Controller and aircraft with takeoff stall protection system

Abstract

A flight control system, flight control rules, and an aircraft are provided. A flight control system includes an input device configured to receive a pitch rate command, a processor operable to receive a pitch angle command, calculate a pitch angle saturation limit, compare a sum of the pitch rate command, a scaled pitch rate, and a scaled pitch angle to the pitch angle saturation limit, convert the pitch rate command system to a pitch angle command system to limit a pilot's pitch up pitch rate command in response to the sum exceeding the pitch angle saturation limit value, and couple the pitch rate command to an aircraft control surface for a failure condition of one of the control surfaces, and the aircraft control surface is configured to adjust the aircraft control surface setting in response to the pitch rate command and / or the pitch angle command to protect the aircraft from a stall condition.

Description

TECHNICAL FIELD

[0001] The technical field is generally related to takeoff stall protection systems for aircraft, and more particularly to flight control systems with pitch rate command systems having pitch angle target limiting functionality to protect the aircraft from ground aerodynamic stall, transitioning to normal in-flight control rules after liftoff. BACKGROUND

[0002] During aircraft takeoff, the pilot must accurately rotate the aircraft to a pitch attitude target, without under- or over-rotation. Accurate rotation enables optimal takeoff field performance and improves passenger and crew safety and comfort. Conventional direct gain pitch controllers used in conjunction with small displacement control inceptors, such as side sticks, can cause pilots to tend to over-rotate the aircraft during takeoff, presenting a real risk of aerodynamic stall before any in-flight stall protection control rules can be activated and protect the aircraft. Reducing control authority or increasing inceptor control force to prevent this tendency is undesirable, as it reduces the ability to overcome stabilizer mis-trim or control surface jams. Furthermore, providing stall protection during the takeoff phase requires knowledge of the height above the ground to provide adequate protection without being overly conservative and impacting performance, as the presence of the ground changes the aerodynamics.

[0003] Accordingly, it is desirable to provide flight systems, flight control algorithms, and aircraft that improve takeoff stall protection during pitch and flight path based flight missions. Additionally, other desirable features and characteristics will become apparent from the ensuing SUMMARY

[0004] Disclosed herein are flight control systems, flight control algorithms, aircraft, and related control logic for provisioning aircraft, methods of manufacturing such systems, and methods for operating such systems, as well as other vehicles equipped with onboard control systems. By way of example and not limitation, an aircraft having a takeoff stall protection system and control system is presented.

[0005] In a first non-limiting embodiment, a flight control system includes, but is not limited to, an input device configured to generate a pitch rate command in response to a pilot input; a processor operable to receive a pitch angle command, calculate a pitch angle saturation limit, compare the pitch angle command to the pitch angle saturation limit, apply a coefficient to the pitch angle command in response to the pitch angle command exceeding the pitch angle saturation limit to generate a damped pitch rate command, and couple the damped pitch rate command to an aircraft control surface; and an aircraft control surface configured to adjust the aircraft control surface setting in response to the damped pitch rate.

[0006] According to another aspect of the disclosure, a method for controlling an aircraft includes receiving an aircraft speed from an aircraft speed sensor; determining a pitch angle saturation limit in response to the aircraft speed; receiving a pitch rate command from an aircraft control system; generating a pitch angle command in response to the pitch rate command, a scaled pitch rate, and a scaled pitch attitude angle exceeding the pitch angle saturation limit; and coupling the pitch angle command to an aircraft control surface that is the same as the pitch saturation limit.

[0007] According to another aspect of the disclosure, an aircraft includes an aircraft control handle configured to receive control motions for attitude adjustment in the aircraft and generate a pitch angle command in response to the control motions for attitude adjustment; an airspeed sensor for determining an airspeed of the aircraft; a processor configured to receive the airspeed of the aircraft and a flight path angle, calculate a pitch angle saturation limit in response to the airspeed of the aircraft, compare a sum of the pitch rate command, a scaled pitch rate, and a scaled pitch attitude angle to the pitch angle saturation limit; and apply a limit to the pitch up pitch rate command to generate a damped pitch angle response to the pitch angle command that is the pitch angle saturation limit. A flight control law is configured to control an aircraft control surface to control the aircraft pitch in response to the damped pitch angle command. BRIEF DESCRIPTION OF DRAWINGS

[0008] The above-mentioned and other features and advantages of this invention, and the manner of attaining them, will become more apparent and the system and method will be better understood by reference to the following description of embodiments of the invention taken together with the accompanying drawings.

