After 107 running hours, 500 test cycles and 30 starts on MTU Aero Engines’ development test stand, this much was clear: The SAGE 4 Clean Sky engine demonstrator has provided proof of the technological readiness of the project. MTU’s experts are extremely pleased with the result: “We’ve tested numerous new technologies, and many of them have been shown to be mature. Some of the hard-ware has reached the point of being ready to fly,” summarizes Dr. Jörg Henne, Senior Vice President Engineering and Technology at MTU. The sophisticated test program was developed and conducted at MTU.
SAGE 4, which is short for Sustainable And Green Engines, is the name of one of five Clean Sky engine demonstrators. With more than 600 research partners involved, Clean Sky is the largest ever EU-funded aeronautics research program. “SAGE 4 is based on the PW1500G geared turbofan engine approved by Pratt & Whitney, which we equipped with cutting-edge compressor and turbine technology,” explains Dr. Stefan Weber, Senior Vice President Technology and Engineering Advanced Programs at MTU in Munich. “We’ve developed these innovations in a joint effort with European partners.”
“The test program, which included stress, vibration and rub-in tests as well as endurance runs, was very challenging,” says Dr. Joachim Wulf, Chief Engineer Technology Demonstrators. During some of the tests, the engine demonstrator was subjected to loads far above the normal mechanical and thermal operating limits. “We wanted to show the technological maturity of new, low-weight constructions and materials when exposed to further increased mechanical and thermal loads and to demonstrate the suitability of advanced aerodynamic airfoil designs from a mechanical point of view,” Wulf continues. Use was also made of advanced simulation methods and measurement techniques. Everything went exactly according to plan. Says Weber: “The tests go to show that we have made an important step forward towards further upgrading the geared turbofan technology with the newly developed technologies.” The novel materials, constructions and designs will directly be used on the next generation of geared turbofans to further improve their eco-efficiency. Henne: “We’re talking here about engines powering aircraft that could fly sometime within the next decade.”
As part of its Clean Sky research activities, MTU is focusing its efforts on the development of innovative technologies for its two core components, the high-pressure compressor and the low-pressure turbine. Among the work performed on the low-pressure turbine was the development and testing of a new air system for the casing and a new damping system for the first rotor stage. “This marked the first time that we’ve been using brush seals in the high-speed low-pressure turbine,” explains Wulf. The results speak for themselves: The seals proved their efficiency even in this environment where they come under high thermal and mechanical loads, resulting in a substantial reduction in leakages. In another first, heat-resistant, lightweight ceramic composites were used as insulation segments. In the high-pressure compressor, for example, a seal carrier made by additive manufacturing demonstrated its outstanding quality; MTU could soon make this part by selective laser melting for production applications. Also, a new, highly heat-resistant seal ring made from carbon-fiber-reinforced plastic with teflon sealing material was successfully tested.
The SAGE 4 demonstrator was built up last year. A so called supermodule – made up of the low-pressure turbine made by MTU, the turbine exit case made by British-Swedish GKN Aerospace, and the shaft and bearing chamber made by Pratt & Whitney – was assembled and integrated into a PurePower® PW1500G geared turbofan engine. Towards the end of last year, the engine demonstrator was mounted on the test bed in Munich, where it was put through its paces for several weeks. At the end of the test runs, the SAGE 4 demonstrator was disassembled, and each module and component was carefully evaluated. The results were more than impressive.