Fuel Cells, Part 3


    KITPLANES Magazine, April 2003

    Electric Powered Aircraft – Part 3
    Motor and propeller selection are the topics this time.

    Budgeting Weight
    The basic target weight breakdown for the E-plane is as follows:
    Empty mass of airframe345 lbs.
    Motor/controller110 lbs.
    Propeller and hub26 lbs.
    Motor mount/heat exchange22 lbs.
    Batteries330 lbs.
    Instruments/equipment33 lbs.
    Total weight867 lbs.

    Target Motor Specs
    Motor type:
    Three-phase brushless DC permanent magnet motor (or AC Induction).
    Continuous power: 15-30 kW (20-40 hp) at prop shaft @ 1600-2200 rpm (direct drive).
    Climb power: 30-50 kW (40-67 hp) for 5 minutes at prop shaft @ 1800-2400 rpm.
    Maximum takeoff power: 45-70 kW peak (60-94 hp) for 1 min. @ 2400-2800 rpm prop speed.
    Maximum torque: 240 Nm from 1200-2700 rpm (torque vs. rpm is flexible with a variable-pitch prop, but high torque at low rpm is important).
    Target weight: 110 lb. total for motor, controller (+ gearbox, if needed).
    Operating Voltage: 200-350 VDC (operating voltage bus target = 270 VDC).
    Motor efficiency: 90-95% over operating range from 15-70 kW.
    Total drive system efficiency: 85-90% overall including loss in controller, motor (and gearbox, if needed). Cooling system: Oil, water or air (typical radiator and pump).
    Motor size: Diameter less than 12 in., length less than 15 in. preferable.
    Controller size: Less than 1 cu. ft., and less than 30 lb.


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