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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 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

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Micro air vehicles have great potential for both civilian and military applications, but for successful deployment they must operate robustly in real world environments including flight in winds. An experimental study was performed to quantify the performance of a micro coaxial helicopter in realistic wind conditions. The experimental study evaluated different representative scenarios including: hover, forward flight, and landing on the edge of a rooftop. Each scenario was flight tested in nominal no wind cases and different wind levels. A synthetic wind generation system was used to create wind disturbances, and digital anemometers were used to measure wind magnitude and velocity at discrete spatial points. A motion capture system was used to measure vehicle position and attitude during flight tests as well as provide feedback for a conventional autopilot. Results show dramatic performance degradation in all wind environments. Flight observations reveal the micro coaxial helicopter could successfully operate in light winds with magnitudes of less than 2 m/s.

A comparison between stationary statistical fault indicators and the discrete harmonic wavelet packet transform (DHWPT) is investieated for accelerometer vibration data ohtained from the OH-58A main rotor transmission. This transmissionis comprised of two stages, a spiral bevel input stage and a planetary stage, resulting in a n overall reduction of 17.44:l.Vibration data from a load-to-failure transn~ission test is used to evaluate the sensitivity of previously developed stationary fault metrics and a new nno-stationary fault metric for early fault detection. The non-stationary fault indicator consists of a normalized energy metric which was developed to quantify the redistribution of sideband energy about the dominant mesh frequency and its harmonics in the presence of actual gearbox faults. This metric is used to qualitatively assess the presence, type and location of gearhox faults. Gearbox faults considered in this study include sun gear spalling and spiral bevel gear scoring. Results from the comparison suggest that the non-stationary normalized energy metric is capable of detecting damage a t a rate that is comparable to the stationary statistical fault indicators. I n addition, the normalized energy metric provides more information about the nature of a fault.