Researchers at NASA’s Armstrong Flight Research Center are developing a concept aircraft for testing turbo-electric distributed propulsion (TeDP) experiments. TeDP generally involves providing thrust to an aircraft via wing-mounted ducted electric fans, which consist of an electric motor, a fan, stators, and other components surrounded by cylindrical ducting within a fan case. The fan motors are powered by a combined battery and turboelectric generator system. To sufficiently power an aircraft approximately 50 ft (≈15 m) in length and with a gross weight of 25,000 lb (≈11,340 kg), this system must be capable of generating 1 MW of power.
Because creating a completely integrated 1-MW TeDP aircraft is a very expensive endeavor, NASA Armstrong researchers are exploring the potential for using a pre-existing airframe as the testbed’s foundation. If successful, this approach would substantially reduce project costs while allowing the aircraft industry the opportunity to gain a fuller understanding of the operational nature of a TeDP system. This, in turn, would allow rapid project turnaround and shorten the overall TeDP development cycle.
The testbed design is for an unmanned, glider-style aircraft, which offers tremendous advantages when experimenting with such a cutting-edge concept as TeDP. Should a problem occur during propulsion testing, the unpowered testbed aircraft can glide safely to the ground. This significant reduction in risk further enhances the progress of TeDP development.
The testbed glider would have a roughly 115-ft (≈35 m) span of detachable composite wings and an empty weight of less than 10,000 lb (≈4,540 kg). The very long wingspan provides a high lift-to-drag ratio, while the low base weight helps maintain a gross weight of less than 20,000 lb (≈9,070 kg). The air-frame also offers a large rear engine pod, which is ideal for housing a turbo-generator that can achieve upwards of 1 MW in power output.
This particular testbed design will offer an excellent means for experimenting with various approaches to TeDP. For example, the root chord structure of the detachable composite wings will allow engineers to attach many smaller fans — as opposed to four or six large fans — without significantly impairing the air-frame’s overall lift capability. Similarly, with this testbed, designers will be able to experiment with the use of high-power, high-frequency pulse-width modulation devices made of silicon carbide or gallium nitride for handling the AC to DC conversion.