Guys,

I have seen folks using carbon rods to add strength to foam. Now the question is as follows

1) Why carbon, why not lets say Balsa spars or for that matter just plain old push rods?

2) Is there a guideline on the thickness of the rod that one should use for a specified length?

Pankaj

Carbon is lighter than balsa and virtually unbreakable compared to balsa. Pushrods (like bicycle wheel spokes) are heavier. Carbon rods or flats are the best bet.

Pankaj

One can use any of several methods to strengthen... it is important that the method should align with the type of flying you are going to do. If you subject the plane to high G's, then the strengthening member should be able to take that sort of load.
As an eg. last weekend, Venkat (Sai's son... IIT sp4mm3r fame last year!) and self were maidening my Tuffy. This plane has a wing made of coro with ... you will not believe, 2x8mm thk foam as the strengthening spar. It flew very well and Venkat decided to try a few aerobatics. He had done about two loops... on the end of the second loop, the wing folded from the centre, and the model came crashing down.... About 20 ft from the ground the folded wing started opening again and when it touched the ground after a short glide, the wing was flat. We flew the model again after attaching a strong wooden spar over the foam spar outside the wing with no further issues... but this is an example of being too over confident and not paying attention to the structure of the wing

Saju

OK, then If I were to use carbon rods or tubes, then how do we cut it to size? In site it mentioned that we should not use 'side cutters' whatever that means.

Pankaj

Pankaj

Do not use a hack saw to cut carbon rods or tubes... This will tear out or strip carbon fibres. Best way is to use a fine steel file preferably triangular. This will give a nice conical end to the rod if you keep rotating the rod while filing across it, without stripping the fibres. If the fibres strip out the rod will gradually splinter as you apply load lateral to it.

Wear a mask if filing as the particles must not be inhaled. I use a wire cutter after wrapping a cloth around the carbon rod to take up any small particles from cutting.

What I saw friends do is to wrap the area to be cut in tape, and then slowly cutting with a sharp knife (like XACTO) from all sides one after the other (like in a rolling motion).

Serious??? I thought this season for mask was reserved for H1N1.

If we were to use wire cutter, then i guess it would only apply to rods and not tubes. Further, how to smoothen out the edges?
Pankaj

BTW
Did we all forget foam can also be strengthened with fibre glass??
But yes carbon/Nomex/Kevlar (if any of these are available) flats/rods/tubes/tows are the easy way to do this without much of weight penalty

Folks,
Check out the thread http://www.rcgroups.com/forums/showthread.php?t=612476&page=2

I have pasted the page 2 link, to highlight a post by someone called chickenstick. Makes interesting reading.

Pankaj