Method and apparatus for in-flight blade folding

A method of spirally folding rotor blades on a rotorcraft during flight, comprising:

• disengaging power from an engine to a driveshaft via a clutch;
• halting the rotation of the driveshaft and the rotor blades;
• changing the pitch of the rotor blades such that a leading edge of each rotor blade is substantially edgewise into an airstream;
• folding each of the rotor blades about a blade fold axis towards a downstream direction, while selectively rotating each of the rotor blades about a grip pin axis, until the rotor blades lie substantially parallel to the direction of the airstream;
• and
• inflating an inflatable air bag so as to provide pressure against the rotor blades;
• wherein the grip pin axis intersects the blade fold axis.

An aircraft, comprising:

• a wing member attached to a fuselage;
• nacelles rotatably coupled to the wing member, each nacelle being rotatable between an airplane mode and a helicopter mode;
• a rotor assembly operably associated with each nacelle, the rotor assembly comprising:
• a swashplate;
• a grip pin rotatable about a grip pin axis by the swashplate;
• a rotor blades connected to each grip pin;
• and
• a blade fold actuator operably connected to each rotor blade for rotating the rotor blade about a blade fold axis;
• wherein the grip pin axis intersects the blade fold axis;
• and
• wherein operation of the swashplate and the blade fold actuator enables each rotor blade to follow a spiral fold path such that each rotor blade remains substantially edgewise through the spiral fold path so as to minimize aerodynamic drag upon each rotor blade;
• and
• an inflatable air bag on each nacelle so as to provide pressure against each rotor blade when each rotor blade is in a folded position.

A rotor assembly comprising:

• a rotor blade connected to a grip pin that is rotatable about a grip pin axis;
• a swashplate operably associated with the grip pin to rotate the rotor blade about the grip pin axis;
• a blade fold actuator operably associated with the rotor blade to rotate the rotor blade about a blade fold axis into a folded position;
• and
• an inflatable air bag configured to act as a buffer for the rotor blade when in the folded position.