Page 22 - May 2015 Volume 9, Number 5

Pratt & Whitney Canada
and the PT6
PART ONE
The revolutionary PT6 gas turbine engine nearly died during development, yet managed to survive its detractors, cost overruns and a dearth of orders to become one of the most successful turboprop engines in the history of business aviation.
by Edward H. Phillips
Old pilots and antique airplane enthusiasts never tire of watching a “round engine” start up, belch a few clouds of smoke, spit out a momentary flash of flame, and then settle into a loping idle whose unique sound cannot be matched by any other piston powerplant. That type of engine (to be technically correct, the static, air-cooled radial engine as opposed to the dynamic radial or rotary), ruled the skies over America from the late 1920s until the early 1960s.
The nearly simultaneous development of gas turbine powerplants by Sir Frank Whittle in England and Hans von Ohain in Germany before the outbreak of World War II, eventually resulted in the introduction of jet- powered fighters such as the Messerschmitt Me-262 and Gloster Meteor (the only Allied jet fighter to enter operational service in the war). By the late 1940s, the jet engine was the way of the future for the military, and to a lesser degree, the commercial aircraft industry.
It was, however, a different story for the postwar business aviation market in the United States, where the reciprocating piston powerplant (in both radial
and opposed cylinder configurations) still reigned supreme. Beech Aircraft Corporation, which had staked its reputation on all-metal monoplanes powered by various static radial engines, developed an array of new airframe designs well into the 1950s that continued to rely on piston engines. During that time, however, the Wichita, Kansas-based company did briefly market the French-built, turbojet-powered MS760 business jet, but it was ahead of its time and the program was eventually terminated.
A chief obstacle to the introduction of early turbine engines into the business aviation segment was three- fold: The powerplants were expensive to manufacture, expensive to operate and expensive to maintain and repair. The military and airlines had the money to deal with these issues, but the general aviation industry did not.
Beginning in 1932, Beechcraft airplanes featured static, air-cooled radial engines such as the Pratt & Whitney R-985 that powered the postwar Model G17S. The nine-cylinder powerplant was rated at 450 horsepower. The reciprocating piston engine had dominated the business aviation segment for more than 40 years, but by 1960 the tide was turning in favor of new, gas turbine technology. (TEXTRON AVIATION)
20 • KING AIR MAGAZINE
MAY 2015