Silk instead of Fiberglass
11-30-2015, 01:50 PM
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Silk instead of Fiberglass
I don't do much kit building, (mostly just ARF stuff), but I have gotten in the habit of using fiberglass in certain areas to help beef up the structure, specifically the center section of wings and other places like if I feel the firewall needs some more strength, etc.
My wife does a lot of stuff with silk, (100% silk), and has a lot of scrap pieces left over. Some of these pieces are pretty good sized and knowing that silk is very strong, I am wondering if it would be of any advantage to use the silk instead of fiberglass for structural enhancement. The silk she has, (she calls it 5mm and 8mm to indicate the weight with the 8mm being alittle heavier), is about the same weight as 3/4 oz. fiberglass cloth but I noticed the weave is much tighter and it would appear the silk would be alot easier to work with around corners and such and even just in general considering it doesn't have a tendency to leave the big strands floating all over the place.
The question is, does anyone think using silk would be any better or even the same as lightweight glass cloth? Does anyone know if there is an issue using regular long cure epoxy with silk? I am just curious since it would be a lot easier to get ahold of without having to buy fiberglass.
Thanks in advance for any help.
My wife does a lot of stuff with silk, (100% silk), and has a lot of scrap pieces left over. Some of these pieces are pretty good sized and knowing that silk is very strong, I am wondering if it would be of any advantage to use the silk instead of fiberglass for structural enhancement. The silk she has, (she calls it 5mm and 8mm to indicate the weight with the 8mm being alittle heavier), is about the same weight as 3/4 oz. fiberglass cloth but I noticed the weave is much tighter and it would appear the silk would be alot easier to work with around corners and such and even just in general considering it doesn't have a tendency to leave the big strands floating all over the place.
The question is, does anyone think using silk would be any better or even the same as lightweight glass cloth? Does anyone know if there is an issue using regular long cure epoxy with silk? I am just curious since it would be a lot easier to get ahold of without having to buy fiberglass.
Thanks in advance for any help.
Last edited by tsawyer148; 11-30-2015 at 01:59 PM.
11-30-2015, 02:24 PM
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I used silk in that fashion years ago when it was harder to get the light grades of glass cloth. Silk will inherently have a lower modulus (it will stretch more in response to load) but I think that either glass or silk probably has adequate tensile strength if you get a good wet out. I used it and it worked, but I prefer glass now that .75 oz and 2oz is easily available. Wetting out many layers of silk leaves you open to delamination if you don't get good wetting. I have really hammered some models and generally do not see the reinforcement failing whether it was glass or equivalent wt of silk.
12-02-2015, 06:46 AM
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I would agree were it not for the fact that the pieces of silk I am referring to are "free to me" considering they are the scrap pieces my wife cannot use for what she is doing. That was the basis of my question; wanting to know if the silk would work since they would probably just be thrown away eventually.
Last edited by tsawyer148; 12-02-2015 at 06:48 AM.
12-03-2015, 04:15 AM
#6
Are your models free, or just the silk ?
If you are paying for your models, then I agree with the above post, stating that silk is a false economy.
Glass cloth isn't expensive and will perform better than silk, for your intended purpose.
If you are paying for your models, then I agree with the above post, stating that silk is a false economy.
Glass cloth isn't expensive and will perform better than silk, for your intended purpose.
12-03-2015, 07:07 AM
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Ok....as I stated the silk is scrap from something my wife does. Is costs me NOTHING, zip, ziltch, zero, nada. She buys it with her own money so it truly is free to me; economics is not a factor in this scenario. To coin a popular current buzz word, I am trying to "re-purpose" something that would end up in the trash anyway and possibly save me from having to drive an hour to a find a place that sells glass cloth or purchase it on line.
To simplify the question, taking into consideration that cost has absolutely nothing to do with anything in this situation, can 100% 5mm or 8mm silk combined with your standard long cure two part epoxy be used in lieu of 3/4 oz. fiberglass cloth for certain structural enhancements?