[0009] Figure 1 is a simplified diagram illustrating a non-limiting embodiment of an aircraft in accordance with the teachings of this disclosure.

[0010] Figure 2 is a simplified block diagram illustrating a non-limiting embodiment of a system for providing takeoff stall protection control in accordance with the teachings of this disclosure.

[0011] Figure 3 is a flowchart illustrating a non-limiting embodiment of a method for providing takeoff stall protection control in accordance with the teachings of this disclosure.

[0012] Figure 4 is a simplified block diagram illustrating another non-limiting embodiment of a system for providing takeoff stall protection control according to the present disclosure.

[0013] Figure 5 is a flowchart illustrating another non-limiting embodiment of a method for providing takeoff stall protection control according to the teachings of the present disclosure.

[0014] The examples set forth herein demonstrate preferred embodiments of the present application and should not be construed as limiting the scope of the present application in any manner. DETAILED DESCRIPTION

[0015] The following detailed description is merely exemplary in nature and is not intended to limit the application or the application and uses of the application. Furthermore, there is no intention to be bound by any theory of operation presented in the preceding background or the following detailed description.

[0016] Various non-limiting embodiments of flight control systems, flight control algorithms, and aircraft are provided. Generally, the disclosure herein describes flight control system designs used during the takeoff phase of flight. During takeoff, the pilot must accurately rotate the aircraft to a pitch attitude target without under- or over-rotation. During takeoff, a pitch angle target limiting function is operable to limit the pilot's pitch up command to avoid putting the aircraft into a stall condition. This is particularly useful for sidestick controls with small displacement pilot controllers. Better understanding can be had with reference to the drawings.

[0017] Figure 1 is a side view of an aircraft 100 in flight. The aircraft 100 has a pitch attitude Θ which indicates the longitudinal orientation 106 of the aircraft 100 relative to the horizon 108 as understood by one of ordinary skill in the art. The aircraft 100 includes a flight control system 102 that performs various flight related tasks. The aircraft 100 has an angle of attack which indicates the angle between the flight path and the longitudinal orientation. The aircraft 100 has a flight path angle which indicates the angle between the longitudinal orientation axis and the flight path. At slower takeoff speeds, increasing the pitch angle Θ results in a larger angle of attack which increases the lift from the aircraft's wings, but if the angle is greater than the stall angle, it can result in a decrease in acceleration which can cause the aircraft to enter a stall condition.

[0018] Reference is now made to Figure 2FIG. 1 shows a block diagram of a flight control system 200 for takeoff stall control in an aircraft, illustrating example embodiments in accordance with the present disclosure. The example flight control system 200 includes an input device 210, a processor 220, a control surface 230, and a pitch regulator 240. The example flight control system 102 is operable to prevent excessive rotation of the aircraft during takeoff to reduce the risk of entering an aerodynamic stall condition. Typically, during takeoff, air stall protection control rules are not activated when the main landing gear is in contact with the ground to eliminate the dependency on ground stall angle information required for reliable radar altitude. In addition, ground aerodynamic effects can adversely affect air stall protection control rule calculations, thereby reducing the effectiveness of these rules.

[0019] The example takeoff stall protection (TSP) is a pitch rate command system with a pitch angle target limit function to protect the aircraft from ground aerodynamic stall. During the takeoff phase, the TSP control rules can protect the aircraft from unintended excessive rotation and aerodynamic stall without the use of radar altitude information in fly by wire control systems. The example TSP system allows consistent forces for normal takeoff and full control authority to manage stabilizer trim malfunctions or control surface failures while preventing rotation rates or pitch attitudes that can lead to ground or just after liftoff aerodynamic stall before transitioning to in-flight alpha limit protection. The TSP can transition to normal in-flight control rules just after liftoff or soon after liftoff.

