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Apr 29, 2019, 05:26 PM
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Andrew207's Avatar
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My first fuse and a question. Why use any fiberglass.


I pulled my first fuse out of the mold today. Overall I am pretty happy with the results. Not really usable, but enough success to encourage me to keep going. This one was is comprised of 1.6 oz fiberglass and 4.1 oz uni. Now that I am somewhat comfortable with the process I ordered some kevlar for the next ones. I have learned a lot from Tom's video
NXT Fuselage molding (51 min 30 sec)
. Thanks Tom.

Here is my question. In the boom part of the layup why use any fiberglass at all? Tom uses a layer of 4.1 uni, 1.7 kevlar, and 1.6 fiberglass. Why not use 2 layers of kevlar and forget about the fiberglass? With the fiberglass being the weakest cloth in the layup doesn't the kevlar and uni take all of the forces, leaving the fiberglass to do nothing? Wouldn't it be stronger and stiffer with 2 layers of kevlar and one layer of uni?

My full layup was,
Boom end: 1 layer 4.1 oz uni, 2 layers 1.6 oz fiberglass on the bias.
Pod end: 5 layers 1.6 oz FG.
Saddle reinforced with 5 layers of FG.
Total weight before trimming (including 2.6 grams of aluminum mounting blocks) was 46 grams. Not bad for a first run.
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Apr 29, 2019, 09:27 PM
Themadartist

Worth the 11 minutes IMO ...


Tom, here's a great video that explains the important characteristics of the three common fabrics used in composite construction. Have a watch and see if this answers your questions. Cheers, Steve.

Carbon Fiber vs Kevlar vs Fiberglass - Which one is right for YOU? (11 min 6 sec)
Apr 30, 2019, 04:32 AM
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Andrew207's Avatar
Thread OP
That is a very good video. I had watched is a couple years ago, but just watched it again. Thanks. On my next layup I will copy Tom's layup.

Andrew
May 07, 2019, 07:23 AM
Father of Fr3aK, DLG Pilot
tom43004's Avatar
The glass is really for cosmetics and for a little more "hoop" strength. Over the years I have varied putting it on 0-90 and bias, but I still use it. It also helps keep chances of carbon splinters to a minimum if you over-dry your layup.

Good luck! Making your own stuff is fun.
May 07, 2019, 09:42 AM
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Andrew207's Avatar
Thread OP
Thanks Tom. I am continuing to experiment and learn. As you know it is a slow but rewarding process. I am pretty pleased with the first molded fuse and have some Kevlar on hand for the next attempt. I am now learning how to make a nose cone for the fuse, rather than a canopy. This fuse is a very tight fit for electronics and I think the nose cone approach will help me to fit everything in with enough access to critical components.
Regards,
Andrew
May 17, 2019, 09:57 PM
Registered User
Another reason to have glass on the outside is that Kevlar isn’t sandable. If sandpaper hits it the result is a puff of fuzz. The glass can be sanded for paint prep but you don’t want to sand through it.
May 24, 2019, 01:49 PM
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Roguedog's Avatar
I don't get why people use kevlar for RC planes. Structually fiberglass is stronger then both carbon fiber and kevlar.

For wings that are thin for world record speed attempts yea add carbon fiber to stiffen the wing make it a bit lighter.

Carbon fiber doesn't make composite stronger jsut stiffens it.

As far as kevlar why do you need to make it bullet proof?

Waste of time IMO specifically in finishing.

Fiberglass provides all that is needed for most sailplanes and powered planes.

Think those using carbon fiber (and Kevlar ?) are doing it for ego polishing more than any other reason. Probably snookered into using it by someone who used it(paid all the extra money for It) just for bragging nothing else. Then convinced others to use it with folklore and wives tails about how much stronger his composite was IMO.
May 24, 2019, 07:47 PM
Entropy is happening!
Jim.Thompson's Avatar
Quote:
Originally Posted by Andrew207
.........................4.1 oz uni. .............................
Andrew:
"Uni" what?
Uni-glass or Uni-carbon?
On threads where you are looking for specific technical information, it is helpful if you supply all relevant information.

