Engines under stress

MTU Aero Engines has great expectations of the PurePower® PW1000G engine, and rightfully so: The highly efficient Geared Turbofan™ engine sold extremely well at this year’s Paris Air Show. It has been selected to power the Airbus A320neo, the Bombardier CSeries, the MRJ Mitsubishi Regional Jet, the Irkut MS-21, and the new generation of Embraer E-Jets in future. To ensure safe flight operations once the engine has entered into service, it is put through its paces in a comprehensive test program. Some of the testing is conducted at MTU’s test facilities in Munich.

11.2013 | Text: Bernd Bundschu

Kurt Scheidt, Senior Manager, Engine and Flight Test at MTU, explains: “Before an engine can go into production, it has to undergo between 3,000 and 5,000 hours of testing. The PW1000G has now been in this test phase for a year and a half.” MTU’s stake in Pratt & Whitney’s geared turbofan program varies between 15 and 18 per­cent, depending on the engine version. The workshare of Germany’s leading engine manufacturer includes the high-speed low-pressure turbine, one of the key com­po­nents of this engine. In the spring of this year, the company received two German innovation awards for its highly advanced turbine. MTU is the only manufacturer world­wide to offer this technology. “We have already conducted two series of stress tests on the low-pressure turbine for the PW1100G-JM, the version destined for the A320neo, at our facility in Munich,” reports Christian Steffen, who heads up the test activities for commercial and military programs at MTU. “Further tests in our large de­vel­op­ment test cell III are planned for the end of this year; preparations are already underway.”

Stress tests are highly complex and a major element of the flight certification process. Their purpose is to ensure that an engine module or entire engine is capable of with-standing the stresses it must sustain to meet the certification requirements, such as high speeds and temperatures, or meeting continuous operation requirements, with­out difficulty. “Measurements of the stresses and temperatures acting on the com­po­nents provide us with vital information that allows us to determine their stress limits,” says Steffen. To obtain this data, it is necessary to fit sensors at as many as 2,000 measuring points. Steffen: “Given the limited space inside the engine and the minute size of the sensors, this is a task that requires utmost precision. The most challenging tests are those involving remote measurements on rotating parts.”

Remote measurement or telemetry is a technique in which measurement data is cap­tured by a sensor and transmitted to a distant recording point. MTU has developed its own systems for this highly sophisticated measuring method. Miniature strain gages are attached to specific areas of blades and disks. They consist of thin strips of metal connected to a power source. As the component expands during engine operation as a result of heat or centrifugal forces, the strain gage expands as well, causing its elec­tric­al resistance to change—even if the deformation is as small as a thousandth of a milli­meter. The recorded data is then transmitted via a wireless connection to the computer and evaluated.

MTU has many years of experience in the testing of commercial and military aircraft engines. As Scheidt points out, stress tests are not the only type of tests that can be conducted at MTU’s test facilities: “We’re also able to carry out any type of test re­quired for engine certification, including performance and system testing, endurance testing, vibration tests, emission measurements, simulation of hot-day conditions, bird-strike tests, destructive testing, ice, water and sand ingestion tests to simulate extreme weather conditions, and high-altitude testing.” Sand ingestion tests are cur­rent­ly underway in Munich on a GE38 turboshaft engine for the Sikorsky CH-53K heavy-lift transport helicopter. The purpose of these tests is to demonstrate the en­gine’s enhanced resistance to erosion by airborne sand particles.

MTU Aero Engines in Munich for the first time performed lightning strike tests on a V2500 engine.

Slideshow

Test stands

Slideshow

 

1-PW1000G_C_0119

A PW1524G engine is being prepared for testing at MTU Aero Engines in Munich.

2-00GE38_C_0002

A GE38 engine in the test cell.

3-GP7000_C_0009

In the test cell: the GP7000, powerplant for the Airbus A380.

In a first for MTU’s test facilities in Munich, lightning strike tests on a V2500 engine for the Embraer KC-390 military transport are being conducted by a specialized U.S. company. The tests began in August. “The engine casing is exposed to defined high-voltage spikes and their effect on the engine control system is analyzed,” explains Technical Program Manager Werner Striegl, who at MTU is responsible for the V2500 and other engine programs. Another V2500 is currently being used by the MTU test engineers as a platform for trials on behalf of a customer: “We are testing a next-generation lubricant under extreme operating conditions such as elevated oil tem­pera­ture or reduced oil pressure,” says Striegl. “If all components of the engine are still in perfect working order at the end of the tests, the new lubricant can be approved for use.”

As engine performance requirements continue to increase, so do the demands on test equipment and methods. “For example, as a result of the trend toward ever-larger en­gines, most of the tests we previously carried out at the high-altitude test facility are now conducted during flight tests,” says Scheidt. “At the same time, we are con­tinu­al­ly investing in measures to enhance the performance and measurement capabilities of our test facilities and improve their noise insulation. By constantly updating our fa­cil­ities in this way, we keep abreast of the latest technological developments.”

Inside MTU MTU’s high-tech test facilities

Power turbine stress tests on the GE38 test engine took place in the turboshaft test cell at MTU in Munich.

MTU Aero Engines has various high-performance ground test facilities configured for different purposes. At its Munich headquarters, the company operates four test cells for turbojet engines and one for turboshaft engines, plus component test rigs. Add­ition­al test facilities for turbojet and turboshaft engines are operated by MTU Maintenance at its various locations in Germany and abroad. For high-altitude tests, MTU has access to Stuttgart University’s high-altitude test facility.

The engineers use these facilities to test turbojets with a thrust of up to 400 kilonewtons, such as the GP7000 for the Airbus A380 and the EJ200 engine for the Eurofighter Typhoon, and for testing turboshaft engines with an output of up to 15 megawatts powering helicopters and propeller aircraft, such as the Sikorsky CH-53K (GE38) or the Airbus A400M military transport (TP400-D6). The full range of tests re­quired for engine certification can be carried out at these facilities, including struc­tural, load, and reliability tests, ingestion tests, and destructive testing. Tests are con­ducted on individual components, assemblies and modules, as well as on complete engines for commercial and military applications.

The majority of these tests form part of contractual agreements with MTU’s OEM partners, including Pratt & Whitney, General Electric and Rolls-Royce, or the International Aero Engines (IAE) consortium. Other tests are performed on behalf of external customers.

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A look inside an engine test cell

11.2017 | Development tests and production accept­ance tests have dif­ferent goals and require different activities but, in both cases, the steps the engine goes through in the test cell are always the same. Accept­ance tests for the PW1100G-JM, for example, are carried out in Munich, while those for the TP400-D6 take place in Ludwigsfelde.