Originally, the aircraft was an upgraded version of the Pressurized Navajo equipped with two Pratt & Whitney Canada PT6A-28 turboprop engines. Later, the aircraft was further refined and developed, including aerodynamic improvements and fuselage extensions. The PA-31T led to the development of the PA-42 Cheyenne III and IV. The Piper Cheyenne prototype first flew in 1969. Designated the PA-31T-620, it was essentially a turboprop evolution of the Piper PA-31 Navajo, powered by two Pratt & Whitney Canada PT6A-28 turboprops rated at 620 hp (460 kW) each. Certification was granted on 3 May 1972. The original Cheyenne, produced from 1974 to 1977, did not carry a Roman numeral suffix designation. Because of difficulties complying with certification standards for longitudinal stability, the Cheyenne and later Cheyenne II are equipped with a Stability Augmentation System (SAS), consisting of a stick-pusher system (actuated by an angle-of-attack sensor) designed to provide the pilot with the appropriate stick force gradient – and to keep the airplane at its trim airspeed when flying near aft center of gravity loadings, high power settings, low airspeeds and high angles of attack. Without the SAS, the aircraft demonstrated neutral static stability in its flight regime. Later in 1978, it was redesignated as the Cheyenne II (PA-31T-2-620), due to the production of the PA-31T-1-500. For more information on the development of these aicraft, and the specifications for each model, click hee for the PA-31T, and here for the PA-42. The specifications below are for the PA-42 model. PA-31T PA-42
