Practical measures for raising propeller efficiency of low speed mini UAV

How to raise the propeller efficiency has been the key problem in airplane propeller design. The conventional theory of propeller design is mainly for large aircraft. However, for a low speed mini UAV (Unmanned Air Vehicle) the propeller has such features as high rotating speed, relatively small diameter, low forward speed, fixed pitch and wooden blade; all these features adversely affect propeller efficiency. Based on our experience in developing a series of different kinds of low speed mini UAV, we performed in a number of years repeated trade-offs and finally evolved optimized practical measures to overcome the influence of the above-mentioned unfavorable factors, thus raising the propeller efficiency to some extent. The following six practical measures are described: selecting high performance blade-foil, lifting the upper limit of Mach number at propeller tip, matching the absorbing power of propeller with the output power of engine, selecting high quality blade material, improving manufacturing technology, and blade surface reinforcement. The results of wind tunnel experiments and flying tests show that with the aid of these practical measures, the propeller efficiency of a low speed mini UAV can be increased by 5-10 percent in general.