Patent Description:
In some known aircraft, a landing gear is held in an extended position when the aircraft is on the ground and is stowed at a retracted position in a landing gear bay once the aircraft has taken off. Such stowage of the landing gear helps to reduce aircraft drag and noise and the risk of the landing gear being damaged in flight. The landing gear subsequently is extended to the extended position again before the aircraft lands. A landing gear bay door may at least partially cover the landing gear bay when closed, and may be openable to enable movement of the landing gear between the retracted position and the extended position. Movement of the landing gear and the landing gear bay door is typically controlled by a pilot using cockpit flight controls of the aircraft, such as a landing gear control lever.

<CIT> discloses a landing gear controller to control extension and retraction of a landing gear for an aircraft.

<CIT> discloses methods and systems for operating aircraft landing gears. <CIT> discloses a shrink strut landing gear system.

A first aspect of the present invention provides a landing gear system for an aircraft, the landing gear system comprising: a landing gear that is movable between an extended position and a retracted position, the landing gear comprising an extendible strut; a position sensor configured to detect a position of a part of the extendible strut and output a signal indicative of the position; and a landing gear controller that is communicably connected to the position sensor and is configured, in use, to: receive the signal from the position sensor; and, on the basis of the signal and at least one further criterion, determine that the strut has extended and the landing gear is in contact with the ground and automatically cause performance of at least a portion of a procedure to move the landing gear from the extended position to the retracted position, wherein the at least one further criterion comprises the signal having been received at the landing gear controller for greater than a predetermined time period.

Optionally, the extendible strut is a telescopically-extendible strut.

Optionally, the predetermined time period is up to half a second, or less than one second. Optionally, the predetermined time period is less than two seconds.

Optionally, the landing gear comprises a bogie and the landing gear system comprises a bogie angle sensor, the bogie angle sensor configured to detect a pitch angle of the bogie and output a signal indicative of the pitch angle, wherein the landing gear controller is communicably connected to the bogie angle sensor, and configured, in use, to receive the signal from the bogie angle sensor, and wherein the at least one further criterion additionally comprises the pitch angle of the bogie of the landing gear.

Optionally, the position sensor is configured to directly detect the position of the part of the extendible strut.

Optionally, the position sensor is configured to detect the position of the part of the extendible strut when the extendible strut has a predetermined length that is less than a maximum length to which the strut is extendible.

Optionally, the predetermined length is at least <NUM>% of the maximum length; optionally the predetermined length is at least <NUM>% of the maximum length; further optionally the predetermined length is at least <NUM>% of the maximum length.

Optionally, the position sensor is configured to detect the position of the part of the extendible strut when the extendible strut has a predetermined length that is substantially equal to a maximum length to which the strut is extendible.

Optionally, the landing gear system comprises an isolator for isolating part of the landing gear system from a power supply, and the portion of the procedure comprises operation of the isolator to enable power to be supplied to the part of the landing gear system.

Optionally, the portion of the procedure comprises one or more avionics processes and/or one or more mechanical processes.

Optionally, the landing gear system comprises one or more landing gear bay door locks to retain the landing gear bay door in the closed position when the landing gear bay door lock is locked, and the portion of the procedure comprises unlocking the, or each, landing gear bay door lock to permit movement of the landing gear bay door to the open position.

Optionally, the portion of the procedure comprises actuating the one or more landing gear bay door actuators to move the landing gear bay door further from the open position before the unlocking of the, or each, landing gear bay door lock, thereby to facilitate unlocking of the, or each, landing gear bay door lock.

Optionally, the landing gear system comprises one or more landing gear bay door actuators configured to move a landing gear bay door from a closed position towards an open position to permit movement of the landing gear between the extended position and the retracted position; and the portion of the procedure comprises the one or more landing gear bay door actuators moving the landing gear bay door from the closed position towards the open position.

Optionally, the landing gear system comprises one or more landing gear actuators configured to move the landing gear from the extended position towards the retracted position; and the portion of the procedure comprises the one or more landing gear actuators moving the landing gear from the extended position towards the retracted position.

Optionally, the landing gear controller is configured, in use, to: receive an input indicative of an event; and automatically cause performance of a preliminary portion of the procedure on the basis of the input, before causing the performance of the portion of the procedure.

