AIRCRAFT LANDING GEAR ASSEMBLY

Abstract

An aircraft landing gear assembly (112) including a shock absorber strut (114), a bogie (120), a link assembly (124), and a movement detector (132). The shock absorber strut includes an upper and a lower telescoping parts (118, 116), the upper part being connectable to the airframe of an aircraft and the lower part being connected to the bogie. The link assembly extends between the upper and lower telescoping parts. The movement detector detects movement of the link assembly relative to the bogie. The movement detector includes: a piston (138) arranged such that relative movement between the link assembly and the bogie causes relative movement of the piston within a cylinder (136); fluid which flows as a result of relative movement between the piston and the cylinder; and a flow sensor (184) arranged to sense a change in flow due to movement of the piston within the cylinder.

Claims

1. An aircraft landing gear assembly comprising: a shock absorber strut, a bogie, a link assembly, and a movement detector; wherein the shock absorber strut comprises an upper telescoping part and a lower telescoping part, the upper telescoping part being connectable to the airframe of an aircraft and the lower telescoping part being connected to the bogie such that the bogie may adopt different pitch angles; the link assembly extends between the upper and lower telescoping parts, such that relative movement between the upper and lower telescoping parts causes relative movement between parts of the link assembly; the movement detector is arranged to detect movement of the link assembly relative to the bogie; and wherein the movement detector comprises: a piston slidably received within a cylinder, arranged such that relative movement between the link assembly and the bogie causes relative movement of the piston within the cylinder, fluid which flows as a result of relative movement between the piston and the cylinder, and a flow sensor arranged to sense a change in flow of the fluid, and wherein relative movement between the link assembly and the bogie is detected by the flow sensor detecting a change in flow due to movement of the piston within the cylinder.

2. The aircraft landing gear assembly according to claim 1, wherein the cylinder comprises a first chamber, the first chamber being in fluid communication with a second chamber by a conduit, the flow sensor being arranged to sense fluid flow in the conduit, and wherein movement of the piston within the cylinder causes fluid flow between the first chamber and the second chamber.

3. The aircraft landing gear assembly according to claim 2, wherein the cylinder comprises the second chamber, the first and second chambers being separated by the piston.

4. The aircraft landing gear assembly according to claim 2, wherein the conduit comprises a constricted section and the flow sensor comprises a first pressure transducer arranged to measure the pressure in the conduit at the constricted section.

5. The aircraft landing gear assembly according to claim 2, wherein the conduit comprises a constricted section and the flow sensor comprises a pair of transducers arranged to measure the pressure each side of the constricted section.

6. The aircraft landing gear assembly according to claim 2, wherein the flow sensor is configured to sense the speed of fluid flow in the conduit.

7. The aircraft landing gear assembly according to claim 2, wherein the conduit and flow sensor are detachably mounted to the cylinder.

8. aircraft landing gear assembly according to claim 2, wherein the piston is mounted to a piston rod, the piston rod extending through both the first chamber and the second chamber such that the total volume of the first chamber and the second chamber is constant during movement of the piston in the cylinder.

9. The aircraft landing gear assembly according to claim 1, wherein the flow sensor comprises a hot wire transducer.

10. The aircraft landing gear assembly according to claim 1, wherein the flow sensor comprises a hot film transducer.

11. The aircraft landing gear assembly according to claim 1, wherein the flow sensor comprises a pair of ultrasonic transducers.

12. The aircraft landing gear assembly according to claim 1, wherein the flow sensor is arranged to sense the fluid flow using a static detection methodology.

13. The aircraft landing gear assembly according to claim 1, wherein the movement detector comprises a signal processor arranged to generate a binary output indicating whether or not there is aircraft weight on wheels.

14. The aircraft landing gear assembly according to claim 1, the movement detector further comprising an accumulator arranged to maintain the average pressure of the volume of fluid.

