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Fiberglass Layup for a Large Model

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Old 06-12-2013, 06:30 PM
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Default Fiberglass Layup for a Large Model

I would appreciate some guidance on the fiberglass layup for a project that I am building. I have never done a complete composite fuselage before, so this is a learning experience for me.

I am building quite a large model of an aircraft that looks much like a Seabee amphibian. It is a high wing pusher aircraft, with a relatively narrow tail boom extending out to a large fin and rudder. The fuselage will be about 9 feet long, 22" deep and 18" wide. Yes I know that it is awfully big! But keeping the weight under control is still an issue.

The wings and tail will be built-up, but the fuselage will be composite construction.
The plug and moulds are almost done, but I need some advice on the composite layup for the fuselage.

The advice that I have so far is to use an initial layer of 3.5 oz. satin cloth. Then two layers of 6 oz. cloth, with a sandwich of 2 mm thick foam in key areas, such as the hull bottom, to improve stiffness and rigidity.

Also some carbon fiber reinforcement in high stress areas, such as a vertical run up the large fin to the stabilizer attachment point, and in the tail boom.

Also a couple of bulkheads in the centre cabin area under the wing to provide stiffness and support from the wing and motor mount down to the hull bottom to carry landing loads.

Am I headed in the right direction with this?


Comments are welcome!
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Old 06-13-2013, 09:45 AM
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Default RE: Fiberglass Layup for a Large Model


Quote:
ORIGINAL: Caygeon Flyer

The advice that I have so far is to use an initial layer of 3.5 oz. satin cloth. Then two layers of 6 oz. cloth, with a sandwich of 2 mm thick foam in key areas, such as the hull bottom, to improve stiffness and rigidity.

Also some carbon fiber reinforcement in high stress areas, such as a vertical run up the large fin to the stabilizer attachment point, and in the tail boom.

Also a couple of bulkheads in the centre cabin area under the wing to provide stiffness and support from the wing and motor mount down to the hull bottom to carry landing loads.

Am I headed in the right direction with this?

Comments are welcome!
Yes I think you are.... A couple things I'd suggest. As your initial fill coat, 3.5 ounce glass is possibly too thick or coarse. You might consider something finer weaved and tightly weaved. There are some very good 1.5 ounce and 2 ounce glass fabrics in various weave patterns that might work better. There is also a nonwoven glass product (looks like silkspan) that is designed as the cosmetic initial layer

Some types of foamare good for noise suppression...polystyrene expanded beads for example. But not terribly strong structurally unless you used higher density foam in the 3-4 pound per cubic foot range.

Airex or Herex foams are much better as structural foams. These are vinyl expanded materials and fairly rigid in the 2 pound density area. That's probably material you should consider. Airex is available in US and Canada and Herex in Europe. For your application, 1/8" thick should be thick enough.

Don't eliminate good ol' balsa from consideration. When sandwiched between 2 layers of 6 ounce glass or carbon, this material becomes incredibly strong and stiff. On the bottom of the hull, 1/8" to 3/16" contest grade balsa will work great. Also in the hull area where it will see lots of wear and tear, maybe a layer of kevlar outside and carbon on the inside. Kevlar is leather tough and should be able to stand up to abuse better, but it doesn't have the max tensile strength or modulus carbon and certain glass have. Something to keep in back of mind....

On the lay-up of the glass and carbon, bias lay-up gives you rigidity in torsion. If you used balsa as the filler run the grain along the long axis of the fuse and the glass and carbon on bias. You will get a good balance between torsional rigidity and longitudinal and transverse rigidity. Fuselages need all of the above

Iassume you know your epoxies. There's an awful lot of them anymore. Several expensive ones are great choices. But there are some inexpensive ones that are also good choices in terms of strength, wet-out and curing with decent pot lives. Aircraft Spruce is one good source. ACP another, CST Sales another, CJ Composites and US Composites are yet other good sources
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Old 06-13-2013, 12:04 PM
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Default RE: Fiberglass Layup for a Large Model

Thanks MattK.

Looks like very solid advice!

