SAFE TAKEOFF SYSTEM

Abstract

An aircraft includes a safe takeoff system that automatically and autonomously rejects a takeoff if actual measured acceleration deviates from calculations based on pre-flight parameters and the speed of the aircraft traveling down the runway is within a safe speed range to guarantee a successful low inertia rejected takeoff.

Claims

1. On an aircraft, a system comprising: at least one inertial sensor producing a first signal; at least one wind speed sensor producing a second signal; and at least one flight computer, operatively coupled to the at least one inertial sensor and the at least one wind speed sensor, the at least one flight computer configured to: determine an acceleration in response to the first signal; compare the determined acceleration with an expected acceleration value; determine, in response to the second signal, whether the aircraft is operating within a safe speed; and issue control signals to automatically abort takeoff conditioned on both the comparison and the safe speed determination.

2. The system of claim 1, wherein the inertial sensor comprises an accelerometer.

3. The system of claim 1, wherein the inertial sensor comprises a gyro-sensor.

4. The system of claim 1, wherein the wind speed sensor comprises an anemometer.

5. The system of claim 1, further including a sensor configured to measure parameters indicative of aircraft configuration.

6. The system of claim 1, wherein the at least one flight computer determines the acceleration in response to the first signal indicating at least one parameter indicative of inertial movement.

7. The system of claim 1, wherein the at least one flight computer is configured to calculate an expected acceleration in response to the aircraft weight, runway information, weather parameters, and takeoff configuration.

8. The system of claim 1, wherein the at least one flight computer uses the comparison to automatically reject takeoff due to discrepancy between takeoff parameters.

9. The system of claim 1, wherein the at least one flight computer further comprises: at least one processor configured to automatically: a) process the first signal and compute in response thereto a current acceleration; b) compare expected longitudinal acceleration value and the current acceleration to predict whether the aircraft is unable to take off safely using current takeoff parameters; and c) determine if the aircraft is operating within a safe speed and is therefore able to perform a safe RTO.

10. A system for monitoring the safe takeoff of an aircraft, comprising: at least one inertial sensor producing a signal; and at least one flight computer, operatively coupled to the at least one inertial sensor, configured to: a) determine an acceleration in response to the signal; b) compare the determined acceleration with an expected acceleration value; and c) issue control signals to automatically abort takeoff conditioned on discrepancy in the comparison.

11. A system for monitoring safe takeoff of an aircraft, comprising: at least one wind speed sensor producing a signal; and at least one flight computer, operatively coupled to the at least one wind speed sensor, the at least one flight computer configured to: a) determine, in response to the signal, whether the aircraft is operating within a safe speed; and b) issue control signals to automatically abort takeoff conditioned on the safe speed determination and at least one additional factor.

12. An aircraft, comprising: at least one inertial sensor producing a first signal; at least one wind speed sensor producing a second signal; at least one flight computer, operatively coupled to the at least one inertial sensor and the at least one wind speed sensor, the at least one flight computer configured to: a) determine a current acceleration in response to the first signal; b) compare the determined current acceleration with an estimated acceleration value; c) determine, in response to the second signal, whether the aircraft is operating within a safe speed; and d) issue control signals to automatically abort takeoff conditioned on both the comparison and the safe speed determination.

13. The aircraft of claim 12, wherein the inertial sensor comprises an accelerometer.

14. The aircraft of claim 12, wherein the inertial sensor comprises a gyro-sensor.

15. The aircraft of claim 12, wherein the wind speed sensor comprises an anemometer.

16. The aircraft of claim 12, further including at least a sensor configured to measure a parameter indicative of aircraft configuration.

17. The aircraft of claim 12, wherein the at least one flight computer determines the current acceleration in response to the first signal indicating inertial movement of the aircraft.

18. The aircraft of claim 12, wherein the at least one flight computer is configured to calculate the expected estimated acceleration value by processing the aircraft weight, runway information, weather parameters, and takeoff configuration.

19. The aircraft of claim 12, wherein the at least one flight computer uses the comparison to automatically reject takeoff due to discrepancy between takeoff parameters.

