So, just what is aeroelasticity anyway?
(Adapted from Bisplinghoff, R.L., Ashley, H., and Halfman, R.L., “Aeroelasticity, Dover,” 1955) Aeroelasticity has been defined as a science that studies the mutual interaction between aerodynamic forces and elastic forces, and the influence of this interaction on airplane design. Modern airplane structures are very flexible, and this flexibility is fundamentally responsible for the various types of aeroelastic phenomena. Aeroelastic phenomena arise when the structural deformations induce additional aerodynamic forces. These additional aerodynamics forces may produce structural deformations that will induce still greater aerodynamic forces. Such interactions may tend to become smaller and smaller until a condition of stable equilibrium is reached, or they may tend to diverge and destroy the structure.
The term aeroelasticity includes phenomena involving interactions among inertial, aerodynamic, and elastic forces, and other phenomena involving interactions between aerodynamic and elastic forces. The former will be referred to as dynamic and the latter as static aeroelastic phenomena.
Common Aeroelastic Terms
- Flutter–A dynamic instability occurring in an aircraft in flight, at a speed called the flutter speed, where the elasticity of the structure plays an essential part in the instability.
- Buffeting–Transient vibrations of aircraft structural components due to aerodynamic impulses produced by the wake behind wings, nacelles, fuselage pods, or other components of the airplane.
- Dynamic Response–Transient response of aircraft structural components produced by rapidly applied loads due to gusts, landing, gun reactions, abrupt control motions, moving shock waves, or other dynamic loads.
- Load Distribution–Influence of elastic deformations of the structure on the distribution of aerodynamic pressures over the structure.
- Divergence–A static instability of a lifting surface of an aircraft in flight, at a speed called the divergence speed, where the elasticity of the lifting surface plays an essential role in the instability.
- Control Effectiveness–Influence of elastic deformations of the structure on the controllability of an airplane.
- Control System Reversal–A condition occurring in flight, at a speed called the control reversal speed, at which the intended effects of displacing a given component of the control system are completely nullified by elastic deformations of the structure.