AIRCRAFT AUTOMATIC FLIGHT CONTROL SYSTEM

• US 3,848,833 A
• Filed: 07/14/1972
• Issued: 11/19/1974
• Est. Priority Date: 07/14/1972
• Status: Expired due to Term

• Current Assignee: Honeywell Incorporated (Honeywell International Inc.)
• Original Assignee: Paul A. Rauschelbach
• Inventors: Rauschelbach, Paul A.
• Primary Examiner(s): Buchler, Milton
• Assistant Examiner(s): Kunin, Stephen G.
• Application Number:
  US05/271,867
• Time in Patent Office: 858 Days
• Field of Search: 235/150.2,150.22 244/77 318/6,143,146,257,294,332,341,345,434,513,563,565,584,585,591,599,635 343/107,18R
• US Class Current: 244/177
• CPC Class Codes: G05D 1/0061 for transition from automatic pilot to manual pilot and vice versa

Abstract

An automatic flight control system for aircraft providing improved aircraft response to input displacement commands, especially of the generally step input type, in a simple and economical manner; and further providing an improved yet economical control wheel steering capability. An improved automatic pilot electric surface servomotor system is also disclosed. Smooth and consistent roll acceleration limiting to step-like or abrupt roll attitude displacement commands are provided by rate limiting the displacement signal and then passing the limited signal through a simple lag filter having a predetermined time constant. Control wheel steering is available to the pilot by means of a wheel mounted switch which, when actuated, declutches the autopilot servoes, synchronizes the autopilot references during manual maneuvering through the aircraft manual control mechanism and, upon release of the switch re-establishes any preselected vertical path mode and/or establishes a roll attitude hold mode. Operation of CWS switch may be used to override various autopilot limits and upon release of switch maintains the overridden limit attitude; the autopilot automatically re-establishing automatic flight path demand control when the path demand signal equals the attitude limit established by the human pilot during control wheel steering. The autopilot surface servomotor control loop is characterized by an improved apparatus for limiting the torque output thereof by providing current feedback to the servo amplifier.

Claims

1. An automatic flight control system for an aircraft having the usual manual control wheel and control mechanism between it and the craft control surface for controlling the attitude of the craft in accordance with movement of said control wheel, the combination comprising an automatic pilot servomotor system having a servomotor, an output member connected with said control mechanism, and clutch means adapted when engaged to move said control mechanism and control surface in accordance with movement of said servomotor and when disengaged to permit free movement of said control mechanism and control surface by said control column, automatic flight control means including stable attitude reference and flight path control means for controlling said servomotor system when engaged to automatically control said control surfaces to automatically maintain said craft attitude and flight path, control wheel steering means for said automatic flight control system including switch means actuable by the human pilot for disengaging said servomotor clutch means during actuation of said switch means whereby the human pilot may alter said attitude and flight path through said manual control mechanism, and logic means responsive to actuation of said switch means for synchronizing said automatic flight control means to the attitude and flight path established by said human pilot through said manual control mechanism and upon deactuation of said switch means to re-engage said servomotor clutch means whereby said automatic flight control means thereafter controls said aircraft from said manually estalished attitude and flight path.

2. The automatic flight control system as set forth in claim 1 wherein said switch means comprises a depressable button switch mounted on the manual control wheel whereby said button can be depressed to actuate said control wheel steering means without the pilot removing his hands from the control wheel or diverting his attention from cockpit tasks.

3. The automatic flight control system as set forth in claim 1 wherein said automatic flight control means further includes attitude reference means and synchronizing means, and said logic means includes switch means for rendering said synchronizing means responsive to said attitude reference means during actuation of said control wheel switch means whereby said synchronizing means continuously follows up on the attitude of said craft established by the human pilot through said control mechanism, and upon deactuation of said control wheel steering switch means for re-engaging servomotor clutch means and for clamping said attitude synchronizer whereby the manually established attitude is maintained.

4. The automatic flight control system as set forth in claim 3 wherein said attitude reference and synchronization means is responsive to aircraft bank attitude and said automatic flight control means further includes heading attitude means and synchronization means responsive thereto, and said logic means further includes switch means for rendering said bank and heading synchronizing means responsive to said bank and heading attitude means during actuation of said control wheel switch means and the bank angle established by the pilot through said control mechanism is greater than a predetermined value, and said logic means further includes, switch means responsive to bank attitudes greater than said predetermined value and to deactuation of said control wheel switch means for re-engaging said autopilot servomotor, clamping said bank angle synchronizing means and for maintaining said heading synchronizer responsive to said heading attitude signal whereby said craft continues tO turn at the bank angle established by the pilot through said control mechanism.

5. The automatic flight control system as set forth in claim 4 wherein said further logic means includes further switch means responsive to bank attitude less than said predetermined value and to deactuation of said control wheel switch means for re-engaging said autopilot servomotor clutch means, clamping said heading synchronizer means, converting said bank synchronizer means to a lag filter means and for rendering said lag filter means responsive to said heading reference means whereby said craft rolls to level flight and thereafter maintains the heading obtaining when said bank attitude attained said predetermined value.

