How do you define flutter?

Answer 1

Aerodynamic Flutter is usually applied to wings or ailerons and is the unstable oscillation caused by interaction between aerodynamic forces, elastic reactions in the structure and the force of inertia. Unless damped quickly flutter will break a wing. The cure for flutter is usually to dispose the weights so that the centre of gravity of the wing is as far forward as possible. Ailerons, elevators and rudders are mass-balanced to prevent flutter. Flutter is a dangerous phenomenon encountered in flexible structures subjected to aerodynamic forces. This includes aircraft, buildings, telegraph wires, stop signs, and bridges. Flutter occurs as a result of interactions between aerodynamics, stiffness, and inertial forces on a structure. Flutter may be initiated by a rotation of the airfoil. As the increased force causes the airfoil to rise, the torsional stiffness of the structure returns the airfoil to zero rotation. The bending stiffness of the structure tries to return the airfoil to the neutral position, but now the airfoil rotates in a nose-down position. Again the increased force causes the airfoil to plunge and the torsional stiffness returns the airfoil to zero rotation. The cycle is completed when the airfoil returns to the neutral position with a nose-up rotation.