Originally Posted by
LGM Graphix
While I haven't had to do much in the world of composites, through years of flying pattern, jets, working on custom cars and bikes, machining etc, I have to agree with both sides.
personally I would prefer carbon. Given the correct diameter and wall thickness carbon is more than up to the task. In pattern with gear in the wings, big vibrating 4 strokes and violent snaps and pulls (the figure z comes to mind]) after competing for 8 years I saw a few aluminum tube failures but never a carbon tube failure granted there were many more aluminum tubes than carbon ones but even in bad crashes I never saw a carbon tube break. As in all situations if you use a piece too small for the job it will fail.
most lean towards aluminum because it is cheap, easy to work with and it's been used for years. We can say "oh the blah blah blah just used that size, it should be fine. Honestly much of what we do is guesswork based on prior experience.
the tube, no matter whether aluminum or carbon or even steel, should never be a concern of the failure point. That piece should always be designed to be stronger than the structure supporting it. In other words no matter what the material it should be the last part to fail.
Agree with that 100%. I'm not saying at all that carbon can't be used. The question is, how do I know that the carbon tube is adequately sized for the given application? Especially if I'm not a composite engineer, just Joe Bag'o Doughnuts trying to scratch build a model jet.
If I'm doing a 40% 3D airplane, or a sailplane, I can look at the myriad number of those that are out there and select a similar carbon tube. For a jet, not so much. You say that you have an F15 and F18 with carbon tubes, and I believe you, but I honestly can't recall ever seeing one myself. The companies out there that sell carbon tubes (and sleeves) for model aircraft sell ones that are intended for the 3D and/or sailplane market, not jets.
We did some work with carbon fiber tubes for a VTOL UAV. It took some looking to find tubes that were readily available and of the right OD and ID. Once we did, we didn't really have any information on their ultimate strength to see if they were up to the job. We resorted to testing one of them to destruction in order to make sure. Not really a viable option for the average modeler with a limited budget.
Now for an aluminum tube, I can look at almost any of my jets and get an idea of what tube I need for that application. I have done that successfully several times when scratch building or modifying jet models.
Bottom line is that what Boeing or Airbus uses for their wing boxes has no bearing on selecting a wing tube of a model jet...
Bob