Commissioning of Split Power Offtake on a Twin-Spool More Electric Engine Demonstrator
Authors: Kreuzer Susanne , Niehuis Reinhard 
Published: August 2017

More electric and all electric aircraft were already discussed in the eighties of the last century, but recent political and ecological issues now reinforce the electrification of aircraft and engine systems. The development of electric machines and components with increasing power to weight ratio enables the installation of power optimized electric accessories instead of pneumatic and hydraulic systems in order to raise overall efficiency and specific fuel consumption of the engine. While pneumatic and hydraulic components are driven by the aircraft engine, a major challenge is in the supply of electric energy. Storage systems lack in reliability and light weight, fuel cell technology is limited to small aircraft and needs further development in various technical disciplines. An appropriate option is the generation of electric power by engine integrated generators. Performance calculations state increased efficiency by means of split spool power offtake, but have not been validated by a real twin-spool demonstrator yet.

At the ground test facility of the Institute of Jet Propulsion a demonstrator engine has been set up for detailed research on the influence of power extraction from a Larzac 04 C5 jet engine. To facilitate the test vehicle for power offtake of two spools the starter-generator has been complemented by a second generator, which is installed in front of the compressor inlet. It is axially connected to the low pressure spool by a coupling and a special flange mounted onto the low pressure spool. Several subsystems enabling for electric power offtake are integrated into the facilities’ data acquisition system (DAQ) and communication structure. The added components influence the engine in various ways: They manipulate power balance of the spools and alter the inlet pressure distribution and the compressor aerodynamics. Additionally the internal flow distribution is changed as well as the vibration characteristics. Before starting with extensive more electric engine (MEE) power offtake test campaigns, all systems need to be installed and tested successively.

This paper describes the test facility and fundamental more electric engine subsystems, with special focus put on instrumentation and system communication. A first function test demonstrates the operability of the engine after the modification of the low pressure spool. In a further step the influence of the inlet modification onto the compressor inlet aerodynamics, total mass flow, and vibrations of the test vehicle is analyzed. The vibration characteristics are vital for the coupling functionality, which is demonstrated subsequently. Presenting the load system check, special focus is given to communication, load definition, and electromagnetic compatibility. Comparisons to component performance predictions and to the performance of the original engine configuration are drawn for all tests and new limits for the operation of the new more electric configuration are defined. Finally, first data of power offtake of two spools is presented to demonstrate the operability of the MEE test vehicle.