Allison T56
turboprop engine family by Allison
The Allison T56 is an American 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 Hercules transport entering production in 1954. It has been a Rolls-Royce product since 1995 when Allison was acquired by Rolls-Royce. The commercial version is designated 501-D. Over 18,000 engines have been produced since 1954, logging over 200 million flying hours.
Design and development
The T56 turboprop, evolved from Allison's previous T38 series, was first flown in the nose of a B-17 test-bed aircraft in 1954. One of the first flight-cleared YT-56 engines was installed in a C-130 nacelle on Lockheed's Super Constellation test aircraft in early 1954. Originally fitted to the Lockheed C-130 Hercules military transport aircraft, the T56 was also installed on the Lockheed P-3 Orion maritime patrol aircraft (MPA), Grumman E-2 Hawkeye airborne early warning (AEW) aircraft, and Grumman C-2 Greyhound carrier onboard delivery (COD) aircraft, as well as civilian airliners such as the Lockheed Electra and the Convair 580.
The T56-A-1 delivered to Lockheed in May, 1953, produced only 3,000 shp (2,237 kW), compared to the required 3,750 shp (2,796 kW) for the YC-130A. Evolution of the T56 has been achieved through increases in pressure ratio and turbine temperature. The T56-A-14 installed on the P-3 Orion has a 4,591 shp (3,424 kW) rating with a pressure ratio of 9.25:1 while the T56-A-427 fitted to the E-2 Hawkeye has a 5,250 shp (3,915 kW) rating and a 12:1 pressure ratio. In addition, the T56 produces approximately 750 lbf (3,336.17 N) residual thrust from its exhaust.
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