Techniques > How to...

How to cut a good foam wing

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billscottni:
If it's dragging Richard it's one of two things.

Not enough heat

Moving the bow too fast.

I have a couple of video's on Youtube of the set up I use currently, or give me a ring

Aidan:
It's a long time since I hot wired foam wings. We used to do it as a two man operation. We'd mark graduations along the templates say at 20mm intervals (closer at the LE) and call out the numbers as we went along to make sure we were in sync. I tried doing them solo a couple of times but found it very difficult to get a good cut this way. I'd agree with Bill's diagnosis. Dragging is caused by going too fast for the heat available. Getting the speed right is the hardest bit, especially for wings with lots of taper.

billscottni:
Try these:
[youtube]http://www.youtube.com/v/kb3Bz7IThkw[/youtube]

[youtube]http://www.youtube.com/v/oVvE9CUALcQ[/youtube]

Good info here: http://www.charlesriverrc.org/articles_foam_vac.htm

Richard Boyd:
Hi Bill thanks for the pointers.
Ron, cutting these wings aint  that easy.
I have had results with small airfoil wings for my indoor planes.
Yet for gliders I have had problems.
The taper in the wing means the wing tip is burning !
I guess its down to the wire traveling less distance than the root of the wing, hence the burning occurs.
One thing , the foam supplier is a happy man , profits are up !
I am going to change my wire thickness tomorrow and see if the results change any.
 
Richard
if one never tries , one never knows

Ron:
Hi Richard,

Ah, that's one thing I hadn't thought of, the wire moving more slowly at the wing tip and burning the foam.
The wing tip distance could easily be half the root, so there's a 2:1 speed difference straight away.
Hmmmmm.....
Can't think of a way around that.

We need a wire that's 1.4 times the cross sectional area at one end from the other, that way the resistance would be 0.707 of the other end, and the power would be halved.
Think I've got that right :?:

But back to the real world...
Nope, still can't think of a solution :x

Ron

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