Two innovative technologies are developed and tested: distributed electric propulsion (DEP) systems with variable inclination (mission-adaptive propellers, MAP) and a novel concept for the utilization of energy harvesting propellers (EHP) as a "flying wind turbine" to decelerate and control the aircraft during the landing phase.
The MAP allow for the adjustment of the distributed propellers according to the specific flight phase and thus to minimize the required energy and improve the STOL capabilites. The EHPs provide a possible solution to the yet unsolved landing problem of DEP systems, which severely limits the high-lift potential of DEP systems in the landing phase. In the eMission project an innovative approach is chosen with EHPs placed at the wingtip position (WTP). As a result of this approach, not only can the landing problem be solved, but also a portion of the kinetic energy of the aircraft can be harvested. The EHPs can also be applied in the descent phase to control the descent angle and harvest a portion of the potential energy. The primary energy requirement of the entire flight mission can thus be reduced via the use of the MAP and EHP technologies.
The project can expand the state of science and technology via the achievement of the following three primary work objectives:
- Solution of the landing problem of DEP systems via the use of EHPs
- Exhausting the potential of MAPs to optimize the DEP system for each flight mission phase, e.g. to minimize the energy requirement or to maximize the STOL potential
- Reducing the noise emission via the use of MAP and EHP
EHPs are being investigated in different research projects, but the focus is generally set on the use of the more conventional "Windmilling" mode. This mode is achieved by a reduction of the rotational speed or a slight adjustment of the blade pitch. An alternative mode, proposed and termed "opposite pitch" by Yokota, more closely matches the operation of a wind turbine. After a large increase in blade pitch (by 90° to 180°) the rotor blades are driven by the inflow and the generated torque can be harvested with a generator. However, in this harvesting mode the rotation direction is inverted compared to the propulsive mode.
In eMission, the following four approaches are examined for the specific application of EHPs on an aircraft:
- the aforementioned large increase in blade pitch alongside an inversion of the rotation direction to obtain the Opposite Pitch mode
- the rotation of the entire WTP nacelle and a slight pitch adjustment to also obtain the Opposite pitch mode without requiring the inversion of the rotation direction
- the installation of additional, folding turbines instead of the off-design operation of propellers in a harvesting mode
- the use of adaptive propeller blades with variable blade geometry
Contact:
Thorsten Lutz
Dr.-Ing.Head of the LuFo VI-3 research project eMission and Head of the Aircraft Aerodynamics and Wind Energy Working Group, Institute of Aerodynamics and Gas Dynamics