Fecha de publicación: 12/12/2018 Fuente: WIPO "swarm" A hovering air vehicle (HAV) 200, such as a quad-rotor HAV, has a propulsion frame which is mounted to a main body (or pod) 210 via a compliant interface. The propulsion frame is made up of a plurality of arms 202 connected to a central frame portion 208 and with motors 204 and propellers 206 mounted to their distal ends. An Inertial Measurement Unit (IMU) 220, provided for flight control of the HAV, is mounted within a carrier 222 which is itself mounted to the central frame portion 208 of the propulsion frame by carrier springs 224 forming a further compliant interface. The compliant interface between propulsion frame and main body comprises soft dampers in the form of helical springs 212 and motion limiters 214 made up of stops 216 enclosed within limiting retainers 218.