Longitudinal trim control motion during takeoff pull-up

Abstract

This invention relates to longitudinal trim control motion during takeoff and pull-up. This technology will allow takeoff from a single initial horizontal stabilizer or trim tab position while maintaining a satisfactory pull-up time, thus allowing for simpler aircraft operation and avoiding scenarios where the crew has not properly trimmed the aircraft (trim failure takeoff scenario) that could reduce safety margins.

Description

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims the benefit of U.S. Provisional Patent Application No. 63 / 043,897 (Attorney Docket No. 4439-359), filed June 25, 2020, which is hereby incorporated by reference in its entirety and for all purposes. TECHNICAL FIELD

[0003] The present technology relates to aircraft flight control, and more particularly to takeoff performance of fly-by-wire aircraft, providing a simpler and more efficient takeoff procedure and safety margin. BACKGROUND

[0004] Nose-up / nose-down pitch of an aircraft is a critical parameter for proper takeoff and flight. An aircraft is said to be “trimmed” in pitch when no force or correction to the flight controls is needed to maintain the aircraft in the desired nose-up / nose-down pitch attitude for stable flight. Once the aircraft is in flight, many modern aircraft automatically adjust the trim to maintain level flight.

[0005] Achieving a certain desired degree of nose-up / nose-down pitch trim during takeoff allows the aircraft to taxi along the runway with the nose wheel not leaving the ground, but still have the correct pitch attitude to lift off when the pilot pulls back on the yoke or control stick when the lift-off speed VR is reached. See, e.g., US-2018-0088593-A1. The pilot typically manually sets (“dials in”) the takeoff pitch trim (e.g., by rotating a trim wheel) to achieve the desired pitch trim for takeoff.

[0006] Longitudinal center of gravity (CG) position affects the nose-up / nose-down pitch trim of an aircraft for takeoff and level flight. Different aircraft fuel and payload configurations and weight distribution result in different configurations of the longitudinal CG position. Such different CG configurations can change the pitch trim of the aircraft. The pilot typically receives a “load sheet” prior to takeoff that indicates the takeoff CG position based on (a) the amount of fuel on board (and the fuel distribution between different fuel tanks) and (b) the weight / distribution of cargo. The pilot uses the “load sheet” to dial in the pitch trim for takeoff. To determine the aircraft weight and CG arm, it is necessary to add all the weight and moment changes related to the loaded items to the basic empty weight (BEW) of the aircraft. The total moment divided by the total weight results in the final CG arm. The CG arm must be converted to %MAC (mean aerodynamic chord). The weight / CG pair must be checked against the weight / CG envelope limits. FIG. 1A An example calculation of CG is shown.

[0007] Aircraft pitch trim is also affected by: changes in engine thrust above or below the CG; changes in the horizontal tail angle or trim tab position (see...). FIG. 2 The pitch trim setting is a function of several factors: the aircraft's takeoff weight; the position of the CG, flaps, and other control surfaces; and engine thrust (engine thrust from under the wings typically produces a nose-up attitude). Before takeoff, the pilot adjusts the trim wheel to change the position of the trim tabs on the horizontal stabilizer and / or the elevator on the tail to compensate for these effects, thereby achieving the desired nose-up / nose-down trim at takeoff.

[0008] Based on the CG configuration under takeoff conditions, modern aircraft provide the flight crew with guidance via the aircraft flight manual or some onboard displays on how to trim the horizontal stabilizer or trim pads within predefined limits known as the "green belt" before takeoff, in order to achieve proper pitch trim for takeoff. FIG. 1B An example trim indicator with a "green stripe" is shown. Other example "green stripes" are placed on the trim wheel so that the crew can see if the pitch trim they are dialing is exceeding the predetermined limits.

[0009] "Aircraft Nose Up" (ANU) trim can be determined as a percentage of the mean aerodynamic chord ("MAC") using existing CG. %MAC converted to ANU units should be within the restricted green band area, indicating the permissible range of takeoff "Stab Trim" for the current aircraft configuration.

[0010] If the flight crew fails to adjust the horizontal stabilizer or trim tabs to the correct CG value (a trim miscalculation takeoff scenario), it can affect the controllability and performance of the aircraft during takeoff, potentially impacting compliance with certification requirements—leading to increased takeoff field length and reduced safety margins. Therefore, a takeoff configuration warning is typically issued when attempting takeoff with pitch trim outside the restricted "green zone." This usually requires the flight crew to potentially abort the takeoff and manually readjust the horizontal stabilizer or trim tabs to achieve pitch trim within the takeoff "green zone" limits. Attached Figure Description

[0011] . FIG. 1A An example load table diagram is shown.

