Abstract:
The present invention is a power lever tactile cueing system for providing tactile alerts to pilots as operational limits of an aircraft are approached. The cueing system generates a tactile cue comprising a variable dive rate and a variable friction force on a power lever of an aircraft. The cueing system provides spring-like tactile cues when power commands reach a predetermined operating limit, without the use of mechanical springs. The cueing system trims down the power lever position and provides the additional friction force based upon aircraft and engine state. The cueing system remains activated until the aircraft is again operated within its operational limits. The pilot may override the cueing system in certain situations.

Description:
TECHNICAL FIELD  
         [0001]    The present invention relates generally to pilot cueing systems for aircraft. In particular, the present invention relates to tactile pilot cueing systems for the power levers, collectives, and throttles of aircraft.  
         DESCRIPTION OF THE PRIOR ART  
         [0002]    Flying an aircraft is a complicated and demanding task. The pilot must be aware of many things going on at once. In particular, the pilot must be aware of the ever-changing operating conditions of the aircraft and all of its systems, such as the power systems and the flight control systems. The pilot must know not only the current state of these systems, but their operational limits as well. To do this, the pilot must scan multiple engine and torque gauges to determine operating conditions and limitations. Failure by the pilot to carefully monitor these systems can lead to serious problems. The following are examples of problems that can result from the pilot failing to monitor the operational parameters of the aircraft: (1) increased operational and maintenance costs as a result of inadvertent power commands in excess of torque or temperature limits; and (2) unpredictable vertical axis control as a result of a power lever deadzone during operations with limited engine power, such as one-engine-inoperative (OEI) flight conditions.  
           [0003]    Some aircraft use mechanical springs to provide a tactile cue to the pilot through the control levers to indicate that the operational limits of the aircraft are being approached. Such mechanical springs engage at set predetermined levels and supply a predetermined amount of resisting force to the controls. These preset levels cannot be changed once the springs are installed. Furthermore, these mechanical springs add weight to the aircraft.  
         SUMMARY OF THE INVENTION  
         [0004]    There is a need for a power lever tactile cueing system for an aircraft for which the magnitude of the tactile force can be altered depending upon certain dynamic conditions of the aircraft, and for which mechanical springs are not required.  
           [0005]    Therefore, it is an object of the present invention to provide a power lever tactile cueing system for an aircraft for which the magnitude of the tactile force can be altered depending upon certain dynamic conditions of the aircraft, and for which mechanical springs are not required.  
           [0006]    The above objects are achieved by providing a power lever tactile cueing system in which mechanical springs are replaced by computer controlled software, a variable friction magnetic particle clutch, and an electric trim motor. In the preferred embodiment of the present invention, the following tactile alerts are employed: a power lever softstop and a power lever backdrive. These tactile alerts provide a spring-like tactile cue when power commands reach a predetermined operating limit. The backdrive commands cause the power lever to be trimmed down at a variable rate based upon the operating conditions of the aircraft and the engines. The tactile cue remains active until the aircraft and engine conditions no longer exceed the operational limits. The pilot can deliberately override the tactile cue in an emergency situation.  
           [0007]    The present invention provides the following advantages: (1) reduces pilot workload by allowing the pilot to determine operating limits without continually monitoring multiple engine and drive system gauges in the cockpit; (2) improves flight safety by reducing the likelihood of exceeding engine and drive system operating limits; (3) improves operational costs by reducing the likelihood of engine and drive system overhauls resulting from inadvertent exceedances of operational limits; (4) improves flight safety by allowing the pilot to override normal operational limits, but not allowing the pilot to override structural design static limits; (5) improves aircraft performance during maximum gross weight vertical takeoffs by allowing the pilot to set power to 100% of the operating limit without continually monitoring multiple engine and drive system gauges; (6) reduces pilot workload following an engine failure by automatically eliminating control deadzone in the power lever when operating on an engine limit; (7) provides a low-weight implementation of the tactile cue by using the same equipment required for autopilot operation; (8) provides an immediate tactile cue to the pilot that the aircraft has become power-limited as a result of a propulsion system malfunction; (9) eliminates the requirement for the pilot to manually modulate the power lever when power limits change as a function of flight condition; and (10) reduces weight by eliminating the need for mechanical springs.  
