Rotor Blade Airfoil Design forHigh-Altitude, Long-Endurance VTOL UAVs

摘要

The problem of minimizing blade profile power for a conceptual high-altitude UAV compound helicopter was addressedrnthrough airfoil design. Some example performance calculations were presented for a generic configuration atrnaltitudes ranging from 5,000 ft to 60,000 ft. These performance estimates helped to define the design requirementsrnfor high-altitude rotor blade airfoils. Results showed that the combination of natural laminar flow with improvedrntransonic characteristics could enable cruise altitudes up to 50,000 ft. The results also showed that for optimumrnendurance the rotor tip Mach number had to be increased with altitude. The objective of the design effort was the development of transonic, natural laminar flow airfoils for cruise at 50,000 ft. The aerodynamic challenges involved therncombination of high-subsonic Mach numbers with low Reynolds numbers. This combination of parameters resultedrnin the appearance of both shock waves and laminar separation bubbles in the relevant flow physics. The design of arnhighly reflexed inboard airfoil, AFDD 50K30, enabled the use of more camber over outboard sections. This allowedrnthe working section airfoil, AFDD 50K60, to be designed for significant runs of laminar flow. Finally the tip airfoil,rnAFDD 50K80 was designed for low drag at zero to slightly negative lift found on the advancing blade at high speeds.rnResults were compared to existing rotorcraft airfoils over the high-altitude design space.