GB2162139A

GB2162139A - Aircraft flutter control

Info

Publication number: GB2162139A
Application number: GB08418816A
Authority: GB
Inventors: Dennis George Mabey
Original assignee: UK Secretary of State for Defence
Current assignee: UK Secretary of State for Defence
Priority date: 1984-07-24
Filing date: 1984-07-24
Publication date: 1986-01-29
Also published as: GB8418816D0

Abstract

A flutter damper at an aircraft wing tip, for suppressing one degree of freedom wing flutter associated with buffet or separated flows. The damper comprises a cantilever and tip weight combination tuned for oscillation at the wing first bending frequency and arranged for immersion in a viscous fluid, such as aircraft fuel. <IMAGE>

Description

SPECIFICATION Improvements in or relating to aircraft flutter control The present invention relates to aircraft flutter control, and is particularly concerned with means for attenuating one degree of freedom wing flutter. In the present specification however 'wing' refers not only to the mainplane but to any aircraft fixed plane, such as the tailplane and fin.

According to the present invention an aircraft wing carries a flutter damper mounted in the tip thereof and comprising a thin cantilever with a weight approximate its free end and arranged for immersion in a viscous damping liquid.

The cantilever may be mounted in a fuel tank on or extending to the wing tip, in which case it may be preferred to ensure that aircraft fuel remains around the cantilever in modes of flight when the wing flutter is a possibility. This can come about if the cantilever is mounted relatively low in the tank, since provided the cantilever is immersed, the amount of liquid present will not greatly affect damper operation, which remains effective to attenuate a wing flutter at quite a wide range of frequencies about the fundamental. In an alternative embodiment however the damper may include its own vessel of viscous liquid.

The cantilever is preferably anchored either in the trailing end or the nose of the wing tip or wing tip tank. The cantilever may have constant thickness and breadth, although the breadth may taper outwards to conform to the contours of its container.

For use in a particular aircraft wing context the dimensions of the damper, and the weight of its components are likely to be tuned for excitation at the first wing bending frequency. The damper can then be effective both to suppress flutter and to reduce the response of the wing to atmospheric turbulance or buffet excitation wrought by separated flows.

An aircraft wing tip flutter damper in accordance with the invention will now be described by way of example with reference to the accompanying draw ing, which depicts a flutter damper in an aircraft mainplane tip fuel tank.

As depicted in the drawing an aircraft main plane 10 has a wing tip fuel tank 11 containing a flutter damper comprising a thin cantilever 12 and a weight 13. The anchorage of the cantilever is in the trailing edge of the tip tank 11, and the cantilever, which is tapered outwards toward the weight 13 is consider ably thinner than even its anchorage breadth. The arrangement is such that the plane of the cantilever and that of the wing are parallel one to the other.

Rubber stops mounted in the tip tank 11 above and below the weight 13to prevent the weight from reaching, and perhaps damaging, walls of the tank.

In a wind tunnel test of a model having a span of 60 inches and a wing weight of 209 Ib, a damper at the wing tip having a total weight (cantilever plus pad plus viscous liquid) of 12.5 Ib was effective as a flutter damper, when tuned to an oscillation frequen cy equal to the first wing bending frequency. The cantilever length was 2 inches. In the preferred embodiment, when the cantilever is arranged to lie in fuel, the weight penalty is considerably lower, anc can be kept low by maximising the extent of the cantilever rather than the size of the weight 13.

1. An aircraft wing carrying a flutter damper mounted in the tip thereof and comprising a thin cantilever with a weight approximate its free end and arranged for immersion in a viscous damping liquid.

2. A wing as claimed in claim 1 and wherein the cantilever is mounted in a fuel tank at the wing tip.

3. A wing as claimed in claim 2 and wherein the cantilever is anchored in the trailing end of the tank.

4. Awing as claimed in claim 2 and wherein the cantilever is anchored in the nose end of the tank.

5. An aircraft wing substantially as hereinbefore described with reference to the accompanying draw ings.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. SPECIFICATION Improvements in or relating to aircraft flutter control The present invention relates to aircraft flutter control, and is particularly concerned with means for attenuating one degree of freedom wing flutter. In the present specification however 'wing' refers not only to the mainplane but to any aircraft fixed plane, such as the tailplane and fin. According to the present invention an aircraft wing carries a flutter damper mounted in the tip thereof and comprising a thin cantilever with a weight approximate its free end and arranged for immersion in a viscous damping liquid. The cantilever may be mounted in a fuel tank on or extending to the wing tip, in which case it may be preferred to ensure that aircraft fuel remains around the cantilever in modes of flight when the wing flutter is a possibility. This can come about if the cantilever is mounted relatively low in the tank, since provided the cantilever is immersed, the amount of liquid present will not greatly affect damper operation, which remains effective to attenuate a wing flutter at quite a wide range of frequencies about the fundamental. In an alternative embodiment however the damper may include its own vessel of viscous liquid. The cantilever is preferably anchored either in the trailing end or the nose of the wing tip or wing tip tank. The cantilever may have constant thickness and breadth, although the breadth may taper outwards to conform to the contours of its container. For use in a particular aircraft wing context the dimensions of the damper, and the weight of its components are likely to be tuned for excitation at the first wing bending frequency. The damper can then be effective both to suppress flutter and to reduce the response of the wing to atmospheric turbulance or buffet excitation wrought by separated flows. An aircraft wing tip flutter damper in accordance with the invention will now be described by way of example with reference to the accompanying draw ing, which depicts a flutter damper in an aircraft mainplane tip fuel tank. As depicted in the drawing an aircraft main plane 10 has a wing tip fuel tank 11 containing a flutter damper comprising a thin cantilever 12 and a weight 13. The anchorage of the cantilever is in the trailing edge of the tip tank 11, and the cantilever, which is tapered outwards toward the weight 13 is consider ably thinner than even its anchorage breadth. The arrangement is such that the plane of the cantilever and that of the wing are parallel one to the other. Rubber stops mounted in the tip tank 11 above and below the weight 13to prevent the weight from reaching, and perhaps damaging, walls of the tank. In a wind tunnel test of a model having a span of 60 inches and a wing weight of 209 Ib, a damper at the wing tip having a total weight (cantilever plus pad plus viscous liquid) of 12.5 Ib was effective as a flutter damper, when tuned to an oscillation frequen cy equal to the first wing bending frequency. The cantilever length was 2 inches. In the preferred embodiment, when the cantilever is arranged to lie in fuel, the weight penalty is considerably lower, anc can be kept low by maximising the extent of the cantilever rather than the size of the weight 13. CLAIMS