15. An aircraft including the landing gear assembly of claim 1.

16. A method of detecting aircraft weight on wheels during a landing of an aircraft, wherein the aircraft comprises a control system and a landing gear assembly, the landing gear assembly comprising: a shock absorber strut, a bogie, a link assembly, and a movement detector; wherein the shock absorber strut comprises an upper and a lower telescoping parts, the upper telescoping part being connected to the airframe of the aircraft and the lower telescoping part being connected to the bogie such that the bogie may adopt different pitch angles; the link assembly extends between the upper and lower telescoping parts, such that relative movement between the upper and lower telescoping parts causes relative movement between parts of the link assembly; the bogie supports at least one wheel on at least one axle; and wherein the movement detector comprises: a piston slidably received within a cylinder, wherein movement of the piston within the cylinder causes fluid to flow in the movement detector, a sensor being arranged to detect the fluid flow; the method comprising the steps of: the link assembly moving relative to the bogie during touchdown of the least one wheel thereby causing the piston to move within the cylinder and the fluid to flow; the sensor sensing the fluid flow; the control system receiving a signal from the sensor, the signal being indicative of fluid flow; and the control system determining, on the basis of the signal, that there is aircraft weight on wheels.

17. The method of claim 16 further comprising: deploying at least one means of slowing the aircraft when the control system determines there to be movement of the link assembly relative to the bogie.

18. A method of determining the rate of descent of an aircraft upon landing, wherein the aircraft comprises a control system and a landing gear assembly, the landing gear assembly comprising: a shock absorber strut, a bogie, a link assembly, and a movement detector; wherein the shock absorber strut comprises an upper and a lower telescoping parts, the upper telescoping part being connected to the airframe of the aircraft and the lower telescoping part being connected to the bogie such that the bogie may adopt different pitch angles; the link assembly extends between the upper and lower telescoping parts, such that relative movement between the upper and lower telescoping parts causes relative movement between parts of the link assembly; the bogie supports at least one wheel on at least one axle; wherein the movement detector comprises: a piston slidably received within a cylinder, wherein movement of the piston within the cylinder causes fluid to flow in the movement detector, a sensor being arranged to detect the fluid flow; the method comprising the steps of: the link assembly moving relative to the bogie during landing thereby causing the piston to move within the cylinder and the fluid to flow; the sensor sensing the speed of fluid flow; the control system receiving a signal from the sensor, the signal being indicative of the speed of fluid flow; and the control system determining, on the basis of the signal, the rate of descent of the aircraft upon landing.

19. (canceled)

Description

DESCRIPTION OF THE DRAWINGS

[0062] Embodiments of the present invention will now be described by way of example only with reference to the accompanying schematic drawings of which:

[0063] FIG. 1 shows a side view of an aircraft comprising a landing gear assembly;

[0064] FIG. 2 shows a side view of a prior art landing gear assembly;

[0065] FIG. 3 shows a side view of a landing gear assembly according to a first embodiment of the invention prior to touchdown;

[0066] FIG. 4 shows a side view of a landing gear assembly according to a first embodiment of the invention after touchdown and before shock absorber compression;

[0067] FIG. 5 shows a side view of a landing gear assembly according to a first embodiment of the invention after shock absorber compression;

[0068] FIG. 6 shows a flow chart of a method of detecting aircraft weight on wheels according to a second embodiment of the invention;

[0069] FIG. 7 shows a cross-sectional view of a movement detector according to the first embodiment of the invention;

[0070] FIG. 8 shows a cross-sectional view of a movement detector according to the third embodiment of the invention;

[0071] FIG. 9 shows a cross-sectional view of a movement detector according to the fourth embodiment of the invention;

[0072] FIG. 10 shows a cross-sectional view of a movement detector according to the fifth embodiment of the invention; and

[0073] FIG. 11 shows a cross-sectional view of a movement detector according to the sixth embodiment of the invention.

DETAILED DESCRIPTION

[0074] FIG. 1 shows an aircraft 10 comprising a main landing gear 12, the aircraft being of a type that may be employed as the aircraft with which the methods and apparatuses of any of the illustrated embodiments may be used. The aircraft 10 thus includes a landing gear assembly 12 including a bogie, which is mounted on the lower end of the landing gear leg in such a way that the bogie may adopt different pitch angles.

