Kevlar Hinge
10-06-2010, 06:49 AM
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Kevlar Hinge
Hi All,
Hi I am new to bagging wings and have some questions re: kevlar hinges, and have searched the forums, without much luck.
(a) One of the main composite suppliers in the States sells a 2.5 oz Uni Direction Kevlar, has anyone used this material to make hinges ? The layup I was planning to use is 3.5-3.7 oz 80/20 carbon and 3/4 oz glass + kevlar. It seems the most common kevlar material is 1.7 oz cut on a 45o bias. However the 2.5 oz would be significantly cheaper as it come's in a 12" width, so less wastage.
The sales blurb is :
UnidirectionalKevlar® is a new and easy to apply type of reinforcement. It consists of a non-woven sheet of unidirectional Kevlar® fibers that are held in position by a fine spider web of polymer fibrils lying on one or both surfaces. The special polymer used is compatible with epoxy and polyester resins. The fibril or web system that bonds the reinforcement fibers together allows the fabric to be cut easily, trimmed, or slit, giving clean edges with absolutely no fraying. The fibers lie flat and straight, and cannot shift or bunch up as often happens with uni-stitched fabrics.
(b) Does anyone know of a supplier in Australia that sells light weight 1.7 oz Kevlar or Carbon e.g. 80/20 in 3.5 oz and up range?
(c) Once you cut the hinge's what is the best way to treat the foam to stop fuel and oil ingress?
Thanks in Advance,
Adrian
Hi I am new to bagging wings and have some questions re: kevlar hinges, and have searched the forums, without much luck.
(a) One of the main composite suppliers in the States sells a 2.5 oz Uni Direction Kevlar, has anyone used this material to make hinges ? The layup I was planning to use is 3.5-3.7 oz 80/20 carbon and 3/4 oz glass + kevlar. It seems the most common kevlar material is 1.7 oz cut on a 45o bias. However the 2.5 oz would be significantly cheaper as it come's in a 12" width, so less wastage.
The sales blurb is :
UnidirectionalKevlar® is a new and easy to apply type of reinforcement. It consists of a non-woven sheet of unidirectional Kevlar® fibers that are held in position by a fine spider web of polymer fibrils lying on one or both surfaces. The special polymer used is compatible with epoxy and polyester resins. The fibril or web system that bonds the reinforcement fibers together allows the fabric to be cut easily, trimmed, or slit, giving clean edges with absolutely no fraying. The fibers lie flat and straight, and cannot shift or bunch up as often happens with uni-stitched fabrics.
(b) Does anyone know of a supplier in Australia that sells light weight 1.7 oz Kevlar or Carbon e.g. 80/20 in 3.5 oz and up range?
(c) Once you cut the hinge's what is the best way to treat the foam to stop fuel and oil ingress?
Thanks in Advance,
Adrian
10-06-2010, 07:23 AM
#2
RE: Kevlar Hinge
There's a great treatment of Kevlar hinges in the "Sticky" posts at the top of the Beginner's forum.
I must be missing something, because I'm not quite making the connection between bagging wings and this Kevlar brand you mention. Could you elaborate?
And, I can't help you find a supplier.
The main reason I respond is because I'm having trouble understanding your (c). What material will your trailing edge be, where the hinges mount? Or, maybe I should just inquire about your bagging process. Maybe I'll learn something here.
In any event, best wishes,
Dave Olson
I must be missing something, because I'm not quite making the connection between bagging wings and this Kevlar brand you mention. Could you elaborate?
And, I can't help you find a supplier.
The main reason I respond is because I'm having trouble understanding your (c). What material will your trailing edge be, where the hinges mount? Or, maybe I should just inquire about your bagging process. Maybe I'll learn something here.
In any event, best wishes,
Dave Olson
10-06-2010, 08:27 AM
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RE: Kevlar Hinge
Hi Dave,
Just to clarify - I am using a blue foam core wing and then covering with Kevlar (just the hinge area top and bottom to the trailing edge say a 2-3" band of kevlar). I am then adding the 80/20 carbon fibre fabric + 3/4 oz glass over the entire wing surface. This will then be put in the vacuum bag and cured. The Ailerons will then be cut out leaving (I think it is the top surface intact) so that the kevlar acts as a skin hinge for that wing. This is a pretty simplified version as some of the carbon fibre tow needs to be removed and there are a few other things that need to be done, but you get the idea.
So the questions that i have relate to the use of uni-direction kevlar and using a considerably heavier weight over the 1.7 oz which seems to be the norm. As way of further explanation for (c) as you aileron is cut from the wing, the foam core will be exposed. I am looking at using this for an aircraft that is glow, and i have a concern that the fuel / oil will get into the exposed foam.
i had a pretty good look in the beginner sticky section and couldn't find anything against kevlar hinges ..... not sure if you are getting this mixed up with CA hinges ??? sorry if i am having some form of domestic blindness, but couldn't find anything using the searches either.
The really simple answer would be to get some and try it ... however I live in Oz and have to order the fabric's from the States; i am trying to avoid buying the wrong product as freight is a killer across the pond.
Hope this explanation helps.
Cheers,
Adrian
Just to clarify - I am using a blue foam core wing and then covering with Kevlar (just the hinge area top and bottom to the trailing edge say a 2-3" band of kevlar). I am then adding the 80/20 carbon fibre fabric + 3/4 oz glass over the entire wing surface. This will then be put in the vacuum bag and cured. The Ailerons will then be cut out leaving (I think it is the top surface intact) so that the kevlar acts as a skin hinge for that wing. This is a pretty simplified version as some of the carbon fibre tow needs to be removed and there are a few other things that need to be done, but you get the idea.