Quote:
Originally Posted by Roguedog
I don't get why people use kevlar for RC planes.......................................

Fiberglass provides all that is needed for most sailplanes and powered planes.
..............................................
I agree!

Edit:
Especially when learning a composite process!

Jim.
May 25, 2019, 07:29 AM
Registered User
Quote:
Originally Posted by Roguedog
I don't get why people use kevlar for RC planes. Structually fiberglass is stronger then both carbon fiber and kevlar.
.......
Think those using carbon fiber (and Kevlar ?) are doing it for ego polishing more than any other reason. Probably snookered into using it by someone who used it(paid all the extra money for It) just for bragging nothing else. Then convinced others to use it with folklore and wives tails about how much stronger his composite was IMO.
I completely agree that there are other materials that have a higher tension stress capability than Kevlar. In my experience, particularly with rocks and debris in the areas I have to land, I have found that Kevlar has greater toughness. Fiberglass and carbon crack and shatter on impact with the rocks we have; Kevlar bends and can be more easily repaired. For this reason, I use Kevlar on the leading edges, the bottom half of the “D box”, and in the fuselage pod.

My planes are all painted, and I have adequate supplies of all the classic materials (including balsa), so I select the most appropriate material for the task. As noted above, in some cases, that would be Kevlar.

Besides ‘strength’, carbon fiber absorbs much more heat unless it is painted which can cause soft epoxy and a weak wing. Kevlar is miserable to work with and can require additional thickness to get the desired ‘strength’. Fiberglass is always my first consideration, particularly due to its cost and the amount of it I already have. Therefore, in some applications, fiberglass is THE material of choice, but it is not the only material I use.

Regardless, “bragging rights” has nothing to do with my material selection.

-Keith
May 25, 2019, 07:47 AM
Registered User
Roguedog's Avatar
Hahaha it you land on the runway instead of on the rocks you wouldn't have to use Kevlar to bullet proof your wing tips and leading edges.
May 25, 2019, 08:08 AM
Registered User
Ahh - if only the “runway” was free of rocks.... At least the “runway” is free of mesquite and saguaros.
May 25, 2019, 01:25 PM
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Andrew207's Avatar
Thread OP
Well, here are some pics of the progress. Yes, kevlar included. I am quite happy with the latest fuses. Layup from inside out is 4.1 oz uni carbon, 2.2 oz kevlar, 1.6 oz fiberglass. Final weight including aluminum mounting blocks below the saddle is 41.5 grams. In total I now have 4 fuses, the first one without kevlar was turned into a small DLG for my son. The nest three are all usable (although not visually perfect) and will be turned into other dlgs and slopers over the years.
Andrew
May 25, 2019, 10:41 PM
Scott
Pylonracr's Avatar
Quote:
Originally Posted by Roguedog
I don't get why people use kevlar for RC planes. Structually fiberglass is stronger then both carbon fiber and kevlar.

For wings that are thin for world record speed attempts yea add carbon fiber to stiffen the wing make it a bit lighter.

Carbon fiber doesn't make composite stronger jsut stiffens it.

As far as kevlar why do you need to make it bullet proof?

Waste of time IMO specifically in finishing.

Fiberglass provides all that is needed for most sailplanes and powered planes.

Think those using carbon fiber (and Kevlar ?) are doing it for ego polishing more than any other reason. Probably snookered into using it by someone who used it(paid all the extra money for It) just for bragging nothing else. Then convinced others to use it with folklore and wives tails about how much stronger his composite was IMO.

Wow, more BS from the BS factory.

First we should clear up the most blatant lies.
1. Most arimid fabric is not Kevlar. Kevlar is a registered trademark of Dupont, so only arimid fabric manufactured by Dupont can be called kevlar.
2. Very, Very little Arimid fabric is ballistic. While it is true that early bullet resistant vests were made using Ballistic Kevlar, the fabric available to the general public is NOT ballistic. I have substantial quantities of both and can state that they are not the same fabric.

