Origins

Interest in designs for vertical takeoff and landing, or VTOL, fighter aircraft began in the 1960s at the height of the Cold War when NATO bases were seen as vulnerable to preemptive attacks. Such aircraft, secured in hardened shelters, could still take off and land from bases with damaged runways.

The United States, United Kingdom, Germany, and France all built and tested multiple VTOL fighter designs. However, only the British Kestrel/Harrier family made it into service. Meanwhile, only the Yak-38, which used a similar engine and nozzle arrangement to the Harrier, saw service on the Russian side.

US Navy studies in the 1960s evaluated Sea Control VTOL aircraft designed to operate from ships with smaller decks than from decks on traditional aircraft carriers. These proposed fighters would take off vertically with full loads. The Navy’s concept of operations would also require these aircraft operate as traditional carrier-launched fighters, which necessitated afterburning engines.

This dual operational approach led to larger, heavier aircraft designs that needed more vertical thrust than could be provided by just the primary engine or engines. The most popular solution was to add small lift engines just aft of the cockpit to provide vertical thrust forward of the aircraft center of gravity. These designs were called Lift Plus Lift/Cruise. Allison, Rolls-Royce, and other engine manufacturers developed compact turbojet engines specifically for such applications. Various combinations of numbers and locations of engines were built and flown on several VTOL prototypes and experimental aircraft.

Three-bearing swivel nozzle designs were studied by virtually all of the engine companies in the mid 1960s. The US Patent Office received applications for many variations of the 3BSD from Pratt & Whitney, General Electric, and even from Boeing Military Aircraft of Wichita, Kansas.