Optionally, the input is indicative of at least one of: braking force being less than a predetermined braking force, thrust being greater than a predetermined thrust, aircraft groundspeed being greater than a predetermined groundspeed, change in length of the extendible strut, a command from a cockpit flight control, and aircraft geographical position (e.g. on a runway).

Optionally, the input is indicative of a command from a landing gear control lever.

Optionally, the preliminary portion of the procedure comprises one or more avionics processes and/or one or more mechanical processes.

Optionally, the preliminary portion of the procedure comprises an avionics side change over.

Optionally, the landing gear system comprises one or more landing gear bay door locks to retain the landing gear bay door in the closed position when the landing gear bay door lock is locked; and the preliminary portion of the procedure comprises unlocking the, or each, landing gear bay door lock to permit movement of the landing gear bay door to the open position.

Optionally, the preliminary portion of the procedure comprises actuating one or more landing gear bay door actuators to move the landing gear bay door further from the open position before the unlocking of the, or each, landing gear bay door lock, thereby to facilitate unlocking of the, or each, landing gear bay door lock.

Optionally, the landing gear system comprises an isolator for isolating part of the landing gear system from a power supply; and the preliminary portion of the procedure comprises operation of the isolator to enable power to be supplied to the part of the landing gear system.

Optionally, the extendible strut is a shock absorber for supporting the aircraft when the aircraft is on the ground. Alternatively, the extendible strut optionally comprises a shock absorber for supporting the aircraft when the aircraft is on the ground, wherein the position sensor is configured to detect a position of a part of the shock absorber and the signal output by the position sensor is indicative of the position of the part of the shock absorber.

A second aspect of the present invention provides a method of controlling a landing gear system of an aircraft using a landing gear controller of the aircraft, the method comprising the landing gear controller: receiving a signal from a position sensor, wherein the signal is indicative of a position of a part of an extendible strut of a landing gear, wherein the landing gear is movable between an extended position and a retracted position, and wherein the receiving occurs when the aircraft, or the landing gear, is in contact with the ground; and automatically causing performance of at least a portion of a procedure for causing movement of the landing gear from the extended position to the retracted position, on the basis of the signal, wherein the landing gear controller automatically causes the performance only when the landing gear controller has determined that the signal has been received at the landing gear controller for greater than a predetermined time period.

Optionally, the predetermined time period is up to half a second, less than one second or less than two seconds.

A third aspect of the present invention provides a non-transitory computer-readable storage medium according to claim <NUM>.

Also disclosed is a landing gear system for an aircraft, the landing gear system comprising a landing gear controller that is configured to carry out the method according to the second aspect of the present invention.

A fourth aspect of the present invention provides an aircraft comprising the landing gear system according to the first aspect of the present invention.

Landing gear can influence aircraft performance. In the extended position, the landing gear may increase aircraft drag, which can reduce the climb rate of the aircraft during take-off, and may increase aircraft noise, which can be disturbing to people on the ground in the vicinity of the aircraft. Similar effects can result from a landing gear bay door being in an open position.

Often, actuation of each landing gear (and associated landing gear bay door, when provided) of an aircraft during a take-off procedure is initiated by a pilot manually operating cockpit flight controls, such as a landing gear control lever. Typically, operation of the cockpit flight controls causes one or more landing gear bay door actuators to drive movement of the landing gear bay door from a closed position to an open position, one or more landing gear actuators to retract the landing gear, and then the one or more landing gear bay door actuators to drive movement of the landing gear bay door from the open position to the closed position. During a take-off procedure, the pilot will typically manually initiate a landing gear retraction procedure upon confirming a positive rate of aircraft climb. Such confirmation may occur at about three seconds after take-off. Since the take-off procedure is one of the highest workload flight phases for flight crew, there is a tendency for retraction of landing gear to be delayed after take-off, in order to spread the various actions that the flight crew must perform during take-off over a greater period of time.

Some examples discussed herein are concerned with enabling landing gear retraction to occur sooner after take-off, in particular since this could help to reduce aircraft drag. In turn, this may enable an increased aircraft climb rate to help avoid obstacles on the ground and/or may allow an increase in maximum take-off weight of the aircraft for a given size of landing gear system, wing capability and engine thrust. Similarly, enabling landing gear retraction to occur sooner in a take-off procedure can help to reduce the total aircraft noise caused during a take-off procedure, or at least reduce a period of time during which the aircraft is making increased noise due to extended landing gear. Decreasing the time for which the landing gear is extended and the landing gear bay door is open can also reduce the risk of the landing gear or the landing gear bay door being damaged, such as by buffeting by wind.

