Once the mold is prepared and painted, I drew the cut
lines. I have to admit that I'm not enough an artist to design
my own look, so I copied on one of the most beautiful CH601 cowlings I've
Note: I learned from Fredy
Hostettler, a CH-701 builder that this cowling was designed by Roland
Aircraft in Germany.
So, here is what it should look like in my case... if I knew I had
enough cooling air, I'd make the fiberglass shark teeth in the mouth :-)
Next step is to prepare the plug for de-molding. There are
various ways of doing this and it was tough for me to make up my
mind. The common approach is to wax a female mold three or four
times, then apply several layers of PVA (Poly-Vinyl Alcohol, or something
like that) and then put the gel coat. BUT I don't have a female
mold, so no Gel Coat. The shop where I bought my fiberglass material
also told me that I don't need the wax (since I have no mold to
preserve). They advised me to seal the mold (with a latex primer),
paint it with any paint and then, apply at least three layers of PVA.
I applied three layers of PVA using a paint gun.
Here is something that made me scratch my head for a while.
Again, there are various ways of laying up fiberglass material:
. Build lay-ups directly on the mold; Sounds simple to me, but
apparently, the complexity is in not creating a total mess in the
workshop. Also, it may be hard to remove the air bubbles.
. Build the lay-ups on a plastic sheet on a table and then transpose it
to the plug. With this approach, we put a plastic sheet large enough
so it can be closed on the lay-ups on a table. We install the
several plies of fiberglass material and then, put the Epoxy resin on with
a carton. After this is done, close the plastic sheet on top of the
lay-ups, and use a squeegee to remove the extra-epoxy and all the air
bubbles. The epoxy can be recuperated in a can for re-use (within 25
minutes). Finally, apply the lay-ups on the aircraft part and take
off and discard the plastic cover.
I decided to lay up the fiberglass directly on the plug. One
reason is that a friend who built a Dragon Fly told me that the lay-ups
may not hold well under the cowling. I pre-cut cloth pieces for four
layers of the top and side parts. I also prepared a fifth layer for
the top. I then cut all the scrap material into rectangular shapes
of three dimensions. The reason I had so much of the scrap material
was that following advise from everybody, I cut the cloth at a 45 degree
angle. I forgot to mention that I'm using 6oz fiberglass cloth that
I purchased at a local body shop material store. I bought 12 yards
of 60 inch wide material.
The pictures above do not show the complete mess we created in the
garage. While I prepared everything so we can work in an organized
manner (my neighbor was helping me), it soon degraded to something that
can't easily be described. We started to mix Epoxy at 10h30 in
the morning and we put the last piece of cloth on at approximately 15h30
(no lunch). I would say that we wasted a bit more than 1/4 of a
gallon of Epoxy due to its pot life. The store told me that I could
expect a pot life of 25 minutes, but we were getting between 15 and 20
minutes. That means we'd better go fast when we start. And the
pot seems to "turn" or to run out always when it's not the best
time (in the middle of laying up a piece).
Talking about "turning", what I mean is that there is an
Exothermic reaction happening in the Epoxy about 15 minutes after
mixing. The glue becomes quite hot and then, at a certain time, it's
gonna solidify... pouf! If the brush happens to be in the container
at that time, it will stay right there. I lost three brushes like
that. I think temperature and humidity will affect behavior of the
Epoxy. (I did this on a rainy and humid day).
After 42 hours, the surface was still "sticky". I call
a friend who worked for a kitplane manufacturing company and he told me I
may have either badly mixed the Epoxy or something else that I don't
remember now. He suggested that I install heating lamps to help the
Epoxy to cure. Not being entirely satisfied with the explanation
(the Epoxy worked well on a smaller test part and I'm sure that we
respected the mix ratio), I called the shop where I purchased it (they
also make that Epoxy). They told me that there is a wax in the
Epoxy and it may have raised to the top during the curing process.
They advised me to clean the part using a mix of water and vinegar.
I tried that and for sure it resolved the problem. My friend told me
that wax is normally a component of Polyester resin, but not Epoxy.
De-molding the cowling
Before releasing the cowling from the mold (OK not releasing, but
rather pulling or extracting), I cut the split line and drilled some holes
in the front flange so I could position the two halves exactly in the same
The PVA did not really work well. The problem was that the joint
compound would separate before the PVA would release from the
fiberglass. When removing the stuff in there, I found that the PVA
was too thin to have enough strength to pull it away. If I'd do
another cowling (which I really hope I never have to do again), I'd
certainly put three more layers of PVA and I would consider to put wax on
the plug before putting the PVA (but I'm not sure about that last point).
Seeing my plug being destroyed gave me a certain feeling... after all,
I spent three weeks working on it and it's been destroyed in less than an