Introduction to Aircraft Aeroelasticity and Loads

8

Static Aeroelasticity – Effect of Wing Flexibility on Lift Distribution and Divergence

Static aeroelasticity is the study of the deflection of flexible aircraft structures under aerodynamic loads, where the forces and motions are considered to be independent of time. Consider the aerodynamic lift and moment acting upon a wing to depend solely upon the incidence of each chord wise strip (i.e. strip theory; see Chapter 5). These loads cause the wing to bend and twist, so changing the incidence and consequently the aerodynamic flow, which in turn changes the loads acting on the wing and the deflections, and so on until an equilibrium condition is usually reached. The interaction between the wing structural deflections and the aerodynamic loads determines the wing bending and twist at each flight condition, and must be considered in order to model the static aeroelastic behaviour. The static aeroelastic deformations are important as they govern the loads in the steady flight condition, the lift distribution, the drag forces, the effectiveness of the control surfaces, the aircraft trim behaviour and also the static stability and control characteristics. The aeroelastic wing shape at the cruise condition is of particular importance as this has a crucial effect on the drag and therefore the range.

Through the elimination of time-dependent forces and motion, the inertial forces can be ignored in the equilibrium equations as these are dependent upon acceleration. Also, only steady aerodynamic ...