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Old 06-13-2013, 07:34 PM
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Default RE: Fiberglass Layup for a Large Model

Caygeon - I use 3.2oz crowfoot for my first layer most of the time. It conforms to curves and tight space very well. My layup is detailed at the web address:
http://www.sidgates.us/HOBBIES/F-94C...se%20Parts.htm

I persoanlly would stay away from Kevlar and would only use carbon cloth in the inside in very high stress areas. I use West Systems epoxy but others are probably just as good.

Added other molding links:
http://www.sidgates.us/HOBBIES/F-94C/F94C%20PROJECT.htm
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Old 06-13-2013, 07:40 PM
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Default RE: Fiberglass Layup for a Large Model

You are going to need some fairly large bulkheads and I forgot to call attention to my foam bulkheads. I use blue foam approx. 1/4" thick and lay up 3 layers of 3.2oz cloth on the bulkhead. They are much lighter that plywood and very stiff. The outer dia. of the bulkhead is exposed blue foam and I glue them in with Gorilla Glue. If you want the bulkhead to fuse joint even stronger I add a string of carbon tow to the bulhhead/fuselage joint wet out in epoxy and tamped into the joint.
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Old 06-16-2013, 07:52 AM
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Default RE: Fiberglass Layup for a Large Model

Good Ideas Sidgates. Thanks

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Old 06-16-2013, 06:40 PM
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Default RE: Fiberglass Layup for a Large Model

All those sound like good advice.
Kevlar is actually a very good product, I've laid up some sample pieces and for the weight it is very stiff even if vacuumed.
Are you using a vacuum system? I didn't see it if you said you were.
Here's a couple laminate bulkers to consider:
http://www.fibreglast.com/product/La...and-synthetics I've used this stuff and it's great. We are going to start a large 100" wing span P-40 soon and this will be my bulker. It's available in 4mm too which I may try to obtain for the larger model.
http://www.fibreglast.com/category/V...acuum_Infusion Lantor Soric and Divinymat are great products. I've laid up some Divinymat, it is extremely stiff and strong but if you have compound curves you will need to work with it a bit. Check out Thomas' thread on the Horton http://www.rcuniverse.com/forum/m_11..._1/key_/tm.htm He used the Lantor Soric and it made the curves beautifully. I'm not sure if it HAS to be used in a vacuum infusion process or if it can be a traditional lay up/vacuum setting.

Looking forward to your posts.

Tim
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Old 06-17-2013, 07:18 AM
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Default RE: Fiberglass Layup for a Large Model

If you are going to resin infuse the the 2.5 Gallon resin pot listed from Fibreglased is to much money when you can purchase a 2.5 gallon paint pot from Harbor Freight for $99.00. Just saying.

Bob
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Old 06-18-2013, 06:19 AM
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Default RE: Fiberglass Layup for a Large Model

i like kevlar. It's lighter than carbon and more impact resistant. Need really sharp shears or a shear made to cut such composites.

No radio blockage either.

Steve
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Old 06-19-2013, 08:44 PM
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Default RE: Fiberglass Layup for a Large Model

I wouldn't bother with resin infusion.. its different, but pretty pricey when you consider all of the consumable materials and specialized setups it requires. A vacuum bagged layup with some airex foam will be just as strong and very light..
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Old 06-20-2013, 11:24 PM
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Default RE: Fiberglass Layup for a Large Model

Anyone know if you get Airex less than 1/8 thick in the U.S.? If so, where?
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Old 06-21-2013, 02:36 AM
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Default RE: Fiberglass Layup for a Large Model


Quote:
ORIGINAL: myersflyers

Anyone know if you get Airex less than 1/8 thick in the U.S.? If so, where?
Airex C71 is typically sold no thinner than .125", so why not utilize Rohacell, you can get that much thinner.

Bob
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Old 06-21-2013, 06:45 AM
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Default RE: Fiberglass Layup for a Large Model


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ORIGINAL: myersflyers

Anyone know if you get Airex less than 1/8 thick in the U.S.? If so, where?
I've done quite a bit of searching in the states, contacted all the principals but still nothing less than 1/8" for Airex (2lb density).