<FIG> shows a schematic view of an example of an aircraft landing gear system. The landing gear system <NUM> comprises a landing gear extension and retraction system <NUM> and a landing gear controller <NUM> that is communicably connected to the landing gear extension and retraction system <NUM>. The landing gear system <NUM> also comprises a landing gear bay door <NUM> that is movable from a closed position towards an open position, one or more landing gear bay door actuators <NUM>, one or more landing gear bay door locks <NUM>, a landing gear <NUM> that is movable from an extended position to a retracted position, one or more landing gear actuators <NUM>, one or more landing gear locks <NUM>, a position sensor <NUM>, and an isolator <NUM>. These and other elements will be described in more detail below.

In this example, the landing gear controller <NUM> is configured to control the landing gear extension and retraction system <NUM>. That is, the landing gear controller <NUM> is to cause the landing gear extension and retraction system <NUM> to cause the elements <NUM>-<NUM> to perform certain actions. In other examples, the landing gear controller <NUM> may be comprised in the landing gear extension and retraction system <NUM>, so that the landing gear controller <NUM> may be configured to cause the elements <NUM>-<NUM> to perform those certain actions.

The landing gear bay door <NUM> is associated with a landing gear bay (not shown). The landing gear bay door <NUM> at least partially covers the landing gear bay when in the closed position. The landing gear <NUM> is at least partially positioned in the landing gear bay when in the retracted position. This way, the landing gear bay door <NUM> helps to protect the landing gear bay, and the landing gear <NUM> when stowed in the bay, from debris that might be thrown towards the bay while the aircraft is moving on the ground or in flight. Moreover, the landing gear bay door <NUM> helps to reduce drag (i.e. create an aerodynamically-cleaner aircraft).

The one or more landing gear bay door actuators <NUM> are for moving the landing gear bay door <NUM> from the closed position towards the open position, to permit movement of the landing gear <NUM> between the extended position and the retracted position. Each of the one or more landing gear bay door actuators <NUM> may take any suitable form, such as a hydraulic actuator, an electro-hydraulic actuator, or an electric actuator. The one or more landing gear bay door actuators <NUM> may also be for moving the landing gear bay door <NUM> from the open position towards the closed position, or an alternative mechanism may be provided for such closure.

The one or more landing gear bay door locks <NUM> are for locking the landing gear bay door <NUM> in the closed position when the landing gear bay door lock(s) <NUM> are locked. Each of the one or more landing gear bay door locks <NUM> may take any suitable form, such as a hydraulically-actuated lock, an electro-hydraulically-actuated lock, an electrically-actuated lock, or a mechanically-actuated lock. In some cases, the one or more landing gear bay door locks <NUM> may be omitted. For example, the landing gear bay door <NUM> may be held in the closed position by the one or more landing gear bay door actuators <NUM> or by a mechanical linkage (such as a re-erecting lock stay).

The one or more landing gear actuators <NUM> are for moving the landing gear <NUM> from the extended position towards the retracted position. Each of the one or more landing gear actuators <NUM> may take any suitable form, such as a hydraulic actuator, an electro-hydraulic actuator, or an electric actuator. The one or more landing gear actuators <NUM> may also be for moving the landing gear <NUM> from the retracted position towards the extended position, or an alternative mechanism may be provided for extension.

The one or more landing gear locks <NUM> are for locking the landing gear <NUM> in the retracted position when the landing gear lock(s) <NUM> are locked. Each of the one or more landing gear locks <NUM> may take any suitable form, such as a hydraulically-actuated lock, an electro-hydraulically-actuated lock, an electrically-actuated lock, or a mechanically-actuated lock. In some cases, the one or more landing gear locks <NUM> may be omitted. For example, the landing gear <NUM> may be held in the retracted position by the one or more landing gear actuators <NUM> or by a mechanical linkage (such as a re-erecting lock stay).

