1. Flutter-a scary instability
AAE Aeroelasticity
Flutter-a scary instability
small disturbances
- big effects
Purdue Aeroelasticity

2. Purdue Aeroelasticity
Lockheed Electra
Purdue Aeroelasticity

3. Purdue Aeroelasticity
Quasi-steady flutter
Flutter is a self-excited, dynamic, oscillatory instability requiring the interaction between two different modes of motion and an external energy supply
Quasi-steady aerodynamic loads ignore the unsteadiness of the flow created by lags between motion and developing forces and momemts
Purdue Aeroelasticity

4. Purdue Aeroelasticity
What we are looking for
Purdue Aeroelasticity

5. Unsteady aerodynamics
Purdue Aeroelasticity

6. Airfoil start-up with vortices
Purdue Aeroelasticity

7. Wagner function - response to a sudden increase in angle of attack
Purdue Aeroelasticity

8. We’ll start with simplified models of the airloads due to motionV
lift
Purdue Aeroelasticity

9. Free vibration with quasi-steady loads
START
divide by
FINISH
Purdue Aeroelasticity

10. Purdue Aeroelasticity
Warning – algebra!!!!
Purdue Aeroelasticity

11. Define new collections of terms
Purdue Aeroelasticity

12. Aerodynamic loads in terms of displacements
Purdue Aeroelasticity

13. Finally - free vibration with the wind blowing
Purdue Aeroelasticity

14. Solve these equations by assuming a harmonic time solution
results after division by eiwt
Purdue Aeroelasticity

15. Combine terms and look for similarity parameters
Purdue Aeroelasticity

16. Purdue Aeroelasticity
Define new parameters
bw=speed
Reduced velocity
Purdue Aeroelasticity

17. Purdue Aeroelasticity
Nondimensional parameters called reduced velocity, frequency ratios... Characterize the models and phenomena causing flutter
Purdue Aeroelasticity

18. Non-dimensionalization
1/b
1/b2
Purdue Aeroelasticity

19. Purdue Aeroelasticity
The prize
Purdue Aeroelasticity