Allison T38

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.{{cite book |last=Kay |first=Anthony L. |title=Turbojet History and Development 1930-1960 vol.2 |publisher=The Crowood Press |location=Ramsbury |year=2007 |edition=1st |isbn=978-1-86126-939-3 |pages=119–121 }}

Initially rated at {{convert|2,000|shp|kW|abbr=on}} 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 {{convert|2,250|shp|kW|abbr=on}}. Problems with gearbox vibration and combustion were dealt with during the test program and were mirrored by problems with the T40, which had a pair of T38 power sections feeding a common gearbox. The engines fitted to the Convair CV-240-21 Turboliner were rated to {{cvt|2,750|shp}} equivalent.

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.{{cite report |title=Report on Review of Contracts for T-36A Trainer Aircraft |publisher=General Accounting Office |docket=B-118676 |date=18 October 1955 | ref = {{harvid|GAO|1955}} |url=https://www.gao.gov/assets/b-118676.pdf |access-date=28 July 2021 |pages=10–13}}

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.

;Model 501-B7: commercial version of the T38-A-6

;XT38:prototypes of the engine, single engine section of the T40, to assist in the development of the T40.

;XT38-A-2:{{cite book |last=Wilkinson |first=Paul H. |title=Aircraft engines of the World 1950 |year=1950 |publisher=Sir Isaac Pitman & Sons Ltd. |location=London |edition=11th |pages=50–51}}

;XT38-A-5: Turboprop fitted to the McDonnell XF-88B.

;T38-A-6: Military version of 501-B7

;T38-A-10: {{cvt|1800|shp}} turboshaft version for the Piasecki YH-16A Transporter

;T39 :(Model 504) A projected {{convert|9,000|shp|kW|abbr=on|2}} development of the T38 which was cancelled before hardware had been produced.{{cite web |title=Designations Of U.S. Military Aero Engines: 3 Jet and Turbine Engines, 1946 - 1968 |url=http://www.designation-systems.net/usmilav/engines.html |website=www.designation-systems.net |access-date=5 January 2019}}

;T40: (Model 500) The {{convert|4,100|shp|kW|abbr=on|2}} turboprop origin of the T38,{{cite journal |last1=Nolan |first1=D. J. |title=TURBO-LINER : Development of the Allison T-38 Engine in a Convair 240 |journal=Flight |date=8 August 1952 |volume=LXII |issue=2272 |pages=157–159 |url=https://www.flightglobal.com/pdfarchive/view/1952/1952%20-%202161.html |access-date=5 January 2019 |format=pdf}} composed of two power sections driving a common gearbox.{{cite book |last=Wilkinson |first=Paul H. |title=Aircraft engines of the World 1953 |year=1953 |publisher=Sir Isaac Pitman & Sons Ltd. |location=London |edition=11th |pages=68–69}}

;T44: (Model 503) large turboprop with three T38 engine sections.

;T56: (Model 502) enlarged and improved version of the T38, destined to enter service by the tens of thousands.

• Beechcraft XT-36 (planned for retrofit; project cancelled)
• Boeing B-17 Anudderone test-bed. mounted in the nose with a 3-bladed propeller.
• Convair CV-240-21 Turboliner
• McDonnell XF-88B
• Piasecki YH-16A Transporter

{{jetspecs

|ref=Aircraft engines of the World 1953{{cite book |last=Wilkinson |first=Paul H. |title=Aircraft engines of the World 1953 |year=1953 |publisher=Sir Isaac Pitman & Sons Ltd. |location=London |edition=11th |pages=66–67}}

|type=Turboprop / Turboshaft

|length={{cvt|84|in}} engine section only

|diameter={{cvt|28.1|in}} (gearbox diameter); {{cvt|510|mm|in|order=flip}} engine section diameter

|weight={{cvt|1225|lb}} with extension shaft and gearbox

|compressor=17-stage axial

|combustion=8 tubular inter-connected stainless steel combustion chambers

|turbine=4-stage axial discs of Timken 16-25-4 alloy with special alloy blades

|fueltype=MIL-F-5572 100/130 Octane Gasoline

|oilsystem=Dry sump, gear pump at {{cvt|65|psi|bar}} with scavenge pump; MIL-O-6081A

|power={{cvt|2550|shp}} + {{cvt|415|lbf|kN}} for take-off at 14,300 rpm at sea level ({{cvt|2750|shp}} equivalent)

|thrust=

|compression=6.3:1

|bypass=

|aircon=

|turbinetemp=

|fuelcon=

|specfuelcon= {{cvt|0.63|lb/hph|kg/kWh}} (equivalent shp)

|power/weight={{cvt|2.273|hp/lb|kW/kg}}

}}

{{Aircontent

|related=

• Allison T40
• Allison T56

|similar engines=

|lists=

• List of aircraft engines

|see also=

}}

{{Reflist}}

• {{cite book|last= Leyes II |first= Richard A. |author2=William A. Fleming |title= The History of North American Small Gas Turbine Aircraft Engines |publisher= Smithsonian Institution |location= Washington, DC |date= 1999 |isbn= 1-56347-332-1 }}

{{Allison aeroengines}}

{{USAF gas turbine engines}}

T38

Category:1950s turboshaft engines