Nonlinear analysis of a flexible half-wing model tested in a subsonic wind tunnel with control-surface freeplay and preloading

ifasd2024 Tracking Number 186

Wind tunnel tests were conducted using a flexible, half-wing model provided with a control surface. The main purpose of these tests was to evaluate the methodology developed at Embraer to accomplish nonlinear aeroelastic analyses. To introduce nonlinear effects in the system, the flexible connection between the control surface and the main surface of the wing was fitted with a freeplay mechanism. Another important feature of the experimental setup was the position of the model inside the test section. For various reasons, the model was installed in the horizontal position and, therefore, the control surface was subjected to preloading due to the moment around the hinge line generated by its own weight. Limit cycle oscillations (LCO) were observed in the subsonic wind tunnel tests but only when the equilibrium position of the control surface, which depended on the tunnel flow velocity, was within the freeplay deadspace. The treatment of preloading found in the literature (see Laurenson and Trn [1]), however, was not developed for such a condition. The condition in which the preloading formulation was developed in Ref. [1] assumed that the equilibrium may only occur outside the freeplay deadspace. Therefore, a special treatment for a preload equilibrium inside the freeplay deadspace was developed for frequency-domain aeroelastic analyses. The special treatment was based on Ref. [1] and new equations were developed, based on the same assumptions, for the present conditions. The new approach needed a method for determining the equilibrium position of the control surface for a given wind tunnel flow condition (preload parameter). The determination of the control surface equilibrium position demanded some specific aerodynamic coefficients along with mass and inertia properties of the aeroelastic system. The aerodynamic characteristics were evaluated both by vortex lattice and CFD methods. The results of such equilibrium position predictions, and then the preloading parameter, agreed well with the measurements in the wind tunnel tests. The predictions of the adapted methodology for the aeroelastic analysis of a nonlinear system with preload were consistent with the experimental LCO frequencies and amplitudes evaluated in the wind tunnel tests. References: [1] Robert M. Laurenson and Robert M. Trn. Flutter of Control Surfaces with Structural Nonlinearities. Technical Report Report MDC E1734, McDonnell Douglas Astronautics Company, East. St Louis, Missouri, 1977.