Deployment mechanisms for aircraft auxiliary airfoils

A deployment mechanism for moving an aircraft wing leading edge slat (2) or trailing edge flap (4) relative to a main airfoil (1) is provided. The mechanism includes an I-section support beam (6) extending between the main airfoil (1) and the slat (2) or flap (4). The support beam (6) is driven into and out of the main airfoil (1) by a rack and pinion mechanism (22, 23), the rack (22) being disposed along a lower boom (20) of the beam (6) and the beam (6) being supported for rolling contact with the main airfoil (1) by upper and lower straddle rollers (8, 9, 10, 11) positioned between wing leading edge ribs (12, 13). Roller tracks (16, 17, 18) extend along upper and lower booms (19, 20) of the beam with at least one roller track (17, 18) co-extending with the rack (22) adjacent thereto along the beam.

BACKGROUND TO THE INVENTION 
This invention relates to deployment mechanisms for moving aircraft 
auxiliary airfoils such as leading edge slats or trailing edge flaps 
relative to main airfoils. In particular the invention relates to such 
mechanisms which include support beams extending between auxiliary and 
main airfoils in which the beam is driven by a rack and pinion 
arrangement. 
DESCRIPTION OF PRIOR ART 
It is well known to modify the lift of an aircraft main aerofoil when the 
aircraft is moving at lower speeds, for example during take off and 
approach or landing, to delay the point at which wing stall occurs. 
Auxiliary airfoils are used for this purpose which are moveable between a 
retracted or cruise position closely adjacent to the main airfoil where 
minimum aerodynamic drag is created and at least one deployed position 
spaced from the main airfoil when modified wing lift is created. 
Various types of deployment mechanism for moving the auxiliary airfoil as 
described above are known. A popular type of mechanism employs at least 
two support beams per auxiliary airfoil which extend between auxiliary and 
main airfoil. The support beams will be fixed to one or other of the 
auxiliary and main airfoil, usually the former, at one end of the beam. 
The beam is movably connected over its length to the other of the two 
airfoils, normally the main airfoil, by a series of rollers mounted on the 
airfoil for rolling engagement with tracks on the support beam. 
One such deployment mechanism which uses a rack and pinion arrangement to 
effect movement is known from U.S. Pat. No. 1,917,428-Burnelli. This 
document discloses the use of a rack and pinion mechanism for deploying 
both wing leading edge and trailing edge lift modifying devices (hereafter 
called "auxiliary airfoils", for the purposes of this application). The 
leading edge mechanism employs a beam with an I-shaped cross section with 
upper and lower booms and a web interconnecting them with a rack being 
formed integral with an upper surface of the beam. A drive pinion is 
rotatably mounted on a main airfoil for engagement with the rack. The beam 
is fixedly supported at one end to an auxiliary airfoil and runs on 
support rollers along its length for support by the main airfoil. In this 
arrangement the beam is supported by a pair of upper and lower straddle 
rollers which act upon rolling tracks formed on upper and lower booms of 
the I-beam respectively. The straddle rollers are bolted to a front spar 
of the main airfoil and the beam is deployable in a space confined between 
adjacent wing ribs of the main airfoil. In order not to interfere with the 
rolling track for the upper straddle roller the rack is truncated 
immediately aft of the upper straddle roller when the auxiliary airfoil is 
in its fully forwardly deployed position. 
Owing to the rack forming a toothed surface in the upper boom of the I-beam 
rearwardly of the straddle rollers, an upper rear roller for supporting 
the I-beam could not be mounted on the main airfoil for contact with an 
upper surface of the I-beam owing to the lack of a smooth upper rolling 
track because of the presence of the rack. Rear mounted upper and lower 
rollers were therefore rotatably attached to a rear end of the I-beam for 
engagement with upper and lower fixed rolling tracks attached to the main 
airfoil. The I-beam was therefore deployable whilst being supported by the 
forward pair of straddle rollers rotatably attached to the forward spar of 
the main airfoil and by two rearward pairs of cantilever rollers rotatably 
attached to the rear end of the I-beam. 
In order to provide an adequate "roller base", ie a fore and aft separation 
of forward and rearward rollers, when the I-beam was fully deployed 
forwardly and therefore subject to maximum aerodynamic loads, it was 
necessary to have an excessively long I-beam so that the roller base in 
the rearward end of the I-beam protruding below the main airfoil, within a 
fairing, when the auxiliary airfoil was fully retracted. The result was 
excessive weight with an added aerodynamic penalty. In addition, in a 
modern aircraft, fuel carrying space within the main airfoil would be 
compromised. This design also necessitated the provision of four 
individual tracks on the main airfoil for the rear rollers, a complex and 
expensive solution for this requirement. 
SUMMARY OF THE INVENTION 
It is an object of the invention to provide a simpler, more efficient and 
more compact deployment mechanism than exhibited by the prior art. 
According to the present invention there is provided a deployment mechanism 
for moving an aircraft auxiliary airfoil such as a leading edge slat or a 
trailing edge flap relative to a main airfoil, the mechanism including a 
support beam extending between auxiliary and main airfoils, the beam 
having an I-shaped cross section with upper and lower booms and a web 
interconnecting them with a rack being formed integral with a surface of 
one of the booms for engagement with a drive pinion rotatably mounted on 
the main airfoil, and at least two support rollers for the beam rotatably 
mounted on the main airfoil for rolling engagement with roller tracks 
extending along upper and lower surfaces of the beam, said at least two 
support rollers being mounted to straddle an adjacent pair of structural 
members of the main airfoil between which the beam is supported, 
characterised in that all the support rollers are rotatably mounted on the 
main airfoil to straddle said adjacent pair of structural members for 
rolling engagement with the roller tracks extending along upper and lower 
surfaces of the beam and at least one roller track co-extends with the 
rack adjacent thereto, along the beam. 
A compact, light, robust and easily adjustable mechanism is thus provided. 
The lower surface of the beam preferably includes the said rack centrally 
disposed between a pair of roller tracks co-extending on either side 
thereof. Symmetry is thus given to the mechanism. 
Each lower roller may have laterally separated rolling surfaces, ie rolling 
surfaces separated in a horizontal direction normal to the longitudinal 
axis of the beam, whereby to engage the said pair of roller tracks on 
either side of the rack whilst providing clearance for the rack between 
the laterally separated rolling surfaces. 
The laterally separated rolling surfaces may be integrally formed as part 
of a single roller or each lower roller may comprise a pair of divided 
rollers with each having a said laterally spaced rolling surface thereon. 
The single roller version may be more rigid but divided rollers may 
provide easier assembly in certain circumstances. 
In any event it will be appreciated that the roller or divided roller will 
be rotatably mounted on a single axle extending between the adjacent pair 
or structural members of the main airfoil. 
The rack may stand proud of at least one said roller track, in which case 
the clearance provided by the rolling surfaces will allow for vertical 
clearance of the rack between the rolling surfaces as well as lateral 
clearance. If for example the rack, whilst being formed integrally with 
the beam, were nevertheless recessed from roller tracks on the beam, then 
rolling surfaces on the roller need not have any radially extending 
cut-out between them to accommodate the rack.

