Design and Joint Control of a Conjoined Biplane and Quadrotor

Unmanned Aerial Vehicles (UAVs) have the potential to perform many different missions, some of which may require a large aircraft for endurance and a small aircraft for maneuverability in wind gusts or cluttered environments such as buildings. This paper proposes a novel combination of a quadrotor and a hybrid biplane capable of joint hover, joint forward flight, and mid-air separation followed by separate flight. We investigate cooperative control strategies during joint flight that do not require any communication between the quadcopter and the biplane. This means that the two aircraft have their own independent control strategy based on their own sensors. The biplane, which is the largest of the two with most control authority, leads the flight and the goal for the quadrotor is to help in producing thrust and increasing rotational stability. Three control strategies for the quadrotor are compared: a proportional angular rate damper, a proportional angular acceleration damper, and constant thrust without attitude control. Simulation and practical tests show that for desired attitude changes of the biplane, the quadrotor rate- and angular acceleration damper strategies lead to a small performance degradation. However, the angular rate damper strategy reduces the roll angle error in disturbance rejection experiments and requires the smallest input command. The in-flight release is successfully tested in joint hover up to a forward pitch angle of −18°.