GB2585913A

GB2585913A - Method of Assessing the health of an aircraft tyre

Info

Publication number: GB2585913A
Application number: GB1910532.9A
Authority: GB
Inventors: Colosimo Antonio
Original assignee: Airbus Operations Ltd
Current assignee: Airbus Operations Ltd
Priority date: 2019-07-23
Filing date: 2019-07-23
Publication date: 2021-01-27
Also published as: GB201910532D0

Abstract

The invention provides a method of assessing the health of an aircraft tyre 111b, 112b,123b, 124b, 135b, 136b the aircraft tyre being mounted on an aircraft wheel 111, 112,123, 124, 135, 136 on a landing gear 110, 120, 130 of an aircraft, the method comprising the steps of measuring a rotational speed of an aircraft wheel that is rotating over the ground, providing an actual speed parameter derived from the measured rotational speed of the aircraft wheel, providing a first estimated speed parameter of the aircraft wheel, and comparing the actual speed parameter and the first estimated speed parameter of the aircraft wheel. The invention also provides a method of assessing the health of at least three aircraft tyres, a controller, an aircraft and a further method of assessing the health of one or more aircraft tyres.

Description

METHOD OF ASSESSING THE HEALTH OF AN AIRCRAFT TYRE

BACKGROUND OF THE INVENTION

[0001] The present disclosure relates to a method of assessing the health of an aircraft tyre.

[0002] The present invention concerns methods of assessing the health of an aircraft tyre. More particularly, but not exclusively, this invention concerns a method of assessing the health of an aircraft tyre, the aircraft tyre being mounted on an aircraft wheel on a landing gear of an aircraft, the method comprising the step of measuring a rotational speed of an aircraft wheel that is rotating over the ground.

[0003] The invention also concerns a method of assessing the health of at least three aircraft tyres, a controller, an aircraft and a further method of assessing the health of one or more aircraft tyres.

[0004] US 4355298 describes a low or flat tire warning system that monitors the rotational speed and thus, the condition of the tyres. A warning signal is generated if the measured speed is higher than a variable reference. The variable reference can be derived from an aircraft ground speed or a rotational speed of another tyre.

[0005] However, this does not provide for being able to determine which of the tyres may be, for example, under or over inflated, as it only identifies whether or not a given tyre has a speed value higher than expected. Hence, the system does not allow a pilot or maintenance person to identify the particular wheel/tyre that may need attention. Furthermore, the method does not apply when the aircraft is being steered.

[0006] The present invention seeks to mitigate the above-mentioned problems.

Alternatively or additionally, the present invention seeks to provide an improved method of assessing the health of an aircraft tyre. -2 -

SUMMARY OF THE INVENTION

[0007] The present invention provides, according to a first aspect, a method of assessing the health of an aircraft tyre, the aircraft tyre being mounted on an aircraft wheel on a landing gear of an aircraft, the method comprising the steps of measuring a rotational speed of an aircraft wheel that is rotating over the ground, providing an actual speed parameter derived from the measured rotational speed of the aircraft wheel, providing a first estimated speed parameter of the aircraft wheel, and comparing the actual speed parameter and the first estimated speed parameter of the aircraft wheel.

[0008] This allows a comparison between an expected speed and an actual speed (or parameters related to/derived from those speeds), and so this method is able to show up where the measured rotational speed is not similar to what would have been expected. This helps to identify where the tyre may be over or under inflated or where it is damaged or it has burst. For example, it may provide an indication where the radius of the wheel is not as expected, which relates to the level of inflation of tyre.

[0009] Rotational speed (omega, w) is same as angular speed of the aircraft wheel, i.e. this is an indication of how fast the wheel completes a full rotation. This speed relates to the radius of the aircraft wheel and the distance needed to be covered by the aircraft wheel along the ground. Thus, it may indicate that the tyre is burst (if the measured rotational speed is close to zero -because a burst tyre may substantially stop the aircraft wheel spinning) or damaged in another way. The rotational speed may he measured with a tachometer.

