The late 1950s and early 1960s witnessed a major change of power plant technology for the expanding and lucrative business aviation market in the United States. During the years following the end of World War II, the static-air-cooled radial engine ruled the skies, powering four-engine airliners built by Boeing, Douglas, Martin as well as small general aviation airplanes such as the ubiquitous twin-engine Beechcraft Model D18S – the first commercial airplane to receive an Approved Type Certificate after the war.
Throughout the 1950s Beech Aircraft Corporation designed and built a series of twin-engine aircraft to meet increasing demand for more cabin volume, comfort and speed. These included the venerable Model E18S, G18S and the H18 Model 50 Twin Bonanza that first flew in November 1949, followed nine years later by the Model 65 Queen Air that flew in August 1958. All of these Beechcrafts were powered by radial or opposed piston engines of 450-340 horsepower. It was the Model 65 Queen Air, however, that represented the future course the company would take in developing more advanced business aircraft.
During the early 1960s a series of improved Queen Air airframes evolved as the A65, 65-80/B80, 65-A80 and the Model 70 that was developed strictly as a commuter aircraft and designated the “Queen Airliner.” Meanwhile, in Europe the French and British were manufacturing gas turbine engines designed to replace aging reciprocating power plants, particularly large displacement radial and inline engines, that had reached the zenith of their development. In addition, the Allison Division of General Motors was developing a gas turbine engine in the 250 shaft horsepower (shp) class.
As early as 1956 Pratt & Whitney Canada began design and development of a gas turbine engine that was compact, lightweight and powerful that could be adopted by general aviation airframe manufacturers in the United States such as Beech Aircraft, Cessna Aircraft and Piper Aircraft companies. Of these, PWC officials eventually focused their marketing efforts on Wichita, Kansas-based, Beech Aircraft Corporation. Early in 1963 a pair of PWC PT6A-6 gas turbines were installed on a Queen Air airframe designated the Model 87, and the airplane began test flights in May of that year before being delivered to the U.S. Army at Fort Rucker, Alabama, for extensive service testing as the NU-8F.
In 1961 Beech Aircraft had conceived the Model 120 – a 300-mph executive transport, and after agreeing to use PT6A-6 engines from PWC, was formally announced as the Model 90 King Air in July 1963. The basic Model 65 airframe was modified to accept pressurization that was provided by a Roots-type supercharger mounted in the left engine nacelle. Pressurization was limited to 3.4 pounds per square inch (psid) with a pressure relief valve set to open at 4.0 psid to prevent over-pressurization of the cabin.
The prototype King Air 65-90 first flew on January 24, 1964, under the command of company engineering test pilot, James D. Webber. More than 3,000 people witnessed the milestone event. The Model 90 featured a wingspan of 45 feet 10 inches, length of 35 feet six inches and stood 14 feet 2.5 inches high at the tip of its swept vertical stabilizer. The two PT6A-6 engines each produced 550 shp and 1,192 pound-feet of torque, and were mated to three-blade, constant-speed, full-feathering propellers (without reversing capability). Maximum speed was 280 mph – more than 50 mph faster than a piston-powered Queen Air.
The King Air sold for $320,000, and by June 1964 the company held orders worth $12 million. United Aircraft of Canada, Ltd., was the first corporate customer to take delivery of the new Beechcraft.