WO1998024688A1

WO1998024688A1 - Aircraft landing gear arrangement

Info

Publication number: WO1998024688A1
Application number: PCT/GB1997/003319
Authority: WO
Inventors: Nigel Higgins
Original assignee: British Aerospace Public Limited Company
Priority date: 1996-12-04
Filing date: 1997-12-02
Publication date: 1998-06-11
Also published as: EA000886B1; EP0950006A1; EA199900586A1; GB2320002A; GB9625241D0

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

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.