20. The aircraft of claim 12, wherein the at least one flight computer further comprises: at least one processor configured to automatically: a) process the first signal and compute in response thereto a current acceleration; b) compare expected estimated longitudinal acceleration and current acceleration to predict whether the aircraft is unable to take off safely; and c) determine if the aircraft is within the upper and lower bounds of the safe speed and is therefore able to perform a safe RTO.

21. A method of automatically rejecting takeoff comprising: a) determining a current acceleration in response to an inertial sensing signal; b) comparing the determined current acceleration with an expected acceleration value; c) determining, in response to a speed signal, whether the aircraft is operating within a safe speed; and d) issuing control signals to automatically abort takeoff conditioned on both the comparison and the safe speed determination.

22. The method of claim 21, further including deriving the expected acceleration value from the estimated aircraft weight, runway information, weather parameters, and takeoff configuration.

23. The method of claim 21, further including deriving said safe speed bounds of lower and upper limits of favorable aircraft speeds.

24. A method of automatically rejecting takeoff, the method comprising: determining a current acceleration in response to a signal; comparing the determined current acceleration with an expected acceleration value; and issuing a control signals to automatically abort takeoff conditioned on the discrepancy of the comparison.

25. The method of claim 24, further including producing the signal is produced by inertial sensor(s).

26. The method of claim 24, further including producing the expected acceleration value from the estimated weight of aircraft, runway information, weather parameters, and takeoff configuration.

27. A method of automatically rejecting takeoff, the method comprising: determining, in response to a speed signal, whether the aircraft is operating within a safe speed window; and issuing control signals to automatically abort takeoff conditioned on the safe speed window determination.

28. The method of claim 27, further including producing the signal using wind speed sensor(s).

29. The method of claim 27, wherein said safe speed window is defines lower and upper limits of favorable aircraft speeds during takeoff.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0015] The following detailed description of exemplary non-limiting illustrative embodiments is to be read in conjunction with the drawings, of which:

[0016] FIG. 1 is a non-limiting illustrative embodiment showing forces (e.g., thrust, wheel friction, wheel drag, configuration drag, etc.) and a resulting longitudinal acceleration that an aircraft incurs during takeoff.

[0017] FIG. 2 is an example schematic block diagram of an example non-limiting safe takeoff system for conditionally automatically rejecting takeoff.

[0018] FIG. 3 schematically shows an example non-limiting data evaluation and system decision process.

[0019] FIG. 4A illustrates an example non-limiting definition of a safe speed window based on ratios of actual vs. predicted aircraft weight, the window providing an upper threshold and a lower threshold.

[0020] FIG. 4B illustrates a non-limiting example of a safe speed window with preferable upper and lower speed ranges.

[0021] FIG. 5 illustrates signal flow of an example non-limiting embodiment of an automatic takeoff rejection system.

[0022] FIG. 6A illustrates how estimated longitudinal acceleration can be calculated.

[0023] FIG. 6B shows example non-limiting automatic takeoff rejection decision logic.

[0024] FIG. 7 illustrates how current acceleration may be measured/determined.

DETAILED DESCRIPTION OF EXAMPLE NON-LIMITING EMBODIMENTS

[0025] FIG. 1 shows forces including drag 100 and wheel friction 105 that an aircraft typically experiences during the takeoff phase of flight. The Figure shows an aircraft moving down a runway at a longitudinal acceleration that is determined in accordance with F=ma, where F are the forces being exerted on the aircraft, m is the mass of the aircraft, and a is the acceleration.

[0026] The mass a is determined based on the total weight of the aircraft, including the aircraft itself, fuel, passengers, baggage and cargo.

[0027] The force F on the aircraft has several components. One component is the amount of thrust produced by the engines. Another component is the friction and drag exerted on the aircraft. Drag is defined as the resistance that opposes the direction 103 that an aircraft is moving.

