Cloth fact and fiction
09-21-2002, 02:10 AM
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Cloth fact and fiction
With all of the different types of cloth available, it can be very confusing on what would work best for a specific task.
Exotics such as Aramid{Kevlar} and Carbon are commonly misunderstood.
First off, you always hear about Kevlar and about how its bulletproof etc. The fact is that it does have incredible impact resistence, but the bullet proof vests use ballistic grade Kevlar.
This is not wetted out with resin, just a thick weave of Kevlar fibers. When you wet it out it becomes something different.
it will crack when hit hard enough, but its laurels are that it wont usually break free, or break in two so you will still have some structural integrity left.
Kevlar is good for its impact resistance and its abrasion resistence. It should not be used to "stiffen" something up, as this is Carbons job.
A good use of Kevlar on our models would be for landing gear, and the corresponding area it attaches to. Models that land on their belly could do good with some Kevlar down there.
Turbine fuel tanks are another, as in a severe crash they can deform and fracture the resin, but wont totally split open dumping their contents everywhere. Basically any area that could be subjected to being impacted with shock loads.
Carbon is a different anamal. It will flex flex flex snap. Kevlar would flex flex flex groan creak give a little then fracture.
Carbon is the "stiffener". And it does this job with a stiffness to weight that is one of the best of any material, better than Kevlar.
Kevlar is strong, Carbon is stiff. Kevlar is a real pain to cut carbon cuts like butter
I know some of you will groan and say why does my model have Carbon landing gear mounting plates instead of kevlar if this is true?:I really dont know, maybe they use carbon for a reason, but knowing the material I would say that it would be better to use Kevlar there, or at least a mix or hybrid.
Regular S-Glass is commonly overlooked for reinforcement.
S stands for structural. I found on one project I was doing that an S-glass/carbon was just about as strong as the Kevlar/carbon part we were testing, and it was certianly easier to handle the construction process because you can cut S-glass with scissors.
I have tried the $70 German scissors that supposedly cut Kevlar
All i can say is that I now have a $70 pair of scissors and I still cut kevlar with tape and a new razorblade.
I hope this cleared up some confusion about these two materials.
There is much to add to this topic, and if anything I have said you feel is misguided, I love to learn new things too!
Exotics such as Aramid{Kevlar} and Carbon are commonly misunderstood.
First off, you always hear about Kevlar and about how its bulletproof etc. The fact is that it does have incredible impact resistence, but the bullet proof vests use ballistic grade Kevlar.
This is not wetted out with resin, just a thick weave of Kevlar fibers. When you wet it out it becomes something different.
it will crack when hit hard enough, but its laurels are that it wont usually break free, or break in two so you will still have some structural integrity left.
Kevlar is good for its impact resistance and its abrasion resistence. It should not be used to "stiffen" something up, as this is Carbons job.
A good use of Kevlar on our models would be for landing gear, and the corresponding area it attaches to. Models that land on their belly could do good with some Kevlar down there.
Turbine fuel tanks are another, as in a severe crash they can deform and fracture the resin, but wont totally split open dumping their contents everywhere. Basically any area that could be subjected to being impacted with shock loads.
Carbon is a different anamal. It will flex flex flex snap. Kevlar would flex flex flex groan creak give a little then fracture.
Carbon is the "stiffener". And it does this job with a stiffness to weight that is one of the best of any material, better than Kevlar.
Kevlar is strong, Carbon is stiff. Kevlar is a real pain to cut carbon cuts like butter
I know some of you will groan and say why does my model have Carbon landing gear mounting plates instead of kevlar if this is true?:I really dont know, maybe they use carbon for a reason, but knowing the material I would say that it would be better to use Kevlar there, or at least a mix or hybrid.
Regular S-Glass is commonly overlooked for reinforcement.
S stands for structural. I found on one project I was doing that an S-glass/carbon was just about as strong as the Kevlar/carbon part we were testing, and it was certianly easier to handle the construction process because you can cut S-glass with scissors.
