Patent Publication Number: US-2021179264-A1

Title: Advanced Emergency Collective Actuator with Friction Pull-Off and Method for a Helicopter

Description:
RELATED APPLICATION 
     The present application is a continuation application of copending U.S. patent application Ser. No. 15/926,972 filed on Mar. 20, 2018, which is a continuation application of U.S. patent application Ser. No. 15/158,521 filed on May 18, 2016 and issued as U.S. Pat. No. 9,957,041 on May 1, 2018, which claims priority from U.S. Provisional Patent Application Ser. No. 62/165,085 filed on May 21, 2015, each of which are hereby incorporated by reference in their entirety. 
    
    
     BACKGROUND 
     The present invention is related at least generally to helicopter control systems and, more particularly, to an emergency collective actuator having a friction pull-off and associated method for a helicopter. 
     It is recognized in the prior art such as is exemplified by U.S. Pat. No. 4,667,909 (hereinafter the &#39;909 patent) that a sudden power failure during the flight of a helicopter requires the immediate attention of the pilot to convert to autorotation by lowering the collective pitch of the main rotor blades of the helicopter. A failure to timely reduce the collective can result in stalling the rotor blades. Such stalling of the rotor blades will generally produce a catastrophic crash wherein the helicopter, quite literally, falls from the sky. One example of such an accident, which likely involved a rotor stall, occurred in the United Kingdom in March of 1998 and is the subject of AAIB Bulletin no. 11/98. Such an accident will generally be fatal to anyone onboard the aircraft. The particular helicopter that was involved in this accident was the Robinson R22, which is a lightweight helicopter having a low-inertia rotor system. It should be appreciated that a low-inertia rotor system can be stalled more easily than a rotor system having a greater level of inertia. The subject accident report outlines operational conditions for the Robinson R22 under which rotor speed will decay to an unrecoverable value in less than 1 second during a climb. 
     As a solution, Applicant developed an emergency collective pull-down apparatus that is described in U.S. Pat. No. 8,360,369 (hereinafter, the &#39;369 patent), issued Nov. 23, 2010, and U.S. Pat. No. 8,651,425 (hereinafter, the 425 patent), issued May 23, 2012, each of which patents is hereby incorporated by reference. The disclosed apparatus, of the &#39;369 and &#39;425 patents, applies a collective pull-down force directly to the collective control. While the &#39;369 and &#39;425 patents represented a significant leap in the then-existing state-of-the-art and continue to provide benefits in terms of enhancing flight safety in a light helicopter, Applicant now brings to light an emergency collective actuator which provides still further benefits. 
     The foregoing examples of the related art and limitations related therewith are intended to be illustrative and not exclusive. Other limitations of the related art will become apparent to those of skill in the art upon a reading of the specification and a study of the drawings. 
     SUMMARY 
     The following embodiments and aspects thereof are described and illustrated in conjunction with systems, tools and methods which are meant to be exemplary and illustrative, not limiting in scope. In various embodiments, one or more of the above-described problems have been reduced or eliminated, while other embodiments are directed to other improvements. 
     In general, an apparatus is described for use with a helicopter including a rotor system having a main rotor with an adjustable pitch that is controlled at least in part by a pilot using a collective control and the collective control pivotally supports a friction control lever as part of a friction control that is engageable by the pilot to selectively increase a control force that is required as a minimum to move the collective control. 
     In one aspect of the disclosure, the apparatus includes an actuator including a motor having an output shaft for rotation to change the adjustable pitch by exerting an actuation force and an actuator linkage that engages the friction lever to apply the actuation force directly to the friction control lever such that the actuation force initially disengages the friction control to decrease the control force and, thereafter, reduces the adjustable pitch toward a minimum collective pitch position. A control arrangement is configured to receive a signal that is indicative of a low rotor RPM condition and to respond to the signal by activating the actuator arrangement to exert the actuation force. 
     In another aspect of the disclosure, an actuator arrangement includes a motor having an output shaft for rotation to change the adjustable pitch by exerting an actuation force and a clutch supported by the output shaft and in operative communication with the collective control such that the clutch slips relative to the output shaft (i) to allow the pilot to overcome the actuation force using the collective control and (ii) responsive to an engagement of the friction control by the pilot, but otherwise the clutch co-rotates with the motor shaft to bias the adjustable pitch toward a minimum collective pitch position. A control arrangement is configured to receive a signal that is indicative of a low rotor RPM condition and to respond to the signal by activating the actuator arrangement to exert the actuation force. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Example embodiments are illustrated in referenced figures of the drawings. It is intended that the embodiments and figures disclosed herein are to be illustrative rather than limiting. 
