Initial Fiberglass

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Initial Fiberglass


Mold Preparation:

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 seen:

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 :-)

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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.

Fiberglass Lay-ups:

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.  

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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 position later.  

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 hour!

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