Scaling characteristics of an electric multi-copter powered by internal combustion engine are investigated. A 1-kW-class internal combustion electric generator is developed, and the energy efficiency of the internal combustion engine is investigated experimentally, and the characteristics of brushless motor are modeled theoretically. The relation between the flight time and the Multi-copter size is investigated on the basis of the statistical modeling of the existing data of the commercial engines and the motors. As a result, the flight time is found maximized at the multi-copter weight of 8 kg.
Recently, Unmanned Aerial Vehicles (UAV), represented by Multi-copters are often used for observation of farm land, forest and volcano, surveying and so on. However, it will take much time for multi-copters to complete the observation of the large farm land. This also requires the change of battery of multi-copters, leads to the increase of cost and make it impossible to get the image of the land under the uniform sun-light conditions. In order to shorten the time, the observation system by fixed wing UAV driven by fuel engine is proposed because the UAV can usually fly faster and longer than multi-copters. This paper describes the design of the UAV, which meets the take-off, climb, cruise and landing performance, and the flight verification of the take-off and onboard equipment weight.