The design and testing of a shrouded single-rotor MAV (Micro Air Vehicle) with antitorque vanes exhibiting improved hover efficiency is described. The final vehicle weighs 257 g and consists of a two-bladed single hingeless rotor of diameter 240 mm enclosed in a shroud. The shroud is attached to axisymmetric vanes that are placed in the rotor downwash to provide antitorque. Bench top tests were conducted to evaluate the performance of the shrouded rotor and antitorque system. (1) This vehicle design proposes improved efficiency by enclosing the rotor in a shroud. The rotor operates at low tip Reynolds number (20,000-100,000). For power loading improvement over an unshrouded rotor MAV, a simple momentum theory based design analysis suggested that for a shroud with a straight diffuser section, its weight should not exceed about 26% of the weight of the unshrouded vehicle. It was found that the shroud shared about 30-40% of the total thrust produced by the shrouded rotor. At an operating thrust of 2.45 N, a 40% improvement in power loading was observed, which translates to about 30-g increase in payload for a given input power. (2) A Hiller stabilizer bar was incorporated in the rotor to improve vehicle stability and control. However, the circular bar cross-section and paddles of the Hiller bar lead to additional losses due to profile drag. It was found that by adjusting the Hiller paddle collective to about 12 deg, it was possible to minimize the profile losses. (3) A hingeless rotor was incorporated to minimize the tip path plane motion in the shroud. The Hiller bar was optimally phased with the blade pitching axis to eliminate possible cross-coupling in pitch and roll due to gust disturbance and fuselage attitude perturbations. At an operating rpm of 3,000, the Hiller bar and the main rotor were set at 40 deg apart. It was also observed that as the operating rpm increased, the phasing increased. (4) Performance tests suggested that vanes placed in the rotor down-wash sufficiently countered the rotor torque and was independent of the operating thrust. For a given input electrical power, the thrust penalty of installing the antitorque vanes was less than 10%. However, there is a degradation in vane performance when operated IGE due to the modified structure of the rotor wake. (5) A series of risk reduction prototypes were constructed to finally demonstrate flight capability of the shrouded rotor. Two prototype vehicles with a single main rotor and turning vanes were built. The first prototype TiFlyer constructed out of aluminum sheet weighed about 340 g. The second prototype Giant was predominantly fabricated out of carbon fiber and has a total mass of 240 g. Both prototypes were test flown and demonstrated stable lateral and yaw characteristics. The final vehicle with the shrouded rotor, TiShrov, was developed and test flown. A PID controller was used to attain stable hover since this configuration had poor inherent stability. Future work involves characterizing the forward-flight and gust response of the vehicle.
Design, development, and testing of a shrouded single-rotor micro air vehicle with antitorque vanes
Design, Entwicklung und Prüfung eines Einzelmantelpropeller-Mikroluftfahrzeugs mit Drehmomentenausgleichsflügeln
Journal of the American Helicopter Society ; 56 , 1 ; 012008/1-012008/11
2011
11 Seiten, 22 Bilder, 3 Tabellen, 19 Quellen
Aufsatz (Zeitschrift)
Englisch
Design and Testing of a Shrouded Rotor Micro Air Vehicle with Anti Torque Vanes
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