From Scramble - The Aviation Magazine
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 C-130 Hercules 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. The engine evolved from Allison's previous T-38 series. It was first flown in the nose of a Boeing B-17 test-bed aircraft in 1954.
Series I include models 501-D13,A, D, and H.
Series II include models 501-D22 and 501-D36A (non-type certified).
Series III include models 501-D22A, C, and G. Rated at 3,424 kW.
A fuel efficient and reliable upgrade to the Series III. Proposed military designations are T56-A-14+, T56-A-15+ and T56-A-16+. First flown September 2012. In 2015 a WP-3D validated the engine's performance, demonstrating fuel savings up to 12%.
Model rated at 3,915 kW, supplied as T56-A-427 and T56-A-427A.
Model studied by the US Navy for helicopter purposes. Not built.
Experimental version, designated YT56-A-3, also tested in the YC-131C Samaritan.
Developed for the YH-16B helicopter.
Model for the E-2A Hawkeye, produced or upgraded in -8, -8A and -8B model.
Series I production model for the C-130A Hercules, powering three-bladed propellers.
Series II model for the P-3A Orion, fitted with water-methanol injection system to improve engine performance during take-off. Existing -10W models could be upgraded to T56-A-14.
The T56-A-11 engine is a T56-A-9 power section which has been modified to operate with kerosene fuel. The T56-A-11 engine uses the same gearbox as the T56-A-7 engine. The weight of the -11 engine is approximately 100 pounds greater than the -9 and has the Aeroproducts Model A6341FN-D1A, 3 bladed propeller.
Series III model for the P-3B/C Orion, lacking the water methanol injection system. Rated at 3,661 kW. In 2012, Rolls-Royce announced the T56-A-14+ conversion kit (commercial designation Series III.V), providing eight percent fuel savings over the existing model.
Series III model for the C-130H Hercules and several C-130 re-engine programs. Rated at 3,210 kW. In 2012, Rolls-Royce announced the T56-A-15+ conversion kit (commercial designation Series III.V), providing eight percent fuel savings over the existing model.
Series III model for the AC-130U Spooky, MC-130H Talon II, MC-130W Combat Spear and KC-130R/T Hercules. In 2012, Rolls-Royce announced the T56-A-16+ conversion kit (commercial designation Series III.V), providing eight percent fuel savings over the existing model.
Series III model for the E-2C Group 0 Hawkeye.