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Cowl layup order of operations question

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Old 03-01-2011, 06:36 AM
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MarkGrabowski
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Default Cowl layup order of operations question

OK, I'm laying up a cowl for a pattern plane I'm building. It has cheeks and a deep nose with recesses in it. I've a question on the order of layups...
I'll need to place small piece of cloth in the cheeks and chin and the flat area behind the spinner in order to bend it to the sharp angles I'm faced with....
should I layup these first and then lay down the larger parts (about 4 larger pieces of cloth) or should I lay down the large pieces first and then finish up the smaller parts...
I did a trial run this weekend and wound up with a bunch of air pockets and sharp corners that the cloth lifted away from...
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Old 03-01-2011, 11:55 AM
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Default RE: Cowl layup order of operations question

Mark, in most cases you would make a paste out of your epoxy resin and Cab o Sil or micro balloons andfill the corners and any other places the cloth won't conform to. In most cases that method works fine. In a pattern application where every ounce counts I would proceed as follows.

Prep your mold as normally then spray a medium coat of epoxy primer in the mold. Let cure for 8 hrs. I would fill/radius all the corners with 2K carbon tow saturated with epoxy then lay in 2 layers of 4 oz cloth. The sequence in which the cloth is applied doesn't really matter for this application except that if you run the cloth bias 45 degrees to any steep contours, it will be easier to work the cloth. Just keep in mind that the cloth can be streched and compressed. Go slow and use as many seperate peices as you think nessesary. You may want to cut yourself a cloth kit by trial fitting/cutting the cloth peices to shape before you get to the resin stage.
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Old 03-01-2011, 07:49 PM
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Default RE: Cowl layup order of operations question

Yeah, I do fill the corners etc. with the paste mix....
I will probably need to make up a set of cutting templates and go that route...
The biggest P.I.T.A. is the sharp 90 degree corners.... the cloth likes to separate and leave a nice fat air pocket behind...
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Old 03-02-2011, 04:41 AM
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Default RE: Cowl layup order of operations question

Several layers of thin cloth is much easier to form around sharp corners than one or two layers of thick cloth.
Do the difficult areas first, then the larger areas.
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Old 03-02-2011, 09:46 AM
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Default RE: Cowl layup order of operations question


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ORIGINAL: Magne

Several layers of thin cloth is much easier to form around sharp corners than one or two layers of thick cloth.
Do the difficult areas first, then the larger areas.
Magne
I had the pockets form even when using 2 ounce cloth (several layers of it).
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Old 03-02-2011, 09:51 AM
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Default RE: Cowl layup order of operations question


Quote:
ORIGINAL: MarkGrabowski

OK, I'm laying up a cowl for a pattern plane I'm building. It has cheeks and a deep nose with recesses in it. I've a question on the order of layups...
I'll need to place small piece of cloth in the cheeks and chin and the flat area behind the spinner in order to bend it to the sharp angles I'm faced with....
should I layup these first and then lay down the larger parts (about 4 larger pieces of cloth) or should I lay down the large pieces first and then finish up the smaller parts...
I did a trial run this weekend and wound up with a bunch of air pockets and sharp corners that the cloth lifted away from...
Mark

Let me suggest that after you lay down some reinforced paste in the corners, you then use a heat gun to gently touch the paste. Any air bubbles will heat up and pop, leaving a smoother corner with no bubbles in the finished part.

For really deep or sharp stuff, let the first layer of paste set-up a liitle, then put in a second layer of paste and then proceed with the 0.6 oz cloth in the whole mold. The 0.6 oz stuff minimizes pinholes in the finished part. You should let this layer of epoxy set up before putting in the reinforcing layer of glass.

I also usually spray my mold with KlassKote primer before any lay-up work is started, as speed mentioned. PartAll wax accepts the primer extremely well.

Almost forgot, when waxing the new mold, wax a couple layers and buff them, then wait an hour before applying the last 2-3 coats of wax. The wax works better at releasing the part. Lately I've only used PartAll with no PVA. PartAll releases well on its own, even from plain unprepped wood, believe it or not. I pleasantly surprised me to find that out, since one of my landing gear molds has a little exposed wood on it's flange

For heating smaller molds during the winter months, I have a cardboard box set-up on top of an oil radiator type of electric space heater. Works very well and I have heat control from the radiator's thermostat. Even slow curing epoxy like ProSet 125 with 229 hardener cures in 12 hours as opposed to a couple days
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Old 03-02-2011, 11:07 AM
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Default RE: Cowl layup order of operations question