I have tried the $70 German scissors that supposedly cut Kevlar
All i can say is that I now have a $70 pair of scissors and I still cut kevlar with tape and a new razorblade.
I hope this cleared up some confusion about these two materials.
There is much to add to this topic, and if anything I have said you feel is misguided, I love to learn new things too!
09-22-2002, 09:39 AM
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Cloth fact and fiction
I made landing gear from UNI-DIRECTIONAL fibreglas which as I was told has great flexing character. My GM van rear springs are made from GF. Dont buy cloth gear carbon or glas, its improper material selection. Carbon would make lighter gear, but like rpm said its stiff, making for more bounce. The glas gear flexs nicely as it absorbs landing loads.
09-27-2002, 08:36 PM
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C.F. Landing Gear
You may have a little more flex with a c.f. gear but that all depends on how thick you make the gear. I have made a set for my 25% Cap to replace the aluminum gear and here is what I have learned.
1. lb for pound c.f. is much stronger, actually my gear is almost half the weight 4.5 oz vs. 8 oz for the aluminum and is stronger then the aluminum gear.
2. c.f gear will not lose its shape unless you really crash it hard and then... its BROKEN.
3. When laying up c.f. gear the best method is to vacum bag them. This eliminates excess builod up of resin between the layers. Excess resin is a weak area and failure at the bends or delamination is most likely if to much resin is built up there. Delamination seems to be the most common failure of c.f. gear and is usually do to poor lay up and/or resin quality.
4. Alternating layers of unidirection and directional c.f makes for a stiff and twist free l.g.
My layup is about the same thickness as the aluminum gear and I feel it is much stronger. On some hard landings the aluminum gear just gave way and bent. On a similar landing the c.f gear remained intact and unstressed.
My vote goes with the c.f gear.
STRONGER
LIGHTER
LESS CHANCE OF DEFORMED GEAR
1. lb for pound c.f. is much stronger, actually my gear is almost half the weight 4.5 oz vs. 8 oz for the aluminum and is stronger then the aluminum gear.
2. c.f gear will not lose its shape unless you really crash it hard and then... its BROKEN.
3. When laying up c.f. gear the best method is to vacum bag them. This eliminates excess builod up of resin between the layers. Excess resin is a weak area and failure at the bends or delamination is most likely if to much resin is built up there. Delamination seems to be the most common failure of c.f. gear and is usually do to poor lay up and/or resin quality.
4. Alternating layers of unidirection and directional c.f makes for a stiff and twist free l.g.
My layup is about the same thickness as the aluminum gear and I feel it is much stronger. On some hard landings the aluminum gear just gave way and bent. On a similar landing the c.f gear remained intact and unstressed.
My vote goes with the c.f gear.
STRONGER
LIGHTER
LESS CHANCE OF DEFORMED GEAR
09-28-2002, 12:06 AM
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Carbon Fiber is SEXIER
Whenever you wonder, why, when Kevlar is more suitable for that job/part, they put Carbon, well the answer is simple, nice, sexier things sell more than practical cheaper solutions.
Roderick Woolvett
www.manque-aircraft.com
Roderick Woolvett
www.manque-aircraft.com
09-29-2002, 08:45 PM
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Composite LG
We've had excellent results using CF and Kevlar in a complimentary fashion to design composite LG.
See our article in the April 2000 issue of RC Modeler magazine.
See our article in the April 2000 issue of RC Modeler magazine.
10-02-2002, 01:35 PM
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Cloth fact and fiction
On these forums and elswhere I saw the recommendation to use two layers that add up to 8-9 - i.e. 5oz glass + 3 oz glass etc for molding fuselages of 40-60 size. Also once I saw somebody mentioning hybrid cloth that is lighter only as one layer.
RPmodeltech, seeing the discussion about properties of Kevlar,
what would you think about molding a 1/12 scale Combat fuselage form either hybrid Kevlar/carbon 5.5 oz single layer or Kevlar 5.5 / glass 3oz two layer maybe also using coremat for sandwich.