The landing gear <NUM> comprises an extendible strut <NUM>. The extendible strut <NUM> may be a telescopically-extendible strut <NUM>. The strut <NUM> may be, or comprise, a shock absorber <NUM> for supporting the aircraft when the aircraft is on the ground in normal use. The shock absorber <NUM> may absorb shock loads during aircraft landing. For example, the shock absorber <NUM> may be a pneumatic air - oil hydraulic shock absorber. Some such struts are known as oleo struts or oleo-pneumatic struts. Example such struts will be known to the skilled person, and so further detail of the strut <NUM> will not be given herein in the interests of brevity.

The landing gear controller <NUM> is operably connected to the isolator <NUM>. The isolator <NUM> is for isolating part of the landing gear system <NUM> from a power supply <NUM>. In particular, the isolator <NUM> is for isolating the landing gear extension and retraction system <NUM> from the power supply <NUM>, in this example. In this example, the isolator <NUM> is an isolation valve <NUM>. In this example, the landing gear extension and retraction system <NUM> is a hydraulic system and the power supply <NUM> is a supply of hydraulic power. The supply of hydraulic power may be a centralised aircraft hydraulic system. The isolation valve <NUM> isolates the landing gear extension and retraction system <NUM> from the supply of hydraulic power when the isolation valve <NUM> is in a closed position. The isolation valve <NUM> permits the flow of hydraulic fluid from the supply of hydraulic power <NUM> to the landing gear extension and retraction system <NUM> when the isolation valve is in an open position. In other examples, the landing gear extension and retraction system <NUM> may be an electric or electro-mechanical system and the isolator <NUM> may be an electrical switch or other appropriate device configured to control the supply of electric power from a power supply to the landing gear extension and retraction system <NUM>. In some cases, the isolator <NUM> may be omitted. For instance, the landing gear extension and retraction system <NUM> may be permanently connected to the power supply <NUM>.

The position sensor <NUM> is configured to detect a position of a part of the extendible strut <NUM> and to output a signal indicative of the position. When the strut <NUM> is, or comprises, a shock absorber <NUM>, the part of the extendible strut <NUM> may be a part of the shock absorber <NUM>. For example, the part could be part of a telescopic assembly. Moreover, when the strut <NUM> is, or comprises, a shock absorber <NUM>, the sensor may be configured to detect a characteristic of the shock absorber <NUM>, such as a length or volume of the shock absorber <NUM>, and the signal may be an indication of the characteristic.

The position sensor <NUM> may detect the position of the part of the strut <NUM> in one of several ways. For example, the strut <NUM> may comprise first and second relatively-movable parts, such as first and second telescopically-movable parts, and the position sensor <NUM> may be mounted on one of the parts and be configured to sense a distance to a target or the other of the parts. For example, the position sensor <NUM> may be mounted on the part in question. Alternatively, the position sensor <NUM> may be mounted separately from the strut <NUM>, and be configured to sense the position of the part of the strut <NUM> relative to the position sensor <NUM>. For example, the position sensor <NUM> may comprise a transmitter of electromagnetic radiation and a receiver, and the position sensor <NUM> may detect the position of the part of the strut <NUM> when the part of the strut <NUM> interrupts, or clears, a path between the transmitter and the receiver. The position sensor <NUM> may comprise a transmitter of electromagnetic radiation and a receiver that are mounted on separate supports, wherein the supports are arranged such that extension or retraction of the strut <NUM> brings the transmitter and receiver into alignment. Other arrangements may be used in other examples. For example, while a number of sensor arrangements for directly detecting the position of the part of the strut <NUM> have been mentioned, in other examples the position or angle of another component (such as part of a torque link of the landing gear <NUM>) may be sensed and indicative of a position of part of the strut <NUM>, so that the position of the part of the strut <NUM> is detected indirectly.

As an aircraft with landing gear including an extendible strut <NUM> (e.g. a shock absorber) approaches a state where it is about to leave contact with the ground during a take-off procedure, the strut <NUM> partially or fully extends from a baseline fully- or partially-compressed state as a result of lift being created by the wings. Due to the architecture of a typical shock absorber, there is often a minimum load required to be applied to the shock absorber before the shock absorber begins to compress. This is sometimes called the "breakout" load. Therefore, even when the shock absorber is fully extended, it is still able to support a load without being compressed. As such, even when a shock absorber is fully extended during a take-off procedure, a point will be reached when the aircraft is nearly flying, the shock absorber is at or close to being fully extended, and yet there is still contact between the landing gear and the ground.

