The union of Pratt & Whitney Canada’s revolutionary PT6 turboprop engine with a pressurized Beechcraft airframe proved an unbeatable combination that set a new standard for small, cabin-class business aircraft.
As World War II drew to a close, the introduction of turbojet-powered military fighters did not escape the notice of Walter H. Beech. Speed was in his blood, and to an aviation pioneer like Beech, the quest for more speed was a never-ending odyssey. After his death in 1950, it fell to his wife and company co-founder, Olive Ann, to take the greatest gamble in Beech Aircraft’s 31-year history.
Beginning in 1958, Pratt & Whitney Canada (PWC) officials consulted with Beech Aircraft Corporation in an attempt to determine the size and configuration of a small gas turbine engine. The Kansas-based company was studying concepts for a new, turbine-powered business airplane and had unveiled its latest design at the National Business Aircraft Association convention in 1961. To the shock and dismay of PWC representatives who saw the design, it was displayed with French Turbomeca Astazou turboprop engines on the wings.
The reason was simple: the PT6 was not even included in Beech Aircraft’s shortlist of potential engines. Instead, in May 1961, company executives attended the 24th International Air Salon in Paris to see the latest in aerospace products. While in France they met with officials of the Societe Francaise d’Entretien et de Reparation de Materiel Aeronautique (SFERMA), with whom the company had previously signed a technical agreement aimed at co-development of turboprop engines. Beech officials proposed installing SFERMA’s Turbomeca Astazou gas turbines in the twin-engine Baron and Travel Air, and the more powerful Turbomeca Bastan in the venerable Model 18.
It is important to note that large turboprop-powered business aircraft, particularly the Gulfstream I equipped with Rolls-Royce Dart engines, already were in service and proving popular with corporate flight departments. What was missing, however, was a small, cabin-class, turbine-powered business airplane. In December 1961, Frank E. Hedrick, executive vice president of Beech Aircraft Corporation, unveiled a wind tunnel model of a turboprop-powered, 300-mph executive transport that was currently under engineering study. If it was placed into production, the new Beechcraft fit into the product line above the Model 18, but would sell for a price well below that of a Gulfstream I.
One year later, Beechcraft salesmen viewed a full-scale mockup of the proposed transport, now designated as the Model 120. Marketing officials listened and carefully recorded every word the dealers and distributors spoke, realizing that there was no one better qualified to render judgment on the mockup than the men who would sell and support the airplane in the field. The airplane would be powered by Turbomeca Astazou engines, although PWC was still pleading its case for Beech to at least consider the Canadian engine. 1
“The first lady of aviation had a great deal to do with the success of the PT6,” said J.C. “Jack” Charleston, a former PWC employee, during a speech before the Canadian Aviation Historical Society. According to Charleson, “Mrs. Beech was behind it all, this very sensible marriage of a Canadian engine to an American airframe.” What Charleson meant by “behind it all” centered on her comments during a meeting in 1961 between Beech Aircraft engineers and PWC president Thor Stephenson, who was in Wichita to once again pitch the PT6 as a potential engine for a new Beechcraft executive transport. The engineers, however, objected to the PT6 claiming its high cost ($15,000) would make the airplane’s price prohibitive.
Suddenly, Olive Ann rose from her seat and is reported to have proclaimed, “Listen, I don’t normally interfere with engineering or management decisions, but I still control this outfit. I’m telling you to take those engines, which are costing us nothing, and put them in the airframe. Just try it.” The airframe she referred to was the Model 67 “Queen Air,” then the company’s flagship product. When the boss spoke, people listened.2
Fortunately for Olive Ann Beech and the company she commanded, the timing of her directive could not have been better. The U.S. Army had recently placed a follow-on order for more Lycoming-powered Beechcraft Model 65 Queen Airs, designated L-23F. Engineering vice president James Lew and PWC president Thor Stephenson worked together and promoted the turbine-powered L-23F to Army brass, explaining that the two company’s would retrofit a commercial Queen Air with PT6 engines at no cost to the service. In addition, a 100-hour flight test program would be part of the proposed package. The Army agreed to the plan.
A Model 87 Queen Air, serial number LG-1, was selected and the conversion process began. The six-cylinder, 340-horspower Lycoming IGSO-480 engines were removed and structural changes were made to accommodate the PT6A-6 engines. The cabin remained unpressurized, the empennage was redesigned and fuel capacity was increased. In May 1963, the modified Beechcraft had been designated the NU-8F and was undergoing ground tests at the Wichita factory. After completing its first flight, the NU-8F entered a test program that lasted 10 months.
