Page 25 - May 2015 Volume 9, Number 5

By 1961, the engine was ready for flight testing. The first aircraft to fly solely under PT6 power was not an airplane but a helicopter, specifically the Hiller Ten99 that flew in July of that year. Meanwhile, back in Longueuil, PWC began searching for a twin-engine, flight test airplane that would be suitable for the PT6. The venerable Douglas DC-3 topped the list of potential candidates, but installing the powerplant in the nose section would require extensive structural modifications and the attendant stress analysis could prove difficult and expensive. The DC-3 was off the list.
Fortunately, PWC was able to obtain a Beechcraft C-45 “Expeditor” on loan from the Royal Canadian Air Force. The C-45 was flown to Downsview, Ontario, where de Havilland aircraft engineers and mechanics completed an extensive conversion of the nose section to accept installation of a pre-production prototype engine, which weighed only 270 pounds. Ground testing of the installation began early in 1961 and continued until May 30, when de Havilland test pilot Bob Fowler and PWC pilot John MacNeil took the C-45 aloft for its maiden flight. Although the Beechcraft flew well, it did exhibit minor instability that was solved by installing 23 pounds of ballast in the cabin.
After initial handling qualities and systems checks were deemed satisfactory, a rigorous test program began that focused on specific fuel consumption, propeller constant- speed operation and feathering; air starts along with noise and vibration surveys. During one flight, MacNeil climbed the C-45 up to 26,000 feet, much to the surprise of air traffic controllers unaccustomed to tracking a small, piston-powered airplane at that lofty altitude.
MacNeil later recalled that the modified C-45 was not the most pleasant airplane to fly. According to a report he filed in September 1961, the Expeditor “...is very unstable longitudinally, particularly at higher altitudes. It also has a rolling tendency about the longitudinal axis when high [power settings] are selected on all three engines...Care must exercised at all times to be mindful of its shortcomings.” MacNeil went on to state that he was “pleased with our engine operation,” and that “it starts quickly, both in the air and on the ground, and makes its thrust very obvious from the surface to 25,000 feet.”
One phase of the flight testing involved applying reverse thrust in flight, which MacNeil described as being “quite interesting” because the airplane “is rather unstable in that configuration and “suffers from elevator buffet.” Eventually, applying reverse thrust in flight was discontinued because of concerns about elevator buffeting and the potential for flutter of the control surfaces. Another important aspect of the test program was cold weather operation, and the icy winter of 1963 afforded PWC an excellent opportunity to test the PT6 under severe conditions. The airplane was flown from Montreal, where the OAT was +38 degrees Fahrenheit, to Knob Lake in
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