Greyhead

When faced with the need for lots of wing ribs, cutting them out individually is very time consuming and boring, an easy way is the use the “sandwich method”, which involves fixing several balsa “blanks” between 2 “template” ribs made from harder material.

Most built up wings use at least 2 ply ribs, which make suitable templates, but if not, templates will have to be cut especially. At least 2 reference holes need to be incorporated; in this case I’ll use the holes for the carbon fibre spars but if you’re using “traditional” wooden spars then drill 2 holes in convenient positions. Make sure you’ve got suitable rods to fit the holes and don’t make them too small, 10swg piano wire is about the minimum, or you can use nuts / bolts which hold things nice and tight. It’s worth taking a bit of time over the templates, as any errors here will be replicated on all the balsa ribs.



If you have a pillar drill or a vertical drill stand you can drill the reference holes through a stack blanks taped together, if not it’s best to drill individually,

The blanks have 1 of the reference holes drilled and a template rib taped in position using the reference hole to line everything up, then the other hole(s) are drilled. The number of blanks that can be accommodated depends on the thickness of the balsa and the length of drill bit available, here I’ve done 16 ribs from 1/16th balsa, which is enough for one wing; don’t be tempted to try to do too many at once, the process is quick enough doing a “sensible” number of ribs, too many and the holes can “wander” even using a pillar drill.



With the other hole(s) drilled suitable rods are fed through and another template fitted to the other side.




Excess wood can be trimmed away with a razor saw and scalpel but be careful and don’t go very close to the template as it is all too easy to cut deeper than you intend.



To sand to the final shape you need a “bar sander”, if you can afford a Permagrit bar than that’s great but I use scraps of deal with various grades of glass paper attached and these work OK. I start with the very rough one until I hit the templates then finish off with the fine one.



If you sand across the ribs using long light strokes there is a definite change to the sound when you hit the ply so you know when to stop with the rough and start with the fine.

Finished sanding.



A set of finished ribs.



The riblets use one the leading edge and 1 spar hole and are made in a similar fashion.



To emphasize just how quick and easy this method is here’s a photo of the finished rib set, all of which I made today except for the 4 templates; and I still had time to spare to take the photos and write this tutorial!

Greyhead

Have just realised that in my tutorial I didn’t explain how to cut “standard” spar slots. I never use them on the sort of wings I make, scale fabric covered, but of course this method is just as useful for sports models!

When the blanks have been sanded to shape and are still held between the templates, make the vertical cuts (shown in red) with either a razor saw or junior hacksaw.



With the ribs still held between the templates the balsa “tabs” will now break off quite easily; then finish the slots with a small file to get neat corners before removing the templates.

wonwinglo

And dont you get a buzz when those pristine ribs just fall from the sanded block,I have used this method myself over the years from everything to small rubber powered model ribs to giant quarter scale creations,the system has been very well described Grahame by yourself,we sometimes take these things for granted and they are well worth sharing as you have done here.

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