[0020] In this example embodiment, the input device 210 can be a flight control column or yoke for controlling the altitude of the aircraft. In the example embodiment, the input device 210 can be a side stick controller, typically located on the pilot’s side, and used to control the altitude of the aircraft in response to a fly by wire control system. One disadvantage of the side stick configuration is that the controller is much shorter than a traditional center stick design, and therefore has a smaller range or linear displacement compared to a longer center stick, making small altitude changes more difficult and increasing the likelihood of over-rotation and / or over-rotation of the aircraft when performing large maneuvers.

[0021] In an exemplary fly-by-wire system, input device 210 is operable to couple control signals indicative of aircraft control stick position to processor 220. Initially, processor 220 can then be operable to couple control signals indicative of input control values (e.g., pitch stick deflection) to control surface 230, such as an elevator. Pitch regulator 240 can then be operable to receive pitch rate, pitch angle, and flight path angle from control surface 230, aircraft sensors, or related control logic. Alternatively, processor 220 can receive airspeed indications from aircraft sensors, global positioning system sensors, or the like. Processor 220 can then calculate a pitch angle saturation limit in response to control surface position, aircraft airspeed, and / or flight path angle. If the sum of pitch rate command, scaled pitch rate, and scaled pitch angle reaches the pitch angle saturation limit, pitch regulator 240 is operable to track the pitch rate command with proportional and integral feedback of the aircraft pitch rate. Pitch regulator 240 is then coupled to processor 220. Processor 220 is then operable to scale input control values from input device 210 by generating a switch between direct control and pitch rate command. In one exemplary embodiment, the pitch regulator coefficients are a set of values related to aircraft airspeed. For example, at below 75 KCAS, the pitch regulator coefficients can be 0, such that pilot control stick position directly generates elevator command for pre-flight control surface checks. Likewise, at above 75 KCAS, the pitch regulator coefficients can be 1, such that pilot control stick input generates a pitch rate command, and the regulator process causes the pitch rate of the aircraft to track the pitch rate command. The scaled control values are then coupled to control surface 230 for pitch control of the aircraft control surface. The scaled control values can be further generated in response to aircraft state measurements of pitch angle, pitch rate, angle of attack, flight path angle, normal acceleration, and / or aircraft airspeed.

[0022] In an exemplary TSP, input device 210 is operable to generate a pitch rate command in response to pitch stick deflection when airspeed is above 75 KCAS. Processor 220 then tracks the pitch rate command when the pitch angle saturation limit function is not active. The pitch angle saturation limit is defined as:

[0023] τ θ *θ limit = τ θ *(α 1p0 -K const + LF τ (0.3)*γ)

[0024] where:

[0025] τ θ is a design parameter representing the pitch angle gain.

[0026] θlimit is the pitch attitude limit that provides sufficient stall margin at full ground effect assuming zero flight path (or runway slope).

[0027] γ is the flight path angle correction.

[0028] LF τ (0.3) is a low pass filter applied to γ with a 0.3 second time constant.

[0029] α 1p0 is the angle of attack at a normalized angle of attack of 1.0, which is a function of the aircraft speed, the aircraft flap configuration, and the aircraft wing de-ice function status. The reference 1.0 angle of attack is defined as from the free air stall angle of attack with a 1 degree margin to the aero stall. This angle of attack can not depend on the radar altitude value.

[0030] K const is a constant value that depends on the margin between the free air and ground effect angles of attack, which in the exemplary embodiment can be between 2 and 3 degrees.

[0031] The pitch lever command directly commands the pitch rate when the sum of the current pitch angle, the current pitch rate multiplied by a gain, and the pitch rate command is less than a saturation limit value. When this sum is above the saturation limit value, the saturation limit value is assigned as the pitch angle command. When saturation is not active, the proportional and integral gains will be active to reduce the error between the pitch rate command and the current aircraft pitch rate. In the exemplary embodiment, when saturation is active, the pitch rate command system can be converted to a pitch angle target follow system with additional pitch angle and pitch rate feedback. Additionally, for the takeoff phase, the flight path angle information is used to correct the pitch attitude to an approximate angle of attack, but also to set a limit to eliminate the dependence on radar altitude in the TSP system.