In the wake of success with the NU-8F program, PWC had finally convinced Beech Aircraft officials to use the PT6 on its next business airplane. By 1963, it was time for a decision – build the Model 120 along with another proposed design, the piston-powered but pressurized Model 85D Queen Air; postpone a decision or maintain the status quo. As William H. McDaniel writes in his history of the company, Beechcraft – 50 Years of Excellence, “a top-level decision of great importance was ready to be made. It was the kind of decision that emphasized the loneliness of command.” 3
Finally, on August 14, 1963, Beech officials announced availability of the new Model 65-90 “King Air” with deliveries beginning in the autumn of 1964. Boasting a cruise speed of 270 mph, a pressurized, well-appointed cabin and the ability to operate into and out of small airports, the King Air was the right airplane for the company’s next-generation executive transport.
The timing, too, was good. By the mid-1960s companies were beginning to buy increasing numbers of first generation business jets such as the Learjet 24 and North American Sabreliner. The King Air benefitted from their success that helped build demand for a small business turboprop.
Beech Aircraft officials, however, were still concerned whether customers accustomed to the age of the radial engine and the Model 18 would place an order for the sophisticated King Air. Opting to proceed with caution, the company ordered 29 PT6A-6 engines from PWC. That number was thought to be sufficient based on a market survey projecting demand for only 10 airplanes annually. Each of those engines, however, cost Beech Aircraft a whopping $25,000. According to PWC, it cost the Canadian manufacturer $21,000 in parts from vendors. A decision was made to quip the factory in Longueuil to manufacture the high-cost items such as gas generator and exhaust cases, turbine wheels, compressor discs, impellers and gears.
Meanwhile, in Wichita, the engineering department was busy preparing the King Air for FAA Type Certification and production. John Wilson was one of the engineers assigned to the program. He recalled that in 1963 his knowledge of turbine engines was nearly nonexistent.
“At Beech we took a “tinker toy” approach to new aircraft. With the Queen Air we mated a [Model 50] Twin Bonanza wing center section, wings and empennage to a larger cabin. Next, we took the PT6 installation that worked so well on the NU-8F and adapted it to a new pressurized fuselage.” 4
The prototype Model 90 made its first flight on January 20, 1964, at the factory. More than 3,000 spectators were on hand to witness the flight, which included a high-speed pass in front of the crowd. The airplane’s two PT6A-6 engines each produced 550 shp for takeoff and 500 shp for continuous operation, along with 1,192 pound-feet of torque. It had three-blade, constant-speed, full-feathering propellers, but did not feature a reversing system. A single Roost-type supercharger mounted in the left wing nacelle provided pressurization of the cabin (the PT6A-6 powerplant lacked sufficient bleed air for pressurization). Cabin pressure was limited to 3.4 pounds per square inch differential (psid) with an overpressure limit of 4.0 psid.
In terms of size, the Model 90 was similar to the Model 65-A80 with a wingspan of 45 feet, 10.5 inches, a height at the tip of the vertical stabilizer of 14 feet 2.5 inches, and a fuselage length of 35 feet six inches. Fuel capacity included 262 gallons in the wing tanks and another 122 gallons in nacelle tanks. Maximum gross weight was 9,300 pounds.
The successful first flight kicked off an intensive certification program that included five aircraft and resulted in the FAA issuing Type Certificate 3A20 on May 19, 1964. In June, the company set a retail price for a standard Model 90 of $320,000. By that time the company was holding orders worth $12 million, and executive vice president Frank Hedrick prophesied that sales of the King Air would climb to $22 million by the end of 1965. The first delivery of a King Air to a corporate operator occurred on July 7, when officials of United Aircraft of Canada, Ltd., accepted the keys from Olive Ann Beech. In September, the sixth Model 90 built was delivered to Atlantic Aviation Corporation’s New York Division, based at Teterboro, N.J.
When the National Business Aircraft Association convention began in November 1964, eight King Airs were already in service, and the fourth airplane built was busy in Europe conducting demonstration flights. The tour resulted in sales of 27 King Airs, including orders from Volkswagen, Daimler-Benz and the Aga Khan.