[0010] The actual speed parameter may not he the measured speed, but is an indication of it and/or derived from it. For example, the parameter may be the rotational speed of the wheel divided by a distance of that wheel from the centre of rotation of the aircraft. Of course, whatever the parameter used, it is compared to an equivalent/corresponding parameter, to determine when the parameter is not as expected.

[0011] Preferably, the step of comparing the actual speed parameter and the estimated speed parameter of the aircraft wheel comprises the step of calculating a -3 -difference between the actual speed parameter and the estimated speed parameter of the aircraft wheel.

[0012] More preferably, the method further comprises the step of providing a signal if the difference is more than a set tolerance level.

[0013] This enables a signal to be passed to the pilot for example. Hence, the pilot can choose to take a different course of action based on the indication. The set tolerance level allows for the measured rotational speed to be substantially the same as, or similar to the expected speed. This allows for differences that come within error margins of the instrumentation and minimises the occurrences of a signal that is potentially unnecessary.

[0014] Preferably, the actual speed parameter is also derived from an expected radius of the aircraft wheel.

[0015] Of course, angular speed relates to the radius of the aircraft wheel and the distance needed to be covered by the aircraft wheel along the ground. Hence, a measurement of angular speed that is very different to what is expected, based on the expected aircraft wheel radius, may indicate that the radius of the aircraft wheel is different to what is expected (for example, a notional or designed radius of the aircraft wheel/tyre). Hence, the method can be used to indicate that the tyre is over inflated (if the measured rotational speed is lower than expected), or underinflated (if the measured rotational speed is higher than expected), for example.

[0016] Preferably, the actual speed parameter is also derived from a distance of the aircraft wheel from a centre of rotation of the aircraft. Hence, the method may allow for a steering angle of the aircraft and the distance the aircraft wheel actually covers over the ground.

[0017] Preferably, the aircraft comprises a second aircraft wheel and wherein the first estimated speed parameter of the first aircraft wheel is derived from a measured rotational speed of the second aircraft wheel.

[0018] More preferably, the first estimated speed parameter of the first aircraft wheel is also derived from an expected radius of the second aircraft wheel. Hence, a difference in nominal or designed wheel radii can he allowed for. -4 -

[0019] Even more preferably, the first estimated speed parameter of the first aircraft wheel is also derived from a distance of the second aircraft wheel from a centre of rotation of the aircraft. Hence, the method allows for the variation of the actual distance covered along the ground by the (first and) second wheels.

[0020] Preferably, the aircraft comprises a third aircraft wheel and wherein the method comprises the steps, for each wheel, of measuring a rotational speed of the aircraft wheel, providing an actual speed parameter derived from the measured rotational speed of the aircraft wheel, providing a first estimated speed parameter of the aircraft wheel, providing a second estimated speed parameter of the aircraft wheel, and comparing the actual speed parameter and the first and second estimated speed parameters of the aircraft wheel, wherein the first estimated speed parameter of the aircraft wheel is derived from a measured rotational speed of a first other aircraft wheel and wherein the second estimated speed parameter of the aircraft wheel is derived from a measured rotational speed of a second other aircraft wheel.

[0021] This allows the method to determine which of the wheels speed is not as expected. For example, if the actual speed parameters of wheel 1 and wheel 2 are different, the actual speed parameters of wheels 2 and 3 are different but the actual speed parameters of wheels 1 and 3 are similar, this may indicate that it is wheel 2 that may be over or underinflated.

[0022] More preferably, the method further comprises the step of, for each wheel calculating a difference between the actual speed parameter and the first and second estimated speed parameters of the aircraft wheel, and providing a signal for that wheel indicating if the difference with both parameters is more than a set tolerance level.

[0023] If there are more than three aircraft wheels, the method may comprise, for each wheel, measuring a rotational speed of the aircraft wheel, providing an actual speed parameter derived from the measured rotational speed of the aircraft wheel, providing a first estimated speed parameter of the aircraft wheel derived from a measured rotational speed of a first other aircraft wheel, providing a second estimated speed parameter of the aircraft wheel derived from a measured rotational speed of a second other aircraft wheel, providing further estimated speed parameters of the aircraft wheel derived from measured -5 -rotational speeds of further other aircraft wheels, and comparing the actual speed parameter and the first, second and further estimated speed parameters of the aircraft wheel.