Herex is the only material of the type that you can get as thin as 1mm in the equivalent of 2 lb density. Considering material cost and shipping from Germany, price per 1m x 2m sheet is somewhat pricy but not terrible. A little more expensive than 1/16" contest grade balsa for equivalent area but at less than half the weight, it may be worthwhile depending on the app.

On the other hand, you may contact Todd Schmidt in Kansas who builds his pattern planes from stock he purchasedfrom Germany. You can find his details in the Pattern Forum. Or maybe look up Herex and make contacts more directly.
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Old 06-21-2013, 05:12 PM
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Default RE: Fiberglass Layup for a Large Model

Here is a photo of the aircraft that I am trying to model - sort of a modernized Seabee

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Old 06-21-2013, 05:14 PM
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Default RE: Fiberglass Layup for a Large Model

I continue to appreciate all the input from folks. It is helping!!!

I have attached some photos of the parts that will be assembled to make the mould.
Today we decided to make the final assembly in about 4 pieces.

We will also be using a variety of layups and techniques for the various bits, although the final layups are not finalized yet.

The fin and aft part of the boom will be largely carbon fibre with some foam in the flat parts of the fin. We need to carry the horizontal tail plane loads down into the structure, and also avoid torsional issues with the boom.

The key structural piece is the bottom of the hull. This will be a glass and foam sandwich to provide stiffness to the bottom of water landings. We will likely use vacuum infusion for this part.

There will be some internal structure built onto the bottom part to carry batteries and electronics and also to transmit loads vertically from the bottom up to the wing spar and motor mount. (or vice versa).

The main part of the fuselage, incorporating the nose, cabin ,and underside of the wing mount, will be dropped over the structure and bonded to the bottom. This will be a multilayer glass layup, with foam as a stiffener in the large flattish areas. Also a big stiffener along the centre top, and vertically on the sides just under the motor area.

At this point we will be able to install the wing tube sleeve, and spars, and motor mount.
This will then be topped with a third glass piece which will primarily be the top of the wing surface and motor cowl. This again will be a glass sandwich with foam in the flattish areas.

I know some folks have suggested putting a coat of primer onto the moulds before the layup, but will not do this. We prefer the transparency of the parts which will let us visibly check bonds and bulkhead joints.

We are thinking of probably a first glass layer of 3 oz., as the large size and radii do not require the flexibility of 2 oz. The foam thickness will be from 2 mm to 6 mm depending on the needs of the individual parts. We have not decided on the final layer weight.


PS - More comments are welcome!

Caygeon FLyer
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Old 06-21-2013, 06:51 PM
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Default RE: Fiberglass Layup for a Large Model


Quote:
ORIGINAL: myersflyers

Anyone know if you get Airex less than 1/8 thick in the U.S.? If so, where?
It is not. you will have to order it from germany or elsewhere in the world. I plan to place a fairly large order (40+ sheets) within the next 3 months though
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Old 06-21-2013, 06:53 PM
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Default RE: Fiberglass Layup for a Large Model


Quote:
ORIGINAL: sensei


Quote:
ORIGINAL: myersflyers

Anyone know if you get Airex less than 1/8 thick in the U.S.? If so, where?
Airex C71 is typically sold no thinner than .125'', so why not utilize Rohacell, you can get that much thinner.

Bob
Rohacell is significantly more expensive than Airex C70.75 and not much stronger than rohacell IG71.. I have also not seen anywhere in the US that sells 1mm rohacell IG 71 for anywhere near the same price as airex (airex is available for under $30 for a 1.2mm x 24"x48" sheet in germany)
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Old 06-21-2013, 11:54 PM
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Default RE: Fiberglass Layup for a Large Model

Thanks MattK and Bob for the info, much appreciated.

Invertmast, i would be interested in part of the airex order you plan to make in the next 3 months, no rush for me.

Rgds,
Keith
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Old 06-22-2013, 02:25 PM
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Default RE: Fiberglass Layup for a Large Model

Keith,

Good call on the primer, I am not a fan...some guys like it but I have a list of reasons not to do it, so I'm with ya!

