Patent Publication Number: US-11027854-B2

Title: Precision operator for an aircraft autothrottle or autopilot system with engine performance adjust

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of U.S. patent application Ser. No. 16/159,348, titled “Precision Operator for an Aircraft Autothrottle or Autopilot System with Engine Performance Adjust” filed on Oct. 12, 2018, which is a continuation-in-part of U.S. patent application Ser. No. 15/900,542, entitled “Precision Operator for an Aircraft Autothrottle or Autopilot System With Engine Performance Adjust” filed Feb. 20, 2018, which is a continuation-in-part of PCT/US2016/045002, entitled “Precision Operator for an Aircraft Autothrottle or Autopilot System,” filed Aug. 1, 2016, and claims priority to U.S. Provisional Patent Application No. 62/250,819, entitled “Precision Operator for an Aircraft Autothrottle or Autopilot System,” filed Nov. 4, 2015; and U.S. Provisional Patent Application No. 62/336,200, entitled “Precision Operator for an Aircraft Autothrottle or Autopilot System,” filed May 13, 2016, all of which are incorporated herein by reference in their entirety. 
    
    
     FIELD OF THE INVENTION 
     The disclosed embodiments relate to an aircraft autopilot system. In particular, the disclosed embodiments relate to a precision operator for an aircraft autopilot system, and more specifically to an arrangement by which selective control for automated mechanical adjustment of aircraft throttle controls and/or aircraft flight control surfaces can be effected while accommodating ready manual override of the automated operator when deemed necessary or otherwise at the behest of the pilot or other operator of the aircraft. Specifically, the autothrottle will handle a rapid decrease or increase of power in a regulated manner despite a vehicle operator&#39;s attempt to override the autothrottle in certain situations, such as a go round. 
     BACKGROUND OF THE INVENTION 
     Aircraft flight decks have become increasingly sophisticated and rely to a large extent on technology and automated controls that have significantly reduced pilot workload and enhanced systems reliability and efficiency and, as such, passenger safety. In addition to advanced navigation capabilities provided by, for example, GPS and graphical displays that contribute to greatly improve situational and operational status awareness, advances in autopilot systems have proven of tremendous assistance to pilots in maintaining both aircraft control and the smooth and efficient operation of those aircraft that are provided with such capabilities. 
     Autopilot systems provide functions that range from, at the lowest end of the range of capabilities, simple wing leveling to, in more advanced systems, aircraft directional and course control to maintain and track a selected course, altitude maintenance and adjustment control, and adjustments to the aircraft throttle(s) to maintain and effect desired changes in aircraft velocity. 
     Automated control of the aircraft throttle(s), in particular, presents special problems that have, in the past, limited such capabilities to only the largest or, at least, the most technologically complex and advanced aircraft, such as large commercial airline passenger jets, advanced regional and general aviation jets, and high-end turbine propeller airplanes. Such autothrottles provide the ability to realize truly automated, hands-off control of the aircraft, thus providing increased aircraft operating efficiencies, reducing cost in, for example, the consumption of fuel, and vastly decreasing pilot workload and thereby notably increasing flight safety. But providing autothrottle capabilities in an aircraft requires, with the technologies currently in use, physical, spatial and mechanical accommodations that limit this functionality to only the largest and/or most technologically advanced aircraft which, in most cases, must be designed and constructed to include and utilize autothrottle functionality. 
     In most aircraft, the throttle(s)—which are selectively adjustable to cause the engine(s) to generate a predetermined amount of power or thrust to propel the aircraft at a desired velocity—are adjusted by pilot-controlled manual override displacement of one or more graspable handles on levers that are pivotally mounted for rotation through a limited arc in a throttle quadrant in the aircraft cockpit or flight control deck. These levers are typically connected to the engines or engine controllers by control cables that are longitudinally displaced as the positions of the throttle levers are pivotally adjusted. 
     In almost any aircraft, not insignificant forces must be applied to the throttle levers—whether manually by a pilot or by an operating motor of an autothrottle system—to vary or adjust the pivoted positions of the levers. The motors of the system, therefore, must be fairly robust, both in size and weight (to provide sufficient torque and operating forces applied to the throttle lever) and in construction (to assure continued reliability through tens of thousands of activations and operations). As a consequence, only aircraft specifically designed and constructed with sufficient clearances and space to accommodate these motors and associated elements at, in and/or alongside the throttles quadrant of the cockpit, and capable of accepting the significant additional weight associated with these systems and their component parts, are able to incorporate such autothrottles into and with their flight controls. There is moreover virtually no ability to retrofit or add autothrottle capabilities into existing aircraft that have not already been specially designed and constructed to accommodate the associated operating components of an autothrottle system. 
     It is in addition important, to assure safe operation of the aircraft under continued control by the pilot, that the pilot can quickly and easily override or otherwise assume manual control of the throttles from an activated autothrottle system in the event that operating conditions in the aircraft may suddenly require that the pilot assume immediate physical control of the throttles, as in an emergency or any circumstance in which the pilot deems it appropriate, without having to first manually disengage the autopilot or autothrottle system(s). Such circumstances, however may have a detrimental result in that sudden pilot engagement may cause operations of the aircraft throttle control outside of a desired throttle range. Such an occurrence can lead to slow engine responses or even a stalling condition at a worst case scenario. Accordingly, an improved autothrottle is beneficial to deter or prevent pilot operation of an autothrottle outside of a desired operating range. 