[0032] In the exemplary embodiment, the TSP can only be applied during the takeoff phase of the aircraft. After the aircraft altitude exceeds a predetermined level, for example after liftoff, 10 feet off the ground, etc., the TSP can be disabled and transitioned to in-flight stall protection or normal in-flight control rules. Additionally, in the exemplary embodiment, the TSP can be enabled when one or more conditions are met, for example, the speed is greater than 75 knots calibrated airspeed (KCAS), the aircraft is on the ground, the flap handle is in the takeoff configuration, and / or the ground spoilers are not activated. When the aircraft is landing and the ground spoilers are extended at the moment of touchdown, the TSP is inactive, but the pitch damper is active.

[0033] Turning now to Figure 3The flowchart illustrates a non-limiting embodiment of a method 300 of providing takeoff stall control in accordance with the teachings of the present disclosure. Initially, the method is operable to receive 310 a pitch rate command from an aircraft control (e.g., yoke, side stick, etc.) in response to a pilot action. For example, the pilot can pull back on the side stick, causing a displacement of the side stick, which indicates a pitch rate. The pitch rate command is generated in response to the side stick displacement and then coupled to an aircraft control processor, etc. For example, the processor 220 can couple the pitch rate command to the aircraft control processor by sending an electronic data signal to the aircraft control processor.

[0034] Next, the method is operable to calculate a pitch angle saturation limit 320 from one or more aircraft sensors. The pitch angle saturation limit can be determined in response to a function of a normalized angle of attack, an aircraft speed, an aircraft flap configuration and WAI state, a flight path angle, and / or a predetermined pitch attitude limit.

[0035] Next, the method is operable to determine whether the sum of the pitch rate command, the scaled pitch rate, and the scaled pitch angle exceeds the pitch angle saturation limit. If the sum does not exceed the pitch angle saturation limit, the method is operable to apply 360 the pitch rate command to an elevator controller, an aircraft control surface controller, etc.

[0036] If the sum does exceed the pitch angle saturation limit, then next the method is operable to determine 340 whether the sum is suitable for TSP 340. In an exemplary embodiment, TSP can only be applied during takeoff of the aircraft. After the aircraft altitude exceeds a predetermined level, such as after liftoff or 10 feet, etc., TSP can be disabled and transitioned to flight stall protection or normal flight control rules. Additionally, in an exemplary embodiment, TSP can be enabled when one or more conditions are met, such as when the speed is greater than 75 knots calibrated airspeed (KCAS), the aircraft is on the ground, the flap handle is in a takeoff configuration, and / or the ground spoilers are not activated. If the sum is not suitable for TSP, the method is operable to apply the pitch rate command to an elevator controller, an aircraft control surface controller, etc.

[0037] If the sum is suitable for TSP, then next the method is operable to apply a regulator or additional pitch damper to convert it to a pitch angle command 350. In one exemplary embodiment, the pitch rate command system converts to a pitch angle limit system when saturation is effective. Next, the method is operable to apply 360 the modified pitch rate command to an elevator controller, an aircraft control surface controller, etc.

[0038] Turning now to Figure 4FIG. 4, shows a block diagram of a system 400 for takeoff stall control in an aircraft for illustrating example embodiments according to the present disclosure. The example system 440 can include a pitch rate controller 410, a processor 420, an airspeed sensor 430, a flap position sensor 440, and control surfaces.

[0039] The pitch rate controller 410 can be an input device, such as a flight control column, a side stick controller, a yoke, etc., configured to generate a pitch rate command in response to a pilot input, such as a deflection of the pitch rate controller 410, etc. The pitch rate controller can be operable to generate a pitch rate command indicative of a direction and a degree of deflection of the pitch rate controller 410, and further operable to couple a control signal to the processor 420 or a flight controller, etc. In example embodiments, the pitch angle command is generated in response to a pilot generated deflection of the pitch rate controller, and wherein the pitch rate controller is a flight control column.

