| T406 / AE 1107 | |
|---|---|
 A T406 engine nacelle on a V-22 | |
| Type | Turboshaft |
| National origin | United States |
| Manufacturer | |
| First run | late 1986[1] |
| Major applications | Bell Boeing V-22 Osprey |
| Number built | 860 (2018)[2] |
| Developed from | Allison T56/T701 |
| Developed into | |
TheRolls-Royce T406 (company designationAE 1107) is aturboshaft engine developed byAllison Engine Company (now part ofRolls-Royce) that powers theBell Boeing V-22 Ospreytiltrotor. The engine delivers 6,000 shp (4,500 kW).
In 1982, Detroit Diesel Allison (DDA) prepared a new engine design to enter theUnited States Army's Modern Technology Demonstrator Engine (MTDE) competition, which was expected to be developed into the powerplant for theUnited States Navy's JVX experimentaltiltrotor aircraft program (which would eventually become theBell Boeing V-22 Osprey).[3] After this engine, which DDA called the Model 580,[4] lost the competition toPratt & Whitney andGeneral Electric in 1983, Allison was separated from Detroit Diesel as a separate division withinGeneral Motors, and Allison's new management decided to pursue the V-22 engine contract anyway.[3]
On 24 December 1985, the U.S. Navy selected Allison's engine for full-scale engine development and production on theU.S. Marine Corps's V-22 Osprey.[5] Before the engine was given itsUnited States military aircraft engine designation of T406, it was known as the Model 501-M80C.[6] The Navy and Allison signed a formal contract on 2 May 1986, and the first engine to test ran six months after.[7]
The T406 is based on theAllison T56 turboprop from theP-3 and theC-130, with thefree power turbine of theAllison T701 turboshaft from the defunctHeavy Lift Helicopter program.It was selected over thePratt & Whitney PW3000 andGeneral Electric GE27 competing for the US Army's Modern Technology Demonstrator Engine program.[8] The T406 beganflight testing on 19 March 1989.[9]
The T406/AE 1107C Liberty shares a common core with theAE 3007turbofan andAE 2100turboprop series of engines, both of which have sold in the thousands of copies.[10][11] 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.[12] In addition, Allison attempted to develop other types of engines based on the T406. In 1988, the company signed amemorandum of understanding (MoU) withMesserschmitt-Bölkow-Blohm (MBB) of West Germany and theChina National Aero-Technology Import & Export Corporation (CATIC) to work on a version of theMPC 75 regional aircraft to be powered by a T406-derivedpropfan.[13] 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 powerEuroflag's proposedmilitary airlift aircraft.[14] Also, the MT7 gas turbines that will be used to power theShip-to-Shore Connector are a derived design of the T406.[15]
Production continued byRolls-Royce after it acquired Allison in 1995 to establish a North American subsidiary. In 2009, theGovernment 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.[16] Multiple updates to the engine platform in 2012–2013 have increased the lifespan significantly.
In April 2012, theUnited States Department of Defense (DoD) ordered 70 AE 1107C engines for the Osprey, with options for up to 268 engines.[17]
Rolls-Royce introduced a "Block 3" turbine upgrade, which replaced the old turbine design with sturdier and more efficient components. The upgrade increased engine power by at least 17 percent, and the engine achieved a power output of over 8,800 shp (6,600 kW) during ground testing.[18] The Block 3 turbine became standard in July 2012 for new production models. By September 2012, all older engines that were undergoing regular maintenance were systematically upgraded to the Block 3 turbine.
Engines with a future planned "Block 4" upgrade would be expected to deliver nearly 10,000 horsepower (7,500 kilowatts).[19]
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 an update to the engine management software that changes how it controls the compressor guide vanes, as internal testing suggested that this could improve the engine's 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.[20]
In October 2021, Bell and Rolls-Royce jointly announced that theBell MV-75 powerplant would switch from the General Electric T64 turboshaft used on the prototype to a derivative of the 1107C used on the Osprey, which would be named the 1107F. The 1107C is a known element in tiltrotor aircraft with its two decades of prior use which lowers sustainment costs and lowers risk associated with the project, and the 1107F increases the engine's power output from 5,000 to 7,000 horsepower.[21]
On the V-22, the T406 engines are housed in wing-tip tilting nacelles, allowing the distinctive flight characteristics of the V-22. For takeoff 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 theCH-47 Chinook and theCH-53.[22]
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