This video shows the experiments of inclined hovering with a tethered quadrotor and its application to take off and landing on/from inclined surfaces
See  for the paper describing the method used in the following video.
- . Takeoff and Landing on Slopes via Inclined Hovering with a Tethered Aerial Robot. In: 2016 IEEE/RSJ Int. Conf. on Intelligent Robots and Systems. 2016 IEEE/RSJ Int. Conf. on Intelligent Robots and Systems. Daejeon, South Korea; 2016. pp. 1702-1707.