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Building from plans - wing ribs?

Advice on how best to cut ribs etc from plans

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John Bisset15/07/2019 12:01:04
140 forum posts

Hi again all.

Having got some repairs/rebuilds done and long stalled kit builds re-started, I'm thinking ahead about a build for later this year. I have quite a few plans 'in stock', some from many moons ago.

I have no great difficulty building fuselages, usually, but wing ribs can cause some headaches. What do you experts do?

For non tapered wings I have used hardboard templates with balsa sandwiched between to cut a number of ribs at once, reasonably successfully. Tapered ribs are harder - I have tried stencilling the rib shapes onto sheet without much success. Any suggestions? All advice welcome to a fumble fingers...

Cheers,

John B

Alan Gorham_15/07/2019 12:18:45
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868 forum posts
95 photos

I use carbon paper between the plan and the balsa sheet.

With a fresh blade in the scalpel I lightly trace the outline of the rib with the blade. No need to break the paper. This gives a neat and accurate outline of the rib on the wood.

I buy the carbon paper in A3 and A4 sizes from ebay.

Here's a pic of my PSS Hurricane built using the exact method above:

pict2929.jpg

Nigel R15/07/2019 13:22:17
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2935 forum posts
470 photos

I don't really like the sandwich method.

So I completely ignore the wing section on the plan and instead use a wing design program (DevWing), I can tell the program the root size, tip size, rib positions, spar position, LE/TE and all that, and get a very accurate set of templates, to stick direct to the wood, for each rib.

It seems to take about as long to do it that way as it does to do the sandwich method.

John Bisset15/07/2019 13:24:35
140 forum posts

Thanks Alan - a great idea.

Why didn't I think of that? I have some carbon paper filed away from the days of typewriters - now where did I put it?!...

Good to hear it can still be found.

Interesting Hurricane build - one of my favourite aircraft

 

Edited By John Bisset on 15/07/2019 13:25:59

Peter Miller15/07/2019 13:53:26
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10016 forum posts
1185 photos
10 articles

I make a 1/16" ply pattern with a strip of 1/4"sq balsa as a grip. insert two map pins so the protrude abou 1/1^2 through the ply and then cut round this to cut out all the ribs.

Usually one can cut all the ribs the same and then modify individual ribs to suit the odd ones.

For tapered and elliptical wings I use Compufoil which is a superb wing design program.

One dodge if a computer program is not available is to take the basic outline of the rib and use a zoom photocopier reducing the size of each rib the required amount each time.

Take a little time with a calculatorto get the required figure for each step.

Then mark the spar slots on each rib

However any decent plan of a tapered wing should show each rib

Engine Doctor15/07/2019 15:55:12
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2254 forum posts
24 photos
Posted by John Bisset on 15/07/2019 13:24:35:

Thanks Alan - a great idea.

Why didn't I think of that? I have some carbon paper filed away from the days of typewriters - now where did I put it?!...

Good to hear it can still be found.

Interesting Hurricane build - one of my favourite aircraft

Edited By John Bisset on 15/07/2019 13:25:59

A bit off topic but I showed my grandson some carbon paper and how to use it he thought it was a great idea ! Some of the old gadgets are still useful.

You can also try getting a second copy of the plan and use it to either prick through the plan with a pin onto the balsa or stick the plan to balsa with low tack adhesive spray and just cut it out.. Good luck and enjoy the build.

John Bisset15/07/2019 19:21:06
140 forum posts

I will indeed enjoy myself. Am tempted to also work up ribs for a built up wing Wot4. I have had several Wots and have often wondered how much lighter a built wing would be, for even better slow flying. Something I'd like to add flaps to, or maybe even slats if I can work out a way to slide them in and out in the style of a Rallye. Possibly fixed slats first...

Rootling through my stock of woods, I found some offcut pieces of material used in some kits a few years back. It is a balsa core with a ply skin either side, around 3/16" thick. Easy to cut, quite tough. Does anyone if it is still made, and what it is called?

Richard Acland15/07/2019 19:53:49
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33 forum posts
27 photos

Unfortunately with some plan built models you have to do it the hard way. Like when building a Spitfire wing each rib has to be cut individually. You have to really love building to do it this way.

RichardSpitfire

i12fly15/07/2019 21:10:09
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541 forum posts
21 photos

Like Peter Miller, I make a ply template. But I don't add the grip so that I can turn the template over so that I can get the most ribs out of a sheet of balsa. Having made the ply template I then make several 'paper ribs', that way I can lay them on the balsa and work out the best arrangement to get the most ribs from the sheet. 4" wide balsa is the most efficient to reduce wastage.

Oh, and any parts left after rib cutting that are bigger than about 1" x 1/2" are kept in a shoe box for making triangular gussets or strengthening pieces. There isn't much wasted.

Don Fry15/07/2019 21:31:08
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3735 forum posts
42 photos

Respect, Richard.

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