|YF-12A undergoing flight testing.|
|Designer||Clarence "Kelly" Johnson|
|First flight||7 August 1963|
|Primary user||United States Air Force|
|Unit cost||US$15–18 million (projected)|
|Developed from||Lockheed A-12|
The Lockheed YF-12 was an American prototype interceptor aircraft, which the United States Air Force evaluated as a development of the highly secret Lockheed A-12, which also spawned the Lockheed SR-71 Blackbird. YF-12 is the world's largest manned interceptor to date.
Design and development 
In the late 1950s the United States Air Force (USAF) sought a replacement for its F-106 Delta Dart interceptor. As part of the Long Range Interceptor Experimental (LRI,X) program, the North American XF-108 Rapier, an interceptor with Mach 3 speed, was selected. However, the F-108 program was canceled by the Department of Defense in September 1959. During this time Lockheed's Skunk Works was developing the A-12 reconnaissance aircraft for the Central Intelligence Agency (CIA) under the Oxcart program. Kelly Johnson, the head of Skunk Works, proposed to build a version of the A-12 named AF-12 by the company; the USAF ordered three AF-12s in mid-1960.
The AF-12s took the seventh through ninth slots on the A-12 assembly line; these were designated as YF-12A interceptors. The main changes involved modifying the A-12's nose to accommodate the Hughes AN/ASG-18 fire-control radar originally developed for the XF-108, and the addition of the second cockpit for a crew member to operate the fire control radar for the air-to-air missile system. The modifications changed the aircraft's aerodynamics enough to require ventral fins to be mounted under the fuselage and engine nacelles to maintain stability. The four bays previously used to house the A-12's reconnaissance equipment were converted to carry Hughes AIM-47 Falcon (GAR-9) missiles. One bay was used for fire control equipment.
The first YF-12A flew on 7 August 1963. President Lyndon B. Johnson announced the existence of the aircraft on 24 February 1964. The YF-12A was announced in part to continue hiding the A-12, its still-secret ancestor; any sightings of CIA/Air Force A-12s based at Area 51 in Nevada could be attributed to the well-publicized Air Force YF-12As based at Edwards Air Force Base in California.
On 14 May 1965 the Air Force placed a production order for 93 F-12Bs for its Air Defense Command (ADC). However, Secretary of Defense Robert McNamara would not release the funding for three consecutive years due to Vietnam War costs. Updated intelligence placed a lower priority on defense of the continental US, so the F-12B was deemed no longer needed. Then in January 1968, the F-12B program was officially ended.
Operational history 
Air Force testing 
During flight tests the YF-12As set a speed record of 2,070.101 mph (3,331.505 km/h) and altitude record of 80,257.86 ft (24,462.6 m), both on 1 May 1965, and demonstrated promising results with its unique weapon system. Six successful firings of the AIM-47 missiles were completed. The last one was launched from the YF-12 at Mach 3.2 at an altitude of 74,000 ft (22,677 m) to a JQB-47E target drone 500 ft (152 m) off the ground. One of the Air Force test pilots, Jim Irwin, would go on to become a NASA astronaut and walk on the Moon.
The program was abandoned following the cancellation of the production F-12B, but the YF-12s continued flying for many years with the USAF and with NASA as research aircraft.
|This section requires expansion with: Fill in holes on USAF and NASA flight testing. (December 2009)|
NASA testing 
The initial phase of this program included test objectives aimed at answering some questions about implementation of the B-1. Air Force objectives included exploration of its use in a tactical environment, and how AWACS would control supersonic aircraft. The Air Force portion was budgeted at US$4 million. The NASA tests would answer questions such as how engine inlet performance affected airframe and propulsion interaction, boundary layer noise, heat transfer under high Mach conditions, and altitude hold at supersonic speeds. The NASA budget for the 2.5-year program was US$14 million.
Of the three YF-12As, #60-6934 was damaged beyond repair by fire at Edwards during a landing mishap on 14 August 1966; its rear half was salvaged and combined with the front half of a Lockheed static test airframe to create the only SR-71C.
YF-12A #60-6936 was lost on 24 June 1971 due to an in-flight fire caused by a failed fuel line; both pilots ejected safely just north of Edwards AFB. YF-12A #60-06935 is the only surviving YF-12A; it was recalled from storage in 1969 for a joint USAF/NASA investigation of supersonic cruise technology, and then flown to the National Museum of the United States Air Force at Wright-Patterson Air Force Base near Dayton, Ohio on 17 November 1979.
A fourth YF-12 aircraft, the "YF-12C", was actually the second SR-71A (61–7951). This SR-71A was re-designated as a YF-12C and given a fictitious serial number 60-6937 from an A-12 to maintain SR-71 secrecy. The YF-12C was loaned to NASA for propulsion testing after the loss of YF-12A (60–6936) in 1971. The YF-12C was operated by NASA until September 1978, when it was returned to the Air Force.
The YF-12 had a real-field sonic-boom overpressure value between 33.5 to 52.7 N/m2 (0.7 to 1.1 lb/ft2) - below 48 was considered "low".
- Pre-production version. Three were built.
- Production version of the YF-12A; canceled before production could begin.
- Fictitious designation for an SR-71 provided to NASA for flight testing. The YF-12 designation was used to keep SR-71 information out of the public domain.