6. The automatic flight control system as set forth in claim 1 wherein said automatic pilot servo as a bank angle control servomotor, said attitude reference means includes a bank attitude reference and, said flight path control means includes flight path computer means for providing a bank angle demand signal proportional to the error between the present craft course and a desired craft course and means for limiting said course error signal to a predetermined value whereby to limit the bank angle demanded thereby, wherein said logic means responsive to actuation of said control wheel switch means synchronizes said bank attitude reference whereby the pilot may manually establish through said control mechanism a bank attitude different from that demanded by said limited course error signal and upon deactuation of said control wheel switch means to re-engage said servomotor and hold said different bank angle, and further logic means responsive to the algebraic sum of said course error signal and said control wheel steering established bank angle signal reducing to zero for automatically releasing said bank attitude hold and thereafter control said servomotor in accordance with said algebraic sum signal whereby said craft thereafter automatically approaches and maintains said desired course.

7. The automatic flight control system as set forth in claim 6 wherein said desired craft course is a course defined by the bearing of a radio beam.

8. The automatic flight control system as set forth in claim 1 wherein said control surface controls craft pitch attitude and said autopilot servomotor controls a pitch control surface, said stable attitude reference means is a pitch attitude reference means and wherein said flight path is a vertical flight path determined by an altitude reference means.

9. The automatic flight control system as set forth in claim 1 wherein said control surface controls craft pitch attitude and said autopilot servomotor controls a pitch control surface, said stable reference means is a pitch attitude reference means and wherein said flight path is a vertical flight path determined by an airspeed reference means.

10. An automatic flight control system for controlling the aileron of an aircraft comprising, a position servomotor coupled with said ailerons for controlling the roll attitude of the craft, means for producing a roll attitude demand signal, and means for supplying said demand signal to said servomotor means, said last-mentioned means including, electronic signal limiting means responsive to said attitude demand signal for limiting the maximum rate of change thereof whereby to limit the displacement of said aileron in response thereto whereby to limit the rate of roll of said aircraft, and an electronic lag filter means having a predetermined time constant and responsive to said rate limited demand signal for limiting the rate of change thereof to limit the rate of change of displacement of said ailerons whereby to limit the resulting roll acceleration of said aircraft in response to said attitude demand signal.

11. The automatic flight control system as set forth in claim 10, wherein said electronic signal limiting means is substantially lag freE.

12. The automatic flight control system as set forth in claim 11 wherein said electronic lag filter has a lag time constant on the order of one second and said electronic signal limiting means has a lag time constant on the order of ten times less than said filter lag.

13. The automatic flight control system as set forth in claim 10 wherein said electronic signal limiting means includes means for varying the limit imposed thereby.

14. The automatic flight control system as set forth in claim 10 wherein said electronic lag filter means comprises an electronic integrating amplifier and a feedback circuit from the output of said amplifier to its input including an impedance, and switch means in said feedback circuit responsive to engagement of said autopilot for closing said feedback circuit whereby to convert said integrator to a lag filter.

15. The automatic flight control system as set forth in claim 14 wherein the value of said feedback impedance is such as to provide a lag filter having a time constant on the order of one second.

16. In an automatic flight control system for aircraft having a control surface for controlling the motion of the aircraft about an axis thereof, the combination comprising, a servomotor including control windings and coupled with said control surface for positioning the same in accordance with a command signal, power amplifier means responsive to said command signal for providing a motor control signal to said control windings, means responsive to the signal across said motor control windings for providing a first feedback signal to said amplifier means responsive to the average voltage across said control windings including any back EMF therein, means responsive to the current drawn by said servomotor for providing a voltage proportional to the torque exerted on said surface thereby, and means responsive to said current responsive means for providing a second feedback signal to said amplifier means proportional to the average magnitude of said current in excess of a predetermined value, whereby for currents below said predetermined value said servomotor is a voltage controlled, back EMF damped motor while for currents above said predetermed value said servomotor is a current controlled, torque limited motor.

17. In the automatic flight control system as set forth in claim 16 wherein said current responsive signal means comprises means for supplying a fixed voltage proportional to the maximum current to be drawn by said servomotor, and means for comparing said fixed voltage with said voltage proportional to motor current and for supplying a signal in accordance with the difference therebetween.

18. In an automatic flight control system for an aircraft having control surfaces for controlling the motion of said aircraft about a plurality of axes, the combination comprising a surface servomotor system for each of said control surfaces, each of said servomotor systems comprising a disconnectable servomotor including control windings and normally connected to drive its associated surface in accordance with a command signal, power amplfiier means responsive to said command signal for providing a motor control signal to said control windings, means responsive to the signal across said motor control windings for providing a first feedback signal to said amplifier means responsive to the average voltage across said control windings incuding any back EMF therein, means responsive to the current drawn by said servomotor for providing a voltage proportional to the torque exerted on said surface thereby, means responsive to said current responsive means for providing a second feedback signal to said amplifier means proportional to the average magnitude of said current in excess of a predetermined value, whereby for currents below said predetermined value said servo motor is a voltage controlled, back EMF damped motor while for currents above said predetermiNed value said servomotor is a current controlled, torque limited motor, and means responsive to each of said current responsive means for disconnecting all of said servomotors from their respective control surface if one or more of said currents exceeds a predetermined value.