To simplify the question, taking into consideration that cost has absolutely nothing to do with anything in this situation, can 100% 5mm or 8mm silk combined with your standard long cure two part epoxy be used in lieu of 3/4 oz. fiberglass cloth for certain structural enhancements?
Last edited by tsawyer148; 12-03-2015 at 07:10 AM.
12-03-2015, 07:57 AM
#8
I feel that you are totally missing the point.
You asked for opinions on using silk in lieu of glass cloth. We are trying to be polite while we telling you not to do it.
You asked for opinions on using silk in lieu of glass cloth. We are trying to be polite while we telling you not to do it.
12-03-2015, 08:26 AM
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No, I am not missing the point. My original post stated that, for me in this situation, silk is not cost prohibitive yet your first reply mentions the point of the economics. If you have another reason why it is not a good idea then I would like to hear it. AwwNaww says he has used it in the past with success so if you have knowledge as to why I shouldn't then please, let me know.
12-03-2015, 08:47 AM
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Ok Tom, so can you think of a reason why it is a not a good idea to use silk instead of fiberglass in any given situation? If so, would you mind sharing the reason so I may be able to make an informed decision on whether to use it for a particular application?
12-03-2015, 10:44 AM
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No, I am not missing the point. My original post stated that, for me in this situation, silk is not cost prohibitive yet your first reply mentions the point of the economics. If you have another reason why it is not a good idea then I would like to hear it. AwwNaww says he has used it in the past with success so if you have knowledge as to why I shouldn't then please, let me know.
12-03-2015, 10:56 AM
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Yes, that is a good point, but cost is not now nor was it ever the main purpose for asking the question. Just for grins let's say I have more money than I know what to do with, (which is not the case by the way), and I am paying over $100.00/yard for the silk. Does that change whether or not it is a good idea to use it to enhance structural integrity in some areas? All I am asking is if it can be used instead of glass in certain applications. If not, then why. If it can, then great and how does it compare to glass, i.e., better/worse/about the same? TomCrump gave me an answer that helped, now I know that silk has less sheer strength than glass so I can use that information and decide if it is worth the risk to use it on high stress areas of any particular airframe.
Like I used to always tell my kids when they were younger, "just because" is not an answer.
Like I used to always tell my kids when they were younger, "just because" is not an answer.
12-03-2015, 11:26 AM
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Geez....typical online forum.....a simple question is asked....then you get the responders who dont even read the question....but respond anyway....then they tell you its all doom and gloom if you dont follow their advice.
I dont know what the answer is because I dont have any silk laying around.....but what I MIGHT do if I were in your delimma is to build two identical "test" fixtures....one reinforced in silk...and one reinforced with FG.....and do some load testing. Doesnt have to be very complicated.....you could probably take a peice of crashed airframe (we ALL have some of those laying around) and experiment with some of the framework. You may find that it is completely workable or totally inadequate......but at least you're thinking outside the box....which is what this hobby needs nowadays.....
CB
I dont know what the answer is because I dont have any silk laying around.....but what I MIGHT do if I were in your delimma is to build two identical "test" fixtures....one reinforced in silk...and one reinforced with FG.....and do some load testing. Doesnt have to be very complicated.....you could probably take a peice of crashed airframe (we ALL have some of those laying around) and experiment with some of the framework. You may find that it is completely workable or totally inadequate......but at least you're thinking outside the box....which is what this hobby needs nowadays.....
CB
12-03-2015, 11:36 AM
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Oh hell, that's a good idea, wow I'm getting old..... I think I have some small pieces of glass somewhere and definitely have more than enough parts of airframes, should be easy enough to give it a try. Thank you for the reply, I appreciate it very much.
12-03-2015, 11:45 AM
#18
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Over my 50 year modeling career I have done and continue to do a lot of work with fiberglass, carbon, Kevlar, silkspan, silk and Esaki Jap tissue, Polyspan polyester tissue, etc... I abhor plastic film and last I used it was probably 30 years ago at least.
Decades ago I used to apply the light glass over sheeted parts using first, polyester resin which I hated, then finishing epoxy which I liked. That's what the "expurts" were using so why not me?? Either of the binders produced a hard surface that was ready for primer after a bunch of elbow grease.
