Pratt & Whitney J58

J58
J58 engine on display at the Evergreen Aviation & Space Museum
Type	Turbojet
Manufacturer	Pratt & Whitney
First run	1958
Major applications	Lockheed A-12 Lockheed SR-71

The Pratt & Whitney J58 (company designation JT11D-20) was a jet engine that powered the Lockheed A-12, and subsequently the YF-12 and the SR-71 aircraft. The J58 was a single-spool turbojet with an afterburner. It had a unique bleed from the compressor to the afterburner which gave increased thrust at high speeds. This feature caused it to be referred to as a turboramjet in some writings. It delivered 25,000 pound-force (110 kN) of thrust without afterburner (dry) and 34,000 (150 kN) with afterburner (wet).

The J58 had its origins in the bigger JT9 (J91) engine. It was a 3/4 scale JT9 with a mass flow of 300 lb/s, down from 400 lb/s and known by the company designation JT11. The JT11 was initially proposed for the US Navy, hence its Navy designation J58. It was also promoted for use on various Navy and Air Force aircraft, e.g. Convair F-106, North American F-108, Convair B-58C, Vought XF8U-3 Crusader III, and North American A3J Vigilante, which never materialized.

The J58 was initially developed for the US Navy to power the planned version (using the J58) of the Martin P6M jet flying boat. The P6M started out using Allison J71-A-4 engines and then switched to the Pratt & Whitney J75 as the J58 wasn't ready due to development problems. Upon cancellation of this aircraft, it was selected for the Convair Kingfish and for the Lockheed A-12, YF-12A and SR-71. Other sources link its origin to the USAF's requirement for a powerplant for the WS-110A, the future XB-70 Valkyrie.

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