Proprotor lockout systems for tiltrotor aircraft

A lockout system for an aircraft having a rotor assembly. The lockout system includes a drive shaft coupled to and rotatable with the rotor assembly, a nonrotating airframe structure disposed proximate the drive shaft and a lock assembly having first and second lock members. The first lock member is rotatable with the drive shaft and includes a plurality of bearing assemblies. The second lock member is coupled to the nonrotating airframe structure and includes a cradle having a plurality of asymmetric slots each with a leading ramp and a trailing stop. The lock assembly has 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 to prevent rotation of the drive shaft. The lock assembly is actuatable between the engaged and disengaged positions.

TECHNICAL FIELD OF THE DISCLOSURE

The present disclosure relates, in general, to tiltrotor aircraft having rotary and non-rotary flight modes and, in particular, to proprotor lockout systems for tiltrotor aircraft configured to selectively prevent rotation of the proprotor assemblies and rotationally align the proprotor blades with blade grips for blade folding during the non-rotary flight mode.

BACKGROUND

Fixed-wing aircraft, such as airplanes, are capable of flight using wings that generate lift responsive to the forward airspeed of the aircraft, which is generated by thrust from one or more jet engines or propellers. The wings generally have an airfoil cross section that deflects air downwardly as the aircraft moves forward, generating the lift force to support the aircraft in flight. Fixed-wing aircraft, however, typically require a runway that is hundreds or thousands of feet long for takeoff and landing.

Unlike fixed-wing aircraft, vertical takeoff and landing (VTOL) aircraft do not require runways. Instead, VTOL aircraft are capable of taking off, hovering and landing vertically. One example of a VTOL aircraft is a helicopter which is a rotorcraft having one or more rotors that provide lift and thrust to the aircraft. Such rotors not only enable hovering and vertical takeoff and landing, but also enable forward, backward and lateral flight. These attributes make helicopters highly versatile for use in congested, isolated or remote areas. Helicopters, however, typically lack the forward airspeed of fixed-wing aircraft due to the phenomena of retreating blade stall and advancing blade compression.

Tiltrotor aircraft attempt to overcome this drawback by utilizing proprotors that can change their plane of rotation based on the operation being performed. Tiltrotor aircraft typically have a pair of nacelles mounted near the outboard ends of a fixed wing with each nacelle housing a propulsion system that provides torque and rotational energy to a proprotor assembly. The nacelles are rotatable relative to the fixed wing such that the proprotor assemblies have a generally horizontal plane of rotation providing vertical thrust for takeoff, hovering and landing, much like a conventional helicopter, and a generally vertical plane of rotation providing forward thrust for cruising in forward flight with the fixed wing providing lift, much like a conventional propeller driven airplane. It has been found, however, that forward airspeed induced proprotor aeroelastic instability is a limiting factor relating to the maximum airspeed of conventional tiltrotor aircraft in forward flight.

SUMMARY

In a first aspect, the present disclosure is directed to a lockout system for an aircraft having a rotor assembly. The lockout system includes a drive shaft coupled to and rotatable with the rotor assembly. A nonrotating airframe structure is disposed proximate the drive shaft. A lock assembly has first and second lock members. The first lock member is coupled to and rotatable with the drive shaft. The second lock member is coupled to the nonrotating airframe structure. The first lock member includes a plurality of bearing assemblies. The second lock member includes a cradle having a plurality of asymmetric slots, each asymmetric slot including a leading ramp and a trailing stop. 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 to prevent rotation of the drive shaft. The lock assembly is actuatable between the disengaged and engaged positions.

In certain embodiments, the drive shaft may be a drive shaft disposed in a wing. In other embodiments, the drive shaft may be a proprotor mast. In some embodiments, the nonrotating airframe structure may be a gearbox housing. In other embodiments, the nonrotating airframe structure may be a wing airframe structure. In certain embodiments, each of the bearing assemblies may include a spherical roller bearing. In some embodiments, each of the bearing assemblies may include at least one of a hardened roller surface or a high lubricity roller surface. In certain embodiments, the plurality of bearing assemblies may include first, second and third bearing assemblies. In such embodiments, the first, second and third bearing assemblies may be uniformly circumferentially distributed at 120 degree intervals. In some embodiments, the first lock may include a collar assembly having internal splines configured to couple with external splines of the drive shaft to prevent relative rotation therebetween.

