Pratt & Whitney J58: Meaning (information, definition, explanation, facts)

The Pratt & Whitney J58 (also known as the JT11D) was the jet engine used on the Lockheed SR-71 "Blackbird".

The J58 was started using a AG330 engine starter cart, which were basically two Buick Wildcat internal combustion engines with a common driveshaft. The cart operators had to get the J58 spinning to 3,200 rpm in order to start.

The J58 produced 32,000 lb_f (142 kN) of thrust. It was the first engine to be able to operate on afterburner for extended periods of time, and the first engine to be flight-qualified by the U.S. Air Force for Mach 3. Another unique feature of the J58 were conical spikes in the variable-geometry inlets, which were automatically moved fore and aft by an Air Inlet Computer. The spike altered the flow of supersonic air, keeping air entering the engine at a subsonic speed. This feature also provided about 80% of the engine's thrust (at Mach 3.2), with the turbine only providing 20%, making the J58 a ramjet at higher speeds. At lower speeds, the J58 operated as a turbojet.

The engine and aircraft operated at such high speeds and temperatures that a new jet fuel formulation had to be invented, JP-7.