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Covering Undercambered aerofoils?

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Old 10-10-2006, 05:23 PM
  #1
Airwarrior
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Default Covering Undercambered aerofoils?

Hello,

I am about ready to cover a Bleriot XI that I recently scratch built. However, covering the wings has got me questioning my sanity. How can I do it? I have no experience with silk and dope, nor any other means of applying covering that is not heat shrink. Does anybody have a link to a How-to, or can explain how?


Thanks!
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Old 10-10-2006, 06:13 PM
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Default RE: Covering Undercambered aerofoils?

I covered my SE5a with antique coverite. My ribs were also undercambered. I put an additional coating of balsa rite (it's a heat activated glue sold by coverite) on the underside of the ribs to insure the covering would stay put. So far it has.
You need to iron the covering onto each rib. Don't use a heat gun as this will pull the covering off the ribs. Just go slow and take your time and it'll work out for you.
Here's a picture of the finished plane.
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Old 10-10-2006, 06:41 PM
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Default RE: Covering Undercambered aerofoils?

You can cover the bottom of the wing first, and use silk thread and rib stitch the covering to the ribs. Talk about scale!!!

Bill, AMa 4720
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Old 10-10-2006, 07:03 PM
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Default RE: Covering Undercambered aerofoils?

You can stitch after covering both top and bottom using what I believe is a scale British method - all the way through the wing, completely around the rib. Avoids having to stitch the capstrip under the covering and use curved needles for the fabric. I'm using that approach on my Pfalz to secure coverite, using a saw tooth stitch (which is German, but normally would only go around the cap strip). I premark the entry and exit points. It takes time but isn't hard. Really anchors the fabric! But Balsa Rite should be enough if you don't want to go to the trouble.
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Old 10-11-2006, 09:17 AM
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Default RE: Covering Undercambered aerofoils?

Before you get too far, it would be well worth your while to read this. It covers how to undercambered wings.

https://www.modelaircraft.org/Member...ge_article.htm

Les
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Old 10-11-2006, 09:42 AM
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Default RE: Covering Undercambered aerofoils?

It won't let me read that page, it says something about an error. Maybe you can tell me the date of that issue? I can look for that date in the database...


Thanks!
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Old 10-11-2006, 05:16 PM
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Default RE: Covering Undercambered aerofoils?

BobH's work is some of the best I've seen. Go with his idea by all means. Just check out his treads on www.rcscalebuilder.com and you'll see what I mean.
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Old 10-11-2006, 07:44 PM
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Default RE: Covering Undercambered aerofoils?

Mike Thank you for the kind words..
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Old 10-11-2006, 07:56 PM
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Default RE: Covering Undercambered aerofoils?

Hi

Last spring I finished a WW1 1/4 scale Albatros DVA from Jim Pepino plans. Previously I have used the F&M St*ts covering process so I was comfortable with it. Like you I was worried about the undercambered wing. This is what I did as a datapoint.

1. Wing covering
I was concerned about the undercambered wing as it has been a long time since covering an A1 Towline glider with silk and dope. Fortunately the ribs on the bottom are cap stripped so there was some surface to apply the covering to. I spoke with Chip at F&M and he suggested the following:
a. Apply three coats of POLYTAK with a little bit of MEK to each of the ribs and let it dry.
b. Carefully apply the F&M covering material and get out as many wrinkles as possible. Attach the covering to the outside edges as is usual. Use one coat POLYTAK adhesive on the ribs to attach the covering to the bottom of the wing.
c. Stretch the covering over the top and apply to the edges of the wing as usual.
d. Then heat shrink the covering on the bottom of the wing to no more then 250 degrees to prevent the covering from “popping” off the ribs. On the topside can get up to the usual 300 > 350 degrees.
This seemed to work out fairly well. So far have had no problems. I then applied POLYBRUSH and POLYSPRAY per the usual F&M process. The video they offer is good.

2. Pinking tapes and rib stitching
Wanted to try some sort of pinking tape/rib stitch detail on this plane but it is fairly large so tried to keep it simple. From looking at the pictures from the NASM book the pinking tapes/rib stitching is actually sort of subdued. Does not stand out a lot. Decided to do the glue dot process for the stitches. What I did was:
a. First cut lengths of Super Coverite the width I wanted. Used a piece of Plexiglas to cut them on using a metal ruler and a scalpel.
b. Applied the first coat of POLYBRUSH to the F&M covering.
c. Applied the Super Coverite strips to the F&M Polyester covering with a covering iron set to just hot enough to activate the Super Coverite adhesive.
d. Then applied a coat of POLYBRUSH using a small stiff brush to the edges of the tapes to help then adhere to the surface.
e. Applied the “rib stitches” using a small “T” pin and RC-56 glue to get a horizontal “stitch” This seemed to take forever.
f. Sprayed on the second coat of POLYBRUSH.
g. After the second coat of POLYBRUSH I sprayed the wings, ailerons, rudder and elevators with a coat of POLYSPRAY and lightly sanded that down with 400 grit sandpaper. Then applied a final light coat of POLYSPRAY around the edges to get a fairly smooth surface for the paint.
The rib stitches look OK to me even though they are not under the pinking strips. Next time I would try to keep the glue dots a bit smaller. Or may try putting the tape over the glue dots.


