prgonzalez

This weekend I created my first two-part mold of a cowl. Mold edges are not defect free. However, being my first experience, I am very happy with the result. I used the West System epoxy with multiple layers of fiberglass.

I am now ready for making up my first fiber glass cowl.

These are the questions I have:

1. Do you start the cowl by laying up the FG at each mold-half and then join the mold halves just before curing? or Do you lay up the cowl within the assembled mold?
2. Which epoxy is better for making up the cowl: West System, regular 1:1 epoxy, finishing epoxy, or poly resin?

Thanks
Pedro

jdeluyck

My Feedback: (6)

Pedro,

Here is my advice.

1. Yes, layup each half, then put togethor, add a couple strips of cloth to the seem with resin
2. Stay with the West Systems

Check out this link... [link]http://www.cstsales.com/tutorials/fiberglass_parts.pdf[/link]

dreadnaut

My Feedback: (5)

1. I do this where there is an issue getting your hand in to work on the layup, like wheel pants and fuselages. For cowls it depends on the shape of the mold. If there is enough room I do the layup in one piece. This was for a 30% Extra, and a 2m pattern plane. That last was a little tight. Smaller than that, it would be easier to do it in two pieces.

2. ditto - or another quality epoxy laminating resin.

As for the imperfections at the parting line; been there done that, and it is frustrating. It just requires more finishing of the molded part. I have reduced this to almost zero by using a product called Fiberglast 1099. (from fiberglast.com) It is an epoxy putty/surface coat. It produces a good mold surface coat. You just need to keep two things in mind. First, it cures really hard (this will take several day to reach full hardness) This makes for a good part surface, but it also becomes brittle, so you need to be careful de-molding. Second, it does not react well to heat. I used to use a heat gun to melt the parting wax onto the mold as a way of pre-seasoning it, but this produced blistering when I tried it on my first mold w/1099.

prgonzalez

Jdeluyck and dreadnut,

Thank you for your advice.

One more question: I have 5 0z fiber cloth for the cowl but it just want to stay flat as it is not much flexible. It act like it has been starched.

How do you work that out? Do you pre-wash it?

MTK

What you feel in the glass cloth is called "sizing". It is an additive coating that fiberglass and carbon cloth manufacturers use to ease the weaving of the cloth. The material is usually epoxy compatible...that is the epoxy will normally wet the material just fine, but takes a few minutes. You do not want to try to wash the material out of the cloth...it may ruin the cloth

On epoxies, West Systems is an excellent laminating epoxy. Personally I prefer Pro Set laminating epoxy which is produced by the same people that make West Systems (Gougeon Bros). I prefer the 229 hardener and 125 resin because the hardener has a 70 minute pot life and is thinner than anything else i've played with....it wets glass, kevlar or carbon extremely well. Cures rock hard. Both epoxies are a bit expensive.

Another much less expensive material that is worth mentioning is the laminating epoxy that US Composites carries. It also cures rock hard.

You do not want the epoxy glue type that is normally used at 1:1 ratio. That material is more for gluing smaller things together and is rather thick. It isn't made for laminating. You should use a laminating epoxy

dreadnaut

My Feedback: (5)

The link that jdeluyck mentioned (CST Sales) has some pretty good basic info on the technical data on FG fabric. It is also where I get most of my fabric from. If you are getting your fabric from the home improvement, or auto-parts store, you can do much better. The stuff that Hobbico sells through the LHS's is a little better, and is probably good enough for what you are doing. In the future you may want to order small batches of the different types of fabric to see how they perform. From my experience;

-Super light like 0.5 to 1.5 oz are good for reducing "print through", that is the fabric weave showing through on the finished part. The problem is that it can be very difficult to work with I have stopped using the .5 oz all together.

-Satin weave - Don't expect to find this stuff at Lowes. I love the stuff. It comes in weights of 3.5 to 8 oz. The stuff is really flexible but in only one direction. They also tend to have higher thread count. This makes it need less resin to get completely saturated. The down side to this is that it is thinner than an equivalent weight standard weave fabric, thus the parts you lay up will have about the same tensile strength (a little higher actually), but less stiffness. This means that they are more prone to oil-canning. This is not a problem for me since I use vacuum to lay up a composite sandwich. 1.5 oz on the outside (against the mold cavity), foam "Coremat" from CST and 3.6 oz satin weave on the inside (against vacuum bag).

tschmidt

My Feedback: (1)

Hey Matt,
Who do you purchase the pro set epoxy through.

Todd

prgonzalez

The fiber cloth I have is Hobbico. This is the one I am planning for building the cowl.

The cloth I used in the mold is different. It is heavier but extremely flexible, sticks on the epoxy real easy, and conforms perfectly to all curves and corners. I got it at the West Marina place where I got the West System epoxy.

For testing, I used a few pieces of the hobbico cloth on the last mold half and I had a lot of trouble making the hobbico cloth conforming to the curves of the plug. It never conformed to the 90° corners. It always came back flat, so I ended up using it in flat section. So, this is what I dread, this hobbico cloth will not conform to the corners inside the mold.

I have a 2 oz cloth that I am planing on using as first layer in the cowl. This will be the outter layer when cowl is done. Then, using two layers of 5 oz. Would these three layers be good enough for a light and strong cowl?

This cowl is for a 60 size airplane. To give you a sense of dimension, a 0.90 2-stroke engine fits loose inside this cowl, no engine head exposure.

I will stay with the West Systems epoxy.

MTK

Todd,

CST Sales carries Pro Set. If I remember right, so does AS&S. I've purchased mine through CST Sales

The 226 hardener is also one to look at....40-45 min pot life which is great for smaller lay-ups. Same resin. Viscosity is in the 200 cps range

dreadnaut

My Feedback: (5)

For the corners, if you have a sharp 90 degree bend is will be difficult to get any fabric to lay against it, even with vacuum. What most, including me, do on sharp inside corners is to mix a putty of Epoxy Resin and micro balloons or Cab-o-Sil. I prefer the latter. Rather than try to describe how I would do it, I'll draw a picture.

prgonzalez

That's a great explanation. Great drawing.

I will do my first cowl tomorrow.

prgonzalez

My first cowl was a fiasco but a learning experience. The cowl cannot be used. But at the same time, I learned the hobbico 5.0 oz FGC is too difficult to work with for this application IMHO. Lots of air gaps between first and second FC layers and difficult to stay in contact even when is fully wet.

For the second attempt, I used a West Systems FGC 6.0 oz medium density. The second cowl was a success. In both cases, I used the same 2.0 oz FGC for first layer.

Now a couple of questions:
1. How do I prepare the surface for painting? Is it the same as an ABS cowl, using wetted 600 sandpaper to kill the shinny finish?
2. Do I have to wait 4 days until the epoxy is fully cured?
3. Can I use same Lustrekote paint primer as for ABS cowls?

dreadnaut

My Feedback: (5)

First start by washing off the PVA with water and dish washing detergent. I do this in the kitchen sink when the wife isn't watching . Then wipe it clean with denatured alcohol, then scuff with sandpaper and continue like you said. I painted my first cowl with Lustercoat, and it worked fine. You will get a better finish with a quality automotive paint, but that is a whole 'nother learning curve.

felker14

My Feedback: (50)

http://www.fibreglast.com/fibreglast...old_fibreglass