In certain embodiments, the plurality of asymmetric slots may include first, second and third asymmetric slots. In such embodiments, the first, second and third asymmetric slots may be uniformly circumferentially distributed at 120 degree intervals. In some embodiments, the second lock member may include a sleeve and a piston wherein the sleeve may be coupled to the nonrotating airframe structure to prevent relative rotation and relative translation therebetween and the piston may be slidably disposed within the sleeve and configured to translate relative thereto to shift the lock assembly between the disengaged and engaged positions. In such embodiments, the sleeve and the piston may include a nonrotation feature to prevent relative rotation therebetween. In certain embodiments, the trailing stop of each asymmetric slot may have a surface that is substantially parallel with a central axis of the second lock member. In some embodiments, the leading ramp of each asymmetric slot may have a curved upper profile. For example, the curved upper profile may have a progressively decreasing angle between 60 degrees and 30 degrees. In certain embodiments, an entry gap of each asymmetric slot may be at least twice as wide as a base gap of each asymmetric slot. In some embodiments, each of the bearing assemblies is seated within one of the asymmetric slots when the bearing assembly contacts both the leading ramp and the trailing stop of the respective asymmetric slot.

In a second aspect, the present disclosure is directed to a tiltrotor aircraft having rotary and non-rotary flight modes. In the rotary flight mode, the tiltrotor aircraft operates 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 includes a proprotor drive shaft coupled to and rotatable with the proprotor assembly. A nonrotating airframe structure is disposed proximate the proprotor drive shaft. A lock assembly has first and second lock members. The first lock member is coupled to and rotatable with the proprotor drive shaft. The second lock member is coupled to the nonrotating airframe structure. The first lock member includes a plurality of bearing assemblies. The second lock member includes a cradle having a plurality of asymmetric slots, each asymmetric slot including a leading ramp and a trailing stop. The lock assembly has a plurality of positions including a disengaged position in which rotation of the proprotor drive shaft is allowed and an engaged position in which each of the bearing assemblies is seated within one of the asymmetric slots to prevent rotation of the proprotor drive shaft. The lock assembly is actuatable between the disengaged and engaged positions.

DETAILED DESCRIPTION

While the making and using of various embodiments of the present disclosure are discussed in detail below, it should be appreciated that the present disclosure provides many applicable inventive concepts, which can be embodied in a wide variety of specific contexts. The specific embodiments discussed herein are merely illustrative and do not delimit the scope of the present disclosure. In the interest of clarity, not all features of an actual implementation may be described in the present disclosure. It will of course be appreciated that in the development of any such actual embodiment, numerous implementation-specific decisions must be made to achieve the developer's specific goals, such as compliance with system-related and business-related constraints, which will vary from one implementation to another. Moreover, it will be appreciated that such a development effort might be complex and time-consuming but would be a routine undertaking for those of ordinary skill in the art having the benefit of this disclosure.

In the specification, reference may be made to the spatial relationships between various components and to the spatial orientation of various aspects of components as the devices are depicted in the attached drawings. However, as will be recognized by those skilled in the art after a complete reading of the present disclosure, the devices, members, apparatuses, and the like described herein may be positioned in any desired orientation. Thus, the use of terms such as “above,” “below,” “upper,” “lower” or other like terms to describe a spatial relationship between various components or to describe the spatial orientation of aspects of such components should be understood to describe a relative relationship between the components or a spatial orientation of aspects of such components, respectively, as the device described herein may be oriented in any desired direction. In addition, as used herein, the term “coupled” may include direct or indirect coupling by any means, including moving and/or non-moving mechanical connections.