     SUMMARY OF THE INVENTION 
     The disclosed embodiments are directed to an aircraft autopilot/autothrottle operator arrangement that is compact, lightweight, reliable and readily installable in an aircraft, even in aircraft in which no special accommodation for adding or providing autopilot/autothrottle capabilities have been designed into or provided for the aircraft, and which can be safely and easily overridden by a pilot wishing to quickly assume manual control of the throttle(s) when under the control of the autopilot/autothrottle system. The disclosed embodiments provide such an operator arrangement that can also be applied, with like advantageous functionality, as part of or in conjunction with an aircraft autopilot system to control the movements of control surfaces of the aircraft whose variable positions are adjustable to control, for example, the pitch, roll and yaw of the aircraft. 
     The disclosed embodiments provides an aircraft autopilot/autothrottle operator that exhibits a number of significant advantages over those currently in widespread use. First, the inventive arrangement is relatively lightweight, especially as compared to current autopilot/autothrottle operating arrangements and components. Second, the inventive arrangement is notably simplified, as compared to current autopilot/autothrottle operating arrangements, which can provide significant increases in physical and operating reliability. Third, the inventive arrangement is notably more compact than current autopilot/autothrottle operating arrangements and is therefore installable in a wider range of aircraft of widely varying size. Fourth, the inventive arrangement is based on the use of a linear operator that is activated from a position remote from the throttle handle pivot, thus allowing its installation—either at the time of initial construction or as an add-on or retrofit to an existing structure—in aircraft having a relatively compact throttle quadrant or that have not otherwise been specially designed to accommodate a conventional autopilot/autothrottle and its heavy-duty motors and clutches and which would otherwise be mounted at and proximate the pivot points of the throttle handles. Fifth, the actuator utilized in the inventive arrangement does not require separate or integrated clutches or clutch components and instead provides inherent override capabilities, and neither does it require a series of gears between an operating motor and its attachment to the throttle handle—thereby greatly decreasing complexity, weight and physical space requirements and increasing operating reliability. 
     In one aspect, the disclosed embodiments provide an autopilot system including a motor configured to impart rotational movement to an elongated shaft extending from the motor, the motor being mounted on a support; an actuator assembly operatively connected to the shaft and to an attachment end of a throttle lever, the throttle lever having a control end, opposite to the attachment end, to which manual force can be applied, and the actuator assembly has a plurality of bearings arranged to apply a thrust force to a longitudinally elongated surface of the shaft such that the actuator assembly is operably translated longitudinally along the shaft surface in response to motor-imparted rotation of the shaft. The shaft surface is smoothly continuous and longitudinally unbroken along its elongation so as to allow the actuator assembly to longitudinally slip along the shaft elongation irrespective of any shaft rotation that may be concurrently imparted by the motor when the thrust force is exceeded by a linear force manually applied at the throttle lever to the actuator assembly; and an electronic controller configured to control the motor to cause movement of the throttle lever so that the motor moves the actuator assembly along the shaft based at least in part on an engine operating parameter monitored by the controller. 
     The disclosed embodiments may include one or more of the following features: a position sensor operatively connected between the motor and a moving portion of the actuator assembly and monitored by the controller; the controller is configured to cause the throttle lever to vibrate, thereby providing haptic feedback to a user under a defined condition; when a condition exists such that an actual engine performance differs from a desired engine performance, the autothrottle operatively advances or retards the throttle lever for optimal performance of the engine over different regions of engine power output; the controller is configured to monitor one or more of air speed, ground speed, and external temperature to determine a windshear condition; the controller is configured to disconnect the autothrottle when the windshear condition is detected to prevent automatic thrust reduction; the controller is configured to monitor multiple engine parameters to detect a loss of an engine and to compute an amount of rudder authority loss due to a reduction of airflow over a rudder; the controller is configured to adjust yaw by varying a necessary reduction in thrust from a remaining engine by a relationship: Max thrust*(IAS/(Vmca+3))∧2, where IAS is indicated air speed and Vmca is a minimum controllable air speed with the lost engine; the motor is a bidirectional stepper motor; the monitored engine parameter comprises at least one of temperature, speed, pressure ratio, torque and horsepower, and the controller is configured to control the motor to prevent the at least one monitored engine parameter from exceeding a defined maximum value; the controller is configured to monitor an aircraft parameter comprising at least one of airspeed and angle of attack, and to control the motor to prevent an out-of-limit condition for the monitored aircraft parameter; and the system is configured to provide a turbulence penetration mode which, when engaged, automatically adjusts engine power to achieve a turbulence penetration speed calculated by the controller based at least in part on a gross weight of the aircraft. 
     The bearing assembly may be configured to accept the shaft in a throughbore thereof and may include at least one set of bearings, each of the bearings being supported in the bearing assembly to contact the surface of the shaft at determined angles relative to a longitudinal axis of the shaft so as to trace a helical pattern on the surface of the shaft as the shaft moves through the bearing assembly. 
     The at least one linkage arm at the second end of the shuttle arm may be rotatively coupled to the attachment end of the throttle lever, the at least one linkage arm being positioned parallel to the shaft to allow free movement of a distal end of the shaft as the bearing assembly moves along the shaft. 
     The system may be installed in an aircraft having two engines and the throttle lever of each engine may be controlled separately. In the event of an engine loss, the power setting of the remaining engine is controlled to stay above stall speed and is further controlled not to exceed an engine power threshold. The engine power threshold may be based at least in part on a maximum power imbalance that can be compensated by action of an aircraft rudder to prevent unwanted rotation of the aircraft. 
