AAE 556 Aeroelasticity Lecture 10 Swept wing aeroelasticity Part 1 5/2/2019 Copyright Purdue University 2008 AAE556 – Spring 2008 - 10

Swept wing static aeroelasticity Reading – pp. 101-115 Goals Determine how bending changes aeroelastic loads on swept wings review simple aerodynamic model and simple stiffness model 5/2/2019 Copyright Purdue University 2008 AAE556 – Spring 2008 - 10

Planform view of wing structure idealization model features Why does bending create lift force???? The letter N springs resist upward and downward motion 5/2/2019 Copyright Purdue University 2008 AAE556 – Spring 2008 - 10

Lift on flexible wing model Use the airspeed component normal to the wing to define dynamic pressure HOW? 5/2/2019 Copyright Purdue University 2008 AAE556 – Spring 2008 - 10

Wing aerodynamic forces matching downwash for lift computation I know that the streamwise coordinates are the favorite of aero people, but I’m a structures guy What is “downwash?” freestream view chordwise view v 5/2/2019 Copyright Purdue University 2008 AAE556 – Spring 2008 - 10

“Preserving” downwash velocity – angle of attack equivalence What angle of attack, when multiplied by YOUR definition of dynamic pressure gives the correct airloads? 5/2/2019 Copyright Purdue University 2008 AAE556 – Spring 2008 - 10

Lift on flexible wing model Use the airspeed component normal to the wing 5/2/2019 Copyright Purdue University 2008 AAE556 – Spring 2008 - 10

Equations of bending and torsional static equilibrium “Bending” equilibrium about the x-axis (f) 5/2/2019 Copyright Purdue University 2008 AAE556 – Spring 2008 - 10

Twisting moment equilibrium about y-axis (q) static torsional equilibrium 5/2/2019 Copyright Purdue University 2008 AAE556 – Spring 2008 - 10

Define (encrypt) problem parameters static equilibrium equations with initial angle of attack or 5/2/2019 Copyright Purdue University 2008 AAE556 – Spring 2008 - 10

Combine matrices - final result or 5/2/2019 Copyright Purdue University 2008 AAE556 – Spring 2008 - 10

Determinant (D) of aeroelastic stiffness matrix 5/2/2019 Copyright Purdue University 2008 AAE556 – Spring 2008 - 10

Copyright Purdue University 2008 Divergence condition so that Hmmm - only one divergence q for a 2 DOF system? 5/2/2019 Copyright Purdue University 2008 AAE556 – Spring 2008 - 10

Eliminate divergence? Just sweep the wing Set denominator equal to zero No divergence if 5/2/2019 Copyright Purdue University 2008 AAE556 – Spring 2008 - 10

Copyright Purdue University 2008 example Torsional stiffening is still good 5/2/2019 Copyright Purdue University 2008 AAE556 – Spring 2008 - 10

Copyright Purdue University 2008 example 5/2/2019 Copyright Purdue University 2008 AAE556 – Spring 2008 - 10

Copyright Purdue University 2008 Summary Bending deflection creates lift reduction Divergence does not occur if the sweep angle is more than about 5 degrees Lift effectiveness is reduced 5/2/2019 Copyright Purdue University 2008 AAE556 – Spring 2008 - 10