Why Do I Struggle with Airframe Structures Exam Preparation?

[Swansea_J]

Hello everybody.

Well, I failed my airframe structures exam in May, and now have to resit it.

I have been attempting to do some exercises to get back into it, but it all looks foreign to me. I'm struggling A LOT, and another fail would mean that I have to resit the year (even though I passed my other 9 modules!).

I figured I would post up some of the exercises I'm struggling with, and anyone who is willing to try and give me some pointers is absolutely welcome.

I may bump the thread every now and again incase it goes right down the bottom of the pile and no one sees it.

Also, I apoligize if these seem stupidly simple, I guess I didn't pay enough attention :(

Thanks

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The first example I'm doing. A simple thin-walled open section.

Finding Iy is simple, but then I have to sketch the tz diagram and the integral of tz. Here is the answer, but I really can't figure it out for myself

My questions are;

Why are the sketches those shapes? (Some are rectangles, some are triangles)
Why are they positive and negative and how do you work out which one is which?
Where do the numbers come from?

BIG THANKYOU to anyone who knows!

 

[Swansea_J]

Incase anybody wanted to know, I have managed to work out the answers to my questions (Little disappointed no one attempted to help!)

The shapes correspond to the tz value. A rectangle shape means the tz value is constant, so the line is a constant, straight line. A triangle means that the tz value is linear (because it changes along the z-axis), so the slope in the line which makes the triangle displays this. Integrating the triangle (linear) value will result in a quadratic, which is the parabola shape.

The positive and negative signs simply correspond to the z co-ordinate of the shape with respect to the global axis.

The numbers come from multiplying the thickness of the bar, by it's z co-ordinate.