You are right here.
After spending 25 years in the aerospace industry, I was always told not to make something too strong, as it would transfer extra stess to another component that was not designed to take it.
Dave
8 ft wingspan jobbies weighing 3lb, and not wanting to 'do an airbus' in turbulence.
IIRC the top spar is stressed to about a 1/4 ton.
You can work it out yourself. The bending moment in a 10g manouever is about 15lbs at half the sub span - 25" acting over half the chord depth of 1.4"..so its 15 x 25 over .7"..I make that +- 500lb force or so.
Bending moment on the joiner is basically about 30 lb foot. That's more or less concentrated over a few mm.
And that's only at 10g. That's a quite weather sailplane. The speed ships have definitely been recorded with accelerometers at 40g+.
Not exactly the same, even if the difference won't be noticable in practice.
For example, at room temperature (21C) the Young's modulus of some different types is:
Austinitic Stainless steel = 28.3 Low carbon steel (
Don't worry, the rest can take it! Its stiffness we want, and not reaching the plastic limit. If the rest of the wing snaps, that's OK.
Normally I'd build the spars straight across, but a 100" wing is too big for most cars..it needs to be joined in the middle.
The rod is in a tube glassed into ply spars and a the interspar webbing.
Plenty of transfer that way..
axial bending mainly.
Axial.
Volume mainly. Weight is really not an issue. Not here.
Space is limited due to the need to have a straight rod in a gull wing. And another reason why carbon is not ideal (although I use it elsewhere) is that it wears sloppy.
See previous post. I want a rod that I can put inside a tube, with that 'held in a vice' and put 30lb foot on without it budging much, and with luck capable of 120ft lb without snapping or deforming. After that the wing snaps anyway, and I don't care that much :-)
As I said, it flew with 4mm, but wing flex was unacceptable.
Don't joint it in the middle.. have removable wing tips. There is less stress on the smaller wing tips so its easier.
Then there is still the problem of removing the wing(s) from the fuselage.
Have a look at what it is. Google 'Minimoa'
I can assure you, thios was the lesser of many weevils.
>
I think you are overdoing the stiffness requirement.. real planes aren't stiff and there is no reason why a quarter scale model should be stiff.
If planes that big were made stiff they would fall out of the sky.
Its been a long time since I built a plane and never one that big but 6 mm steel rods goes against my gut feeling.
I think I might have a go at building a quadrocopter though.
39.3700787 inches by any chance?
All I want is that the wing joiner is not 3 times less stiff than the rest of the wing.
EEr..one just did! :-(
130" model we know of uses 10mm steel rod.
Dont. Just buy one. The control electronics are fierce.
That's a silly number of decimal places, isn't it
At what temperature would you expect a steel rod to be a metre to that degree of accuracy
You weren't paying attention to my previous post, were you
I would expect 37 inches, the point being that you can cut the ends off to get a 3' rod whose ends have not suffered from distortion or heating effects from initial cutting
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