[0024] According to a second aspect of the invention there is also provided a method of assessing the health of at least three aircraft tyres, each of the three (or more) aircraft tyres being mounted on a different aircraft wheel on one or more landing gears of an aircraft, the method comprising the steps of measuring a rotational speed of each of the three (or more) aircraft wheels that are rotating over the ground, providing an actual speed parameter of each of the three (or more) aircraft wheels, the actual speed parameter for each aircraft wheel being derived from the measured rotational speed of that aircraft wheel, and comparing the actual speed parameter of each of the three (or more) aircraft wheels with the actual speed parameters of each of the other aircraft wheels.

[0025] Preferably, the step of comparing the actual speed parameters comprises the step of calculating a difference between the actual speed parameters.

[0026] Even more preferably, the method further comprises the step of providing a signal to indicate an aircraft wheel if its actual speed parameter is different to both the other two actual speed parameters by more than a set tolerance level.

[0027] Preferably, the actual speed parameter of each of the three aircraft wheels is also derived from an expected radius of that aircraft wheel.

[0028] Preferably, the actual speed parameter of each of the three aircraft wheels is also derived from a distance of that aircraft wheel from a centre of rotation of the aircraft. Hence, the method may allow for a steering angle of the aircraft and the distance the aircraft wheel actually covers over the ground.

[0029] Preferably, an estimated speed parameter of an aircraft wheel is derived from a measured ground speed of the aircraft and wherein the actual speed parameter of the aircraft wheel is compared to the estimated speed parameter. In the situation, the aircraft may be travelling in a substantially straight line.

[0030] Preferably, the health of one or more aircraft tyres mounted on a main landing gear wheel is assessed. Tyres mounted on a main and/or nose landing gear wheel may be assessed. All tyres mounted on the landing gear wheels of the aircraft may be assessed. -6 -

[0031] Preferably, one or more aircraft tyres whose health is being assessed is mounted on a wheel that is drivable by a landing gear drive system. In other words, the wheel concerned is caused to rotate using the drive system (rather than the aircraft engines or an external tug). The one or more aircraft tyres whose health is being assessed may be mounted on a wheel that is adjacent a landing gear drive system. Hence, the inflation level of a tyre that is adjacent the landing gear drive system may be assessed. This is especially beneficial as this minimises a risk of a tyre flexing into the space envelope of the landing gear drive system.

[0032] Preferably, the measuring, providing and comparing steps are repeatedly carried out, thus providing ongoing monitoring of the aircraft tyre(s).

[0033] According to a third aspect of the invention there is also provided a controller having a first input for receiving a measured rotational speed of an aircraft wheel, an actual speed parameter calculator for calculating an actual speed parameter from the measured rotational speed of the aircraft wheel, a second input for receiving a first estimated speed parameter of the aircraft wheel, and a comparator for comparing the actual speed parameter and the first estimated speed parameter of the aircraft wheel.

[0034] Preferably, the comparator calculates a difference between the actual speed parameter and the estimated speed parameter of the aircraft wheel.

[0035] More preferably, the controller provides a signal if the difference is more than a set tolerance level.

[0036] Preferably, the actual speed parameter is also derived from an expected radius of the aircraft wheel.

[0037] Preferably, the actual speed parameter is also derived from a distance of the aircraft wheel from a centre of rotation of the aircraft. Hence, the method may allow for a steering angle of the aircraft and the distance the aircraft wheel actually covers over the ground.

[0038] Preferably, the aircraft comprises a second aircraft wheel and wherein the first estimated speed parameter of the first aircraft wheel, is derived from a measured rotational speed of the second aircraft wheel. The controller may he connected to a -7 -second (similar) controller, which provides the first estimated speed parameter to the first controller.

