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How to cut a good foam wing

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Aidan:

--- Quote from: "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...
--- End quote ---

You're going to get a little more melt at the tip one way or the other. The only way to eliminate that is to leave the template at the tip a fraction oversize. The big problem I remember having is pacing the small end so that you didn't get ahead or fall behind the pace of the big end. When doing it with two people the guy at the long end sets the pace by the feel of the resistance. If the graduations at the long end are 20mm apart and the taper is 2:1 then the graduations at the tip would be 10mm apart. As long as you hit the corresponding graduations together the wing should be the correct shape. The short end is the difficult one. It's difficult to maintain a steady slow pace with no real resistance. If the templates aren't good enough you can also find the wire snagging and then jumping on when it comes free.
Difficult to do well with two people. Extremely difficult, in fact nearly impossible, with one.

Aidan

billscottni:
if it's an extreme taper, you may be better off with a single point cutter, see the video I posted earlier.
One end is fixed and the foam blank is positioned along the wire so that the two ends exit the foam at the same time

Aidan:

--- Quote from: "billscottni" ---if it's an extreme taper, you may be better off with a single point cutter, see the video I posted earlier.
One end is fixed and the foam blank is positioned along the wire so that the two ends exit the foam at the same time
--- End quote ---

Doesn't work if you want washout or transitioning aerofoils though!

Richard Boyd:

--- Quote from: "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
--- End quote ---



Hi Ron, for small wings that have depth of profile the cutting was pretty successful !
The wing profile for my glider has a very thin profile at the root 20mm and then the idea was to taper it to 4mm at the tip.
I have been up extremely early and have tried all the different gauges of wire that I have in the workshop, the results stay the same, melted foam.
The results are not what I wanted.
For this style of wing I think I would have been better spending my time cutting the ribs and building a traditional wing.

Bill and Aiden , thanks for the help and insight into cutting winds.
One point on the cutting method I was using with the anchor point ,
I needed a long wire to cut the wing as the further away from the anchor point the wider the wing tip is cut !
Aiden I was using only one templete as per video I posted earlier.
I thought this method would be the simplest for my pea brain, yet it has lots of pit falls.

Bill I may take you up on that offer after all.

Richard
leave it up to the experts

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