With suitable configuration of the position sensor <NUM>, the position sensor <NUM> may thus be able to sense when the part of the extendible strut <NUM> is in a position indicative of the strut <NUM> being of the length the strut <NUM> would adopt when the aircraft is about to leave contact with the ground. Therefore, the position sensor <NUM> may be configured to output the signal, and the landing gear controller <NUM> may be configured to receive the signal, when the landing gear <NUM> is in contact with the ground.

The position sensor <NUM> may be configured and arranged (e.g. suitably located) to detect the position of the part of the extendible strut <NUM> when the extendible strut <NUM> has a predetermined length that is less than a maximum length to which the strut <NUM> is extendible in normal use. For example, the predetermined length may be at least <NUM>% of the maximum length, at least <NUM>% of the maximum length, at least <NUM>% of the maximum length, at least <NUM>% of the maximum length, at least <NUM>% of the maximum length, or at least <NUM>% of the maximum length. Alternatively, the position sensor <NUM> may be configured and arranged (e.g. suitably located) to detect the position of the part of the extendible strut <NUM> when the extendible strut <NUM> has a predetermined length that is equal, or substantially equal, to a maximum length to which the strut <NUM> is extendible in normal use.

The position sensor <NUM> may, for example, be an absolute position sensor or a relative position sensor. The position sensor <NUM> may, for example, be a linear position sensor, an angular position sensor, or a multi-axis position sensor. Example position sensors that could be used include: Linear Variable Differential Transformers (LVDTs), Rotary Variable Differential Transformers (RVDTs), proximity sensors, optical sensors, microswitches, and load sensors. Other types of sensor may be used in other examples.

The position sensor <NUM> may be configured to output the signal indicative of the position of the part of the strut <NUM> when the position sensor <NUM> senses the part, or the absence of the part. Alternatively, the position sensor <NUM> may be configured to output the signal indicative of the position of the part of the strut <NUM> when the position sensor <NUM> senses movement of the part. Alternatively, the position sensor <NUM> may be configured to output the signal indicative of the position of the part of the strut <NUM> constantly. As a still further alternative, the position sensor <NUM> may be configured to output the signal indicative of the position of the part of the strut <NUM> periodically, such as once every second, or once every half second, or once every <NUM> milliseconds, or once every <NUM> milliseconds, for example. Other frequencies may of course be employed.

Typically, a procedure for causing movement of a landing gear of a landing gear system from an extended position to a retracted position may comprise the following actions (although it is to be noted that some of the actions, such as (a) and/or (b), may not be present in some procedures):.

The landing gear controller <NUM> is communicably connected to the position sensor <NUM> and is configured, in use, to receive the signal from the position sensor <NUM>. The signal may, for example, be an electrical or electronic signal. Alternatively, it may be a mechanical or fluid signal, such as a hydraulic or pneumatic signal. The landing gear controller <NUM> is configured, in use, and on the basis of the signal, to determine that the strut <NUM> has extended and the landing gear <NUM> is in contact with the ground and automatically cause performance of at least a portion of a landing gear retraction procedure.

The portion of the procedure may comprise operation of the isolator <NUM> to enable power to be supplied to the part of the landing gear system <NUM>.

The portion of the procedure may comprise one or more avionics processes and/or one or more mechanical processes. The avionics may function to check on the state of one or more components of the landing gear system <NUM>. The avionics may be configured to control one or more components of the landing gear system <NUM>.

The portion of the procedure may comprise unlocking the, or each, landing gear bay door lock <NUM> to permit movement of the landing gear bay door <NUM> to the open position. The portion of the procedure may comprise actuating the one or more landing gear bay door actuators <NUM> to move the landing gear bay door <NUM> further from the open position before the unlocking of the, or each, landing gear bay door lock <NUM>, thereby to reduce the load on the lock(s) <NUM> and thus facilitate unlocking of the, or each, landing gear bay door lock <NUM>.