You seem to be on the right track but I just have a small caution. Some planes have a 'gel' coat on the lay-up and they can start with 6 oz cloth if they want but I'm not a fan. The older planes we use in pattern are done that way...it's almost all polyester resin with a little cloth. In a quest to go lighter I've made fuselages that are sieves, when I went to wash the PVA off the water was going through the fuselage because I started with 2 oz cloth.
I went back to making the first layer 3/4 oz and all is fine again, no pin holes even with vacuum.

That's an awesome project, thanks for sharing...keep it coming

Tim
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Old 06-28-2013, 02:06 PM
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Default RE: Fiberglass Layup for a Large Model

with a initial layer of 3oz of glass, it is very likely you will get fabric print-through to the surface of the part. Lighter weight cloth's are typically put on at first to prevent this. I also have some 2oz cloth that is less conformable than my 3.16oz cloth. Conformability really comes primarily from the weave style and the number of yarns per inch, then weight. A tightly woven lighter cloth can easily be less conformable than a loosely woven (or crowfoot) heavier cloth.

2mm foam (especially airex or rohacell) is some very strong stuff with a layer of 2oz or 3oz glass on both sides, it also starts gaining ALLOT of weight the thicker the foam is. An Airex or Rohacell fuselage is very strong AND light with only 1 or 1.2mm foam sandwiched with 1 layer of glass on either side. And if you have a fairly significant amount of internal structure, there isn't much reason to go with a thicker foam.

Parts primed in the mold also nearly always come out pin-hole free (mine do), and if your layup isn't dry to begin with before vacuum bagging, you don't have to worry about there being bonding issues.
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Old 07-18-2013, 04:55 AM
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Default RE: Fiberglass Layup for a Large Model

Here is one of our first parts;
Lay up is 9 oz. and 3 oz. sandwich in epoxy with 6mm diviny foam in flat areas, vacuum bagged.

Weight is good and stiffness is great.
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Old 07-19-2013, 07:39 AM
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Default RE: Fiberglass Layup for a Large Model

Quote:
ORIGINAL: Caygeon Flyer

I continue to appreciate all the input from folks. It is helping!!!

I have attached some photos of the parts that will be assembled to make the mould.
Today we decided to make the final assembly in about 4 pieces.

We will also be using a variety of layups and techniques for the various bits, although the final layups are not finalized yet.

The fin and aft part of the boom will be largely carbon fibre with some foam in the flat parts of the fin. We need to carry the horizontal tail plane loads down into the structure, and also avoid torsional issues with the boom.

The key structural piece is the bottom of the hull. This will be a glass and foam sandwich to provide stiffness to the bottom of water landings. We will likely use vacuum infusion for this part.

There will be some internal structure built onto the bottom part to carry batteries and electronics and also to transmit loads vertically from the bottom up to the wing spar and motor mount. (or vice versa).

The main part of the fuselage, incorporating the nose, cabin ,and underside of the wing mount, will be dropped over the structure and bonded to the bottom. This will be a multilayer glass layup, with foam as a stiffener in the large flattish areas. Also a big stiffener along the centre top, and vertically on the sides just under the motor area.

At this point we will be able to install the wing tube sleeve, and spars, and motor mount.
This will then be topped with a third glass piece which will primarily be the top of the wing surface and motor cowl. This again will be a glass sandwich with foam in the flattish areas.

I know some folks have suggested putting a coat of primer onto the moulds before the layup, but will not do this. We prefer the transparency of the parts which will let us visibly check bonds and bulkhead joints.

We are thinking of probably a first glass layer of 3 oz., as the large size and radii do not require the flexibility of 2 oz. The foam thickness will be from 2 mm to 6 mm depending on the needs of the individual parts. We have not decided on the final layer weight.


PS - More comments are welcome!

Caygeon FLyer
The T tail or cruciform, (As per Turbonut) like your tail section can be made very strong and reliable with sections of wood framing. 5 ply or light ply with glass or a carbon/kevlar skin layer sandwich.

Kinda like our prototype test flight F-104 lay up..

Steve
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