Design, Analysis and Hover Performance of a Rotary Wing Micro Air Vehicle Felipe Bohorquez, Paul Samuel, Jayant Sirohi, Darryll Pines, Lael Rudd Smart Structures Laboratory, Alfred Gessow Rotorcraft Center Department of Aerospace Engineering, University of Maryland College Park, MD 20742 Ron Perel Johns Hopkins University/Applied Physics Laboratory Laurel, MD 20725 An initial design concept for a micro-coaxial rotorcraft using custom manufacturing techniques and commercial off-the-shelf components is discussed. Issues associated with the feasibility of achieving hover and fully functional flight control at small scale for a coaxial rotor configuration are addressed. Results from this initial feasibility study suggest that it is possible to develop a small scale coaxial rotorcraft weighing approximately 100 gm, and that moment control is sufficient for roll, yaw and lateral trim. A prototype vehicle was built and its rotors were tested in a custom hover stand used to measure thrust and power. The best measured rotor Figure of Merit, 0.42, was obtained for a single rotor configuration. A blade element momentum theory (BEMT) model of the rotor was implemented, and airfoil characteristics were estimated from the rotor tests. The model showed that profile drag accounts for 45% of the losses as opposed to 30% in full-scale helicopters. The radio controlled vehicle was flown untethered with its own onboard power source and exhibited good flight stability and control dynamics. Nomenclature A f flap area A g reference area A r rotor disk area C D sectional drag coefficient C D0 zero lift drag coefficient C Df sectional flap drag coefficient C lα lift-curve slope C lαf flap lift-curve slope C P power coefficient C P0 profile power coefficient C Pi induced power coefficient C T thrust coefficient d f flap moment arm d g gust moment arm d T thrust moment arm F f flap force M f vechicle roll/pitching moment produced by flap deflection M g moment acting on a cylinder in a gust M T vechicle roll/pitching moment produced by thrust deflection n blade element number r n radius of blade element n T rotor thrust V local wind velocity perceived by flap V g gust velocity α blade section angle of attack α f flap angle of attack θ blade pitch angle θ T deflection of thrust vector θ 75 pitch angle at 75% radius κ induced power factor Manuscript received July 2001; accepted January 2003. λ rotor inflow ratio ρ air density σ rotor solidity Abbreviations BEMT blade element momentum theory FM figure of merit IGE in-ground effect MAV micro air vehicle MICOR micro coaxial rotorcraft RPM revolutions per minute Introduction Recent advances in electrical and mechanical system miniaturization have spurred interest in finding new solutions to an array of military and civilian missions. One such solution is the Micro Air Vehicle (MAV) (Refs. 1, 2). These vehicles are an order of magnitude smaller than pre- viously developed systems and operate in a low Reynolds number aero- dynamic regime (Fig. 1). Due to their unique capabilities, MAVs are applicable to such missions as covert imaging, biological and chemical agent detection, battlefield surveillance, traffic monitoring, and urban in- telligence gathering. Rotary wing vehicles have significant advantages over fixed wing vehicles for these types of missions, particularly when the vehicle is required to remain stationary (hover) or maneuver in tightly constrained environments. For example, intelligence gathering around or within buildings requires a hovering vehicle with good maneuverability characteristics. It is important to point out that hover is an intrinsically high-power flight state and energy consumption will be a primary consid- eration. It is expected that recent advances in both battery and novel power supply technology (e.g. fuel cell) will allow reasonable endurance to be achieved without sacrificing hover capability. Hovering vehicle cofigu- rations include conventional rotorcraft, ducted fans, and coaxial rotors. This paper presents an initial design and analysis of a prototype rotary wing MAV called MICOR (MIcro-COaxial Rotorcraft). MICOR has been designed to exploit the advantages of rotary wing flight and is expected 80