The Elastic Airplane

Aeroelasticity deals with the interactions of aerodynamic and inertial forces and aircraft structural stiffness. Additional significant interactions with aerodynamic heating and automatic control systems give rise to the Germanic-length terms aerothermoe – lasticity and aeroservoelasticity. Aeroelasticity concerns stability and control, dealt with here, but also flutter and structural loads arising from maneuvers and atmospheric turbu­lence. Aeroelasticity affects airplane stability and control in a number of areas. Prediction of aerodynamic data at the design stage (Chapter 6), tactical airplane maneuverability (Chapter 10), the equations of motion (Chapter 18), and stability augmentation (Chapter 20) are all affected.

Aeroelastic effects are considered as distractions by many stability and control engineers, obscure problems that get in the way of the real work at hand. Aeroelastic methods are certainly abstract, involving such arcana as normal modes. How does one fix body axes in a flexible structure? What is its angle of attack? We trace this difficult but important branch of stability and control from the early days of Samuel Langley, the Wright brothers, and Anthony Fokker to the present.

The early days were dominated by isolated occurrences of aeroelastic problems and ad hoc solutions. The advent of large-scale digital computers and finite-element or panel methods for the first time provides, if not a general theory, at least an organized approach to prediction and solution of stability and control aeroelastic problems.