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Rules of thumb in structural design?

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karoliina.t.salminen

Well-Known Member
Joined
Oct 7, 2008
Messages
407
Location
Finland
I have been concentrating on aerodynamics for years and have
avoided the structural design part quite completely. However
now I would like to get started on it too. Before going to complicated
stuff I would like to understand the relations of length, mass and force
(as generated by drag due to and lift).

So a very basic question in roughly rule of thumb category:
- we have sailplane wing that is 25 meters long with AR=25.
Sailplane has vne at 200 km/h and best L/D at 80 km/h and
the mass of the plane is 1000 kg. This is imaginary example, not
a spec of some plane.
-> it is cut into two and it results a wing that is 12.5m long and AR 12.5
If mass stays 1000 what would be the Vne?
How much mass could be carried with the shorter wing
before exceeding the twisting moment or bending limits?

When I was studying, the understanding part (ie rule of thumb) was
lacking and it was putting numbers into equations or integrating
something or stuff like that but a more simple relations probably
exist and I would like to understand those, otherwise I would
blindly trust whatever some excel outputs and believe it to be
right if I could not verify if that is roughly correct and I have learned
to not blindly trust anything I compute without checking if
the answer is anyhow realistic.
 
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