GB2625544A - Aircraft braking system - Google Patents

Abstract

An aircraft braking system (fig.10,200) has an airbrake 132 which is moveable between a retracted position, where it does not project from the aircraft’s fuselage 110, to a deployed position where the airbrake projects from a lower surface 112 of the fuselage, generating drag on the aircraft when moving in a forward direction when landing gear 130 is extended. Also claimed is a controller (fig.11,300) suitable for controlling an aircraft braking system to, and a method of, selectively generating drag to slow an aircraft involving the step of causing the airbrake to be deployed from the lower fuselage surface when a certain criteria is met, such as: aircraft speed in a certain range or below a minimum; the aircraft is on the ground; a braking command has been issued; or landing gear is extended. Preferably the airbrake is rotated between positions, there may be multiple airbrakes (fig.10,136) on an aircraft connected by a linkage, and an actuator (fig.10,204) moves the linkage (fig.10,210) causing all airbrakes to move. Protective panels ((fig.10,206) may be provided which block part of an aperture in the fuselage from which the airbrake extends, the panel may be formed from a number of linkage connected sub-panels.

Description

AIRCRAFT BRAKING SYSTEM

TECHNICAL FIELD

[0001] The present invention relates to an aircraft braking system, a controller for an aircraft braking system, a method of braking an aircraft, and an aircraft.

BACKGROUND

100021 Upon aircraft landing or an aborted take-off, an aircraft is required to rapidly decelerate. This is primarily achieved by mechanical braking caused by friction at the landing gear wheels, but air braking is also used by deploying wing flaps.

100031 Wear of braking components in a landing gear braking system, such as brake pads, can result in reduced aircraft braking forces being applied to the landing gear wheels, and a resultant need for maintenance of the landing gear braking system.

SUMMARY

100041 According to a first aspect of the present invention, there is provided an aircraft braking system for installation in an aircraft and to selectively generate drag to slow the aircraft when landing gear of the aircraft are extended, the aircraft braking system comprising an airbrake movable between a retracted position, in which, when the aircraft braking system is installed in the aircraft, the airbrake does not project from a fuselage of the aircraft, and a deployed position, in which, when the aircraft braking system is installed in the aircraft, the airbrake projects from a lower surface of the fuselage such that, when the aircraft is moving in a forward direction and the airbrake is in the deployed position, the airbrake generates drag on the aircraft.

100051 Providing an airbrake that is selectively projectable from the lower surface of the fuselage may help to increase aircraft braking, for example after landing or in an aborted take-off In turn, this may help to reduce wear on brake pads of the aircraft and/or enhance braking performance of the aircraft. For example, increased braking may help to reduce a distance travelled by the aircraft during braking 100061 Optionally, the airbrake is configured to form part of an outer skin of the fuselage when the aircraft braking system is installed in the aircraft and the airbrake is in the retracted position. This may permit use of a relatively simple mechanism to move the airbrake between the retracted and deployed positions, since no part of a skin of the fuselage may need to be moved to permit movement of the airbrake between the retracted and deployed positions This may also reduce a time to move the airbrake between the retracted and deployed positions compared to an example in which the airbrake is within the fuselage in the retracted position, since no part of a skin of the fuselage may need to be moved to permit movement of the airbrake between the retracted and deployed positions.

100071 Optionally, the airbrake is rotatable between the retracted position and the deployed position about an airbrake axis. This may permit use of a relatively simple mechanism to move the airbrake between the retracted and deployed positions.

100081 Optionally, the aircraft braking system comprises a protective panel movable between a first position and a second position, wherein, in the first position, when the aircraft braking system is installed in the aircraft, the protective panel blocks at least part of an aperture in the fuselage of the aircrafl from which the airbrake extends when the airbrake is in the deployed position, and, in the second position, when the aircraft braking system is installed in the aircraft, the protective panel blocks the aperture by a lesser amount than in the first position. The protective panel may inhibit debris passing through the aperture, thus reducing a risk of damage to the aircraft by the debris in use. The protective panel may also help to reduce airflow in a bay into which the aperture opens, which may reduce turbulence induced by such airflow and increase the drag generated by the airbrake in the deployed position.

100091 Optionally, the aircraft braking system is configured to move the protective panel between the first position and the second position dependent on receipt of a command to move the airbrake between the retracted position and the deployed position. This may permit time-efficient movement of both the airbrake and the protective panel 100101 Optionally, the aircraft braking system is configured such that movement of the airbrake from the retracted position towards the deployed position causes movement of the protective panel from the second position to the first position Accordingly, the protective panel is moved to the first position to at least partially block the aperture in use as the airbrake is moved to the deployed position, thus helping to inhibit debris from passing through the aperture even before the airbrake reaches the deployed position.

100111 Optionally, the airbrake has a length that is greater than a length of the protective panel. The length of the airbrake extends from a free end of the airbrake to a fixed end of the airbrake, and the length of the protective panel extends from a free end of the protective panel to a fixed end of the protective panel. The fixed ends are an end of the respective airbrake or protective panel at which the airbrake or protective panel is attachable to the aircraft, and the free ends are opposite the respective fixed ends. Accordingly, in use, the airbrake may extend further from the fuselage than the protective panel to generate drag on the aircraft.

100121 Optionally, the protective panel is rotatable between the first and second positions about a panel axis. This may permit use of a relatively simple mechanism to move the protective panel between the first and second positions.

100131 Optionally, the aircraft braking system comprises an actuation system configured to move the airbrake between the deployed and retracted positions Optionally, the actuation system is configured to move the protective panel between the first and second positions 100141 Optionally, the airbrake is one of a plurality of airbrakes of the aircraft braking system, each airbrake movable between a retracted position, in which, when the aircraft braking system is installed in the aircraft, the respective airbrake does not project from a fuselage of the aircraft, and a deployed position, in which, when the aircraft braking system is installed in the aircraft, the respective airbrake projects from a lower surface of the fuselage such that, when the aircraft is moving in a forward direction and the airbrakes are in their respective deployed positions, each of the plurality of airbrakes generates drag on the aircraft.

