YF-12A 60-6935, early in the program as evidenced by the "Buzz numbers" on the nacelles and the unpainted titanium fuselage, rudders and nacelles.
In October of 1955, the USAF laid out specifications of the Long-Range Interceptor, Experimental (LRI-X) program, which was to procure a replacement for the F-102 Delta Dagger and F-106 Delta Dart. North American Aviation, Northrop and Lockheed all produced concepts, but the program was canceled less than a year later. The program was later reinstated in April 1957, this time with a supplementary role as a penetration fighter and escort for the B-70 Valkyrie. North American was awarded a contract for two prototypes of their NA-257 design, which shared the engine and ejection capsule with the Valk. A mockup of the XF-108, given the name "Rapier", was delivered to the USAF in January 1959, but the program was terminated on 23 September of that year due to delays in development, shifting goals for the USAF, and the debunking of the so-called "Bomber Gap".
Mockup of the F-108 Rapier on display for the USAF, 1959
Part of the XF-108 program funded the development of the radar and missiles the Rapier was to carry, the Hughes AN/ASG-18 fire control system and the complimenting GAR-9 Falcon missile. The massive AN/ASG-18 was made up of 41 separate modules, and weighed 2,100lbs in total. The antenna was 40 inches in diameter, and was the first Pulse-Doppler radar to be fitted to an American aircraft. The unit was anticipated to have a maximum range of 300miles, and was proved to be able to detect B-47-sized aircraft at 100 miles. The ASG-18 also incorporated two IR seekers for use in detecting aircraft by their heat signatures. The GAR-9 missiles (later redesignated AIM-47 under the 1962 scheme) were similarly huge, nearly 13' long and more than 13 inches in diameter, with a range of 100+ miles at a speed of Mach 4. The type was originally spec'd for a W-42 nuclear warhead, with a yield of 0.25kt, though those plans were later scrapped and a 100lb high explosive warhead was later fitted. For testing purposes, a B-58 Hustler was modified to accept the radar, and a special mission pod was built to carry and fire the GAR-9 missiles. The modified B-58 gained the nickname "Snoopy" due to the extended radome for the ASG-18, and was also fitted with the IRST blisters and cameras on the outer two engines to film the missile launch.
Snoopy taking off for a test flight.
Close-up of Snoopy with the radome removed, showing the antenna and IRSTs of the AN/ASG-18
At around the same time, Lockheed's special projects group, known as the Skunk Works, was developing a high-speed, high-altitude airplane to replace the CIA's U-2 Dragon Lady. This plane, known by the internal code A-12, "Archangel" being the program code, 12 being the accepted design, was to be capable of Mach 3+ speeds, at altitudes over 60,000 feet. These atributes were expected to place the new plane out of range of the Soviet SAMs that had brought down Gary Powers' U-2. The A-12 was built and operated under the code name OXCART, which was occasionally applied to the aircraft as well, though Lockheed pilots preferred to call the plane the Cygnus, following company tradition of naming aircraft for celestial bodies.
Lockheed A-12, tail number 60-6332, in flight.
The legendary head of the Skunk Works, Kelly Johnson, suggested an armed version of the OXCART for the USAF, under the designation AF-12. The USAF formally ordered three prototypes in 1960 under Project KEDLOCK, with the aircraft taking up the seventh, eighth and ninth slots in the A-12 production line. To accept the ASG-18 the A-12 design was modified, which mainly involved cutting back the chines around the nose to fit a new radome, as well as fairing the IRST in the chine below the cockpit. These changes were extensive enough to require the addition of fixed fins underneath the engine nacelles, as well as a larger fin under the fuselage that folded up while the plane was on the ground. A second cockpit was also added in the Q Bay for the Weapons Systems Officer; similar modifications were made to the TA-12 trainer and M-21 motherships.
One of the YF-12As under construction. Note the security fence to keep the workers from the regular A-12 line from seeing the interceptor variant.
A wider shot of the YF-12 being assembled. Note the shorter tail, a trait carried over from the A-12, but not shared with the later SR-71 Blackbird, and the all-moving rudders.
A YF-12A with the radome removed, showing the antenna of its radar system
Schematic of the YF-12A
The first YF-12 flight occurred on 7 August 1963, with #934 taking wing over the Groom Lake (popularly called "Area 51") airfield.