[0028] Graphic 105 is a free-body-diagram used to show that the force related to forward acceleration (F.sub.a) is greater than all other forces involved in the aircraft's takeoff phase. Such other forces include the force of gravity (F.sub.g) that is pulling the aircraft towards the ground, the force of friction (F.sub.) (opposite to the direction of aircraft movement) and the normal force (F.sub.n), which are responsible for the drag that the aircraft incurs during takeoff.

[0029] There are many factors that affect the magnitude of the drag force 100 including the aerodynamic shape of the aircraft (including its current configuration, such as the position of the flaps), the viscosity of the air (which depends on air temperature and altitude), and the velocity of the aircraft. All of the individual components of drag are combined into a single aircraft drag magnitude.

[0030] Rolling friction 105 is the resistive force that slows down the motion of a rolling wheel. It is also called rolling resistance.

[0031] Once a wheel is rolling, the resistance to the motion is typically a combination of several friction forces at the point of contact between the wheel and the ground or other surface. This assumes the brakes are offsince the brakes are designed to increase rolling friction. The amount of rolling friction depends on several factors including the weight of the aircraft (since the weight exerts a downward force on the wheels that increase the friction coefficient), the inflation and type of tires, and the composition of the runway surface.

[0032] One of the insights provided by the present non-limiting technology: the longitudinal acceleration can be directly measured using an inertial sensor, and used as a check against the weight and associated parameters calculated by the flight engineer/dispatch.

[0033] FIG. 2 illustrates schematic logic following the flight computer 200 to decide whether to reject takeoff. The flight computer/fly-by-wire (FBW) controller 200 is in this case comprised of at least one processor 222, a memory 224, and a safe takeoff program 224. It is configured to automatically and autonomously reject takeoff under certain criteria. The flight computer 200 determines takeoff rejection by processing various takeoff parameters including: [0034] signals from the airspeed sensor(s) 202, [0035] signals from inertial sensor(s) 204, [0036] signals from aircraft configuration sensor(s) 206, [0037] dispatch/pilot input 208, and [0038] thrust lever 210 selection.

[0039] Flight computer 200 conditionally outputs: [0040] a signal to the pilots' display 212 (e.g., PDF, EICAS), [0041] a signal to the engine control 214, [0042] a signal to the braking control 216, [0043] a signal to the flaps control 218, and [0044] signals to other control(s) 220.

[0045] In appropriate cases, the flight computer 200's output signals command the aircraft automatically execute an RTO by reducing or reversing thrust, applying brakes, increasing drag by controlling flaps down, and decelerate safely to a stop.

[0046] In determining whether to execute an RTO, the flight computer 200 is able to determine whether the operational procedures of the aircraft during takeoff are either safe or unsafe. The operational procedures during takeoff are defined by the input takeoff parameters. A safe takeoff involves agreement between (a) estimated longitudinal acceleration calculated based on presumed weight of the aircraft, and (b) current actual acceleration as measured by an inertial sensor. An unsafe set of parameters, which leads to a rejection of takeoff, is detected based on an incongruence in the comparison of the estimated longitudinal acceleration and the current measured acceleration.

[0047] However, not all such incongruences are the basis for an automatic RTO in the example non-limiting embodiments. In particular, the example non-limiting embodiment flight computer 200 also determines whether an RTO can be safely executed. It is well known that RTO's at high speeds approaching or exceeding V1 can be dangerous. Therefore, the example non-limiting embodiment will only perform an automatic RTO if the measured speed of the aircraft is within a safe range.

[0048] If an incongruence is detected, the flight computer 200 executes the rejection of takeoff by displaying on the cockpit that the system has decided to reject takeoff, while reducing the thrust of the aircraft, activating the wheel brakes, and controlling the aerodynamic surfaces (e.g., raising spoilers, lowering flaps, etc.) in order to increase drag to try and bring the aircraft to a safe stop.

