Rotor blade optimization and flight testing of a small UAV rotorcraft

Abstract

Rotor blade optimization with blade airfoil Reynolds numbers between 100 000 and 500 000 — characteristic of small single-rotor unmanned aerial vehicles (UAV) — was performed for hover using blade element momentum theory (BEMT) and demonstrated via flight tests. BEMT was used to test various airfoil profiles and rotor blade shapes using airfoil data from 2D computational fluid dynamics simulations with Reynolds numbers representative of the blade elements. Selected blade designs were manufactured and flight tested on a Blade 600X single main-rotor UAV (671 mm blade radius) to validate the theoretical results. The parameters considered during the optimization process were the rotor frequency, radius, taper ratio, twist, chord length, airfoil profile, and blade number. The best of the improved blade designs increased the figure of merit, a measure of rotor efficiency, from 0.31 to 0.68 and reduced power consumption by 54%. Reducing the rotational frequency accounted for 45% of the improvement in power consumption, while the taper ratio and blade number accounted for 25% and 17%, respectively. The blade twist and airfoil profile only had a minor effect on the power consumption, contributing 7% and 6% to the improvement. The rotor diameter and root chord were kept identical to the original rotor and hence had no contribution. The presented results could serve as useful guidelines to single-rotor UAV manufacturers and operators for increasing endurance and payload capabilities.