Aircraft weight on wheel system

Abstract

An aircraft weight-on-wheels (WOW) system a number of sensors 30, in use to be attached to an aircraft in line of sight of at least one landing gear tyre, which detect electro-magnetic radiation refle

Description

Background It is common practice for aircraft to include one or more systems to detect whether the aircraft is on the ground or in the air. This information is typically used to enable or disable, or otherwise control, other aircraft systems that if enabled incorrectly would pose a safety hazard. For example, for larger aircraft such as commercial passenger planes, operation of the engine thrust reversers or the nose wheel steering system is generally not permitted unless the aircraft is no longer in the air. Similarly, operation of certain in-flight systems, such as the Auto-Pilot system, is generally only enabled when the aircraft is no longer on the ground. Depending on the size and nature of the aircraft there may be other control systems where it is highly desirable, if not essential, that they may only be operational when the aircraft is either on the ground or in the air, but not for both. For larger aircraft such as commercial passenger planes and other similar sized aircraft the above determination is accomplished using a 'weight-on-wheels' (WoW) system which detects when at least a portion of the weight of the aircraft is supported by the wheels and landing gear, which therefore implies that the aircraft is on the ground. Such WoW systems often utilise mechanical switches or proximity sensors to provide a signal when certain parts of the landing gear adopt a physical configuration that is indicative of the landing gear supporting the weight of the aircraft. For example, a proximity sensor may be placed on a set of torque links. As the aircraft lands the landing gear is compressed bring the torque links closer to one another and thus triggering the proximity sensor. A disadvantage of such WoW systems is that at the point of landing there is a time delay between one or more of the aircraft wheels coming into contact with the ground and sufficient weight being placed on the landing gear to trigger or activate the proximity sensors or switches. If the sink rate of the aircraft (the rate of descent at the point of contacting the runway) is particularly slow then the time delay becomes extended to the extent that the pilot may wish to activate or utilise one or more of the ground based systems, such as the thrust reversers before the proximity sensors or switches of the WoW system have supplied the necessary signal(s) to enable those systems, This situation is potentially hazardous. It is therefore a need for a weight-on-wheels system that mitigates or eliminates the time delay. 06 06 24 Summary of the Invention According to a first aspect of the present invention there is provided an aircraft weight-on-wheels, WoW, system comprising an aircraft landing gear having one or more elastically deformable tyres, an data processing system, one or more sensors arranged to 5 be affixed to the aircraft in line of sight of at least one of the tyres and arranged to detect electro-magnetic radiation reflected from the tyre and provide associated sensor data to the data processing system, wherein each sensor further comprises a camera arranged to provide one or more images of the tyre to the data processing system, the sensor data comprising said images, and wherein the data processing system comprises an image 10 processing system, and wherein the data processing system Is arranged to process the sensor data and determine a change in shape of the tyre that corresponds to the tyre leaving or coming into contact with the ground. Each tyre may have a geometric pattern provided on a side of the tyre in line of sight of 15 the associated camera. The aircraft weight-on-wheels system may further comprise one or more lights arranged to illuminate each tyre. 20 Each sensor may be arranged to be affixed to an aircraft fuselage or arranged to be affixed to the landing gear. The landing gear may comprise a nose landing gear and the sensor may be arranged to be affixed to a jacking dome of the landing gear. 25 Alternatively, the landing gear may comprise a main landing gear having a bogie beam and the sensor is arranged to be affixed to the bogie beam. The aircraft weight-on-wheels system may be arranged to be activated when the landing 30 gear is extended. Each sensor may include a self-cleaning mechanism. According to another aspect of the present invention there is provided an aircraft weight-on-wheels, WoW, system comprising an aircraft landing gear having one or more elastically deformable tyres, an image processing system, a camera arranged to be affixed to the aircraft in line of sight of at least one of the tyres and arranged to provide one or more images of the tyre to the image processing system, wherein the image processing system is arranged to detect from the images provided by the camera a change in shape of the tyre that corresponds to the tyre leaving or coming into contact with the ground. According to a further aspect of the present invention there is provided an aircraft comprising an aircraft weight-on-wheels system according to the preceding aspects. Brief Description of the Drawings Various embodiments of the present invention are described below, by way of nonlimiting examples only, with reference to the accompanying drawings, of which: Figure 1 is an illustrative diagram of an aircraft; Figure 2 schematically illustrates an aircraft landing gear; Figure 3 schematically illustrates an aircraft weight-on-wheels system; Figure 4 illustrates a geometric pattern on an aircraft tyre for use with the system of Figure 3; Figure 5 illustrates a further geometric pattern on an aircraft tyre for use with the system of Figure 3; Figure 6 schematically illustrates the change in cross-section of a single tyre under an increasing load; and Figure 7 provides an alternative illustration of how the cross-section of a tyre changes under an increasing load. Detailed Description Figure 1 is a schematic diagram of an aircraft 2. The aircraft includes assemblies such as a nose landing gear 4, main landing gear 6 and engines 8. Other aircraft assemblies will be apparent to the skilled person. An aircraft assembly can be a group of interconnected parts which are arranged to be fitted to one or more other aircraft assemblies as a unit. The term aircraft as used herein includes aeroplanes, helicopters, UAVs and the like. Figure 2 schematically illustrates a typical arrangement for the main landing gear 6, which includes a support member 10 that has an upper portion 12 arranged to be pivotally coupled to the main body of the aircraft (not illustrated) and a lower portion 14 that is slidably received within the upper portion 12. The support member 10 typically, but not necessarily, comprises a telescopic oleo-pneumatic shock strut. The lower portion 14 of the support member is pivotally coupled to a bogie beam 16 by means of a