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I am revising for my final examination. I came across this simple problem which I can not solve. the problem is from a text book (Introduction to Structural Dynamics and Aeroelasticity). It is the 7th question in the problem sets of the 3rd chapter. Here is the question:

By Dewey H. Hodges, G. Alvin Pierce

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Consider a torsionally elastic wind tunnel model of a uniform wing, the ends of which are rigidly fastened to the wind tunnel walls.

The model has a symmetric aerofoil section and the following characteristics:

Span = 0.9144 m

Chord = 0.1524 m

Torsional Rigidity GJ = 22.9677 Nm2

Lift curve slope =6.0 per radian

The aerodynamic centre may be taken as lying at the quarter-chord position measured from the leading edge of the wing.

The CG and the elastic axis are located at the mid-chord.

Calculate:

(i) The divergence dynamic pressure (Answer: 7781.86 N/m2)

(ii) The divergence speed at sea level (Answer: 112.69 m/s)

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My attempt was to find it directly using the formula:

Divergence dynamic pressure = [GJ*(∏/2l)^2]/ eca

I have used the given values and taken "e" to be "0.25*c" (quarter chord).

My answer is not even close, its 1945.46 N/m2 :(

I can solve the second part of the question by equating 7781.86 with 0.5ρU^2. U is the speed that we need to find, and my answer matches.

Can anyone help ?

My exam is on 20th June, I hope someone who knows aeroelasticity (divergence) can help me out :)

Regards

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# Calculation of Divergence dynamic Pressure

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