[0039] More preferably, the aircraft comprises a third aircraft wheel and wherein a second estimated speed parameter of the first aircraft wheel, is derived from a measured rotational speed of the third aircraft wheel. The controller may be connected to a third (similar) controller, which provides the second estimated speed parameter to the first controller.

[0040] According to a fourth aspect of the invention there is also provided an aircraft comprising one or more aircraft tyres, each mounted on an aircraft wheel on a landing gear of the aircraft, the aircraft also comprising the controller as described above.

[0041] Preferably, the aircraft further comprises a landing drive system on one or more of the landing gear of the aircraft.

[0042] According to a fifth aspect of the invention there is also provided a method of assessing the health of one or more aircraft tyres, each aircraft tyre being mounted on a respective aircraft wheel of one or more landing gears of an aircraft, the method comprising the steps of measuring a rotational speed of each of a plurality of two or more aircraft wheels, as the aircraft wheels move over the ground when the aircraft is performing a turn on the ground at a turning angle, a controller, with the use of received data comprising an indication of the turning angle and indications of the measured rotational speeds, determining whether one of the measured rotational speeds is inconsistent with the other received data.

[0043] Hence, the method may indicate when a wheel (or tyre) does not have a radius that is expected.

[0044] The rotational speed of each of the wheels may be measured at the same time.

[0045] Where there are three or more wheels being measured, the method can provide an indication of which wheel has a different radius (i.e. the wheel, if any, whose rotational speed value is inconsistent with the at least two others).

[0046] It will of course he appreciated that features described in relation to one aspect of the present invention may he incorporated into other aspects of the present -8 -invention. For example, the method of the invention may incorporate any of the features described with reference to the apparatus of the invention and vice versa.

DESCRIPTION OF THE DRAWINGS

[0047] Embodiments of the present invention will now be described by way of example only with reference to the accompanying schematic drawings of which: [0048] Figure 1 shows a side view of an aircraft, the health of the tyres of the aircraft being monitored according to a first embodiment of the invention; [0049] Figure 2 shows a schematic view of a monitoring device for a first wheel of the aircraft according to a second embodiment; [0050] Figure 3 shows a schematic view of an actual speed parameter calculation device for a first wheel of the aircraft according to a third embodiment; [0051] Figure 4 shows a schematic view of a wheel monitoring device, including the actual speed parameter calculation device of Figure 3; and [0052] Figure 5 shows a schematic view of the landing gear of the aircraft of Figure 1.

DETAILED DESCRIPTION

[0053] Figure I shows a side view of an aircraft 100 on the ground 200. The aircraft comprises a nose landing gear 110 and two sets of main landing gear (left set 120 shown in Figure 1, right set 130 shown only in Figure 5).

[0054] As can be seen in Figure 5, which is a schematic view of the landing gear of the aircraft of Figure 1, each landing gear 110, 120, 130 comprises an axle and two wheels, provided with tyres.

[0055] Namely: The nose landing gear 110 comprises a left wheel (called wheel 1) 111. This left nose wheel 111 is provided with a tyre 111b and the middle of the wheel is shown by dashed line 111a. -9 -

- The nose landing gear 110 comprises a right wheel (called wheel 2) 112. This right nose wheel 112 is provided with a tyre 112b and the middle of the wheel is shown by dashed line 112a.

- The nose landing gear 110 comprises an axle 113 upon which both wheels 111, 112 are mounted. The centre of the axle 113 is shown by dashed line 113a.

- The left main landing gear 120 comprises a left wheel (called wheel 3) 123. This left wheel of the left main landing gear is provided with a tyre 123h and the middle of the wheel is shown by dashed line 123a.

- The left main landing gear 120 comprises a right wheel (called wheel 4) 124. This right wheel of the left main landing gear is provided with a tyre 124h and the middle of the wheel is shown by dashed line 124a.

The left main landing gear 120 comprises an axle 121 upon which both wheels 123, 124 are mounted. Adjacent the axle 121 is located a drive system 128 for driving rotation of the right (inner) wheel 124.

