Parallel hybrid-electric propulsion systems would be beneficial for small unmanned aerial vehicles used for military, homeland security, and disaster-monitoring missions involving intelligence, surveillance, or reconnaissance (ISR). The benefits include increased time on station and range as compared to electric-powered unmanned aerial vehicles and reduced acoustic and thermal signatures not available with gasoline-powered unmanned aerial vehicles. A conceptual design of a small unmanned aerial vehicle with a parallel hybrid-electric propulsion system, the application of a rule-based controller to the hybrid-electric system, and simulation results are provided. The twopoint conceptual design includes an internal combustion engine sized for cruise speed and an electric motor and lithium-ion battery pack sized for endurance speed. A rule-based controller based on ideal operating line concepts is applied to the control of the parallel hybrid-electric propulsion system. The energy use for the 13.6 kg (30 lb) hybridelectric unmanned aerial vehicle with the rule-based controller during one-hour and three-hour ISR missions is 54% and 22% less, respectively, than for a four-stroke gasoline-powered unmanned aerial vehicle.
Nomenclature= maximum lift coefficient e = Oswald efficiency factor et = speed error signal, m=s J = objective function to be minimized m = mass, kg or lbs P EM = power output of the electric motor, W P ICE = power output of the internal combustion engine, W PR = power required, W S = wing area, m 2 TR = thrust required, N ut = controller command signals V Cruise = cruise speed, m=s or kn V Endurance = endurance speed, m=s or kn V Stall = stall speed, m=s or kn W = weight of UAV, N or lbs W Empty = empty weight, N or lbs W Fuel = fuel weight, N or lbs W 0 = gross takeoff weight, N or lbs W Payload = payload weight, N or lbs W Propulsion = propulsion system weight, N or lbs yt = output signal, UAV speed, m=s Prop = propeller efficiency = air density, kg=m 3