           [0008]    The above objects and advantages, as well as others, will be evident from the following detailed description of the present invention. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0009]    [0009]FIG. 1 is a perspective view of a tiltrotor aircraft having a power lever tactile cueing system according to the present invention.  
         [0010]    [0010]FIG. 2A is a schematic of the power lever tactile cueing system of the present invention.  
         [0011]    [0011]FIG. 2B is a perspective view of a power lever grip for the power lever tactile cueing system of the present invention.  
         [0012]    [0012]FIG. 3 is a schematic of the command algorithm for the power lever tactile cueing system of the present invention.  
         [0013]    [0013]FIG. 4 is a tabular representation of the control law and backdrive interaction for the power lever tactile cueing system of the present invention.  
         [0014]    [0014]FIG. 5 is a schematic of the interface between an aircraft engine and flight control computers for the power lever tactile cueing system of the present invention.  
         [0015]    [0015]FIG. 6 is an electronic schematic for the power lever tactile cueing system of the present invention.  
         [0016]    FIGS.  7 A- 7 G are detailed schematics of the interface between an aircraft engine and flight control computers for the power lever tactile cueing system of the present invention.  
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0017]    Referring to FIG. 1 in the drawings, a tiltrotor aircraft  11  having a power lever tactile cueing system  13  according to the present invention is illustrated. Tiltrotor aircraft  11  comprises the following components: a fuselage  15 , a tail section  17  coupled to the aft portion of fuselage  15 , a horizontal stabilizer  19  carried by tail section  17 , a left wing member  21   a  coupled to fuselage  15 , a right wing member  21   b  coupled to fuselage  15 , a left engine nacelle  23   a  pivotally coupled to left wing member  21   a , a right engine nacelle  23   b  pivotally coupled to right wing member  21   b,  a left engine and prop rotor gear box (not shown) carried by left engine nacelle  23   a , a right engine and prop rotor gear box (not shown) carried by right engine nacelle  23   b , a left prop rotor  25   a  coupled to left engine and prop rotor gear box, and a right prop rotor  25   b  coupled to right engine and prop rotor gear box. Tiltrotor aircraft  11  can operate in either an airplane mode, in which aircraft  11  flies like a fixed wing aircraft, or in a helicopter mode, in which aircraft  11  can take off, fly, land, and hover like a helicopter or other rotary wing aircraft. In FIG. 1, tiltrotor aircraft  11  is shown in the airplane mode. Although the preferred embodiment of the present invention is in a tiltrotor aircraft application, it should be understood that the present invention may be used on a wide variety of aircraft.  
         [0018]    In the preferred embodiment, cueing system  13  is utilized in aircraft  11  to generate a tactile cue to a pilot through the aircraft&#39;s power lever in response to certain flight conditions. Because the present invention is particularly well suited for a tiltrotor aircraft application, the present invention will be described with regard to tiltrotor aircraft  11 . However, it should be understood that cueing system  11  may be used in other applications involving the movement of a power lever, collective, or throttle to control power limits.  
         [0019]    Referring now to FIG. 2A in the drawings, power lever tactile cueing system  13  is shown in a schematic view. According to the present invention, a tactile force cue, represented by arrow C, is provided on a power lever  33  of aircraft  11  when flight control computers (FCC&#39;s)  205  (see FIG. 4) and cueing system  13  detect that aircraft  11  has reached or is approaching an engine or drive system operating limit. Power lever  33  in aircraft  11  is synonymous with the collective in a helicopter, or the throttle in a fixed wing aircraft. Cueing system  13  includes a plurality of engine sensors  35  disposed at various locations throughout aircraft  11 . In the preferred embodiment, engine sensors  35  provide sensor signals  37  which correspond to certain operating parameters, such as engine torque, transmission torque, measured gas temperature, and/or nacelle angle.  