In some cases, the portion of the procedure may exclude actuation of the one or more landing gear bay door actuators <NUM> and the one or more landing gear actuators <NUM>. Therefore, actuation of these actuators <NUM>, <NUM> may remain under the control of the flight crew, so that the flight crew retain authority for causing actual opening of the landing gear bay door and the actual extension of the landing gear. Nevertheless, the landing gear controller <NUM> causing performance of these other actions reduces the time required to subsequently retract the landing gear when the flight crew command the retraction. This can lead to one or more of the advantages discussed above. This may be particularly the case when these other actions involve avionics, because functions involving avionics can cause latency. For instance, hydraulic or electrical valves or switches take time to respond to avionic signals.

Movement of a landing gear bay door from a closed position to an open position typically takes in the order of three seconds. Moreover, as mentioned above, during a take-off procedure, the pilot will conventionally initiate a landing gear retraction procedure only upon confirming a positive rate of aircraft climb, and such confirmation may occur at about three seconds after take-off. Therefore, conventionally, about six or more seconds elapse after take-off before the landing gear begins to be retracted.

In some cases, therefore, the portion of the procedure may comprise the one or more landing gear bay door actuators <NUM> moving the landing gear bay door <NUM> from the closed position towards the open position. Again, actuation of the one or more landing gear actuators <NUM> may remain under the control of the flight crew, but the landing gear controller <NUM> causing automatic opening of the landing gear bay door <NUM> still further reduces the time required to subsequently retract the landing gear when the flight crew commands the retraction. As such, some of the systems described herein enable movement of the landing gear bay door <NUM> from the closed position towards the open position to be initiated sooner, such as before take-off, on take-off, or immediately after take-off. Therefore, subsequent movement of the landing gear <NUM> from the extended position towards the retracted position may also be initiated sooner after take-off, for example in the order of three seconds sooner. This helps to provide the benefits of drag and noise reduction described above.

In still further cases, the portion of the procedure may comprise the one or more landing gear actuators <NUM> moving the landing gear <NUM> from the extended position towards the retracted position, although this should only be performed when it is known that the aircraft is off the ground. Such an airborne state may be determined by the landing gear controller <NUM> by any method known in the art, such as through the use of sensors for sensing landing gear wheel speed or load, sensors for sensing height of the aircraft above the ground (such as radio altimeters), or other suitable sensors that will be apparent to the skilled reader.

The portion of the procedure may further comprise the one or more landing gear bay door actuators <NUM> subsequently moving the landing gear bay door <NUM> from the open position towards the closed position. Accordingly, in some cases, there may be no need for the flight crew to instigate performance of any portion of the procedure. It will be appreciated that this may advantageously reduce their workload during the take-off procedure.

In some examples, the landing gear controller <NUM> is configured to determine that the strut <NUM> has extended, yet the landing gear <NUM> is still in contact with the ground, on the basis of the signal from the position sensor <NUM> alone. For example, the position sensor <NUM> may be configured to sense when the part of the extendible strut <NUM> has reached a position indicative of the strut <NUM> being of a length at which the landing gear <NUM> is about to leave contact with the ground. That is, the part of the extendible strut <NUM> may only reach that position in normal use when the landing gear <NUM> is still on the ground but is about to leave the ground. Alternatively, or additionally, the position sensor <NUM> may be configured to sense when the part of the extendible strut <NUM> has reached the position at a certain rate of movement that indicates that the landing gear <NUM> is about to leave the ground.

The landing gear controller <NUM> is configured, in use, to determine that the strut <NUM> has extended and the landing gear <NUM> is in contact with the ground and automatically cause the performance of at least the portion of the procedure, on the basis of a combination of the signal from the position sensor <NUM> and at least one further criterion.

The at least one further criterion comprises the signal having been received at the landing gear controller <NUM> for greater than a predetermined time period. The predetermined time period may, by way of example only, be up to half a second, less than one second or less than two seconds. A different predetermined time period may be used in another example. However, the predetermined time period is preferably selected so as to be long enough that very short periods of strut extension do not result in the landing gear controller <NUM> causing retraction of the landing gear <NUM>. This may be useful when, for example, the aircraft is rolling along uneven ground such that the length of the strut <NUM> may increase temporarily and then shorten again quickly thereafter. In such circumstances, the landing gear <NUM> may leave, or be about to leave, contact with the ground, but the landing gear <NUM> and the aircraft are not to become airborne to the extent that landing gear <NUM> retraction is appropriate.