- The right main landing gear 130 comprises a left wheel (called wheel 5) 135. 'This left wheel of the right main landing gear is provided with a tyre 135b and the middle of the wheel is shown by dashed line 135a.

- The right main landing gear 130 comprises a right wheel (called wheel 6) 136.

This right wheel of the right main landing gear is provided with a tyre 136b and the middle of the wheel is shown by dashed line 136a.

- The right main landing gear 130 comprises an axle 131 upon which both wheels 135, 136 are mounted. Adjacent the axle 131 is located a drive system 138 for driving rotation of the left (inner) wheel 135.

[0056] In Figures 1 and 5, the aircraft is turning, as can be seen by the steering angle of the nose gear 110, depicted by alpha (a). This steering angle 140 corresponds to a centre of rotation of the aircraft depicted at 150, in line with the centre of the main landing gear wheels 123, 124, 135, 136.

[0957] Various distances are shown on Figure 5.

[0958] These are: -10 - - D = the longitudinal distance (along the longitudinal axis / centre line of the aircraft) between the axle 113 of the nose landing gear 110 and the axles 121, 131 of the two sets of main landing gear 120, 130. In other words, this is representative of the longitudinal distance between the nose landing gear and the two main landing gears.

- A = the distance between the centre of each wheel and the centre of the corresponding axle (i.e. shown as the distance between II la and 1 I3a, but is also the distance between 1 I 2a and 113a and the distances between 123a and 124a with the centre of axle 121 and the distances between 135a and I36a with the centre of axle 131).

B = the distance between the collective centre (shown as 132) of the two main landing gear axles 121, 131 (on the longitudinal axis /centre line of the aircraft) and the middle of the axles 121, 131. In other words, this is representative of the lateral distance of the main landing gears away from the centre line (longitudinal axis) of the aircraft.

- = the distance from the middle 1 1 la of wheel 111 (called wheel 1) and the centre of rotation 150 of the aircraft. This equals D/sin(a) + A. - Lz = the distance from the middle 112a of wheel 112 (called wheel 2) and the centre of rotation 150 of the aircraft. This equals D/sin(a) -A. - L3 = the distance from the middle 123a of wheel 123 (called wheel 3) and the centre of rotation 150 of the aircraft. This equals D/tan(a) + B + A. - La = the distance from the middle 124a of wheel 124 (called wheel 4) and the centre of rotation 150 of the aircraft. D/tan(a) + B -A. - L5 = the distance from the middle 135a of wheel 135 (called wheel 5) and the centre of rotation 150 of the aircraft. This equals D/tan(a) -B + A. -L6 = the distance from the middle 136a of wheel 136 (called wheel 6) and the centre of rotation 150 of the aircraft. This equals D/tan(a) -B -A. [0059] The values of A, B and D are fixed and known for a given aircraft. The value of the steering angle (alpha) 140 varies with time (t). However, given a steering angle (alpha) 140 at a certain point of time (t), the various distances Li to L6 can be calculated at that time (t), using the equations above.

[0060] Each wheel 111, 112, 123, 124, 135, 136 is also provided with a rotational speed sensor (or tachometer), not shown, that monitors an angular velocity (w) of the wheel over time (t). If an expected radius (r) of the wheel is known (i.e. the radius of a properly inflated tyre on the wheel), this can he used to calculate a parameter that indicates a linear velocity (V) for the outside of the wheel/tyre. In other words: - VI (the linear velocity for the outside of wheel 1) = - V, (the linear velocity for the outside of wheel 2) = ay's, V3 (the linear velocity for the outside of wheel 3) = a)3.1-3 V4 (the linear velocity for the outside of wheel 4) = w4s4 V5 (the linear velocity for the outside of wheel 5) = a)5.1-5 V6 (the linear velocity for the outside of wheel 6) = a)6.1-6 [0061] The values of ri to 1-6 can be estimated as fixed and know for a given aircraft wheel/tyre. The value of the angular velocity (omega w) varies with time (t) and can be used to calculate the various velocities VI to V6 at that time (t), using the equations above.

