Design and aerodynamic considerations about the civil VTOL aircraft Ray

The Ray design consists of a fan-in-wing aircraft specialized as a quadrocopter enhanced with a pair of tilt-ducts at the stabilator. We explain how the civil needs influence the design. To keep operational costs acceptable, the installed power needs to be kept in a moderate range. To reduce the power need in hover flight the wing-fans have a low disc loading. The big fans lead to a low wing loading and high Reynolds numbers in fast cruise flight. These special conditions lead to a wing layout with a big wing area and small aspect ratio. This unorthodox wing layout is discussed and evaluated for the cruise flight. We conclude that the chosen small aspect ratio is optimal for the Ray design. For the critical transition phase we focus on the interaction of the wing-fans with the wings and the tilt-ducts. Fan-in-wing designs have a tendency for additional pitch up moments in the transition. With the tilt-ducts placed behind the center of gravity we can control the pitch in hover, transition and cruise flight. They perfectly fit the need for a controlled pitch down moment to counter the pitch up tendency of the fan-in-wing arrangement in transition.