be perceived as a significant threat.  Lockheed 
suggested to the Air Force that the A-12 design would make a good 
platform for a Mach 3+ interceptor, and might make a good replacement 
for the F-106 at a more reasonable cost than the abortive F-108 
Rapier.  Sufficient interest was expressed by the Air Force that in 
October of 1960 they gave Lockheed permission to modify three A-12 
airframes to interceptor configuration.  Serial numbers were 
60-6934/6936.  One of the unsaid reasons for the Defense Department 
approval of the interceptor project was perhaps that it might make a 
good cover for the real CIA-supported intelligence-gathering nature of 
the project.  In September of 1962, these three aircraft were secretly 
assigned the designation YF-12A in the new Defense Department 
tri-service scheme..  

The YF-12A was quite similar in overall configuration to the A-12 from 
which it was derived.  It differed from the A-12 primarily in having a 
second crewman in a position immediately behind the pilot This second 
crewman was added to operate the extremely powerful and capable Hughes 
AN/ASG-18 pulse doppler fire control radar, which had originally been 
developed for the F-108 Rapier.  The AN/ASG-18 was installed in the 
extreme nose of the aircraft, with the forward chines being cut back 
to accommodate the 40-inch radome.  The ASG-18 radar supposedly had a 
search range as great as 500 miles.  Infrared sensors were installed 
in the forward edges of the cut-back chines.  

The YF-12A also differed from the A-12 in having armament.  This 
armament consisted of four Hughes AIM-47A Falcon air-to-air missiles 
housed internally in chine bays that had previously been used to carry 
the reconnaissance equipment.  The AIM-47A had originally been known 
as the GAR-9 and (like the ASG-18 radar) had originally been intended 
for the F-108 Rapier.  When fired, the Falcon missiles were 
explosively ejected from their bays, and their rocket motors were 
fired.  Powered by a storable-propellant liquid-fuelled rocket, the 
AIM-47A had a maximum speed of Mach 6 and an interception range of 115 
miles.  It had a launch weight of about 800 pounds.  The missile 
relied on semiactive radar homing for midcourse guidance to the 
immediate vicinity of the target, homing in on reflections off the 
target resulting from transmissions from the huge ASG-18 radar.  
However, it used terminal infrared homing for the final run in to the 
target.  

The first YF-12A (60-6934) took off on its initial flight on August 7, 
1963, piloted by James D. Eastham.  It was equipped with a 
streamlined camera pod mounted underneath each engine nacelle for 
photographing AIM-47 missile launches.  Three YF-12As were built.  
Serials were 60-6934/6936, which were drawn .  

While on a routine INS test flight with A-12 number 123 on May 24, 
1963, CIA detachment pilot Kenneth Collins entered some clouds.  Water 
vapor froze in the pitot tube, giving an erroneous airspeed reading.  
With the airspeed indicator giving the wrong reading, the aircraft 
stalled.  Collins ejected safely from the aircraft after it entered an 
inverted flat spin.  The aircraft crashed 14 miles south of Wendover, 
Utah.  The wreckage was recovered in two days, and people at the scene 
were indentified and requested to sign secrecy agreements.  A cover 
story for the press described the accident as occurring to a F-105, 
and is still listed in this way on official records.  

Although this particular loss was ultimately traced to a problem that 
was easily corrected, it nevertheless precipitated a policy problem 
within the Agency.  With the growing number of A-12s flying out in the 
western desert, the CIA felt that there was a danger that the OXCART 
project's cover could be blown at any moment.  Although the program 
had gone through development, construction, and a year of flight 
testing without attracting any public attention, the Department of 
Defense was experiencing increasing difficulty in concealing its 
participation in the OXCART program because of the delays and cost 
overruns that had increased the rate of expenditures to such an extent 
that they might eventually get large enough to attract unwanted 
attention from congressional budget oversight committees.  There was 
also a realization that the technological data would be extremely 
valuable in connection with feasibility studies for the SST.  Finally, 
there was a growing awareness in the higher reaches of the aircraft 
industry that something new and remarkable was going on.  Several 
commercial airline crews had reported sighting unidentified aircraft 
in flight.  Aviation Week indicated to its readers that it was vaguely 
aware that there was some rather unusual project going on at the Skunk 
Works at Burbank.  

Soon after President Lyndon Johnson took office following the 
assassination of President John Kennedy on November 22, 1963, he was 
briefed on the OXCART project and directed that some sort of cover 
announcement be prepared for the spring of 1964.  In February of 1964, 
President Johnson announced that "The United States has successfully 
developed an advanced experimental jet aircraft, the A-11, which has 
been tested in sustained flight at more than 2,000 miles per hour and 
at altitudes in excess of 70,000 feet.  The performance of the A-11 
far exceeds that of any other aircraft in the world today.  The 
development of this aircraft has been made possible by major advances 
in aircraft technology of great significance for both military and 
commercial applications.  Several A-11 aircraft are now being flight 
tested at Edwards Air Force Base in California.  The existence of this 
program is being disclosed today to permit the orderly exploitation of 
this advanced technology in our military and commercial program." 

The "A-11" referred to by President Johnson had been the original 
design designation for the aircraft first proposed by Lockheed prior 
to the adoption of stealth technology for the design.  Subsequently, 
it became the design designation for the YF-12A interceptor version.  
The parallel OXCART project remained black.  Although there was at the 
time considerable speculation about a Central Intelligence Agency role 
in the A-11 development, this was never acknowledged by the 
government.  