[0012] . FIG. 1B An example stabilizer trim setup with a "green band" is shown.

[0013] . FIG. 2 An example aircraft with a balancing plate is shown.

[0014] . FIG. 2A to FIG. 2DIt is a series of animated wall charts illustrating the dynamic operation of an aircraft, including:

[0015] . FIG. 2A The example conditions at the start of takeoff acceleration are shown—the horizontal stabilizer is fixed and the elevator is in the neutral position.

[0016] . FIG. 2B This demonstrates that upon reaching pull-up speed, the pilot will command the nose to point upwards and the elevator will move its trailing edge upwards. If the CG is at the FWD limit, the aircraft will not respond immediately, and the elevator will reach a value close to the detent (maximum permissible position).

[0017] . FIG. 2C It is shown that within a given duration (e.g., 0.5 seconds), with the elevator deflected and the aircraft response limited, the horizontal stabilizer or trim plate will move its trailing edge upward and help the aircraft generate a pull-up moment to perform takeoff.

[0018] . FIG. 2D This demonstrates that once the aircraft has taken off and the elevator has returned to the neutral position, the function will be deactivated and the aircraft will transition to normal flight control.

[0019] . FIG. 2E An example non-restrictive timing diagram is shown.

[0020] . FIG. 3 , FIG. 3A and FIG. 3B An example fly-by-wire aircraft control architecture is shown.

[0021] . FIG. 4 Example non-limiting functional logic of a processor-based fly-by-wire system controlled by a flight computer is shown. Detailed Implementation

[0022] The proposed solution addresses trim failure scenarios by providing an initial, single horizontal stabilizer position for takeoff, which is automatically set / adjusted upon energization. Given certain parameters during aircraft pull-up dynamics (e.g., airspeed, elevator position, receiver displacement, pitch rate, wheel weight (WOW) sensor readings, thrust lever angle), the example embodiment adjusts the horizontal stabilizer in the ANU (nose up) sense to ensure a satisfactory pull-up. Under the control of the fly-by-wire control system, the horizontal stabilizer or trim plate is constrained to move in a certain sense or direction for a predetermined time or period (e.g., 3 seconds) to provide a satisfactory pull-up motion.

[0023] The flight phases of an aircraft

[0024] . FIG. 2A to FIG. 2DThis is a series of animated wall charts illustrating the dynamic operations of an aircraft before and during takeoff. To view the animation, please use full-page view to view this patent electronically and use the "page down" key to navigate through the animation.

[0025] . FIG. 2A The diagram illustrates example conditions at the start of takeoff acceleration, with the horizontal stabilizer fixed and the elevator in the neutral position. Note the positions of the horizontal stabilizer and elevator. From this position, the aircraft will begin accelerating along the runway, with its wheels maintaining contact with the ground.

[0026] . FIG. 2B This illustrates that upon reaching pull-up speed (VR), the pilot will command the nose to tilt upwards and the elevator will move its trailing edge upwards. If the CG is at the FWD limit, the aircraft will not respond immediately, and the elevator will reach a near-locked value (maximum permissible position).

[0027] . FIG. 2C It is shown that during a given duration (e.g., time period T1 = 0.5 seconds), the elevator deflects and the aircraft responds in a limited way. The horizontal stabilizer or trim plate will move its trailing edge upward and help the aircraft generate a pull-up moment to perform takeoff during a limited time period T2 (e.g., = 3 seconds).

[0028] . FIG. 2D This demonstrates that once the aircraft has taken off and the elevator has returned to the neutral position, the trim function will be deactivated and the aircraft will transition to normal flight control.

[0029] . FIG. 2E An example timeline is shown. The aircraft will first taxi to its position at the runway threshold and remain stationary until the pilot gives the takeoff command. During this time, the horizontal stabilizer and elevator are in their neutral positions. FIG. 2A At the pilot's command, the aircraft then began taxiing along the runway and accelerated during its takeoff roll. Upon reaching pull-up speed VR, the pilot commanded the aircraft to pull up by deflecting the elevator to a nose-up position. FIG. 2B The example embodiment's automated system uses sensors to detect limited aircraft response (i.e., inability to pull up) during time period T1, even though the elevator begins in its latching position. If limited response is detected, the example embodiment's automated system intervenes by automatically moving the horizontal stabilizer and / or trim tabs during time period T2 to help the aircraft generate a pull-up motion to perform takeoff. FIG. 2C Once time period T2 expires, the automatic system in the example embodiment is deactivated, and the aircraft will transition to normal flight control. FIG. 2D .