         FIG. 1  is a diagrammatic view, in perspective, of an embodiment of a helicopter collective control coupled with an emergency collective actuator of the present disclosure. 
         FIG. 2  is another diagrammatic view, taken from a different perspective, of the embodiment of the helicopter collective control and emergency collective actuator of  FIG. 1 . 
         FIGS. 3 and 4  are further enlarged cutaway diagrammatic views, in perspective, illustrating details of a friction control and collective control as well as an embodiment of the interface of the friction control to the emergency collective control of the present application. 
         FIG. 5  is a flow diagram illustrating an embodiment of a method for operating an emergency collective actuator in accordance with the present disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     The following description is presented to enable one of ordinary skill in the art to make and use the invention and is provided in the context of a patent application and its requirements. Various modifications to the described embodiments will be readily apparent to those skilled in the art and the generic principles taught herein may be applied to other embodiments. Thus, the present invention is not intended to be limited to the embodiment shown, but is to be accorded the widest scope consistent with the principles and features described herein including modifications and equivalents. It is noted that the drawings are not to scale and are diagrammatic in nature in a way that is thought to best illustrate features of interest. Descriptive terminology may be adopted for purposes of enhancing the reader&#39;s understanding, with respect to the various views provided in the figures, and is in no way intended as being limiting. 
     As discussed above, the &#39;369 and &#39;425 patents continue to provide enhanced flight safety in light helicopters. At this juncture, however, Applicant recognizes that still further improvements can be provided. In this regard, weight is a precious commodity, particularly in light helicopters. Any reduction of the weight of control components in a helicopter is desirable with the caveat that there can be no compromise in flight safety solely for the sake of weight reduction. One approach to this concern is to simply substitute redesigned lightweight components for original components, with the lightweight components being proven as even more robust than the original components. Applicant, however, brings to light a completely different approach that allows for a reduction in the physical weight as well as size of an emergency collective actuator without introducing a safety compromise. By way of background, most helicopters include a friction control that allows the pilot to set or lock the collective stick or control into a given position such that pilot can at least momentarily release his or her hand from the collective stick to perform other actions. During normal operation of the helicopter, the collective control will not move when the friction control is engaged, although the pilot can overcome the resistance of the friction control and move the collective stick, for example, in response to an emergency. As will be seen, the advanced approach of the present application involves automated manipulation of the friction control that is provided as a standard feature in association with the helicopter. This advanced approach provides for reducing both the physical weight and dimensions of the emergency collective actuator. 
     Attention is now directed to the figures wherein like reference numbers may refer to like items throughout the various views.  FIGS. 1 and 2  are diagrammatic illustrations, in differing perspective views, of a helicopter collective control that is generally indicated by the reference number  10  and which is representative of the collective control in a helicopter such as, for example, the Robinson R22. It is noted that the collective control changes the pitch of all the blades of the main rotor in unison or collectively for purposes of controlling lift. Collective control  10  pivots about points  12  proximate to a pivot end of the collective control. A handle or free end  20  of the collective control is configured for gripping by a pilot and includes a throttle control that is actuatable by twisting handle  20  as indicated by a double headed arrow  22 . The pilot can increase the collective by moving handle  20  pivotally in the direction indicated by an arrow  24  or reduce collective by moving handle  20  oppositely.  FIGS. 1 and 2  illustrate the collective control in a fully raised position while  FIG. 1  further illustrates the collective control at a fully lowered position in phantom using dashed lines and indicated by the reference number  10 ′. 
