Assessment of power sources and electric motors for hybrid electric tiltrotors

Abstract

Tiltrotors operate in two distinctly different regimes: helicopter mode and rotor mode. In optimized designs, the rotors operate at continually varying RPMs and the cruise power can be as low as 50% of the hover power. This places unique demands on the power source and the drive system. It is necessary to understand and to match the best operating points of the rotor, drive system, and the power source to obtain an efficient vehicle. The influence of several powerplant and drive options, including electric batteries, fuel cells, gasoline and diesel powered piston engines, turboshaft engines, electric generators, and electric motors, are evaluated for a tiltrotor based on the University of Maryland’s Excalibur (2011 AHS Student Design) as a baseline system. Results of parametric studies are presented to show that current batteries and fuel cells do not have the energy densities necessary to be useful for tiltrotors. It is shown that the diesel engine option can result in a fuel saving of over 50% compared with the baseline turboshaft version. A diesel hybrid electric option is shown to result in 34% lower fuel consumption and to be a viable lead-in for all electric tiltrotors. The parametric studies are used to identify areas of high payoff research for making hybrid/electric tiltrotors a reality.