An evaluative review of the VTOL technologies for unmanned and manned aerial vehicles.

VTOL (Vertical Take-Off and Landing) capabilities are desired features of both UAVs (Unmanned Aerial Vehicles) and MAVs (Manned Aerial Vehicles) on condition that a comparable flight performance is achieved. VTOL is not only a very suitable technology for UAVs due to the convenience and concealment mission requirements of UAVs, but also very important for both military and civil MAVs due to the advantages of less or even no dependency on airports/air fields. As such, it is necessary to study and compare the VTOL technology of MAVs and UAVs at the same time. This paper highlights the major VTOL technologies and the representing aircraft configurations. The recent VTOL projects in the US are reviewed and compared to give insight into the technological diversities, application opportunities as well as the future development trend for urban air mobility. Then, an intuitive summary and comparison of famous projects and models has been made. Based on the above research, challenges and constraints of VTOL aircraft are summarized. As a supplement to the review of VTOL technologies, the current research activities on short takeoff and landing technologies via active flow control for large commercial aircraft in Europe is also reviewed. At the end, based on the above analysis, this paper points out the future development direction of VTOL vehicles.