[NSRCA-discussion] Sheeting built up wings...old school!

Tue Dec 15 05:08:50 AKST 2020

If the skeleton can twist then I would think it would be very difficult to get it straight.  Once the first skin is glued in place any twist is locked in.  A properly designed jig is the only way to be sure it stays straight.
One other option is to cut a foam core.  The outer shucks can be a very good jig.

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On Dec 15, 2020, at 9:01 AM, Richard Lewis via NSRCA-discussion <nsrca-discussion at lists.nsrca.org> wrote:

 Thanks Andre,Mark,Don, etc...

Y’all gave given me a good idea of how to proceed.  The jig Andre describes seems like a good idea.  I’ll have to mock that up and see how it looks.

I was considering doing the first skin just using the table as the flat surface.  Laying the skin good side down and pressing the TE down against it and CA’ing the TE to the skin, then rolling the wing forward onto the spar and tacking it there with CA and then rolling it up onto the false LE and gluing there.  The second skin, I could then do with Andre’s jig suggestion maybe?

I did the stab this way when I built it, but I was able to attach the second skin with just the pressure of my hand and medium CA on the skeleton.

Richard
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On Dec 14, 2020, at 8:43 PM, Andre Bouchard via NSRCA-discussion <nsrca-discussion at lists.nsrca.org> wrote:

Richard,

I have built a lot of MK kits.  If the 40-size is built like the 60-size models the sheeting will go over the trailing edge stock and a false leading edge, so those pieces should already be part of your skeleton.  You are going to need a jig.  You can make a jig out of 1”-2” wide x 1/4”-3/8” thick x 36” hard balsa sheets.  Glue the sheets width dimension vertical on a piece of glass or melamine in the shape of the wing planform.  You will need two jigs.  Draw a center-line on the false leading edge and trailing edge.  Pin the wing skeleton to the “jig” such that the center-lines are at the top edge of the balsa sheets that constitute the jig.  This keeps everything at the same height off of the work table (ie straight). There will be enough false LE and TE material below the top of the balsa sheets to pin to (pins horizontal). With enough pins you can put sufficient weight on the wing skin to hold it in place while the glue drys.  Do top or bottom sheeting on both wing halves then “flip” them in the jigs for the opposite side sheeting.

For additional support of the wing you could cut a tapered piece of wood than sits between your table and the spar, but note that the thickness of that piece will have to be adjusted once the sheeting is put on.  I do not think this is needed for the size of wing you are building.

As Don noted, sanding the wing skins should be done before putting them on the skeleton. Basically, finish ready on one side.  Make sure you keep track of which side is the finished side when gluing the skins on.

With the skeleton on the jig you should check the ribs with a straight edge along multiple chord lines.  Lightly, carefully sand if needed (likely) with a sanding bar longer than the wing panel.  You do not want to change the airfoil shape, but you want to remove the high spots.  If you find a low spot, glue a soft strip of balsa on and sand to the shape of the other ribs.  Put masking tape on the root and tip ribs to preserve the airfoil shape of the other ribs while sanding to level them.

As Mark noted, without a jig that supports the sheeting at each rib station (eg, Allure/Alchemy builders kits, FlightHobby kits, Revo built-up wings), I would not use Poly glue.  I suggest also using Titebond, put on with a hypodermic needle.  You will not need a lot of weight with an non-expandable glue.  Small pins and/or Green 3M auto tape can be used to help hold the sheeting at the LE and TE.

Regards,

Andre

On Dec 14, 2020, at 10:50 AM, Atwood, Mark via NSRCA-discussion <nsrca-discussion at lists.nsrca.org<mailto:nsrca-discussion at lists.nsrca.org>> wrote:

Regarding weighing down the top side, I’ve had very good luck using Lead Shot.   I double bag it in Large Ziplocks (trust me on the double bag… if one splits, it’s a DISASTER.)  I typically have about 10-15# in each bag and probably use upward of 100lbs when all is done.   It forms to fit the curve of the wing and holds the sheeting down nicely especially if you’re using an expanding glue like Gorilla.    If you don’t have a form, I’d probably not use Gorilla for that reason and stick with titebond.    A good piece of dense memory foam will support the underside.   Avoiding twists without building a jig though is pretty difficult and will depend a lot on how you secured the first side.

-M
MARK ATWOOD
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On Dec 14, 2020, at 9:31 AM, Don Ramsey via NSRCA-discussion <nsrca-discussion at lists.nsrca.org<mailto:nsrca-discussion at lists.nsrca.org>> wrote:

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Richard,
Maybe my last post was a little simplistic.  Here's more detail:
1.  Glue up panels that fit the skeleton.
2.  Sand the panels so at least the outside of each panel is smooth.  Do this before gluing the panel to the skeleton because the skeleton does not provide underlying support to support sanding as well as a solid structure.
3.  Glue the first side with CA or your choice of glue.  Wait for glue to dry.
4.  Glue the second side with a slow drying glue (in your case maybe poly glue) so you can fit the side easily. Weight the side to keep it the entire structure straight.
5.  Add the remaining components, LE, TE, root, tip, etc.
6.  That's it.

Don

-----Original Message-----
From: NSRCA-discussion [mailto:nsrca-discussion-bounces at lists.nsrca.org] On Behalf Of Richard Lewis via NSRCA-discussion
Sent: Sunday, December 13, 2020 9:20 PM
To: General pattern discussion
Subject: [NSRCA-discussion] Sheeting built up wings...old school!

Alright, let’s see if this list is still alive!!

I’m building a classic 40 sized MK kit.  The wings are fully sheeted.  There are no construction aids such as tabs, cradles, jigs, etc. for the wing construction.  I’ve got the wing skeleton framed up and ready to sheet.  The wing is tapered thickness and the top is flat span wise giving the wing a slight dihedral.

So the question for the builders is...What’s the best method/trick to sheeting a built up , fully sheeted wing structure?

Thanks in advance!

Richard Lewis
Sent from my mobile device.
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