         [0020]    A backdrive command selector  40  receives sensor signals  37  from engine sensors  35  and generates tactile cue C. Backdrive command selector  40  includes a plurality of “red line” limit algorithms  39  which calculate certain operational limits of aircraft  11 . Backdrive command selector  40  is a component of an overall tactile cue command algorithm  41  (see FIG. 3). Tactile command algorithm  41  includes compensation to account for engine dynamics, aircraft dynamics, and system latency. An algorithm signal  43  corresponds to each red line limit algorithm  39 . Sensor signals  37  and algorithm signals  43  are compared by a comparator  45 . Comparator  45  generates a power limit error signal  47  by comparing the corresponding value of algorithm signals  43  with the corresponding value of sensor signals  37 . The value of power limit error signal  47  is queried at block  49 , and a result of “YES” or “NO” is returned. If the value of power limit error signal  47  is less than or equal to zero, then cueing system  13  has no effect on power lever  33 , as is shown by the “NO” result and block  48 . On the other hand, if the value of power limit error signal  47  is greater than zero, then tactile cue C is provided on power lever  33 , as is shown by the two “YES” results.  
         [0021]    Tactile cue C is comprised of two components: a variable drive rate  51  to automatically trim down power lever  33 ; and a variable friction force  53  that resists pilot commanded motion. For variable drive rate  51 , power lever  33  is trimmed down at a rate that is proportional to the corresponding value of power limit error signal  47 , the rate being preferably between about 0.08 and 0.8 inches per second. For variable friction force  53 , the magnitude of the force is a function of the selected operating conditions of the engine and drive systems of aircraft  11 . Variable friction force  53  is calculated by an algorithm in FCC&#39;s  205 , and preferably simulates a “breakout” force and a “softstop” force, as represented by block  55 . The breakout force is a threshold static force that the pilot must overcome before he can begin to move power lever  33 . The breakout force is preferably between about 0.0 and 2.0 pounds. The softstop force is an increasing force that the pilot must overcome to continue moving power lever  33  toward a position that exceeds the operational limits of aircraft  11 . Because variable friction force  53  is a softstop force, the pilot is allowed to overcome variable friction force  53  and pull power lever  33  through tactile cue C and access emergency power. The softstop force is preferably between about 4.0 and 8.0 pounds. Beyond the softstop force, tactile cue C acts like a mechanical spring. In addition, because cueing system  13  cause an immediate actuation of power lever  33  in response to an engine failure, the present invention reduces pilot workload following an engine failure by automatically eliminating control deadzone in power lever  33  when operating on an engine limit. One notable example of reduced workload is when the pilot switches from a thirty second engine power rating to a two minute engine power rating. Without cueing system  13 , the pilot is forced to “hunt” with power lever  33  to eliminate the deadzone, which simulation has shown can take up to seven seconds during a crucial portion of the recovery.  
         [0022]    In preparing aircraft  11  for flight, the pilot may preset a baseline friction force  59  for power lever  33  by either increasing or decreasing a preset power lever friction value, as shown in block  57 . Typically, baseline friction force  59  is between about 0.0 and 3.0 pounds. Preset friction force  59  is combined with variable friction force  53  at an accumulator  61  to produce a total friction force  63  which is provided on power lever  33 . Total friction force  63  is preferably between about 2.0 and 8.0 pounds.  
         [0023]    Referring now to FIG. 2B in the drawings, a power lever grip  31  according to the present invention is illustrated. Tiltrotor aircraft  11  includes at least two such power lever grips  31 : one coupled to a pilot&#39;s power lever  33   a , and another coupled to the co-pilot&#39;s power lever  33   b . Power lever grips  31  are mechanically and electrically coupled to power levers  33   a  and  33   b . Each power lever grip  31  includes a one engine inoperative switch  32  which may be activated by the pilot or co-pilot as necessary under certain conditions. Power lever grip  31  may include additional switches  34 , buttons  36 , thumbwheels  38 , and other control mechanisms for controlling various aircraft functions and maneuvers.  
