This invention relates to vibration damping arrangements for aircraft. More particularly it relates to means for damping out fundamental vibrations in an aircraft high lift system, for example wing trailing edge flaps and leading edge slats.

In well known arrangements of wing high lift systems, spanwise portions of flaps or slats are mounted upon the fixed wing structure by chordwise support tracks by which means they are translatable or extendable with respect to the fixed wing structure to adopt a high lift configuration for the landing mode or intermediate take-off settings. In certain flight conditions fundamental vibrations may be induced in the flap portions which may give rise to significant structural distortion and damage. It is the object of the present invention to provide means for damping these induced vibrations and substantially minimising structural distortion.

According to one aspect of the present invention there is provided a method of damping induced fundamental vibration in an aircraft high lift device including the steps of transmitting a signal indicative of the scale of the vibrations to a damping device, inducing a reactive force in said damping device in response to said signal and applying said reactive force to the high lift device to substantially nullify said fundamental vibrations.

According to a further aspect of the present invention, there is provided an arrangement for damping induced fundamental vibrations in an aircraft wing high lift device, said arrangement including a wing, a high lift device mounted upon and movable along a pre-determined path with respect to said wing between a stowed cruise position and an extended high lift position, a track beam interconnecting said wing and said high lift device and being pivotally connected to said wing and including a trackway for sliding interconnection with said high-lift device, and a damping device interconnecting said track beam and said wing for damping of angular displacement therebetween, the arrangement being such that whilst the high lift device operatea within acceptable vibrational tolerances the damping device is isolated but induced fundamental vibrations will cause angular displacement of the track beam inducing a reactive force in the damping device to substantially nullify said fundamental vibrations.

One embodiment of the invention will now be described, by way of example only, and with reference to the following drawings in which :-

Figure 1 illustrates in diagrammatic plan form a typical aircraft wing incorporating a pair of trailing edge flaps.

Figure 2 graphically illustrates the fundamental vibrations associated with a portion of trailing edge flap.

Figure 3 illustrates in diagrammatic side elevation a wing trailing edge flap installation incorporating the present invention.

Figure 4 is a section through a portion of the installation taken along a line 4-4 in Figure 3.

Referring to the drawings, Figure 1 illustrates indiagrammatic plan form a typical port side wing 2 of an aircraft, having a leading edge 2A a tralling edge 2B and a pair of spanwise trailing edge flaps 3 and 4. Both flaps are supported on chordwise extending tracks 5 by which means they are translatable rearwardly with respect to the fixed wing structure over a range of operating positions.

In certain flight conditions with extended high lift devices fundamental vibrations can be induced in one or more of the flap portions such that the flap may be subjected to extreme conditions of curvature over the Span 'S' as illustrated with associated structural distortion and possible failure or damage. In extreme conditions, if the overall effective distortion 'D' at the extremity of one flap portion is at variance with that occurring at the adjoining extremity of an adjacent flap portion, structural interference between these adjacent parts may result in jamming. In extreme modes of vibration one or more flap portions could become detached from the aircraft with catastrophic results. It is known that such condition can be at least minimised by the application of a force at some point along the flap span and which will effectively dampen out the vibration. It is necessary, however, to ensure that such a damping force is ineffective in normal operating conditions such that it cannot influence the normal control forces on the flap.

Such an arrangement is illustrated with reference to Figure 3 and 4 in which a trailing edge flap 3 is shown in its stowed cruise location relative to the fixed trailing edge upper shroud structure 18, the shroud extending rearwardly of the rear spar 6 of the wing 2. In operation the flap 3 translates rearwardly from its stowed position to a rotated fully deployed landing setting 3,. It may alternatively adopt an intermediate take-off position not shown here. The flap position and attitude is controlled by a flap operating mechanism, not shown and is supported relative to the wing 2 on flap support tracks 5 (see Figure 1).

In accordance with the present invention the flap installation incorporates a vibration damping installation 19 in which the flap 3 is indirectly connected to a damper strut 15 by means of a track beam 8 which is pivotally connected at 13 to a mounting bracket 12 located to the wing lower surface. The track beam 8 further includes a trackway 20 for engaging a pair of rollers 10 mounted to a lug 7 about a pivot axis 9, the lug 7 depending from the lower surface of the flap 3 adjacent to its leading edge. A mounting bracket 14 provides an upper pivotal attachment 16 for the damper strut 15, the lower end of which is pivotally attached at 17 to the track beam 8.

The geometry is arranged so that the track beam 8 lies substantially parallel to the lower surface of the flap 3 and although the flap is constrained by its flap support and operating mechanism (previously referred to) and follows a pre defined path, the location of roller pair 10 in relation to the flap 3 and the geometry of the trackway 20 in the pivotally attached track beam 8 are so configured that the change in length of the damper strut 15 resulting from development of the flap produces damping forces which are very low compared with those resulting from the free or induced vibration of the flap, and hence give rise to negligible effects during flap translation. If however, induced fundamental vibrations occur in the flap in its extended location, the consequential distortion of the flap relative to its datum position, as described with reference to Figure 2, will be transmitted to the trackbeam 8 via the leading edge roller 10 engaging with the track beam 8, with a resultant angular displacement of the beam about its pivotal attachment 13. This, in turn, will induce in the damper strut 15 a countering load.

Although this invention is described in the context of an aircraft trailing edge flap system, it may equally be applicable to other translating high lift devices such as leading edge slats irrespective of their deployment loci.