     The disclosed embodiment also implements a method by which an autothrottle adjusts engine performance to substantially conform to preferred performance parameters. An electronic controller is configured to control the motor to cause movement of the throttle lever so that the motor moves an actuator assembly along the shaft based at least in part on an engine operating parameter monitored by the controller One such condition is a surge condition. Haptic feedback is provided via a throttle lever until the actual engine performance matches the preferred engine performance. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above and/or other aspects and advantages will become more apparent and more readily appreciated from the following detailed description of the disclosed embodiments taken in conjunction with the accompanying drawings of which: 
         FIG. 1  is an elevated perspective view of an aircraft autothrottle operator and associated elements constructed in accordance with an embodiment of the disclosed invention; 
         FIG. 2  is a side view of the embodiment of the autothrottle operator depicted in  FIG. 1 ; 
         FIG. 3  is a perspective view of a second embodiment of the aircraft autothrottle operator with a housing cover removed; 
         FIG. 3A  is a partial perspective view of another embodiment of the aircraft autothrottle operator; 
         FIG. 4  is an enlarged view of the bearing assembly and shaft of the embodiment of the autothrottle depicted in  FIG. 3 ; 
         FIG. 5  is a side view of the embodiment of the autothrottle operator depicted in  FIG. 3 ; 
         FIG. 6  is a flow chart illustrating a method for operating an autothrottle system for an aircraft; and 
         FIG. 7  is a schematic representation of a segment of a flight path. 
     
    
    
     DETAILED DESCRIPTION 
       FIGS. 1 and 2  present two views of an embodiment of the precision aircraft autothrottle operator. The autothrottle operator system or arrangement, identified in the drawing figures by the general reference numeral  10 , is attached for use to a conventional throttle handle or lever  12  of an aircraft. The throttle lever  12 , the configuration and construction of which is conventional, is mounted for pivoted movement or displacement about a shaft or other pivot point or fulcrum  14  at which the lever  12  is secured in place at the throttle quadrant (not shown) of the aircraft. The distal end  16  of throttle lever  12  is configured for ease of grasping and manipulation, to advance and retard the lever  12  through its arcuate range of displacement, by a pilot manually controlling the power output of the associated aircraft engine and, thereby, the airspeed or velocity of the aircraft. The opposite or proximal end  18  of throttle lever  12  connects at attachment pin or shaft or point  20  at one end of a cable  22  that itself connects, generally at its far end, to the engine or engine controller associated with lever  12 . Thus, pilot manipulation, i.e., counterclockwise (in the figures) advancement or clockwise retarding—of the lever distal end  16  about pivot point  14  causes opposite-sense arcuate motion of attachment point  20 , thus effecting linear displacement of cable  22  and corresponding changes in the power output of the associated engine. Aircraft implementations in which the motion-transmitting functionality of cable  22  is instead provided by other elements or systems are known in the art, but changes in the power or thrust generated by an aircraft engine are in any event generally controlled in accordance with sensed displacement of the proximal extension of the corresponding throttle lever. 
     The autothrottle operator of the embodiment depicted in  FIGS. 1 and 2  is formed by an actuator assembly  24 , a motor  26 , and a position sensor  28 . 
     In particular implementations, actuator assembly  24  comprises an arrangement formed of a bearing assembly  30  (also referred to herein as shuttle body  30 ), an elongated shaft  32  and a linear fork  34 . 
     The combination of bearing assembly  30  and shaft  32  function to convert rotary motion into linear displacement. In the embodiment depicted in the figures, this functionality is implemented using a commercially-available assembly identified by its manufacturer, Zero-Max, Inc. of Plymouth, Minn. as a Roh&#39;lix Linear Actuator. Six rolling-element bearings  36 , in sets of three, are supported in a base block  38  at predetermined angles about a throughbore  40  defined in block  38  and through which shaft  32  extends for longitudinal displacement of block  38  along the shaft (a more detailed view of the block  38  and shaft  32  can be seen in  FIG. 4 , which is discussed below in the context of the second embodiment). Each of the bearings  36  contacts the surface of shaft  32  at an angle, such that the bearings  36  trace a helical pattern along the shaft and thereby longitudinally displace block  38  along the shaft as the shaft is rotated. Put another way, as the shaft  32  is rotated, i.e., by selective operation of motor  26 , the bearings  36  trace out an imaginary screw thread, causing linear longitudinal displacement of block  38  on and along shaft  32 . Base block  38  is constructed as two halves that are coupled by the combination of springs  42  and associated screws  44  that are adjusted to selectively setting the thrust force that bearings  36  apply to and against shaft  32  and, correspondingly, the amount of linear force that must be manually applied to the block  38  to overcome the thrust force and allow the bearings  36  to slip longitudinally along the surface of shaft Thus, when the thrust forces set or provided by a predetermined adjustment of screws  44  are exceeded, block  38  slips on and along shaft  32  irrespective of any rotation that may be concurrently imparted to the shaft by, e.g., motor  26 . 
