Avoiding overburn on highly tapered wings? - RC Groups
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May 30, 2003, 01:47 AM
Blue Stick's Dad
Brian Koester's Avatar

Avoiding overburn on highly tapered wings?


I've already asked some very experienced builders if they have any tips to avoid overburn on the tips of a highly tapered wing but I thought I'd throw it out to this group in the hopes someone has solved this thorny problem. I have a wing with a 13 inch root and 4" tip. Length is 25 inches, sweep is 15" and there's 3.5 degrees washout. When I cut this wing I get a overburn cuping that covers about 5 to 8 inches long from the wing tip.

TFLG's thought was to wrap some copper wire right next to the tip as a heat sink. and maybe I could spritz water on it to get that side to cool down. But I haven't tried that theory yet and wonder if it would even work since the over burn extends 8 or so inches into the foam.
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May 30, 2003, 12:25 PM
Free as a bird now.
Have you considered cutting each wing in two seperate panels?

It's going to be very tough to get the cutting wire to move 13" at one end in the same time that it moves only 3" at the other end without burning the tips. If you cut the wing in half and cut seperate outboard and inboard panels you might get away with that extreme taper.
May 30, 2003, 01:21 PM
Blue Stick's Dad
Brian Koester's Avatar
Hmmmm. That's a real interesting idea.
May 31, 2003, 07:33 PM
Blue Stick's Dad
Brian Koester's Avatar
Brian, It worked perfectly. I went from major over burn on top and bottom to no detectable over burn at all. Thanks a whole bunch for that great tip. I also discovered that It would work better if I put the tip side through a pivot point instead of a percentage of the root side. It created a perfect wing panel. I've included some photos to show the set up.
May 31, 2003, 07:33 PM
Blue Stick's Dad
Brian Koester's Avatar
Other side
May 31, 2003, 07:35 PM
Blue Stick's Dad
Brian Koester's Avatar
The two panels. The mid point ended up being 8.625" in chord length.
May 31, 2003, 07:41 PM
Free as a bird now.
I'm glad that worked out for you Brian.

(Hey, how come every other guy on this forum is named Brian anyway???)

It's a pain to have to make at least 3 sets of airfoil templates and set everything up twice and make two cuts just for one wing panel, but at least it worked!

What the heck are you building anyway? I'm asuming another jet. An A-4 maybe?
May 31, 2003, 07:45 PM
Free as a bird now.
On second thought, now that I notice the amount of sweep in that wing, I'm guessing a Saber or Mig...
May 31, 2003, 07:55 PM
Free as a bird now.
Hey Brian, did you happen to a take set of pictures of the building sequence of your foamie su-35? That had to be one of the most ambitious foamie projects I've seen, and very well executed too. I'm sure we would all love to see more details about that plane and how you made it.
Jun 01, 2003, 12:52 AM
Blue Stick's Dad
Brian Koester's Avatar
The wing is for the SU-35. The uncovered plane I flew at the Festival was the first one to test the idea. #2 I painted and incorporated what I learned from #1. I flew both at the festival. If you happened to see them both fly you would have noticed how #2 was at least 3 times faster. There's a third that's 70% done that will benefit from what I'm learning about #2. One of my biggest problems was that damn taper and overburn. But based on the wing I cut last night, It's no longer a problem. #2 flew real well but, with a more accurate airfoil, slightly less washout and a more smooth twist to that washout, I hope it flies better.

I have been thinking about building one and taking pictures and writing instructions for anyone who might want to build one themselves as an EPP kit after I've worked all the kinks out (BTW this whole project will culminate in a fiberglass fuselage.). I personally think it has the most beautiful profile of any modern jet and lends itself to PSS but I haven't heard much interest. It's the kind of project someone with intermediate skills could attempt. the hardest part is just the labor sanding all the curves even with most of the shaping being done by the cutter.
Jun 01, 2003, 01:02 AM
Blue Stick's Dad
Brian Koester's Avatar
This is me and #1. Thanks to TFLG for the pics. Brought a camera. Didn't take one pic. Having to much fun. And the other thing I didn't do since I was having so much fun was go around and say hi to all the people I've gotten to know on the ISR e-mail group like you Brian. Maybe next year.
Jun 01, 2003, 01:33 AM
Registered User
Hi Brian,


Have you tried hanging your FeatherCut from the ceiling instead of using the little wheel?

You will be surprised at the difference it makes in the ease and quality of core cutting especially when cutting extreme tapers.

I drilled a small hole in the centre of the bow and use a piece of wire to hang it, when you set the wire on the template for the cut have the bow at about a 30degree angle.

Works great.



T.D.
Jun 01, 2003, 01:52 AM
Free as a bird now.
I can relate to what you are saying Brian. There was just so much going on that you just couldn't meet everyone, nor could you not help missing out on some of the planes and action.

I plan to go back next year for sure.

I'm looking forward to seeing pics and details as you build the next one, and when you finally get a mold done, I'll be waiting in line for a layup.


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