Terrain Envelope for Landing Stability of a Multirotor UAV with Adaptive Landing Gear

Severe accidents may occur when a traditional multirotor unmanned aerial vehicle (UAV) with fixed landing gears lands on rugged mountains or swinging decks. In this paper, a multirotor UAV with adaptive landing gears is designed for achieving stable landing on complex terrains. To predict the landing stability before touchdown, a novel concept—terrain envelope describing the stable landing boundary on complex terrains—is proposed so that the terrain parameters in the safety regions can be obtained in advance to avoid overturning or damage of the UAV. A landing dynamic model is established, and a drop test is carried out to verify the validity of the model. In addition, the calculation process of the landing safety criteria is given under the consideration of the foot-pat relative position, shock compression stroke, and rotor-ground clearance. Then the terrain envelope and terrain-velocity envelope are obtained by changing landing conditions cyclically in the dynamic simulation, and several typical landing conditions are selected from the above envelopes for analysis. Conclusions show that the stable landing region of the UAV is primarily limited by the static boundary and dynamic boundary, and it can be further expanded by increasing the positive lateral landing velocity, which can give a multirotor UAV more chances to land stably under slope terrains.