This is an improvement of the 1968 Trailing Rotor V/STOL aircraft (Ref. 1). Rotors are mounted on wing-tip pods which can be tilted from the vertical to the horizontal aft position. Rotors are then stopped in the axial-flow condition and indexed to an azimuth position, aft of the wing trailing-edge. Rotor blades are then folded forward (blade-tips upstream of rotor-hubs) and locked into grooves in the tip-pods.
The main improvements over Ref. 1 are: a smaller shift of center-of-gravity during transition to cruise mode, and an easier task of locking blades into the tip-pods.
The main feature of the autorotative aft rotor tilt is that a soft-inplane rotor can be used, which reduces rotor weight. The blade-folding axis is also the blade-flapping axis.
The autorotative mode is used frequently by helicopters during descent. It has been found to be a good, stable mode with rpm-stability. During aft tilt on the UFR, the rotors provide pitching stability to the airframe. During stopping of the rotor, the stability of the autorotating rotor eases the task of passing thru rotor resonance.
Also, the wing can be swept back, which is desirable for 400 kt. cruise speeds and can be used for external stores such as fuel and weapons.