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Building Tips and technical articles. => Building techniques => Topic started by: Dwayne on September 02, 2018, 08:22:35 PM
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Hey all, how do I run leadouts that are adjustable through the spar of a foam core wing?
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Hey all, how do I run leadouts that are adjustable through the spar of a foam core wing?
I'm guessing your spar is already in place?
Is your spar balsa or plywood?
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Dwayne- sounds like you have a wing with a full vertical spar(it's not necessary, but some people do it). Getting leadout holes will be difficult. I got a small diameter soldering iron cartridge, about 10 watts or so. You'll also need an adjustable voltage power supply. I mounted the cartridge on a 1/4 in. hardwood dowel and soldered wires to it that run to the power supply. If you plan on doing this a lot you have to build a jig that will allow you to slide the foam onto the dowel to melt a hole until it reaches the spar. Then find a 5/16 in. diameter long drill, or solder a short drill into a piece of tubing. Feed it into the hole slowly until it hits the spar. Then work it in and out a little to dig through the spar. The you can continue melting the hole through to the root of the wing.
If you only have one to do, you can do a pretty fair job by marking the line to follow on the surface and feeding the melter through by hand.
This will be a real pain, no matter how you do it.
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In my many years of working with foam wings, I found that piece of 1/8" piano wire heated with a blow torch is an effective tool for such jobs.
The heat allowed the severed edges to freeze back together with more strength than a cut channel.
The original writer brought up an issue that has always troubled me. That is the strength lost to the easement needed for adjustable leadouts. There just isn't any structure left to connect the top & bottom of the wing. This is true of either foam or wood wings. The only answer is to limit the easement to the range of travel you really need. And, of course, heavier construction to compensate for the lack to top-to-bottom structure.
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In my many years of working with foam wings, I found that piece of 1/8" piano wire heated with a blow torch is an effective tool for such jobs.
The heat allowed the severed edges to freeze back together with more strength than a cut channel.
The original writer brought up an issue that has always troubled me. That is the strength lost to the easement needed for adjustable leadouts. There just isn't any structure left to connect the top & bottom of the wing. This is true of either foam or wood wings. The only answer is to limit the easement to the range of travel you really need. And, of course, heavier construction to compensate for the lack to top-to-bottom structure.
Fortunately, at the tips, the load is also nearly nothing.
Brett
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Fortunately, at the tips, the load is also nearly nothing.
Unless you cartwheel on landing. Which is kinda hard to accomplish with CL.
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Dwayne might just be referencing the foam spars that are in a triple cored wing to support the airfoil. The front foam spar can easily be relieved at the tip end of the core to allow the front leadout to swing rearward enough to get the desired adjustment without hitting the spar. It is wise to not relieve the foam spar too much (distance in from the tip of the core...), as it might cause the end of the wing to collapse in over time. Use a rat tail file to relieve the foam spar, and make an angled "channel" to allow front leadout movement as required..
I try to design my wings to place that foam spar aft enough to avoid having to relieve the spar too much.
Sorry if I misinterpreted your needs Dwayne...
Bob Hunt
Thanks Bob you nailed it. I should have updated as I also got a helpful PM from someone as well, thanks everyone, I'll be using a hacksaw blade or file to make a "channel"
Thanks again. y1 ~> ;D