Meeting future goals for aircraft and air traffic system performance will require new airframes with more highly integrated propulsion. Previous studies have evaluated hybrid wing body (HWB) configurations with various numbers of engines and with increasing degrees of propulsion-airframe integration. A recently published configuration with 12 small engines partially embedded in a HWB aircraft serves as the airframe baseline for the new concept aircraft.

To achieve high cruise efficiency, a high lift-to-drag ratio HWB was adopted as the baseline airframe along with boundary layer ingestion inlets and distributed thrust nozzles to fill in the wakes generated by the vehicle. The distributed powered-lift propulsion concept for the baseline vehicle used a simple, high-lift-capable internally blown flap or jet flap system with a number of small high bypass ratio turbofan engines in the airframe. In that concept, the engine flow path from the inlet to the nozzle is direct and does not involve complicated internal ducts through the airframe to redistribute the engine flow. In addition, partially embedded engines, distributed along the upper surface of the HWB airframe, provide noise reduction through airframe shielding and promote jet flow mixing with the ambient airflow.

To improve performance and to reduce noise and environmental impact even further, a drastic change in the propulsion system is proposed. The new concept adopts the previous baseline cruise-efficient short take-off and landing (CESTOL) airframe but employs a number of superconducting motors to drive the distributed fans rather than using many small conventional engines. The power to drive these electric fans is generated by two remotely located gas-turbine-driven superconducting generators. This arrangement allows many small partially embedded fans while retaining the superior efficiency of large core engines, which are physically separated but connected through electric power lines to the fans.

Descriptions of the vehicle, the superconducting system, and the propulsion system were presented with some "zeroth-order" weight and efficiency comparisons to the multiple turbofan system. Preliminary analysis suggests that fuel savings may be greater than six percent for a turboelectric propulsion system compared to distributed discrete turbofans.

Beyond fuel savings, however, turboelectric propulsion systems introduce a very high degree of aircraft design and operational flexibility as a result of decoupling power production from power consumption. Lightweight superconducting generators, motors and power cables allow a small number of large turbo-generators to power an arbitrary number of propulsor units. Either can be placed practically anywhere and in various orientations on the vehicle. This flexibility opens up design possibilities not obtainable with discrete turbofans or with distributed propulsion systems that employ mechanical power distribution by gearboxes and shafts.

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Find out more about this research:
Felder, J.; Kim, H.; and Brown, G.: Turboelectric Distributed Propulsion Engine Cycle Analysis for Hybrid-Wing-Body Aircraft, 47th AIAA Aerospace Sciences Meeting, Paper AIAA-2009-1132, 2009.
Kim, H.; Brown, G.; and Felder, J.: Distributed Turboelectric Propulsion for Hybrid Wing Body Aircraft, International Powered Lift Conference, July 22-24, 2008.

Glenn Contacts:
Hyun D. Kim, 216.433.8344, Hyun.D.Kim@nasa.gov
Gerald V. Brown, 216.433.6047, Gerald.V.Brown@nasa.gov
James L. Felder, 216.433.3956, James.L.Felder@nasa.gov

Programs/Projects:
Fundamental Aeronautics Program, Subsonic Fixed Wing Project