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Composite design factors - 12/1/2007 6:46:31 PM   
madfreestyler


 

Posts: 69
Joined: 1/25/2004
From: newportuk, UNITED KINGDOM
Status: offline 		Can anyone recommend a good site for calculating the stregnth of composite structures.

I know it will depend on thickness, resin, cloth etc etc.

The question stems from some ideas that i have to make a few composite planes and hopefully if i can get it right maybe produce a few. What i am trying to figure out is if i need an internal structure to add to the stregnth of the aircraft or if the right resin and thickness is used maybe not required i need to get my head round the trade offs?

Same applies to the wings, if you are going composite like the comp arf stuff do you still need formers in the wings? More to the point how do you mould a wing and get the leading and trailing edges joined right.

I know i had a eurosport a while back and im sure that only had a former at the root. The fus was pretty much the same, there were formers for the turbine and i think there was 1 towards the back where the under faring was fixed.

Any pointers much appreciated.

< Message edited by madfreestyler -- 12/1/2007 6:47:38 PM >

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RE: Composite design factors - 12/1/2007 7:00:23 PM   
ByLoudDesign



Posts: 373
Joined: 9/19/2005
From: Mesa, AZ, USA
Status: offline 		Although this site is for tubes the properties are the same for sheet or layup!
http://www.carbonfibertubeshop.com/tube%20properties.html

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bylouddesign.com "Scale without compromise"

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RE: Composite design factors - 12/1/2007 10:51:22 PM   
seanreit



Posts: 6979
Joined: 4/17/2002
From: Cedar Park, TX, USA
Status: offline 		It all depends on design. This jet has NO formers! The "formers" were built into the design to be composite. See where the hatches are, there is structural support across the fuse from the original glass lay up. This jet is 3 layers of 6 ounce, doubled up around the intake area for about 3 inches.

Mileage may vary, but this one is a good example of what can be achieved to save some weight and extra work.

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RE: Composite design factors - 12/1/2007 11:02:20 PM   
madfreestyler


 

Posts: 69
Joined: 1/25/2004
From: newportuk, UNITED KINGDOM
Status: offline 		Awesome!!!!!!!!! Dont suppose you would care to share your mould making and moulding technique?

What do you use to design your models?

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RE: Composite design factors - 12/1/2007 11:52:21 PM   
seanreit



Posts: 6979
Joined: 4/17/2002
From: Cedar Park, TX, USA
Status: offline 		There isn't really a secret. As incredible as it may seem, I have read every single thread in this forum related to composites and mold making. I was out of town on business a few years ago, and spent literally about 40 hours in the evenings reading and absorbing information. I've invested thousands in technology, materials, and equipment to make my dreams a reality. It's a lot of work, but can be very rewarding.

Good luck, and when you get going, if you run into questions, post them, there are many here with more experience than me that can help.

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RE: Composite design factors - 12/3/2007 3:09:14 PM   
Magne


 

Posts: 333
Joined: 3/7/2004
From: Moss, NORWAY
Status: offline 		It is also worth noting that models such as the Comp-ARF (and others) that don't have formers, are all sandwich structures, i.e. fibres (glass/carbon/kevlar) laid up on each side of a light weight core material. The core material could be balsa wood, honeycomb or foam. The core material separates the two skins, and make a stiff, lightweight structure. A single skinned structure would need to be many times heavier to achieve the same stiffness.

Magne

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RE: Composite design factors - 12/4/2007 5:09:02 AM   
SCALECRAFT


 

Posts: 1500
Joined: 1/7/2002
From: MONTEBELLO, CA, USA
Status: offline 		Fuses have been done for years,lot of info. The wings/stabs are the trick..

I would also like to make a point about stiffness in the glass "skin"construction. For the last 16 years my buddy and I have been making/flying all composite warbirds that have a few layers of glass along with minor wood/composite framework in the fuse and hollow glass wings.

The glass skin in wings mainly, without a sandwich core material may not be stiff to the touch at some points as a core type wing, but the glass/frame wing is just as light and has never failed us in flight. Plus the glass skin coreless wings don't dent as do the sandwich construction type, like the old fiberclassics P-51 for example. Not a very durable surface, the foam core would dent and not bounce back.

ALso glass coreless wings are cheaper and easier to do. No vacuum bagging needed. Well this is what has worked well for us for many years.

Once you start to work with glass , shapes, and angles, you'll see how it can all work together.

Jet remember, its not going to be crash proof.

Steve

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RE: Composite design factors - 12/4/2007 8:43:01 AM   
Magne


 

Posts: 333
Joined: 3/7/2004
From: Moss, NORWAY
Status: offline 		Steve.
I am very interested in what you are saying.
Could you please indicate what lay-up schedule has worked for you.
What material thicknesses are required for adequate handling strength, and what is you recommended distance between the ribs/formers.

