AIRCRAFT FLIGHT CONTROL APPARATUS

• US 3,743,221 A
• Filed: 04/09/1970
• Issued: 07/03/1973
• Est. Priority Date: 04/09/1970
• Status: Expired due to Term

• Current Assignee: Lowell O. Lykken, Naren M. Shah
• Original Assignee: Lowell O. Lykken, Naren M. Shah
• Inventors: Lykken, Lowell O., Shah, Naren M.
• Primary Examiner(s): Buchler, Milton
• Assistant Examiner(s): Kunin, Stephen G.
• Application Number:
  US05/026,890
• Time in Patent Office: 1,181 Days
• Field of Search: 244/77A,77D,77V 343/5LS,18R,18M 235/150.22 35/10.2
• US Class Current: 244/180
• CPC Class Codes: G05D 1/0676 specially adapted for landing

Abstract

Apparatus for generating a command signal to control an aircraft in the vertical direction. A signal representative of the desired rate of descent of the aircraft is combined with a signal representative of the actual rate of descent. The latter signal is derived from a source that accurately represents the rate of descent at high altitude, e.g., the integrated output of a normal accelerometer or the differentiated output of a barometric altimeter, and a source that accurately represents the rate of descent at low altitude, e.g., the differentiated output of a radio altimeter. At high altitude, the first source is used; at low altitude, the second source is used; and at intermediate altitude, a decreasing percentage of the signal from the first source is blended with an increasing percentage of the signal from the second source. In one embodiment, the signals from the two sources are complementarily blended by means of a single gain changing circuit. The difference between the two signals is applied to the input of the gain changing circuit and the output signal of the gain changing circuit is added to one of the signals. In another embodiment, the integrator that operates on the glide slope error is used to derive from a normal accelerometer the signal representative of the actual rate of descent at high altitude and the gain changing circuit that controls the flare profile is used to blend the signals from the two sources. In forming the command signal to control the aircraft elevator, a vertical acceleration term is employed instead of a pitch attitude term. With appropriate shaping, this command signal is suitable for controlling aircraft spoilers as well.

Claims

1. Apparatus for generating an aircraft flight control signal that is representative of the actual rate of altitude change of an aircraft at all altitudes during descent or ascent, the apparatus comprising:

a first source of first signals that is an accurate representation of the rate of altitude change of the aircraft at high altitude and an unreliable representation of the rate of altitude change of the aircraft at low altitude;

a second source of second signals that is an unreliable representation of the rate of altitude change of the aircraft at high altitude and an accurate representation of the rate of altitude change of the aircraft at low altitude, said second source comprising a radio altimeter and means for differentiating the output of said radio altimeter; and

generating means for generating a flight control signal from said first signals at altitudes higher than a selected altitude, and with a combination of said first and second signals at altitudes lower than said selected altitude, the percentage of said first signals being decreased and the percentage of said second signal being increased in response to descent of said aircraft at altitudes below said selected altitude, said generating means comprising first means for combining said first and second signals in a first sense;

means for transmitting a constant maximum percentage of the amplitude of the combined signals at altitudes above said selected altitude, and below said selected altitude a decreasing percentage of the combined signals in response to descent towards zero altitude; and

second means for combining the transmitted signal and the second signal in a second sense that is opposite said first sense.

2. Apparatus for generating an aircraft flight control signal to control an aircraft in the vertical direction during descent, the apparatus comprising:

a first source of signals representing a desired rate of descent, said first source comprising means for producing a signal representing a glide slope error signal of the aircraft from the center of the beam, means for reducing the gain of the glide slope error signal from a constant value at high altitude to zero at a given low altitude, means for dividing the reduced glide slope error signal into a first portion and a second portion, means for integrating the first portion, and means for combining the integrated first portion and the second portion to produce the signal from the first source;

a second source of signals representing the actual rate of descent of the aircraft, the signal from the second source being accurate at high altitude and unreliable at low altitude, said second source comprising a sensor of vertical acceleration of the aircraft and means for integrating the output of the sensor;

a third source of signals representing the actual rate of descent of the aircraft, the signal from the third source being unreliable at high altitude and accurate at low altitude; and

means for generating a control signal representative of the difference between the signal from the first source and a blend of signals from the second and third sources, the control signal comprising a reduction of the gain of the signal from the second source from full gain at and above the given low altitude towards zero gain at ground level and an increase in the gain of blended signals from zero gain at the given low altitude towards full gain at ground level, said blended signals including a combination of signals from said second and third sources.

