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The next challenge was the empennage. Throughout the design process, the engineering team had made every effort to reduce drag, and a V-tail arrangement was favored over the conventional configuration. The reason for that choice centered not only on drag reduction and weight (two surfaces instead of three), but also because a V-tail could be located higher on the fuselage to avoid turbulent airflow coming off the wing. As early as 1943, the company had conducted wind tunnel tests of a V-tail and in 1944 installed an experimental assembly on a Model 26, AT-10 multi-engine trainer. The assembly featured a dihedral of 40 degrees and flight tests indicated that the V-tail was a promising design alternative.
Ralph Harmon and Jerry Gordon successfully campaigned for adoption of that configuration for the new monoplane, but the dihedral was reduced to 30 degrees. Extensive wind tunnel tests of a 1/5-scale model of the airplane showed that the V-tail was equal to a conventional empennage in terms of controllability, but produced less drag.
Throughout 1945 the team made slow but important progress, including an exhaustive stress analysis and fatigue testing program using two prototype airframes. These Beechcrafts would never take to the sky, yet they “flew” for a simulated 20,000 hours to prove the airplane’s robust airframe design and to ensure that no
fatigue failures would occur during the certification flight test program. It is important to note that the fatigue tests were performed in addition to the normal static and fatigue tests mandated by the government’s Civil Aviation Authority.
By late 1945, Beech Aircraft Corporation’s ongoing effort to design and manufacture the most advanced four-place airplane in the world was nearing fruition. Five pre-production airplanes were built (including two for static/fatigue tests). One featured a laminar flow wing and was powered by Lycoming’s engine, and another was built with the NACA 23000 airfoil section and the Continental engine. Veteran Beechcraft test pilot Vern Carstens was chosen to fly the Lycoming-powered Beechcraft on its maiden flight. After performing thorough ground-based tests of the engine, fuel system, flight control rigging and subsystems, a series of taxi runs were completed on the factory’s paved runway that was oriented north- south in accordance with prevailing winds.
Those tests went smoothly, and on December 22, 1945, Carstens took the airplane aloft for a 40-minute evaluation. He found the airplane was about 10 mph faster than calculations had predicted, with a cruise speed of 175 mph. He cautiously probed the airplane’s low-speed flight characteristics with flaps and landing gear extended and retracted, investigated control response in pitch, roll and yaw, as well as determining
OCTOBER 2015
KING AIR MAGAZINE • 25