Referring toFIGS.1A-1Din the drawings, a tiltrotor aircraft is schematically illustrated and generally designated10. Aircraft10includes a fuselage12, a wing14and a tail assembly16including control surfaces operable for horizontal and/or vertical stabilization during forward flight. Located proximate the outboard ends of wing14are pylon assemblies18a,18bthat are tiltable relative to wing14between a generally vertical orientation, as best seen inFIG.1A, and a generally horizontal orientation, as best seen inFIGS.1B-1D. Pylon assemblies18a,18beach house a portion of the drive system that is used to rotate rotor assemblies depicted as proprotor assemblies20a,20b, respectively. For example, a proprotor gearbox22ais housed within pylon assembly18aand a proprotor gearbox22bis housed within pylon assembly18b. Proprotor gearbox22aincludes a proprotor gearbox housing24athat is part of the nonrotating airframe structure of aircraft10. Similarly, proprotor gearbox22bincludes a proprotor gearbox housing24bthat is part of the nonrotating airframe structure of aircraft10. Disposed within each of proprotor gearbox22aand proprotor gearbox22bare a plurality of gears, such as planetary gears, used to adjust the engine output to a suitable rotational speed so that the engines and the proprotor assemblies may rotate at optimum speeds in the rotary flight modes of aircraft10.

Each proprotor assembly20a,20bincludes a plurality of proprotor blades26that are operable to be rotated, as best seen inFIGS.1A-1B, operable to be feathered, stopped, clocked and locked, as best seen inFIG.1Cand operable to be folded, as best seen inFIG.1D. Proprotor assembly20ais rotated responsive to torque and rotational energy provided by one or both of engines28a,28bvia a mid-wing gearbox30, a drive shaft32a, proprotor gearbox22aand a drive shaft depicted as mast34a. Similarly, proprotor assembly20bis rotated responsive to torque and rotational energy provided by one or both of engines28a,28bvia mid-wing gearbox30, a drive shaft32b, proprotor gearbox22band a drive shaft depicted as mast34b. Engines28a,28bare located along an aft portion of fuselage12. Engines28a,28bmay be operated in a turboshaft mode, as best seen inFIGS.1A-1Bor a turbofan mode, as best seen inFIGS.1C-1D.

FIG.1Aillustrates aircraft10in VTOL or helicopter flight mode, in which proprotor assemblies20a,20bare rotating in a substantially horizontal plane to provide vertical lift, such that aircraft10flies much like a conventional helicopter. In this configuration, engines28a,28bare operating in turboshaft mode wherein hot combustion gases in each engine28a,28bcause rotation of a power turbine coupled to a respective input shaft of mid-wing gearbox30. Thus, in this configuration, aircraft10is considered to be in a rotary flight mode as proprotor assemblies20a,20bare rotating and operable to provide thrust for aircraft10.FIG.1Billustrates aircraft10in proprotor forward flight mode, in which proprotor assemblies20a,20bare rotating in a substantially vertical plane to provide a forward thrust enabling wing14to provide a lifting force responsive to the forward airspeed, such that aircraft10flies much like a conventional propeller driven aircraft. In this configuration, engines28a,28bare operating in the turboshaft mode and aircraft10is considered to be in the rotary flight mode.

In the rotary flight mode of aircraft10, proprotor assemblies20a,20brotate in opposite directions to provide torque balancing to aircraft10. For example, when viewed from the front of aircraft10in proprotor forward flight mode (FIG.1B) or from the top in helicopter mode (FIG.1A), proprotor assembly20arotates clockwise, as indicated by motion arrows36a, and proprotor assembly20brotates counterclockwise, as indicated by motion arrows36b. In the illustrated embodiment, proprotor assemblies20a,20beach include three proprotor blades26that are uniformly spaced apart circumferentially at approximately 120 degree intervals. It should be understood by those having ordinary skill in the art, however, that the proprotor assemblies of the present disclosure could have proprotor blades with other designs and other configurations including proprotor assemblies having four, five or more proprotor blades. In addition, it should be appreciated that aircraft10can be operated such that proprotor assemblies20bare selectively positioned between proprotor forward flight mode and helicopter mode, which can be referred to as a conversion flight mode.

