Electric Propulsion Aircraft Systems

Aircraft systems can now achieve higher efficiency, capability, and robustness thanks to distributed electric propulsion (DEP). Using electrically driven propulsors only connected electrically to energy sources or power-generating devices, distributed electric propulsion systems take an innovative approach. It is now possible to arrange, size, and operate propulsors with greater flexibility to take advantage of the synergistic benefits of aero-propulsive coupling and increase performance over more traditional designs. In addition to numerous short and vertical takeoff and landing platforms, several conventional aircraft ideas that use distributed electric propulsion have been created. It is possible to increase the propelling efficiency and fill the wake by carefully integrating electrically driven propellers for boundary-layer ingestion. To improve lift performance, propulsor placement and arrangement can be employed to reduce the trailing vortex system of a lifting surface or leverage improvements in dynamic pressure across blown surfaces for improved lift performance. Aside from minimizing the need for traditional control surfaces and boosting the vehicle control system's tolerance to engine-out or propulsor-out circumstances, distributed electric propulsion can be used to provide new capabilities in vehicle control. There are numerous advantages to using a turboelectric generator or two and multiple electric fans for propulsion, including decreased noise levels during takeoff and landing and increased efficiency at all times. A DEP system's small propellers can also be placed to use the airframe's acoustic shielding effect to reduce noise signatures even more. New enabling technologies for future DEP concepts have been offered by the rapid rise in flight-weight electrical systems and power architectures. These new concepts provide flexible operational capabilities much beyond those of current systems. Even if there are specific integration issues, the disruptive nature of the DEP idea has the potential to yield previously unimaginable gains in aircraft design.

Disruptive technology such as Distributed Electric Propulsion (DEP) can make significant gains in future aircraft performance, efficiency, and robustness. The push needed for flight is provided by distributing electrically driven propulsors across a vehicle, but this design has other benefits associated with synergistic propulsion-airframe integration. Several platforms for testing and simulation of DEP components and architectures have recently been developed due to the increasing use of DEP. Concepts for large-scale commercial transports, regional transports, general aviation vehicles for personal mobility, and unmanned plane platforms have also been introduced. These planes can also do a variety of takeoffs and landings, including short takeoffs and landings and electric vertical takeoffs and landings.

One of the benefits of DEP systems is better propulsive efficiency and reduced turbulent kinetic energy losses in the wake of the vehicle. Other aero-propulsive benefits include using blown surfaces to generate dynamic pressure across aerodynamic surfaces and reducing aircraft-induced drag by interacting wingtip propulsors and wing trailing vortex systems. The distributed nature of propulsors can be exploited to give control assurance under critical faults and failures of other systems for vehicle control. The significant link between the aerodynamic performance of a local wing-body surface and the thrust level of an integrated propulsor is driving ongoing research into how tightly integrated propulsors might be used in an aircraft control architecture. DEP devices can also reduce airplane noise, especially during takeoff and landing. Because the electrically powered propulsors are only electrically coupled to power-producing engine cores, the decoupling of the propulsion system's power-generating and thrust-producing components allows for substantial effective bypass ratios. These hig
h effective bypass ratio devices can significantly reduce vehicle noise, and propulsor placement can take advantage of the noise shielding benefits of wing-body surfaces.

While DEP systems are presently being used on small unmanned and passenger aircraft, more advancements in component-level electrical system technology are required before large-scale vehicle systems may be used. Current research aims to increase the maximum power capability and power density of electrical machines and power electronics. More research is needed to better understand power distribution and circuit safety. While DEP vehicle power distribution systems might be complex, they offer unprecedented system-level flexibility and adaptability. Several obstacles associated with DEP systems must be overcome before widespread production may begin. The impact of inlet distortion on fan efficiency and structural robustness, noise reduction measures, and existing battery technologies' low specific energy.

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 Kim, H. D., Brown, G. V., and Felder, J. L., “Distributed Turboelectric Propulsion for Hybrid Wing Body Aircraft,” 2008 International Powered Lift Conference, London, 2008, pp. 1-11.

National Aeronautics and Space Administration Lewis Research Center, Aircraft Propulsion, NASA SP-259, 1971, pp. 142- 144.