[0030] . FIG. 3AThe control system of an example aircraft A is shown. Two elevators or trim tabs (1) are mounted in the horizontal stabilizer / tail TW for pitch control, and two flaps F are mounted in the main wing W to control lift and slow the aircraft during landing. The tail elevator / trimming tab 1 controls the pitch of aircraft A during takeoff, flight, and landing. The pilot in cockpit C interacts with aircraft A using receiver 2 and flap stick 7 to control the control surfaces, including the flaps F and elevators / trimming tabs 1. Fly-by-wire electronic flight control system (see...) FIG. 3B The system receives pilot input (e.g., via manual operation of flap stick 7 and pilot receiver 2) and controls the actuators using an automatic control law typically implemented by a digital (computer) processing system coupled to a non-transitory memory for storing data and instructions (see [link to relevant documentation]). FIG. 3B These actuators then control the position of the flaps F and the elevator / trimming plate 1.

[0031] . FIG. 4 An example non-limiting flowchart illustrating the procedural control steps performed by a fly-by-wire system is shown. In one example embodiment, the initial takeoff trim position prior to takeoff is defined (box 102; see...). FIG. 2A To meet all of these conditions:

[0032] Takeoff under extreme AFT (rear) CG conditions (this condition will not require movement of the horizontal stabilizer or trim plate during takeoff pull-up) – The initial horizontal stabilizer or trim plate position before takeoff must allow the nose landing gear to remain on the ground before reaching the initial pull-up speed (VR).

[0033] Takeoff under extreme FWD (forward) CG conditions (which would require movement of the horizontal stabilizer or trim plate during takeoff pull-up) – after the horizontal stabilizer or trim plate has moved from its initial position for a finite time (e.g., T2 = 3 seconds) during takeoff pull-up, the horizontal stabilizer or trim plate must provide satisfactory performance and handling qualities during takeoff pull-up. In this case, the system... FIG. 3 The system is "armed" and begins sensing wheel weight (to determine if the aircraft is still on the ground), airspeed data (to determine when the aircraft reaches pull-up speed VR), and thrust lever angle (to determine how much thrust the pilot commands the engines to produce). It should be noted that the system does not arm itself if the CG is behind the intended position on the aircraft—it armes only if the CG is ahead of the intended position. This determination is typically made by the processor in response to load table information.

[0034] After taxiing, the aircraft advances to the center of the runway and (usually in response to air traffic control clearance) begins its takeoff roll (the process of aligning the aircraft with the runway centerline and moving forward in preparation for takeoff). At this point, the pilot increases the angle of the engine thrust stick, commanding the engines to produce significant or maximum thrust—and the aircraft begins to accelerate as it rolls along the runway. During this takeoff roll, as the aircraft accelerates and, in extreme AFT CG conditions, a denial-of-take (RTO) scenario may occur, the nose landing gear must remain on the ground throughout the maneuver. Therefore, the processor will not cause the aircraft to pitch further up, as this would increase the chance of a tail strike.

[0035] The system then detects when the aircraft reaches pull-up speed (e.g., speed = VR). At this point, the pilot commands the nose to turn upward by pulling back the control stick or receiver. This causes the elevator to move, with the trailing edge pointing upward. If the aircraft has been properly pitch-trimmed for the current load and thrust, the aircraft will pull up and leave the ground without any automatic assistance. However, if the center of gravity is at the FWD limit, the aircraft will not respond immediately, and the pilot will continue to pull back the receiver or control stick until the elevator reaches a near-locked value (i.e., the maximum permissible position within its range of motion). This means the elevator is controlling the maximum pitch angle, but the aircraft is still not pulling up. If this situation persists for more than a certain period of time (e.g., T1 = 0.5 seconds), instead of immediately issuing an RTO (Reject Takeoff) warning, the fly-by-wire system automatically provides assistance by controlling the horizontal stabilizer and / or trim tabs to move the trailing edge upward, and assists the aircraft in generating a pitch pull-up motion to perform takeoff (the RTO warning will not be heard after the aircraft reaches a "commit to fly" speed of V1 ≤ VR; the system must ensure that all takeoffs within the weight and center of gravity range to be certified will provide a satisfactory pull-up). While monitoring the pitch response, the system controls the horizontal stabilizer and / or trim tabs for a limited duration (e.g., T2 = 3 seconds) (see...). FIG. 3 (The "Functional Participation" box).

