Abstract:
A system and method for adjusting a yaw of an aircraft having an antilock braking system is disclosed. The antilock braking system includes a controller configured to receive a directional input from a rudder. The controller is further configured to deliver a braking output to at least one of a left wheel brake and a right wheel brake. A position of the rudder indicates a pilot&#39;s desired steering response, and to allow for braking optimization by the antilock braking system, the pilot depresses fully the left wheel brake pedal and the right wheel brake pedal. The controller receives the directional input after both the right wheel brake pedal and the left wheel brake pedal have been fully depressed. The controller then delivers the braking output and a pressure on one of the left wheel brake and the right wheel brake is reduced in accordance with the directional input.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The invention relates generally to the field of antilock braking systems. More specifically, the invention relates to the field of antilock braking systems for use with aircraft. 
         [0003]    2. Description of the Related Art 
         [0004]    Antilock braking systems have been employed for the past several decades to enhance braking efficiency of aircraft. Initially, such antilock braking systems included elaborate and expensive hydraulic controls that cycled the brakes on and off rapidly, and permitted the aircraft to be stopped with greater efficiency by preventing the wheels of the aircraft from slipping excessively or locking up. Electronic controls were later implemented and allowed for antilock action that is more responsive to actual ground conditions. 
         [0005]    U.S. Pat. No. 3,880,475 to Booher discloses an antilock braking system consisting of a wheel speed transducer for each of the right and left wheels of the aircraft, a deceleration detection circuit, and a skid detector circuit. The speed transducers generate signals that are proportional in frequency to the wheel rotational velocity. A modulator circuit receives the outputs of the deceleration detector and skid detector circuits, and causes a control valve to regulate brake pressure in accordance with these signals. A logic circuit responsive to a locked wheel condition or a bounced landing is also included, and may temporarily override the normal control of the brakes. 
         [0006]    U.S. Pat. No. 6,851,649 to Radford discloses an antilock braking system for use with aircraft and other vehicles. A speed sensor is associated with each wheel of the aircraft, and as the brake is applied to a wheel, the speed sensor measures the wheel speed and transmits this information to a processor. The processor then monitors the deceleration of the wheel, and compares this deceleration to a maximum allowable deceleration, which is a threshold above which the wheel would lock up and skid. If the deceleration of the wheel exceeds the maximum allowable deceleration, the processor transmits a signal to the brake causing the brake to release momentarily. Release of the wheel allows the wheel to momentarily rotate freely, thereby preventing wheel skids. The processor may also be configured to perform other routines, such as hydroplane protection operations. 
       SUMMARY 
       [0007]    Systems and method for adjusting a yaw of an aircraft having an antilock braking system are disclosed. According to one embodiment, the antilock braking system includes a controller configured to receive a directional input from a rudder. The controller is further configured to deliver a braking output to at least one of a left wheel brake and a right wheel brake. A position of the rudder indicates a pilot&#39;s desired steering response, and to allow for braking optimization by the antilock braking system, the pilot depresses fully the left wheel brake pedal and the right wheel brake pedal. The controller receives the directional input from the rudder after both the right wheel brake pedal and the left wheel brake pedal have been fully depressed. The controller then delivers the braking output and a pressure on one of the left wheel brake and the right wheel brake is reduced in accordance with the directional input. 
         [0008]    According to another embodiment, a method for slowing an aircraft travelling on a runway comprises the step of receiving a full-on signal from a left hand wheel brake and a right hand wheel brake. A directional input is then received, and a pulsing cycle is imposed wherein an intermittent and automatic release of both of the left and right hand wheel brakes occurs. The pressure on one of the left hand wheel brake and the right hand wheel brake is reduced according to the directional input. 
         [0009]    According to yet another embodiment, a system configured to eliminate a need for manual differential braking to steer on a runway an aircraft having a free-castering nosewheel is disclosed. The aircraft has a rudder, a right wheel, a left wheel, a right wheel brake, a left wheel brake, a right brake pedal for braking of the right wheel, and a left brake pedal for braking of the left wheel. A left wheel speed sensor is coupled to the left wheel and is adapted to determine a speed of the left wheel. A right wheel speed sensor is coupled to the right wheel and is adapted to determine a speed of the right wheel. The system comprises at least one computer memory configured for storing data, and a processor that is in data communication with the at least one computer memory. The processor is adapted to obtain a directional input from the rudder, a speed of the left wheel from the left wheel speed sensor, and a speed of the right wheel from the right wheel speed sensor. The processor is configured to provide a braking output to at least one of the left wheel brake and the right wheel brake. The processor obtains the directional input once both the right brake pedal and the left brake pedal have been fully depressed. The processor then reduces a slip of one of the left wheel and the right wheel according to the directional input. The braking output is proportional to the directional input. 