     With continued reference to  FIGS. 1 and 2 , the operatively-rotated shaft of motor  26  is coupled to the end of shaft  32  remote from block  38 . The motor  26  may be, for example, a precision stepper motor that steps in response to the input of pulses or other electrical signals from a diagrammatically-depicted controller  48  through  200  consecutive rotative positions spaced about 1.8 degrees apart. Motor  26  is operable to incrementally (i.e., step-wise) rotate bidirectionally, i.e., selectively in both/either the clockwise and/or counterclockwise directions, based on the operating signals from controller  48 . One or more gears may optionally between the motor shaft and shaft  32  if needed or desired to attain a rotational speed of shaft  32  deemed suitable for the particular implementation and/or aircraft. Motor  26  is mounted on a motor bracket  46  having an opening  47  for unimpeded passage of shaft  32  and/or the motor shaft, bracket  46  being itself securable to a fixed structure in the aircraft cockpit to secure the motor  26  against movement as it operatively rotates shaft  32 . 
     Controller  48  may by way of illustration comprise an electronic controller having a processor and memory dedicated to the operation of motor  26  and, optionally, also to associated elements and functionality of the inventive autothrottle system, or its functionality may be incorporated in or as a part of the control system or elements of an autopilot system or of a flight management system or of other avionics and/or automation systems of the aircraft. 
     Linear fork  34  connects shuttle block  38  to throttle lever attachment point  20 . Fork  34 , which may be implemented as a unitary element (as described below in the context of the second embodiment), comprises in the illustrated embodiment a shell or tray  50  to which block  38  is secured, a pair of opposed linkage arms  52  that are rotatively coupled at one of their ends to attachment point  20  of the throttle lever, and a web  54  that joins tray  50  to arms  52 . The free end portion  56  of shaft  32  that is opposite its coupled connection to motor  26  is freely movable through and relative to apertures, passages and voids and the like that are defined in web  54  to accommodate the shaft end  56  as shuttle block  38  is operatively displaced or “shuttles” along shaft  32 . 
     The current relative displacement or position of shuttle block or body  38  along the elongation of shaft  32  is determined by monitoring changes in the distance or spacing between, by way of illustration, the positionally-fixed motor  26  and the movable shuttle body  38 . To provide this functionality, in the illustrated embodiment the position sensor  28  is implemented by a linear potentiometer  58 , such as, for example, an MLP miniature linear potentiometer manufactured by Celesco Transducer Products, Inc. of Chatsworth, Calif., that is connected as a position sensor between motor bracket  46  (to which the motor is secured) and tray  50  (on which the shuttle body is mounted). Potentiometer sensor  58  is electrically connected to controller  48  which thereby monitors changes in the linear position of shuttle body  38  (and thus, correspondingly, of the attachment point  20  at the proximal end of the throttle lever) on and along shaft  32 . The throttle position is accurately mapped and recorded using the potentiometer sensor  58  when the system is installed in the aircraft. Because the linear actuator is controlled with a stepper motor, a map of the throttle position for an individual step is determined and used as a means of detecting un-commanded movement or slip in the movement due to obstruction of the throttle lever. In particular embodiments, such detection could ultimately result in the system disengaging the autothrottle. 
       FIGS. 3-5  depict a second embodiment of the aircraft autothrottle operator. In this embodiment, the shuttle block  38  is connected to the throttle lever attachment point  20  by a shuttle arm  34 ′ which is implemented as a unitary element, rather than a dual-pronged fork  34 , as discussed above (the controller  48  is not shown in these views). The shuttle arm  34 ′ has a shell or tray  50 ′ at one end thereof to which block  38  is secured. The tray  50 ′ is oriented so that a mounting surface of the bearing assembly  30  is oriented in a vertical plane, whereas in the first embodiment, the mounting surface is oriented in a horizontal plane. The motor  26  may be held in place at a pivoting joint of a bracket  41  which can be attached to an interior structure of an aircraft. A detailed view of the block  38  and shaft  32  can be seen in  FIG. 4 . In  FIG. 3 , the cover of the housing  39  containing the block  38  is not shown so that the block  38  can be seen in the figure.  FIG. 5  shows the housing  39  with its cover in place. At the distal end of the shuttle arm  34 ′ is a linkage arm  52 ′ which is rotatively coupled to attachment point  20  of the throttle lever. The distal, i.e., free end portion  56 , of shaft  32  that is opposite its coupled connection to motor  26  is parallel to the linkage arm  52 ′ and therefore can move freely as shuttle block  38  is operatively displaced or “shuttles” along shaft  32 . 
     The basic manner of operation of the inventive autothrottle operator  10 , to selectively control an aircraft throttle in an automated operating mode (e.g. under the control of an autopilot system), will now be described. In response to electrical signals from controller  48 , stepper motor  26  is operated to selectively rotate coupled shaft  32  in a desired direction (to respectively increase or decrease engine thrust) and, as shaft  32  rotates, shuttle body  38  is linearly displaced along and relative to shaft  32  as the bearings  36  trace a helical path along the surface of rotating shaft  32 . This linear displacement of shuttle body  38  is transferred through linkage fork  34  to throttle lever  12  at attachment point  20 , causing throttle lever  12  to pivot about its fulcrum  14 , just as though throttle lever  12  were being manually moved about fulcrum  14  by a pilot grasping its distal end  16 . The resulting displacement of attachment point  20  at the proximal end  18  of throttle lever  12  likewise causes linear displacement of engine control cable  22 , thus causing the engine to vary the power output or thrust of the aircraft engine associated with that throttle lever. Thus, as shuttle body  38  is displaced along shaft  32  toward motor  26 , throttle lever  12  is rotated counterclockwise (in the Figures) to reduce engine power and, as shuttle block  38  is displaced along shaft  32  away from motor  26 , throttle lever  12  is rotated clockwise to increase engine power—again, just as though the throttle lever were being manually adjusted by a pilot grasping the throttle lever at its distal end  16 . 