Which combination do you think would be the lightest and yet have reasonably good impact resistance - to midairs, dirtnaps and similar ? As you know combat planes take a lot of abuse
Bach
RPmodeltech, seeing the discussion about properties of Kevlar,
what would you think about molding a 1/12 scale Combat fuselage form either hybrid Kevlar/carbon 5.5 oz single layer or Kevlar 5.5 / glass 3oz two layer maybe also using coremat for sandwich.
Which combination do you think would be the lightest and yet have reasonably good impact resistance - to midairs, dirtnaps and similar ? As you know combat planes take a lot of abuse
Bach
10-02-2002, 11:37 PM
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Cloth fact and fiction
Bach, 5 oz Kevlar would brobably be a bear to work with on this small of a plane. Kevlar wets out best with Vinylester resin too.
I thin that the use of a hybrid {carbon/Kevlar} would also cause difficulties. I have been using 6 oz S glass in a single layer for my RPMjet {.18-.21 ducted fan} and using 9 oz carbon unidirectional strips about 1/4" wide where the fuse needs it, in place of bulkheads. This setup is plenty stiff enough for my application, and light. I would make my first one out of the 6oz cloth, pull it and see where it is flimsey and add some carbon strips there.
If you want to try kevlar I would suggest you use a layer of the fine kevlar cloth{1.9oz I think} and a layer of 5-6oz. Put the regular cloth down as the first layer, then the Kevlar. The kevlar also is almost impossible to sand without it fuzzing.
As for a core it woulld certianly make the fuse very stiff, but would probably betoo much of everything for your small plane.
Its hard to say without first pulling an experimental part first. So make a flimsey one first too see where you need reinforcements.
Hope this helps some.
I thin that the use of a hybrid {carbon/Kevlar} would also cause difficulties. I have been using 6 oz S glass in a single layer for my RPMjet {.18-.21 ducted fan} and using 9 oz carbon unidirectional strips about 1/4" wide where the fuse needs it, in place of bulkheads. This setup is plenty stiff enough for my application, and light. I would make my first one out of the 6oz cloth, pull it and see where it is flimsey and add some carbon strips there.
If you want to try kevlar I would suggest you use a layer of the fine kevlar cloth{1.9oz I think} and a layer of 5-6oz. Put the regular cloth down as the first layer, then the Kevlar. The kevlar also is almost impossible to sand without it fuzzing.
As for a core it woulld certianly make the fuse very stiff, but would probably betoo much of everything for your small plane.
Its hard to say without first pulling an experimental part first. So make a flimsey one first too see where you need reinforcements.
Hope this helps some.
10-22-2002, 02:29 AM
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Cloth fact and fiction
For strength:
1.) Is it better to use many layers of a light weight cloth, or a few with a heavier one?
2.) Thread count: 1K, 3K, 6K, 12K?
3.) What if you can't vacuum bag gear?
4.) Polyester Resin, or epoxy?
5.) What are the down falls of each?
6.) Will the composite parts get soft in the sun's heat? (FL)
Sorry for all the questions, I just want to get the right stuff. I had a sample of 8oz woven w/mat backing, and it was very difficult to work with.
Thanks,
--Rick
1.) Is it better to use many layers of a light weight cloth, or a few with a heavier one?
2.) Thread count: 1K, 3K, 6K, 12K?
3.) What if you can't vacuum bag gear?
4.) Polyester Resin, or epoxy?
5.) What are the down falls of each?
6.) Will the composite parts get soft in the sun's heat? (FL)
Sorry for all the questions, I just want to get the right stuff. I had a sample of 8oz woven w/mat backing, and it was very difficult to work with.
Thanks,
--Rick
10-22-2002, 06:05 AM
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Cloth fact and fiction
1.) Is it better to use many layers of a light weight cloth, or a few with a heavier one?
Optimally, per weight, I think it would proove stronger to use layers of thin cloth, instead of one heavy one. Everything is a compromise, ease of construction vs optimum construction and finish value.
2.) Thread count: 1K, 3K, 6K, 12K?
