Technical Aspects of Microscale Flight Systems

Micro Air Vehicles (MAVs) have excellent potential utility as flight platforms for optical, acoustic, electronic and chemical sensors for operation in hazardous sites with aerial access. The dimensions and performance specifications call for a 100 g take-off mass with 100-200 mm wingspan that must fly at 5-20 m/s for approximately 30 minutes. Owing to the low operating Reynolds number (Re), the aerodynamic performance of all lifting surfaces is degraded. The small scales and speeds also mean that atmospheric turbulence has a severe effect, and small thermal cycle engines that could profit from the high energy densities of fossil fuels are unavailable. It is thus difficult to obtain good performance. Studies have been made of wing plus propeller systems, rotor systems and flapping wing systems. In all cases, L/D is in the range of 5-10. Flapping is about as efficient as propeller motion at this Re, but more complicated mechanically. The ThrustWing is a configuration derivative of the dragonfly, with characteristics lying between a helicopter and an ornithopter. It has both zero and forward flight capabilities, and appears to have good potential as a MAV configuration. Finally, the effects of atmospheric turbulence are described and shown to fall into four qualitatively different categories as turbulence intensity increases. Due to favourable scaling, the stresses in MAVs will be very low, and although turbulence will cause large G loads on the MAV, no structural damage will result.