Pratt & Whitney J57 Engine (U2)

The J57 engine was used on the early U-2 variants before some of the U-2’s were upgraded to J75 engines. It was developed by Pratt & Whitney in the early 1950’s, and was the first 10,000 lbf (pound-force) thrust class engine in the United States. Because the J57 was a twin-spool, axial flow configuration, which was a substantial departure from earlier centrifugal-flow designs, the J57 engine won the prestigious Collier Trophy in 1952. A Collier Trophy is awarded annually to those who have made “the greatest achievement in aeronautics or astronautics in America, with respect to improving the performance, efficiency, and safety of air or space vehicles, the value of which has been thoroughly demonstrated by actual use during the preceding year.”

The military turned to the J57 for its fighter squadrons. In May 1953 it was used on a North American F-100 Super Sabre, when it became the first production aircraft to exceed the speed of sound in level flight, a feat accomplished on its maiden flight. The popular Convair F-102 Delta Dart was the next J57-powered aircraft. The Navy’s Chance Vought F8U-1 used its power to set the first official speed record in excess of 1,000 miles per hour. Other aircraft included Lockheed’s U-2 reconnaissance plane, the prototype of Republic’s F-105 Thunderchief fighter-bomber and Northrop’s Snark intercontinental guided missile.

The early U-2 J57 engine had 10,000 pounds of thrust; at 70,000 feet, only 7 percent of the engine’s sea level thrust could be reproduced. In flight, there was less than a ten knot difference between a speed so fast that it would rip the wings off the aircraft and a speed so slow that it would stall the engine.

From 70,000 feet, the U-2 could glide 300 miles without power. The engine for this aircraft was originally the Pratt and Whitney J57-37, a 10,500 lb. thrust unit built for the B-52. A later 11,500 lbf version, known as the -31, was developed specifically for the U-2s. Pratt and Whitney President Jack Horner and Chief Engineer Wright Parkins crammed a normal three-year engine development program into 12 months. The new engine had a 16-stage compressor with 9 stages in the low range, and 7 in the high pressure chamber.

The low-range compressor was driven by a hollow shaft, and turned at a lower speed than the high compressors. The Pratt and Whitney engine operated at full power for the duration of the flight. At sea level this unit gulped nearly 9,000 pounds of fuel per hour.

At 70,000 feet fuel consumption dropped to 700 pounds per hour. At 74,600 feet, the engine would normally quit from oxygen starvation. In early stages of the program as many as six flameouts occurred on a single flight. With the new fuel system and turbine design of the -31 engine, flameouts at high altitudes have ceased to be a critical problem. An improved ignitions system of a J57-31 ensured air restarts at high altitudes. Eventually, most U-2 were upgraded with J75 Pratt & Whitney engines.

The engine displayed next to the U-2D aircraft at the Blackbird Airpark is a J57-13-B model.

 

Sources: www.cia.gov and www.pw.utc.com/J57_JT3_Engine