I threw that technique out the window. Much too heavy for my taste. I started using epoxy paint (K&B superpoxy) as the binder and I used that technique for many years producing many models in the process. It was much lighter and the surface was ding resistant enough but needed care. Thickness is the key variable and as thickness goes down so does ding resistance. Finishing epoxy was ding resistant but was applied thick, say around 0.006" where epoxy paint was half that thickness.
I occasionally use epoxy paint now (Klass Kote) to bind and bed coverings; however most of the covering is now applied using the old fashioned nitrate dope or Minwax polyurethane. These produce the thinnest and lightest of finishes even lighter than plastic film in some cases. Thickness will range from about 0.001" - 0.002" depending on the type and grade of covering I use, and directly translate to weigh savings. But these are not very ding resistant finishes and need special care.
With that as background, let me answer the question of the OP as follows:
I would not hesitate to use Silk to reinforce specific areas on a model. The thicker silk would work fine in 3-4 layers even for wing joints and firewalls. I would use epoxy for those apps. Real silk has plenty of strength for what we do in model building.
Don't be afraid to use silk as a direct substitute for 3/4 oz glass cloth over fully sheeted surfaces. Plus the great thing about silk is the fact that it is so resilient it can be used over open bays in a wing or stick built fuse. Apply it with dope for a smooth, wrinkle free base for paint. The much finer weave of good silk (expensive) as compared to 1/2 ounce glass cloth (less expensive) tends to telegraph through the finish much less than the glass does. Try it and I'm sure you would like the results
Decades ago I used to apply the light glass over sheeted parts using first, polyester resin which I hated, then finishing epoxy which I liked. That's what the "expurts" were using so why not me?? Either of the binders produced a hard surface that was ready for primer after a bunch of elbow grease.
I threw that technique out the window. Much too heavy for my taste. I started using epoxy paint (K&B superpoxy) as the binder and I used that technique for many years producing many models in the process. It was much lighter and the surface was ding resistant enough but needed care. Thickness is the key variable and as thickness goes down so does ding resistance. Finishing epoxy was ding resistant but was applied thick, say around 0.006" where epoxy paint was half that thickness.
I occasionally use epoxy paint now (Klass Kote) to bind and bed coverings; however most of the covering is now applied using the old fashioned nitrate dope or Minwax polyurethane. These produce the thinnest and lightest of finishes even lighter than plastic film in some cases. Thickness will range from about 0.001" - 0.002" depending on the type and grade of covering I use, and directly translate to weigh savings. But these are not very ding resistant finishes and need special care.
With that as background, let me answer the question of the OP as follows:
I would not hesitate to use Silk to reinforce specific areas on a model. The thicker silk would work fine in 3-4 layers even for wing joints and firewalls. I would use epoxy for those apps. Real silk has plenty of strength for what we do in model building.
Don't be afraid to use silk as a direct substitute for 3/4 oz glass cloth over fully sheeted surfaces. Plus the great thing about silk is the fact that it is so resilient it can be used over open bays in a wing or stick built fuse. Apply it with dope for a smooth, wrinkle free base for paint. The much finer weave of good silk (expensive) as compared to 1/2 ounce glass cloth (less expensive) tends to telegraph through the finish much less than the glass does. Try it and I'm sure you would like the results
12-03-2015, 11:50 AM
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Matt, THANK YOU for the reply. That helps immensely. I have a few old wing and fuse pieces and a little time on my hands this weekend. I'll try some things and see if I can get them to translate well enough to use on something I'm trying to get in the air.
Thanks again!
Thanks again!
12-04-2015, 12:58 PM
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12-06-2015, 01:59 PM
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Glass doesn't stretch. Silk does. Silk is good over wing bays where you need tension to keep the skin from sagging. Glass is good for making things stiff. That's why they make car hoods and bow limbs out of it. It may be the case that either will be plenty strong enough for your application. But glass will no doubt be stronger for reinforcing your structures.
