Rolls-Royce T406

On 24 December 1985, the United States Navy selected Allison's engine for full-scale engine development and production on the U.S. Marine Corps's V-22 Osprey.[3] The Navy and Allison signed a formal contract on 2 May 1986, and the first engine to test ran six months after.[4]

The T406 is based on the Allison T56 turboprop from the P-3 and the C-130, with the free power turbine of the Allison T701 turboshaft from the defunct Heavy Lift Helicopter program. It was selected over the Pratt & Whitney PW3000 and General Electric GE27 competing for the US Army's Modern Technology Demonstrator Engine program.[5] The T406, which was originally known as the Model 501-M80C,[6] began flight testing on 19 March 1989.[7]

The T406/AE 1107C Liberty shares a common core with the AE 3007 turbofan and AE 2100 turboprop series of engines, both of which have sold in the thousands of copies.[8][9] 44-46 percent of parts are common between the T406 and the AE 3007, while about 76 percent of parts are common between the T406 and the AE 2100.[10] In addition, Allison attempted to develop other types of engines based on the T406. In 1988, the company signed a memorandum of understanding (MoU) with Messerschmitt-Bölkow-Blohm (MBB) of West Germany and the China National Aero-Technology Import & Export Corporation (CATIC) to work on a version of the MPC 75 regional aircraft to be powered by a T406-derived propfan.[11] In 1990, Allison studied a 9,000 shp (6,700 kW) propfan powerplant driving 8.5 ft diameter (2.6 m) contra-rotating propellers to power Euroflag's proposed military airlift aircraft.[12] Also, the MT7 gas turbines that will be used to power the Ship-to-Shore Connector are a derived design of the T406.[13]

In 2009, the Government Accountability Office (GAO) found that the engines failed after less than 400 hours of service, as compared to the estimated life of 500–600 hours.[14] Multiple updates to the engine platform in 2012-2013 have increased the lifespan significantly.

In April 2012, the United States Department of Defense (DoD) ordered 70 AE 1107C engines for the Osprey, with options for up to 268 engines.[15]

Engines with a future block 4 upgrade are expected to deliver 10,000 horsepower (7,500 kilowatts).[16]

An ongoing problem with the engines was their propensity for surging or stalling with 68 incidents reported between 2003 and October 2016 though this rate had reduced after the introduction of the Block 3 engine version. The US Naval Air Systems Command intends to award Rolls Royce two contracts to examine the effectiveness of proposed reliability improvements, the first is a software tweak to the engine management software for the compressor guide vanes that internal testing showed could improve surge margin by 0.8% at sea level and 3% at altitude. The second is the discovery that a temperature sensor at the inlet of the compressor sends incorrect readings leading to 2.5% out of 4% steady power shortfall at the compressors correct rotational speed again correctable with a software fix. In addition, Bell Boeing is developing an inlet barrier system to reduce the power loss from the engine ingesting dust and sand particles to supplement the engines existing centrifugal based particle separators as they can only do so much to improve the quality of air they receive.[17]

The V-22's T406 powerplants are housed in wing-tip tilting nacelles, allowing the distinctive flight characteristics of the V-22. For take off and landing the nacelles are directed vertically (90° to fuselage), while for forward flight they are rotated parallel to fuselage. The engine has been considered as a cost-effective upgrade for existing heavylift helicopters such as the CH-47 Chinook and the CH-53.[18]

• Bell Boeing V-22 Osprey

General characteristics

• Type: Turboshaft
• Length: 78.1 in (1,980 mm)
• Diameter: 34.2 in (890 mm)
• Dry weight: 971 lb (440 kg)

Components

• Compressor: 14-stage high pressure axial compressor, variable geometry vanes in the inlet and the first 5 stages[7]
• Combustors: Diffuser annular combustor with 16 air-blast fuel nozzles and 2 igniters[7]
• Turbine: 2-stage high pressure turbine with air-cooling in the first and second-stage vanes and the first-stage blade; 2-stage shrouded power turbine with uncooled vanes and blades[7]

Performance

• Maximum power output: 6,150 shp (4,586 kW)
• Overall pressure ratio: 16.7:1
• Fuel consumption: 0.426 lb/shp hr SFC,[19] efficiency 32%
• Power-to-weight ratio: 6.33 shp/lb (10.4 kW/kg)

Related development

• Allison T56/T701
• Rolls-Royce AE 2100
• Rolls-Royce AE 3007

Comparable engines

• General Electric GE38
• Lycoming T55

Related lists

• List of aircraft engines

• Leyes II, Richard A.; William A. Fleming (1999). The History of North American Small Gas Turbine Aircraft Engines. Washington, DC: Smithsonian Institution. ISBN 1-56347-332-1.
• Newill, David B. (13–18 September 1998). Common core development approach for Allison T406/AE family of turboshaft, turboprop, and turbofan engines (PDF). ICAS Congress (21st ed.). Melbourne, Victoria, Australia. ISBN 978-1-56347-287-9. OCLC 43888882.
• "Allison cites low-cost, low-risk design approach as key to V-22 engine award" (PDF). Aviation Week & Space Technology. Vol. 124. Indianapolis, Indiana, USA. 17 March 1986. pp. 52, 57. ISSN 0005-2175.

Wikimedia Commons has media related to Rolls-Royce AE 1107C (T406).

• AE 1107C-Liberty at Rolls-Royce site
• AE 1107C-Liberty Fact Sheet
• Allison (February 1988). "Allison introduces new technologies for the V-22 Osprey". Marine Corps Gazette. Vol. 72 no. 2. p. 9. ISSN 0025-3170.