Approved for Release: 2013/06/25
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Secret NOFORN
Chapter 6
290
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[figure]
*First flight of the A-12, 30 April 1962*
Initial testing could not explore the A-12’s maximum potential, since the J58 engine was still not ready. Developing this power plant to OXCART specifications was proving much more difficult than had been expected because the J58 had to reach performance levels never before achieved by a jet engine, while operating under extremely difficult environmental conditions. To simulate the stress that the J58 would undergo during maximum power output (Mach 3.2 at 97,000 feet), the power plant was tested in the exhaust stream of a J75 engine. In the course of this extremely severe testing, the J58’s problems were gradually overcome. By January 1963, Pratt & Whitney had delivered 10 J58 engines to the Nevada testing site. The first flight of an A-12 with two J58 engines took place on 15 January 1963.³⁴
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SPEED-RELATED PROBLEMS
As J58-equipped A-12s reached higher and higher speeds, more difficulties arose. Major problems developed at speeds between Mach 2.4 and 2.8 because the aircraft’s shock wave interfered with the flow of air into the engine, greatly reducing its performance. Solving this problem required long and often highly frustrating experimentation
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³⁴ William H. Brown, “J58/SR-71 Propulsion Integration,” *Studies in Intelligence* 26 (Summer 1982): pp. 17-18 (U); *OSA History*, chap. 20, pp. 58, 67 (TS Codeword).
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Secret
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Approved for Release: 2013/06/25