AAE 556 Aeroelasticity Lecture 12 Swept wing aeroelasticity The flexural axis concept Purdue Aeroelasticity

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 Purdue Aeroelasticity

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 … Purdue Aeroelasticity

Friday’s Homework Problem 3.3 Purdue Aeroelasticity

Reminder - Wing structure idealization with aerodynamic loads springs resist upward and downward motion Purdue Aeroelasticity

Static equilibrium equations Purdue Aeroelasticity

Purdue Aeroelasticity Deflections bending slope twist angle Purdue Aeroelasticity

Lift effectiveness Substitute for the angles q and f Purdue Aeroelasticity

Flexible wing lift intermediate result Purdue Aeroelasticity

Purdue Aeroelasticity Final result Lift on rigid surface lift effectiveness definition Purdue Aeroelasticity

Purdue Aeroelasticity An example wing let Purdue Aeroelasticity

Lift effectiveness vs. q So what? What are the consequences? Purdue Aeroelasticity

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 Purdue Aeroelasticity

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 Purdue Aeroelasticity

Flexural axis concept an attempt to explain aeroelastic effects b yo xo Purdue Aeroelasticity

Step #1 Compute angular displacements Purdue Aeroelasticity

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 Purdue Aeroelasticity

Purdue Aeroelasticity example Purdue Aeroelasticity

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 Purdue Aeroelasticity