         [0024]    Referring now to FIG. 3 in the drawings, tactile cue command algorithm  41  is shown in a schematic view. Tactile cue command algorithm  41  determines the magnitude of multi-component tactile cue C that is generated on power lever  33  of aircraft  11 . In the preferred embodiment, the following red line limits are determined: a measured gas temperature red line limit  43   a , an engine torque red line limit  43   b , and a transmission torque red line limit  43   c . Measured gas temperature red line limit  43   a  is calculated by a measured gas temperature backdrive command algorithm  81  by using a measured gas temperature input  83 , a nacelle angle input  85 , and a status input  87  for a one-engine-inoperable switch  32  located on power lever  33 . Engine torque red line limit  43   b  is calculated by an engine torque backdrive command algorithm  91  by using an engine torque input  93  and a nacelle angle input  95 . Transmission torque red line limit  43   c  is calculated by a transmission torque backdrive command algorithm  101  by using a transmission torque input  103  and a nacelle angle input  105 . It should be understood that other engine and drive system parameters may also be considered in lieu of, in addition to, or in combination with the above parameters. Nacelle angle inputs  85 ,  95 , and  105  are the average angles α (see FIG. 1) between nacelles  23   a  and  23   b  and wings  21   a  and  21   b . Inputs  83 ,  85 ,  87 ,  93 ,  95 ,  103 , and  105  are all passed to tactile cue command algorithm by FCC&#39;s  205 .  
         [0025]    Comparator  45  determines which backdrive command algorithm  81 ,  91 , or  101  is the most critical at any given time, depending upon the actual operating conditions of aircraft  11 . Tactile cue command algorithm  41  is used to command tactile cue C based upon the engine or drive system parameter that is most critical relative to that parameter&#39;s respective operating limit. For example, an increase in measured gas temperature will increase the likelihood that measured gas temperature backdrive command  81  will be the most critical red line limit  43 , but will not increase the likelihood that transmission torque backdrive command  101  will be the most critical red line limit  43 . Only the most critical backdrive command, i.e., the backdrive command that is relatively the closet to the actual operational limits, is passed through comparator  45  to be used in the generation of variable drive rate  51  and variable friction force  53  of tactile cue C. Tactile cue C characteristics are varied depending on which parameter exceeds its operating limit. For example, when average mast torque or engine torque exceeds its limit, tactile cue C is a strong spring-type force that provides a resisting force proportional to the error magnitude, plus variable drive rate  53  to return power lever  33  to its limit. For another example, when an engine temperature limit is exceeded, tactile cue C is a force detent, plus a slow drive rate  53  to return power lever  33  to limit.  
         [0026]    Power lever  33  includes a “hardstop” position which represents the operational limits of aircraft  11 . The hardstop position prevents the pilot from exceeding aircraft structural design static limits. An emergency power condition is provided which can be activated by the pilot if the pilot maintains a selected force on power lever  33  in order to exceed engine operating limits, but the hardstop limits the amount of emergency power available. For example, after an engine failure has occurred, the power lever is automatically driven down at a slow rate when FCC&#39;s  205  detect that power lever  33  exceeds the single engine power capability of aircraft  11 . The single engine power capability is set at the thirty second engine rating automatically after an engine failure is detected. A one engine inoperative limit switch (not shown) is provided on power lever grip  31  that allows the pilot to switch the single engine power capability from thirty second rating to two minute power rating.  
         [0027]    Referring now to FIG. 4 in the drawings, a tabular representation of the control law and backdrive interaction for the power lever tactile cueing system of the present invention is illustrated. The limits shown are based on an exemplary aircraft configuration. A table  121  sets forth some typical operational limits for aircraft  11  which are utilized and generated by tactile cue command algorithm  41 . In other words, table  121  represents typical red line limits  43  of tactile cue command algorithm  41 . It should be understood that the values in table  121  will change if the configuration of aircraft  11  changes.  
         [0028]    Rows  123 ,  125 , and  127  of table  121  represent certain operational limits for aircraft  11  while in either the helicopter mode or while converting from helicopter mode to airplane mode. For row  123 , all engines are operative; for row  125 , one engine is inoperative; and for row  127 , one engine is inoperative and the one engine inoperative switch has been activated. Rows  129 ,  131 , and  133  of table  121  represent certain operational limits for aircraft  11  while in the airplane mode. For row  129 , all engines are operative; for row  131 , one engine is inoperative; and for row  133 , one engine is inoperative and the one engine inoperative switch has been activated.  
