  Unmanned aerial vehicles have been demonstrated successfully in a variety of
tasks, including surveying and sampling tasks over large areas. These vehicles
can take many forms. Quadrotors' agility and ability to hover makes them well
suited for navigating potentially tight spaces, while fixed wing aircraft are
capable of efficient flight over long distances. Hybrid aerial vehicles (HAVs)
attempt to achieve both of these benefits by exhibiting multiple modes;
however, morphing HAVs typically require extra actuators which add mass,
reducing both agility and efficiency. We propose a morphing HAV with folding
wings that exhibits both a quadrotor and a fixed wing mode without requiring
any extra actuation. This is achieved by leveraging the motion of a bistable
mechanism at the center of the aircraft to drive folding of the wing using only
the existing motors and the inertia of the system. We optimize both the
bistable mechanism and the folding wing using a topology optimization approach.
The resulting mechanisms were fabricated on a 3D printer and attached to an
existing quadrotor frame. Our prototype successfully transitions between both
modes and our experiments demonstrate that the behavior of the fabricated
prototype is consistent with that of the simulation.