     
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
         [0010]    Illustrative embodiments of the present invention are described in detail below with reference to the attached drawing figures, which are incorporated by reference herein and wherein: 
           [0011]      FIG. 1  is a top view of an aircraft having a free-castering nosewheel; 
           [0012]      FIG. 2  shows a top view of the aircraft of  FIG. 1  taxiing on a runway and having an unintended direction of travel; 
           [0013]      FIG. 3  shows a top view of the aircraft of  FIG. 2  after its direction of travel has been adjusted; 
           [0014]      FIG. 4  is a block diagram showing some of the various components of an antilock braking system in accordance with the teachings of the current invention; 
           [0015]      FIG. 5  shows a top view of an aircraft equipped with the antilock braking system of  FIG. 4  taxiing on a runway in an unintended direction; and 
           [0016]      FIG. 6  is a flowchart outlining some of the steps taken by the antilock braking system of  FIG. 4 . 
       
    
    
     DETAILED DESCRIPTION 
       [0017]    Embodiments of the present invention provide systems and methods for an antilock braking system that enables a pilot to maintain directional control of an aircraft travelling on the ground (e.g., a runway or other such surface) without manual differential braking. In this document, references are made to directions such as left, right, front, back, and the like. These references are exemplary only and are used to describe the disclosed apparatus in a typical orientation or operation, but are not independently limiting. 
         [0018]    Controlling the direction of an aircraft during braking can be challenging, particularly where strong crosswinds are present. On aircraft having a nosewheel steering, directional control on the ground is primarily accomplished using rudder control at higher aircraft speeds (where aerodynamic forces are significant), and via the nosewheel steering at lower speeds. Differential braking and/or differential thrust may also be used as secondary directional control mechanisms on aircraft having nosewheel steerings. On aircraft having a free-castering nosewheel, however, differential braking (along with rudder control) is required for directional control. The current invention, though not so limited, is particularly useful for maintaining directional control of aircraft having a free-castering nosewheel. 
         [0019]      FIG. 1  shows an aircraft  100  with a free-castering nosewheel  102 . When viewed from the top, facing the back of the aircraft  100 , it can be seen that the aircraft  100  has a right wheel  104 R and a left wheel  106 L. Although not clearly visible in the figures, a right brake pedal  108 R is used to control a right brake  108 B that is linked to the right wheel  104 R, and a left brake pedal  110 L is used to control a left brake  110 B that is linked to the left wheel  106 L. The aircraft  100  also has a tail  114 , atop which a vertical fin  115  having a rudder  117  is disposed. The aircraft  100  is not equipped with an antilock braking system. 
         [0020]      FIGS. 2-3  illustrate directional control of the aircraft  100  via differential braking. Specifically,  FIG. 2  shows the aircraft  100  taxiing on a runway  110  (for e.g., during landing) and traveling in a direction  112 . When facing the tail  114  of the aircraft  100 , it can be seen that a nose  103  of the aircraft  100  in  FIG. 2  has an undesired right hand yaw, and needs to be steered to the left so that the aircraft  100  travels in an intended direction  116  along the center of the runway  110 . A corrective left hand yaw may be introduced via differential braking to ensure that the direction of travel  112  of the aircraft  100  corresponds to the intended direction of travel  116 . To achieve this objective, the pilot may depress the left brake pedal  110 L with a greater force than the right brake pedal  108 R, causing the left wheel  106 L to rotate at a slower rate than the right wheel  104 R. Because the right wheel  104 R will generally travel a greater distance than the left wheel  106 L as a result, the aircraft will desirably yaw to the left. Once the direction of travel of the aircraft  100  tracks the intended direction of travel  116  (see  FIG. 3 ), both the left brake pedal  110 L and the right brake pedal  108 R can be depressed with equal force. 