Usually included in the CLOTH weight. Once again a compromise,the more threads the more strenght and weight.
3.) What if you can't vacuum bag gear?
You dont need too. I have made a set for my H-9 cap, and they have survives 2 crashes where the aluminum gear would be scrap{not my crashes, as I sold them to a friend who flys cap's} I can post a picture of a PANCAKED cap and the gear lived!, 2 times! and is still here.
4.) Polyester Resin, or epoxy?
Ultimately it comes to adjustability, For the gear I built above I use Vinylester, which is a more refined version of polyester. Polyester keeps on hardening till it turns into dust {really}
Vinylester reaches a certian point in the cure stage and STOPS, instead of keep getting harder and harder over time like Polyester does. Also you really cant adjust the pot life of epoxy like you can vinylesters { I hear an objection coming on, but in real life this is what I found}
Its tough to say where to use what, There are alot of people who will say that epoxy is superior to vinylester, most of whome have never used the latter.
I find that they bolth work well, and epoxy has the edge when it comes to bonding and ultimate inpact resistance.
5.) What are the down falls of each?
Vinylester/polyester falldown: smells bad, can be brittle with wrong usages, can detiorate with time{polyester}.
Epoxy falldown: finickey mixtures, have to buy a different hardener or system to adjust work time, you must mix WELL, the more the better.
6.) Will the composite parts get soft in the sun's heat? (FL)
generally if used correctly none will get soft in ambient{baking in the Florida sun} heat. Without going into alot of details, if you subject your part to a mild postcure heating{controlled} it will be resistent to softening in heat. Usually it is because it is the wrong mixture or not cured enough that causes softening.
They paint composite planes white for a reason!!!
Hope this helps, This is what I have found over the years, composites is a very "varied" science!
Mr Minski, very nice quote from leo!!!
Optimally, per weight, I think it would proove stronger to use layers of thin cloth, instead of one heavy one. Everything is a compromise, ease of construction vs optimum construction and finish value.
2.) Thread count: 1K, 3K, 6K, 12K?
Usually included in the CLOTH weight. Once again a compromise,the more threads the more strenght and weight.
3.) What if you can't vacuum bag gear?
You dont need too. I have made a set for my H-9 cap, and they have survives 2 crashes where the aluminum gear would be scrap{not my crashes, as I sold them to a friend who flys cap's} I can post a picture of a PANCAKED cap and the gear lived!, 2 times! and is still here.
4.) Polyester Resin, or epoxy?
Ultimately it comes to adjustability, For the gear I built above I use Vinylester, which is a more refined version of polyester. Polyester keeps on hardening till it turns into dust {really}
Vinylester reaches a certian point in the cure stage and STOPS, instead of keep getting harder and harder over time like Polyester does. Also you really cant adjust the pot life of epoxy like you can vinylesters { I hear an objection coming on, but in real life this is what I found}
Its tough to say where to use what, There are alot of people who will say that epoxy is superior to vinylester, most of whome have never used the latter.
I find that they bolth work well, and epoxy has the edge when it comes to bonding and ultimate inpact resistance.
5.) What are the down falls of each?
Vinylester/polyester falldown: smells bad, can be brittle with wrong usages, can detiorate with time{polyester}.
Epoxy falldown: finickey mixtures, have to buy a different hardener or system to adjust work time, you must mix WELL, the more the better.
6.) Will the composite parts get soft in the sun's heat? (FL)
generally if used correctly none will get soft in ambient{baking in the Florida sun} heat. Without going into alot of details, if you subject your part to a mild postcure heating{controlled} it will be resistent to softening in heat. Usually it is because it is the wrong mixture or not cured enough that causes softening.
They paint composite planes white for a reason!!!
Hope this helps, This is what I have found over the years, composites is a very "varied" science!
Mr Minski, very nice quote from leo!!!
10-22-2002, 03:37 PM
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Cloth fact and fiction
Are they painted white for the heat or protection from UV rays?
I made a mold for my landing gear out of Arborite( plastic laminate) Wax well and then I clamped a cap on top which has the same effect as bagging. I trimmed the gear to width after, but with glass! I hear those carbon fibres are not good for you.
