AIRCRAFT LANDING GEAR ARRANGEMENT

Abstract: An arrangement for an aircraft main landing gear is provided which includes a main oleo strut (7) having forward and aft trunnion bearings (8, 10), an aircraft wing rear spar (2) having a mounting (9) for the forward trunnion bearing (8) thereon, a gear beam (4) mounted at one end to the rear spar and at the other end to a fuselage. The gear beam (4) has a mounting (11) for the aft trunnion bearing (10) at a position intermediate its ends. The mounting for the forward trunnion bearing (8) includes a fusible element (12) adapted to fail upon the application of an excessive drag load. The mounting (11) for the aft trunnion bearing is integral with the structure of the gear beam (4) and is rotatable about the longitudinal axis of the gear beam to permit controlled detachment of the landing gear in an emergency.

Description: AIRCRAFT LANDING GEAR ARRANGEMENT This invention concerns aircraft landing gear arrangements and in particular an arrangement for an aircraft main landing gear mounted at least in part from a wing of the aircraft. A well known type of main landing gear for an aircraft, in particular a commercial passenger-carrying aircraft, comprises a main oleo strut supporting wheels and a bogie and having a pair of pintle or trunnion bearings ( the two terms being regarded as interchangeable for this invention) disposed in a generally horizontal plane for rotatably mounting the landing gear for pivotal movement between a generally horizontal stowed position and a generally vertical deployed position for supporting the aircraft. The trunnion bearings are arranged to pivot about an axis running generally parallel to a longitudinal axis of the aircraft fuselage. A forward trunnion bearing is pivotally attached to a rear spar of the wing and an aft trunnion bearing is pivotally attached to a gear beam which is mounted at one end either directly or indirectly to the rear spar and at the other end either directly or indirectly to the aircraft fuselage. To meet crashworthiness requirements it is necessary that the main landing gear detaches cleanly from the aircraft in the event of crash or other overload forces, usually "drag" forces, being applied to the landing gear. In particular, it is a requirement that the rear spar of the wing remain intact should the main landing gear become detached therefrom in order to maintain integrity of a fuel cell within a wing box structure of which the rear spar forms a part. It is known to provide a main landing gear arrangement for an aircraft having a forward trunnion mounting to the rear spar of the wing and an aft trunnion mounting to a gear beam extending between the rear spar of the wing and the fuselage. However the aft trunnion mounting has so far been attached via a bracket attached to an underside of the gear beam. This has meant that the application of an excessive drag load to the landing gear has enabled detachment of the gear from the forward and aft trunnion mountings by for example the failure in tension of fuse bolts attaching the rear trunnion bearing to the underside of the gear beam and to failure in shear or tension of forward trunnion fuse pins connecting a forward trunnion bearing mounting bracket to the rear spar. Such an arrangement, whilst working adequately for some cases, still carries an unpredictability as to the precise way in which the landing gear will behave during detachment, owing to the requirement for two separate fusible devices to fail. Greater predictability and control of the detachment path for the landing gear is therefore desirable. In addition to the above, for the latest proposed large passenger-carrying aircraft, adapted to carry 500 plus passengers, the aft trunnion bearing for the gear can be required to react drag loads, particularly during deflections of the gear during landing. The use of a trunnion bearing mounting bracket attached to an underside of the gear beam is not therefore acceptable and the trunnion bearing has therefore to be incorporated within the gear beam structure. It will be appreciated that the application of a drag load to such an aft trunnion bearing will not allow breakaway of the gear trunnion from the beam without destroying the structure of the gear beam as the aft trunnion must inevitably enter its bearing within the structure of the bear beam from a forward direction. Also, because any crash loads will be transferred into the rear spar via the gear beam in these circumstances , an alternative design would be desirable. It is an object of the invention to provide a main landing gear arrangement which overcomes the disadvantages of the prior art. According