Fundamental wind tunnel tests of fixed wing VTOL UAV without control surface

Unmanned Aerial Vehicles (UAVs) have been developed and put into practical use at a rapid pace around the world. Especially, Urban Air Mobility (UAM) vehicles using electric power and eVTOL (electrical Vertical Take-Off and Landing) vehicles are being studied actively in recent days. NASA, industries, and academic partners are working on Urban Air Mobility, as shown in Figure 1. (Ventura Diaz et al. 2019) have described the side-by-side urban air taxi, which is one of NASA's concepts. Many companies are developing UAM aircraft such as Airbus' CityAirbus UAM, as shwon in Figure 2. One of the most required features for the UAVs is the VTOL capability. The most popular VTOL UAVs are multi-rotors such as the DJI Phantom 4. The strong points of multi-rotors are their simple mechanism, being controllable by only motor control and their hover capability. On the other hand, they have some issues involving poor endurance, small payload, and so on. To resolve these problems, several types of VTOL UAVs with a wing such as tail-sitter, tilt-rotor, and tilt-wing are being studied. NASA studied Distributed Electric Propulsion (DEP) using a Greased Lightning (GL-10), which is a small Unmanned Aerial System (UAS), as shown in Figure 3. Amazon is developing UAVs for small package delivery. The new UAVs are of the tail-sitter type. However, they require some redundant thrust mechanisms, a complex tilt mechanism, and transition flight control is difficult.