[0062] Figure 2 shows a schematic view of a monitoring device 1100 for a first wheel 111 of the aircraft according to a second embodiment.

[0063] The monitoring device 1100 has a first input 1106 of an angular velocity col of wheel 1. This varies with time, as noted above. It also has a second input 1107 of steering angle (alpha) 140. Again, this varies with time.

[0064] The device 1100 knows the values of D, A and ri.

[0065] Input 1106 is used, according to the equation above, to calculate VI values by Vi calculator 1101. Input 1107 is used, according to the equation above, to calculate Li values by Li calculator 1102. These Vi and Li values are transferred 1103 to a VI i Li calculator 1104, which calculates Vi /1Li values over time.

[0066] These values are compared, by comparator 1105, with expected Vi t Li values input at 1108. If the calculated values are very different to the expected values, a signal 1109 can he sent to alert a pilot or maintenance crew. This may be an indication that the -12 -radius of wheel 1 is different to what has been expected and so may be under or over inflated. For example, when a tyre is deflated (or under inflated) it has a smaller radius than expected and so, for the required linear velocity of the outside of the tyre, the angular velocity of the wheel has to increase. Hence, the calculated V/L value will be higher than expected. Conversely, when a tyre is overinflated it has a larger radius and so, for the required linear velocity of the outside of the tyre, the angular velocity of the wheel decreases. Hence, the V/L value will he lower than expected. A very low V/L value, however, may he an indication that the wheel has substantially stopped spinning, indicating a burst tyre.

[0967] The expected Vii Li values are obtained from data from other wheels of the aircraft. This is because the values of VI i Li are expected to he similar to V21 L2, V31 L3, V4 / L4, V5 / L5 and V6 / L6. Hence, for example, the value of V21 L2 may he used as an expected value of VI/ Li.

[0968] Figure 3 shows a schematic view of an actual speed parameter calculation device 1100' for a first wheel of the aircraft according to a third embodiment. Here, the VI i Li value is calculated as before, using the same inputs and calculators 1106, 1107, 1101, 1102, 1103, 1104. However, here, the V11L1 value is simply output as 1110'.

[0069] Figure 4 shows a schematic view of a wheel monitoring device 1000, including the actual speed parameter calculation device 1100' of Figure 3.

[0070] Here, is can be seen that actual speed parameter calculation device 1100' of wheel 1 is part of the wheel monitoring device 1000. The V1 / Li value output 1100' is transferred to a comparator 1001 that compares this value with equivalent values of V2 L2, V3 / L3 etc. from corresponding actual speed parameter calculation devices 1200', 1300' etc. for the second, third wheel etc. The devices 1200', 1300' know the values of D, A, B and the corresponding r value, as appropriate.

[0071] The comparator 100I includes an algorithm that checks that Vi/Li = YID? = V3/L3 = V4/L4 = Vs/L5 = VO/Lo. If any of these values is significantly different to the others then a signal 1002 is output that indicates which wheel has its V/L value not as expected (not within the set tolerance level of the other wheels). This signal 1002 is used to alert a pilot or maintenance crew. This may be an indication that the radius of that -13 -wheel is different to what has been expected and so may be under or over inflated. For example, when a tyre is deflated (or under inflated) it has a smaller radius than expected and so, for the required linear velocity of the outside of the tyre, the angular velocity of the wheel has to increase. Hence, the calculated V/L value will be higher than expected. Conversely, when a tyre is overinflated it has a larger radius and so, for the required linear velocity of the outside of the tyre, the angular velocity of the wheel decreases. Hence, the V/L value will be lower than expected. A very low V/L value, however, may be an indication that the wheel has substantially stopped spinning, indicating a burst tyre.

[0072] The aircraft 100 may also comprise a tyre pressure indicating system (TPTS) that can he used in combination with the methods and/or apparatus described above.

