SR-71C was a hybrid aircraft composed of the rear fuselage of the first YF-12A (S/N 60-6934) and the forward fuselage from an SR-71 static test unit. The YF-12 had been wrecked in a 1966 landing accident. This Blackbird was seemingly not quite straight and had a yaw at supersonic speeds. It was nicknamed "The Bastard".
Being a hybrid of 2 separate aircraft initially caused some unforeseen problems, most noticably with the aircraft's geometry. During the first sixteen flights for the Air Force, these issues were addressed and resolved by a team of pilots and engineers led by William Campbell (LtGen-Ret).
" 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."
By the time 981 was delivered to Beale on March 9, 1970, she flew just like the B model. The "Double Eagle" flight of 7 October 1969 was a completely normal flight apart from two minor unstarts (which were themselves completely normal before DAFICS came along). The only major difference was that the C model only had 5 fuel tanks, whereas the B's had six, so refueling was a slightly different procedure.
The flight crews for 981's first 20 USAF flights were:
8 May 1969 81-05-448 Bill Skliar/Dameron Spruill
16 May 1969 81-06-449 Bill Skliar/Dameron Spruill
25 July 1969 81-07-461William Campbell/Joe Rogers
1 August 1969 81-08-463 William Campbell/Joe Rogers
5 August 1969 81-09-465 Joe Rogers/Revedy Allender
7 August 1969 81-10-466 Alton Slay/Joe Rogers
12 August 1969 81-11-468 William Campbell/John Storrie
19 August 1969 81-12-469 John Storrie/William Campbell
26 August 1969 81-13-470 Ted Moeller/William Campbell
28 August 1969 81-14-471Richard Gerard/William Campbell
3 September 1969 81-15-472 Joe Rogers/William Campbell
4 September 1969 81-16-474 William Campbell/Richard Gerard
2 October 1969 81-17-480 William Campbell/Slip Slater
7 October 1969 81-18-483 Joe Rogers/Slip Slater ("Double Eagle" flight)
15 October 1969 81-19-485 William Campbell/E.L. Pyne
24 October 1969 81-20-488 Joe Rogers/William Campbell
2 December 1969 81-21-489 William Campbell/Joe Rogers
4 March 1970 81-23-499 Fitz Fulton (SP)/William Campbell (IP)
9 March 1970 81-24-500 William Campbell/Red McNeer (delivery to Beale)