[0075] FIG. 3 shows an aircraft landing gear assembly 112 according to a first embodiment of the invention. The landing gear assembly 112 comprises a shock absorber strut 114 comprising a piston 116 received within a cylinder 118. Cylinder 118 is connected to the airframe of an aircraft. The direction of the front of the aircraft is indicated by arrow F. Piston 116 is at its lower end pivotally connected to a bogie 120. The bogie 120 can thereby adopt different pitch angles relative the shock absorber strut 114. A pitch trimmer (not shown) controls the position of the bogie 120 relative to the shock absorber strut 114 in flight.

[0076] A plurality of wheels 122 are mounted on the bogie 120. In this embodiment three pairs of wheels 122a, 122b, 122c are mounted to bogie 120 by three axles. A link assembly 124 in the form of a torque link connects the cylinder 118 and the piston 116 of the shock absorber strut. The link assembly 124 comprises an upper arm 126 which is pivotally mounted to the cylinder 118 and a lower arm 128 which is pivotally mounted to the piston 116. The upper arm 126 and lower arm 128 are pivotally attached to each other at a hinge location. The link assembly 124 acts against rotational movement of the piston 116/bogie 120 relative to the cylinder 118/airframe. FIG. 3 also shows a second link assembly 130 in the form of a false link.

[0077] A movement detector 132 extends between the link assembly 124 and the bogie 120. One end of the movement detector is pivotally connected to the link assembly 124 at the hinge location. An opposing end of the movement detector 132 is pivotally connected to the bogie 120 proximate the aft end of the bogie 120.

[0078] FIG. 7 shows the movement detector 132 in more detail. Movement detector 132 comprises a cylinder 136 having an internal space which houses a piston 138. The piston 138 divides the internal space into a first chamber 140 and a second chamber 142. The first chamber 140 and the second chamber 142 are filled with a hydraulic fluid. A hydraulic accumulator 150 keeps the hydraulic fluid in the first and second chambers 140, 142 topped up and at a substantially constant average pressure (PA).

[0079] The piston 138 is received on a piston rod 144 which extends through both end walls of the internal space. Two apertures 146, 148 are located at opposing ends of the movement detector. A first aperture 146 being located on the piston rod and a second aperture being located on the cylinder 136. The movement detector 132 is pivotally mounted to the bogie 120 and the link assembly 124 via the apertures 146, 148.

[0080] A conduit 180 puts the first chamber 140 into fluid communication with the second chamber 142. The conduit 180 connects with the first chamber 140 and second chamber 142 by inlet/outlet ports proximate the end walls of the chambers 140, 142 The conduit is located in a body 176 detachably mounted to the cylinder 136.

[0081] The conduit comprises a constricted section 182. The conduit 180 thereby forms a Venturi tube. A sensor in the form of a hot wire transducer 184 is arranged to measure the speed of the fluid flow in the constricted section 182 of the conduit 180.

[0082] A movement of the link assembly 124 relative to the bogie 120 causes compression or extension of the movement detector 132 and thereby causes movement of the piston 138 within the cylinder 136. Movement of the piston 138 within the cylinder 136 in turn causes fluid to flow between the first chamber 140 and the second chamber 142 via the conduit 180. The hot wire transducer 184 thereby measures a non-zero speed of fluid flow during a movement of the link assembly 124 relative to the bogie 120. Graph 178 shows an example of how the speed of fluid flow varies with time over a movement of the link assembly 124 relative to the bogie 120.

[0083] The hot wire transducer 184 is in communication with a control system 134 of the aircraft. The hot wire transducer 184 provides an output from which the control system 134 can determine the measured speed of the fluid flow. The control system 134 can thus determine whether (i) there has been movement of the link assembly 124 relative to the bogie 120 and (ii) therefore there is aircraft weight on wheels.

[0084] The landing gear assembly 112 of the first embodiment has a trail angle of less than 10 degrees. During landing of the aircraft the aft pair of wheels 122a touchdown first. The bogie 120 subsequently pivots around the bottom of the shock absorber strut 114 until the centre 122b and front 122c pair of wheels have also touched down. At which point the bogie 120 is oriented substantially parallel to the ground G. In the present arrangement, the movement detector 132 is therefore compressed, as shown in FIG. 4. The piston 138 will therefore move so as to cause fluid to flow from the second chamber 142 to the first chamber 142.