[0040] The processor 420 can be operable to receive the pitch rate command from the pitch rate controller 410, and generate a control signal for coupling to the control surfaces 450, so as to control the pitch rate and other control aspects of the aircraft. In example embodiments, the processor 420 can be operable to receive the pitch rate command from the pitch rate controller 410, calculate a pitch angle saturation limit, and compare the sum of the pitch rate command, the scaled pitch rate, and the scaled pitch angle to the pitch angle saturation limit. In example embodiments, the pitch angle saturation limit is a safe aircraft pitch limit at a given airspeed, which is selected to limit the risk of a stall event. The pitch angle saturation limit can be determined in response to the aircraft speed, the aircraft flight path angle, and the free air stall angle of attack. If the sum exceeds the pitch angle saturation limit, indicating a potential stall risk, the processor 420 can be operable to convert it to a pitch rate command to adjust the pitch angle and limit the pilot up pitch rate command. In example embodiments, the pilot up pitch rate command is nullified when the saturation is active. When the pilot input generates a down pitch rate command sufficient to make the sum less than the saturation limit, the system converts to the pitch rate command system. This process can further take into account that the aircraft flaps configuration is in a takeoff state.

[0041] The processor 420 can then be operable to couple the damped pitch rate command to the aircraft control surfaces 450. The aircraft control surfaces 450 can be configured to adjust the aircraft control surface settings in response to the damped pitch rate to adjust the pitch angle. For example, the aircraft control surfaces 450 can be elevators, and can further include control circuitry or other controllers and / or processors for adjusting the aircraft control surfaces, such as ailerons and / or elevators.

[0042] Turning now to Figure 5The flowchart illustrates another non-limiting embodiment of a method 500 of providing takeoff stall control. The exemplary method for controlling an aircraft can be operable to receive 510 an aircraft speed from an aircraft speed sensor.

[0043] Next, the method can be operable to determine 520 a pitch angle saturation limit in response to the aircraft speed. The pitch angle saturation limit can also be determined in response to an aircraft flight path angle. In an exemplary embodiment, the pitch angle saturation limit is determined in response to the aircraft speed, the aircraft flight path angle, and a free air stall angle of attack, which can not be dependent on a radar altitude value.

[0044] Next, the method can be operable to receive 530 a pitch rate command from an aircraft control system. In an exemplary embodiment, the aircraft control system is a side stick aircraft control column. Alternatively, the aircraft control system can be an aircraft control column, yoke, control wheel, etc., operable to pilot and control an aircraft attitude. The pitch rate command represents a degree of deflection of the aircraft control system in response to pilot input. For example, a pilot pulling back on a side stick aircraft control column can result in a +9 degrees per second pitch rate command being coupled to an aircraft control processor, etc.

[0045] Next, the method can be operable to generate 540 a limited pitch up pitch rate command in response to the pitch angle saturation limit. If the sum of the pitch rate command, the scaled pitch rate, and the scaled pitch angle exceeds the pitch angle saturation limit in the aircraft airspeed range at ground state, an adjuster coefficient is applied to the pitch angle and pitch rate as an additional feedback signal to facilitate a conversion of the pitch rate command control law to a pitch angle tracking control law. In an exemplary embodiment, if the sum exceeds the pitch angle saturation limit, the pitch angle limit value is equal to the pitch angle command. In this example, the control law is effective as a pitch angle command system instead of a pitch rate angle command. In an exemplary embodiment, the limited pitch up pitch rate command can be superimposed on the pitch angle command, and the adjuster process causes the aircraft pitch angle to be tracked to the pitch angle command. In this example, when the pilot input generates a pitch down pitch rate command, the sum can be less than the saturation limit. The processor converts from the pitch angle command system to the pitch rate command system. The processor generates control surface commands to track the aircraft pitch rate to the pitch down pitch rate command. The pitch angle command can be further generated in response to a takeoff state indicator indicating that the aircraft is in a takeoff configuration. In another exemplary embodiment, the TSP is effective in response to the aircraft speed exceeding a 75 knot calibrated airspeed.

[0046] Then, the method can be operable to couple 550 the pitch angle command to an aircraft control surface. The aircraft control surface is an elevator. In an alternative embodiment, the method can be operable to couple the pitch angle command to the aircraft control surface in response to a control surface failure condition, an elevator stuck, or an elevator float.