Thanks,
Magne

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RE: Composite design factors - 12/4/2007 11:46:33 AM   
Ed Smith


 

Posts: 2875
Joined: 12/29/2001
From: Brantford, ON, CANADA
Status: offline 		I am always experimenting. As seanreit stated there are no secrets. Many years ago I incorporated Carbon tow in my fuselage layups. The added stiffnes was quite amazing. I wind the tow into a string and sandwich it between the layers of cloth. The pictures illustrate this, The tow is sandwiched between two layers of six ounce cloth. The extra strips above the front of the wing saddle stiffen the fuselage above the landing gear. The weight of the added carbon was less than one ounce. No additional resin was needed the carbon just suck up what was being used for the layup. I use only epoxy resin. The fuselage in the picture is 48" long. Apart from the firewall and the servo tray there are no other formers in the fuselage.

The strips in the cheek cowls did not do what I wanted. I should have laid them across the cowl not along them. Next time. The wheel pant strips of carbon are self explanatory.

Ed S

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RE: Composite design factors - 12/4/2007 3:04:56 PM   
seanreit



Posts: 6979
Joined: 4/17/2002
From: Cedar Park, TX, USA
Status: offline 		Ed, on my fuse, on the jets one of the factors is that we carry a lot of weight in the nose that has to be supported (we figure supported around the intake area). I have never used Tow, and we were thinking just lay in some carbon fiber triangle cut from the intake area up the sides towards the nose.

Does tow have much strength say over a two foot run? I was thinking surface area of carbon fiber, but if this stuff makes a beam over length, might be just the trick??

Note: fuse is three layers of really loose weave 6 ounce. Lots of curves in this baby and the loose makes the turns quite well.

< Message edited by seanreit -- 12/4/2007 3:05:48 PM >

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RE: Composite design factors - 12/4/2007 3:36:42 PM   
Ed Smith


 

Posts: 2875
Joined: 12/29/2001
From: Brantford, ON, CANADA
Status: offline 		Sean,

The lengthways strip in that fuselage is 20" long. It is 1" tow twisted into a string. Just laid in flat the tow does not add much stiffness. Twisted into a string the difference is quit amazing. Two or three strands laid side by side would definitely give you a "Beam" like structure add a couple of verticals and the fuselage would be very stiff.

I mold my own Pyon Racing fuselages. I use the same principle with those. For me Carbon Tow strategically placed is the lightest easiest way to stiffen a fuselage.

Ed S

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RE: Composite design factors - 12/4/2007 4:19:01 PM   
tony-howard


 

Posts: 286
Joined: 9/28/2004
From: Monroe, WA, USA
Status: offline 		One of the best books on composite structures the I've seen is:

Composite Basics by Andrew C Marshall
Published by Marshall Consulting
720 Appaloosa Drive
Walnut Creek CA 94596

My copy was purchased in 1994 and finding a copy may not be easy now.

It is intended for full scale homebuilt design, but it contains a wealth of information for any composite structure designer. It's well organized, easy to understand and has one of the better sections on cloth weaves. Edition 4 includes carbon fiber.

HTH

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pacific-scaled-aircraft.com

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RE: Composite design factors - 12/4/2007 6:25:18 PM   
HO-229



Posts: 228
Joined: 4/30/2004
From: California, MD, USA
Status: offline 		Ed,
I like what you have done with the "tow" material, I find it to be a very innovative way of incorporation stiffeners/ribs within the fuselage structure without the fuss of making stand alone rib structures & bonding them to the inner skin structure


Thanks for the tip

Regards
Dave

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RE: Composite design factors - 12/5/2007 4:25:40 AM   
Spike


 

Posts: 72
Joined: 12/15/2001
From: Saint Paul, MN, USA
Status: offline
quote:

ORIGINAL: tony-howard

One of the best books on composite structures the I've seen is:

Composite Basics by Andrew C Marshall
Published by Marshall Consulting
720 Appaloosa Drive
Walnut Creek CA 94596

My copy was purchased in 1994 and finding a copy may not be easy now.

It is intended for full scale homebuilt design, but it contains a wealth of information for any composite structure designer. It's well organized, easy to understand and has one of the better sections on cloth weaves. Edition 4 includes carbon fiber.

HTH


I found a copy here: http://www.actechbooks.com/composite_basics.htm

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RE: Composite design factors - 12/5/2007 6:36:07 AM   
tony-howard


 

Posts: 286
Joined: 9/28/2004
From: Monroe, WA, USA
Status: offline