[0085] Until the centre 122b and front 122c pair of wheels have touched down, there is unlikely to be enough aircraft weight going through the shock absorber strut 114 to cause it to compress. The link assembly 124 will therefore remain stationary relative to the airframe during this initial movement of the bogie 120 relative to the link assembly 124.

[0086] Thereafter, the shock absorber strut 114 begins to compress due to the weight of the aircraft. The link assembly 124 again moves relative to the bogie 120. The hinge location of the link assembly 124 moves aft and downwards. In the present arrangement this causes further compression of the movement detector 132, as shown in FIG. 5. There will therefore be further fluid flow from the second chamber 142 to the first chamber 142.

[0087] In the event of a flat landing of the bogie 120, in which all pairs of wheels 122 touchdown at substantially the same time, it will be seen that movement is still detected due to shock absorber 114 compression, despite there being no or negligible pivotal movement of the bogie 120 about the shock absorber strut 114.

[0088] The aircraft may land with a negative trail angle, such that the front pair of wheels 122c touch down before the rear pair of wheels 122a. In this case the aft portion of the bogie 120 will initially pivot away from the link assembly 124. Thus the movement detector 132 extends in length until the bogie 120 is parallel to the ground. The piston 138 will therefore move so as to cause fluid to flow from the first chamber 140 to the second chamber 140. Subsequent shock absorber 114 compression then moves the link assembly 124 back towards the point on the bogie 120 where the movement detector is attached, thus causing compression of the movement detector 132 and fluid flow back from the second chamber 142 to the first chamber 142. Both such movements could be used to detect aircraft weight on wheels, and could also be used to detect the time of shock absorber 114 compression.

[0089] In alternative embodiments the movement detector 132 may be mounted between the forward portion of the bogie 120 and the false link 130. In other alternative embodiments the movement detector 132 may be connected to the lower arm 128 below the hinge location.

[0090] A method 200 of detecting aircraft weight on wheels will now be described according to a second embodiment of the invention and with reference to FIG. 6. The method will be described with reference to an aircraft landing gear assembly according to the first embodiment.

[0091] The method begins subsequent to deploying (lowering) the aircraft landing gear from the aircraft wheel well. However the method may include a step of lowering the aircraft landing gear. The first step includes the control system 134 determining 202, from a radar altimeter, whether the altitude is below a predetermined value, in this example whether the altitude is below 10 feet. Provided the altitude condition is met, i.e. provided the altitude is below 10 feet, the control system 134 is configured to use the signal received from the movement detector 132 to determine whether there is aircraft weight on wheels.

[0092] The method subsequently comprises a step of at least one wheel of the aircraft touching down 204 on the ground and concurrently the link assembly 124 moving 206 relative to the bogie 120. Depending on the orientation of the bogie 120 relative to the ground immediately prior to touchdown, and whether there is any equipment failures for example deflation of one or more of the tyres, the link assembly 124 moves relative to the bogie 120 by (i) the bogie 120 pivoting relative to the shock absorber strut 114 and/or (ii) the shock absorber strut 114 compressing thereby causing outward movement of the link assembly 124.

[0093] The movement of the link assembly 124 relative to the bogie 120 causes the piston 138 to move within the cylinder 136. This in turn causes the fluid present in the chambers 140, 142 to flow through the conduit. The flow will either be from the first chamber 140 to the second chamber 142 during expansion of the movement detector 132 or from the second chamber 142 to the first chamber 140 during compression of the movement detector 132.

[0094] The method comprises a step of the hot wire transducer 184 sensing 208 the speed of fluid flow through the conduit 180. The step of sensing 208 comprises the hot wire transducer 184 providing an output signal corresponding to the speed of fluid flow.

[0095] The method comprises a step of the control system 134 receiving 210 the signal output from the hot wire transducer 184. The control system is arranged to interpret this signal. The method comprises a step of the control system 134 determining 212, on the basis of the signal, that there is aircraft weight on wheels. The control system 134 determines there to be aircraft weight on wheels when the speed of fluid flow is non-zero. In other embodiments the control system 134 determines there to be aircraft weight on wheels when the speed of fluid flow is above a threshold amount.