[0047] While at least one exemplary embodiment has been given in the above detailed description of the application, it will be understood to those skilled in the art that there are further modifications that can be made to the example embodiments described therein without departing from the scope of the application. It is also to be understood that the one or more example embodiments are only examples and are not intended to limit the scope, applicability, or configuration of the application in any way. Rather, the foregoing detailed description will provide those skilled in the art with a convenient road map for implementing an exemplary embodiment of the application. It should be understood that various changes can be made in the function and arrangement of elements described in the example embodiments without departing from the scope of the application as set forth in the appended claims.

Claims

1. A flight control system comprising: an input device configured to generate a position signal in response to pilot input; and a processor operable to receive the position signal, compute a pitch rate command in response to the position signal, compute a pitch angle saturation limit at least partially in response to a flight path angle and a free air stall angle of attack, compare a sum of the pitch rate command, a scaled pitch rate, and a scaled pitch angle to the pitch angle saturation limit, generate a damped pitch rate command in response to the sum exceeding the pitch angle saturation limit, and couple the damped pitch rate command to an aircraft control surface.

2. The flight control system of claim 1, wherein the input device is an aircraft control column.

3. The flight control system of claim 1, wherein the input device is a side stick aircraft control column.

4. The flight control system of claim 1, wherein the pitch rate command is generated in response to pilot generated deflection of the input device, and wherein the input device is a side stick controller.

5. The flight control system of claim 1, wherein the aircraft control surface is an elevator.

6. The flight control system of claim 1, wherein the pitch angle saturation limit is determined in response to an aircraft speed, an aircraft attitude, an aircraft flight path angle, and a free air stall angle of attack.

7. The flight control system of claim 1, wherein the damped pitch rate command is configured to increase an effective damping of the aircraft control surface.

8. The flight control system of claim 1, wherein the damped pitch rate command is generated in response to the aircraft exceeding a predetermined speed and aircraft flaps being in a takeoff state.

9. A method for controlling an aircraft comprising: receiving an aircraft speed from an aircraft speed sensor; determining a pitch angle saturation limit at least partially in response to a flight path angle and a free air stall angle of attack; receiving a pitch rate command from an aircraft control system; generating a damped pitch rate command in response to a sum of the pitch rate command, a scaled pitch rate, and a scaled pitch angle exceeding the pitch angle saturation limit; and coupling the damped pitch rate command to an aircraft control surface.

10. The method for controlling an aircraft of claim 9, wherein the damped pitch rate command is generated in response to the aircraft exceeding a predetermined speed and aircraft flaps being in a takeoff state.

11. The method for controlling an aircraft of claim 9, wherein the aircraft control surface is an elevator.

12. The method for controlling an aircraft of claim 9, wherein the aircraft control system is a side stick aircraft control column.

13. The method for controlling an aircraft of claim 9, wherein the damped pitch rate command is determined in response to a free air stall angle of attack and a flight path angle.

14. The method for controlling an aircraft of claim 9, wherein the pitch angle saturation limit is further determined in response to an aircraft pitch attitude. coupling the pitch rate command to the aircraft control surface in response to the pitch angle saturation limit exceeding the pitch rate command.

15. The method for controlling an aircraft according to claim 9, comprising: ​ 16. The method for controlling an aircraft of claim 9, wherein the pitch rate command is generated in response to the aircraft speed exceeding a 75 knot calibrated airspeed.

17. An aircraft, comprising: an aircraft control handle configured to receive control motions for attitude adjustment in the aircraft and to generate a pitch rate command in response to the control motions for attitude adjustment; an airspeed sensor for determining an airspeed of the aircraft; a processor configured to receive the airspeed of the aircraft, the pitch rate command, and a flight path angle, to calculate a pitch angle saturation limit at least partially in response to the flight path angle and a free air stall angle of attack, to compare a sum of the pitch rate command, a scaled pitch rate, and a scaled pitch angle to the pitch angle saturation limit, to generate a damped pitch rate command in response to the sum of the pitch rate command, the scaled pitch rate, and the scaled pitch angle exceeding the pitch angle saturation limit; and a controller configured to control an aircraft control surface to control aircraft pitch in response to the damped pitch rate command.

18. The aircraft of claim 17, wherein the pitch angle saturation limit is determined in response to the aircraft speed, an aircraft flight path angle, and a stall angle of attack.

19. The aircraft of claim 17, wherein the damped pitch rate command is determined in response to a free air stall angle of attack and a flight path angle. ​

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