3. The apparatus of claim 2, in which:

the means for integrating the first portion of the glide slope error signal comprises an integrator having an input and means for applying the first portion to the input of the integrator; and

the means for integrating the output of the sensor comprises means for connecting the output of the sensor to the input of the integrator.

4. The apparatus of claim 3, in which said means for generating a control signal includes:

a gain changing circuit having an input and an output;

means for applying the glide slope error signal to the input of the gain changing circuit;

means for applying said signals from said second source to the input of said gain changing circuit; and

means for applying the blended signals to the input of the gain changing circuit in one sense and means for applying the blended signals to the output of the gain changing circuit in the opposite sense, whereby said blended signals are cancelled from said control signal at altitudes equal to or higher than said given low altitude.

5. The apparatus of claim 4, in which the third source is a radio altimeter and a rate circuit responsive to the output of the radio altimeter.

6. An automatic flight control system for an aircraft comprising:

a plurality of nominally identical channels, each channel producing a pitch command signal;

a signal voter that selectively transmits to its output the signal applied to one of its inputs, depending upon the relative amplitude of the input signals;

means for coupling the command signals produced by the plurality of channels to the respective inputs of the signal voter;

pitch control means for effecting pitch control of said aircraft;

means for coupling the output of the signal voter to the input of said pitch control means to operate said pitch control means responsive to the selectively transmitted command signal; and

direct lift control means for effecting lift control of said aircraft concurrently with and in response to operation of said first control means in accordance with said command signals.

7. The flight control system of claim 6 wherein said direct lift control means comprises:

a transducer that is mechanically coupled to the pitch control means to produce an electrical signal representative of the movements of the pitch control means; and

means for coupling said electrical signal produced by the transducer to the input of the direct lift control means.

8. The flight control system of claim 7, in which the means for coupling the electrical signal produced by the transducer to the input of the direct lift control means comprises a network for shaping the signal produced by the transducer.

9. The flight control system of claim 8, in which a pilot operated input device is mechanically coupled to the pitch control means to introduce input commands from the pilot.

10. The flight control system of claim 9, in which each channel comprises a first source of signals representative of vertical velocity error of the aircraft, a second source of signals representative of vertical acceleration of the aircraft, and a third source of signals representative of pitch rate of the aircraft, and the command signal is generated by additively combining the outputs of the first, second and third sources.

11. The flight control system of claim 7, in which a pilot operated input device is mechanically coupled to the pitch control means to introduce input commands from the pilot.

12. The flight control system of claim 6, in which each channel comprises a first source of signals representative of vertical velocity error of the aircraft, a second source of signals representative of the vertical acceleration of the aircraft, and a third source of signals representative of the pitch rate of the aircraft, and the command signal is generated by additively combining the outputs of the first, second, and third sources.

13. A flight control system for an aircraft comprising:

a first source of signals representative of the vertical velocity error of the aircraft from a desired value;

a second source of signals representative of the vertical acceleration of the aircraft;

a third source of signals representative of the pitch rate of the aircraft;

means for combining the outputs of the first, second and third sources to produce a pitch command signal;

aircraft pitch control means responsive to the pitch command signal;

means for monitoring the operation of said aircraft pitch control means to generate direct lift command signals representative of the operation of the pitch control means; and

aircraft direct lift control means, responsive to the direct lift command signal, for altering lift in accordance with operation of said pitch control means.

14. The flight control system of claim 13, in which a shaping network is provided and the direct lift command signal is coupled by the shaping network to the input of the direct lift control means.

