Lockheed YF-12A
Description
Role	Prototype interceptor
Crew	two, pilot and RIO
First Flight	August 7 1963
Manufacturer	Lockheed
Dimensions
Length	101 ft 7 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
Weights
Empty	60,730 lb	27,604 kg
Loaded	lb	kg
Maximum takeoff	127,000 lb	57,727 kg
Powerplant
Engines	2x Pratt & Whitney J58
Thrust	65,000 lb	290 kN
Performance
Maximum speed	2,110 mph	3,376 km/h
	Mach 3.2
Unrefuelled range	2,500 miles	4,000 km
Service ceiling	85,000 ft	25,914 m
Rate of climb	ft/min	m/min
Wing loading	lb/ft²	kg/m²
Thrust/Weight
Avionics
Fire control radar	Hughes ASG-18
Armament
Missiles	3x Hughes AIM-47B

The Lockheed YF-12 was a prototype interceptor aircraft that formed the basis for the SR-71 Blackbird.

The YF-12 program was a development of the A-12 Oxcart spy plane designed for the CIA. Lockheed was able to interest the Air Force in the project after it had been forced to cancel the XF-108 Rapier, a Mach 3 capable interceptor intended to replace the F-106 Delta Dart in service. It was pointed out that an aircraft based on the A-12 would provide a far cheaper alternative because much of the design and development work had already been done and paid for. In 1960, the USAF agreed to fund the conversion of three A-12s to YF-12A prototype interceptor configuration.

The main changes were modifying the aircraft's nose to accommodate the fire-control radar originally developed for the F-108, and the addition of a second cockpit for a crewmember to operate it. The nose modifications changed the aircraft's aerodynamics enough to require ventral fins to be mounted under the fuselage and engine nacelles to maintain stability. Finally, bays that had been used to house the A-12's reconnaissance equipment were converted to carry missiles.

Tests were extremely impressive, with the YF-12As setting a number of new speed and altitude records and demonstrating very promising results with their unique weapon system. In 1965, the Air Force placed an order for 93 F-12Bs, but this was cancelled due to budget cuts by Secretary of Defense Robert McNamara. The program was abandoned at that point, but the YF-12s continued flying for many years both with the Air Force and NASA as research aircraft.

Of the three YF-12s, one crashed during tests, one was cannibalised to provide parts for the SR-71C trainer, and the last is on display at the USAF Museum at Wright-Patterson Air Force Base, Dayton, Ohio.

A fourth aircraft, designated YF-12C, is believed to be an SR-71A converted for test purposes.

External link

• USAF Museum: YF-12