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

The problem of the design of a wind turbine for maximum output is addressed from an aerodynamical point of view. It is shown that the optimum inviscid design, based on the Goldstein model, satifies the minimum energy condition of Betz only for light loading. The more general equation governing the optimum is derived and an integral relation is obtained, stating that the optimum solution satisfies the minimum energy condition of Betz in the Trefftz plane “in the average”. The discretization of the problem is detailed, including the viscous correction based on the 2-D viscous profile data. A constraint is added to account for the force on the tower. The minimization problem is solved very efficiently by relaxation. Several optimized solutions are calculated and compared with the NREL rotor, using the same profile, but different chord and twist distributions. In all cases, the optimization produces a more efficient design.

Numerical treatment in Prandtl lifting-line theory of the nonlinearity associated with a 2-D lift curve, when the local incidence is larger than the incidence of maximum lift, is proposed. It is shown that the use of an artificial viscosity term makes the solution unique and allows the iterative method to converge to a physically meaningful solution, that is in agreement with the exact solution for the test case. The design and analysis of winglets is presented. The winglets considered are small fences placed upward at the tip of the wing to improve the wing efficiency by decreasing the induced drag. The effect of yaw on a wing equipped with such optimal winglets indicates that they provide weathercock stability.

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