to the present invention there is provided an aircraft landing gear arrangement including a main oleo strut having forward and aft trunnion bearings, a mounting on the aircraft for the forward trunnion bearing, a gear beam mounted on the aircraft at either end thereof and having a mounting intermediate the ends for the aft trunnion bearing, the mounting for the forward trunnion bearing including a fusible element, and the mounting for the aft trunnion bearing being rotatable about a longitudinal axis of the gear beam, whereby to permit detachment of the landing gear from the aircraft in a controlled manner in the event of an overload being applied thereto causing the fusible element to shear. This arrangement allows the safe detachment of the landing gear from its forward and aft trunnion mountings without risk of unacceptable damage to the structure of the aircraft. It has the additional advantage of releasing the landing gear from its mountings without applying any lateral directional force to the gear which might deflect the detached gear toward the fuselage of the aircraft. The mounting for the forward trunnion bearing may be carried on a rear spar of a wing for the aircraft and the gear beam may be mounted at one end to the rear spar and at the other end to a fuselage of the aircraft. Damage to the rear spar and to any fuel cell contained thereby is thus avoided. The mounting for the aft trunnion bearing may be integral with the structure of the gear beam, thus allowing reaction of drag loads by the gear beam. The mounting for the aft trunnion bearing may include a supplemental bearing having a pivotal axis generally parallel with the longitudinal axis of the gear beam. For example the supplemental bearing may comprise a pair of trunnions mounted for rotational movement about the said axis generally parallel with the longitudinal axis of the gear beam. Once the landing gear has rotated sufficiently in the supplemental bearing therefore the aft trunnion will simply drop out of the aft trunnion bearing. The supplemental bearing may conveniently be mounted in a recess formed in the structure of the gear beam. An alternative arrangement according to the invention includes an end bearing at either end of the gear beam for rotatably mounting the gear beam to the rear spar and fuselage respectively. In order to maintain orientation of the gear beam about the said longitudinal axis during normal operation fusible locating means may be provided. Such fusible locating means may be located in the vicinity of one or both end bearings of the gear beam. Alternatively the fusible locating means may comprise at least one strut attached between a position on the gear beam spaced from the said longitudinal rotational axis and a fixed position on a member of the aircraft, for example the rear spar. The aft trunnion bearing may permit limited relative rotational movement between the landing gear and gear beam about a longitudinal axis of the gear beam. For example, the aft trunnion bearing may include an additional spherical bearing therein. This may be provided to take up manufacturing tolerances. The invention will now be described by way of example with reference to the accompanying drawings of which Figure 1 is a rear isometric view of a main landing gear arrangement according to the prior art, Figure 2 is a sectional view taken on the line II-II of Figure 1, Figure 3 is a rear isometric view of a main landing gear arrangement according to a first aspect of the invention in its normal operating position supporting an aircraft, Figure 4 is an enlarged part sectional view of the landing gear oleo strut of Figure 3 and gear beam, shown detached from the rear spar, taken through the gear beam along a plane bisecting the rear trunnion bearing, Figure 5 is a horizontal section taken through a gear beam and trunnion bearing similar to that shown in Figure 3, Figure 6 shows the arrangement of Figure 3 with forward trunnion shear pins severed and the landing gear slightly rotated rearwardly, Figure 7 shows the arrangement of Figure 6 further rotated, Figure 8 is a rear isometric view of a main landing gear arrangement according to a second aspect of the invention in an operative position. Figure 9 is a part sectional view through a gear beam and trunnion bearing similar to that shown in Figure 8 in a plane bisecting the aft trunnion bearing, Figure 10 is a horizontal part sectional view of a trunnion bearing and landing gear beam similar to that shown in Figure 8 , Figure 11 shows the arrangement of Figure 8 with forward trunnion mounting shear pins severed and the gear slightly rotated rearwardly. Figure 12 shows the