load distribution along wing spars
load distribution along wing spars
(OP)
Hi folks I am a builder of model sailplanes so all that follows must be taken in context. My current project is an 18ft span hi-performance electric motor launched radio controlled sailplane. The total weight will be no more than ten pounds in flying trim and the maximum "G" load that I want to stress for is 5 G. The spar must therefore be capable of supporting 50 lbs at the centre which I have already designed, tested and am happy with. My question is this:
1) How far from the centre of the fuselage can I start to reduce the strength of the spar, and by how much? If I was hanging weights on the (inverted) spar to simulate positive wing loads, and the 50 lb limit is in force, what would the weight be at say 1 ft, 2 ft, 3 ft, 4ft,etc. In other words, how is the weight distributed along the span?
2) Is there a rule of thumb about this that will enable me to easily adapt, for instance, if I find the the spar is too strong (and heavy) my next project would use lighter construction and so on?
Thanks Guys
1) How far from the centre of the fuselage can I start to reduce the strength of the spar, and by how much? If I was hanging weights on the (inverted) spar to simulate positive wing loads, and the 50 lb limit is in force, what would the weight be at say 1 ft, 2 ft, 3 ft, 4ft,etc. In other words, how is the weight distributed along the span?
2) Is there a rule of thumb about this that will enable me to easily adapt, for instance, if I find the the spar is too strong (and heavy) my next project would use lighter construction and so on?
Thanks Guys





RE: load distribution along wing spars
Your exercise here is basically a cantilever beam in bending, one going left and one going right. Your plan to test by inverting the aircraft and holding the fuselage fixed is correct. Hanging indivudual weights is fine, the more the merrier. Don't want to have the individual weights applying concentrated point loads. Your one per foot (9 per side, 18 total) is probably the least to try. So if a rectangular wing, then all weights are equal.
As far as rules of thumb - there are all sorts of good references out in the internet, heck, even Wikipedia. The property of your spar that relates to its strength is called Moment of Inertia. So do a few word searches, and just follow the links.
RE: load distribution along wing spars
Normally your post would be redflagged as we try to keep no students and homebuilds in our traffic, but i must admit a sympathy for homebuilds, as i feel they embody a nature of engineering whereby failure is just another hurdle to pass over.
the answers your looking for are simple mechanics/statics, as you dont want to overcomplicate it with actulaties.
The answers out there just stop, think, google, and calculate.
good luck.
RE: load distribution along wing spars
http://www
But as 40818 said: Keep it simple.
Good luck :)
RE: load distribution along wing spars
RE: load distribution along wing spars
personally, i'm surprised that you can be happy with your root section if you don't know the root bending moment.
to learn more google "spanwise lift distribution", "shrenk" (not shrek !)
RE: load distribution along wing spars
ie "Scaled Composites"