Another Air Loads Question Wing Drag/Stress

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proppastie

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All the wing loading calculations for stressing the wing (at least those I have found) do not figure the wing drag as a loading condition. Is this because it is less than torque loading, or in the case of the glider wing tip landing forces? Am I just not finding it or is it not done for stress, performance yes.
 

Matt G.

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My guess would be that for a glider, either the 150 lb drag load at the wingtip, or the drag load imposed by the dive brakes, or the forward loading at stall is going to be critical.
 

Topaz

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The tip loading is a ground-loop case, where the glider hooks a wing. It may very well be the critical case in the rearward direction chordwise.

In terms of air-loads, the forward component of lift in a max-g pull-up is probably going to be the bigger chordwise load by far, compared to drag. Speed brakes are going to be well inboard, and not a major loading contribution to the entire wing except the rearward shear load at the wing attach. That could be a significant load.
 
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proppastie

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Yes, most of the bags are over the main spar (25% of chord) and some forward up to the leading edge.
That would test the wing in bending, torsion and drag in one test, I think.

like this

basic 1.jpg
Now if I only could figure Euler out, makes my head hurt.
 

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proppastie

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There you go.

Looks like page 64 from FAA Basic Glider Criteria.

Yes, Lots of great stuff, but typically missing some symbol definitions, never any units for unit analysis. For example problems I have had everywhere not necessarily with this publication, for example calculation of drag. There are many definitions of air density. I finally found the one that gave reasonable results and it was in "slugs" (again not labeled, but correlated with another source ) . Now of course I had to convert slugs. My unit analysis was (Lbf-sec^2* Ft^2*Ft^2)/(sec^2 * Ft*Ft^3) = Lbf= pounds force. I do not understand how you guys do it without making mistakes. The unit analysis is so important and seems like no one does it. Perry or Timoshenko for example is total gibberish.
 
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Matt G.

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I wouldn't expect to find a good explanation of air density in a structures book like Peery or Timoshenko. One of the aerodynamics books listed in the references section of this forum would be a good place to find that ;)
 

proppastie

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I wouldn't expect to find a good explanation of air density in a structures book like Peery or Timoshenko. One of the aerodynamics books listed in the references section of this forum would be a good place to find that ;)

Right, except can't stress the plane without knowing the aerodynamic loads. I thought I could get away without doing any aerodynamics, Wrong.
 

proppastie

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I am getting horrible twist deflections calculations on my 22 ft flaperon. The actual flaperon rib load test passes with flying colors. When looking at Irv Culver's original wood design there is no "D" nose on the flaperon and my the recent thought I have is that the fabric is keeping it from twisting. Do you guys figure in the fabric in the stess calculations. (Looks like I will have to here).
 
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