FIG.1Cillustrates aircraft10in transition between proprotor forward flight mode and airplane forward flight mode, in which engines28a,28bhave been disengaged from proprotor assemblies20a,20band proprotor blades26have been feathered, or oriented to be streamlined in the direction of flight, such that proprotor blades26act as brakes to aerodynamically slow the rotation of proprotor assemblies20a,20b. Alternatively or additionally, the rotation of proprotor assemblies20a,20bmay be slowed or stopped using brake systems38a,38bthat are operably associated with mid-wing gearbox30, as best seen inFIG.1A. In other embodiments, brake systems could be positioned at other locations along drive shafts32a,32b. Preferably, brake systems38a,38binclude position sensors such that drive shafts32a,32bcan be stopped at predetermined rotational positions. By stopping drive shafts32a,32bin known rotational positions, the rotational position of each proprotor assembly20a, is also known. This rotational clocking of proprotor blades26is important to prevent contact with wing14during blade folding and to align each proprotor blade26with a respective blade grip40operably associated with pylon assemblies18a,18bfor blade folding.

Due to the distance between brake systems38a,38band proprotor assemblies20a, as well as the gear systems therebetween, however, use of the position sensors may result in only a coarse rotational clocking of proprotor assemblies20a,20b. Once proprotor assemblies20bhave been slowed or stopped and have been coarsely rotationally clocked, proprotor lockout systems42a,42bdisposed within proprotor gearboxes22a,22bare shifted from a disengaged position to an engaged position to lock proprotor assemblies20a,20bagainst rotation and to precisely rotationally clock proprotor assemblies20a,20bsuch that each proprotor blade26will be circumferentially aligned with one of blade grips40for blade folding. In the illustrated configuration of aircraft10inFIG.1C, engines28a,28bare operating in turbofan mode wherein hot combustion gases in each engine28a,28bcause rotation of a power turbine coupled to an output shaft that is used to power a turbofan that forces bypass air through a fan duct to create forward thrust enabling wing14to provide a lifting force responsive to the forward airspeed, such that aircraft10flies much like a conventional jet aircraft. In this configuration, aircraft10is considered to be in a non-rotary flight mode as proprotor assemblies20a,20bare no longer rotating and thus, not providing thrust for aircraft10.

FIG.1Dillustrates aircraft10in high speed, airplane forward flight mode, in which proprotor blades26have been folded and are oriented substantially parallel to respective pylon assemblies18a,18bto minimize the drag force generated by proprotor blades26. To prevent chatter or other movement of proprotor blades26when folded, proprotor blades26are preferably received within blade grips40of pylon assemblies18a,18b. In this configuration, engines28a,28bare operating in the turbofan mode and aircraft10is considered to be in the non-rotary flight mode. The forward cruising speed of aircraft10can be significantly higher in airplane forward flight mode versus proprotor forward flight mode as the risk of forward airspeed induced proprotor aeroelastic instability has been removed.

Even though aircraft10has been described as having two engines fixed to the fuselage, it should be understood by those having ordinary skill in the art that other engine arrangements are possible and are considered to be within the scope of the present disclosure including, for example, having a single engine that provides torque and rotational energy to both of the proprotor assemblies. In addition, it should be appreciated that tiltrotor aircraft10is merely illustrative of a variety of aircraft that can implement the embodiments disclosed herein. Indeed, the proprotor lockout systems of the present disclosure may be utilized on any type of rotorcraft in which locking of a rotor system against rotation during flight or during storage is desired. Other aircraft implementations can include helicopters, quad tiltrotor aircraft, hybrid aircraft, compound aircraft, unmanned aerial systems and the like. As such, those having ordinary skill in the art will recognize that the proprotor lockout systems disclosed herein can be integrated into a variety of aircraft configurations. It should be appreciated that even though aircraft are particularly well-suited to implement the embodiments of the present disclosure, non-aircraft vehicles and devices can also implement the embodiments.