         [0021]    If the aircraft  100  had been equipped with an antilock braking system, the pilot may not have been able to steer the aircraft  100  via differential braking in this way. As known to those skilled in the art, antilock braking systems are feedback control systems that modulate brake pressure in response to a measured wheel&#39;s (e.g., the right wheel  104 R or the left wheel  106 L) deceleration, and prevent the wheel from locking up during braking. It is also known that the braking system of an aircraft  100  is most effective (i.e., produces the optimum retarding force) when the speed of the right wheel  104 R and the left wheel  106 L is approximately 85% of the ground speed of the aircraft  100 . This difference (100%−85%=15%) between the speed of the aircraft  100  and the speed of a particular wheel is known as the percent slip of that wheel. In the absence of an antilock braking system, if the brakes are applied fully, the wheels may lock up (i.e., a 100% slip), thereby reducing both braking effectiveness and steering ability. An antilock braking system prevents the wheels from locking up and generally maintains the 15% target slip for each of the left ( 106 L) and right ( 104 R) wheels by pulsing the brakes  108 R,  110 L, at different frequencies if required, sometimes as quickly as twenty to thirty times a second. 
         [0022]    To compute the slip of a wheel (e.g., the right wheel  104 R) for maintenance of the slip target, the antilock braking system&#39;s controller compares the speed of that wheel ( 104 R) to the ground speed of the aircraft  100 . Typically, the speed of the wheels (e.g., the right wheel  104 R or the left wheel  106 L) may be measured directly by speed sensors that are coupled to the wheels. The ground speed of the aircraft  100 , on the other hand, may be difficult to measure directly, and may be estimated using proprietary algorithms. 
         [0023]    Effectuating differential braking by depressing one brake pedal (e.g., the left brake pedal  110 L) with a greater force than the opposite brake pedal (e.g., the right brake pedal  108 R to cause the aircraft to yaw to the left) is both simple and intuitive for pilots. As noted however, where the aircraft  100  is equipped with an antilock braking system, differential braking is not commonly employed for directional control. This is because, pilots maneuvering aircraft having antilock braking systems are trained to depress the right ( 108 R) and left ( 110 L) brake pedals fully to optimize braking performance by the antilock braking system (as opposed to drivers of cars, where it is recommended that the brakes be firmly and steadily applied). Thus, as the right brake pedal  108 R and the left brake pedal  110 L of the aircraft  100  equipped with an antilock braking system are already fully depressed during braking, the pilot is unable to depress further, for example, the left brake pedal  110 L to cause a yaw to the left. Instead, to steer such an aircraft  100  to the left by differential braking, the pilot would have to resort to a counter intuitive response and reduce the force with which the right brake pedal  108 R is depressed. 
         [0024]    Such a course of action, in addition to being counter intuitive, is also highly nonlinear. Specifically, the braking pressure commanded by the pilot by fully depressing the brake pedals  108 R and  110 L is generally much higher than the braking pressure actually delivered to the wheels  104 R,  106 L respectively by the antilock braking system. Thus, to achieve a braking pressure that is less than this commanded braking pressure, the reduction in the force with which the right brake pedal  108 R is depressed (for a yaw to the left) will have to be significant. In the interim, the pilot may experience a ‘deadband’, i.e., the pilot may, at least initially, notice no perceptible effect on the direction of travel of the aircraft  100  as he progressively reduces the force on the right brake pedal  108 R. Moreover, the slip of the right wheel  104 R may go too far below the desired 15%, thereby degrading stopping performance. 
         [0025]    The present invention discloses an antilock braking system  200  that dispenses with the need to counter intuitively reduce the pressure on the right brake pedal  108 R to cause the aircraft  100  to yaw to the left, or the left brake pedal  110 L to cause the aircraft  100  to yaw to the right. As shown in  FIG. 4 , the antilock braking system  200  may include a processor  202 , and a computer memory  206 . The antilock braking system  200  may also include a separate storage unit  204 , or the storage unit  204  may be incorporated within the computer memory  206 . The storage unit  204  and the computer memory  206  are in data communication with the processor  202 . The storage unit  204  may be, for example, a hard drive or disk drive that stores programs and data, and the storage unit  204  is illustratively shown storing a program  208  embodying the steps and methods set forth below. It should be understood that the program  208  could be broken into subprograms and stored in storage units of separate computers and that data could be transferred between those storage units using methods known in the art. A dashed outline within the computer memory  206  represents the software program  208  loaded into the computer memory  206  and a dashed line between the storage unit  204  and the computer memory  206  illustrates the transfer of the program  208  between the storage unit  204  and the computer memory  206 . 