Good luck

Ray
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Old 10-11-2006, 11:44 PM
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Default RE: Covering Undercambered aerofoils?


Bob, that really looks like a full scale aircraft - sure you're not pulling our legs here?! Great work!
(formerly from Ashburn, VA)

Where do you fly?
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Old 10-12-2006, 06:39 AM
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Default RE: Covering Undercambered aerofoils?

That's my model, honest! And thank you.
I fly with NVRC but we lost our field this spring. Hence we don't have a field per se so I've been flying at PGRC. An excellent field.
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Old 10-12-2006, 09:23 AM
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LesUyeda
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Default RE: Covering Undercambered aerofoils?

Airwarrior. It is in October 1993. An article worth printing and keeping.

Les
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Old 10-12-2006, 09:44 AM
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Default RE: Covering Undercambered aerofoils?

Thanks!

I think I'll try something other than silk though, that is a bit too translucent for me...

This is the best Idea I have come up with so far. I'll use white or antique solartex, or any other kind of heat shrink fabric it doesn't really matter. Then I tack it down to the ribs on the top mand bottom with just enough heat to hold it down, but not enough to make it pull off the ribs. Then, using some thread I'll stitch the covering onto the ribs. After that, I'll go back over the wing surface with a covering Iron pulling it tight allong the front and fuselage quarter, leaving the trailing edge on the side away from the plane loose enough to not restrict the wing warping. After this is done I'll apply strips over top of the rib stiches to form rib tape. I may even apply a rib tape before the stitching to to add extra strength. After all of this is done I will weather the sides using paint and different wood stains, maybe a wash of heavily thinned stain in normally fuel soaked areas. Then I will seal it with some sort of flat coat.


Do you think this will work?
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Old 10-12-2006, 10:17 AM
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Default RE: Covering Undercambered aerofoils?

I use Solartex and place several magazines either side of the rib to hold the material down on the undercamber while I tack. Then move on to the next rib. Never had a problem.

Bud
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Old 10-12-2006, 10:16 PM
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Default RE: Covering Undercambered aerofoils?

That sounds like it will work. I've used the method Bobh describes, coating the rib with balsarite and then attaching the fabric. The first model I did that way is now four or five years old and the fabric is still attached to all the ribs...I used Nelson Litefab, natural color. One other suggestion...use a trim iron to tack the material to the ribs, that way you won't heat the areas between the ribs and cause unneeded shrinking...

We'd love to see pictures of your progress....

Randy
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Old 10-13-2006, 09:12 AM
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Default RE: Covering Undercambered aerofoils?

Randy, thanks for adding the trim iron idea. That's something I forgot to mention.
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Old 10-13-2006, 09:42 AM
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Default RE: Covering Undercambered aerofoils?

You beat me to it, Randy. Trim iron really does do a great job, and you'll appreciate it even more if you've done the job a few times without it. Bud, I like the idea about laying magazines down on either side of the rib, will be sure to try that![8D]

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Old 10-13-2006, 10:02 AM
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Default RE: Covering Undercambered aerofoils?

It does work good John, model aviation mag. works great if you have a few laying around.
How's the eindecker? Get it back in shape?

I forgot to mention I work from the center of the rib out like you didn't know that already.
Bud
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Old 10-14-2006, 01:37 PM
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Default RE: Covering Undercambered aerofoils?

The E-III is no more... I did get 25 or so flights on it first, as least. It went FF in round 4 of our qualifier, shot down.

Airwarrior, follow these tips and you'll be fine. Like Bud sez, work from the inside out. Tack the middle of a rib, work to the le and te, pull fabric a little and repeat on next rib, etc. Bond the fabric thoroughly to each rib. Fun once you've done a few bays.

Bond LE and TE last, apply top fabric as usual and seal, THEN shrink it up. I shrink a few bays on the bottom, then the top, etc. Use iron only to control where the heat is applied(stay off of the undercambered ribs!!), as others have mentioned. Good luck!

John
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