Even though aircraft10has been described as having proprotor lockout systems42a,42bdisposed within proprotor gearboxes22a,22b, it should be understood by those having ordinary skill in the art that proprotor lockout systems could be positioned at any location along the proprotor drive shaft. For example,FIG.2depicts aircraft10having two standalone proprotor lockout systems44a,44bthat are coupled to nonrotating airframe structure within wing14to prevent relative rotation and relative translation therebetween. In the illustrated embodiment, proprotor lockout system44ais operably associated with proprotor drive shaft32aand configured to selectively prevent rotation of proprotor assembly20a. Likewise, proprotor lockout system44bis operably associated with proprotor drive shaft32band configured to selectively prevent rotation of proprotor assembly20b. As another example,FIG.3depicts aircraft10having two proprotor lockout systems46a,46bthat are integrated into mid-wing gearbox30that includes a mid-wing gearbox housing48that is part of the nonrotating airframe structure of aircraft10. In the illustrated embodiment, proprotor lockout system46ais operably associated with proprotor drive shaft32aand configured to selectively prevent rotation of proprotor assembly20a. Likewise, proprotor lockout system46bis operably associated with proprotor drive shaft32band configured to selectively prevent rotation of proprotor assembly20b.

Referring next toFIGS.4A-4Bin the drawings, various mechanical systems of tiltrotor aircraft10are depicted in a block diagram format. Aircraft10includes a powerplant depicted as engines28a,28bthat have turboshaft modes, represented inFIG.4A, and turbofan modes, represented inFIG.4B. In their turboshaft modes, engines28a,28bprovide torque and rotational energy to mid-wing gearbox30, as indicated by the arrows therebetween. Mid-wing gearbox30receives torque and rotational energy from one or both of engines28a,28band provides torque and rotational energy to proprotor gearboxes22a,22b, as indicated by the arrows therebetween. Proprotor gearbox22areceives torque and rotational energy from mid-wing gearbox30and provides torque and rotational energy to proprotor assembly20a, as indicated by the arrow therebetween. Proprotor gearbox22breceives torque and rotational energy from mid-wing gearbox30and provides torque and rotational energy to proprotor assembly20b, as indicated by the arrow therebetween.

When it is desired to transition aircraft10from proprotor forward flight mode to airplane forward flight mode, engines28a,28bare disengaged from proprotor assemblies20a, as indicated by the dashed lines between engines28a,28b, mid-wing gearbox30and proprotor gearboxes22a,22binFIG.4B. The proprotor blades may now be feathered for aerodynamic braking and/or brake systems may be used to slow or fully stop the rotation of proprotor assemblies20a,20b. Thereafter, aircraft10uses lock assemblies42a,42bto stop, clock and lock proprotor assemblies20a,20b. Lock assemblies42a,42bmay be positioned between any nonrotating airframe structure and any portion of the drive shafts providing torque and rotational energy from engines28a,28bto proprotor assemblies20a,20b. In the illustrated embodiment, lock assemblies42a,42bare proximate to or within proprotor gearboxes22a,22b. As discussed herein, lock assemblies could alternatively be located between mid-wing gearbox and proprotor gearboxes22a,22b, proximate to or within mid-wing gearbox30or other suitable location along the drive shafts. As discussed herein, each lock assemblies42a,42bhas a rotating lock member that is operably associated with the drive shaft and a nonrotating lock member that is operably associated with nonrotating airframe structure.

During rotary flight modes, respective rotating lock members and nonrotating lock members are disengaged from one another. During airplane forward flight mode, respective rotating lock members and nonrotating lock members are engaged with one another. Lock assembly42ais shifted between the disengaged and the engaged positions by actuator50a. Lock assembly42bis shifted between the disengaged and the engaged positions by actuator50b. Actuators50a,50bmay be hydraulically operated actuators, electrically operated actuators including linear actuators and rotary actuators or other suitable types of actuators. For example, actuators50a,50bmay be of the type disclosed and described in U.S. Pat. Nos. 10,843,798 or 10,875,640, the entire contents of each are hereby incorporated by reference.