[0073] It is noted that when the aircraft is travelling in a straight line (when alpha is zero), the centre of rotation is effectively at infinity and the distances Li, Lz, L3 etc. are the same (infinity) as each other. Hence, in this situation, the comparators 1105, 1001 simply compare the V values.

[0074] Whilst the present invention has been described and illustrated with reference to particular embodiments, it will be appreciated by those of ordinary skill in the art that the invention lends itself to many different variations not specifically illustrated herein. By way of example only, certain possible variations will now be described.

[0975] The methods and apparatus described above can be applied to an aircraft with any number of wheels, and for all or only some of the wheels of the aircraft.

[0976] A drive system 128, 138 may or may not be present on some or all of the wheels or landing gear.

[0977] In the situation of the aircraft travelling in a straight line, the aircraft ground speed may be used (as an alternative or in addition) to provide an expected V value for a wheel.

[0078] Where in the foregoing description, integers or elements are mentioned which have known, obvious or foreseeable equivalents, then such equivalents are herein incorporated as if individually set forth. Reference should be made to the claims for determining the true scope of the present invention, which should be construed so as to encompass any such equivalents. It will also he appreciated by the reader that integers or -14 -features of the invention that are described as preferable, advantageous, convenient or the like are optional and do not limit the scope of the independent claims. Moreover, it is to be understood that such optional integers or features, whilst of possible benefit in some embodiments of the invention, may not be desirable, and may therefore be absent, in other embodiments.

[0079] It should be noted that throughout this specification, "or" should he interpreted as "and/or".