bogie beam pivot pin 18. In the particular example illustrated in Figure 1, the bogie beam 16 has first and second axles rotatably mounted at either end on which respective pairs of wheels 20 are mounted. In Figure 2 only a single one of each pair of wheels 20 is illustrated for the sake of clarity. A pair of torque links comprising an upper torque link 22 and a lower torque link 24 are pivotably coupled respectively to the upper and lower portions 12, 14 of the shock strut and also to one another. Fastened to, or integrated in, the torque links is at least one proximity sensor which includes a first proximity sensor element on the upper torque link 22 and a second proximity sensor element on the lower torque link 24. In figure 2, the main landing gear is illustrated in a configuration corresponding to the landing gear being extended (deployed) but not supporting any of the aircraft's weight, e.g. shortly before landing or shortly after take-off. In this configuration the torque links are 'opened out' from one another and the first and second proximity sensor elements are not in close proximity to one another. During a landing event, the landing gear shock strut 10 will begin to compress as the weight of the aircraft comes onto the landing gear. Consequently, the torque links 22, 24 'close up' and the proximity sensor elements will come into closer proximity to one another. The proximity sensor will be arranged such that at a predefined position of the torque links the proximity sensor will output a 'weight-on-wheels' signal to one or more other systems of the aircraft. The reverse occurs during a take-off event - as the aircraft begins to leave the ground the shock strut extends, the torque links move apart and at a predefined position the proximity sensor ceases to output the weight-on-wheels signal (or outputs a separate 'weight-off-wheels' signal). It will also be appreciated that the proximity sensor could be located on other elements of the landing gear that move between different configurations as the landing gear compresses or extends and / or could be replaced by a switch arrangement. The above weight-on-wheels / weight-off-wheels detection system suffers from a number of disadvantages. Primary amongst these is that during landing there is generally a time delay between one or more of the landing gear wheels 20 actually touching the ground and the proximity sensor providing the weight-on-wheels signal due to the shock strut 10 not starting to compress, and therefore the torque links not beginning to move relative to one another, until sufficient aircraft weight is placed on the shock strut. There are a number of mechanisms that contribute to this time delay. One contributory factor is the presence of some friction between the various moving elements of the landing gear, including the upper and lower portions of the support / shock strut, that therefore requires a certain amount of weight to be placed on the landing gear to overcome this friction and for the landing gear to start to compress. A further factor is relevant to main landing gear having multiple axles carried on a bogie beam (truck) pivotally connected to the shock strut, as illustrated in Figure 2. With such main landing gear configurations it is typical for the bogie beam to be orientated with either the front or rear axles pitched downwards, such that at the point of contact with the runway during landing only one set of wheels on one of the axles contacts the ground first and subsequently the bogie beam pivots until the wheels on both axles are in contact with the ground. Only after this phase will the shock strut start to compress. Finally, the tyres on the wheels will deform under the weight of the aircraft before the shock strut starts to compress. As will be appreciated, the same mechanisms as described above also contribute 'in reverse' during a take-off event to introduce a time difference between a proximity / switch based system generating a weight-off-wheels signal and the aircraft tyres actually leaving the ground. Figure 3 schematically illustrates an example of a system that seeks to provide a more accurate indication of aircraft weight-on-wheels / weight-off-wheels. The system includes a camera unit 30 mounted to the underside of an aircraft landing gear 6, for example on the underside of the bogie beam, such that the camera unit 30 has a clear line of sight to at least one of the landing gear tyres, and more specifically to the lower area of the tyre closest to the ground when the aircraft is on the ground. The camera unit is connected, either physically or wirelessly, to a data processing system 32 and is arranged to provide one or more images of the tyre to the data processing system, either as a sequence of discrete still images or as video. In the system illustrated in Figure 3, the data processing system 32 is configured to function as an image recognition and image processing system and is arranged to process the images of the tyre received from the camera to identify a change in shape (deformation) of the tyre that corresponds to the tyre either coming into contact with the ground or leaving the ground. In other words, the system utilises the mechanism identified above of the aircraft tyre undergoing a change in shape / deformation as an indication of Weight-on wheels, WoW, or weight-off-wheels, WoffW. The implementation and functionality of the image recognition and image processing system is considered to be within the existing knowledge of the skilled person and therefore falls outside the scope of the present invention. In general, it is envisaged that the image recognition system will be trained to identify the shape of the tyre that corresponds to the tyre either coming into contact with the ground or leaving the ground using a dataset of multiple 'training' images that have already been classified. It is also envisaged that the system will utilise known artificial intelligence (AI) learning algorithms to further learn from the images captured in use what a tyre looks like at the point of WoW or WoffW. The data processing system 32 is preferably connected to one or more further systems of the aircraft that can utilise, or require, a WoW and / or WoffW signal generated by the data processing system. Examples of such further systems illustrated in Figure 3 include, but are not limited to, engine thrust reversers and nose wheel steering system. In some embodiments of the WoW system illustrated in Figure 3 the camera unit may be capable and arranged to capture images of more than one of the landing gear tyres simultaneously. The image recognition and image processing system may then in turn be arranged to determine a WoW / WoffW event for the separate tyres. This greater level of fidelity in comparison with the prior art WoW systems discussed above may be useful in providing enhanced operation of other aircraft systems. For example, the thrust reverser system may be arranged to be enabled only if two or more wheels on the same landing gear are deemed to be in