Rollout of 60-6934 in early 1963. The aircraft is almost entirely unpainted titanium, with the radome, inlet spikes and leading edges being high-temperature composite materials.
On 24 February, President LBJ took the extraordinary step of announcing the YF-12 program to the public, partially as a smokescreen for the CIA's A-12 program. On 30 September 1964, a public showing of the YF-12 was held at Edwards AFB .
First flight of the YF-12A. Note that, as with the A-12, the plane was mostly unpainted titanium during early flights. The cylindrical objects hanging off the engines are cameras to record the missile launch sequence.
60-6934 flies past the crowd at Edwards. Note the large ventral fin in the lowered position, as well as the plane now being painted black.
60-6936 taxis past onlookers. Note the MP approaching to tell the photographer to step back.
Testing continued into 1965, during which the YF-12s set a speed record of 2,070.101 mph and an altitude record of 80,257.86 feet. Seven tests of the AIM-47 missiles were carried out, with six being successful (the 7th failed due to a faulty gyro in the missile). During the final test, the YF-12 launched a missile at Mach 3.2 from 74,000', striking a JQB-47E target drone flying at 500 feet. Though inert, the missile impacted the target directly, removing a four foot section of its tail. The USAF considered the YF-12A program a complete success, and on 14 May 1965 ordered 93 F-12Bs for the Air Defence Command (ADC).
The first YF-12 being prepped for a test flight
#936 during its record setting flight. The white cross was to assist tracking cameras
The F-12B, the production model, would have been moderately redesigned based on experiences gleaned during the test program. A chine would have been added to the radome, and the IRST would have been more completely faired into the existing chine. Both of these changes would have allowed the deletion of the large movable fin, though the two fixed fins would have remained. Changes to the radar avionics would have allowed carriage of four AIM-47s, up from the 3 that the YF-12A could hold. Due to spiraling costs associated with the Vietnam War, and the decreasing threat of Soviet bombers, SecDef McNamara withheld funding for the F-12B however, and in January 1968 the program was canceled.
Mockup of the F-12B forward fuselage.
After the program was canceled, the YF-12s were bailed to NASA for use as high-speed test aircraft. Tests included how engine inlet performance affected airframe and propulsion interaction, boundary layer noise, heat transfer under high Mach conditions, and altitude hold at supersonic speeds. A program under joint NASA Dryden and USAF auspices created several systems to improve the performance of the SR-71, which almost completely eliminated unstarts (the ejection of the inlet shockwave, which caused violent shuddering of the aircraft and could result in loss of the airframe) as well as improving range. Another NASA program was the "Coldwall" series, which involved mounting an insulated cylinder filled with nitrogen under the aircraft, in the space formerly used by the missile bays. Once in flight and at Mach 3+, the insulating layer would be blown away, exposing the test cylinder to the thermal environment of high-speed flight.
Of the three YF-12As produced, 60-6934 was damaged by fire after a rough landing in 1966. The aft fuselage was salvaged, and after the second SR-71B trainer was lost, the SR-71C was created by mating the salvaged YF-12 with the forward fuselage of a static test frame.
60-6935 was retired on 17 November 1979 to the USAF Museum in Dayton, Ohio, where it remains on display.
The remaining YF-12 landing at Wright-Patterson AFB in Ohio in 1979.
60-6936 was destroyed on 24 June 1971 after an in-flight fire. Both of the crew successfully ejected from the stricken craft. As a result of the accident, the USAF loaned an SR-71 to NASA to complete the test program; in order to disguise the still-secret Blackbird, it was given the fictitious designation YF-12C, and the serial number of an A-12 (60-6937). The "YF-12C" was operated by NASA until 1978, after which it was returned to the USAF.
YF-12A 6935 and "YF-12C" 6937 in flight during the Coldwall experiments in 1975
One of the YF-12s photographed with the XB-70, one of the few aircraft that could pace it.
Hyphen no like your pictures....
phenotyp last edited by phenotyp
Funny to think that there was a "secret" production line separate from the "regular" A-12 production line.
Also, they look so damn cool unpainted.
Anyone else having issues? I came in on my phone via the app and Chrome, and I see them.
@skyfire77 I'm not seeing them on my phone, either.
jayvincent last edited by
@skyfire77 - I can see them just fine on Opera / desktop