So, some idiot thinks that we add carbon fiber just to stroke our ego?? Does that explain why every Indy car tub and Formula 1 Car is manufactured out of Carbon fiber?? Why is every Satellite and Launch vehicle made out of Carbon. Why is every fighter plane and most modern passenger planes made out of Carbon?? Are we all just trying to stroke our EGO??????

The answer is NO. We know better and know what the best material for the job is. No one cares what your opinion is, we care about the facts. Some of us have been doing this for many years and are trying to share factual experience with others, not BS in a vain attempt to make ourselves look good.

Here is a comparison of various fabrics, done in a laboratory environment.

Weight per Unit Volume or Density of Carbon fibre, Kevlar, and E Glass
The Denser a material is the heavier it will feel for an equal sized chunk.

When we compare the density of our 3 materials we see a significant difference. If you make up 3 samples exactly the same size and weight them you quickly see that Kevlar® fiber is much lighter, Carbon Fibre is next and the E Glass is the heaviest. So for the same weight of composite we get more strength.

In other words, any structure, where we require a given strength, can be smaller or thinner if made out of carbon fiber or Kevlar® composite than if made out of glass.

After making your samples and testing them, you would find that the Glass composite is almost twice as heavy as the Kevlar® or the Carbon Fiber Laminates. In other words it takes half as much Carbon or Aramid fiber to get the same strength as the glass sample. You can save a lot of weight using Kevlar® or Carbon Fibre. This property is called strength-to-weight ratio.

Kevlar® (Aramid) and Carbon Fibers have a high strength-to-weight ratio when tested unidirectionally in direction of the fibers, while e glass has a lower strength-to-weight ratio. Glass is still quite high, just not as good as Kevlar® or Carbon. The units are kN.m/kg. N stands for Newton

                          Strength-to-Weight
E Glass                        564   
Carbon Fiber               1013
Kevlar                          993
Epoxy                           28
Compression Stregth Comparison of Kevlar, Carbon and Glass Fibers
Whereas Carbon and Glass are only slightly less strong and stiff in compression than in tension, Kevlar® is much less stiff and strong when compressed. In fact in some tests the Kevlar® was failing before the resin matrix. According to Researchers at Rowan University, pdf document, "The compressive strength of Kevlar® is 1/10 of its ultimate tensile strength". Again look at this figure as relative because there are many variations but it shows a significant characteristic of Kevlar® well known by Kayak and boat builders everywhere. Kevlar® is strong but does not like to be hit sideway which causes a compression strain, and often a crack.

From this we can clearly see that Carbon Fiber is superior. If you are only concerned with strength, then do as Rogedog does, and carve your parts out of Steel. They will be strong......... Those of us that are competent use carbon to achieve our target strength with the minimum of weight. I will admit, I make EF 1 cowls out of fiberglass, as the cost is not worth the weight; since my EF1 planes need about 4 ounces of lead to bring them up to the minimum class legal weight anyway, further weight savings is kind of a waste of money.

Back to the real world, The use of carbon fiber, by those of us that are competent in its use, is what gives us the winning advantage. The Loosers always CRY.....

Scott
May 26, 2019, 01:30 AM
Registered User
Roguedog's Avatar
Well it didn't take long did it. I'm sure he's feeling quite superior after that dissertation.

Would like to point out that we are making and flying RC planes not satellites or military airplanes.

As far as Ego's are concerned I'm not a psychologist but I do read and the ego only shows itself when it's threatened by some real fact that it's not prepared to confront.

My intent was to present a simple factual and logical question as to why someone would want to Kevlar and or carbon fiber on an RC plane not satellites or military planes. Why that even came up is well beyond the simply scope of the question i asked.

I am educated in the uses of composites and the fabrics used. But didn't feel the need to present a dissertation on the subject matter, and still don't. hehe.
May 26, 2019, 05:13 AM
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Andrew207's Avatar
Thread OP
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