Once rotation of proprotor assemblies20a,20bhas been suitably slowed or fully stopped, actuators50a,50bare activated, as indicated by the arrows inFIG.4B, to shift lock assemblies42a,42bfrom disengaged positions to engaged positions, preventing rotation of proprotor assemblies20a,20band clocking the proprotor blades to be in rotational alignment with respective blade grips as discussed herein. When it is desired to transition aircraft10from the airplane forward flight mode back to the proprotor forward flight mode, actuators50a,50bare activated, as indicated by the arrows inFIG.4B, to shift lock assemblies42a,42bfrom engaged positions to disengaged positions to allow rotation of proprotor assemblies20a,20b. Thereafter, engines28a,28bare reengaged with proprotor assemblies20a,20b, as indicated by the arrows between engines28a,28b, mid-wing gearbox30and proprotor gearboxes22a,22binFIG.4A, returning aircraft10to the rotary flight mode.

Referring now toFIGS.5A-5Cin the drawings, a lock assembly100will be discussed in detail. Lock assembly100is representative of lock assemblies42a,42bofFIGS.1A and4A-4B, lock assemblies44a,44bofFIG.2and lock assemblies46a,46bofFIG.3. Lock assembly100includes a rotating lock member102and a nonrotating lock member104. Rotating lock member102is coupled to a mast106at flange connection108and to a proprotor drive shaft110at a spline connection112(seeFIG.8) such that rotating lock member102rotates with mast106during proprotor operations, as indicated by the arrow inFIG.5A. Rotating lock member102includes a collar assembly114having in internal splines116and an upper flange end118, as best seen inFIG.8. Collar assembly114has three openings, only opening120being visible inFIG.8, that receive bearing pins therethrough such as bearing pin122received through opening120. Each bearing pin is part of a bearing assembly124a,124b,124c. In the illustrated embodiment, bearing assemblies124a,124b,124care spherical roller bearings having outer roller surfaces. For example, bearing assembly124ahas a spherical element126and an outer roller surface128, as best seen inFIG.8. Using spherical roller bearings is beneficial in overcoming any misalignment between the axis of rotation130of rotating lock member102and a central axis132of nonrotating lock member104(seeFIGS.9A-9B) during engagement operations. Depending upon the specific implementation, the outer roller surfaces may be hardened roller surfaces, which helps to prolong the life of bearing assemblies124a,124b,124cor may be high lubricity roller surfaces, which reduces friction between bearing assemblies124a,124b,124cand contact surfaces. In the illustrated embodiment, bearing assemblies124a,124b,124care uniformly circumferentially distributed at 120 degree intervals about collar assembly114. In other embodiments, a rotating lock member could have other numbers of bearing assemblies both less than or greater than three in other uniform or nonuniform circumferential distributions.

Nonrotating lock member104is coupled to a nonrotating airframe structure (not pictured inFIGS.5A-5Cfor clarity) such as the housing of a gearbox or a wing airframe structure. For example, nonrotating lock member104may be coupled to the nonrotating airframe structure at a flange connection formed by bolting flange134to a mating flange of the nonrotating airframe structure. Nonrotating lock member104includes a sleeve136that supports flange134and a piston138that is slidably received within sleeve136. Sleeve136is depicted with a section cutaway to better reveal components therein. Sleeve136and piston138include a nonrotation feature to prevent relative rotation therebetween depicted in the illustrated embodiment as a plurality of exterior lugs140on piston138that mate with an equal plurality of interior rails (not visible) on sleeve136. In other embodiments, a sleeve and piston of a nonrotating lock member could have other types of nonrotation features such as mating splines. At its upper end, piston138includes a cradle142having three asymmetric slots, such as asymmetric slot144, as best seen inFIG.7.

Each asymmetric slot includes a leading ramp and a trailing stop, such as leading ramp146and trailing stop148of asymmetric slot144. In the illustrated embodiment, leading ramp146has a curved upper profile with a progressively decreasing angle between about 60 degrees (see angle150inFIG.9B) to about 30 degrees (see angle152inFIG.9B). In other embodiments, leading ramp146could have other profile configurations including non-curved profiles, profiles having a constant angle, profiles having a step function, profiles having a horizontal portion or other suitable profiles. Trailing stop148has a surface154that is substantially parallel with central axis132. The parallel surface154of trailing stop148and the profile of leading ramp146create the asymmetry of asymmetric slot144such that an entry gap156of asymmetric slot144is wider than a base gap158of asymmetric slot144. In the illustrated embodiment, entry gap156is at least twice as wide as base gap158. In other embodiments, the ratio of the entry gap to the base gap could be greater than or less than 2 to 1 such as 1.5 to 1, 3 to 1, 4 to 1 or other suitable ratio, wherein maximizing the width of entry gap156is desirable.

