ETLB Squawk Forums — Archive

when you covered the fuselage: did you and how, did you cover the front part that is skinned with plywood? I am using the stewart system. did you cover all the plywood with glue or just the couple of inches at the corners?

According to the stewart systems video , you glue the edges, shrink the fabric and then brush glue through the fabric into the ply

https://www.youtube.com/watch?v=75fgJF5HZvk

I did not cover the front fuselage-ply with fabric. Just coated with ekofill as prime-coat, and painted over   with latex paint.

Not suggesting it is the right approach, but I didn't cover it anyway. Since then I am left wondering whether there has been a trade-off in structural strength of my Max's front fuselage, (though indications are the fabric covering does not add to strength of structure.)

Ekofill ( or Ekoprime can also be used as primer on the ply,) protects the ply from uv, in addition to uv protection provided by the latex top coats. Big Box store paint primer may also work just fine, but I had some ekofill left over from wing and empennage fabric work.

https://stewartsystems.aero/product/ekoprime/

The minimax stress analysis (which was done on the original "1984" version I think) shows the safety factor of the forward ply box fuselage at greater than 10x (see page 19 of attached analysis) so the absence of fabric there should not be a structural problem.

I think many methods of covering would work fine but that is a large area of glue surface.  IIRC I put glue on the entire surface and glued down the edges and the "low spot" (the concave area created by the "buckling" of the ply when pulling the fuselage sides inward toward each other) then shrunk it a bit and then activated the rest of the surface area by brushing MEK or acetone through the fabric.  It is easy to get "lumpy" glue under the fabric on this large surface area and thinning the glue and being conservative on the amount applied is probably a good idea.  Perhaps it would even work fine to not apply any glue before the fabric (except around the edges) and simply brush a thinned coat or two on afterward.  

Note that if you fully shrink the fabric before gluing down the entire area you may find that it is very difficult to get the fabric to stick to the "low spot" as it will want to "bridge" across it.  

Also herein lies the question of to varnish or not under the fabric.  I think (but stand to be corrected) most recommend varnishing all the wood and not depending on the fabric and paint to protect the wood.  The varnish used depends on the covering system used. Some "activators" are reported to turn "normal" varnish into goo and require a 2 part epoxy varnish to be used on areas that will be exposed to the glue activator/thinner.

As a point of reference I used "poly tak" for glue and used acetone for a thinner/solvent/activator.  I also used "common" polyurethane varnish from wal mart (minwax, red devil, etc.) and experienced no problems with the acetone dissolving the varnish.  YMMV

In selecting varnish from wal mart or Lowe's you can usually choose a gloss or matte finish.  I first used matte because the gloss "sounded" like it would be harder to get the glue to stick to.  But then discovered that the matte is simply glossy with "flattening agents" added to it which must be stirred a lot to mix evenly in the product.  The next time I used gloss to prevent all that stirring.  Other than the stirring I found no difference in the performance of either one.  This time I'm using gloss again.

It appears the minimax stress analysis file is too large to attach.  Here attached is the relevant page 19.

Quoted from Fenix It appears the minimax stress analysis file is too large to attach.  Here attached is the relevant page 19.

Thanks for the information.

I didn't cover mine.