         [0026]    As noted above, to maintain directional control during braking of an aircraft  100  having the free-castering nosewheel  102 , pilots utilize both rudder control and differential braking. Position of the rudder  117 , thus, serves as a reliable indicator of the pilot&#39;s desired steering response. The rudder  117  is typically located at the rear of the fuselage (see  FIG. 1 ), and while not clearly shown in the figures, the position of the rudder  117  is generally controlled by a left rudder pedal  120 L and a right rudder pedal  120 R. Depressing the left rudder pedal  120 L deflects the rudder  117  to the left (for causing the nose  103  of the aircraft  100  to yaw to the left), while depressing the right rudder pedal  120 R deflects the rudder to the right (for causing the nose  103  of the aircraft  100  to yaw to the right). As is conventional, the aircraft  100  may also include gauges that convey the current position of the rudder  117 . The antilock braking system  200  utilizes the position of the rudder  117  to estimate the pilot&#39;s desired steering response, and then automates differential braking to steer the aircraft  100  in accordance with this desired steering response. 
         [0027]    To illustrate, consider an aircraft  300  taxiing on a runway  310  as shown in  FIG. 5 . The aircraft  300  is equipped with the antilock braking system  200  disclosed herein. The aircraft  300  has a free-castering nosewheel  302 , a right wheel  304 R, and a left wheel  306 L. A right brake  308 B is linked to the right wheel  304 R and is controlled by a right brake pedal  308 R. Similarly, a left brake  310 B is linked to the left wheel  306 L and is controlled by a left brake pedal  310 L. The aircraft  300  also has a tail  314 , atop which a vertical fin  315  having a rudder  317  is disposed. The rudder  317  may be deflected to the left (to cause a nose  303  to yaw to the left) by a left rudder pedal  320 L, and may be deflected to the right (to cause the nose  303  to yaw to the right) by a right rudder pedal  320 R. As can be seen in  FIG. 5 , the aircraft  300  has an unintended right hand yaw, and the nose  303  of the aircraft needs to be steered to the left so that a direction of travel  312  of the aircraft  300  corresponds to an intended direction of travel  316  along the center of the runway  310 . 
         [0028]    As the aircraft  300  is off-course, and because it is equipped with an antilock braking system, the pilot may depress fully both the right brake pedal  308 R and the left brake pedal  310 L to optimize braking performance by the antilock braking system  200  (note that the antilock braking system  200  does not require that the brake pedals  308 R,  310 L be depressed fully, and may be triggered when the brake pedals  308 R,  310 L are depressed significantly.) Also, to steer the nose  303  of the aircraft  300  to the left, the pilot may depress the left rudder pedal  320 L with a certain force, causing the rudder  317  to deflect to the left. The processor  202  may use the fact that both the right ( 308 R) and left ( 310 L) brake pedals are fully (or significantly) depressed, along with the off-center position of the rudder  317 , to establish that the pilot desires for the nose  303  of the aircraft  300  to yaw to the left. The processor  202  may also utilize the extent to which the rudder  317  is off-center to determine the specifics of this intended yaw; for example, where the rudder  317  is at its left most position (i.e., where the left rudder pedal  320 L is fully depressed), the processor  202  may determine that the pilot desires for the aircraft  300  to sharply yaw to the left; similarly, where the rudder  317  is only slightly off-center (i.e., where the left rudder pedal  320 L is slightly depressed), the processor  202  may determine that the pilot desires for the aircraft  300  to slowly yaw to the left, and so on. 
         [0029]    Once the processor  202  of the antilock braking system  200  determines the intended steering response (yaw towards the left in this example), the processor  202  may query right wheel speed sensor  314 R (see  FIG. 4 ), which is coupled to the right wheel  304 R, to determine the speed of the right wheel  304 R. The processor  202  may also determine the speed of the aircraft  100 , which as noted, is conventionally estimated by using proprietary algorithms. The processor  202  may then calculate the slip of the right wheel  304 R, and reduce this slip in proportion to the position of the rudder  317  (e.g., from 15% to 13% to allow for a slow left yaw, or from 15% to 5% to allow for a sudden left yaw). Differential braking, thus, is automatically effectuated, and the aircraft  300  may yaw to the left as desired. The antilock braking system  200  may similarly cause the aircraft  300  to yaw to the right by reducing the target slip of the left hand wheel  306 L. The processor  202  may then reinstate the original slip target of the left ( 306 L) or right ( 304 R) wheels (e.g., to 15%) after the aircraft  300  has been steered as desired and the pilot releases the rudder pedals  320 L and  320 R. 
