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Old Mar 29, 2013, 04:43 PM
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United States, MN, St Paul
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Wing Ribs with only sheeting for TE???

I'm laying out the parts of my 1st build a RCM 1/2a Basic Trainer, and am noticing some differences between the kit I ordered and the plans I found on Outerzone http://www.outerzone.co.uk/plan_details.asp?ID=3030

The one that has me most concerned at the moment is wing ribs. The plans show the outer ribs (W2) with a blunt aft to accept a trailing edge wedge. The kit I received has the same ribs tapered to a point with a notch in the top and bottom for a 1/16th inch sheet skin(?).

The plans and article I have make no mention of the change and I'm not quite sure how to proceed. Should I just sheet the trailing edge with 1/16" balsa (or Plywood)? Or is there something that I'm missing here?
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Old Mar 29, 2013, 04:51 PM
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Toronto (Don Mills), Canada
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1/16 sheet top and bottom is fine for the TE, it is a very common method of making them.

They probably changed it because they did not want to provide the special trailing edge stock.

You should pre-taper the back end where the two sheets meet.

Are you doing it electric, or glow?

Pat MacKenzie
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Old Mar 29, 2013, 06:32 PM
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United States, KY, Taylorsville
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Sheeting the TE would be lighter but slightly more difficult. You can always cut the ends of the ribs to match pre-made TE stock.
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Old Mar 29, 2013, 06:45 PM
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United States, MN, St Paul
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Quote:
Originally Posted by pmackenzie View Post
1/16 sheet top and bottom is fine for the TE, it is a very common method of making them.

They probably changed it because they did not want to provide the special trailing edge stock.

You should pre-taper the back end where the two sheets meet.

Are you doing it electric, or glow?

Pat MacKenzie
Thanks for the response Pat,

What do you mean by pre-taper? I understand that you are talking about where the two sheets meet but I'm not sure how to put them together. Any suggestions are more than welcome. Should I use Balsa or ply?


I'm going to try to run it with a cox 049 reed w/ throttle (not sure which version yet). and if that doesn't get it off the ground I'll figure it out at that point .
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Old Mar 29, 2013, 06:58 PM
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Definitely use balsa, plywood will be too heavy.

Taper was perhaps the wrong word, bevel would have been better.

Normally the ribs are a bit shorter than the chord. If you simply glue the ribs to the bottom sheet then try to glue on the top sheet it will not sit properly. By putting a small bevel in the back behind the ends of the ribs it can sit much better when you glue on the top piece.

There is a picture of a bevelled trailing edge here:
http://www.skybench.com/wf-xf_buildi...tructions.html

Second picture.
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Old Mar 29, 2013, 08:55 PM
Jim C Patrick
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Shenandoah County
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If the sheeting is very thin, like 1/64" veneer, then beveling isn't needed. But if you have 1/16" or 3/32" sheeting you want to bevel one of the sheets to fit onto the other so you don't end up with a 1/8" thick (or thicker) trailing edge.

You still need to have some thickness on an all-balsa TE or it will break and be ragged. Some people taper the TE to a sharp edge, then run some thin CA glue on it to harden it up. Maybe this photo makes it clearer
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Old Mar 29, 2013, 09:04 PM
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FWIW, I prefer to bevel both sheets, so the glue seam ends up splitting the trailling edge. Easier to sand for covering.
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Old Mar 29, 2013, 11:23 PM
B for Bruce
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The 'Wack, BC, Canada
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Pat's method shown in the last post is ideal. But it requires a shade more skill than the other option.

My own choice, because I tend towards skillful laziness, is to lay up the wing on the building board with the trailing edge right at the edge. Then once the lower parts and ribs are in place I can sand the bevel into the lower TE piece so the angle matches the ribs. Only then would I glue the upper TE sheet piece into place.

This is sort of like what Pat showed in his first post but I find it easier to match the angle of the ribs than to pre-shape the upper portion's bevel out in the open.
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