Composite Cowling

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fasilpereira

Member
Joined
Jul 11, 2010
Messages
11
Location
Araraquara, SP / Brazil
Dear friends,

I’ll build a composite cowling for an O-360 powered aircraft and I’d like to know what is the common layup schedule for a part like that.

I’ll be using glass (7781) at 45 deg, epoxy resin and maybe some core on the flat areas, but most of the area will be a solid laminate.

How many layers are typically used for a part like this? I was considering 3 to 4 layers and some extra reinforcements where needed. Does it sounds reasonable?

Thank you,

Fabricio
 
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fasilpereira

Member
Joined
Jul 11, 2010
Messages
11
Location
Araraquara, SP / Brazil
Hi Bob, If I go with the glass, I’ll add some extra layers as per your recommendation.

Regarding the 7725 vs 7781, I’ll probably use the 7781, just because I have some in stock. I have tried the 7725 in the past, but I preferred the 7781. Maybe because it is much easier to conform to any part and also because I’m using the 5052 epoxy system, so wetting it out is really not q problem.

I have just found a good source for a 200g 2x2 twill 3k carbon fiber fabric, and now I’m also considering it as an option. In that case, how many plies would you recommend?

Thank you,

Fabricio
 
Last edited:
Joined
Aug 15, 2013
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3,089
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Western US
Hi Bob, I’d I go with the glass, I’ll add some extra layers as per your recommendation.

Regarding the 7725 vs 7781, I’ll probably use the 7781, just because I have some in stock. I have tried the 7725 in the past, but I preferred the 7781. Maybe because it is much easier to conform to any part and also because I’m using the 5052 epoxy system, so wetting it out is really not q problem.

I have just found a good source for a 200g 2x2 twill 3k carbon fiber fabric, and now I’m also considering it as an option. In that case, how many plies would you recommend?

Thank you,

Fabricio
I'd go with carbon only if I had a mold in which I could vacuum bag the part. I'd use 4 or 5 plies of 200g (6oz) carbon.
 

fasilpereira

Member
Joined
Jul 11, 2010
Messages
11
Location
Araraquara, SP / Brazil
Bob,

That is exactly the case. I have access to a cowling for the same aircraft model and I’m planning to use it to make a mold so that I can make a new part.

Regarding core, I think I’ll have to use a core at least on some flat areas to reduce the deformation due to airloads and pressure, but it will have to be a very thin core due to limited space.

I don’t think I’d get a good result with honeycomb because I’ll not use prepreg. Divinycell is out of the temperature range for a cowling. Rohacell would work, but it is a little bit expensive and very hard to obtain in Brazil…

So, I’m considering Soric, but I have never worked with this type of core and from its data sheet data, it seems to be on the heavy side. I’d have to set up an infusion system for that, but I think it may be interesting to do it.

What is your opinion on Soric for this application? What other core would you recommend?

Thank you for the very valuable advices,

Fabricio
 

pbk3

New Member
Joined
Apr 19, 2022
Messages
2
Make sure to use the core intended for epoxy resins (not polyester!). For my cowl I'm following this guide: CoreMat cowl 2.pptx

Since I'm not at OSH, I'll aim to have a good weekend on the project. Build on...

PK
 

Heliano

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Dec 24, 2015
Messages
179
Location
Campinas, SP, Brazil
May I suggest that you add a thermal insulation layer on the inside of the upper part of the cowling. A typical scenario where the inside temperatures go up significantly: after engine shutdown, or during taxi in with engine at idle. Some designs include a "venetian blind" in the upper cowling (behind the baffle) to allow for the hot air do flow out.
 

BJC

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Joined
Oct 7, 2013
Messages
15,421
Location
97FL, Florida, USA
May I suggest that you add a thermal insulation layer on the inside of the upper part of the cowling. A typical scenario where the inside temperatures go up significantly: after engine shutdown, or during taxi in with engine at idle. Some designs include a "venetian blind" in the upper cowling (behind the baffle) to allow for the hot air do flow out.
That hasn’t proven to be necessary in 1,000 plus vinyl ester resin / glass cowlings on Glasairs, (with very tight cowls), GlaStars and Sportsman aircraft. More common is reflective paint and, on the bottom cowl, below the exhaust pipes, reflective aluminum foil / tape.


BJC
 

speedracer

Well-Known Member
Joined
Feb 4, 2020
Messages
360
May I suggest that you add a thermal insulation layer on the inside of the upper part of the cowling. A typical scenario where the inside temperatures go up significantly: after engine shutdown, or during taxi in with engine at idle. Some designs include a "venetian blind" in the upper cowling (behind the baffle) to allow for the hot air do flow out.
I've made a few "drop in" doors for Long EZ upper cowlings. It's just a small door, say, 2"X 4" with a hinge on the 2" side. When flying, air pressure holds it closed. When it stops, it falls open. Here's one I made yesterday.
 

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