arrangement of Figure 11 with the gear rotated rearwardly to the extent of clearing the gear beam, Figure 13 is a rear isometric view of a main landing gear arrangement according to a third aspect of the invention, and Figure 14 is an enlarged detail view of detail XIV of Figure 13. Referring to Figures 1 and 2 of the drawings, a main landing gear arrangement 1 according to the prior art is shown. The arrangement comprises a wing rear spar 2, an aircraft fuselage 3 , a landing gear beam 4 attached at one end 5 to the rear spar 2 and at the other end 6 to the fuselage 3. A main landing gear oleo strut 7 is shown diagrammatically. The oleo strut has a forward trunnion bearing 8 housed in a forward trunnion bearing housing 9 , and an aft trunnion bearing 10 mounted in an aft trunnion bearing housing 11. The forward trunnion bearing housing 9 is attached to the rear spar 2 via four forward trunnion fusible elements in the form of fuse pins 12 and the aft trunnion bearing housing 11 is secured to the gear beam 4 on an undersurface thereof by aft trunnion fuse pins 13. If an excessive rearwardly directed or "drag" load is applied to the oleo strut 7 the forward trunnion fuse pins 12 and the aft trunnion fuse pins 13 will sever respectively, usually in succession, to release the oleo strut 7 from the rear spar 2 and gear beam 4. Referring to Figures 3 to 7 , like components have been given like reference numerals to the components of figures 1 and 2, for consistency and clarity. As with the prior art arrangement a main landing gear oleo strut 7 has a forward and an aft trunnion bearing 8, 10 mounted in respective forward and aft mountings in the form of forward and aft trunnion bearing housings 9, 11. The forward trunnion bearing housing is secured to the rear spar 2 by forward trunnion fusible elements in the form of fuse pins 12 connected between the forward trunnion bearing housing 9 and a forward trunnion fitting 14. The rear trunnion bearing housing 11 is rotatable about a central longitudinal axis 15 of the gear beam 4 on a pair of trunnions 16, 17 on an aft trunnion bearing rotating housing 11. Trunnions 16, 17, are rotatable in trunnions bearings 18, 19 in the gear beam 4. Upon the application of an excessive rearward force to the oleo strut 7, possibly by wheels 20 carried on a bogie 21 of the landing gear striking an object during take-off, landing or landing approach, forward trunnion fuse pins 12 will be severed by the resultant downward force on the forward trunnion bearing housing 9 and the oleo strut 7 will start to rotate rearwardly about the axis 15 by the trunnions 16, 17 rotating in their beam bearings 18, 19 respectively, see Figure 6. Subsequent rotation of the strut 7 will clear the forward trunnion bearing housing 9 from the fitting 14 as the rear trunnion bearing rotatable housing 11 continues to rotate, see Figure 7, and eventually the gear 7, 20, 21 will drop out of the aft trunnion bearing rotatable housing 11 in a controlled manner. It will be noted that the rear spar and gear beam remain intact and that the gear 7, 20, 21 has not been deflected sideways by the manner of its detachment from its trunnion bearing housings 9, 11. In addition the central and integral mounting of the aft trunnion bearing housing 11 in a recess 22 within the structure of the gear beam 4 ensures adequate strength in the mounting of the aft trunnion bearing 10 to the gear beam 4 in order to react any rearwardly directed loads against the gear beam 4. It will be noted from the drawings, and from Figure 4 in particular, that clearance between the aft trunnion bearing rotatable housing 11 and a wall 23 of the recess in the gear beam is of adequate proportions to ensure sufficient freedom of rotational movement of the housing 11 to rotate and allow the aft trunnion bearing 10 to drop out of the housing 11 as the gear rotates. Referring now to Figures 8 to 12, a second embodiment of the invention is illustrated. Once again, like components have been given like reference numerals for consistency. In this embodiment rearward rotation of the landing gear 7, 20, 21 upon the application of an excessive rearward load thereto is provided by rotation of the gear beam 4 itself about its longitudinal axis 15. In this embodiment the aft trunnion bearing housing is firmly mounted in a recess 22 which is a tight sliding or interference fit therewith. The aft trunnion bearing 10 comprises a spherical bearing having an inner bearing surface 24 of cylindrical shape and an outer spherical bearing surface 25 to allow limited rotational movement of the oleo strut 7 about the longitudinal axis 15 of the gear beam to take up manufacturing