Lift-Force Measurement for Hovering Flight of Four-Winged Flapping Micro Aerial Vehicle

In order to establish the measurement technique of the hovering force of a flapping aerial vehicle the indirect method was proposed. In the indirect measurement the flapping vehicle was placed over a horizontal plate with a certain distance, and the force acting on the plate was measured by the loadcell installed beneath the plate. First, this technique was evaluated by the thrust force measurement of a rotating propeller. The indirectly measured force was compared with that of the direct measurement. The averaged values of the two measurements agreed quite well. It is also proved that the standard deviation of the indirect measurement was only 7.6 percent of that of the direct measurement. The measured force was insensitive to the vertical position of the plate below the propeller. When the propeller was inclined toward the horizontal plate, the measured values coincided nearly to the normal component of the force vector. This indirect technique was applied to the flapping aerial vehicle. The standard deviation of the indirect measurement was 10 percent of that of the direct measurement. The highest hovering force was obtained at 80 degrees in attitude angle, which is nearly vertical nose-up attitude. This fact corresponded to that the air stream generated by the flapping motion was at maximum in the direction of 80 degrees. The obtained hovering force was 0.126 N, and this value is quite close to the gravitational force acting on the flapping aerial vehicle, which was 0.131 N.