     Attention is now directed to  FIGS. 3 and 4  in conjunction with  FIGS. 1 and 2 .  FIGS. 3 and 4  are diagrammatic, further enlarged partially cut-away views, in perspective, illustrating details of a friction control, generally indicated by the reference number  30 . The friction control includes a friction control lever  34  having a distal end that supports a control knob  38  that is accessible by the pilot. An opposing end of the friction control lever is supported by a shaft  40  with the friction control lever being clamped to the shaft. The latter is threadingly received by a tube  44  ( FIGS. 3 and 4 ) that is itself supported by the collective control. As best seen in  FIG. 4 , shaft  40  is terminated by a head  50 . The shaft, proximate to head  50  extends through an elongated slot  54  that is defined by a friction bar  58 . Shaft  40  supports a pair of friction washers such that a friction washer  60  is received against each side of friction bar  58  and captured between tube  44  and head  50 . The friction control is shown in an engaged position such that the pilot has rotated friction control lever  34  in a direction that is indicated by an arrow  68 . Accordingly, the rotation of the friction control lever causes shaft  40  to threadingly engage tube  44  in a way that selectively biases friction washers  60  against the sides of friction bar  58  to allow the pilot to at least temporarily lock the collective control in position such that the friction bar will not move inadvertently, but the pilot can affirmatively move the collective control by overcoming the friction force. During movement of the collective control, shaft  40  slides in slot  54  of the friction bar to allow for normal movement of the collective by the pilot and to allow the pilot to set the collective to any selected position using the friction control so that the pilot is able to at least momentarily release his or her hand from the collective control. Having described the friction control of the Robinson R22, it should be appreciated that the teachings that have been brought to light herein can readily be applied without limitation to pull-off the friction control of other helicopters prior to lowering the collective, irrespective of whether the friction control is implemented with mechanical or electronic actuation. 
     Referring again to  FIG. 1 , an emergency friction pull-off collective actuator is generally indicated by the reference number  100 . The emergency actuator includes a main unit  110  that can be configured to receive an actuation signal  114  such as, for example, a Low RPM signal that is generated by the helicopter. In another embodiment, an autopilot can generate the activation signal. In the instance of the Robinson R22, the Low RPM signal is produced when the rotor speed falls to 97% of normal or less. Normally, the Low RPM signal is used to actuate a warning horn and light to draw the pilot&#39;s attention to the status of the rotor speed. The manner in which main unit  110  uses the activation signal will become evident in the discussions which follow. 
     A control cable or actuator linkage  112  extends from main unit  110  to a guide tube arrangement  120  (best seen in  FIGS. 3 and 4 ). The guide tube arrangement can be clamped, as shown, or otherwise fixed to a suitable intermediate position on the collective control that is forward of friction control  30 . It is noted that the term “forward”, with reference to direction, is intended to indicate a direction toward the front or nose of the helicopter. The guide tube arrangement can be located sufficiently away from the friction control and the pivot end of the collective control so as to avoid any interference with normal operation of the collective control or with actuation by the pilot. The guide tube arrangement includes a guide tube  124  through which cable  112  is extended such that the guide tube translates motion of the cable from a generally vertical direction to a direction that is at least generally aligned with the elongated length of the collective control. The guide tube can be formed from any suitable material such as, for example, stainless steel and is not limited to the specific shape that has been illustrated. In the present embodiment, cable  112  is terminated by an end fitting  130  that is pivotally received at an intermediate position along a length of friction control lever  34 , for example, using a fastener  134 . 
     Main unit  110  includes a pulley arrangement  140  that receives cable  112  and a motor  144  can drive a gear box  146  for rotating the pulley arrangement in a direction that takes up the cable. The pulley arrangement can apply a light retraction force on cable  112  that is sufficient to avoid slack in the cable as the pilot moves the collective. In response to actuation signal  114 , main unit  110  retracts cable  112  so as to apply force to friction control lever  34  at least generally in a direction that is indicated by an arrow  150 . In this way, friction control lever  34 , if engaged, is initially moved in a disengagement direction, opposite arrow  68 , such that friction control  30  is at least essentially disengaged without moving the collective control. Once the friction control lever rotates at least substantially to a disengaged or released position (indicated by the reference number  34 ′ and shown in phantom using dashed lines in  FIG. 3 ) at which the friction lever stops rotating, the force that is applied to friction arm  34  at the end of cable  112  is then translated to an at least generally vertical direction by guide tube  124  to pull down collective  12  toward a minimum collective position. Of course, if the friction control is initially in a released position, the actuation force automatically serves to immediately lower the collective. The actuation force can be applied, by way of non-limiting example, for a suitable period of time, for instance, up to approximately 3 seconds. Actuator  110  can include a clutch  152  such that the clutch can slip, if necessary, once the collective control reaches the minimum collective position. The pilot can also apply an override force to cause the clutch to slip such that the pilot can maintain the position of the collective control or raise the collective control, irrespective of the application of the actuation force. In an embodiment, the clutch can be configured such that the clutch slips if the friction control is engaged to at least some limited extent, thereby maintaining the current position of the collective control. This could occur, for example, responsive to the pilot actively holding the friction control lever in an engaged position, as opposed to holding the collective in position, during the application of the actuation force or if the friction lever is somehow jammed. 