[0049] FIG. 3 depicts a non-limiting example data evaluation and system decision process. In response to estimated weight 208 provided by the flight engineer/dispatch system, weather parameters 208 (e.g., temperature, wind, etc.) and airport data 208 (runway information), a computer (either the flight computer 200 on board the aircraft, a ground computer at dispatch, or some other computer) is configured to calculate the thrust 210 and V-speeds 302 that should be applied during a takeoff procedure. V-speeds or Velocity-speeds are well-known conventional velocity terms used to define critical airspeeds for the operational procedures of aircraft.

[0050] V.sub.1 is the so called decision pointnamely the maximum speed during takeoff at which a pilot can safely execute an RTO without overrunning the runway. V.sub.2 is defined as the takeoff safety speed. And V.sub.R is the rotation speed, the speed at which the pilot may rotate the aircraft so its nosewheel leaves the ground and it begins to climb into the air.

[0051] Based on these same parameters inputted into the dispatch computer 300, (weight 208, takeoff configuration 206, V-speeds 302, and thrust 210) it is also possible to estimate the aircraft's drag 100 and wheel friction forces 105. By estimating thrust 210, drag 100, and wheel friction forces 105 it is possible to estimate a longitudinal acceleration value 204-A of the aircraft based on the dispatch information. This estimated acceleration value can be checked to measured acceleration 204-B that is obtained from the inertial sensor(s) 204 of the aircraft as the aircraft accelerates down the runway.

[0052] In simple terms, if the measured acceleration differs significantly from the estimated acceleration, then the actual weight of the aircraft is likely not the same as the estimated weight used to calculate the estimates acceleration. F=ma can be rewritten as a=F/m. So for the equation:

F/m.sub.estimated:a.sub.measured

if the estimated mass (m) very wrong, then the measured acceleration will not match the estimated acceleration calculated based on the estimated mass.

[0053] In the example shown, the expected longitudinal acceleration value 204-A and the measured acceleration value 204-B are compared in the flight computer 200 of the aircraft as the aircraft begins moving down the runway. This is in the nature of a physics experiment with practical consequences: if the flight computer 200 determines that the two acceleration values are consistent, then normal takeoff procedure 312 is followed and no intervention is required. However, if the flight computer 200 determines that the two acceleration values are not consistent, then there is a problem. Specifically, the estimated weight of the aircraft has been experimentally determined to be incorrect. The pilot is notified of this discrepancy; and in the example non-limiting embodiment, the flight computer 200 autonomously performs an RTO if it is safe to do so.

[0054] To determine safety of an RTO, the safe takeoff program 224-B in one example non-limiting embodiment is configured to determine whether the aircraft's speed 202 is inside a safe speed window. Therefore, for example, takeoff rejection 311 is conditioned on whether the measured speed of the aircraft is below a safe stopping speed. If the aircraft is within the safe speed window, then the flight computer 200 automatically aborts the takeoff 311. On the other hand, if the aircraft speed is outside the defined margin of a safe stopping speeds, then the safe takeoff program 224-B is configured to repeat 313 the comparison of the acceleration values while potentially also warning the pilot that something may be wrong.

[0055] In one example non-limiting embodiment, the entire process is transparent to the pilot. The pilot does not need to perform any procedure. This will reduce the pilot's workload in a very demanding flight phase, as well as to produce a more consistent operation.

[0056] The new non-limiting technology herein thus proposes a system that automatically rejects or aborts takeoff if erroneous takeoff parameters or data are detected. In order to prevent a runway excursion or overrun, the rejected takeoff shall occur only in a well-defined speed window between a Lower limit speed and an upper limit speed, where: [0057] Lower Limit Speed: Below this value, the anemometric system is not capable of estimating the speed of the aircraft with a necessary accuracy. [0058] Upper Limit Speed: Up to this speed, it is possible to guarantee that the aircraft can safely abort the takeoff without the risk of a runway excursion or overrun. In layman's terms, this means a low kinetic energy rejected takeoff.