Additionally, the at least one further criterion may comprise a pitch angle of a bogie of the landing gear <NUM>. When the landing gear <NUM> (such as a main landing gear) has a bogie upon which the wheels are rotationally mounted, then bogie rotation can be monitored. This may be used to detect whether the landing gear <NUM> is traversing bumpy ground (such that the bogie angle fluctuates frequently) or whether the aircraft is rotating steadily ready for take-off (such that the bogie angle changes smoothly). The landing gear system <NUM> may comprise a bogie angle sensor (not shown) that is configured to detect an angle of the bogie and output a signal indicative of the angle, and the landing gear controller <NUM> may be communicably connected to the bogie angle sensor and be configured, in use, to receive the signal from the bogie angle sensor. The landing gear controller <NUM> may determine that the strut <NUM> has extended and the landing gear <NUM> is in contact with the ground and automatically cause the performance, on the basis of the signal from the position sensor <NUM> and the signal from the bogie angle sensor.

One or more other criteria may be considered in other examples.

In some cases, the landing gear controller <NUM> is configured, in use, to receive an input indicative of an event, and automatically cause performance of a preliminary portion of the landing gear retraction procedure on the basis of the input, before causing the performance of the portion of the landing gear retraction procedure. The input may, for example, be an electrical or electronic signal. Alternatively, it may be a mechanical or fluid signal, such as a hydraulic or pneumatic signal. Therefore, in some cases, the landing gear controller <NUM> may cause performance of some of the procedure before the landing gear controller <NUM> receives the signal from the position sensor <NUM>.

The event may, for example, be the commencement of a take-off run. At such a time, the aircraft may have a certain geographical position, a command may be given from the cockpit flight control, brakes of the aircraft may be released, engine thrust (whether by a jet engine, electric engine, or a different form of engine) may be increased, the groundspeed of the aircraft would increase, and the extendible strut <NUM> may even change in length as the aircraft experiences load transfer. Accordingly, the input may, for example, be indicative of at least one of: the aircraft's geographical position, braking force being less than a predetermined braking force, thrust being greater than a predetermined thrust, aircraft groundspeed being greater than a predetermined groundspeed, change in length of the extendible strut, and a command from a cockpit flight control (such as a landing gear control lever, a different type of user-movable device, a touchpad, a touchscreen, a gesture-operable device, a voice-operable device, or any combination thereof).

The preliminary portion of the procedure may comprise operation of the isolator <NUM> to enable power to be supplied to the part of the landing gear system <NUM>.

The preliminary portion of the procedure may comprise one or more avionics processes and/or one or more mechanical processes. Aircraft sometimes have first and second substantially identical avionics systems for redundancy purposes. The preliminary portion of the procedure may comprise an avionics side change over, during which the avionics system enabled for a take-off procedure is switched from one of the available systems to the other. This avoids either avionics system being dormant for a prolonged period, which in turn helps to keep each system well exercised and enables sooner identification of any faults.

The preliminary portion of the procedure may comprise unlocking the, or each, landing gear bay door lock <NUM> to permit movement of the landing gear bay door <NUM> to the open position. The preliminary portion of the procedure may comprise actuating the one or more landing gear bay door actuators <NUM> to move the landing gear bay door <NUM> further from the open position before the unlocking of the, or each, landing gear bay door lock <NUM>, thereby to reduce the load on the lock(s) <NUM> and thus facilitate unlocking of the, or each, landing gear bay door lock <NUM>. The preliminary portion of the procedure may even comprise actuating the one or more landing gear bay door actuators <NUM> to move the landing gear bay door <NUM> from the closed position towards the open position. If the actuation system is capable, such opening of the landing gear bay door <NUM> while the aircraft accelerates along the runway is preferably very slow, so as to better ensure that the landing gear bay door is acting to protect the landing gear bay from debris that might be thrown towards the bay and to reduce drag.

It will be appreciated that such event-triggered performance of the preliminary portion of the landing gear retraction procedure may still further lessen the time subsequently required to perform the portion of the procedure on the basis of the signal from the position sensor <NUM>.

