Allison T56

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 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. It has logged over 200 million flying hours.

The engine evolved from Allison’s previous T38 series. It was first flown in the nose of a B-17 test-bed aircraft in 1954. Originally fitted to the Lockheed C-130 Hercules, the T56 is 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. A shipboard version, the 501K engine, is used to generate electrical power for some destroyer-class ships in the U.S. Navy.

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 2412 pounds per hour
  • Oil system: 2 systems (1 each for power section and reduction gearbox)


  • Maximum power output: 4,350 shp (3,915 kW) limited to 4,100
  • Overall pressure ratio: 14.5:1
  • Turbine inlet temperature: 860 c
  • Power-to-weight ratio: 2.75:1 (shp/lb)