FLUG REVUE May 2006: EPI TPÜ400-D6 runs at Istres

May 2006

TP400-D6 COMPLETES FIRST RUN WITH PROP

By Patrick Hoeveler

The engine starts up with a muffled drone. The 5.33m wide propeller begins to rotate but is still feathered. After two minutes, the test team powers the TP400-D6 for the Airbus A400M military airlifter up to ground idle (745 kW, eleven degree blade angle). 45 seconds later, the test engineer pushes the throttle further forward, and the engine is now running at 1,192kW with a blade angle of fifteen degrees in flight idle. The eight-blade propeller has now mastered its first test, and the engine is powered down again in reverse sequence.

TP400-D6

With this first engine test on 28 February in Istres in the south-west of France, the most powerful turboprop engine in the Western world delivers the proof required under the terms of the contract that its control system is able to control the propeller. The engineers from Europrop International (EPI), a consortium made up from ITP, MTU Aero Engines, Rolls-Royce and Snecma, have had less than two weeks to test out new software required for the test which had arrived late. This software automatically adapts the speed and blade angle of the propeller to the engine output demanded.

But the biggest challenge faced by the FH386 propeller from Ratier-Figeac is still to come: “The problem is the speed of the A400M. Instead of the Mach 0.6 which is customary for such aircraft, the airlifter will fly at Mach 0.72. This is something that no other aircraft in this class has achieved,” said Dr. Karsten Mühlenfeld, Technical Director of EPI, in an interview with FLUG REVUE. For this reason the designers chose a new, sabre-shaped profile for the composite blades for the approx. 655kg propeller. But the 5.33m diameter was itself breaking new ground. As Dr. Mühlenfeld of Rolls-Royce Deutschland points out, “The Western world has not seen a propeller of this size before.”

The engine alone has already demonstrated its power. Since the first run on 28 October 2005 on the test cell of MTU Maintenance Berlin-Brandenburg in Ludwigsfelde (see FLUG REVUE 12/2005), the engine has clocked up 35 hours. And successfully too, as Dr. Mühlenfeld points out: “The TP400-D6 behaved as it was supposed to and produced the full power output of 7,965kW. For a first prototype, its performance was very robust. There were no problems with compressor stalls or similar.”

During these tests, the gearbox supplied by Avio had a lot to endure. It possesses a reducing gear ratio of 9.5:1 and has to transfer a huge torque of 100,000Nm. “So far there have not been any problems here,” says Dr. Mühlenfeld. “In Ludwigsfelde we have already achieved the full output, even though we had a water brake simulating the propeller.” The trials have covered all three propeller speeds of the powerplant: 655 rpm for the low attitude cruise, 730 rpm for the normal cruise and 842 rpm for take-off and special manoeuvres. The pilot will then set the required rpm in the cockpit of the A400M.

So far the tests in Istres have been conducted only at low speed. The next job is to investigate how the propeller behaves under higher load and whether the control system functions in every respect. Dr. Mühlenfeld is confident: “The more power output demanded, the better the engine behaves.” He expects the simulation of a complete flight cycle on Snecma's specially reactivated outdoor test rig to be carried out early in the summer.

This should then show how much noise the entire propulsion system actually generates. Due to its high power, the TP400-D6 could in Dr. Mühlenfeld's view turn out to be louder than other propeller engines. “The TP400-D6 will of course be not as quiet as a turbofan because of its propeller concept and its high power. But we will certainly meet all specifications regarding noise emissions”, said Dr. Mühlenfeld. The Europrop product will be the first military engine that has to comply with civil noise limits.

The approach is the most critical phase. “Due to the lower engine speed, the propeller will not necessarily be the biggest noise source. If it becomes necessary to take corrective action, acoustic dampers in the intake and front duct could be considered. The propeller itself cannot be changed any more.” Dedicated noise tests and cross-wind tests scheduled to commence in mid-2007 with the fifth engine, assembled by MTU, on the outdoor test rig of ITP in Moron, near Seville, could provide some answers.

Meanwhile the tests in the south of France are continuing, following the installation of reinforced damping elements and a modified mount system. In actual fact the second engine, assembled at ITP in Spain, was to have been used for the tests in Istres. But due to lack of time and to minimise the risk, the EPI management decided to use the first prototype from Ludwigsfelde instead. Apart from installation of the propeller, the main changes lay in the new software and connections for the instrumentation. The Spanish propulsion unit, which has since been completed, is instead bound after initial testing in Ludwigsfelde for the high altitude test chamber of the Centre d'Essai des Propulseurs (CEPr) in Saclay. “There we will check whether the engine's behaviour matches predictions at various altitudes up to 11,200m.” Then, according to the EPI Technical Director, the third engine, this time assembled by Snecma, will serve as a telemetry platform in the summer. “Due to the tight schedule, we will use two telemetry systems in one engine, something that is done relatively rarely in this form.” Here, sensors on the intermediate and high-pressure spools will measure blade vibration and thermal influences.

The tests have to be completed before the next milestone, the flight test campaign on a C-130 Hercules. At the end of the year, EPI plans to deliver the ninth TP400-D6 to Marshall for installation on the flying test bed. At this point the other engines should have completed 1,000 hours between them.

But also the designers have plenty of work ahead of them. Before the target weight of 1863kg can be achieved, another 60kg has to be shed.

„This does not sound much, and the existing possibilities for reductions are not inexhaustible, but EPI already has identified and planned the necessary modifications”, confirms Dr. Mühlenfeld. The main savings potential lies in the materials. “We have used a lot of titanium, but we have to optimise further. For example, the power gearbox has up to now been constructed entirely from aluminium. Now we are also using magnesium as well in order to save weight. But that will increase the manufacturing costs” The changes are to be integrated into the fourth engine (to be assembled at Snecma), which is earmarked for endurance tests from the early summer.

From FLUG REVUE 6/2006

Last updated 10 April 2006

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