Experimental Investigation of Coaxial Rotor Performance for a Tube-Launched Micro Air Vehicle

This paper presents an experimental parametric study to investigate the hover performance of a coaxial rotor at low Reynolds numbers ( Re ) for a micro air vehicle that could be launched from a 40-mm grenade launcher. The coaxial rotor was torque-balanced using differential rotation speed. First, isolated rotor experiments investigated single rotor performance via varying blade pitch angle, thickness-to-chord ratio ( t/c ), chord length, and Re . The gure of merit ( FM ) increased with reducing t/c until 4%, below which it had minimal impact. Increasing blade chord improved FM . The maximum isolated rotor FM was 0.59 at Re = 70,000. Next, coaxial rotors were tested while vertical rotor separation and lower rotor pitch angle were varied. The separation had a marginal impact on performance. However, below 0.5 R , the lower rotor thrust and FM improved and the upper rotor performance degraded. The coaxial FM was improved by operating the lower rotor at increased collective. On average, the coaxial rotor generated 1.64 times the thrust of an isolated rotor while consuming twice the power.