     Changes in the linear position of shuttle body  38  relative to motor  26 —and, correspondingly, of the rotative position of the throttle lever  12 —can be determined by controller  48  by monitoring the output of the potentiometer position sensor  58 , as can the current position of the shuttle body. However, since it is the function of an autothrottle to vary engine output power to, for example, attain and/or maintain a predetermined airspeed, controller operation of motor  26  to increase or decrease engine power is dependent not so much on the absolute position or relative spacing of shuttle block  38  and motor  26  but, rather, on whether an increase or decrease in engine power (and, thus, whether operation of motor  26 ) is needed to provide the desired airspeed; accordingly, monitoring of the output of position sensor provides feedback to controller  48  for use in, inter alia, confirming proper operation of the autothrottle system. 
     An important and highly advantageous feature of the inventive autothrottle system  10 , as compared to conventional commercial autothrottle arrangements, is the provision of override capabilities without the use of clutches and their associated apparatus and connections. The capability of the inventive system  10  to be easily overridden for manual pilot control of the throttle(s), when the system  10  is engaged and even while it remains so, is an important and inherent feature of the system  10  and its construction. By physically grasping throttle lever  12  at its distal end  16  and applying sufficient force to advance or retard the throttle, shuttle body  38  is caused (by its coupled connection to the proximal end  18  of lever  12 ) to slip or slide longitudinally along shaft  32 , thus providing manual pilot control of the throttle even if controller  48  were to remain operationally activated to effect rotation of the motor and shaft  32 . Of course, it is generally intended that, when manual manipulation of throttle lever  12  is initiated, autothrottle controller  48  will normally be, automatically deactivated from continued operation of motor  26 , but the ability to readily assume manual control of the throttle in the event of, for example, a systemic or component failure to easily and immediately override the autothrottle functionality presents a particularly noteworthy improvement in assuring failsafe operation of the aircraft. 
     As previously described, pilot-effected manual override of the autothrottle arrangement requires that the pilot advance or retard the throttle lever  12  with a force that, at a minimum, exceeds the thrust force that the bearings  36  apply to the surface of shaft  32 . Since that thrust force is adjustable by selective rotation of adjustment screws  44  of shuttle body  38 , in particular implementations of the inventive arrangement the thrust force is preset to assure that manual override by the pilot is readily available using a reasonable magnitude of pilot-applied force that is deemed suitable for the particular application and for assuring continued safe operation of the aircraft. Setting of the bearings thrust force to a magnitude sufficient to assure linear movement of shuttle body  38  along and in response to rotation of shaft  32  will provide both reliable automated autothrottle control of the throttle and manual override control using reasonable pilot-applied forces on the throttle lever. 
     For example, a stepper motor contemplated for use in the inventive autothrottle assembly operatively generates a fairly high torque that rotates the shaft  32  to produce, for example, about 12 pounds of torque on the engine throttle control cable  22  (i.e., at the proximal end  18  of throttle lever  12 ) and about 4 to 6 pounds of force at the distal end  16  of throttle lever  12 . This means that, in a typical intended implementation of the system  10 , the aircraft pilot can easily override the autothrottle simply by pushing or pulling back, with a force of at least the same 4 to 6 pounds, on the distal end  16  of the throttle lever even if the motor  26  is engaged and operatively rotating the shaft  32  and/or even if the entire assembly is frozen. By manually applying to the throttle lever a force of about or in excess of, e.g., 4 to 6 pounds—which is a relatively small amount not appreciably greater than the force required to manually adjust the throttle lever without an engaged autothrottle—the shuttle body  38  will slip on and longitudinally along shaft  32  whether or not the shaft is being rotated by motor  26  and the pilot will thereby immediately obtain full, unconstrained and unconditional manual control of the throttle. The autothrottle arrangement thus presents an inherently safe system that assures a pilot the ability to readily assume manual control of the aircraft throttle(s) at any time. When combined with or forming an element of an aircraft autopilot system, the autothrottle arrangement  10  provides an intrinsically safe ability to quickly and easily override the forces applied by the autothrottle controller and the autopilot—instructed operations. 
     The inventive autothrottle arrangement can also be implemented to provide a warning to a pilot in the event that the aircraft is determined to be operating, for example, at too high or too low an airspeed for the current operating conditions or maneuvers of the aircraft. As is known, stepper motors such as the motor  26  generally contemplated for inclusion in the system  10  have (e.g.) three coils which are, in normal use, selectively actuated to cause the motor to bidirectionally rotate its shaft from step to step. In accordance with this embodiment, haptic feedback can be applied to the throttle lever, i.e., in the nature of “stickshaker” functionality—when the controller  48  determines, e.g. by monitoring at least the aircraft airspeed, that the airspeed is approaching the bounds or limits of a predetermined range of values. 
     Thus, if the controller  48  determines that the aircraft&#39;s increasing airspeed is approaching a predetermined safety limit value (e.g. the maximum structural cruising speed of the aircraft), or that its decreasing airspeed is approaching a predetermined minimum limit value (such as the minimum controllable airspeed or stall speed of the aircraft), motor  26  can be operated to cause the throttle lever to oscillate or shake and thereby alert the pilot to the impending unsafe overspeed or underspeed condition. Similarly, by monitoring engine torque, controller  48  can likewise provide a warning to the pilot by applying like haptic feedback through the throttle handle  12  if it is determined that the engine is at or approaching an unsafe operating condition, e.g. excessive torque. 
