Page 26 - May 2015 Volume 9, Number 5

24 • KING AIR MAGAZINE
Left-side view of the first PT6 to be tested in flight, as installed on a Beechcraft C45 borrowed from the Royal Canadian Air Force. The conversion was accomplished by De Havilland Canada.
(DE HAVILLAND CANADA, PRATT & WHITNEY CANADA)
northern Quebec province where the OAT had plunged to a frigid -21 degrees Fahrenheit.
Although the winter at Knob Lake promised to provide temperatures below -45 degrees Fahrenheit, that phase of the program was cut short when the C-45 was dispatched by PWC to the United States. The purpose of the diversion was to demonstrate the airplane and its PT6 to the military as a potential airborne counter-insurgency platform. MacNeil and flight test engineer John Hunt flew 45 hours of demonstration flights. One concern expressed by customers was whether the free-turbine design of the engine would provide adequate drag during steep descents to landing. Demonstrations allayed any concerns customers had, but MacNeil reported to PWC that he was not satisfied with a brief hesitation that persisted when propeller reversing was selected. 6
Investigation revealed the problem – the propeller reduction
gearbox (RGB) was overheating and close to seizing entirely. Another RGB was sent from Canada, but again the same problem surfaced. Finally, disassembly and close examination of the unit showed that during reverse operation, when the gas generator was turning at a low RPM, the reversing system was demanding more oil than the engine’s lubrication pumps could provide. The problem was resolved by increasing the size of the pumps, relocating their position on the engine case, and installing a diverter valve.
Despite successful engine devel- opment and flight test programs, by early 1963 the future of the PT6 was still uncertain. The key issue was millions of dollars that had been spent to bring the engine to fruition, coupled with zero orders from any major airframe manufacturer. In addition, the competition was heat- ing up. Garrett Air Research had a small gas turbine, dubbed the TPE 335, under development that packed
MAY 2015