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- Grahame
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!
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!
