Page 30 - Volume 15 Number 4

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28 • KING AIR MAGAZINE
APRIL 2021
It should be mentioned that the first airplane built with PT6A engines, designated as the Model 87 and carrying serial number LG-1, had been undergoing rigorous flight tests at the Wichita, Kansas, factory since May 1963. Throughout the airplane’s nearly 10 months of intensive testing, company engineers gradually worked out the inevitable “bugs” associated with any new design, especially one that represented a major leap in technology involving not only an entirely new type of engine, but also a highly-modified airframe that came with its own set of unique challenges from the pressurization system.
Designated NU-8F by the Army, the airplane was delivered to Fort Rucker, Alabama, in March 1964 when it began an in-depth evaluation by Army pilots, maintenance officers and mechanics. Prompted in part by the service’s success with the L-23F, of which 71 examples were delivered from 1960-1963, the Army brass wanted an opportunity to take a hard, long look at Beech Aircraft’s latest creation and investigate its potential for military service.
Meanwhile, back in Wichita, preparations were underway to begin production of the Model 90 King Air. With a wingspan of 45 feet, 10.5 inches, a length of 35 feet, 6 inches and a height of 14 feet, 2.5 inches to the top of its swept vertical stabilizer, the Model 90 had a maximum gross weight of 9,300 pounds and a fuel capacity of 122 gallons of jet fuel carried in nacelle mounted tanks with another 262 gallons in wing tanks. Three-blade, constant-speed, full-feathering propellers were standard equipment.
By comparison with current pressurization systems that are fully automatic and often digitally-controlled, “set-and-forget” installations, the Model 90 had to make do with a single, mechanical, Roots-type supercharger mounted in the left nacelle that supplied adequate airflow to inflate the passenger compartment. The primary reason for this necessity centered on the PT6A engine that, in its early configuration, did not have sufficient capability to produce rated power and “spare” enough bleed air from the compressor section to pressurize the cabin – a less than desirable situation that was remedied with more powerful versions of the engine. A pressure relief valve was set to vent cabin air overboard if pressurization exceeded 4.0 psid.
In terms of performance, the Model 90 increased cruise speeds to nearly 300 mph and the Beechcraft marketing department lost no time in espousing the many virtues of the King Air. As aviation pioneer Clyde V. Cessna once said, “Speed is the only reason for flying,” and customers were soon selling or trading in their venerable Model 18s or Queen Airs for the ultramodern, 280-mph King Air. The airplane was enthusiastically embraced by every corporation and company that took delivery of the “jetprop” executive transport. Pilots long