The President also said that "the A-11 aircraft now at Edwards Air 
Force Base are undergoing extensive tests to determine their 
capabilities as long-range interceptors." This statement was untrue, 
since at the time the President spoke, there were no A-11's actually 
at Edwards and there never had been.  Project officials were aware 
that some sort of public announcement was about to be made, but they 
had not been told exactly when.  Caught by surprise, they hastily 
arranged to fly two of the Air Force YF-12A's to Edwards to support 
the President's statement.  Thenceforth, while the OXCART continued 
its secret career out at the Groom Lake site, the A-11 performed in 
its YF-12A guise at Edwards Air Force Base under a considerable glare 
of publicity.  

In 1964, Kelly Johnson was awarded the prestigous Collier trophy for 
his achievements in the YF-12A project, becoming the first person in 
history ever to be honored by this recognition twice.  

The three YF-12As served initially with the 4786th Test Squadron at 
Edwards AFB.  The USAF was sufficiently impressed with the performance 
of the YF-12A that they ordered a total of 93 definitive F-12B 
aircraft into production and Congress had voted $90 million toward the 
project.  However, Secretary of Defense Robert McNamara saw no need 
for the F-12B and refused to free up the money, the reason being given 
that the expanding war in Southeast Asia was consuming all available 
funds in the USAF budget.  McNamara chose instead to purse the cheaper 
"F-106X" interceptor.  The YF-12As served primarily in various and 
sundry operational evaluation projects throughout the remainder of the 
1960s.  

Even though there was to be no production of the YF-12A, the three 
prototypes carried out an extensive program of flight research with 
the Air Force.  On May 1, 1965, the following world records were set 
by YF-12A 60-6936:  

  15/25 km closed-circuit speed record:  2070.102 mph.  Piloted by Col 
  Robert L. Stephens and LtCol Daniel Andre.  This counted as a new 
  world absolute speed record and was the first record to exceed 2000 
  mph.  

  Sustained altitude record of 80,257.86 feet.  Piloted by Col.  Robert 
  L. Stephens and LtCol Daniel Andre.  

  500-km closed-circuit speed record:  1642.042 mph.  Piloted by Majors 
  Walter F. Daniel and Noel T. Warner.  

  1000-km closed circuit speed record:  1688.891 mph.  Piloted by Major 
  Walter F. Daniel and Capt James P. Cooney.  

In December of 1969, YF-12A 60-6935 was handed over to NASA at the 
Dryden Flight Research Facility.  60-6936 was delivered to Dryden a 
year later.  

While serving with NASA, YF-12A 60-6936 was lost on June 24, 1971 when 
USAF pilot LtCol Ronald J. Layton and WSO Maj. William A. Curtis 
were forced to eject after the plane caught fire due to a fuel 
line fatigue failure during approach to Edwards.  Both crewmembers 
survived.  

In November of 1979, its research program being completed, YF-12A 
60-6935 was donated to the USAF Museum at Wright Patterson AFB in 
Dayton, Ohio.  It is now permanently on display at the museum.  

The prototype YF-12A (60-6934) was briefly placed in storage following 
the end of its flight test program.  In 1969, it was taken out of 
storage and cut up and used for parts in the construction of SR-71C 
64-17981, a two seat trainer.  

There was actually a FOURTH YF-12, sometimes referred to as a YF-12C.  
Its serial number is 60-6937.  However, Aerofax claims that this 
aircraft is really SR-71A serial number 64-17951 that had been 
retained by Lockheed until 1969.  In that year, Lockheed turned the 
aircraft over to the USAF.  For some reason, the Air Force then 
changed its designation to YF-12C and assigned it a new serial number 
(60-6937) prior its delivery to NASA in July of 1971.  NASA returned 
the plane to the Air Force in December of 1978.  It was later put on 
outdoor display at Edwards AFB.  The latest information I have is that 
the plane is now with the Pima Air Museum of Tucson, Arizona.  Anyone 
have more current information on its whereabouts?  

The A-12s continued on to become operational spy planes and carried 
out numerous reconnaissance missions, the details of which are still 
highly classified even today.  The OXCART document (assuming it to be 
genuine) gives a few of the details.  The OXCART fleet was taken out 
of service and placed in storage in the late 1960s.  

In February 1963, Lockheed undertook redesign of the basic A-12 with 
additional fuel tankage, broader forward nose chines, and the 
provision for inflight refueling and a seat for a second crewman.  
This eventually emerged as the SR-71, which I shall discuss when I get 
to the 71st entry in the bomber series.  

Specification of Lockheed YF-12A:  

Two Pratt and Whitney J-58 (JT11D-20B) turbojets, each rated at 32,500 
lb.s.t. with afterburning.  Performance (estimated):  Maximum cruise 
speed:  2110 mph at altitude (Mach 3.2) Maximum operational ceiling:  
85,000 feet Maximum unrefuelled range:  2500 miles 
Dimensions:  Length: 101 feet 7 inches, Wingspan: 55 feet 7 inches.   
Height: 18 feet 6 inches.  Wing Area: 1795 square feet 
Weights:  60,730 pounds empty, 127,000 pounds maximum takeoff.  
Armament:  Four Hughes AIM-47A air to air missiles which are 
explosively ejected downwards from paired tandem missile bays.  

Sources:  

  Lockheed Aircraft Since 1913, Rene J.  Francillon, Naval Institute 
  Press, 1987.  

  The American Fighter, Enzo Angelucci and Peter Bowers, Orion Books, 
  1987.  

  The Illustrated Encyclopedia of Aircraft Armament, Bill Gunston, Orion 
  Books, 1988.  

  Lockheed Blackbirds, Anthony M. Thorborough and Peter E. Davies, 
  Motorbooks International, 1988.  

  The OXCART Story, Thomas P. McIninch, available from Skunk Works 
  Digest.  

Joe Baugher			  **************************************
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jfb@uscbu.ih.att.com
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