contact with the ground during a landing event, or only if at least one wheel on each of the two main landing gears are deemed to be in contact with the ground, so as to prevent a premature and potentially unsafe activation of the engine thrust reversers. Additionally or alternatively, one more than one camera unit may be included within the system, either arranged to capture images of separate wheels or arranged to capture multiple images (or sets of images) of the same wheel so as to enhance the image recognition process. Whilst Figure 3 illustrates the camera unit being mounted to the underside of the bogie beam, the camera may be mounted anywhere on the landing gear or elsewhere on the aircraft that provides the camera with a line of sight to the respective wheel. The camera may be fitted with a self-cleaning functionality, such as a water jet or removable film mechanism, to avoid dirt, moisture, debris etc. from obscuring the tyre. One or more lights arranged to illuminate the area of the tyre of interest may also be included for operation at night-time or low light levels. The camera may also be capable of infrared operation. In further embodiments one or more geometric patterns may be provided on the side of the tyre(s) to facilitate identification of the change of shape of the tyre by the data processing system. Figure 4 schematically illustrates one such possible pattern. Figure 4 represents two views of the same aircraft tyre displaced by approximately 90 degrees of rotation. The tyre 40 is represented as being in contact with the ground 42 and under a load, i.e. with at least some of the weight of the aircraft applied to the tyre. A number of geometric patterns 44 are provided on the side of the tyre, for example by being printed or painted on. The pattern 44 is selected such that its visual appearance is different when the pattern occupies a portion of the tyre that is deformed due to the applied weight of the aircraft, i.e. the portion of the tyre in contact with the ground, and when the pattern occupies an undeformed portion of the tyre. This is illustrated in Figure 4 by the three highlighted pattern segments 44a in the left-hand image appearing less 'compressed' than the equivalent three segments 44b in the right-hand image. It will of course be appreciated that many geometric patterns may be suitable for this purpose. As a further example, Figure 5 illustrates an aircraft tyre having a number of radial lines 46 marked on the side of the tyre. In those portions of the tyre that is not deformed due to the aircraft weight the radial lines appear straight, whereas in the portion 48 of the tyre that is in contact with the ground, and therefore loaded and deformed, the radial lines are distorted. In other embodiments, rather than using a camera unit, one or more sensors that are capable of at least detecting electro-magnetic radiation reflected from the tyres are provided. Examples of such sensors include, but are not limited to, laser and ultrasonic sensors. In such embodiments the data processing system 32 is arranged to receive the sensor signals and use those signals to measure the deformation of the tyre. A measurement in excess of a predetermined threshold will denote WoW or WoffW. In such embodiments the deformation of the tyre may be measured as the cross-section of the tyre or as the rolling radius. Figure 6 schematically illustrates the typical change in cross-section of a single tyre under an increasing load, the leftmost image representing least load, the rightmost image the most load. As the load increases the width of the tyre, labelled 'w', at the portion of the tyre in contact with the ground increases, known as tyre bulge. Referring back to Figure 3, a sensor can be mounted on the landing gear in the same general location as the camera unit 30, i.e. in line of sight of the portion of the tyre in contact with the ground of one side of a tyre. By using a sensor that is capable of determining the distance between the sensor and the side of the tyre, or providing sensor data that permits the data processor to determine the distance, the change in cross-section, or tyre bulge, can be detected due to the distance between the side of the tyre and the sensor decreasing or increasing as the width of the tyre increases or decreases as the load on the tyre increases or decreases. Suitable sensors include laser and ultrasonic sensors that are arranged to emit electromagnetic waves (typically as a focussed beam), such as laser or ultrasound respectively, and to detect returning electro-magnetic waves that have been reflected of an object, in this case the side of the tyre, and provide an indication of the 'time of flight' of the emitted and received waves. From the time of flight the distance of the object from the sensor can be determined. Other so called 'range finding' sensors may also be used, such as radar and lidar. Figure 7 provides an alternative illustration of how the cross-section of a tyre changes under an increasing load. As with Figure 6, the leftmost image represents the least load, the rightmost image the most load. In Figure 7 the nominal centre of rotation of the tyre is indicated by the broken lines 70a and 70b, line 70a being for the unloaded (left) tyre and line 70b being for the most loaded (right) tyre. As illustrated in Figure 7, due to the compression of the tyre under load, the centre of rotation of the loaded tyre is displaced relative to that of the unloaded tyre. This may also be expressed as a change in the rolling radius of the tyre. By placing one or more sensors of the type described above in respect of Figure 6 at appropriate places on the landing gear or other aircraft structures, this change in rolling radius can be detected and used as an indication of weight-on-wheels or weight-off-wheels. For example, for a camera-based system a camera may be placed having a clear view of a wheel centre and an area beneath the respective tyre. Using the image processing system, the distance between the wheel centre and the ground can be calculated. A distance threshold value equal to the nominal (expected) rolling radius can be stored in the image processing system. When the calculated distance either decreases to less than the threshold value due to compression of the tyre (landing event) or increases to greater than the threshold value (take-off event) a respective weight-on-wheel or weight-off-wheel signal is generated. Alternatively, a suitable marker, such as a circumferential line, may be provided on the tyre sidewall which in conjunction with the wheel centre can be used to calculate the effective rolling radius of a tyre. The provision of a sensor or camera based system for detecting the change in shape of the tyre at the point of contact with or departure from the ground allows a greater degree of accuracy in determining the WoW or WoffW, with a reduced time delay for making that determination. The system also brings gains in reduced weight due to a potentially lower parts count and / or lighter weight components.