     This functionality is implemented by selectively applying electrical signals to individual ones or combinations of the multiple actuating coils of the motor, for example by activating only two of the three coils, or rapidly cycling electrical signals to a selected one or more of the motor coils—and does not require that, at the time of such haptic warning, the autothrottle must be or have been engaged or active to autocontrol the throttle and, thereby, the engine power. Thus, for purposes of this pilot-warning functionality the inventive autothrottle system  10  provides “always-on” sensing and haptic alert capabilities. In any event, if controller  48  senses that no manually-input changes to the position of throttle lever  12  have been applied in response to its haptic warning, the system  10  can be configured to operatively adjust the engine power or torque to correct the airspeed or overtorque condition by suitable motor-driven rotation of shaft  32  and the resulting linear displacement of shuttle body  38  as explained hereinabove. 
     Accordingly, by implementing this functionality the system  10  can be viewed as always engaged, with controller  48  continuously monitoring relevant characteristics and operating conditions of the aircraft that may warrant or necessitate a warning—delivered with haptic feedback delivered by shaking or oscillating or vibrating the throttle lever  12  and/or the initiation of automated controlled movement of the throttle lever by operation of motor  26  to correct or ameliorate the out of bounds condition. 
     Another advantageous feature of the inventive autothrottle arrangement is realized in an aircraft having, for example, two (or more) throttle levers each controlling the power output of a corresponding engine. In such multi-engine aircraft, manual control of airspeed, through manipulation of the throttle levers, is effected by concurrently advancing (or retarding) the two (or more) throttle levers. An issue that can arise in manual pilot control of the throttles of such multi-engine aircraft is that if the multiple throttle levers are not adjusted together, i.e., so that each lever is advanced or retarded by about the same amount, the engines may produce different levels of power or torque, as a result of which the propulsion of the aircraft may be unbalanced with one engine producing more thrust or torque than another, as the engine on one wing is producing less (or more) thrust than the engine on the other wing. Similarly, operating characteristics of one engine, with respect to another engine of the aircraft, may result in each engine generating different amounts of thrust or torque even if the respective throttle handles are correspondingly positioned or adjusted. 
     In a multi-engine aircraft in which an inventive autothrottle system  10  is provided for each of the engines, an imbalance of the thrust or torque produced by the two (or more) engines can be sensed and used by the controller(s)  48  to warn or alert the pilot of the imbalance by haptically shaking or vibrating (or the like) one or both/all of the throttle levers, using the procedure described hereinabove. As previously noted, this functionality does not require that the autothrottle system  10  be in operational use to autocontrol the positions of the throttle levers and, correspondingly, to automatically vary or adjust the thrust or power output of the engines. In addition, as also described above, the system can be configured so that detection that the multiple engines are out of sync or not generating the same levels of thrust or torque will cause the autothrottle system  10  of one or more of the engines to automatically readjust the corresponding throttle lever(s)  12  and thereby equalize the relevant operating characteristics of the multiple engines. 
     Another advantageous application of the inventive autothrottle arrangement in multi-engine aircraft is warning of and preventing the application of too much thrust to, for example, one of the two engines when one engine fails or is otherwise determined to be generating less than the intended, or expected, thrust. In a (by way of illustrative example) two engine aircraft, the manufacturer will have established an airspeed, VMCA, as the minimum controllable airspeed on a single engine when the aircraft is airborne, i.e., the minimum airspeed at which, with only one of the two engines operating, the pilot will have sufficient rudder authority to prevent the aircraft from yawing to an extent that will cause the aircraft to, in effect, roll over and dive into the ground. Thus, the failure—or degraded performance—of one engine in flight creates an asymmetric thrust condition requiring that the pilot of a multi-engine aircraft immediately level off, apply significant rudder and increase power to the remaining engine to maintain an airspeed at or above VMCA. And where the aircraft airspeed is, when one engine fails, below VMCA—such as in the landing phase of flight when engine power is generally brought back to a fraction of full power or thrust—the application of too much power to the engine that remains in operation will create a dangerous asymmetry in thrust and adverse yaw from which the application of rudder may not enable a safe recovery. 
     Accordingly, in this further use of the inventive autothrottle arrangement, controller  48  monitors (at least) the current airspeed (and, preferably, the acceleration) of the multi-engine aircraft and continuously calculates, for single engine operation, the maximum safe or allowable thrust that should or can be placed on the remaining engine under current flight and operating conditions. Put another way, the controller  48  continuously calculates, for the current airspeed below VMCA, the allowable power limit (i.e., the maximum safe or permissible generated thrust) for the remaining engine for that airspeed. If the power or thrust being produced by that remaining engine, in accordance with the position of throttle lever  12 , is increasing and approaching (or at or beyond) the calculated maximum thrust that the engine should be permitted to produce at the current airspeed, an alarm or warning will be generated by the inventive arrangement  10  by vibrating or oscillating the engine&#39;s throttle lever  12  (as described hereinabove) to alert the pilot of the impending or existing over-throttle condition. 
     If the position of throttle lever  12  is not manually adjusted by the pilot in response to the alert, then the motor  26  of the inventive autothrottle arrangement  10  may under appropriate conditions be operated to adjust the position of the throttle lever (and thus retard the throttle) under control of the system  10 , without pilot input and irrespective of whether the autothrottle system  10  had theretofore been operatively controlling the aircraft throttles, and thereby avoid or terminate the over-throttle condition of the operating engine. 
