The Allison T38 (company Model 501) was an early turboprop engine developed by Allison Engine Company during the late 1940s. The T38 became the basis for the very successful family of Allison T56 turboprop engine.[1]
Developed as a stand-alone single section of the T40 (Model 500) twin engine to aid in development of the T40, the T38 started life with a 19-stage axial compressor, eight can type combustion chambers, a 4-stage turbine driving the compressor and the extension shaft to the reduction gearbox.[2]
Initially rated at 2,000 shp (1,500 kW) the T38 first ran in 1947 and flew in the nose of a Boeing B-17 Flying Fortress test-bed on 19 April 1949, rated at 2,250 shp (1,680 kW). Problems with gearbox vibration and combustion were dealt with during the test program and were mirrored by problems in the Allison T40 programme. The engines fitted to the Convair CV-240-21 Turboliner were rated to 2,750 shp (2,050 kW) equivalent.[2]
In 1951, the United States Air Force decided that the production version of the Beechcraft XT-36 trainer—then in the mockup stage and designed for the Pratt & Whitney R-2800—would be retrofitted with the T38 when the engine entered full-scale production, which was anticipated to occur in 1955–1960. This decision ultimately doomed the aircraft, as the design changes required to accommodate the T38 delayed the project and rendered the aircraft overweight and over budget.[3]
Although the only other aircraft slated to receive the T38 as a production engine, the Convair T-29E, was cancelled, the T38 did power a converted Convair CV-240 (the CV-240-21 Turboliner, a project that would be abandoned due to engine problems), and was fitted in the nose of the McDonnell XF-88B to drive experimental supersonic propellers. Further development of the T38 provided the power sections for the Allison T40 as well as forming the basis for the Allison T56/Model 501 and the projected Allison T39.[2]
^Gunston, Bill (2006). The Development of Jet and Turbine Aero Engines, 4th Edition. Sparkford, Somerset, England, UK: Patrick Stephens, Haynes Publishing. pp. 204–205. ISBN0-7509-4477-3.
^ abcdefghKay, Anthony L. (2007). Turbojet History and Development 1930-1960 vol.2 (1st ed.). Ramsbury: The Crowood Press. pp. 119–121. ISBN978-1-86126-939-3.
Leyes II, Richard A.; William A. Fleming (1999). The History of North American Small Gas Turbine Aircraft Engines. Washington, DC: Smithsonian Institution. ISBN1-56347-332-1.