[0059] FIG. 4A depicts a graph wherein the concept of a speed window is defined. The speed window 403 is a margin, bounded by an upper threshold 402 and a lower threshold 401. The lower threshold 401, referred to as the Lower Limit Speed (LLS), is the specific value where any airspeed below this limit is unmeasurable by the anemometric system due to the fact that the aircraft is not moving fast enough. In the same manner, the upper threshold 402, referred to as the Upper Limit Speed (ULS), is the limit that guarantees a safe rejection of takeoff without the risk of a runway excursion. Although the graph compares the ratio of calculated and actual weight, acceleration should be the parameter compared, but weight and acceleration are correlated and the final effect is similar.

[0060] FIG. 4B considers a non-limiting embodiment of a speed window, that has a: [0061] Lower Limit: Typically, this value should be around 30 to 50 knots, preferably around 30-40 knots. [0062] Upper Limit: This speed should be in the order of 70 to 100 knots, preferably around 80-100 knots.

[0063] In the non-limiting example, with the speed window considered, it is not necessary to estimate the remaining distance on the runway, since with low energy the aircraft will be capable to abort the takeoff in any runway that it can be dispatched to.

[0064] It should be noted that the safety aspect of the safe speed window results from the upper speed limit. In the example embodiment, the lower speed limit is used merely to ensure that the measured aircraft speed is accurate. As is well known, typical anemometric speed sensors do not begin providing valid speed data until the aircraft is moving at above a minimum speed. However, there are other known ways to measure aircraft speed such as GPS, and the particular nature of the low speed threshold (or if any is applied) may depend on the type of speed sensor(s) being used.

[0065] However, it can be seen from FIGS. 4A and 4B that for a wide range of estimated to actual weight values, the resulting speed data statistically converge at above a low speed threshold. This is because for a given thrust, the rate of change of velocity depends on weight. This means that above a low speed threshold, the same procedure can be applied to a wide variety of weight discrepancies to result in a valid test.

[0066] FIG. 5 illustrates example non-limiting signal flow of the aircraft's auto rejection system. The system is configured to receive dispatch data (e.g., estimated weight 208, weather parameters 208, runway info 208, takeoff configuration 206, etc.) from the ground computer. Among the parameters calculated by the dispatch computer 300 using the dispatch data are V-speeds (e.g., V.sub.1, V.sub.R, V.sub.2), and thrust lever 210 selection. As explained before, with these parameters inputted into the dispatch computer 300 it is also possible to estimate the aircraft's drag 100 and wheel friction forces 105. With drag 100 and wheel friction forces 105 calculated, it is possible to estimate a longitudinal acceleration value 204-A. This estimated acceleration value can be compared 224-A to measured acceleration 204 that is obtained from the inertial sensor(s) 204.

[0067] If the measured and estimated acceleration values match within a certain tolerance, then normal takeoff procedure 312 is followed from the safe takeoff program 224-A. However, if the flight computer 200 determines that the acceleration values are very different, then the safe takeoff program 224-B is configured to determine whether the aircraft's speed 202 is inside a safe speed window. If the aircraft is within the speed window, then the flight computer 200 automatically aborts the takeoff 311 and autonomously performs an RTO. On the other hand, if the measured speed of the aircraft is outside of the safe speed window, then the safe takeoff program 224-B is configured to take no action and repeat 313 the comparison of the acceleration values.

[0068] FIG. 6A shows a non-limiting means that can be used by the aircraft to calculate the estimated longitudinal acceleration. Some inputs used to calculate the estimated longitudinal 610 acceleration come from different sensors or state information that indicate aircraft takeoff configuration 206 (e.g., flap/slat configuration). Other input parameters (the ones to be tested) are obtained from dispatch, such parameters including estimated weight 208. Dispatch also supplies additional information such as weather 208 (including air density), runway info 208, etc.). Criteria such as V-speeds 302 and thrust settings 210 are calculated using such inputs (e.g., estimated weight 208, weather 208, runway information 208, etc., as explained above). All inputs are processed by a processing unit (e.g., microprocessor) 608 in the aircraft's flight computer 200 and/or by the ground computer or some other computer. The processing unit is able to calculate the aircraft's drag and wheel friction forces, making it possible to estimate the longitudinal acceleration of the aircraft 204-A.