         [0029]    In FCC&#39;s  205 , a hard limit exists for measured gas temperature. This hard temperature limit is dependent upon three parameters: measured gas temperature  83 , nacelle angle  85 , and status of one engine inoperative switch  87 . This measured gas temperature limiter is represented by column  135  of table  121 . For the situations represented by rows  123  and  125 , the measured gas temperature hard limit is set to the thirty second one engine inoperative limit of 945° C., which corresponds to the maximum temperature at which the engine can operate for thirty seconds. While at this temperature, a one engine inoperative warning alert counts down from thirty seconds. For the situation represented by row  127 , the measured gas temperature hard limit is equal to the engine two minute one engine inoperative limit of 890° C. and the one engine inoperative warning alert counts down from two minutes. Continuing with the airplane mode situations represented by rows  129  and  131 , the measured gas temperature hard limit is 890° C. and the one engine inoperative warning alert counts down from two minutes. For the situation represented by row  133 , the measured gas temperature hard limit is equal to the engine thirty minute one engine inoperative limit of 870° C. and the one engine inoperative warning alert counts down from thirty minutes.  
         [0030]    However, according to the present invention, tactile cue C is generated through power lever  33  prior to reaching these hard limits. Tactile cue C remains active until the situation is no longer present. Of course, the pilot can override the commands of power lever tactile cueing system  13  if required.  
         [0031]    Column  137  represents typical measured gas temperature situations which trigger activation of cueing system  13 . For example, for the situation represented by row  123 , if during takeoff, the measured gas temperature reaches 835° C., cueing system  13  causes power lever  33  to trim back at a selected variable drive rate  51  (see FIG. 2A). For the situations represented by rows  125  and  127 , cueing system  13  is not activated until the hard limit from column  135  is reached. Continuing with the situations in which aircraft  11  is in airplane mode, for the situation represented by row  129 , the maximum tactile cueing force is generated when the measured gas temperature exceeds 805° C. For the situations represented by rows  131  and  133 , cueing system  13  is not activated until the measured gas temperature exceeds 870° C.  
         [0032]    Column  139  represents a combination of engine torque limits and transmission torque limits that, if exceeded, will activate cueing system  13 . The tactile cue C is a simulated spring force that is proportional to the exceedance. For the situation represented by row  123 , if at takeoff, the transmission torque exceeds the takeoff limit of 100%, then cueing system  13  generates tactile cue C through power lever  33 . For the situations represented by rows  125  and  127 , once the engine torque has been maintained for the allotted warning time interval, then cueing system  13  is activated. For the airplane mode situation of row  129 , if the transmission torque reaches the maximum continuous rating of 81.6%, then cueing system  13  is activated. For the one engine inoperative situation represented by row  131 , once the engine torque, reaches the two minute engine torque limit, then cueing system  13  is activated. Finally, for the situation represented by row  133 , if the one engine inoperative switch has been activated, cueing system  13  will allow the engine torque to reach the continuous one engine inoperative limit before activating.  
         [0033]    Referring now to FIG. 5 in the drawings, a schematic of the engine and FCC interface  201  is illustrated. Interface  201  is shown in more detail in FIGS.  7 A- 7 G. Power lever  33  includes a plurality of switches and controls  203  for pilot inputs, including: power lever position; an engine condition lever which is used primarily when starting aircraft  11 ; and a one engine inoperable switch, which is activated by the pilot to switch between a thirty second operating limit for the remaining operable engine to a two minute operating limit. These pilot inputs are fed to a plurality of FCC&#39;s  205 . In addition, a plurality of airframe measurements  204 , including nacelle angle, ambient temperature, and ambient pressure, are fed to FCC&#39;s  205 .  
         [0034]    Triplex torque motor commands  207  are sent from FCC&#39;s  205  to a fuel control unit  209 . Fuel control unit  209  includes an acceleration cam  211  that generates fuel flow limits  213 . Fuel control unit  209  sends fuel flow commands  215  to engines  217 , and receives compressor discharge pressure data  219  from engines  217 . Some ignition and start commands  221  are passed directly from FCC&#39;s  205  to engines  217  bypassing fuel control unit  209 . A plurality of a linear voltage differential transducers  223  provide position feedback to FCC&#39;s  205 . FCC&#39;s  205  are electrically coupled to an engine control panel  225  which includes a fuel shut off path  227  for fuel control unit  209 .  
         [0035]    Engine  217  includes a plurality of sensors, such as engine sensors  35  (see FIG.  2 A), which send feedback commands  229  to FCC&#39;s  205 . Such input commands include signals corresponding to engine torque, power turbine speed, and the operation of engine gas generator  211 . A nacelle interface unit  231  is a computer that receives the value of measured gas temperature  233  from engines  217  and sends a corresponding feedback command  235  to FCC&#39;s  205 .  
