Proving aPowerplant.

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Developing the EngineAirbus’ most recent venture into the military transport marketemerged as the A400M Atlas – a high-wing, four-engined, large-capacity airlifter. During the development phase, an increasingemphasis on the aircraft’s tactical role led to the decision to useturboprop engines, rather than jet or turbofan as initially planned.

With no suitable turboprop available “off the shelf”, EuropropInternational developed a new 11,000 shp engine: the eight-bladed TP400-D6. Needing the aircraft to be certified to civilstandards and following the advice of Rolls-Royce, Airbusdecided to reduce the risk of the programme by testing theTP400-D6 on an engine Flying Test Bed (FTB), and contractedMarshall to develop and operate the FTB.

Modifying the AirframeMarshall already had experience of developing an FTB, havingpreviously converted a C-130K Hercules to test the upgradedAllison/Dowty-propeller C-130J engine in the No2 (port inboard)position. With over 40 years’ experience on this airframe,Marshall decided to once again use a C-130 as the base for theFTB and selected XV208, a meteorological research aircraftoriginally converted by Marshall in 1973.

Testing the TP400-D6 would be a similar undertaking as for theC-130J engine, but on a much larger scale. Systems integrationwas a challenge due to the fact that the C-130 was an analogueairframe and the TP400-D6 a digitally-controlled engine. AnAvionics Full-Duplex Switched Ethernet (AFDX) converter wasproduced to allow the engine to “talk” to the airframe. During thecourse of the modification, Marshall also needed to integrate theengine with a number of the aircraft systems, including firedetection, fire extinguishers, hydraulics, bleed air and engineinstrument displays.

Considerable structural work was required to accommodate forthe size, weight and power output of the test engine. In additionto the structural modifications, two Lynx hydraulic dampers wereadapted to join the engine mountings to the upper and lowerfuselage, to reduce the severe load imposed on them by the eightRatier-Figeac blades rotating at 655-842 rpm.

The test propeller would also rotate in the opposite direction toXV208’s own engines, introducing possible difficulties with theairflow around the elevator and rudder of the aircraft. Little windtunnel data was available to indicate what these would be, andany problems would most likely only manifest for the first timeduring fast taxiing.

Understanding the RisksIn order to remove a great deal of the “unknown” from theprogramme, Marshall built a simulator with a fully-representativeflight deck. This retained the analogue flight instruments, butbasic test engine parameters and power from all engines wereshown on a purpose-built digital display mounted above the glareshield, to allow immediate comparison of the test engine output.

This proved invaluable in establishing the correct throttle settingsto balance the engines’ power for take-off, as the test engineproduced more thrust at flight idle than the standard engines atfull power. Tests with the real aircraft proved close toexpectations.

The simulator allowed the flight test crew to establish protocolsand emergency procedures and thoroughly investigate theramifications of engine failure immediately before or after takeoff. They could familiarise themselves with the atypical controlsetup: the test engine was controlled by an extended power leverto the left of the throttle quadrant, so that P1 in the left seatcontrolled the test engine and yaw, and P2 controlled thestandard throttles, pitch and roll, allowing P1 to concentrate onthe test engine behaviour.

Marshall also designed and built a “mock-up” engine, in order toidentify and resolve any problems that might arise during theinstallation of the test engine. This allowed refinement of thecowling design so once the real test engine arrived, theinstallation encountered only very minor issues.

Performing the TestsAirbus had specified over 700 parameters that would need to bemeasured during the testing. Marshall had added 200 more,including strain gauging of the No1 propeller for comparison withthe adjacent test unit. Altogether during testing, some 900 datachannels were constantly being monitored, using consolesdesigned and integrated by Marshall. During the installation ofthe test recording and data retrieval equipment, over 30km ofwiring were changed or added.

The TP400-D6 ran for the first time on the FTB in June 2008, andthe design appeared from the outset to be sound. Only thevibration levels caused concern, especially in the cabin floor,testing the crew to the limit. The fuselage was carefully inspectedfor any signs of fatigue cracking.

The 18 taxiing tests were completed by 10th December, and at10.30am on 17th December, XV208 took to the skies again for aflight lasting 75 minutes, reaching 8000ft. The hours practisingcoordination of throttle movements in the simulator proved theirworth as both take off and landing went smoothly. During the testflights, the TP400-D6 was advanced to take-off power, themaximum thrust the engine would produce, and shut down andrestarted using an airframe bleed supply. 18 flights wereconducted, reassuring Airbus that the behaviour of the FTB inmost circumstances was well understood.

Throughout the whole FTB project, the team at Marshall adopteda flexible and open-minded approach, taking problems in theirstride and keeping pace with changes to the maturing A400Mdesign. Thanks to the hard work and dedication of the Marshallteam, the FTB achieved precisely what it set out to do: improvethe understanding of the TP400-D6 and as a result, greatly de-risk the A400M programme.

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Marshall identified XV208, a C-130K the company had previously adapted formeteorological research, as the most suitable platform for the FTB

Marshall developed a simulator of the FTB flight deck which allowed the flighttest crew to establish protocols and procedures and further de-risked the project

The first test flight took place on 17th December 2008, following a series ofconfidence-building ground tests and authorisation to fly from the UK MoD

Marshall Aerospace and Defence Group de-risked Airbus’A400M airlifter programme by designing and developing aFlying Test Bed for the TP400-D6 engine.

Considerable structural work was required to accommodate the test engine’ssize, weight and power, including the installation of a forward and rear pylon

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