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T56 / Model 501
Allison T56 turboprop for C-130 2007.JPEG

The Allison T56 is a single shaft, modular design military turboprop with a 14-stage axial flow compressor driven by a four-stage turbine. It was originally developed by the Allison Engine Company for the Lockheed C-130 transport[1] entering production in 1954. It is now produced under Rolls-Royce which acquired Allison in 1995. The commercial version is designated 501-D. With an unusually long and numerous production run, over 18,000 engines have been produced since 1954, logging over 200 million flying hours.[2]

Design and developmentEdit

Allison T56-A1 Turboprop Engine Cutaway

Allison T56-A1 turboprop engine cutaway, at the Smithsonian National Air and Space Museum

The T56 turboshaft evolved from Allison's previous T38 series.[3] It was first flown in the nose of a B-17 test-bed aircraft in 1954.[3] Originally fitted to the Lockheed C-130 Hercules, the T56 was also installed on the P-3 and E-2/C-2 aircraft, as well as civilian airliners such as the Lockheed Electra and Convair 580.[3] T56 development almost ended before it began when the T56-A-1 engine Allison delivered to Lockheed in May, 1953 produced only 3,000 hp, not the required 3,750 shp needed for the C-130. Further setbacks occurred in August 1953 when the engine under test only ran for 6 ½ hours before exploding on the test stand. A re-design of the engine ended in the same fate in September of the same year. After a second re-design, success was realized by the Allison team. Evolution of the T56 has been achieved through increase of internal pressure and temperature factors. The T56-A-14 installed on the P-3 Orion has a 4591 shp rating with a compression ratio of 9.25:1 while the T56-A-427 fitted to the E-2 Hawkeye has a 5250 shp rating and a 12:1 compression. In addition, the T56 produces approximately 750 lbs of thrust from its exhaust.[4]

A shipboard version, the 501K engine, is used to generate electrical power for all U.S. Navy cruisers and destroyers currently in commission.[2]

An engine enhancement program saving fuel and providing lower temperatures in the T56 engine was approved in 2013, and the US Air Force expects to save $2 billion and extend the C-130 fleet life.[5]

In the Lockheed Martin C-130J Super Hercules which first flew in 1996, the T56 is replaced by the Rolls-Royce AE 2100, which uses dual FADECs (Full Authority Digital Engine Control) to control the engines and propellers.[6] It drives new six-bladed scimitar propellers from Dowty Rotol.


(Series I) Lockheed L-188 Electra and Convair CV-580 (Replacing P&W R-2800) starting December 1957
(Series I) Similar to -D13
(Series I) Similar to -D13
(Series I) Similar to -D13
(Series II) Lockheed L-100 Hercules
(Series II) (non-type certified)
(Series III)
(Series III) similar to -D22A
(Series III) similar to -D22A
Company designation for the T701-AD-700 turboshaft engine to power the Boeing-Vertol XCH-62 Heavy-lift helicopter
Allison T56 mobile test unit MCAS Futenma 1982

A T56 on a mobile test unit at MCAS Futenma, 1982

US Navy 081219-N-5142K-048 Bob Maiuvo works alongside Aviation Machinist Mate 2nd Class Tim Triest and Aviation Machinist Mate 2nd Class Marquette Beasley

Maintenance of a T56-A-16, 2009

(Series I)
(Series I)
(Series I)
(Series I) Lockheed C-130A Hercules Starting December 1956 and on all Grumman E-2A Hawkeyes from 1960
(Series I) Similar to -A-9D
(Series I) with water injection
(Series II) Lockheed C-130B Hercules Starting May 1959
(Series II) Similar to -A-7A
(Series II)
(Series III) Lockheed/Kawasaki P-3/EP-3/WP-3/AP-3/CP-140 Aurora from August 1962
(Series III) Lockheed C-130H Hercules from June 1974
(Series III)
(Series III) Grumman C-2A Greyhound from June 1974
(Series 3.5) Fuel efficiency and reliability upgrade, Lockheed WP-3D Orion from May 2015.
(Series 3.5)
(Series 3.5)
(Series 3.5) Northrop Grumman E-2 Hawkeye from August 2011
(Series IV) Northrop Grumman E-2 Hawkeye upgrades from 1972
(Series IV) similar to the -A-427
(501-M62) Turbo-shaft engine for the Boeing-Vertol XCH-62 Heavy-lift helicopter.




Specifications (T56 Series IV)Edit

Data from Rolls-Royce.[7]

General characteristics
  • Type: Turboprop
  • Length: 146.1 in (3,711 mm)
  • Diameter: 27 in (690 mm)
  • Dry weight: 1,940 lb (880 kg)
  • Compressor: 14 stage axial flow
  • Combustors: 6 cylindrical flow-through
  • Turbine: 4 stage
  • Fuel type: JP8
  • Maximum power output: 4,350 shp (3,915 kW) limited to 4,100
  • Turbine inlet temperature: 860°C
  • Fuel consumption: 2,412 pounds per hour
  • Power-to-weight ratio: 2.75:1 (shp/lb)

See alsoEdit


  1. Global Security T56
  2. 2.0 2.1 "Rolls Royce T56 Product Sheet".  Retrieved on 1 November 2012.
  3. 3.0 3.1 3.2 "Global Security". Retrieved on 1 November 2012.
  4. "The Rolls-Royce Allison T56 is fifty". New Zealand Aviation News, September, 2004.  Retrieved on 2 November 2013
  5. "NOAA 'Hurricane Hunters' First To Get T56 Series 3.5 Engine Enhancement" Aero News, November 14, 2013. Accessed: December 1, 2013.
  6. "Rolls Royce AE-2100 Product Sheet".  Retrieved on 1 November 2012.
  7. Rolls, Royce . Training Manual . T56/501D Series III. Rolls-Royce, 2003. 8-1 To 8-24. Print.

External linksEdit

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