page_title: Aeroelasticity
section_title: Prediction and cure
hierarchical_section_title: Aeroelasticity / Prediction and cure
caption_attribution_description: English: External mass balancing of the ailerons of a Messerschmitt Bf110 long range fighter aircraft. Photograph taken at the RAF Museum Hendon
context_page_description: Aeroelasticity is the branch of physics and engineering studying the interactions between the inertial, elastic, and aerodynamic forces occurring while an elastic body is exposed to a fluid flow. The study of aeroelasticity may be broadly classified in two fields: static aeroelasticity dealing with the static or steady state response of an elastic body to a fluid flow; and dynamic aeroelasticity dealing with the body's dynamic response.
  Aircraft are prone to aeroelastic effects because they need to be lightweight and withstand large aerodynamic loads. Aircraft are designed to avoid the following aeroelastic problems:
  divergence where the aerodynamic forces increase the angle of attack of a wing which further increases the force;
  control reversal where control activation produces an opposite aerodynamic moment that reduces, or in extreme cases, reverses the control effectiveness; and
  flutter which is the uncontained vibration that can lead to the destruction of an aircraft.
context_section_description: In the period 1950–1970, AGARD developed the Manual on Aeroelasticity which details the processes used in solving and verifying aeroelastic problems along with standard examples that can be used to test numerical solutions.
  Aeroelasticity involves not just the external aerodynamic loads and the way they change but also the structural, damping and mass characteristics of the aircraft. Prediction involves making a mathematical model of the aircraft as a series of masses connected by springs and dampers which are tuned to represent the dynamic characteristics of the aircraft structure. The model also includes details of applied aerodynamic forces and how they vary.
  The model can be used to predict the flutter margin and, if necessary, test fixes to potential problems. Small carefully chosen changes to mass distribution and local structural stiffness can be very effective in solving aeroelastic problems.
  Methods of predicting flutter in linear structures include the p-method, the k-method and the p-k method.
  For nonlinear systems, flutter is usually interpreted as a limit cycle oscillation (LCO), and methods from the study of dynamical systems can be used to determine the speed at which flutter will occur.
caption: Mass balance protruding from an aileron used to suppress flutter
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