As the King Air matured in the next few years, Beech engineers implemented a series of improvements to the airframe and PWC upgraded the PT6 to keep pace with those changes. After manufacturing 122 Model 90s from 1964-1966, Beech Aircraft introduced the A90 powered by PT6A-20 engines rated at 550 shp for takeoff. In addition, the pressurization system’s maximum differential increased to 4.0 psid, providing a sea-level cabin altitude at a flight altitude of 10,000 feet and an 8,000-foot cabin at 21,000 feet. In addition, the A90 was first to be equipped with reversible propellers that reduced landing rollout and wear on brakes while taxiing. The B90 followed in 1968 and led to introduction of the C90 in 1971.
The C90 was the first major upgrade to the King Air product line. Wingspan was increased to 50 feet, three inches, and PT6A-20A engines were installed that retained the B90’s 550 shp for takeoff. Maximum gross weight rose to 9,650 pounds. Maximum cruising speed was 253 mph, and the C90 could climb to a service ceiling of 26,600 feet. A total of 507 C90s were built from 1971 until 1982 when the C90-1 entered production. The latest version of the King Air boasted a maximum differential of 5.0 psid, PT6A-21 engines, 384 gallons of useable fuel, and a maximum cruising speed of 273 mph.
Always seeking to expand the product line in an effort to appeal to a wider range of customers, in 1972 Beech Aircraft offered the Model E90 that featured 680-shp PT6A-28 engines flat-rated to 550 shp. Production of the E90 totaled 347 airplanes, with the last example built in 1981. The last Model 90 to go on sale was the F90, of which 202 were built from 1979 to 1983. Featuring a T-tail empennage similar to that installed on the flagship Model 200 Super King Air, the F90 was powered by PT6A-135 engines each developing 750 shp. Cruising speed increased to 307 mph, and four-blade propellers were installed to reduce noise in the cabin.
The F90 was the first Beechcraft to use the new multi-bus electrical system that provided automatic load shedding, five separate buses and solid-state current sensors of ground fault protection and bus isolation. In 1983, the F90-1 was introduced. It was an improved F90 featuring PT6A-135A engines installed in new pitot-type cowlings that improved air intake characteristics. Only 33 airplanes were built from 1983 to 1985. The benchmark Model 65-90 led to development of a complete line of King Air models that are still evolving more than 50 years later with no end in sight.
The great gamble taken by PWC in 1958, coupled with a key decision by Olive Ann Beech in 1961 to mate PT6A-6 engines to a Beechcraft airframe, created an icon of business aviation. As of early 2015, more than 7,300 King Airs of all types, including commercial and military versions, have been built, and total fleet flying time has surpassed 60 million flight hours.5 Fifty-two years after PWC shipped the first PT6 engine to Beech Aircraft Corporation, more than 54,000 versions of the powerplant are operating around the globe and have exceeded 400 million flight hours.
Notes:
1. McDaniel, William H.; “Beechcraft – Fifty Years of
Excellence;” McCormick-Armstrong Co., Inc., Publishing Division, Wichita, Kansas; Copyright, Beech Aircraft Corporation, 1982.
2. Parmerter, Robert K.: “Beech 18 – A Civil and Military History.” Published by the Staggerwing Museum Foundation, for the Twin Beech Society, 2004. J.C. Charleson was a long-time friend of Walter and Olive Ann Beech, and was familiar with the ongoing discussions between Beech Aircraft Corporation and PWC that resulted in the NU-8F and later the Model 65-90 program.
Beech Aircraft delivered the NU-8F to the Army Aviation Test Board, Fort Rucker, Alabama, on March 12, 1964, where it underwent six months of testing. After being retired from flying the NU-8F served as a maintenance training aid for mechanics at Fort Eustis, Virginia, until it was placed on static display at the Army Aviation Museum at Fort Rucker.
3. Sullivan, Kenneth H. and Milberry, Larry: “Power: The Pratt & Whitney Canada Story,” Volume 1; Pratt & Whitney Corporation, 1989, 2013.
4. The pressurized fuselage had been developed in 1962 for the Model 85 Queen Air that became the Model 85D in 1963 and, in 1965, to introduction of the Model 88. Only four were built in 1965 followed by another 36 in 1966. Beech officials soon realized that there was no business case for continuing production of the Model 88 because of increasing demand for the King Air. Plans for an upgraded version, the Model A88, were cancelled and the last Model 88 was built in 1969.
5. Textron Aviation
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