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| Allison T38 | |
|---|---|
| Name | Allison T38 |
| Type | Turboprop aero engine |
| Manufacturer | Allison Engine Company |
| First run | 1948 |
| Status | Prototype / limited production |
Allison T38 The Allison T38 was an early American turboprop engine developed by the Allison Engine Company in the late 1940s as part of post‑World War II efforts to adapt gas turbine technology for aircraft propulsion. It served as a testbed and demonstrator that influenced subsequent designs such as the Allison T56 and informed projects undertaken by General Electric, Pratt & Whitney, and Rolls-Royce during the Cold War aviation expansion. Development and trials involved collaborations with organizations including the United States Air Force, United States Navy, National Advisory Committee for Aeronautics, and manufacturers like Convair and Lockheed.
Development of the engine began when the Allison Engine Company expanded its turbine research efforts influenced by advances from Frank Whittle and Hans von Ohain and by programs at the Royal Aircraft Establishment and National Advisory Committee for Aeronautics. The T38 program drew on Allison’s experience with earlier experimental units and paralleled contemporaneous work at General Electric on the J47 and at Pratt & Whitney on the JT3. Initial bench tests were conducted at Allison facilities with technical input from Wright Field, coordination with the Air Materiel Command, and oversight from procurement offices within the United States Army Air Forces transitioning into the United States Air Force. Flight installation trials used airframes converted by airframers such as Convair and Lockheed, reflecting ties to the United States Navy and export interests involving companies like Sikorsky.
The T38 was a free‑turbine turboprop featuring a multi‑stage axial compressor and an annular combustion chamber, followed by a two‑stage power turbine and reduction gearbox to drive a propeller similar to arrangements in later Allison T56 installations. Its design incorporated metallurgy developments pioneered by firms linked to Bendix Corporation and General Dynamics material programs, and it applied turbine cooling techniques comparable to those used in engines like the Rolls-Royce Griffon and Pratt & Whitney R‑2800 piston precedents. Control systems for the T38 referenced early engine management concepts under investigation at NASA and mirrored governors and fuel control philosophies seen in contemporary Bristol Proteus and Napier Eland designs. The engine’s packaging allowed evaluation of propeller‑driven performance regimes relevant to transports such as the Douglas DC‑7 family and military types analogous to the C‑130 Hercules conceptually informed by turboprop research.
Several experimental and development variants of the basic T38 configuration were produced to test different compressor, combustor, and turbine arrangements, mirroring variant proliferation seen in programs like the Rolls-Royce Dart and General Electric TF34. Allison explored changes in gearbox ratios, shaft arrangements, and accessory gearboxes to satisfy requirements from airframers such as Lockheed and Boeing and military end users including the United States Air Force and United States Navy. Design evolution of the T38 directly influenced the series that led to the commercial and military success of the Allison T56, which powered aircraft like the Lockheed C-130 Hercules and spin‑off applications used by contractors including Fairchild and Northrop.
Although the T38 did not enter widespread production, it saw extensive bench testing and flight trials, being fitted to prototype and modified aircraft during evaluations by Wright Field and testing squadrons associated with the Air Proving Ground Command. Trials provided data that fed into procurement assessments at the Air Materiel Command and influenced engine selection for projects undertaken by Douglas Aircraft Company and Lockheed Corporation. The program contributed to standards adopted by agencies such as Civil Aeronautics Administration and later Federal Aviation Administration rulemaking for turbine installations and maintenance procedures, paralleling regulatory evolutions that affected engines like the Rolls-Royce Dart and Pratt & Whitney JT8D.
The T38 was installed primarily as a testbed and demonstrator in modified airframes and ground test rigs; examples of host aircraft for turboprop evaluation in the era included modified types from Convair, Lockheed, Douglas, and prototype transports that would influence designs like the Lockheed Electra and the C‑130 Hercules concept. Its role was analogous to that of engines used experimentally on Boeing prototypes and evaluation platforms employed by NASA and military test agencies, contributing experience later applied to production engines used by operators such as United States Air Force transport commands and civil carriers like Pan American World Airways in the jet and turboprop transition.
Surviving examples of T38 hardware have been preserved in museum and institutional collections associated with aviation history, engine archives maintained by organizations such as the Smithsonian Institution National Air and Space Museum and regional museums that document post‑war propulsion development. Components and display engines have appeared in exhibits alongside artifacts from companies like Allison Engine Company, General Electric, and Pratt & Whitney, and in technical collections curated by universities with ties to Wright-Patterson Air Force Base research archives and restoration groups linked to the Experimental Aircraft Association.
Category:Aircraft engines Category:Allison aircraft engines