Passive Load Alleviation by Nonlinear Mounting of Airfoils in 2-DOF Models

A two degree of freedom (2-DOF) heave-pitch aeroelastic model with nonlinear spring attachments is set up and used to investigate the load alleviation capabilities of a new passive load alleviation concept. The concept is to exploit the nonlinear behaviour of structural wing components to trigger a deformation which reduces loads once a certain load level is reached. The deformation is a wing twist reducing the angle of attack. This structural nonlinear behavior is introduced into the 2-DOF model by implementing springs, which become weaker at a critical displacement, as attachment. Analyses with stationary loads and dynamic gust encounters at different flight conditions and different weights of the wing section are made. The best alleviation is achieved in stationary cruise and in long gusts and low wing mass. In slow flight the alleviation capability is reduced because of less aerodynamic pitching moment. The alleviation capabilities are reduced in short gusts and with high wing masses due to inertia.