100151 Providing a plurality of airbrakes may increase the drag generated by the aircraft braking system. Providing a plurality of airbrakes may permit each airbrake to be smaller in cross-sectional area to provide a given amount of drag compared to an aircraft braking system having one airbrake The plurality of airbrake panels may thus extend from the aircraft fuselage by a lesser distance than the aircraft braking system having one airbrake to generate the same amount of drag.

100161 Optionally, each of the plurality of airbrakes is rotatable by the actuation system about a respective airbrake axis to move the airbrake between the retracted and deployed positions. This may permit use of a relatively simple mechanism to move each airbrake between their respective retracted and deployed positions.

100171 Optionally, each of the airbrake axes is parallel to the other airbrake axes.

100181 Optionally, the airbrakes are connected to one another by an airbrake linkage, and the actuation system comprises an actuator configured to move the airbrake linkage to cause each airbrake of the plurality of airbrakes to move between the respective retracted and deployed positions. This may provide a relatively simple and lightweight mechanism for moving all of the airbrakes between the respective retracted and deployed positions together.

100191 Optionally, the protective panel comprises a plurality of sub-panels each configured to block at least part of a sub-region of the aperture and movable between respective first and second positions, each sub-region being a portion of the aperture between adjacent airbrakes when the airbrakes are in the deployed position. Thus, debris may be inhibited from passing through a sub-region between adjacent airbrakes.

100201 Optionally, the sub-panels are connected to one another by a panel linkage, the panel linkage operably connected to the airbrake linkage such that movement of the airbrake linkage by the actuator causes movement of the panel linkage to move the sub-panels between the first and second positions. This may provide a relatively simple and lightweight mechanism for moving all of the sub-panels between the respective first and second positions together.

100211 Optionally, when installed on the aircraft, the airbrake is configured to generate a downward force on the aircraft when the aircraft is moving in a forward direction and the airbrake is in the deployed position. This may help to reduce wear on brake pads of the aircraft and/or enhance braking performance of the aircraft.

100221 According to a second aspect of the present invention, there is provided an aircraft landing gear system, comprising: a landing gear; a landing gear bay door rotatable about a landing gear axis between a closed position, in which the landing gear bay door is to block a landing gear bay aperture in a fuselage of an aircraft in use, and an open position, in which the landing gear may pass through the aperture; and an aircraft braking system according to the first aspect, wherein: the landing gear bay door comprises the airbrake, the closed position is the retracted position, and the landing gear bay door is movable between the closed position and the deployed position about a different axis to the landing gear axis.

100231 The landing gear bay door may thus be dual-functional: operable to permit movement of the landing gear through the landing gear bay aperture, and to act as an airbrake. This may permit retrofitting of the aircraft braking system to existing aircraft with relatively minimal modifications to the aircraft. For example, existing controllers and/or actuation systems may be modified to provide the functionality of the aircraft braking system.

100241 Optionally, the aircraft landing gear system is configured to cause the landing gear bay door to move to the deployed position in response to a determination by a controller of the aircraft that the landing gear is in an extended position, the landing gear bay door is in the closed position and, optionally, a transition from Weight off Wheels to Weight on Wheels has occurred 100251 According to a third aspect of the present invention, there is provided a controller for controlling an aircraft braking system to selectively generate drag to slow an aircraft, the controller configured to: determine whether the at least one predetermined criterion is met; and when the controller determines that the at least one predetermined criterion is met, cause an airbrake to move to a deployed position, in which the airbrake projects from a lower surface of a fuselage of the aircraft, to generate drag on the aircraft.

100261 The airbrake is thus inhibited from moving to the deployed position until the at least one predetermined criterion is met, which may help to avoid inadvertent deployment of the airbrake.

100271 Optionally, the at least one predetermined criterion comprises that landing gear of the aircraft are in an extended position. This may help to ensure that the airbrake does not move to the deployed position prematurely, for example during a cruise phase of a flight.

100281 Optionally, the at least one predetermined criterion comprises that a braking command has been issued. This may help to ensure that the airbrake does not move to the deployed position prematurely, for example if a landing is aborted after touch-down. The braking command may be issued by a flight crew of the aircraft.

100291 Optionally, the at least one predetermined criterion comprises that a speed of the aircraft is within a predefined range. This may help to ensure that the airbrake does not move to the deployed position prematurely, for example at a speed that exceeds a maximum safe speed at which the airbrake can be moved to the deployed position 100301 Optionally, the predefined range is above a predefined permitted landing speed of the aircraft. An aircraft may exceed the predefined permitted landing speed due to, for example, the presence of a tail wind, a downwardly sloping runway or excess aircraft weight. Accordingly, the aircraft braking system may be employed if additional braking is required compared to normal braking 100311 Optionally, the at least one predetermined criterion comprises that a failure is detected in another braking system of the aircraft. Accordingly, the aircraft braking system may be employed if additional braking is required compared to normal braking.

100321 Optionally, the at least one predetermined criterion comprises that the aircraft is on the ground. Accordingly, the airbrake may only be deployed when the aircraft is on the ground, which may prevent the airbrake negatively impacting in-flight performance.

100331 Optionally, the at least one predetermined criterion comprises a signal indicative that Weight on Wheels has occurred. Typical aircraft already comprise an indicator, or sensor, able to determine that Weight on Wheels has occurred. Therefore, there would be no need for additional sensors or logic to enable the controller to determine that Weight on Wheels has occurred.

100341 Optionally, the at least one predetermined criterion comprises a signal indicative that a transition from Weight off Wheels to Weight on Wheels has occurred. This may help to ensure that the airbrake does not move to the deployed position during aircraft take-off or during flight.

100351 Optionally, the at least one predetermined criterion comprises that a predetermined period of time has elapsed since the controller determined that the aircraft is on the ground. This may help to ensure that the airbrake does not move to the deployed position prematurely, for example at a speed that exceeds a maximum safe speed at which the airbrake is moveable to the deployed position 100361 Optionally, the airbrake is configured to generate a downward force on the aircraft when the aircraft is moving in a forward direction and the airbrake is in the deployed position This may help to reduce wear on brake pads of the aircraft and/or enhance braking performance of the aircraft.