         [0036]    In this manner, pilot inputs  203  and airframe measurements  204  can be monitored, manipulated, and compared by FCC&#39;s  205  to provide a purely electrical cueing system  13  that does not require mechanical springs to provide tactile cue C to the pilot when movement of power lever  33  approaches the operational limits of aircraft  11 .  
         [0037]    Referring now to FIG. 6 in the drawings, a schematic of the electronics  301  of cueing system  13  is illustrated. An electric trim motor  303  provides the force and actuation of power lever  33 . Motor  303  is controlled by a controller  305  that includes motor control electronics, tachometer demodulation electronics, and electromagnetic interference filtering electronics. Motor  303  is preferably powered by a 28 Volt AC power supply  307 . Controller  305  also controls a variable friction magnetic particle clutch  309  having a primary clutch coil  311  and a secondary clutch coil  313 . In the preferred embodiment, motor  303  is coupled to clutch  309 , and clutch  309  is coupled to power lever  33 . A rotary variable differential transducer  317  serves as a position sensor to detect and transmit the position of power lever  33  to controller  305 . If rotary variable differential transducer  317  detects that the position of power lever  33  is approaching a position that represents the operational limits of tiltrotor aircraft  11 , a signal is sent to motor  303  and an appropriate tactile cue C is generated on power lever  33 . Cueing system  13  accomplishes this without the need or use of mechanical springs.  
         [0038]    Clutch  309  is a “slipping” clutch which allows cueing system  13  to provide a variable tactile cue on power lever  33 . The closer power lever  33  gets to a position which would cause tiltrotor aircraft  11  to operate at unsafe conditions, the greater the force of tactile cue C that clutch  309  allows to be transmitted to power lever  33 . In other words, clutch  309  slips less and creates more force that the pilot must overcome when power lever  33  approaches the operational limits of tiltrotor aircraft  11 .  
         [0039]    Electronics  301  are electrically coupled to FCC&#39;s  205 . FCC&#39;s  205  convert drive rate commands in inches per second into revolutions per minute to control a tachometer servo loop  315  that controls the speed of motor  303 . FCC&#39;s  205  convert force commands in pounds into an electric current in amperes that varies the friction force of magnetic particle clutch  309 .  
         [0040]    Tactile cue C is provided by variable friction magnetic particle clutch  309  and trim motor  303  which increase the friction of power lever  33  when a critical engine parameter limit is reached. This increase in friction is achieved by increasing the current in variable friction magnetic particle clutch  309 . In this manner, power lever  33  is trimmed down, or “backdriven,” to the predetermined limit setting. This increase in friction is perceived by the pilot as a spring breakout and gradient, as shown in block  55  of FIG. 2A. The pilot can command variable friction magnetic particle clutch  309  to slip by applying a force to power lever  33  of greater than about  8  pounds.  
         [0041]    The present invention provides the following advantages: (1) reduces pilot workload by allowing the pilot to determine operating limits without continually monitoring multiple engine and drive system gauges in the cockpit; (2) improves flight safety by reducing the likelihood of exceeding engine and drive system operating limits; (3) improves operational costs by reducing the likelihood of engine and drive system overhauls resulting from inadvertent exceedances of operational limits; (4) improves flight safety by allowing the pilot to override normal operational limits, but not allowing the pilot to override structural design static limits; (5) improves aircraft performance during maximum gross weight vertical takeoffs by allowing the pilot to set power to 100% of the operating limit without continually monitoring multiple engine and drive system gauges; (6) reduces pilot workload following an engine failure by automatically eliminating control deadzone when operating on an engine limit; (7) provides a low-weight implementation of the tactile cue by using the same equipment required for autopilot operation; (8) provides an immediate tactile cue to the pilot that the aircraft has become power-limited as a result of a propulsion system malfunction; and (9) eliminates the requirement for the pilot to manually modulate the power lever when power limits change as a function of flight condition.  
         [0042]    Although the present invention is shown in a limited number of forms, it is not limited to just these forms, but is amenable to various changes and modifications without departing from the spirit thereof.