[0036] If the aircraft begins to pull up satisfactorily and there is still sufficient runway, the fly-by-wire system continues to control the horizontal stabilizer and / or trim tabs to continue automatically commanding the aircraft to pitch up and thus pull up. Once the aircraft is airborne and the elevator position returns to normal (e.g., by the pilot pushing back the control stick or lever), the fly-by-wire system deactivates the trim overrun, and the aircraft transitions to normal flight control.

[0037] The position of the horizontal stabilizer and trim plate after a finite amount of time (e.g., 3 seconds) must guarantee the optimal minimum takeoff speed (VMU) (i.e., the calibrated airspeed at which the aircraft can safely take off and continue takeoff, and at airspeeds above that; see Federal Aviation Administration Standard Part 25, Section 107(d)). The aircraft's VMU speed is selected within the thrust-to-weight ratio range to be certified, typically established based on free-air data validated through ground takeoff tests. The position and time of movement of the horizontal stabilizer and trim plate in the example embodiment provide an appropriate VMU for aircraft certification.

[0038] To limit when the horizontal stabilizer or trim plate moves during takeoff and pull-up (boxes 104-108), some constraints are used:

[0039] The movement of the horizontal stabilizer or trim plate during takeoff pull-up occurs when all of the following conditions are met (see...). FIG. 2B , FIG. 2C (Boxes 106 and 108) will begin:

[0040] (1) The plane is still on the ground.

[0041] (2) The elevator or longitudinal receiver control approaches its latch (maximum permissible position) and the aircraft does not respond to pitch rate within a predetermined time (e.g., 0.5 seconds).

[0042] (3) The angle of the thrust rod is at the TOGA position.

[0043] (4) The calibrated airspeed is higher than a certain airspeed (e.g., VMU-10kt).

[0044] In other words, when the aircraft reaches pull-up speed, if the aircraft sensors determine that the elevator is deflected and the aircraft response is limited within a certain time period (e.g., 0.5 seconds), the automatic pitch function is activated.

[0045] The movement of the horizontal stabilizer or balancing plate will stop when any of the following conditions are met (box 110; see also...). FIG. 2D ):

[0046] (1) The elevator returns to a value closer to neutral.

[0047] (2) The thrust lever angle is reduced to the idle position (indicating that the pilot has aborted takeoff).

[0048] (3) The movement duration becomes greater than the predefined maximum value (e.g., 3 seconds).

[0049] In other words, if the pilot commands the elevator to return to neutral or closer to neutral (which may indicate RTO or pull-up completion); or if the pilot returns the engine thrust lever control to idle (thus indicating RTO); or if the overdrive duration times out, the fly-by-wire system will cease its forced pitch command to the trim control surfaces.

[0050] This technology will allow takeoff from a single initial horizontal stabilizer or trim tab position while maintaining a satisfactory pull-up time, thus allowing for simpler aircraft operation and avoiding scenarios where the crew has not properly trimmed the aircraft, which could reduce safety margins (trim failure takeoff scenario).

[0051] In one embodiment, the automatic trim function is not considered "over-control" because the pilot can counteract it and regain control by pressing the pitch trim switch.

[0052] All patents and publications cited in this article are incorporated herein by reference as if explicitly stated.

[0053] While the invention has been described in conjunction with embodiments that are now considered to be the most practical and preferred, it should be understood that the invention is not limited to the disclosed embodiments, but rather is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims.

[0054] Some abbreviations:

[0055]

[0056]

Claims

1. A method for controlling an aircraft during takeoff, comprising: Sensing the pull-up command; Sensing the aircraft's pull-up response to the pull-up command; Detect the position of the elevator; as well as When it is sensed that the aircraft cannot pull up and the sensed elevator position is at its maximum or moving from the neutral position toward its maximum, at least one processor is used to automatically move the pitch trim control surface from the initial takeoff position to help the aircraft pitch up to pull up. The processor automatically moves the pitch trim control surface during takeoff and pull-up when all of the following conditions are met: a. The aircraft is on the ground; b. The elevator or longitudinal receiver control moves toward its maximum permissible position, and the aircraft is unable to pull up within a predetermined time. c. The thrust rod angle is in the takeoff / go-around position; and d. The calibrated airspeed is higher than a certain airspeed at which the aircraft can safely take off and continue its takeoff; and / or The processor stops moving the pitch trim control surface when any of the following conditions are met: e. The elevator returns to the neutral position; f. The thrust lever angle decreases to the idle position, indicating to the pilot that takeoff has been aborted; g. The duration of movement of the pitch trim control surface becomes greater than the predefined maximum value.