Claims

06 06 241. An aircraft weight-on-wheels, WoW, system comprisingan aircraft landing gear having one or more elastically deformable tyres;a data processing system;one or more sensors arranged to be affixed to the aircraft in line of sight of at least one of the tyres and arranged to detect electro-magnetic radiation reflected from the tyre and provide associated sensor data to the data processing system,wherein each sensor further comprises a camera arranged to provide one or more Images of the tyre to the data processing system, the sensor data comprising said images, and wherein the data processing system comprises an image processing system; andwherein the data processing system is arranged to process the sensor data and determine a change in shape of the tyre that corresponds to the tyre leaving or coming into contact with the ground.

2. An aircraft weight-on-wheels system according to claim 1, wherein each tyre has a geometric pattern provided on a side of the tyre in line of sight of the associated camera.

3. An aircraft weight-on-wheels system according to claim 1 or 2 further comprising one or more lights arranged to illuminate each tyre.

4. An aircraft weight-on-wheels system according to any preceding claim, wherein each sensor is arranged to be affixed to an aircraft fuselage.

5. An aircraft weight-on-wheels system according to any one of claims 1 to 4, wherein each sensor is arranged to be affixed to the landing gear.

6. An aircraft weight-on-wheels system according to claim 5, wherein the landing gear comprises a nose landing gear and the sensor is arranged to be affixed to a jacking dome of the landing gear.

7. An aircraft weight-on-wheels system according to claim 6, wherein the landing gear comprises a main landing gear having a bogie beam and the sensor is arranged to be affixed to the bogie beam.

8. An aircraft weight-on-wheels system according to any preceding claim, wherein the system is arranged to be activated when the landing gear is extended.

9. An aircraft weight-on-wheels system according to any preceding claim, wherein each sensor comprises a self-cleaning mechanism.

10. An aircraft weight-on-wheels, WoW, system comprisingan aircraft landing gear having one or more elastically deformable tyres;an image processing system;a camera arranged to be affixed to the aircraft in line of sight of at least one of the tyres and arranged to provide one or more images of the tyre to the image processing system,wherein the image processing system is arranged to detect from the images provided by the camera a change in shape of the tyre that corresponds to the tyre leaving or coming into contact with the ground.

11. An aircraft comprising an aircraft weight-on-wheels system according to any preceding claim.06 06 24

Images