Flight control system
A system and method for a controlling an aircraft with flight control surfaces that are controlled both manually and by a computing device is disclosed. The present invention improves overall flight control operation by reducing the mechanical flight control surface components while providing sufficient back-up control capability in the event of either a mechanical or power-related failure. Through the present invention, natural feedback is provided to the operator from the mechanical flight control surface which operates independent of computer-aided flight control surfaces. Further, through the present invention, force input signals received from the pilot are filtered to improve the operation of the computer-aided flight control surfaces.
1. A process for operating a powered control surface of an aircraft, the aircraft having a powered control surface operated by a powered actuator and an unpowered control surface operated by a pilot of the aircraft using a control means, wherein the control means are mechanically coupled to the unpowered control surface so that aerodynamic forces acting on the unpowered control surface are exerted on the control means, the process comprising the steps of:
operating the control means to position the unpowered control surface with a desired deflection;
measuring a force signal representing the force applied to the control means by a pilot in response to aerodynamic forces acting on the unpowered control surface at the desired deflection;
converting the force signal into a desired powered control surface deflection; and
operating the powered actuator to position the powered control surface at the desired powered control surface deflection.
2. The process of claim 1 wherein the step of converting the force signal further comprises the steps of:
selecting a filter to generate a desired aircraft response;
applying the filter to the force signal to produce the desired powered control surface deflection.
3. The process of claim 2 wherein the desired aircraft response comprises the response of the aircraft to the force applied to the control means as measured by at least one aircraft state variable.
4. The process of claim 3 wherein the at least one aircraft state variable is selected from the group consisting of roll rate, load factor, sideslip angle, Mach number, airspeed and angle of attack.
5. The process of claim 3 wherein the step of selecting a filter comprises selecting a second order filter that models a mass-spring-damper system with an effective mass and an effective stiffness that are chosen based on the desired aircraft response.
6. The process of claim 5 wherein the step of converting the force signal further comprises the steps of:
measuring the at least one aircraft state variable; and
modifying the effective stiffness of the filter in response to changes in the measured value of the at least one aircraft state variable.
7. The process of claim 6 wherein the step of modifying the effective stiffness comprises selecting the effective stiffness from a schedule based on the measured value of the at least one aircraft state variable.
8. The process of claim 6 wherein the effective stiffness of the filter is increased when the at least one aircraft state variable approaches a predetermined limit.
9. The process of claim 7 wherein the step of converting the force signal further comprises the steps of:
applying a decoupling filter to the desired powered control surface deflection;
selecting a gain value for each measured value of the at least one aircraft state variable; and
multiplying the desired powered control surface deflection by each of the gain values to calculate a modified powered control surface deflection.
10. The process of claim 9 wherein the step of selecting a gain value comprises selecting a gain value from a schedule of gain values for the measured value of the at least one aircraft state variable.
11. The process of claim 10 wherein the decoupling filter has a time constant that is slower than the natural modes of the aircraft.
12. The process of claim 1 wherein the step of converting the force signal comprises the steps of:
selecting a filter;
applying the filter to the force signal to produce a nominal powered surface command;
measuring at least one aircraft state variable;
modifying the nominal powered surface command in response to each of the at least one aircraft state variables to generate the desired powered control surface deflection.
13. The process of claim 12 wherein the step of modifying the nominal powered surface command comprises the steps of:
selecting a gain value for each measured value of the at least one aircraft state variables;
multiplying the nominal powered surface command by each gain value.
14. The process of claim 13 wherein the at least one aircraft state variable is selected from the group consisting of angle of attack, load factor, sideslip, Mach number and airspeed.
15. The process of claim 14 wherein the step of modifying the nominal powered surface command further comprises applying a decoupling filter to the nominal powered surface command.
16. The process of claim 15 wherein the decoupling filter has a time constant that is slower than the natural modes of the aircraft.
17. The process of claim 13 wherein the gain value is selected from a schedule of gain values for each of the at least one aircraft state variables.
18. The process of claim 1 wherein the step of converting the force signal further comprises the steps of:
selecting a filter that is a second order physical model of the control means and the unpowered control surface;
applying the filter to the force signal to produce the desired powered control surface deflection.
19. The process of claim 18 further comprising the steps of:
measuring the actual deflection of the unpowered control surface;
calculating the difference between the actual deflection and the desired powered control surface deflection;
applying a time constant to the difference to calculate a correction factor; and
incorporating the correction factor into the desired powered control surface deflection.
20. The process of claim 1 further comprising the steps of:
detecting that the control means or the unpowered control surface are jammed;
measuring the force applied by the pilot to the control means while the control means or the unpowered control surface are jammed; and
operating the powered actuator in proportion to the measured force while the control means or the unpowered control surface are jammed.
21. A flight control system for an aircraft comprising:
control means for receiving control input from a pilot;
a first control surface mechanically coupled to the control means without any powered actuators and operated by the control means to a desired deflection;
a second control surface operated by powered actuators;
a force sensor coupled to the control means for measuring a force applied to the control means by a pilot; and
a computing device configured to receive the measured force, apply a control law to the measured force, and operate the powered actuators to position the second control surface in response to the control law;
wherein the control law comprises the steps of:
measuring a force signal representing the force applied to the control means by a pilot in response to aerodynamic forces acting on the first control surface at the desired deflection;
selecting a filter to generate a desired aircraft response;
applying the filter to the force signal to produce a desired powered control surface deflection, wherein the filter is a second order filter that models a mass-spring-damper system; and
operating the powered actuator to position the second control surface at the desired powered control surface deflection.
22. The flight control system of claim 21 wherein the control law further comprises the steps of:
measuring the at least one aircraft state variable; and
modifying the effective stiffness of the filter in response to changes in the measured value of the at least one aircraft state variable.
23. The flight control system of claim 22 wherein the control law step of modifying the effective stiffness comprises selecting the effective stiffness from a schedule based on the measured value of the at least one aircraft state variable.
24. The flight control system of claim 21 wherein the control law step of selecting a filter to generate a desired aircraft response comprises selecting a filter that is a second order physical model of the control means and the first control surface.