Unmanned Aerial Vehicles, UAVs, serve many purposes
these days, such as short-range inspections
and long-distance search and rescue missions. Long-distance missions can entail a search in a building. Such missions require a large aircraft for endurance and a small aircraft for manoeuvrability in a building.

This paper proposes a novel combination of a quadrotor and a hybrid biplane capable of joint hover, joint forward flight, and mid-air disassembly followed by separate flight. During joint flight, the quadcopter and the biplane have no intercommunication.

This paper covers the design of a release system and a joint control strategy. Firstly, the in-flight
release is successfully tested in joint hover up to a forward pitch angle of -18 [deg]. Secondly, three control strategies for the quadrotor are compared:
a proportional angular rate damper, a proportional angular acceleration damper, and constant thrust without attitude control.
In all cases, the biplane uses a cascaded INDI attitude controller. Simulation and practical tests show that for intentional attitude changes, the different strategies
are of minimal influence. However, the angular rate damper
strategy for disturbance rejection has the lowest roll angle error and requires the smallest input command.