15. A control system for controlling the flight of an aircraft in a vertical direction during descent or ascent, by providing control signals, the control system comprising:

a first source of signals representing a desired rate of change of altitude, said first source comprising a glide slope receiver that produces an error signal representative of the vertical displacement of the aircraft from a glide slope path;

means for dividing the error signal of the glide slope receiver into first and second portions;

an integrator to which the first portion of said error signal is applied;

means for combining the output of the integrator and the second portion of said error signal to form the signal from the first source; and

a first gain changing circuit for reducing the gain of said error signals from a full gain at a first selected high altitude to zero gain at a second selected lower altitude;

a second source of signals representing an actual rate of change of altitude of the aircraft, said second source including a sensor of vertical acceleration;

a third source of signals including a radio altimeter for providing signals representing a derived rate of change of altitude of the aircraft;

a second gain changing circuit for reducing the gain of signals applied as inputs thereto, from a full gain at said second selected lower altitude towards a zero gain at ground level, said second gain changing circuit receiving as inputs thereto the combined output of the integrator and the second portion of said error signal, said integrator receiving signals from said second source as an input thereto;

blending means for producing a blended rate of change of altitude signal by combining the signals from said second and third sources, said blending means including means for combining said blended rate of change of altitude signal, in opposite senses, with the input signals and the output signals of said second gain changing circuit to have said blended signal effectively cancelled and of no effect at altitudes higher than said second selected lower altitude, and the effect of said blended signal change towards becoming exclusive at ground level.

16. The control system defined by claim 15, in which the third source comprises a radio altimeter and a rate circuit responsive to the output of the radio altimeter, and the gain changing circuits are responsive to the output of the radio altimeter.

17. The control system defined by claim 15, in which the output of the second gain changing circuit is reduced to precisely zero at ground level and a source of direct current bias is combined with the output of the second gain changing circuit to produce a selected minimum rate of descent for an aircraft to be controlled by said system.

18. An aircraft control system for generating a command signal that may be used to control the pitch of an aircraft by having the command signal applied to operate the elevators of an aircraft, the control system comprising:

first means for providing an inertially derived vertical velocity signal, said first means including an accelerometer for sensing the acceleration of said aircraft along a vertical axis;

second means for providing a radio derived vertical velocity signal, said second means including a radio altimeter;

gain control means for changing as a function of height the gain of signals applied therethrough, the gain of output signals of said gain control means being reduced from full gain at a preselected height towards zero gain at ground level in accordance with changes in height between said preselected height and ground level;

means for applying said velocity signals from said first and second means as inputs to said gain control means, said signals from said second means being applied in a first sense; and

means for combining, in a sense opposite said first sense, said velocity signal from said second means with the output signals of said gain control means to form said command signals whereby the velocity signals from said second means are effectively cancelled at heights equal to or exceeding said preselected height, and said velocity signals from said second source increasingly replace said velocity signals from said first source in accordance with the changes in gain of said gain control means, said velocity signals from said second source fully replacing said velocity signals from said first source at ground level.

19. The control system defined by claim 18, said second means including a complementary filter for blending signals from said radio altimeter and said accelerometer to provide said radio derived vertical velocity signals.

20. The control system defined by claim 19, said first means including an integrator for integrating said signals from said first means to provide said inertially derived vertical velocity signals.

21. The control system defined by claim 20 further including:

third means for providing signals representative of the vertical acceleration of said aircraft;

fourth means for providing signals representative of the pitch rate of said aircraft;

pitch control means for controlling the pitch of said aircraft in response to said signals from said third and fourth means and said command signals;

means for monitoring the operation of said pitch control means to generate direct lift command signals representative of the operation of said pitch control means; and

direct lift control means for altering lift in response to operation of said pitch control means.

22. The control system defined by claim 21 wherein said pitch control means includes the elevators of said aircraft and said direct lift control means includes the spoilers of said aircraft.

23. The control system defined by claim 22, further including means for providing a glide slope error signal which is selectively applied to said gain control means in accordance with the altitude of said aircraft.