     Applicants recognize that less than 4 pounds of force, as measured at the pull location on the friction lever, is needed to move the friction lever forward in a disengagement direction while over 6 pounds of force, as measured at the free end of the collective, is needed to move the collective control arm toward the minimum collective position, even when the friction control is in the disengaged position. Applicants further recognize that with the friction control engaged, even to a relatively limited extent, the force required to move the collective control, as applied by either the pilot or the emergency actuator, can be much higher. The significant differential between a first amount of force that is needed to move the friction control lever toward the disengaged position and a second, higher amount of force that is needed to move the collective control toward the minimum position, irrespective of a current setting of the friction control, allows the emergency actuator of the present disclosure to disengage the friction control prior to lowering the collective control. On this basis, the overall physical size of actuator  110  can be reduced, utilizing a relatively smaller motor  144  and gearbox  146 . Further, a clutch override force that is applied by a pilot to the collective to prevent the emergency actuator from lowering the collective control can be reduced, thereby making the helicopter more flyable. The reduction of the clutch override force further assists in reducing the tendency of the pilot to apply an upward impulse of force to the collective control when the emergency actuator terminates the application of the actuation force. 
     Operation of the emergency actuator can proceed automatically in response to reception of actuation signal  114  and can be initiated essentially instantaneously, at least from a practical standpoint, e.g. in 0.001 seconds (1 ms) or less in response to the actuation signal, but in any event significantly less than the reaction time of even an attentive pilot. In one embodiment, the reaction time of main unit  110  can be adjustable, and yet remain far less than the typical reaction time of the pilot to provide a significant safety enhancement. Typically, however, the circuitry will be allowed to react as quickly as it is capable of reacting without introducing any additional delay. As will be described in further detail, the retraction force that is applied to collective control  10  by emergency actuator  100  can be overcome by the pilot, although the force is sufficient to inform the pilot that the unit is attempting to lower the collective when the left hand of the pilot is holding collective handle  20 . In an embodiment, the retraction force can be configured such that the collective can be lowered by the emergency actuator only if friction control lever  34  has been moved at least approximately to or within some limited range from a released or disengaged position. 
     Attention is now directed to  FIG. 5  which illustrates an embodiment of a method for operating an emergency collective actuator, according to the present disclosure, having friction pull-off capability, generally indicated by the reference number  200 . The method begins at  204  and proceeds to  208  which receives the activation signal. As discussed above, the activation signal, for example, can be a low RPM signal, a signal that is generated by an autopilot or any suitable signal. At  210 , an actuator force is applied to the friction control lever to release the friction control from an engaged position, if the friction control is in the engaged position, thereby moving the friction control to a disengaged position. At  214 , application of the actuator force continues to lower the collective toward a minimum collective position. 
     In view of the foregoing, a significant reduction in the size and weight of the emergency collective actuator of the present disclosure is realized. As a result of eliminating the need to overcome additional resistance due to an engaged friction control, the magnitude of actuation force that is needed to pull down the collective does not exceed a minimum amount of force that is need to move the collective stick with the friction control in a disengaged position. Based on this sweeping reduction in the magnitude of actuation force that is needed, virtually all the components of the emergency collective actuator can be made smaller and/or lighter. For example, a smaller electrical drive motor can be used which consumes a lesser amount of electrical power. As another example, the drive motor can drive a smaller, lighter gearbox. Still further benefits are attendant to the advanced emergency collective actuator of the present disclosure. For example, if the pilot chooses to override the actuator from pulling down the collective stick, the pilot has the option of simply engaging and/or holding the friction control lever, as opposed to the collective stick itself. As another, benefit Applicant submits that the relatively lower magnitude of collective actuation force that is applied is less likely to result in over compensation by the pilot when overriding the actuation force. 
     While a number of exemplary aspects and embodiments have been discussed above, those of skill in the art will recognize certain modifications, permutations, additions and sub-combinations thereof. For example, in some embodiments, a rigid linkage can be used without the need for a flexible cable for purposes of pulling off the friction control and, thereafter, lowering the collective control. It is therefore intended that the following appended claims and claims hereafter introduced are interpreted to include all such modifications, permutations, additions and sub-combinations as are within their true spirit and scope.