So the questions that i have relate to the use of uni-direction kevlar and using a considerably heavier weight over the 1.7 oz which seems to be the norm. As way of further explanation for (c) as you aileron is cut from the wing, the foam core will be exposed. I am looking at using this for an aircraft that is glow, and i have a concern that the fuel / oil will get into the exposed foam.
i had a pretty good look in the beginner sticky section and couldn't find anything against kevlar hinges ..... not sure if you are getting this mixed up with CA hinges ??? sorry if i am having some form of domestic blindness, but couldn't find anything using the searches either.
The really simple answer would be to get some and try it ... however I live in Oz and have to order the fabric's from the States; i am trying to avoid buying the wrong product as freight is a killer across the pond.
Hope this explanation helps.
Cheers,
Adrian
10-06-2010, 12:50 PM
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RE: Kevlar Hinge
Adrian,
I think you have the Kevlar in the wrong place for a hing to be affective. All the ones I have seen are just under the top layer of fiberglass and are on top of the wood on the outside of the composite sandwich.
The most common layup for a molded composite wing would be something like this:
1. 3/4oz. fiberglass cloth
2. Kevlar hinge material cut on a 45 bias (could also be nylon or even peel ply)
3. 1.4oz fiberglass cloth
4. Balsa wing skins with a v notch trimmed out toward the hinge material (inside the wing)
5. Carbon spar caps
6. Inner 3/4oz fiberglass cloth
The internal structure would then be built inside the skins after they are bagged and cured. If you do it this way, the hinge material is sandwiched between the fiberglass and encased with resin. The balsa skins are also underneath them, so you would not be trying to buckle the skins as it flexes.
The uni Kevlar will not work too well. You really need a balanced thread count fabric cut on the bias (45 degree) so it retains its strength, but will flex easily too.
Is that any help to you?
I think you have the Kevlar in the wrong place for a hing to be affective. All the ones I have seen are just under the top layer of fiberglass and are on top of the wood on the outside of the composite sandwich.
The most common layup for a molded composite wing would be something like this:
1. 3/4oz. fiberglass cloth
2. Kevlar hinge material cut on a 45 bias (could also be nylon or even peel ply)
3. 1.4oz fiberglass cloth
4. Balsa wing skins with a v notch trimmed out toward the hinge material (inside the wing)
5. Carbon spar caps
6. Inner 3/4oz fiberglass cloth
The internal structure would then be built inside the skins after they are bagged and cured. If you do it this way, the hinge material is sandwiched between the fiberglass and encased with resin. The balsa skins are also underneath them, so you would not be trying to buckle the skins as it flexes.
The uni Kevlar will not work too well. You really need a balanced thread count fabric cut on the bias (45 degree) so it retains its strength, but will flex easily too.
Is that any help to you?
10-06-2010, 09:02 PM
#7
RE: Kevlar Hinge
Unidirectional is a no-go for me too.
Scar, the kevlar ends long before the TE, it's only a strip about .75 wide at the hinge line.
As far as sealing the foam you can either make the slot on the bottom wide enough to put some wood in there.
Usually my first few coats of primer are light enough they start the sealing process without eating the foam. I have also wetted out .75 glass and sealed it.
Scar, the kevlar ends long before the TE, it's only a strip about .75 wide at the hinge line.
As far as sealing the foam you can either make the slot on the bottom wide enough to put some wood in there.
Usually my first few coats of primer are light enough they start the sealing process without eating the foam. I have also wetted out .75 glass and sealed it.
10-11-2010, 03:58 AM
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RE: Kevlar Hinge
Hi All,
Thank you for your responses - i have ditched the idea of using the unidirectional kevlar. I hope to avoid using the a balsa wood / foam sandwich and get away with using the carbon.
By way of a quick explanation I have seen people use 80/20 carbon (This is where the carbon runs in one direction and is held together with a light amount of glass running at 90o to the carbon. To avoid the issue of having carbon over the kevlar hinge, you remove say a 1/4" of carbon toe from what will be the hinge line. So when you are cutting the hinge it is basically just the 3/4 ounce and the kevlar so you get good flexibility, I have seen this done for F3A wings and it works well by all reports.
Thanks Again - unless anyone else has any additional comments.
Cheers,
Adrian
Thank you for your responses - i have ditched the idea of using the unidirectional kevlar. I hope to avoid using the a balsa wood / foam sandwich and get away with using the carbon.
By way of a quick explanation I have seen people use 80/20 carbon (This is where the carbon runs in one direction and is held together with a light amount of glass running at 90o to the carbon. To avoid the issue of having carbon over the kevlar hinge, you remove say a 1/4" of carbon toe from what will be the hinge line. So when you are cutting the hinge it is basically just the 3/4 ounce and the kevlar so you get good flexibility, I have seen this done for F3A wings and it works well by all reports.
Thanks Again - unless anyone else has any additional comments.
Cheers,
Adrian
10-11-2010, 08:14 AM
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RE: Kevlar Hinge
Unidirectional Carbon fibre or Kevlar works well where a few layers are sandwitched. It serves teh purpose of aligning carbon in the direction where it is best able to cope with stress. For a hinge, this type of material is impractical.
Unidirectional fibres would work tremendously well in moulding a light strong torsionally resistant wing or fuselage
Unidirectional fibres would work tremendously well in moulding a light strong torsionally resistant wing or fuselage