2. The method according to claim 1, wherein, The pull-up command is entered by the pilot.

3. The method according to claim 1, wherein, The pitch trim control surface includes a horizontal stabilizer or a trim plate.

4. The method of claim 1, further comprising defining an initial takeoff position of the pitch trim control surface prior to takeoff.

5. A system for controlling an aircraft during takeoff, comprising: At least one processor, operatively coupled to a pilot receiver input and a control surface actuator output, the at least one processor performing operations based on executing instructions stored in a non-transitory memory, the operations including: Sensing the pull-up command; Sensing the aircraft's pull-up response to the pull-up command; Sensing the position of the elevator; and When it is sensed that the aircraft cannot pull up and the sensed elevator position is at its maximum or moving from a neutral position toward its maximum, the pitch trim control surface will be automatically moved from the initial takeoff position to assist the aircraft in pitching up for a pull-up; and The processor automatically moves the pitch trim control surface during takeoff and pull-up when all of the following conditions are met: a. The aircraft is on the ground; b. The elevator or longitudinal receiver control moves toward its maximum permissible position, and the aircraft is unable to pull up within a predetermined time. c. The thrust rod angle is in the takeoff / go-around position; and d. The calibrated airspeed is higher than a certain airspeed at which the aircraft can safely take off and continue its takeoff; and / or The processor stops moving the pitch trim control surface when any of the following conditions are met: e. The elevator returns to the neutral position; f. The thrust lever angle decreases to the idle position, indicating to the pilot that takeoff has been aborted; g. The duration of movement of the pitch trim control surface becomes greater than the predefined maximum value.

6. The system according to claim 5, wherein, The pull-up command is entered by the pilot.

7. The system according to claim 5, wherein, The pitch trim control surface includes a horizontal stabilizer or a trim plate.

8. The system according to claim 5, wherein, The at least one processor is further configured to define the initial takeoff position of the pitch trim control surface prior to takeoff.

9. The system according to claim 5, wherein, The at least one processor is further configured to adjust the automatic movement of the pitch trim control surface based on whether the aircraft's center of gravity is behind or in front of the predetermined aircraft position.

10. An aircraft comprising: An aerodynamic body, the aerodynamic body including a pilot receiver and elevator, as well as a horizontal stabilizer and / or trim plate; elevator actuator; Horizontal stabilizer actuator and / or flat plate actuator; Inertial sensor; A fly-by-wire control system that enables the pilot to control the elevator via the elevator actuator by operating the pilot receiver. The fly-by-wire control system includes at least one processor operatively coupled to an inertial sensor, the pilot receiver, and operatively coupled to the horizontal stabilizer actuator and / or trim plate actuator. The at least one processor performs operations based on executing instructions stored in a non-transitory memory, the operations including: Based on the pilot's receiver sensing the pull-up command; The inertial sensor is used to sense the aircraft's pull-up response to the pull-up command; Determine and / or control the position of the elevator; and When it is sensed that the aircraft cannot pull up and the determined and / or controlled elevator position is at its maximum or moving from a neutral position toward its maximum, the horizontal stabilizer and / or trim tabs are automatically moved from the initial takeoff position to assist the aircraft in pitching up for a pull-up; and The processor automatically moves the pitch trim control surfaces during takeoff and pull-up when all of the following conditions are met: a. The aircraft is on the ground; b. The elevator or longitudinal receiver control moves toward its maximum permissible position, and the aircraft is unable to pull up within a predetermined time. c. The thrust rod angle is in the takeoff / go-around position; and d. Calibrate an airspeed higher than a certain airspeed that allows the aircraft to safely take off and continue its takeoff journey; and / or The processor stops moving the pitch trim control surface when any of the following conditions are met: e. The elevator returns to the neutral position; f. The thrust lever angle decreases to the idle position, indicating to the pilot that takeoff has been aborted; g. The duration of movement of the pitch trim control surface becomes greater than the predefined maximum value.

11. The aircraft according to claim 10, wherein, The pull-up command is entered by the pilot.

12. The aircraft according to claim 10, wherein, The processor automatically moves the trim piece after the aircraft reaches a speed exceeding the takeoff speed.

13. The aircraft according to claim 10, wherein, The at least one processor is further configured to define the initial takeoff position of the horizontal stabilizer and / or trim plate prior to takeoff.

14. The aircraft according to claim 10, wherein, The at least one processor is further configured to adjust the automatic movement of the horizontal stabilizer and / or trim plate based on whether the aircraft's center of gravity is behind or in front of the predetermined aircraft position.

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