Aircraft disposition 
- 60-6934 - Hill Aerospace Museum, Hill AFB, Utah. Transformed into SR-71C 61-7981 after fire damage in 1966.
- 60-6935 - National Museum of the U.S. Air Force, Wright-Patterson AFB, Dayton, Ohio. This aircraft has small patches in its skin, on the starboard side below the cockpit. The patches cover holes caused by the "spurs" of a crewman who had to evacuate the plane after an emergency landing.
- 60-6936 - Lost, 24 June 1971
Specifications (YF-12A) 
Data from Lockheed's SR-71 'Blackbird' Family
- Crew: 2
- Length: 101 ft 8 in (30.97 m)
- Wingspan: 55 ft 7 in (16.95 m)
- Height: 18 ft 6 in (5.64 m)
- Wing area: 1,795 ft² (167 m²)
- Empty weight: 60,730 lb (27,604 kg)
- Loaded weight: 124,000 lb (56,200 kg)
- Max. takeoff weight: 140,000 lb (63,504 kg)
- Powerplant: 2 × Pratt & Whitney J58/JTD11D-20A high-bypass-ratio turbojet with afterburner
- Maximum speed: Mach 3.35 (2,275 mph, 3,661 km/h) at 80,000 ft (24,400 m)
- Range: 3,000 mi (4,800 km)
- Service ceiling: 90,000 ft (27,400 m)
- Hughes AN/ASG-18 look-down/shoot-down fire control radar
See also 
- Related development
- Related lists
- Knaack, 1978.
- Pace, Steve (1995). X-Planes at Edwards. p. 11. ISBN 9781610607865.
- Pace 2004, pp. 45–46.
- Pace 2004, pp. 46–47.
- Landis and Jenkins 2005, pp. 40–41.
- Green and Swanborough, 1988, p. 350.
- Hughes AIM-47 Falcon
- Johnson's speech named the plane A-11, the name for the two-seat design.
- McIninch 1996, p. 15.
- Air Force Museum Foundation, 1983, p. 133.
- McIninch 1996, p. 14.
- Pace 2004, p. 53.
- Donald 2003, pp. 148, 150.
- Landis and Jenkins 2005, p. 44.
- Drendel 1982, p. 6.
- Landis and Jenkins 2005, pp. 62, 75.
- Pace 2004, pp. 109–110.
- Landis and Jenkins 2005, pp. 49–55.
- Dugan, James F. Jr. Preliminary study of supersonic-transport configurations with low values of sonic boom p18. NASA Lewis Research Center, March 1973. Accessed: March 2012.
- Landis and Jenkins 2005, p. 40.
- Landis and Jenkins 2005, p. 46.
- Landis and Jenkins 2005, pp. 49–50.
- "YF-12A/60-6934." Hill Aerospace Museum. Retrieved: 16 April 2013.
- "YF-12A/60-6935." National Museum of the USAF. Retrieved: 16 April 2013.
- Goodall and Miller, 2002.
- Air Force Museum Foundation Inc. US Air Force Museum. Dayton, Ohio: Wright-Patterson AFB, Ohio, 1983.
- Donald, David, ed. "Lockheed's Blackbirds: A-12, YF-12 and SR-71". Black Jets. AIRtime, 2003. ISBN 1-880588-67-6.
- Drendel, Lou. SR-71 Blackbird in Action. Carrollton, Texas: Squadron/Signal Publications, 1982, ISBN 0-89747-136-9.
- Goodall, James and Jay Miller. Lockheed's SR-71 'Blackbird' Family. Hinchley, England: Midland Publishing, 2002. ISBN 1-85780-138-5.
- Green, William and Gordon Swanborough. The Complete Book of Fighters. New York: Barnes & Noble Inc., 1988. ISBN 0-7607-0904-1.
- Jenkins, Dennis R. Lockheed Secret Projects: Inside the Skunk Works. St. Paul, Minnesota: MBI Publishing Company, 2001. ISBN 978-0-7603-0914-8.
- Jenkins, Dennis R. and Tony R. Landis. Experimental & Prototype U.S. Air Force Jet Fighters. Minnesota, US:Specialty Press, 2008. ISBN 978-1-58007-111-6.
- Knaack, Marcelle Size. Encyclopedia of US Air Force Aircraft and Missile Systems: Volume 1 Post-World War II Fighters 1945–1973. Washington, DC: Office of Air Force History, 1978. ISBN 0-912799-59-5.
- Landis, Tony R. and Dennis R. Jenkins. Lockheed Blackbirds. North Branch, Minnesota: Specialty Press, revised edition, 2005. ISBN 1-58007-086-8.
- McIninch, Thomas. "THE OXCART STORY". Center for the Study of Intelligence, Central Intelligence Agency, 2 July 1996. Retrieved 10 April 2009.
- Pace, Steve. Lockheed SR-71 Blackbird. Swindon: Crowood Press, 2004. ISBN 1-86126-697-9.
|Wikimedia Commons has media related to: Lockheed YF-12|
- Mach 3+: NASA/USAF YF-12 Flight Research, 1969–1979 by Peter W. Merlin (PDF book)
- YF-12A Flight Manual and YF-12A #60-6935 Photos on SR-71.org
- YF-12 fact sheet on USAF Museum site
- Blackbird Spotting maps the location of every existing Blackbird, with aerial photos from Google Maps
- USAF Aircraft Serial Numbers for 1960, including all A-12s, YF-12As, and M-21s