Quote:
ORIGINAL: MTK


Quote:
ORIGINAL: MarkGrabowski

OK, I'm laying up a cowl for a pattern plane I'm building. It has cheeks and a deep nose with recesses in it. I've a question on the order of layups...
I'll need to place small piece of cloth in the cheeks and chin and the flat area behind the spinner in order to bend it to the sharp angles I'm faced with....
should I layup these first and then lay down the larger parts (about 4 larger pieces of cloth) or should I lay down the large pieces first and then finish up the smaller parts...
I did a trial run this weekend and wound up with a bunch of air pockets and sharp corners that the cloth lifted away from...
Mark

Let me suggest that after you lay down some reinforced paste in the corners, you then use a heat gun to gently touch the paste. Any air bubbles will heat up and pop, leaving a smoother corner with no bubbles in the finished part.

For really deep or sharp stuff, let the first layer of paste set-up a liitle, then put in a second layer of paste and then proceed with the 0.6 oz cloth in the whole mold. The 0.6 oz stuff minimizes pinholes in the finished part. You should let this layer of epoxy set up before putting in the reinforcing layer of glass.

I also usually spray my mold with KlassKote primer before any lay-up work is started, as speed mentioned. PartAll wax accepts the primer extremely well.

Almost forgot, when waxing the new mold, wax a couple layers and buff them, then wait an hour before applying the last 2-3 coats of wax. The wax works better at releasing the part. Lately I've only used PartAll with no PVA. PartAll releases well on its own, even from plain unprepped wood, believe it or not. I pleasantly surprised me to find that out, since one of my landing gear molds has a little exposed wood on it's flange

For heating smaller molds during the winter months, I have a cardboard box set-up on top of an oil radiator type of electric space heater. Works very well and I have heat control from the radiator's thermostat. Even slow curing epoxy like ProSet 125 with 229 hardener cures in 12 hours as opposed to a couple days
Matt, how many total ounces of glass layup should I be looking at?
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Old 03-02-2011, 02:39 PM
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Default RE: Cowl layup order of operations question


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ORIGINAL: MarkGrabowski


Matt, how many total ounces of glass layup should I be looking at?
For a straight glass canopy, chin cowl or wheel pants I use about 5 ozs cloth combinations. Just made a short purchase (10 yards) of 3 oz glass cloth from CST. Very nice cloth which will do the job when coupled with 0.75 oz as the first layer. I add an extra strip around the edges to build up the mounting flange. Also add a second layer of 2 oz to the middle to reduce drumming.

If you use foam or balsa in a vacuum sandwich, the extra layer in the middle isn't needed. Produces a lighter and a little stiffer part with zero drumming

Your gauge should be total weight for a typical canopy which is around 3 1/2 ozs give or take for 2 meter sized canopies. Paint will add another 5 grams give or take
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Old 03-04-2011, 07:23 AM
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Default RE: Cowl layup order of operations question

Speedracerntrixie does what I do. Mix Cabosil with your resin to the consistency of catsup (ketchup) and paint into crevices and corners then apply some small strips of lightweight cloth to form a radius to which the heavier cloth will conform. I made a nosebowl for a 1/4 Hansa Brandenberg 'Startstrutter' and the lower portion has 90 degree angles and it looks great!
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Old 03-04-2011, 08:45 AM
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Default RE: Cowl layup order of operations question


Quote:
ORIGINAL: ARUP

Speedracerntrixie does what I do. Mix Cabosil with your resin to the consistency of catsup (ketchup) and paint into crevices and corners then apply some small strips of lightweight cloth to form a radius to which the heavier cloth will conform. I made a nosebowl for a 1/4 Hansa Brandenberg 'Startstrutter' and the lower portion has 90 degree angles and it looks great!
I also add finely ground glass fiber to the paste to give real strength. Fumed silica alone has very little but is the better thickener.

Mark is making parts for a pattern plane where weight drives most decisions. How much one uses of anything is most important. For lightest weight build up, you want just enough paste in the corners that can't be filled directly with the glass you are laying up. Too much and the part comes out heavier than necessary. My experience anyway!
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Old 03-05-2011, 08:28 AM
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Default RE: Cowl layup order of operations question

Mark,

I build this Q40 pylon racer where weight is at a premium and my fuse lay up is 3oz crowsfoot weave (conforms to curves better than plain weave) 5.7oz carbon in tail and firewall area. Then I put some 6oz in higher stress areas and follow up with another layer of 3oz crowsfoot over all. Good for 200 mph and 30g. I think that if I was doing a largeish pattern cowl I would substitute the last layer or 3oz for a layer of 6oz. You can get all you need from Aircraft Spruce, much better prices than CST.

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