The combination of the large entry gap156, the curved upper profile of leading ramp146and the parallel surface154of trailing stop148enables entry of a coarsely aligned bearing assembly into asymmetric slot144, provides a guided path for the received bearing assembly and offers a positive seat for the received bearing assembly. For example, bearing assembly124ais fully seated in asymmetric slot144when bearing assembly124ahas two points of contact within asymmetric slot144at contact point160with trailing stop148and contact point162with leading ramp146. In addition, the combination of the outer roller surface128of bearing assembly124aand the angle152of leading ramp146proximate contact point162provides freedom for bearing assembly124ato exit asymmetric slot144when it is desired to disengage lock assembly100. In the illustrated embodiment, the asymmetric slots are uniformly circumferentially distributed at 120 degree intervals about cradle142. In other embodiments, a cradle could have other numbers of asymmetric slots both less than or greater than three in other uniform or nonuniform circumferential distributions with the number of asymmetric slots and the circumferential distribution thereof matching that of the bearing assemblies of the rotating lock member.

A first operating scenario of lock assembly100will now be described with reference toFIGS.5A-5C. During rotary flight modes, rotating lock member102and nonrotating lock member104are disengaged from one another to allow rotation of rotating lock members102and thus mast106as indicated by the arrow inFIG.5A. When it is desired to transition aircraft10from proprotor forward flight mode to airplane forward flight mode, the engines are disengaged from the proprotor assemblies and the proprotor blades are feathered for aerodynamic braking and/or brake systems may be used to stop the rotation of the proprotor assemblies. In the illustrated embodiment depicted inFIG.5B, each of the bearing assemblies124a,124b,124chas stopped in substantial circumferential alignment with a base gap of a respective asymmetric slot144using, for example, position sensors associated with the brake systems to stop the associated drive shaft in a desired rotational position. Lock assembly100is now operated from the disengaged position (FIG.5B) to the engaged position (FIG.5C) responsive to hydraulic or electrical actuator commands that shift piston138relative to sleeve136which results in cradle142moving toward radial bearings124a,124b,124cuntil each of radial bearings124a,124b,124cis seated within one of asymmetric slots144in contact with both trailing stop148and leading ramp146. In this position, rotating lock member102is fixed against rotation by nonrotating lock member104which prevents rotation of the associated proprotor assembly and clocks the proprotor blades to be in rotational alignment with respective blade grips for blade folding as discussed herein.

When it is desired to transition aircraft10from the airplane forward flight mode back to the proprotor forward flight mode, lock assembly100is operated from the engaged position (FIG.5C) to the disengaged position (FIG.5B) responsive to hydraulic or electrical actuator commands that shift piston138relative to sleeve136. This unseats each of radial bearings124a,124b,124cfrom the respective asymmetric slot144as cradle142moves away from radial bearings124a,124b,124c. This axial movement continues until radial bearings124a,124b,124care axially separated from cradle142and able to rotate relative thereto as indicated by the arrow inFIG.5A.

A second operating scenario of lock assembly100will now be described with reference toFIGS.6A-6C. In this case, when it is desired to transition aircraft10from proprotor forward flight mode to airplane forward flight mode, the engines are disengaged from the proprotor assemblies and the proprotor blades are feathered for aerodynamic braking and/or brake systems may be used to stop the rotation of the proprotor assemblies. In the illustrated embodiment depicted inFIG.6B, each of the bearing assemblies124a,124b,124chas stopped in circumferential misalignment with a base gap of a respective asymmetric slot144but within circumferential alignment with an entry gap of a respective asymmetric slot144. Lock assembly100is now actuated to shift piston138relative to sleeve136which results in cradle142moving toward radial bearings124a,124b,124c. Upon contact between a leading ramp of each asymmetric slot144and one of the radial bearings124a,124b,124c, rotating lock member102is urged to rotate, as indicated by the arrows inFIG.6B. The leading ramps now serve as guides for radial bearings124a,124b,124c, as radial bearings124a,124b,124cmove along the leading ramps responsive to the continued axially movement of cradle142until each of radial bearings124a,124b,124cis seated within one of asymmetric slots144in contact with both trailing stop148and leading ramp146. In this position, rotating lock member102is fixed against rotation by nonrotating lock member104which prevents rotation of the associated proprotor assembly and clocks the proprotor blades to be in rotational alignment with respective blade grips for blade folding as discussed herein.

