Of the 32 SR-71s built, two were SR-71B trainer models (s/n 61-7956 and -957), with a raised cockpit for the instructor behind the student. These humped cockpits disrupted the airflow enough that the trainers were fitted with fixed fins under the engine nacelles to stabilize the aircraft, and as they were not operational aircraft, were not fitted with the cameras and ECM gear of the SR-71a models. 61-7956 was retired with the rest of the Blackbirds, and is now on display at the Kalamazoo Air Zoo, but -957 was destroyed in 1968 after a double generator failure. The crew ejected safely, but the Blackbird stalled and entered a flat spin, impacting tail first and falling onto its back.
A new trainer was needed, however tooling for the A-12/YF-12/SR-71s had been destroyed per USAF orders. A solution was found in the remains of YF-12A 60-6934, which had been irreparably damaged by overheating in 1966. The aft fuselage, which had been preserved, was mated to a static test article, producing 61-7981, the only SR-71C, also known as “The Bastard”.
As she had the aft sections of a YF-12, -981 had a shorter tail cone than the rest of the SR-71s, though the folding ventral fin was removed. Also, owing to its hybrid nature, 981 was difficult to fly at first, needing extended testing:
“ 981 took a long time to pass the acceptance testing at Edwards because the inlets were acting so unusually. We had more than 10 unstarts on several flights and by-pass doors and spike positions were hardly ever in synch.
“I had Palmdale install a sideslip (Beta) indicator in the front cockpit because the aircraft seemed to be out of rig. Once installed, with indications of zero sideslip, the rudders needed to be trimmed out of the streamlined position and the inlets were still acting up. For the next flight, I asked to have a yaw string (made out of Nomex) placed ahead of the cockpit.
“On that mission, the yaw string was centered when the Beta indicator showed a 4 degree yaw and the rudders were then in streamlined trim. However, the inlets were still not matched in position. To determine what was wrong, Palmdale finally determined that the pitot boom was out of alignment in yaw by 4 degrees and thus feeding bad information to the inlet computers. Once they straightened the boom, 981 flew normally and we delivered the aircraft to Beale.”
-Lt Gen (Ret) William Campbell
Despite early difficulties and her ominous nickname, the Bastard flew like the rest of the fleet after her teething problems were ironed out, and was the favored Blackbird for VIP flights early in the program. Although stationed at Beale AFB until retirement in 1990, -981 had last flown in 1976, and was added at the last minute to the “group photo” taken in February.
The Bastard is now on display at Hill AFB in Utah.