     This functionality can also be applied to assist the pilot in manually advancing the throttle, in response to the failure of the other engine, by only that amount appropriate to avoid an over-throttle condition of the remaining engine, by providing haptic feedback (by vibrating or oscillating the throttle lever  12 ) as the allowable thrust limit for the engine is approached; the pilot can proceed to manually advance the throttle lever until it starts to vibrate and, as the aircraft airspeed begins to increase, continue to manually advance the throttle lever until, again, the autothrottle system  10  resumes vibration of the throttle lever. Since the controller  48  is continuously calculating and determining an increasing maximum allowable engine thrust as the airspeed increases, the pilot can continue to manually adjust the throttle lever  12  in accordance with the vibration, or lack thereof, applied to the throttle lever by the autothrottle system  10 . In this manner the pilot is continuously guided in manually adjusting the throttle so that the engine is always operating to generate the maximum safe thrust based on the current airspeed and other relevant flight and environmental factors that the controller  48  can monitor. 
     For this and other implementations and applications of the inventive autothrottle system, the system can itself adjust or vary or scale the magnitude of such haptic vibrations or oscillations of the throttle lever as a function of the urgency of the need for pilot action—so that, for example, the system applies relatively small magnitude vibrations to the throttle lever as the limit value of airspeed or thrust or the like is first approached, with vibrations of increasing magnitude applied to the throttle lever as the limit value continues to be approached and is reached or exceeded. 
     Accordingly, by implementing this functionality the system  10  can be viewed as always engaged, with controller  48  continuously monitoring relevant characteristics and operating conditions of the aircraft. By, for example, such monitoring, the inventive autopilot system is additionally configured to provide additional advantageous modes of operation, as set forth below. 
     For example, the system  10  may be configured to provide a Speed Hold Mode. In the speed hold mode the system  10  adjusts the engine thrust to achieve and maintain the selected airspeed. 
     The system  10  also may be configured to provide a Torque Control Mode, in which the system  10  is configured to adjust the engine thrust to achieve and maintain the selected engine torque. 
     The system  10  also may be configured to provide a Temperature Limit Control Mode. In this mode, the engine thrust is adjusted to achieve and maintain the selected engine turbine inlet temperature. 
     The system  10  also may be configured to provide an Engine Protection mode in which the system  10  will adjust engine thrust to keep engine torque, speed and temperature from exceeding pre-defined targets in all modes of operations. In particular embodiments, the autothrottle may be configured to protect the engine from exceeding the limits for one or more of the following: torque, shaft horsepower, engine and propeller speeds, engine temperature, engine pressure ratio. 
     The system  10  also may be configured to provide a Speed Protection Mode. In this mode, at all times the autopilot system protects the aircraft from over-speed or under-speed by adjustment of the engine thrust. 
     The system  10  also may be configured to provide a mode in which, during manual manipulation of throttles, if the throttles are moved too rapidly by the pilot such that it could result in an engine power surge, the autopilot mechanism provides a warning to the pilot, e.g., by vibrating the throttle lever. 
     The system  10  also may be configured to provide a turbulence penetration mode that, when engaged by the pilot, automatically adjusts the power to achieve a turbulence penetration speed calculated based on gross weight and aerodynamic characteristics of the aircraft. 
     The system  10  also may be configured to provide a mode in which approach and take off speeds are calculated and entered into the speed control mode of the autothrottle. Landing approach speed is typically calculated as a function of gross weight and stall margin and may also include factors such as, for example, wind speed and flap configuration. The system  10  may also calculate and control airspeed to maintain optimum Lift over Drag (L/D), e.g., by using an average Angle Of Attack (AOA) from the aircraft AOA sensor. 
     The system  10  also may be configured to provide multiple autothrottle modes, such as, for example, automatic, airspeed control, and angle of attack control. In automatic mode, the autothrottle flies the airplane at maximum speed by controlling to the torque limit during initial take off and climb until the temperature becomes critical, at which point the autothrottle controls the engine to the maximum allowed temperature. In particular embodiments the autothrottle may be configured to protect the aircraft from out of limit conditions for one or more of the following: minimum airspeed; maximum angle of attack; and maximum airspeed under normal and turbulence conditions. 
     The system  10  also may be configured so that when it is installed with an engine that has no protection mechanism such as a full-authority digital engine control (FADEC), the autopilot monitors critical engine parameters, such as, for example, temperature, speed pressure ratio, torque, horse power, etc., and acts to prevent these parameters from exceeding the maximum values. 
     The system  10  also may be configured so that in the event of an engine power loss in a two engine aircraft, the autopilot manages the power setting of the remaining engine to stay above stall speed. At the same time the system controls the remaining engine to maintain safe operating conditions. In one embodiment, in the event of engine loss the throttle lever for the stalled or inoperative engine will vibrate or provide other haptic feedback to the pilot that the subject throttle lever has no effect. 
     In one embodiment, the autothrottle addresses a problem occurring from gas generator surges during throttle increase; which is a problem occurring, for example, on Pratt &amp; Whitney turboprops. Specifically, the autothrottle tailors throttle lever performance and response to match or substantially correspond to an ideal or preferred engine performance curve. The autothrottle can be configured to monitor conditions and provide haptic feedback, assume control, be disengaged, or the like. 