When it is desired to transition aircraft10from the airplane forward flight mode back to the proprotor forward flight mode, lock assembly100is operated from the engaged position to the disengaged position responsive to hydraulic or electrical actuator commands that shift piston138relative to sleeve136. The actuation unseats each of radial bearings124a,124b,124cfrom the respective asymmetric slot144as cradle142moves away from radial bearings124a,124b,124c. This axial movement continues until radial bearings124a,124b,124care axially separated from cradle142and able to rotate relative thereto as indicated by the arrow inFIG.6A.

A third operating scenario of lock assembly100will now be described with reference toFIGS.6A-6C. In this case, when it is desired to transition aircraft10from proprotor forward flight mode to airplane forward flight mode, the engines are disengaged from the proprotor assemblies and the proprotor blades are feathered for aerodynamic braking and/or brake systems may be used to slow the rotation of the proprotor assemblies. In the illustrated embodiment, rotating lock member102continues to slowly rotate with the rotating proprotor assembly as indicated by the arrows inFIG.6B. Lock assembly100is now actuated to shift piston138relative to sleeve136which results in cradle142moving toward radial bearings124a,124b,124c. Due to the configuration of asymmetric slots144of cradle142, each of the moving radial bearings124a,124b,124cis captured in an entry gap of one of the asymmetric slots144. Depending upon the speed of rotation of radial bearings124a,124b,124crelative to the speed of axial movement of cradle142, the leading ramps will serve as guides for radial bearings124a,124b,124cuntil radial bearings124a,124b,124care seating within the asymmetric slots144, which stops the rotation of rotating lock member102or radial bearings124a,124b,124cwill contact respective trailing stops148, which stops the rotation of rotating lock member102and further axial movement of cradle142seats radial bearings124a,124b,124c. In either case, rotating lock member102is now fixed against rotation by nonrotating lock member104which prevents rotation of the associated proprotor assembly and clocks the proprotor blades to be in rotational alignment with respective blade grips for blade folding as discussed herein. As should be apparent to those having ordinary skill in the art, for proprotor assemblies rotating in the opposite direction as that depicted inFIGS.6A-6B, the orientation of the leading ramps and the trailing stops of the asymmetric slots would be reversed such that moving radial bearings would be properly captured, guided, stopped and seated in the asymmetric slots.

When it is desired to transition aircraft10from the airplane forward flight mode back to the proprotor forward flight mode, lock assembly100is operated from the engaged position to the disengaged position responsive to hydraulic or electrical actuator commands that shift piston138relative to sleeve136. The actuation unseats each of radial bearings124a,124b,124cfrom the respective asymmetric slot144as cradle142moves away from radial bearings124a,124b,124c. This axial movement continues until radial bearings124a,124b,124care axially separated from cradle142and able to rotate relative thereto as indicated by the arrow inFIG.6A.

The foregoing description of embodiments of the disclosure has been presented for purposes of illustration and description. It is not intended to be exhaustive or to limit the disclosure to the precise form disclosed, and modifications and variations are possible in light of the above teachings or may be acquired from practice of the disclosure. The embodiments were chosen and described in order to explain the principals of the disclosure and its practical application to enable one skilled in the art to utilize the disclosure in various embodiments and with various modifications as are suited to the particular use contemplated. Other substitutions, modifications, changes and omissions may be made in the design, operating conditions and arrangement of the embodiments without departing from the scope of the present disclosure. Such modifications and combinations of the illustrative embodiments as well as other embodiments will be apparent to persons skilled in the art upon reference to the description. It is, therefore, intended that the appended claims encompass any such modifications or embodiments.