Proprotor lockout systems for tiltrotor aircraft

A tiltrotor aircraft having rotary and non-rotary flight modes, in the rotary flight mode, the tiltrotor aircraft operating at least two proprotor assemblies each having a plurality of proprotor blades, in the non-rotary flight mode, the proprotor assemblies are rotationally locked and circumferentially clocked for blade folding, for each proprotor assembly, the aircraft comprising:

• a proprotor drive shaft coupled to and rotatable with the proprotor assembly;
• a nonrotating airframe structure disposed proximate the proprotor drive shaft;
• and
• a lock assembly having first and second lock members, the first lock member coupled to and rotatable with the drive shaft, the second lock member coupled to the nonrotating airframe structure, the first lock member including a plurality of bearing assemblies, the second lock member including a cradle having a plurality of asymmetric slots, each asymmetric slot including a leading ramp, a trailing stop and an entry gap;
• wherein, the lock assembly has a plurality of positions including a disengaged position in which rotation of the drive shaft is allowed and an engaged position in which each of the bearing assemblies is seated within one of the asymmetric slots;
• and
• wherein, the lock assembly is actuated from the disengaged position to the engaged position by moving the cradle toward the bearing assemblies, capturing each of the bearing assemblies in a respective one of the entry gaps, and guiding each of the bearing assemblies with the respective leading ramp as the cradle rotates relative to the bearing assemblies until a leading surface of each of the bearing assemblies contacts a respective one of the trailing stops, thereby seating the bearing assemblies within the asymmetric slots and preventing relative rotation between the drive shaft and the nonrotating airframe structure.