Julian Moxon / London
Halfway through its development programme, the West’s most powerful turboprop is showing every sign of meeting its performance goals as it heads towards certification at the end of 2007.
The 11,000shp (8,200kW) Europrop International (EPI) TP400-D6 will power the Airbus Military A400M into the history books as the first European-developed transport and the first military aircraft developed by the Airbus group.
As such, a lot is riding on the programme, and particularly on the engine, since the three-shaft TP400 and its 5.2m (17ft)-diameter, eight-bladed Ratier-Figeac all-composite propeller must not only provide the A400M with a Mach 0.72 cruising speed, but meet demanding schedule and operational targets as well.
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“We’re on schedule and the first technical results are very good,” says TP400 programme and operations director Jacques Desclaux. The first engine run in October 2005 at EPI partner MTU’s site near Berlin, Germany saw an instrumented engine driving a water brake achieve 10,690shp during the first 35h test campaign.
The first test of the A400M’s full propulsion system took place on 28 February at Snecma’s Istres test facility, the propeller running for the first time on the Avio-designed and -built gearbox. The test took the powerplant through feathered and flight idle conditions at outputs of 1,000shp and 1,600shp, reaching around 15% of full power. “We’re building up the hours progressively, as we have to check for vibration and mechanical problems,” says Desclaux. “So far we haven’t seen any problems. It is running extremely well.”
EPI is responsible for management and co-ordination of the TP400 programme and will be the engine type certificate holder. The consortium is running an aggressive schedule that calls for delivery of the first production TP400 to EADS Casa’s A400M final assembly line in Seville, Spain in June-July 2007.
EPI partners ITP, MTU, Rolls-Royce and Snecma have workshares respectively of 20.6%, 22.2%, 25% and 32.2% of the programme. ITP is responsible for the front frame, power turbine, turbine exit casing and nozzle, and external dressings; MTU the intermediate-pressure (IP) compressor and turbine, and engine protection and monitoring unit; R-R for mechanical integration and performance, high-pressure (HP) compressor, low-pressure (LP) shaft and bearing support structures; and Snecma the combustor, HP turbine, engine installation, engine control unit and the accessory gearbox.
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Unusual gearbox
EPI also chose Italy’s Avio to supply the power gearbox as a subcontractor. This has an unusual feature in being capable of driving the output shaft either to the left or the right to cater for the opposite direction of rotation of the A400M’s left- and right-wing propellers. This creates a “down between engines” (DBE) effect, producing a symmetrical airflow over the wing, improving lift and lateral stability. The DBE also allows for better optimisation of the wing and tailplane, eliminating most of the effects of torque and prop-wash, as well as reducing severe yaw in the event of an outboard engine failure. As a result the tailplane area – and hence its drag – can be reduced and overall handling improved.
This decision created some extra complexity on the engine side, since the left-hand version has an extra shaft and gears, weighing around 30kg (66lb), requiring a little more certification work as well as generating even more challenges in the development and certification schedule.
Desclaux admits weight targets for the TP400 are “difficult to meet – as for every engine programme”. The competition with Pratt & Whitney Canada to win the A400M powerplant contract resulted in a particularly demanding target of around 1,860kg per engine. Initial indications were that this was going to be exceeded, which led to the creation of a “suggestion box” for ideas to reduce the weight. “Thanks to this we were able to define concrete, detailed modifications to be introduced no later than at the qualification/certification stage,” he says. “The modifications are coming in and we don’t see any problems.”
The TP400 test programme is extensive and is spread throughout the EPI consortium. “There’s a lot of pressure on time,” says Desclaux. “You have to remember that this is a military-engine programme being run to civil engine schedules.” MTU is responsible for development testing until 2007, and after that for production testing. Snecma’s Belgian subsidiary Techspace Aero is taking care of birdstrike and other specific testing, and ITP the overpower, crosswind and noise tests.
Further TP400 tests this year will include simulated altitude runs and bird ingestion testing. One prototype will begin an estimated 200h flight-test programme in 2007, on a Lockheed Martin C-130 being modified by the UK’s Marshall Aerospace.
Desclaux says one of the main challenges is the size and complexity of the engine control and monitoring system (CMS), partly due to the military mission requirements and also because turboprop control units are necessarily more complex than those for a turbofan, because of the need to match the propeller and engine throughout the flight envelope.
Another Snecma company, Hispano-Suiza, is teamed with MTU and R-R to develop the complete CMS, which includes a full-authority digital engine control system. The CMS also contains an electronic protection and monitoring unit, fuel pump, fuel metering unit, fuel-cooled oil cooler, high-pressure compressor variable stator-vane actuators and a fuel filter. The first test of the complete CMS took place at Snecma’s Villaroche plant in May 2005 on a new “wet” rig that simulated the full operating conditions of the engine. “It is working perfectly,” says Desclaux.
Another challenge is an operational demand for two separate systems: the electronic control unit (ECU) to control the engine, and the electronic protection and monitoring unit (EPMU), which has to be located in a protected area of the engine pylon, out of the “firing zone”.
The successful first tests of the TP400 have come as a relief to a programme that in terms of technical and managerial complexity was always going to be challenging. Some of the difficulties could not easily have been foreseen, however. The first test run, for example, was delayed because of supply chain issues resulting partly from the unexpected growth of commercial engine programmes, following the upturn in the airline industry. A longer than expected definition phase for integrating the new aircraft, engine and propeller systems was another factor that created difficulties in concurrent engineering process and led to the decision to transfer final assembly of the first engine from MTU’s Berlin plant to its Munich factory, which has more prototype assembly experience.
New headquarters
The TP400 contract award came in May 2003 and the EPI headquarters opened in Madrid the following October, ending years of tough negotiations to establish a European consortium. The eventual agreement saw Snecma’s two-shaft M88 military engine core technology adapted with R-R’s three-shaft philosophy, a solution which appears to have worked.
TP400 partners ITP, MTU, R-R and Snecma are talking with the A400M nations over the future provision of engine support services – potentially on a “power-by-the-hour” basis. “We are bringing support concepts to the customers based on our wide civil engine experience,” says EPI managing director José Massol. Talks are expected to achieve a first decision within the next year, he says. Europe’s OCCAR procurement agency may oversee an initial 10-year support package, to come into effect following the first aircraft delivery – to the French air force in October 2009.
The pressure is still on as more engines are produced in addition to the 10-unit development test programme. “We’re moving quickly to production of the first 24 engines by April 2008 to power the first six flight-test A400Ms,” says Desclaux. Production will rise again to six engines a month by 2010 and eventually reach the 720 engines required for Europe’s biggest-ever military-transport programme.
Source: Flight International