100371 Optionally, the controller is configured to: determine whether the at least one further predetermined criterion is met; and when the controller determines that the at least one further predetermined criterion is met, cause the airbrake to move from the deployed position towards a retracted position in which the airbrake does not project from the fuselage of the aircraft. Accordingly, the airbrake can be actively retracted when no longer required to generate the amount of drag generated by the airbrake in the deployed position.

100381 Optionally, the controller is configured to cause the airbrake to move to the retracted position if it is determined that the at least one further predetermined criterion is met.

100391 Optionally, the at least one further predetermined criterion comprises that a speed of the aircraft is below a minimum speed threshold. This may help to ensure that the airbrake is only in the deployed position for as long as necessary as the aircraft decelerates, for example after landing or an aborted take-off The drag generated by the airbrake reduces as aircraft speed reduces and becomes relatively insignificant. This may also help to ensure that the airbrake doesn't affect steering of the aircraft during taxiing.

100401 According to a fourth aspect of the present invention, there is provided an aircraft braking system of the first aspect comprising a controller of the third aspect.

100411 According to a fifth aspect of the present invention, there is provided a landing gear system of the second aspect comprising a controller of the third aspect.

100421 According to a sixth aspect of the present invention, there is provided a method of selectively generating drag to slow an aircraft, the method comprising determining whether at least one predetermined criterion is met; and on the basis of determining that the at least one predetermined criterion is met, causing an airbrake to move to a deployed position, in which the airbrake projects from a lower surface of a fuselage of the aircraft to generate drag on the aircraft. The benefits of such a method are as explained above with regard to the first and third aspects 100431 Optionally, the method comprises determining whether at least one further predetermined criterion is met, and, on the basis of determining that the at least one further predetermined criterion is met, causing the airbrake to move towards a retracted position, in which the airbrake does not project from the fuselage of the aircraft. Accordingly, the airbrake may be actively retracted when no longer required to generate the amount of drag generated by the airbrake in the deployed position 100441 Optionally, the at least one predetermined criterion comprises that the aircraft is on the ground. Accordingly, the airbrake may only be deployed when the aircraft is on the ground, which may prevent the airbrake negatively impacting in-flight performance.

100451 Optionally, the at least one predetermined criterion comprises that an aircraft braking command has been issued. This may help to ensure that the airbrake does not move to the deployed position prematurely, for example if a landing is aborted after touch-down. The braking command may be issued by a flight crew of the aircraft.

100461 Optionally, the at least one predetermined criterion comprises that landing gear of the aircraft are in an extended position. This may help to ensure that the airbrake does not move to the deployed position prematurely, for example during a cruise phase of a flight.

100471 Optionally, the airbrake is configured to generate a downward force on the aircraft when the aircraft is moving in a forward direction and the airbrake is in the deployed position. This may help to reduce wear on brake pads of the aircraft and/or enhance braking performance of the aircraft 100481 According to a seventh aspect of the present invention, there is provided a non-transitory computer-readable storage medium storing instructions that, if executed by a controller of an aircraft braking system of an aircraft, cause the controller to carry out a method of the sixth aspect.

100491 According to an eight aspect of the present invention, there is provided an aircraft comprising: an aircraft braking system of the first aspect or the fourth aspect; an aircraft landing gear system of the second aspect or the fifth aspect; a controller of the third aspect; or a non-transitory computer-readable storage medium of the seventh aspect.

100501 Optionally, when the aircraft comprises the aircraft braking system and the airbrake is rotatable between the retracted position and the deployed position about an airbrake axis, the airbrake axis extends in a lateral direction, relative to a forward direction of the aircraft. This may help to increase the drag generated by airbrake in the deployed position compared to an airbrake axis extending in a non-lateral direction.

100511 Optionally, when the aircraft comprises an aperture in the fuselage and the aircraft braking system, and the aircraft braking system comprises a protective panel, in the second position, the protective panel permits movement of the airbrake between the retracted and deployed positions, via the aperture. The second position may be a position in which the protective panel is within the fuselage and does not generate drag on the aircraft when the aircraft is moving.

100521 Optionally, the protective panel is rotatable between the first and second positions about a panel axis that extends in a lateral direction relative to a forward direction of the aircraft. Optionally, the panel axis is parallel to the airbrake axis. This may permit use of a relatively simple mechanism for moving the airbrake and the protective panel between the retracted and deployed positions or first and second positions, respectively.

100531 Optionally, in the deployed position, a free end of the airbrake extends from the fuselage by a first distance, and, in the first position, a free end of the protective panel extends from the fuselage by a second distance, the first distance and the second distance measured in a direction normal to the fuselage, and the first distance greater than the second distance. This may help to ensure that the protective panel does not inhibit drag generation by the airbrake in the deployed position [0054] Optionally, with the airbrake in the deployed position, a free end of the airbrake is closer to a forward end of the aircraft than a fixed end of the airbrake, the free end being an end of the airbrake that projects from the lower surface of the fuselage, and the fixed end being opposite the free end. Thus, in the deployed position, the airbrake is at an oblique angle relative to the lower surface of the fuselage of the aircraft. This may help to increase a downward force generated by the airbrake in the deployed position 100551 Optionally, in the first position, a free end of the protective panel is further from a forward end of the aircraft than a fixed end of the protective panel, the free end being an end of the protective panel that projects from the lower surface of the fuselage, and the fixed end being opposite the free end. This may allow the protective panel to inhibit debris from passing through the aperture without the protective panel generating a downward force on the aircraft.

[0056] It will be appreciated that optional features of aspects of the present invention may be equally applied to other aspects of the present invention, where appropriate.

