I'm rebuilding an arf and am looking for balsa stringers. I have found the 1/4 x 1/4 stringers but am having difficulty finding the "triangle stringers". I orginally thougt the triangle stringers were just 45 degree angle but there not, the angle is more acute. The cross section is more like a 45% stringer ripped in half lenghwise. So the angle of the pices might be 27% or so.

Kind of hard to describe in words

The reason I'm posting this on the building site, is I'm hoping you guys that build kits would have a good idea of where one could find the balsa stringers.

Thanks!

Do you have trailing edge stock?, use a balsa stripper and rip the width you need, just an idea, always think outside the box or is that fuselage?

What is the triangle stock being used for? If it's just for strengthing a corner joint you could use any piece of triangle stock. If it's gotta be that unusual shape you'll either have to shape one by hand or change the part it mates to.

A balsa plane would make quick work of taking a piece of triangle stock down to the profile you need. Or as Planebuilder said, cut it from aileron or trailing edge stock.

Dave

I have only seen one of the Tristock stringers on an ARF. It took be a bit by susprise, but it made sense. I thought that they were 45-45-90 angles with the 90 down and flat side out. Given the way they build though it would make sense for the stock to be 60-60-60 as which ever side they put down in the grove would be correct. I don't remember which guy at the field had that plane, so I can't check. Do a bit of simple trig. Measure each side. With that info, there is only one answer to the angles.

Don

Ok, it is 60-60-60. The stringers are used for the fuse - with a 1/16" balsa sheeting over the stringers.

I have included some pics.

So does anyone have any ideas where one could find this type of balsa stringers?

Thanks.

That's one heck of a non-standard shape. If it was me, I'd add a doubler to the former and recut the notches for a standard square stock stringer.

Dave

I agree with you dbacque. Just make the triangle slots the same as the square slots on the formers, and resheet with the 1/16th. Probably will make the fuse stronger besides. I have not seen this triangler wood used for stringers before, and cannot think of a reason for doing so. Most of my repair use of triangler wood has been to strenghten fuse sides and bottom sheeting when the glue line between the two are loose, or weak.

Let us know how the repair works out, and a view when the stringers are installed.

Rich S.

The reason is that you get more pcs out of your stock using equilateral triangles instead of squares. In a sample I laid out I got 9 pcs instead of 5 pcs. It is also easier to cut trianglular groves than square notches in your formers. Leave it to the Chinese to cut costs.

Not only the cost, but they are lighter than square stock.

Don

what say "modelling theory" about triangular stringers? Do they weaken former comparing to square?
in fact making them by splitting square strips is not difficult.

Kostya

It stands to reason that that they will not be a strong as a square stringer with dementions the same as one surface of the tri stringer. There will be about 60% ( a guess as I didn't calculate it but guessed) of the cross section area compaired to a square stick. What it may do though is let you use a harder and stronger wood with no increase in weight.

From the photo, they are not a 90-45-45 shape, but closer to a 60-60-60. That will complicate things a bit. However cutting them from a sheet would be quite easy, setup you blade at 60 degrees and make a length wise cut, flip the sheet over and make you next, flip and cut until you are done. It would take two cuts on square stock with scrap on both cuts.

Don

It stands to reason that that they will not be a strong as a square stringer with dementions the same as one surface of the tri stringer. There will be about 60% ( a guess as I didn't calculate it but guessed) of the cross section area compaired to a square stick. What it may do though is let you use a harder and stronger wood with no increase in weight.

From the photo, they are not a 90-45-45 shape, but closer to a 60-60-60. That will complicate things a bit. However cutting them from a sheet would be quite easy, setup you blade at 60 degrees and make a length wise cut, flip the sheet over and make you next, flip and cut until you are done. It would take two cuts on square stock with scrap on both cuts.

Don