tolerances. Essentially however the aft trunnion bearing and housing are not adapted to provide sufficient rotational movement to allow the oleo strut 7 to drop out of the gear beam 4 during application of excessive rearwardly directed force to the gear. Such rotational movement is provided for, as expressed above, by rotation of the gear beam 4 on a pair of cylindrical end bearings 26, 27 at one end 5 and the other end 6 of the beam respectively, see Figure 10 in particular. End bearing 26 rotatably mounts end 5 of the gear beam to a bracket 28 attached to the rear spar 2. The end bearing 26 has an eyelet 29 for the passage of a pin (not shown) therethrough and through a corresponding fork attachment 30 on the bracket 28. A similar arrangement exists at the other end 6 of the beam where a fuselage bracket 31 pivotally supports a double linkage 32 which is pivotally attached in turn to a further eyelet 33 via a pin (not shown) to the second end bearing 27. Unwanted rotational movement of the gear beam 4 about its longitudinal axis 15 is controlled by a control strut 34 attached at one end to the rear spar 2 via a bracket 35 and at the other end to the gear beam 4 at a position spaced from the axis 15. During the application of an excessive rearwardly directed force against the gear, forward fuse pins 12 will again sever, as shown in Figure 11 and in addition a fuse pin 36 in the control strut 34 will sever allowing the gear beam 4 to rotate about its longitudinal axis with the gear. Eventually, as shown in Figure 12, the gear will fall out of its recess 22 in the gear beam for the gear to detach itself from the aircraft in a controlled manner. Referring to Figures 13 and 14, an embodiment according to a third aspect of the invention is illustrated. In this embodiment the control strut 34 is replaced by fuse pins 37, 38, 39, 40 which prevent rotation of the gear beam until an excessive load is applied thereto by rotational movement of the oleo strut 7 about the longitudinal axis 15 of the beam whereupon the fuse pins will be severed to allow the said rotation to take place for disengagement of the landing gear from the beam. In all other respects the invention according to the third embodiment works in the same manner as the invention according to the second embodiment.

Claims: CLAIMS 1. An aircraft landing gear arrangement including a main oleo strut having forward and aft trunnion bearings, a mounting on the aircraft for the forward trunnion bearing, a gear beam mounted on the aircraft at either end thereof and having a mounting intermediate the ends for the aft trunnion bearing, the mounting for the forward trunnion bearing including a fusible element, and the mounting for the aft trunnion bearing being rotatable about a longitudinal axis of the gear beam, whereby to permit detachment of the landing gear from the aircraft in a controlled manner in the event of an overload being applied thereto causing the fusible element to shear. 2. An arrangement as in claim 1 in which the mounting for the forward trunnion bearing is carried on a rear spar of a wing for the aircraft and the gear beam is mounted at one end to the rear spar and at the other end to a fuselage of the aircraft. 3. An arrangement as in claim 1 or 2 in which the mounting for the aft trunnion bearing is integral with the structure of the gear beam. 4. An arrangement as in claim 1, 2 or 3 in which the mounting for the aft trunnion bearing includes a supplemental bearing having as its pivotal axis the said longitudinal axis of the gear beam. 5. An arrangement as in claim 4 in which the supplemental bearing is mounted in a recess formed in the structure of the gear beam. 6. An arrangement as in claim 1, 2, 3 or 4 including an end bearing at either end of the gear beam for rotatably mounting the gear beam to the aircraft. 7. An arrangement as in claim 6 including fusible locating means to maintain orientation of the gear beam about the said longitudinal axis during normal operation of the landing gear. 8. An arrangement as in claim 7 in which the fusible locating means are located in the vicinity of at least one end bearing of the gear beam. 9. An arrangement as in claim 7 in which the fusible locating means comprise at least one strut extending between a position on the gear beam spaced from the said longitudinal axis and a fixed position on the aircraft. 10. An aircraft including a landing gear arrangement according to any preceding claim.

Inventors: HIGGINS NIGEL, HIGGINS, NIGEL
Applicants: BRITISH AEROSPACE, HIGGINS NIGEL, BRITISH AEROSPACE PUBLIC LIMITED COMPANY, HIGGINS, NIGEL
Application year: 1997
Main classification: B64C25
IPC codes: B64C25