Molded Balsa Stressed Skin Monocoque

[W.D. Roland]

Or attempting to restore a melt down from last year.
Molded Balsa Stressed Skin Monocoque Fuselage.

Foam blocks are laminated to center line profile cut out of handy piece of paneling..
Couple of formers to guide shaping of foam. Shaped with 40 then 80grit. When close to shape stroke in one direction only to avoid peeling/tearing of foam.
Couple coats of minwax polyurethane(oil base) and then a couple coats of kit car wax.
4-6 hours to make plug.off and on day for minwax and next day wax.

The Skin is 2 layers of 1/16th around 5lb cf Balsa from Lone Star.
Edges of sheets are fitted and joined flat, rough cut over size.
First(inner) layer the grain is aligned with of fuselage(form) bottom center line and pined to the center line.
outer side of skin is whetted with paper towel, worked around form and overlapped, wrapped with masking tape and left to dry over night.
Trim to fit at overlap.(on top)
Tape seam tight, slide off of form and super glue seam.
Slid it back on form

Second(outer) skin is done same with the inner skin in place on the form WITH OUT laminating!
For the outer skin the grain centered with the TOP of form center line.
In this case the grain bias or ply measured out to around 20deg.
The bias to the grain stops grain spiting from torsion loading and results in a high strength in torsion as well as locking shape in place(cross sections)

Now trim over lap of outer skin (on bottom)and leave about 1/8th inch gap.

Thin down Tight Bond Aliphatic resin with water.
Make sure inner skin is in place on form.
Paint the Aliphatic resin resin on to outside of inner skin.
Keep a water mister handy in case it try's to thicken while the coat is evened out and dry spots tended to to get even thin coat. Also the balsa is going to absorb some amount so 2 coats might be needed.
I wound up applying to much and then wiping excess off with paper towel.
GLUE IS WEIGHT!

Make sure the resin is wet and quickly slip outer skin into place.
Work any 'slack' into the bottom 1/8th inch gap area.
Wrap with tape(ace bandage works good also)and let dry overnight.

This fuselage is tapered so it can be slid off the rear.
For other simply split inner skin through 1/8th gap and then remove and re glue.
Fit a strip of balsa to gap and glue.

IF skins stick to mold(it will) long,rounded and smooth strip of around .032 aluminum slid betewwn form and skin
very gently. just where it will go with out excess force.
Compressed air gently blown between skins and form will do most of the rest.
Rubbing and gentle pushing on skin will do the rest.

Weight upon removing from form was right at 3oz.
After a few days of drying this dropped to something under 2 ounces.(1.5 is what I seem to remember.)

1 former at the front of cockpit/T.E. of wing
Fire wall at the front, no other formers.
There is 2 vertical grained pieces(1/16th) placed inside below Stab for load transfer.

[W.D. Roland]

One picture per post it looks like.
Is there a way to remove an attachment after finding it is to big with out starting over on post?

[W.D. Roland]

Last part of first post.
The fit of skins is during forming and was more than adequate for laminating fit.

[Avaiojet]

W.D.,

Nice, I like it!!

I have something I may try this on.

Do you have a photo of what this attaches to?

Charles

[W.D. Roland]

Yes Charles.
Did you ever get the 3 line unit into the Gee Bee?

Tonight was going to post construction pics and just not up to it so here are a few finished.

[W.D. Roland]

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[W.D. Roland]

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[W.D. Roland]

Date on pics are wrong. usually to lazy to reset from default. all are from 2011.

[Larry Cunningham]

Well done. Wish I had the skill you demonstrate.

I really love laminated balsa skins, although mine haven't been so radical and I prefer epoxy over aliphatic for lamination. For a typical molded turtledeck or fuse bottom, 1/32" laminated to 1/16" balsa yields plenty of strength. Mold both sheets together first, then laminate them over the buck, which is covered in Saran Wrap.

I've carefully molded a mildly double convex belly pan over a buck, with a little patient stretching.

In the photo, I show two versions of the removable belly pan for my Special Effects stunter. In the back you can see the two bucks,  mounted on opposite sides of the same pine base. In the middle, the finished red part is the shallower original version {I went nuts on pipe vent holes}, and in the front is the unfinished deeper version, freshly off the mold. To the right you can see the puckered front end piece which was trimmed off the front.  On these parts, I also added .5 oz fiberglass on the inner surface, binding was brushed on thinned epoxy glue - I think it was overkill; the laminated part was already very rigid and the prefinish layer of medium silkspan on the external surface seems plenty adequate.

What I really CAN'T seem to do well is a molded cowl, even my simple one (last 3 photos) took me three attempts and was shaped and hollowed from glued balsa blocks. Labor intensive and I still wasn't happy with the finished product. I smeared a thin layer of JB Weld on inside to protect it. Overkill again.

I'd love to make some super accurate complex female molds and learn to lay up fiberglass, but what I'd really like to be able to do is make up bucks and piece laminates balsa sheet laminates like you are doing.

Congratulations on your fine work.

L.

"Luxury is more deadly than any foe." -Juvenal

[Avaiojet]

Yes Charles.Did you ever get the 3 line unit into the Gee Bee?Tonight was going to post construction pics and just not up to it so here are a few finished.

 W.D.,

Oh, your the guy that overcharged me for that. Just kidding. 

Funny, I was playing with it yesterday. Actually couldn't figure it out had to go to the drawing. 
You know Clancy has a system, but I will use that bellcrank on the Gee Bee Z.

Dug around for my Aero silk, but I couldn't find my dope. I think I trashed it?

I'll be pinning the ailerons permanently and installing the bellcrank sometime in 2012. 

Got other stuff on the grill.

Charles