The flutter test rig is used to induce flutter oscillation in aerofoil models in the two degrees of freedom pitch and yaw. To do this, a 2-D airfoil model is suspended elastically from a pitch spring and torsional spring respectively. The models are commonly made of carbon-fibre-reinforced polymer to ensure high stiffness and low weight. A piezoelectric sensor is fitted on each side between the outer pitch spring and the inner torsional spring to measure the steady and unsteady proportions of the force and moment vector. Both springs – and therefore the degrees of freedom – can be blocked independently. For instance, if the purpose is to induce forced pitch vibration, the torsional springs are blocked and the pitch springs coupled with the hydraulic linear cylinder on both sides.