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Author Topic: Getting Balsa outlines flat with Boron?  (Read 425 times)
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Rossclements
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« on: October 25, 2017, 01:52:16 PM »

As I built my first F1D and subsequent surfaces, I am finding that once the outlines have Boron on them that they warp, both forward and aft between each rib. There is always a more gradual warp up and down too. These make the surfaces look terrible and must have an affect on the models drag. I try to keep the leading and trailing edges of wings and outlines of stabs as straight as possible during building, It is only when I add boron they go bad. I have been able to correct extreme bends and warps by removing the Boron and re-gluing it again, but it is still not perfect. Seeing the models at Lakehurst showed that I have a long way to go to having nice models!
I am using full strength duco (and sometimes a drop or two of acetone) in a Harlan glue pot, and using Acetone to stick the Boron down to the completed outline.
What am I doing wrong?

Thanks!
Ross Clements
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Tapio Linkosalo
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« Reply #1 on: October 25, 2017, 11:40:42 PM »


Add the boron under (constant) tension before constructing the outlines. I build on a glass plate over the tabletop, take a steel ruler to the table and set the spar next to the ruler. Then I glue the boron to a small piece of balsa glued to the table, and glue a thread to the other end of the boron. Attached to the thread is a small weight, which I hand over the end of the table. This thread and weight pulls the boron straight and under tension, and they are placed so that the boron lies over the center of the spar. Now I use acetone to melt the glue and attach boron to the spar. Once set, I turn it over and do the other side.

The tension keeps the boron straight and avoids warps to and fro. But most of all, the tension of the boron is the same, top and bottom, which avoids warps up and down.
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Rossclements
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« Reply #2 on: October 26, 2017, 12:27:30 PM »

Right now I am flying Kangs' Salt Jr, I was not sure if the boron would delaminate when it is curved. I need to build new flying surfaces anyway so I will try it out.

Thanks!
Ross
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ram
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« Reply #3 on: October 26, 2017, 12:47:55 PM »

Ross,

I am sure you have already seen this excellent and comprehensive article on the NFFS website:

https://thef1dblog.wordpress.com/2016/09/09/f1d-how-to/

If you click through to the F1D Construction article...see page 11 for a tutorial on boron and spars.  It even explains how to straighten the spars after adding boron (but before using in your wing assembly).  In the few times I have used the method in the article to build the spars I haven't had any curvature issues.  I think having enough patience to wait at least an hour before removing the spars from between the brass strips helps.  I left mine overnight and had no problems.  Duco tends to keep shrinking for a while, even after it appears dry, so the longer you can keep them in the jig the better.

Rey
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Indoorfly
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« Reply #4 on: November 04, 2017, 11:36:10 PM »

Ross
Here is my Facebook post on this

Someone told me recently that his spars with boron not always come out straight. I promised to post some pictures next time making them. It's a classical way to attach boron. Two things to look at - first, make sure your part is always straight in all the directions, second - use constant tension on the filament. I use a set of 1/2" x 18" rulers and jam spars between them. Loading with a few 5/8" nuts on top. For tension I use 20 g weight (calibration weight from digital scale). Yes, you can't really stretch boron with 20g weight. But it helps to keep it straight. Flat table and weight will keep spar straight in vertical direction. We need attach boron straight and through the middle of a spar to avoid waving in the horizontal direction. If you don't know what the boron is or don't use it - please continue to do so. Unless you absolutely have to
https://goo.gl/photos/QBGzzTkC3qLvjWMe7
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