Claims

-15 -CLAIMSA method of assessing the health of an aircraft tyre, the aircraft tyre being mounted on an aircraft wheel on a landing gear of an aircraft, the method comprising the steps of: i) measuring a rotational speed of an aircraft wheel that is rotating over the ground, ii) providing an actual speed parameter derived from the measured rotational speed of the aircraft wheel, iii) providing a first estimated speed parameter of the aircraft wheel, and iv) comparing the actual speed parameter and the first estimated speed parameter of the aircraft wheel.
2. A method of assessing the health of an aircraft tyre as claimed in claim 1, wherein the step of comparing the actual speed parameter and the estimated speed parameter of the aircraft wheel comprises the step of calculating a difference between the actual speed parameter and the estimated speed parameter of the aircraft wheel.
3. A method of assessing the health of an aircraft tyre as claimed in claim 2, wherein the method further comprises the step of providing a signal if the difference is more than a set tolerance level.
4. A method of assessing the health of an aircraft tyre as claimed in any preceding claim, wherein the actual speed parameter is also derived from an expected radius of the aircraft wheel.
5. A method of assessing the health of an aircraft tyre as claimed in any preceding claim, wherein the actual speed parameter is also derived from a distance of the aircraft wheel from a centre of rotation of the aircraft.
-16 - 6. A method of assessing the health of an aircraft tyre as claimed in any preceding claim, wherein the aircraft comprises a second aircraft wheel and wherein the first estimated speed parameter of the first aircraft wheel is derived from a measured rotational speed of the second aircraft wheel.
7. A method of assessing the health of an aircraft tyre as claimed in claim 6, wherein the first estimated speed parameter of the first aircraft wheel is also derived from an expected radius of the second aircraft wheel.
8. A method of assessing the health of an aircraft tyre as claimed in claim 6 or claim 7, wherein the first estimated speed parameter of the first aircraft wheel is also derived from a distance of the second aircraft wheel from a centre of rotation of the aircraft.
9. A method of assessing the health of an aircraft tyre as claimed in any of claims 6 to 8, wherein the aircraft comprises a third aircraft wheel and wherein the method comprises the steps, for each wheel, of: i) measuring a rotational speed of the aircraft wheel, ii) providing an actual speed parameter derived from the measured rotational speed of the aircraft wheel, iii) providing a first estimated speed parameter of the aircraft wheel, iv) providing a second estimated speed parameter of the aircraft wheel, and vi) comparing the actual speed parameter and the first and second estimated speed parameters of the aircraft wheel, wherein the first estimated speed parameter of the aircraft wheel is derived from a measured rotational speed of a first other aircraft wheel and wherein the second estimated speed parameter of the aircraft wheel is derived from a measured rotational speed of a second other aircraft wheel.
-17 - 10. A method of assessing the health of an aircraft tyre as claimed in claim 9, wherein the method further comprises the step of, for each wheel: a) calculating a difference between the actual speed parameter and the first and second estimated speed parameters of the aircraft wheel, and b) providing a signal for that wheel indicating if the difference with both parameters is more than a set tolerance level.
11. A method of assessing the health of at least three aircraft tyres, each of the three aircraft tyres being mounted on a different aircraft wheel on one or more landing gears of an aircraft, the method comprising the steps of: i) measuring a rotational speed of each of the three aircraft wheels that are rotating over the ground, ii) providing an actual speed parameter of each of the three aircraft wheels, the actual speed parameter for each aircraft wheel being derived from the measured rotational speed of that aircraft wheel, and iv) comparing the actual speed parameter of each of the three aircraft wheels with the actual speed parameters of each of the other aircraft wheels.
12. A method of assessing the health of at least three aircraft tyres as claimed in claim 11, wherein the step of comparing the actual speed parameters comprises the step of calculating a difference between the actual speed parameters.
13. A method of assessing the health of at least three aircraft tyres as claimed in claim 12, wherein the method further comprises the step of providing a signal to indicate an aircraft wheel if its actual speed parameter is different to both the other two actual speed parameters by more than a set tolerance level.
14. A method of assessing the health of at least three aircraft tyres as claimed in any of claims I I, 12 or 13, wherein the actual speed parameter of each of the three aircraft wheels is also derived from an expected radius of that aircraft wheel.
-18 - 15. A method of assessing the health of at least three aircraft tyres as claimed in claim 13 or 14, wherein the actual speed parameter of each of the three aircraft wheels is also derived from a distance of that aircraft wheel from a centre of rotation of the aircraft.
16. A method of assessing the health of one or more aircraft tyres as claimed in any preceding claim, wherein an estimated speed parameter of an aircraft wheel is derived from a measured ground speed of the aircraft and wherein the actual speed parameter of the aircraft wheel is compared to the estimated speed parameter.
17. A method of assessing the health of one or more aircraft tyres as claimed in any preceding claim, wherein the health of one or more aircraft tyres mounted on main landing gear wheels is assessed.
18. A method of assessing the health of one or more aircraft tyres as claimed in any preceding claim, wherein one or more aircraft tyres whose health is being assessed is mounted on a wheel that is drivable by a landing gear drive system.
19. A method of assessing the health of one or more aircraft tyres as claimed in any preceding claim, wherein the measuring, providing and comparing steps are repeatedly carried out, thus providing ongoing monitoring of the aircraft tyres.
20. A controller having: i) a first input for receiving a measured rotational speed of an aircraft wheel, ii) an actual speed parameter calculator for calculating an actual speed parameter from the measured rotational speed of the aircraft wheel, iii) a second input for receiving a first estimated speed parameter of the aircraft wheel, and iv) a comparator for comparing the actual speed parameter and the first estimated speed parameter of the aircraft wheel.
-19 - 21. An aircraft comprising one or more aircraft tyres, each mounted on an aircraft wheel on a landing gear of the aircraft, the aircraft also comprising the controller of claim 20.
22. An aircraft as claimed in claim 21, further comprising a landing drive system on one or more of the landing gear of the aircraft.
23. A method of assessing the health of one or more aircraft tyres, each aircraft tyre being mounted on a respective aircraft wheel of one or more landing gears of an aircraft, the method comprising the steps of: i) measuring a rotational speed of each of a plurality of two or more aircraft wheels, as the aircraft wheels move over the ground when the aircraft is performing a turn on the ground at a turning angle, ii) a controller, with the use of received data comprising an indication of the turning angle and indications of the measured rotational speeds, determining whether one of the measured rotational speeds is inconsistent with the other received data.