DESCRIPTION OF PREFERRED EMBODIMENT 
Referring to the drawings, FIG. 1 shows in a chordwise section an aircraft 
wing having a main airfoil or wing box 1 to which are movably attached 
auxiliary airfoils in the form of a leading edge slat 2 and trailing edge 
flaps 3 and 4. Both slat 2 and flaps 3, 4 are movable between stowed or 
cruise positions shown in normal outline and at least two deployed 
positions shown in chain dotted line. 
This document will concentrate on a mechanism for deploying a leading edge 
slat and the remaining figures of the drawings illustrate slats and their 
operating mechanisms. 
FIG. 3a shows the slat 2 in its retracted or cruise position and FIG. 3b 
shows the slat in its extended or fully deployed position. A number of 
intermediate positions may be available according to flight requirements. 
Referring to FIGS. 3a, 3b and 4 in particular, the slat 2 is supported with 
respect to the main airfoil 1 by means of an I-section beam 6. The beam 6 
is affixed at one end to the slat 2 by means of fasteners 7. The beam, and 
thereby the slat 2, are supported by the main airfoil 1 by four straddle 
rollers 8, 9, 10, 11. The straddle rollers are rotatably mounted on the 
main airfoil 1 between an adjacent pair of wing ribs 12, 13 upon axles 14, 
15 passing therethrough (see in particular FIG. 6). The rollers 8, 9, 10, 
11 run on roller tracks 16, 17, 18, of the beam 6 to support it during 
extension and retraction movement and to withstand all aerodynamic loads 
imposed on the slat 2 save those imposed in an extension or retraction 
direction. 
The beam 6 comprises an upper boom 19 and a lower boom 20 separated by a 
web 21. On a lower surface of the lower boom 20 is integrally formed 
therewith a gear rack 22 which stands proud of the lower surface of the 
boom 20. The rack 22 engages a drive pinion 23 connected via a reduction 
gear box 24 (see FIG. 2) to torque shafting 25 (see FIG. 2) which 
transmits drive to the pinion from a drive motor (not shown) located in 
the wing or in the fuselage of the aircraft. 
The rack 22 is centrally disposed on the lower boom 20 of the beam and is 
flanked by lower roller tracks 17, 18 which co-extend therewith adjacent 
to it. 
Lower rollers 10, 11 have laterally separated rolling surfaces 26, 27 to 
provide clearance for the rack 22. The rollers 10, 11 are in fact single 
piece items although a vertically split roller with rolling surfaces 26, 
27 formed on separately rotatable hubs would be feasible where required. 
The beam 6 extends rearwardly of a forward spar 28 inside a sealed 
container called a track can 29. It will be observed that the overall 
length of the beam 6 is considerably shorter than that shown in the prior 
art embodiment causing minimal intrusion into a fuel tank area contained 
behind the front spar 28. 
The arrangement as shown is extremely compact and strong. Adjustability of 
the rollers for rigging the slat is relatively straightforward in 
comparison with the prior art embodiment and the provision of the roller 
tracks 17, 18 either side of the rack 22, provides a compact, symmetrical 
and inherently strong arrangement with low potential maintenance being 
required. 
Straddle rollers, as provided in this invention are inherently more stable 
than cantilever rollers, as shown at the rear of the beam in the prior art 
embodiment. The particular roller arrangement shown in the illustrations 
is symmetrical about a central axis of the beam 6 and the lateral spacing 
of the rolling surfaces 26, 27 of the lower rollers provides a stable 
support for the beam 6.