[0057] Further features and advantages of the invention will become apparent from the following description of preferred embodiments of the invention, given by way of example only, which is made with reference to the accompanying drawings

BRIEF DESCRIPTION OF THE DRAWINGS

[0058] Embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings, in which: [0059] Figure 1 shows a schematic front view of an aircraft according to an example, the aircraft comprising an aircraft braking system with airbrakes of the aircraft braking system in a retracted position; [0060] Figure 2 shows a schematic side view of the aircraft of Figure 1; [0061] Figure 3 shows a schematic side view of a front portion of the aircraft of Figure 1 with nose landing gear doors according to an example in a closed position; [0062] Figure 4 shows a schematic perspective view of nose landing gear doors of the aircraft of Figure 1 in the closed position; [0063] Figure 5 shows a schematic side view of a front portion of the aircraft of Figure 1 with nose landing gear doors according to an example in an open position; [0064] Figure 6 shows a schematic perspective view of the nose landing gear doors of the aircraft of Figure 1 in the open position; [0065] Figure 7 shows a schematic side view of a front portion of the aircraft of Figure 1 with nose landing gear doors according to an example in an airbrake position; [0066] Figure 8 shows a schematic perspective view of the nose landing gear doors of the aircraft of Figure 1 in the airbrake position; [0067] Figure 9 shows a schematic side view of an aircraft braking system according to an example, the aircraft braking system in a closed position; [0068] Figure 10 shows a schematic side view of the aircraft braking system of Figure 9 in an airbrake, or deployed, position; [0069] Figure 11 shows a schematic diagram of a control system of an aircraft according to an example; [0070] Figure 12 shows a flowchart depicting logic employed by a controller according to an example, the controller for controlling the aircraft braking system of Figure 9 and Figure 10; [0071] Figure 13 shows a schematic side view of an aircraft braking system according to an example, the aircraft braking system in a closed position; [0072] Figure 14 shows a schematic side view of the aircraft braking system of Figure 13 in an airbrake, or deployed, position and [0073] Figure 15 depicts a method according to an example

DETAILED DESCRIPTION

[0074] Figures 1 and 2 show an aircraft 100 according to an example. The aircraft 100 comprises a fuselage 110 in which passengers and/or cargo are located in use of the aircraft 100. Wings 120 extend outwardly from sides of the fuselage 110. A nose landing gear 130 is positioned towards a front end 102 of the aircraft 100 on an underside 112 of the fuselage 110. Main landing gears 140 are positioned beneath the respective wings 120 close to the fuselage 110.

100751 The nose landing gear 130 and the main landing gears 140 are movable between respective retracted and extended positions by respective landing gear extension and retraction systems (not shown). Typically, shortly after take-off, the landing gears 130, 140 are moved from the extended position to the retracted position and remain in the retracted position during flight of the aircraft 100. In the retracted position, the landing gears 130, 140 are positioned within the fuselage 110 in respective landing gear bays (not shown). Shortly before landing of the aircraft 100, the landing gears 130, 140 are moved to the extended position, as shown in Figure 1. In the extended position, the landing gears 130, 140 extend beneath the fuselage 100 and are configured to support the weight of the aircraft 100 during landing and on the ground [0076] The landing gears 130, 140 each pass through respective apertures in the fuselage 100 as they are moved into and out of their respective landing gear bay to retract or extend the landing gear 130, 140. The apertures are each covered by a respective landing gear bay door (or doors) (not shown in Figures 1 and 2), which are movable from a closed position to an open position to allow the landing gear 130, 140 to pass through the aperture into and out of the landing gear bay. The landing gear bay doors form part of an outer skin of the underside 112 of the fuselage 110 when in the closed position.

100771 Figure 3 shows a side view of the front end 102 of the aircraft 100, with the nose landing gear bay door 132 in the closed position and Figure 5 shows the same view, but with the nose landing gear bay door 132 in the open position. Figure 4 shows a perspective view of the nose landing gear bay door 132, in isolation, in the closed position and Figure 6 shows a perspective view of the nose landing gear bay door 132, in isolation, in the open position. In Figures 4 and 6, a nose landing gear aperture 116 in the underside 112 of the fuselage 110 is shown in dashed lines 100781 The nose landing gear bay door 132 comprises a pair of doors 134 and 136 positioned either side of a central longitudinal vertical plane 104 of the aircraft 100 (see Figure 1). The landing gear bay doors 134, 136 open outwardly of the fuselage 110. The landing gear bay doors 134, 136 are movable between the closed and open positions by respective landing gear bay door actuators (not shown) configured to rotate the respective doors 134, 136 about respective door axes 135, 137. The door axes 135, 137 extend along opposite edges of the aperture 116 to one another, and the doors 134, 136 rotate in opposite directions to each other about their respective axes 135, 137. The door axes 135, 136 extend in a direction parallel to the central longitudinal vertical plane 104 of the aircraft 100.

100791 Each door 134, 136 is comprised of three sub-doors 134a, 134b, 134c, 136a, 136b, 136c, which move together as a single unit about the respective door axis 135, 137 between the closed and open positions, as best shown in Figures 5 and 6. In other examples, each door 134, 136 may comprise a different number of sub-doors, for example one door, two doors, four doors, five doors, or more than five doors.

100801 Each door 134, 136 rotates around its respective axis 135, 137 by around 90 degrees between the closed and open positions. In other examples, the closed and open positions may be at a different angle relative to one another.

100811 In this example, the nose landing gear bay door 132 is multi-functional and is additionally operable to act as an airbrake for the aircraft 100. In addition to being movable between the closed and open positions, the nose landing gear bay doors 134, 136 are moveable between the closed position and an airbrake position (also called a "deployed position" herein). Figure 7 shows a side view of the front end 102 of the aircraft 100, with the nose landing gear bay doors 134, 136 in the airbrake position. Figure 8 shows a perspective view of the nose landing gear bay doors 134, 136, in isolation, in the airbrake position. In Figure 8, the nose landing gear aperture 116 in the underside 112 of the fuselage 110 is shown in dashed lines.

100821 The landing gear bay doors 134, 136 are movable between the closed and airbrake positions by an airbrake actuator of an aircraft braking system (described in more detail herein with reference to Figures 9 and 10) The airbrake actuator is configured to rotate the sub-doors 134a, 134b, 134c, 136a, 136b, 136c about respective airbrake axes 201, 202, 203. The airbrake axes 201, 202, 203 are parallel to one another and extend in a direction normal to the central longitudinal vertical plane 104 of the aircraft 100. That is, the airbrake axes 201, 202, 203 extend laterally across the aircraft 100.

100831 The sub-doors 134a, 134b, 134c, 136a, 1366, 136c move between the closed and airbrake positions as three pairs, about the respective airbrake axes 201, 202, 203, as best shown in Figure 8.

100841 In the airbrake position, a free end 138, opposite the door axis 201, 202, 203, of each sub-door projects from the underside 112 of the fuselage 110 and is closer to the front end 102 of the aircraft 100 than a fixed end 139, at the airbrake axis 201, 202, 203 of that sub-door.

100851 In the closed position, the free end 138 of each sub-door 134a, 134b, 134c, 136a, 136b, 136c is closer to the front end 102 of the aircraft 100 than the fixed end 139. However, in other examples, the free end 138 may be further from the front of the aircraft 100 than the fixed end 139 in the closed position.

100861 Each pair of sub-doors 134a, 134b, 134c, 136a, 136b, 136c rotates around its respective airbrake axis 201, 202, 203 by around 60 degrees between the closed position and the airbrake position. In other examples the closed and airbrake positions may be at a different angle relative to one another, for example 80 degrees or 120 degrees.

100871 The aircraft comprises an aircraft braking system 200 configured to cause the nose landing gear bay doors 134, 136 to move between the closed position and the airbrake position. Figures 9 and 10 show schematic side views of an example of the aircraft braking system 200, in the closed position and airbrake position, respectively. The aircraft braking system 200 comprises an airbrake actuator 204, a mechanical linkage 210, and three protective panels 206a, 206b, 206c. The nose landing gear bay doors 134, 136 are comprised in the aircraft braking system 200.

100881 The three protective panels, referenced collectively 206, are each rotatable about a respective panel axis between a first position and a second position. In the first position, as shown in Figure 10, the protective panels 206 project outwardly from the underside 112 of the fuselage 110 of the aircraft 110. In the first position, a free end 207 of the protective panel, opposite the respective panel axis, is further from the front end of the aircraft 100 than a fixed end 208, at the panel axis. In the second position, the protective panels 206 do not project from the fuselage 110.

100891 The panel axes are parallel to one another and to the airbrake axes 201, 202, 203, and extend in a direction normal to the central longitudinal vertical plane 104 of the aircraft 100. That is, the panel axes extend laterally across the aircraft 100.

100901 The mechanical linkage 210 comprises a first member 212 in connection with the airbrake actuator 204. The first member 212 is connected to each pair of sub-doors 134a, 134b, 134c, 136a, 136b, 136c of the landing gear bay door 132 by a respective airbrake shackle 214. The airbrake shackles 214 connect the first member 212 to a point of rotation of a respective pair of sub-doors 134a, 134b, 134c, 136a, 1366, 136c 100911 The mechanical linkage 210 further comprises a second member 216 connected to each protective panel 206 by a respective panel shackle 218 The panel shackles 218 connect the second member 216 to a point of rotation of a respective protective panel 206. The second member 216 is positioned above the first member 212. An arm 220 extends from the second member 216 towards the first member 216 and comprises a scotch yoke 222. The scotch yoke 222 comprises an elongate aperture 224 in the arm 220, and a pin 226 connected to the first member 212 and extending through the elongate aperture 224.

100921 An elastic element 228, in this example a spring 228, connects at one end of the elastic spring to a frame 108 of the aircraft 100 and at an opposing end of the elastic spring to the second member 216. In this example, the frame 108 forms part of a wall of the nose landing gear bay 131. The elastic element 228 biases the protective panels 206 to the first position and the landing gear bay door 132 to the closed position by exerting a tension force between the frame 108 and the second member 216 100931 With the landing gear bay door 132 in the closed position and the protective panels 206 in the second position, the landing gear bay door 132 forms part of an outer skin of the fuselage 110 and covers the protective panels 206.

100941 With the sub-doors 134a, 134b, 134c, 136a, 136b, 136c in the airbrake position and the protective panels 206 in the first position, the protective panels 206 act to inhibit movement of airflow and/or debris through the aperture 116 between the sub-doors 134a, 134b, 134c, 136a, 136b, 136c, 100951 The aircraft 100 comprises a controller 300, which in this example is comprised in a Landing Gear Control Interface Unit (LGCIU) 106 of the aircraft 100, as shown schematically in Figure 11 The LGCIU 106 controls movement of thc nose landing gear 130 between the extended and retracted positions and movement of the nose landing gear door 132 between the closed and open positions. The controller 300 controls movement of the nose landing gear door 132 between the closed and airbrake positions. In other examples, the controller 300 is a stand-alone controller or is comprised in another control unit of the aircraft 100. In this example, the controller 300 forms part of the aircraft braking system 200 100961 The controller 300 is configured to arm or disarm the aircraft braking system 200 based on one or more determinations, and to cause actuation of the airbrake actuator 204 based on one or more further determinations. Figure 14 shows a flowchart schematically depicting logic employed by the controller 300 for controlling the aircraft braking system 200. In this example, some of the determinations and further determinations are made by the controller 300, and others of the determinations and further determinations are received by the controller 300 as an input signal from another controller of the aircraft 100. In other examples, all of the determinations and further determinations are made by the controller. In yet other examples, all of the determinations and further determinations are received by the controller 300 as respective input signals from one or more other controllers of the aircraft 100.

100971 In use of the controller 300, with the aircraft braking system 200 disarmed, the controller 300 if configured to determine whether requirements for arming the aircraft braking system 200 are met. If the requirements are met, the controller 300 is configured to arm the aircraft braking system 200, which in this example comprises providing power to the airbrake actuator 204.

100981 In this example, determinations required to cause the controller 300 to arm the aircraft braking system 200 comprise: that the landing gears 130, 140 are extended, that Weight on Wheels has been confirmed (i.e., that the aircraft is on the ground), that a speed of the aircraft 100 is below a predetermined speed, in this example 200 knots, and that the landing gear bay door 132 is uplocked in the closed position.

100991 In some examples, a determination required to cause the controller 300 to arm the aircraft braking system 200 comprises that a transition from Weight off Wheels to Weight on Wheels has occurred, which may help to ensure that the aircraft braking system is not armed during aircraft take-off In other examples, this determination may not be required, for example if an aborted take-off is determined by the controller 300.

101001 With the aircraft braking system 200 armed, the landing gear bay door 132 in the closed position and the protective panels 206 in the second position, the controller 300 is configured to determine whether requirements for deploying the sub-doors 134a, 134b, 134c, 136a, 136b, 136c to the airbrake position are met. If the requirements are met, the controller 300 is configured to cause actuation of the airbrake actuator 204.

101011 Actuation of the airbrake actuator 204 causes the first member 212 to be drawn by the actuator 204 in a direction parallel to the central longitudinal vertical plane 104 of the aircraft 100 and towards a rear of the aircraft 100. Such movement of the first member 212 causes the sub-doors 134a, 134b, 134c, 136a, fob, 136c to rotate about the respective airbrake axes 201, 202, 203 from the closed position towards the airbrake position. In addition, the pin 226 acts on the arm 220 to cause the second member 216 to move in the same direction as the first member 212, towards the rear of the aircraft 100. In turn, this causes the protective panels 206 to rotate about the respective panel axes 207 from the second position towards the first position. Accordingly, movement of the protective panels 206 to the first position is dependent on movement of the sub-doors 134a, 134b, 134c, 136a, 136b, 136c to the airbrake position.

101021 Rotational movement of the first member 212 about the points of rotation of the pairs of sub-doors 134a, 134b, 134c, 136a, 136b, 136c is converted into linear movement by the scotch yoke 222. With the sub-doors in the closed position, the pin 226 is located at a top of the elongate aperture 224, as shown in Figure 9. As the sub-doors are moved towards the airbrake position, the pin 226 moves towards a bottom of the elongate aperture 224, as shown in Figure 10. This allows the first member 212 and the second member 216 to travel along different paths during actuation of the airbrake actuator 204. In this example, during deployment of the aircraft braking system 200, the sub-doors 134a, 134b, 134c, 136a, 136b, 136c rotate from the closed position to the airbrake position in an anti-clockwise direction, as viewed in Figures 9 and 10, and the protective panels 206 rotate from the second position to the first position in a clockwise direction, as viewed in Figures 9 and 10.

101031 When the sub-doors 134a, 134b, 134c, 136a, 136b, 136c are in the airbrake position and the aircraft 100 is moving in a forward direction, as denoted by the arrow in Figures 9 and 10, the sub-doors 134a, 134b, 134c, 136a, 136b, 136c generate drag and a downward force on the aircraft, thus aiding braking of the aircraft.

101041 In this example, the further determination required to cause the controller 300 to deploy the aircraft braking system 200 comprises that an aircraft braking command is issued, for example by flight crew of the aircraft pressing a brake pedal in a cockpit of the aircraft 100. In some examples, other further determinations are additionally or alternatively required to cause the controller 300 to deploy the aircraft braking system 200, such as: that a failure in another braking system of the aircraft is detected, that a rate of aircraft deceleration exceeds a threshold rate, or that a weight of the aircraft exceeds a threshold weight.

101051 If the controller 300 determines that requirements are met to move the airbrake actuator 204 to an intermediate position, the controller 300 is configured to cause the aircraft actuator 204 to move to the intermediate position. This moves the sub-doors 134a, 134b, 134c, 136a, I36b, 136c to a position between the closed and airbrake positions and the protective panels 206 to a position between the first and second positions, which permits control over the amount of drag and downward force generated by the sub-doors 134a, 134b, 134c, 136a, 136b, 136c, 101061 A requirement to move the airbrake actuator to an intermediate position is that a speed of the aircraft is within a predefined speed range, in this example between 50 and 120 knots. At such speeds, the greater drag and downward force generated at the airbrake position may not be required when braking the aircraft 100.

101071 With the sub-doors 134a, I34b, 134c, I36a, 136b, 136c in the airbrake position and the protective panels 206 in the first position, the controller 300 is configured to determine whether requirements for retracting the aircraft braking system 200 are met. If the requirements are met, the controller 300 is configured to actuate the airbrake actuator 204 to cause the first member 212 to be pushed by the actuator 204 in a direction parallel to the central longitudinal vertical plane 104 of the aircraft 100 and towards a front of the aircraft 100. Such movement of the first member 212 causes the sub-doors 134a, 134b, 134c, 136a, 136b, 136c to rotate about the respective airbrake axes 201, 202, 203 from the airbrake position towards the closed position. In addition, the pin 226 acts on the arm 220 to cause the second member 216 to move in the same direction as the first member 212, towards the front of the aircraft 100. In turn, this causes the protective panels 206 to rotate about the respective panel axes 207 from the first position towards the second position. Accordingly, movement of the protective panels 206 to the second position is dependent on movement of the sub-doors 134a, 134b, 134c, 136a, 136b, 136c to the closed position. In turn, the protective panels 206 continue to inhibit debris from passing through the aperture 116 as the sub-doors 134a, 134b, 134c, 136a, 136b, 136c are closed.

101081 In this example, further determinations required to cause the controller to close the aircraft braking system 200 comprise: that a speed of the aircraft is below a threshold closing speed, in this example 30 knots, or that the aircraft braking system 200 has been deployed for a predetermined deployment time.

[0109] With the aircraft braking system 200 armed, the landing gear bay door 132 in the closed position and the protective panels 206 in the second position, the controller 300 is configured to determine whether the requirements for disarming the aircraft braking system 200 are met. If the requirements are met, the controller 300 is configured to disarm the aircraft braking system 200, which in this example comprises disconnecting the airbrake actuator 204 from a power source of the aircraft actuator 204.

10110:1 In this example, determinations required to cause the controller 300 to disarm the aircraft braking system 200 comprise one or more of: that the landing gear bay door 132 is in the closed position, that the nose landing gear 130 is commanded to retract, for example by movement of a landing gear lever of the aircraft 100 to a 'Lever Up' position, that Weight off Wheels has been confirmed, that a speed of the aircraft 100 on the ground is below a threshold, in this example 30 knots, and that the aircraft braking system 200 has been armed for a predetermined period, in this example 1 minute, without being deployed.

101111 Figures 13 and 14 show schematic side views of an alternative aircraft braking system 500 according to an example, in the retracted, or closed, and deployed positions, respectively. The aircraft braking system 500 is similar to the aircraft braking system 200 described above, and may be controlled by the controller 300 described with reference to Figures 11 and 12. For brevity, only the differences between the aircraft braking systems 200, 500 are described herein. Common components have the same reference numerals, but increased by 300.

101121 In this example, the aircraft braking system 500 is configured such that, in the closed position, the fixed end of each sub-door 134a, 134b, 134c, 136a, 136b, 136c is closer to the front end 102 of the aircraft than the free end. In the deployed position, the free end of each sub-door 134a, 134b, 134c, 136a, 136b, 136c projects from the underside 112 of the fuselage 100 with the fixed end closer to the front end 102 of the aircraft than the free end. The protective panels 506 are positioned such that, in the closed position, the fixed end 508 of each protective panel 506 is further from the front end 102 of the aircraft than the free end 507. In the deployed position, the fixed end 508 of each protective panel 506 is further from the front end 102 of the aircraft than the free end 507.

101131 The airbrake actuator 504 is positioned forward of the landing gear door 132. Actuation of the airbrake actuator 504 to deploy the aircraft braking system 500 causes the first member 512 to be drawn by the actuator 504 in a direction parallel to the central longitudinal vertical plane 104 of the aircraft 100 and towards the front end 102 of the aircraft 100. Actuation of the airbrake actuator 504 to retract the aircraft braking system 500 causes the first member 512 to be pushed by the actuator 504 in a direction parallel to the central longitudinal vertical plane 104 of the aircraft 100 and towards a rear of the aircraft 100 101141 The aircraft braking system 500 may reduce load on the sub-doors 134a, 134b, 134c, 136a, 136b, 136c when in the deployed position compared to the aircraft braking system 200, whilst still generating sufficient drag to help slow the aircraft 100. In use of the aircraft braking system 500, little or no downward force may be generated on the aircraft 100 101151 Figure 15 depicts a method 400 of braking an aircraft according to an example. The aircraft may be the aircraft 100 described herein. The method comprises determining whether at least one predetermined criterion is met (block 402), and, on the basis of determining that the at least one predetermined criterion is met, causing an airbrake to move to a deployed position, in which the airbrake projects from a lower surface of a fuselage of the aircraft to generate drag on the aircraft (block 404).

101161 The method 400 may be performed by the controller 300 described with reference to Figures 11 and 12, controlling one of the aircraft braking systems 200, 500 described herein. The airbrake may be the landing gear bay door 132 described herein, or may be a different airbrake that is movable to the deployed position For example, the airbrake may project from the underside 112 of the fuselage 110 of the aircraft 100 at a position rearward of the wings 120 of the aircraft 100.

101171 In this example the predetermined criterion comprises that: landing gears of the aircraft are extended, Weight on Wheels has been confirmed (i.e., that the aircraft is on the ground), a speed of the aircraft is below a predetermined speed, and an aircraft braking command has been issued. In other examples, the predetermined criterion additionally or alternatively comprises that: a landing gear bay door of the aircraft is uplocked in the closed position, a transition from Weight off Wheels to Weight on Wheels has occurred, a failure in another braking system of the aircraft is detected, a rate of aircraft deceleration exceeds a threshold rate, and/or a weight of the aircraft exceeds a threshold weight.

101181 Although not shown in the example in Figure 15, in some examples, the method 400 comprises determining whether at least one further predetermined criterion is met, and, on the basis of determining that the at least one further predetermined criterion is met, causing the airbrake to move to a closed position, in which the airbrake does not project from the lower surface of a fuselage. In some examples, the further predetermined criterion comprises that: a speed of the aircraft is below a threshold closing speed, the airbrake has been in the deployed position for a predetermined deployment time, the landing gear bay door is in the closed position, the nose landing gear is commanded to retract, for example by movement of a landing gear lever of the aircraft to a 'Lever Up' position, Weight off Wheels has been confirmed, and/or a speed of the aircraft on the around is below a thresholds.

[0119] Although the aircraft braking systems 200, 500 are shown as part of an aircraft in the enclosed Figures, it will be appreciated that the aircraft braking system 200, 500 may be supplied in isolation to, for example, an aircraft manufacturer.

[0120] The above embodiments are to be understood as illustrative examples of the invention. Further embodiments of the invention are envisaged. For example, the aircraft braking system may be configured to move any airbrake, additionally or alternatively to the nose landing gear bay door, to an airbrake position in which the airbrake projects from the underside of the fuselage to generate drag on the aircraft when the aircraft is moving in a forward direction. For example, the airbrake may be combined with one or more main landing gear bay doors, or may be separate from any landing gear bay doors. It is to be understood that any feature described in relation to any one embodiment may be used alone, or in combination with other features described, and may also be used in combination with one or more features of any other of the embodiments, or any combination of any other of the embodiments. Furthermore, equivalents and modifications not described above may also be employed without departing from the scope of the invention, which is defined in the accompanying claims.

