Optimizing Electric Propulsion Systems for Unmanned Aerial Vehicles

Design of an electric propulsion system for an unmanned aerial vehicle incorporates various disciplines such as the propeller’s aerodynamic and structural properties, characteristics of the electric system, and characteristics of the vehicle itself. This makes the design of this propulsion system amultidisciplinary design optimization task. Although thepresent propellermodel is based onprevious derivations that are described verybriefly, newmodels of the electric motor and battery pack,which are based on examining existing products on themarket, are described inmore detail. The propeller model and a model of the electric system, together with various optimization schemes, are used to design optimal propulsion systems for a mini unmanned aerial vehicle for various goals and under various constraints. Important design trends are presented, discussed, and explained. Although the first part of the investigation is based on typical characteristics of the electric system, the second part includes a sensitivity study of the influence of variations of these characteristics on the optimal system design. Nomenclature BEB = battery energy density BI0 = no-load current parameter BKV = motor speed-constant parameter BP-M = maximum power-to-mass ratio BRa = internal-resistance parameter CD, CL = vehicle’s drag and lift coefficients Cd = blade cross-sectional drag coefficient CLmax = vehicle’s maximum lift coefficient c = chord EB = battery energy capacity g = gravity acceleration KV = motor speed constant Iin = driver input current I0 = motor no-load current mB = battery-pack mass mM = electric motor mass Mtip = blade tip Mach number mtotal = total vehicle mass m0 = vehicle mass without the propulsion system Pin = electric system input power Pout = motor output power Pout-max = maximum motor output power R = propeller radius Ra = motor resistance r = radial coordinate SW = wing area T = thrust t = cross-sectional thickness VF = airspeed Vin = driver input voltage Vl = loitering airspeed Vst = stall airspeed Wa = axial induced velocity D = driver efficiency P = propeller efficiency P-ideal = ideal propeller efficiency S = electric system efficiency a = air density = maximal von Mises stress = rotational speed