<FIG> is a flow diagram showing an example of a method of controlling a landing gear system of an aircraft using a landing gear controller of the aircraft. The method <NUM> comprises: receiving <NUM> an input indicative of an event (such as any one or more of the examples given above); causing <NUM> performance of a preliminary portion of a landing gear retraction procedure on the basis of the input; receiving <NUM> a signal from a position sensor, the signal being indicative of a position of a part of an extendible strut of a landing gear, wherein the landing gear is movable between an extended position and a retracted position, and wherein the receiving occurs when the aircraft, or the landing gear, is in contact with the ground; and automatically causing <NUM> performance of at least a portion of the landing gear retraction procedure on the basis of the signal.

The method <NUM> may be performed by the landing gear controller <NUM> discussed herein or any variant thereof discussed herein. The position sensor may be the position sensor <NUM> discussed herein or any variant thereof discussed herein. The strut may be the strut <NUM> discussed herein or any variant thereof discussed herein. The landing gear may be the landing gear <NUM> discussed herein or any variant thereof discussed herein.

In some examples, the receiving <NUM> action may be omitted. In some examples, the causing <NUM> action may be omitted.

In some examples, the preliminary portion of the procedure comprises at least one of: operation <NUM> of an isolator (such as the isolator <NUM>) to enable power to be supplied to the part of the landing gear system; actuation <NUM> of one or more landing gear bay door actuators (such as actuator <NUM>) to move a landing gear bay door (such as door <NUM>) further from an open position; and/or unlocking <NUM> of one or more landing gear bay door locks (such as locks <NUM>) to permit movement of the landing gear bay door to the open position.

In some examples, the portion of the procedure comprises at least one of: actuation <NUM> of the one or more landing gear bay door actuators to move the landing gear bay door from the closed position towards the open position; actuation <NUM> of the one or more landing gear actuators to move the landing gear from the extended position towards the retracted position; and/or actuation <NUM> of the one or more landing gear bay door actuators to move the landing gear bay door from the open position towards the closed position.

<FIG> shows a schematic diagram of a non-transitory computer-readable storage medium <NUM> according to an example. The non-transitory computer-readable storage medium <NUM> stores instructions <NUM> that, if executed by a processor <NUM> of a controller <NUM> of an aircraft, cause the processor <NUM> to perform one of the methods described herein. In some examples, the controller <NUM> is the landing gear controller <NUM> described above with reference to <FIG> or a variant thereof described herein. The instructions <NUM> comprise: receiving <NUM> an input indicative of an event (such as any one or more of the examples given above); causing <NUM> performance of a preliminary portion of a landing gear retraction procedure on the basis of the input; receiving <NUM> a signal from a position sensor, the signal being indicative of a position of a part of an extendible strut of a landing gear, wherein the landing gear is movable between an extended position and a retracted position, and wherein the receiving occurs when the aircraft, or the landing gear, is in contact with the ground; and automatically causing <NUM> performance of at least a portion of the landing gear retraction procedure on the basis of the signal. The instructions <NUM> may comprise instructions to perform any of the methods <NUM> described above with reference to <FIG>.

<FIG> is a schematic front view of an aircraft <NUM>. The aircraft <NUM> comprises two main landing gears <NUM> and a nose landing gear <NUM>. The aircraft <NUM> also comprises a landing gear system <NUM> as discussed herein, such as the system <NUM> discussed herein with reference to <FIG>. The landing gear system <NUM> may be operatively connected to all of the landing gears <NUM>, <NUM> or just to one or some of the landing gears, such as the main landing gears <NUM>. The aircraft <NUM> also comprises the non-transitory computer-readable storage medium <NUM> discussed herein with reference to <FIG>.

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

Claim 1:
A landing gear system (<NUM>) for an aircraft (<NUM>), the landing gear system comprising:
a landing gear (<NUM>) that is movable between an extended position and a retracted position, the landing gear comprising an extendible strut (<NUM>);
a position sensor (<NUM>) configured to detect a position of a part of the extendible strut and output a signal indicative of the position; and
a landing gear controller (<NUM>) that is communicably connected to the position sensor and is configured, in use, to:
receive the signal from the position sensor; and,
on the basis of the signal and at least one further criterion, determine that the strut has extended and the landing gear is in contact with the ground and automatically cause performance of at least a portion of a procedure to move the landing gear from the extended position to the retracted position, wherein the at least one further criterion comprises the signal having been received at the landing gear controller for greater than a predetermined time period.