[0069] FIG. 6B illustrates an example non-limiting means of determining takeoff rejection by comparing the estimated longitudinal acceleration with the measured acceleration, and determining whether the aircraft is moving at a safe stopping speed. Such logic can be implemented in a variety of ways such as by a software controlled process, a gate/logic array, or any other suitable implementation. The estimated longitudinal acceleration signal 704 and the measured acceleration signal 702 are received by a subprocessing unit 700 in the flight computer 200. The flight computer is configured to receive both acceleration values and compare them using a comparator 706. Comparator 706 determines whether to output a safe takeoff signal 312 (meaning that both accelerations are substantially equal) or send a signal 708 to a structural and/or software based logic to check whether it is safe to reject takeoff.

[0070] Concurrently, the anemometric system 804 measures wind speed to determine whether the aircrafts' speed is within a range defined by a safe speed window. The anemometric system 804 measures the speed of the wind relative to the aircraft and thus the speed of the aircraft (once wind speed and direction is taken into account). The anemometric system 804 outputs a measurement value to comparator 806, which determines whether the measured wind speed value is between the lower limit and the upper limit defined by the speed window. If the measured value is within the range defined between the limits, then a signal 808 is sent to the structural and/or software based logic AND gate.

[0071] The structural and/or software based logic AND gate is configured to follow the Boolean logic of an AND gate, meaning that both conditions must be true in order for the gate to generate a true output. Positive or negative logic (e.g., NAND) can be used in a well-known manner. For the system to execute the automatic takeoff rejection, both discrepancy in acceleration values and airspeed within designated speed window, must be true.

[0072] FIG. 7 illustrates a non-limiting example of how an aircraft's inertial sensors 204 can be used to measure longitudinal acceleration. Generally speaking, inertial sensors are devices designed to measure inertial values such as acceleration and rotation. Examples of inertial sensors include gyrosensors 500 and accelerometers 501.

[0073] There are many types of accelerometers 501, such as mechanical accelerometers that consists of devices that measures the displacement of an inertial mass suspended by a spring. Another type of accelerometer is the surface acoustic wave (SAW) accelerometer which consists of a cantilever beam which resonates at a particular frequency, when acceleration is applied the beam bends changing the frequency, the change in frequency can be used to determine the acceleration. Yet another type of accelerometer is the MEMS accelerometers that uses capacitance to measure displacement of a minute mass floating on springs.

[0074] There are many different varieties of gyrosensors, such as mechanical, optical, and MEMS. Mechanical gyroscopes often used in the aircraft industry to determine aircraft attitude during flight consist of a spinning wheel mounted on two gimbals which allow the wheel to rotate in all three axes. Optical gyroscopes (e.g., fiber optic gyroscopes FOG) use the interference of light to measure angular velocity. A MEMS gyrosensor usually contains a vibratory elements to measure the Coriolis effect. For example, a single mass which is driven to vibrate along a drive axis. When the gyroscope is rotation a secondary vibration is induced along the perpendicular axis due to the Coriolis force. The angular velocity or rate output by such a system indicates the rate of change of attitude. This can be differentiated to determine acceleration.

[0075] Such devices can have any number of axes, including triaxial meaning that they measure all three degrees of freedom. Once such inertial values are sensed, they can be processed using conventional matrix multiplication to determine the component of acceleration in any desired particular direction.

[0076] Inertial sensors 500, 501 are thus able to measure inertial values such as the angular velocities (.sub.x 500-A, .sub.y 500-B, .sub.z 500-C) via the gyroscopes 500, and the accelerations (a.sub.x 501-A, a.sub.y 501-B, a.sub.z 501-C) via the accelerometers 501. Appropriate conventional axes transformations (which also involve knowing the orientation of the measured axes to the physical longitudinal centerline of the aircraft) can be used to calculate current longitudinal acceleration of the aircraft.

[0077] While the invention has been described in connection with what is presently considered to be the most practical and preferred embodiments, it is to be understood that the invention is not to be limited to the disclosed embodiments, but on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims.