I just received my Mk II Chrysalis. It looks great so far. Is it acceptable to use "white glue" (alphatic type) on the glass tape instead of epoxy?

I try to stay away from epoxy as much as possible. I used white glue on glass tape before on a powered model and it seemed to work fine. However, I'm don't know if the white glue tape is as strong as using epoxy.

From : Don Stackhouse

I can appreciate your concerns about the toxicity of epoxy. I do not have an epoxy allergy, but I have a number of friends who have had that unpleasant experience, including Joe. It's not something you would wish on your worst enemy. However, the 5, 15 and 30 minute epoxies commonly sold in hobby shops do not seem to be nearly as bad as the industrial laminating resins in this regard.

White glue is not as strong as epoxy, and its bond strength to the glass fibers (particularly the straps of S-glass unidirectional material that reinforce the spar caps across the center section), as well as its ability to soak completely through to the fibers in the middle of the tape, may be a problem. The coatings on the fibers that help create the bond between the fibers and the matrix material were designed to work with epoxy, not white glue Your power models were most likely overbuilt in those areas and didn't really rely on the fiberglass for much help. You can probably get away with it on the polyhedral breaks and the straps on the fuselage. However, if you absolutely can't use slow epoxy for the reinforcements at the wing center section, then fast cyanoacrylate is probably a better alternative; at least you can be reasonably sure it will completely penetrate the entire thickness of the tape, and will cure all the way through.

Why do you call for glass tape at various spots around the fuselage? I don't see much gain in doing this, but it does add a lot more work--to make it smooth.

If you wet out the tapes on a flat surface so you can squeegee out all the excess resin before placing the tape on the fuselage, it will help make the layer smoother and easier to finish. Another trick that works with epoxy, although not with white glue or cyano, is to put the epoxy-saturated tape in place, then smoothly and evenly wrap the joint with masking tape. For example, on the wing center section, put all the glass tapes in place, then start spiral-wrapping the center section with chord-wise wraps of masking tape, overlapping the wraps about 1/8" to 1/4", starting on dry wood just to one side of the joint, spiral-wrapping right across the epoxy-wetted glass tapes and onto the dry wood on the other side of the center section. As you're wrapping, wipe off any excess resin that's squeezed out by the masking tape.

The tape will act like a vacuum bag, keeping pressure on the reinforcement while it cures so it lays flat on the surface, and doesn't soak up air bubbles. Let the epoxy cure completely (if you try to take it off too soon, the masking tape will stick and tear and make an ugly mess). Once the epoxy is completely hard (not just rubbery) you should be able to unwrap the masking tape reasonably easily. The epoxy underneath will have a slightly rough surface (essentially a copy of the surface of the masking tape), which should smooth out fairly easily with just a little sanding. Be careful not to damage the wood right beside the fiberglassed area. One way to help with that is to put some masking tape (or better yet, polyethylene tape) over the wood while you're doing most of the sanding of the fiberglass, then peel it off for the final light blending around the edges of the reinforced areas.

The reinforcements on the fuselage are there for a variety of reasons. They were added after the plane had originally been developed, in response to things we saw happening in service. The straps around the tail section help reduce splitting in that area. The strap just ahead of the tail leading edge helps distribute and even-out the bending loads in that area, reducing the problems caused by the natural stress concentration caused by the structural discontinuity created by the tail.

In the nose, we found that in a "dork" landing there are stresses that tend to burst the nose open, particularly at the top, ahead of the corners of the hatch.The straps around the nose, particularly the one just ahead of the hatch, increase the hoop strength and help eliminate the problem. Also, the load path from the skid plate on the belly, and from the nose block, into the plywood doublers (which do most of the structural work in the forward part of the fuselage) needed some help. The strap around the nose at F1 accomplishes this, in addition to helping with the hoop stress issues.

Don Stackhouse
DJ Aerotech