     For turboprops, the prop is turned by blowing hot gas over a turbine. Sudden throttle increase may cause gas generator surges, which causes uneven engine performance. Thus, the throttle needs to be delicately increased to alleviate this problem, according to one aspect of the invention, the autothrottle will automatically resist pilot manipulation of the throttle lever based on monitoring of engine performance and other parameters, thereby making it more difficult for manual control of the throttle lever until an existing gas surge dissipates. It should be noted that the autothrottle will provide haptic feedback or automatically increase throttle lever response if the throttle lever is moved too slowly. If a gas surge condition is detected and the autothrottle is not yet engaged, the autothrottle will automatically engage to counteract the surge condition. Alternatively or in addition, the autothrottle will provide a haptic warning such as vibration of the throttle lever when a surge condition is detected without engaging the throttle. 
     More particularly, the autothrottle feature will control an increase in the throttle in a regulated manner. This is helpful because the response of the engine is nonlinear such that small increases or decreases of throttle level result in relatively large and disproportionate power changes. Thus, by “mapping” the power performance of the engine and then using that information for throttle control, the throttle can be automatically controlled to optimally perform over the different regions of the engine&#39;s power output performance curve. For instances in which the autopilot is not engaged, as the engine performance deviates from the preferred performance curve, the autothrottle will provide haptic feedback to the pilot via the throttle lever to signal to the pilot to adjust the throttle until the throttle engine performance is bought back into alignment with the preferred performance curve of the engine. 
     In one embodiment, the autothrottle will automatically retard the lever motion to scale the lever motion based on a monitoring of the engine until the gas surge dissipates. In one embodiment, the midrange is slowed down until the surge dissipates. Alternatively, if the autothrottle is not engaged or an autothrottle override is engaged, haptic feedback is provided until the surge condition dissipates. Typically, this situation arises during landing, specifically during a landing abort. When landing is aborted and the aircraft has to make another attempt, the power needs to be increases quickly. However, this will create a power surge which can lead to temporary engine failure. The autothrottle will control the power increase in a regulated manner and engage in high stress situations, such as an aborted landing attempt. A mapping of throttle position and power identifies the problem issues and regulates the response to avoid surge conditions. 
     In one embodiment, as the engine performance deviates from the performance curve the autothrottle increases or decreases lever tension as required to make the throttle lever easier or harder to adjust so that the engine performance returns to an optimal point on the performance curve. Additionally or alternatively, when the engine performance deviates from the performance curve, a haptic or other warning is provided. Additionally or alternatively, the autothrottle can be automatically engaged or disengaged. 
     In an aircraft in which an inventive autothrottle system  10  is present, a surge can be sensed and used by the controller(s)  48  to warn or alert the pilot of the surge by haptically shaking, vibrating, or the like, of the throttle lever(s), using the procedure described hereinabove. As previously noted, this functionality does not require that the autothrottle system  10  be in operational use to autocontrol the positions of the throttle levers and, correspondingly, to automatically vary or adjust the thrust or power output of the engines. Rather, the system can be configured so that detection of a surge will cause the autothrottle system to automatically adjust the corresponding throttle lever(s)  12  to control the relevant operating characteristics of the engines. Alternatively, the system can be configured so that detection of a surge will cause the autothrottle system to provide haptic feedback to the corresponding throttle lever(s)  12 . 
     The application of the inventive autothrottle arrangement provides warning of and substantially prevents the surge condition. Controller  48  monitors (at least) the current airspeed (and, preferably, the acceleration) of the aircraft and continuously calculates the maximum safe or allowable thrust that should or can be placed on the engine under current flight and operating conditions. In other words, the controller  48  continuously calculates, for the current airspeed below VMCA, the allowable power limit (i.e., the maximum safe or permissible generated thrust) for the engine for that airspeed. If the power or thrust being produced by that engine, in accordance with the position of throttle lever  12 , is increasing and approaching (or at or beyond) the calculated maximum thrust that the engine should be permitted to produce at the current airspeed, an alarm or warning will be generated by the inventive arrangement  10  by vibrating or oscillating the engine&#39;s throttle lever  12  (as described hereinabove) to alert the pilot of the impending or existing surge condition. 
       FIG. 6  is a flow chart for method for operating an autothrottle system for an aircraft. The method includes monitoring engine performance of an aircraft engine (S 10 ). When a gas surge is detected (S 20 ), the autothrottle system is automatically engaged (S 30 ). In one embodiment, the monitored engine performance is compared to a power performance curve of the aircraft engine (S 40 ). The autothrottle provides haptic feedback to an aircraft pilot via a throttle lever until the monitored engine performance matches the preferred engine performance (S 50 ). According to one aspect of the invention, the haptic feedback comprises increasing or decreasing a throttle lever tension. The autothrottle manipulates the throttle lever in a regulated manner until an existing gas surge dissipates (S 60 ). The manipulating of the throttle lever is based on the monitoring of engine performance until the existing gas surge dissipates. 
     The herein-described and other embodiments of the inventive system, with little or relatively little modification, can also be applied to the automated control of aircraft flight control systems and elements other than the engine throttle controls. For example, the arrangement  10  can be connected or coupled, instead of to the throttle lever, to aircraft control surface elements such as the ailerons, trimtab(s), horizontal stabilizer and rudder to auto-adjust the positions of these flight control surfaces as part of or under the control of the aircraft&#39;s autopilot system. 
     Although example embodiments have been shown and described in this specification and figures, it would be appreciated by those skilled in the art that changes may be made to the illustrated and/or described example embodiments without departing from their principles and spirit.