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Bendy Balsa

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VinceC
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Bendy Balsa

Post by VinceC »

Is it just me, or has anyone else come across the phenomenon when cutting a long length of balsa from sheet, using a straight edge as a guide to the Balsa Knife, the cut length comes out with a bow in it. I usually get around the problem with a bit of force when gluing in place, but today I have a length with a ridiculous amount of bend and is unusable.

Thoughts and answers please

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mjcp
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Re: Bendy Balsa

Post by mjcp »

Yup... causes problems in many ways, both your situation and in large scale / heavy woodworking:

https://www.woodmagazine.com/materials- ... ber-stress

M
m̶j̶c̶p̶ Marc

Hanger -
Graupner (old) K-8b, Mini Solius chuck glider conversion, UMX ASK-21, HF/Czech 2m ASW27, DG808s 4m, X-models Mini-blade, Lidl glider pitcheron.

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VinceC
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Re: Bendy Balsa

Post by VinceC »

Thanks, good link.

In my present case I cut off the fixed inboard trailing edge of a foam wing to create a flap. Now there is a 15mm gap in the middle when I try to hinge it back

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Peter Balcombe
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Re: Bendy Balsa

Post by Peter Balcombe »

VinceC wrote:
19 May 2020, 16:25
Thanks, good link.

In my present case I cut off the fixed inboard trailing edge of a foam wing to create a flap. Now there is a 15mm gap in the middle when I try to hinge it back
Gosh, that’s rather a lot!! :o

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Trevor
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Re: Bendy Balsa

Post by Trevor »

Vince, I had just this problem when cutting out the aileron spars for my Petrel. I trimmed one edge straight, glued it back onto the other side of the original sheet, then cut it out again oversize. So Basically the part is now made from two pieces, joined lengthwise. This makes it a lot more stable, rather like laminating.

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terry white
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Re: Bendy Balsa

Post by terry white »

Hi Vince, a quick and easy way to fit an aileron or flap to an alread finished wing.

After drawing out the hinge line on both the top and bottom sufaces (best way to get a perfect match is to draw the line on top surface then press pins through at the each end of the line through to bottom surface to show the exact line of the hinge), cut out a strip of the veneer and foam approx 2.5-- 3.5 either side of the marked line down through the bottom veneer to the top veneer. taking care not to go through the top veneer. With a soldering iron run it along this newly created channel just touching the foam. The foam will shrink back under the heat of the iron, the speed of run to be adjusted so that the foam shrinks back to ony about 2mm from the false trailing edge of the wing and the leading edge of the aileron/flap. When done lay onto the bottom surface of the top veneer a strip of peel-ply glass cloth which will become your hinging meadium. Now fill in the void you made with the iron with an epoxy/silicon mix to a butter like constiunancy, This will be from the site of the cut on the bottom veneer to the internal hinge line on the top veneer leaving the required 'V' to allow for the controll surface movement. When cured carfully cut through the top veneer to the peel ply to make the hinge line.This is best done with a straight edge and a small three cornered file. Finaly cut into the wing from the trailing edge to the hinge line to release the new flying surface.

The advantage of doing it this way is that you do not ever seperate the aileron/ flap from the wing and then having to make good with balsa and match back the two surfaces as you have done. You will never have a better hinge medium then that created by the peel ply whch is what is used on an all glass wing. and if the wing is completly finished before you have decided to fit aileron or flaps very little damage will be done to the top surface of the wing. If you finish the bottom surface with a cover strip of mylar very little making good will be needed here as well.
Hope this helps, I have spelt it out somewhat for the new to modelling guys,I never mean to tell anyone how to suck eggs. I have some peel ply for those who wish to try it. I just need a return stamped envelope to send it back in. Regards Terry.

Nigel Argall
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Re: Bendy Balsa

Post by Nigel Argall »

Terry - I found your description really interesting as I'm hoping to maybe do some glass wings one day with 'live hinges' but... my brain started to struggle about half way through - any chance of a diagram??! Some of us will find that easier to interpret than words but thanks again for such a comprehensive description of a technique that obviously works for you!

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terry white
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Re: Bendy Balsa

Post by terry white »

High Nigel, The technique is very easy, takes me much longer to say it then do it.I have rectro-fitted this to many of my flying friends models\when they have either decided that they shoud have fitted flaps but were in a rush to get their creation in the air and didn't,Or they wished that the aileron authority was better so longer ailerons were called for.
I am very capable of drawing a number of diagrams to highlight my discription,however getting them onto the computer then into SSUK would be another matter. Leave it with me and if there is enough interest I will manage it some how. Best of luck with your up and comming project. Dont forget I have the hinging peel ply material should you want some.
Regards Terry.

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