[0096] The method of the second embodiment may be a part of a method of slowing an aircraft. In which case there is a subsequent step of deploying 214 at least one means of slowing the aircraft when the control system determines there to be aircraft weight on wheels.

[0097] FIG. 8 shows a movement detector 332 according to a third embodiment of the invention. The movement detector 332 is arranged in a similar manner to the movement detector 132 according to the first embodiment. The movement detector 332 differs from the movement detector 132 according to the first embodiment in that the movement detector 332 comprises a sensor in the form of a hot film transducer 384. The hot film transducer 384 being in communication with a control system 334. Graph 378 shows an example of how the speed of fluid flow varies with time over a movement of the link assembly relative to the bogie.

[0098] FIG. 9 shows a movement detector 423 according to a fourth embodiment of the invention. The movement detector 432 is arranged in a similar manner to the movement detector 132 according to the first embodiment. The movement detector 432 differs from the movement detector 132 according to the first embodiment in that the movement detector 432 comprises a sensor in the form of a pressure transducer 484. The pressure transducer 484 being in communication with control system 434

[0099] When fluid flows through the constricted section 482 of the conduit 480, the pressure of the fluid will decrease (Venturi's principle). Thus when the pressure transducer 484 measures a pressure below the average pressure of the chambers 440, 442 (i.e. below the accumulator pressure, PA) it is indicative of fluid flow and thus movement of the link assembly relative to the bogie. Graph 478 shows an example of how the measured pressure varies with time over a movement of the link assembly relative to the bogie.

[0100] FIG. 10 shows a movement detector 523 according to a fifth embodiment of the invention. The movement detector 532 is arranged in a similar manner to the movement detector 432 according to the fourth embodiment. The movement detector 532 further comprises a second pressure transducer 585 and a third pressure transducer 586, in addition to the first pressure transducer 584. The second and third pressure transducers 585, 586 are arranged to measure the pressure in the conduit 580 either side of the constricted section 582.

[0101] When the piston 538 moves within the cylinder 536, one of the chambers decreases in volume, therefore the fluid in that chamber is compressed and the pressure increases. The other chamber increases in volume, therefore the fluid in that chamber expands and the pressure decreases. One of the second and third pressure transducers 585, 586 therefore measures a pressure increase and the other of the second and third pressure transducers 585, 586 measures a pressure decrease. Again, as the fluid flows through the constricted section (as the pressure equalises) the speed of the fluid flow increases and the pressure in the constricted section decreases.

[0102] Graph 578 shows an example of how the pressure (P1, P2, P3) measured by the first, second and third transducers 584, 585, 586 varies with time over a movement of the link assembly relative to the bogie. The pressure (P2, P3) measured by the second and third transducers 585, 586 during movement of the piston may differ because the pressure decrease in one chamber may not necessarily match the pressure increase in the other. It may therefore possible to determine the direction of fluid flow in the conduit and therefore the direction of movement of the link assembly relative to the bogie beam.

[0103] FIG. 11 shows a movement detector 623 according to a sixth embodiment of the invention. The movement detector 632 is arranged in a similar manner to the movement detector 132 according to the first embodiment. The movement detector 632 differs from the movement detector 132 of the first embodiment in that the conduit is in the form of a pipe 680 having a substantially constant diameter. The sensor is in the form of a pair of ultrasonic transducers 684 arranged to measure the velocity of fluid flow in the pipe 680. The ultrasonic transducers 684 are in communication with a control system 634. Graph 678 shows an example of how the speed of fluid flow varies with time over a movement of the link assembly relative to the bogie.

[0104] It will be appreciated that the movement detectors of the second to fifth embodiments could be used in the landing gear assembly of the first embodiment by taking the place of the movement detector 132 used therein.

[0105] 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. Some examples of such variations will now be described by way of example only.

[0106] In an alternative embodiment the second chamber is located outside the cylinder, the conduit linking the inside and the outside of the cylinder. In other alternative embodiments the movement detector comprises only a single chamber located to one side of the piston, the sensor arranged to sense the movement of the fluid relative to the chamber.

[0107] 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 be appreciated by the reader that integers or 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.