         [0030]      FIG. 6  shows a flowchart outlining the steps discussed above. Specifically, the process begins at step  400 , and at step  402 , the antilock braking system  200  (e.g., the processor  202 ) checks whether the right ( 308 R) and left ( 310 L) brake pedals of the aircraft  300  are fully depressed. If both the right ( 308 R) and left ( 310 L) brake pedals are fully depressed, then at step  404 , the antilock braking system  200  checks whether the rudder  317  is off-center. If at step  406  the antilock braking system  200  determines that the rudder  317  is deflected to the right, it establishes that the pilot desires for the nose  303  of the aircraft  300  to yaw to the right, and estimates the specifics of this right yaw by evaluating the extent to which the rudder  317  is off-center at step  408 A. Then, at step  410 A, the antilock braking system  200  reduces the slip target of the left wheel  110 L in proportion to the position of the rudder  317 . The aircraft  300 , consequently, yaws to the right. At step  412 , the antilock braking system  200  checks whether the rudder  317  is still off-center, to determine whether the pilot wants the aircraft  300  to be steered further. If neither of the rudder pedals  220 L,  220 R are depressed, the antilock braking system  200  establishes that the aircraft  300  has been steered as intended, and reinstates the original slip target (e.g., 15%) of the left wheel  310 L at step  414 . The process then ends at step  416 . If the rudder  317  is still off-center at step  412 , however, the antilock braking system  200  establishes that the aircraft  300  has not steered as desired (for e.g., the intended right yaw has not completed, or the aircraft  300  has over-steered), and repeats step  406  through  416  until the rudder  317  is returned to the center by the pilot. 
         [0031]    Similarly, if the antilock braking system  200  determines at step  406  that the rudder  317  is deflected towards the left, it establishes that the pilot desires for the aircraft  300  to yaw to the left, and evaluates the position of the rudder  317  to determine the specifics of this intended yaw at step  408 B. It then, at step  410 B, reduces the slip target of the right wheel  308 R to cause the aircraft  300  to yaw to the left. If at step  412  the antilock braking system  200  determines that the rudder  317  is no longer off-center, it reinstates the original slip target of the right wheel  308 R. In this way, the antilock braking system  200  automatically commands differential braking and dispenses with the need for the pilot to counter intuitively reduce the force on the right brake pedal  308 R to cause the aircraft  300  to yaw to the left, or the left brake pedal  310 R to cause the aircraft  300  to yaw to the right. 
         [0032]    According to an alternate embodiment, instead of modifying the target slip of the right ( 308 R) or left ( 310 L) wheels to effectuate a yaw to the left or right respectively, the antilock braking system  200  may artificially modify the calculated ground speed that is used to compute the slip of the right ( 308 R) or the left ( 310 L) wheel in proportion to the position of the rudder  317 . Specifically, once the processor  202  of the antilock braking system  200  determines the intended steering response (yaw towards the left, for example) via position of the rudder  317 , it may artificially increase the calculated ground speed of the aircraft  300  before it is used to compute the slip of the right wheel  304 R (the calculated ground speed of the aircraft  300  used to compute the slip of the left wheel  306 L will not be artificially modified in this example). Artificially increasing the calculated ground speed of the aircraft  300  in computing the slip of the right wheel  304 R will consequently cause the slip of the right wheel  304 R to also artificially increase. The antilock braking system  200  may subsequently reduce this slip (e.g., from 20% to the target slip of 15%) by reducing the braking pressure on the right wheel  304 R. The aircraft  300  will therefore yaw in the intended direction (towards the left in this example). The artificially increased ground speed of the aircraft  300  may be subsequently adjusted (i.e. reduced) to reflect the calculated ground speed once the aircraft  200  has been steered as desired and the pilot releases the rudder pedals  320 L or  320 R. 
         [0033]    While the invention has been described with reference to an aircraft  300  having a free-castering nosewheel  302 , the antilock braking system  200  may also be used in aircraft  500  having nosewheel steerings  502  to reduce pilot workload and to improve path control. Moreover, during antiskid braking of such aircraft  500 , the antilock braking system  200  may provide a transparent backup to the nosewheel steering  502 . A pilot may thus be able to maintain directional control of the aircraft  500  during braking even where the nosewheel steering  502  fails. Additional inputs, such as the lateral acceleration of the aircraft  502 , may also be fed to the processor  202  to automatically negate any path deviations that have not been commanded. 
         [0034]    Many different arrangements of the various components depicted, as well as components not shown, are possible without departing from the spirit and scope of the present invention. Embodiments of the present invention have been described with the intent to be illustrative rather than restrictive. Alternative embodiments will become apparent to those skilled in the art that do not depart from its scope. A skilled artisan may develop alternative means of implementing the aforementioned improvements without departing from the scope of the present invention. 
         [0035]    It will be understood that certain features and subcombinations are of utility and may be employed without reference to other features and subcombinations and are contemplated within the scope of the claims. Not all steps listed in the various figures need be carried out in the specific order described.