I made a mold for my landing gear out of Arborite( plastic laminate) Wax well and then I clamped a cap on top which has the same effect as bagging. I trimmed the gear to width after, but with glass! I hear those carbon fibres are not good for you.
10-27-2002, 06:18 AM
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Cloth fact and fiction
I made my first 2 LG this week, and posted pictures here:
http://www.rcuniverse.com/showthread...05&forumid=206
They look pretty good, and it was really easy!!
http://www.rcuniverse.com/showthread...05&forumid=206
They look pretty good, and it was really easy!!
10-27-2002, 07:26 AM
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Cloth fact and fiction
I'm sorry, I screwed up and forgot to take picts of the gear . I will try to have a few picts tomorrow night.
They are still attached to a friends plane {my plane originally, and sold to him} that is totally destroyed {by him}, These things are so overbuilt I dont think you COULD break them on a 1/4 scale CAP. I learned about making tough gear with a 15# Goldberg Extra {dont ask} I had, that had to land on a rough strip daily.
They are still attached to a friends plane {my plane originally, and sold to him} that is totally destroyed {by him}, These things are so overbuilt I dont think you COULD break them on a 1/4 scale CAP. I learned about making tough gear with a 15# Goldberg Extra {dont ask} I had, that had to land on a rough strip daily.
11-24-2002, 12:55 AM
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Cloth fact and fiction
Is CF really bad for you?
I've looked in several toxicology texts and have not found it. I know of no pulmonary disorders associated with CF. Are there only anecdotal reports or has someone done a study?
I've looked in several toxicology texts and have not found it. I know of no pulmonary disorders associated with CF. Are there only anecdotal reports or has someone done a study?
11-24-2002, 01:46 AM
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Cloth fact and fiction
OK, I found this in an OSHA report:
Toxicological Information:
Graphite causes benign pneumoconiosis (graphitosis). Symptoms of pneumoconiosis from graphite exposure are dypsnea, coughing, black sputum, bronchitis, ventricular hypertropy and impairment of pulmonary function. X-rays will show progressive nodulation of the lungs. The theshold limit value was set in conformity with the limit for free crystalline silica, which may be present in graphite.
Essentially this says that CF exposure may decrease pulmonary function to the point that it could cause right heart failure. Much of this may be due to the silica in CF. Silica can cause silicosis which is nasty. They recommend cutting CF under a hood for ventilation to avoid inhaling the fibers. Frankly, as a health care professional, I much more concerned about all the solvents we are exposed to.
Toxicological Information:
Graphite causes benign pneumoconiosis (graphitosis). Symptoms of pneumoconiosis from graphite exposure are dypsnea, coughing, black sputum, bronchitis, ventricular hypertropy and impairment of pulmonary function. X-rays will show progressive nodulation of the lungs. The theshold limit value was set in conformity with the limit for free crystalline silica, which may be present in graphite.
Essentially this says that CF exposure may decrease pulmonary function to the point that it could cause right heart failure. Much of this may be due to the silica in CF. Silica can cause silicosis which is nasty. They recommend cutting CF under a hood for ventilation to avoid inhaling the fibers. Frankly, as a health care professional, I much more concerned about all the solvents we are exposed to.
01-04-2003, 09:34 PM
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Cloth fact and fiction
Bla Bla Bla, you all seen to know the differant propertys of Exotic Materials, but still not hit the nail on the head..
I will post the entire property list of Exotics and it's easy to read.
It's on my machine at work..
Advanced Composite Engineering
(707) 762-6542
Mike
I will post the entire property list of Exotics and it's easy to read.
It's on my machine at work..
Advanced Composite Engineering
(707) 762-6542
Mike
01-05-2003, 01:54 AM
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Cloth fact and fiction
I posted to Composites Questions and answers: I have a list of all the types of Composite Materials we use in the industries, its easy to understand the proper type of material to use in your lay-ups. Hope this will help you all..
Mike
Mike
