1. AAE 556 Aeroelasticity Lecture 12
Swept wing aeroelasticity
The flexural axis concept
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2. Swept wing static aeroelasticity Reading Sections 3.1 through 3.6
Goals
Compute changes in aeroelastic load on swept wings – lift effectiveness
Explain effects using the flexural axis concept
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3. Notes on Homework handed back today
You must draw accurate, meaningful, decipherable Free Body Diagrams (FBDs)
You must make your HW neat and organized
You must clearly identify your answers
You must check for dimensional compatibility
Ordering equations …
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4. Friday’s Homework Problem 3.3
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5. Reminder - Wing structure idealization with aerodynamic loads
springs resist upward and downward motion
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6. Static equilibrium equations
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7. Purdue Aeroelasticity
Deflections
bending
slope
twist
angle
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8. Lift effectiveness Substitute for the angles q and f
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9. Flexible wing lift intermediate result
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10. Purdue Aeroelasticity
Final result
Lift on rigid surface
lift effectiveness
definition
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11. Purdue Aeroelasticity
An example wing
let
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12. Lift effectiveness vs. q
So what?
What are the consequences?
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13. Flexural axis concept an attempt to explain aeroelastic effects
Definition - the line along which the streamwise (or chordwise) angle of attack does not change when a discrete load is applied there. L yo xo
upward load
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14. Purdue Aeroelasticity
Flexural axis definition Why the confusing definitions? What is the difference between flexural axis and elastic axis?
The air is off!!!
flexural axis b L x
upward
load y
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15. Flexural axis concept an attempt to explain aeroelastic effectsb yo xo
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16. Step #1 Compute angular displacements
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17. Use flexural axis definition
This result always gives us a flexural axis location forward of the usual elastic axis. Increased wing sweepback rotates the flexural axis further forward and opens up the distance between aero loads and the hypothetical flexural axis
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18. Purdue Aeroelasticity
example
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19. Purdue Aeroelasticity
Summary
A load placed at the flexural axis creates no streamwise angle of attack at that section
the flexural axis position depends on the stiffness ratio and the sweep angle
the flexural axis and the elastic axis coincide when there is no wing sweep
the flexural axis is upstream for a swept back wing and downstream for a swept forward wing
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