RC Groups

RC Groups
    Composites Fabrication
        Question Kevlar Hing

#1 ian murdock Jan 31, 2013 07:21 AM

Kevlar Hing
 
Hi guys, this question probable has already be answered before but, what thickness of Kevlar do you recommend for a slope/DS glider? or weight? Also should I lay it on a biases?

Thanks for any help:popcorn:

#2 sarmoby Jan 31, 2013 10:08 AM

Hey Ian-

DS= go round in circles while pulling 40 g.

Kevlar is a high tenacity fiber which means when it re-kits itself, you will likely have fewer parts.
Kevlar weaknesses:
1. hard to machine/sand/cut
2. does not bond to resin in a similar way to glass or carbon, more of a encapsulation.
3. poor compression strength!!!

If you want if for the bottom of the fuse for abrasion, fine.
Do no put it as a wing skin in a DS airplane as it will crease and buckle on the top of the wing skin( most likely) and your broken taco will fly off course at ballistic speeds...

What part do you want to make?
How are you planning the main spar and fuse lay-up to handle the massive bending loads they will see?

Let us know what help you need.
Cheers,
Scott

#3 ian murdock Jan 31, 2013 12:16 PM

Hi Scott, sorry I should have gone into more detail. What I'm doing is make a hollow core flying wing. The first ones are just going to be fiberglass with carbon reinforcement, then I would like to build a few that are all carbon. What I'm trying to do is create a live hing in the wing using Kevlar. The hing will be on the bottom surface; question about laying the Kevlar, should it be on a bias or use something like a tap around 1 inch wide using the Kevlar as the hing material. One nice thing about an all Kevlar wing would be when it "Claps" (folds or breaks in half) I will have a bag to carry the parts in:D.

#4 wyowindworks Jan 31, 2013 08:54 PM

You want the hinge material to be bias cut. This gives you the maximum amount of fiber to span the hinge line and create the hinge.

#5 Jim.Thompson Jan 31, 2013 09:38 PM

Ian,

I have had two attempts at kevlar hinges so far, and both were an astonishing amount of fuss. The first was a complete failure. The second one, on a wing that is in service now, I eventually got to free up and articulate sufficiently freely to fly it. It tooks many hours work, (and lots of cursing) over several sessions, to get them functional. I eventually had to resort to burning them with a heated wire to get them to articulate.

I have a set of wings in the building stage now with kevlar hinges. I'm hoping that they will free up like in the demo videos to be found on utube.
After long discussions in person with successful builders, and much discussion online here, I'm still not totally clear what the problem was. Nor are they, for that matter! The only possible suggestion is that I had too much resin in the hinge line.

I hope you get it right first up, unlike me.

Jim.

#6 Upvector Jan 31, 2013 11:03 PM

definitely as Wyowindworks states... bias is the only way to get Kevlar to work
as a hinge.
...and bias it as far as it will go, not just the classical 45 deg. Our experience showed
the kevlar (1.7 weight) to actually break on a hinge line with no biasing, but further testing samples at the max bias (about 65 deg, as far as it would go) obtainable made a very strong and resilient hinge, with amazingly smooth "feel" to it.
You have to allow for a much wider strip of unbiased material of course, to get it to shrink to the width you want to cover the hinge line.
fwiw
Ray

#7 Jim.Thompson Jan 31, 2013 11:09 PM

Shearing.
 
Quote:

Originally Posted by Upvector (Post 23997334)
definitely as Wyowindworks states... bias is the only way to get Kevlar to work
as a hinge.
...and bias it as far as it will go, not just the classical 45 deg. ..........Ray

Known as "shearing" I think.

#8 Fubar 123 Feb 01, 2013 12:48 AM

Quote:

Originally Posted by ian murdock (Post 23988762)
Hi guys, this question probable has already be answered before but, what thickness of Kevlar do you recommend for a slope/DS glider? or weight? Also should I lay it on a biases?

Thanks for any help:popcorn:

Is peel ply unsuitable for the application of DS ing as a hinge material ?

#9 ian murdock Feb 01, 2013 08:28 AM

What weight of Kevlar would you guys recommend?

#10 pirulin Feb 01, 2013 09:40 PM

edited :off topic sorry

#11 SlowBarless Feb 02, 2013 01:00 AM

What about uni Kevlar for a hinge?

#12 Jim.Thompson Feb 02, 2013 02:27 AM

Quote:

Originally Posted by SlowBarless (Post 24008199)
What about uni Kevlar for a hinge?

This is purely a guess.
I think it would not provide sufficient diagonal support like the sheared conventional woven cloth would, which stops the surface from moving laterally.

#13 ron gijzen Feb 04, 2013 01:48 AM

Quote:

Originally Posted by ian murdock (Post 23999808)
What weight of Kevlar would you guys recommend?

I use Aramid 61 grams/m2 for flaps, ailerons and v-tail hinges on an F3B model, oriented at 45deg witrh respect to the hinge line.


All times are GMT -5. The time now is 09:14 PM.