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Process and apparatus for suppressing external load carrying wing flutter for aircraft
| Details |
Inventors: Breitbach, Elmar;
Assignee: Deutsche Forschungs- und Versuchsanstalt fur Luft-und Raumfahrt e.V. (Cologne, DE)
Primary Examiner: Blix; Trygve M.
Assistant Examiner: Corl; Rodney A.
Attorney, Agent or Firm: Thomas & Kennedy
In a semi-active system for suppressing external load-carrying wing flutter in aircraft, the carrying wing (1) is provided with one or more external loads (2), and the suspension of the external load (2) on the carrying wing (1) about an axis is arranged at right angles to the plane of symmetry of the aircraft. The external load (2) is mounted to pivot about the axis (3). A spring is provided between the carrying wing (1) and the external load (2); however, it is constructed, to take up the stationary and quasi-stationary moments, as a linear spring (7) with relatively great stiffness and permitting only small spring excursions. A further spring (8) is arranged in parallel with spring (7) and is constructed to be nonlinear and also to have negative stiffness and passage through zero in the region of the negative stiffness. The springs (7 and 8) form a spring system of small stiffness in and about the operating point defined by the passage through zero of the nonlinear spring (8) and the stationary moments. The operating point of the nonlinear spring (8) is slaved in each equilibrium position between the carrying wing (1) and external load (2). |
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DETAILED DESCRIPTION Here use is made of the present invention, the object of which is to teach a process and an apparatus of the kind described at the beginning and which are suitable for suppression of external load-carrying wing flutter more effectively and with smaller total cost.
According to the invention, this is achieved in the process of the kind described at the beginning in that the stationary and quasi-stationary and also dynamic moments acting on the external load about the axis during flying motions are taken up by a spring system of two springs, one spring being made linear, relatively stiff, and permitting only small spring excursions for taking up the stationary and quasi-stationary moments (e.
g.
long-wave gusts, maneuvers), while the other spring is made nonlinear and also with negative stiffness and passage through zero in the region of the negative stiffness and is connected in parallel to the one spring, so that to take up the dynamic moments the low stiffness of the spring system in and about the working point defined by the passage through zero of the nonlinear spring and the stationary moments is used, and that the working point of the nonlinear spring in each equilibrium position between carrying wing and external load is followed.
The present invention uses from the state of the art the concept of using a low-stiffness spring between the carrying wing and the external load to decouple the external load pitching and the wing torsion, and in fact such that the pitching frequency of the external load relative to the carrying wing is essentially smaller than the torsional frequency of the carrying wing without load.
Otherwise, the present invention departs from the state of the art.
In the state of the art, an expensive hydraulic device is used in parallel with the substantially soft spring, for restoring the relative position of the wing and external load, and the following disadvantages arise in dependence on the speed at which the restoration by the hydraulic device occurs at corresponding deflections
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