[0121] It is to be noted that the term or" as used herein is to be interpreted to mean "and/or", unless expressly stated otherwise

Claims (1)

1. CLAIMS: 1. An aircraft braking system for installation in an aircraft and to selectively generate drag to slow the aircraft when landing gear of the aircraft are extended, the aircraft braking system comprising an airbrake movable between a retracted position, in which, when the aircraft braking system is installed in the aircraft, the airbrake does not project from a fuselage of the aircraft, and a deployed position, in which, when the aircraft braking system is installed in the aircraft, the airbrake projects from a lower surface of the fuselage such that, when the aircraft is moving in a forward direction and the airbrake is in the deployed position, the airbrake generates drag on the aircraft 2. The aircraft braking system according to claim 1, wherein the airbrake is rotatable between the retracted position and the deployed position about an airbrake axis.3. The aircraft braking system according to any preceding claim, comprising a protective panel movable between a first position and a second position, wherein, in the first position, when the aircraft braking system is installed in the aircraft, the protective panel blocks at least part of an aperture in the fuselage of the aircraft from which the airbrake extends when the airbrake is in the deployed position, and, in the second position, when the aircraft braking system is installed in the aircraft, the protective panel blocks the aperture by a lesser amount than in the first position.4. The aircraft braking system according to claim 3, configured to move the protective panel between the first position and the second position dependent on receipt of a command to move the airbrake between the retracted position and the deployed position.5. The aircraft braking system according to any preceding claim, comprising an actuation system configured to move the airbrake between the deployed and retracted positions.6. The aircraft braking system according to any preceding claim, wherein the airbrake is one of a plurality of airbrakes of the aircraft braking system, each airbrake movable between a retracted position, in which, when the aircraft braking system is installed in the aircraft, the respective airbrake does not project from a fuselage of the aircraft, and a deployed position, in which, when the aircraft braking system is installed in the aircraft, the respective airbrake projects from a lower surface of the fuselage such that, when the aircraft is moving in a forward direction and the airbrakes are in their respective deployed positions, each of the plurality of airbrakes generates drag on the aircraft 7. The aircraft braking system according to claim 5 and claim 6, wherein the airbrakes are connected to one another by an airbrake linkage, and the actuation system comprises an actuator configured to move the airbrake linkage to cause each airbrake of the plurality of airbrakes to move between the respective retracted and deployed positions 8. The aircraft braking system according to claim 6 or claim 7 when dependent on claim 3 or claim 4, wherein the protective panel comprises a plurality of sub-panels each configured to block at least part of a sub-region of the aperture and movable between respective first and second positions, each sub-region being a portion of the aperture between adjacent airbrakes when the airbrakes are in the deployed position.9. The aircraft braking system according to claim 8 when dependent on claim 7, wherein the sub-panels are connected to one another by a panel linkage, the panel linkage operably connected to the airbrake linkage such that movement of the airbrake linkage by the actuator causes movement of the panel linkage to move the sub-panels between the first and second positions.10. A controller for controlling an aircraft braking system to selectively generate drag to slow an aircraft, the controller configured to: determine whether at least one predetermined criterion is met; and when the controller determines that the at least one predetermined criterion is met, cause an airbrake to move to a deployed position, in which the airbrake projects from a lower surface of a fuselage of the aircraft, to generate drag on the aircraft.11. The controller according to claim 10, wherein the at least one predetermined criterion comprises that a speed of the aircraft is within a predefined range 12. The controller according to claim 10 or claim 11, wherein the controller is configured to: determine whether at least one further predetermined criterion is met; and when the controller determines that the at least one further predetermined criterion is met, cause the airbrake to move from the deployed position towards a retracted position in which the airbrake does not project from the fuselage of the aircraft.13. The controller according to claim 12, wherein the at least one further predetermined criterion comprises that a speed of the aircraft is below a minimum speed threshold.14. The aircraft braking system according to any one of claims Ito 9 comprising the controller of any one of claims 10 to 13.15. A method of selectively generating drag to slow an aircraft, the method comprising: determining whether at least one predetermined criterion is met; and on the basis of determining that the at least one predetermined criterion is met, causing an airbrake to move to a deployed position, in which the airbrake projects from a lower surface of a fuselage of the aircraft to generate drag on the aircraft.16. The method according to claim 15, or the controller according to any one of claims to 13, wherein the at least one predetermined criterion comprises that the aircraft is on the ground.17. The method according to claim 15 or claim 16, or the controller according to any one of claims 10 to 13 or claim 16, wherein the at least one predetermined criterion comprises that an aircraft braking command has been issued.18. The method according to any one of claims 15 to 17, or the controller according to any one of claims 10 to 13, claim 16 or claim 17, wherein the at least one predetermined criterion comprises that landing gear of the aircraft are in an extended position.19. A non-transitory computer-readable storage medium storing instructions that, if executed by a controller of an aircraft braking system of an aircraft, cause the controller to carry out the method according to any one of claims 15 to 18.20. The aircraft braking system according to any one of claims Ito 9 or claim 14, the controller according to any one of claims 10 to 13 or any one of claims 16 to 18, or the method according to any one of claims 15 to 18, wherein the airbrake is configured to generate a downward force on the aircraft when the aircraft is moving in a forward and the airbrake is in the deployed position.21. An aircraft landing gear system, comprising: a landing gear; a landing gear bay door rotatable about a landing gear axis between a closed position, in which the landing gear bay door is to block a landing gear bay aperture in a fuselage of an aircraft in use, and an open position, in which the landing gear may pass through the aperture; and the aircraft braking system according to any of claims 1 to 9, claim 14 or claim 20, wherein: the landing gear bay door comprises the airbrake, the closed position is the retracted position, and the landing gear bay door is movable between the closed position and the deployed position about a different axis to the landing gear axis.22. An aircraft comprising: the aircraft braking system according to any one of claims 1 to 9, claim 14 or claim the aircraft landing gear system according to claim 21; the controller according to any one of claims 10 to 13, claims 16 to 18, or claim 20; or the non-transitory computer-readable storage medium according to claim 19.23. The aircraft of claim 22, comprising the aircraft braking system of any one of claims 1 to 9, claim 14 or claim 20, wherein the airbrake is rotatable between the retracted position and the deployed position about an airbrake axis, and the airbrake axis extends in a lateral direction, relative to a forward direction of the aircraft.24. The aircraft of claim 22 or claim 23, comprising the aircraft braking system of any one of claims 1 to 9, claim 14 or claim 20, the aircraft braking system comprising a protective panel movable between a first position and a second position, wherein, in the first position, the protective panel blocks at least part of an aperture in the fuselage of the aircraft from which the airbrake extends when the airbrake is in the deployed position, and, in the second position, the protective panel blocks the aperture by a lesser amount than in the first position and permits movement of the airbrake between the retracted and deployed positions, via the aperture.