5.7oz carbon plain weave for stressed skin 2m wing

[rtbrowntrout]

Hi,

I am interested in creating a stressed skin 2m thermal duration wing since I would prefer to keep the spar to a simple carbon tube. I have 5.7oz plain weave cloth and 1.7oz plain weave kevlar. I was thinking of using the plain weave carbon from the leading edge to the hinge line and using the kevlar from the hinge line to the trailing edge. My concern is that it appears that most (if not all) stressed skin designs of this nature use uni-directional carbon instead of carbon plain weave fabric. Can plain weave carbon be used for a stressed skin wing design? It would be a 'winch launchable' wing, but I don't necessarily need one that can handle a full pedal launch.

Any help is appreciated.

[nuevo]

yes, CF weave cloth will work. A lot of planes in the 90's were made that way. Grand Esteem and Pelican to name a few that I owned. I vac bagged a few of my own designs using carbon tube and CF plain weave cloth. I would say 5.7 is a little heavy weight cloth for your application, but if you have it, use it.

Consider orienting the kevlar at 45 degrees to help reduce twist in the ailerons & flaps. Also consider moving the CF/kevlar line in front of the hinge line. That way, you can use the kevlar cloth as a hinge.

[rtbrowntrout]

Hi nuevo,

Thanks for the response. So, are you recommending using the carbon cloth in a non-bias configuration (fibers spanwise and chordwise)?

Yes, I like your suggestion of putting the kevlar on a bias and a little in front of the hinge line to make use of the kevlar for the hinge.

Thanks again.

[nuevo]

So, are you recommending using the carbon cloth in a non-bias configuration (fibers spanwise and chordwise)? .

Yes. That's the way it was done.

Other planes that used CF cloth as you described. Addiction, Compulsion, bagged Psyko, Fusion, 2m Laser, etc.

[T.D.]

"So, are you recommending using the carbon cloth in a non-bias configuration (fibers spanwise and chordwise)?"

"Addiction, Compulsion, bagged Psyko, Fusion, 2m Laser"

IIRC those gliders used 3.5oz. or 4.7 oz. carbon uni (or 80/20) with 1.4oz. 'glass over, not bias or non-bias woven carbon cloth.

rtbrowntrout, if you use woven cloth in a non-bias app. the chord wise fibres add no real strength but do add weight and are for the most part just along for the ride.

5.7oz. woven carbon is serious overkill on a two metre TD ship, especially if you are planning on using something like the Drela airfoils.

There are a couple ways of making it work effeciently though, firstly you can strip the individual fibres out and make uni from them...it's a lot of work and fiddling around but it can be done. A lite dusting of 3M-77 on wax paper and an iorn set on low will work for this.

A much better way is to strip the individual fibres out and lay up carbon spar caps, cut up some end grain balsa and make Drela type carbon capped spars.

I know you stated your desire to use carbon tubes as the spars so if you do use the woven carbon cloth you don't need to take the carbon all the way back to the hinge line, 50% of chord from the leading edge will work and use the bias Kevlar from there back. This will result in a significant weight saving.

I would also recommend inserting a carbon uni spar cap on top of the carbon tube spar, it doesn't have to be very big, even 1/8 thick 3/16" or 1/4" wide will make a difference in the stiffness of your wing. After you install the tube spar just cut a slot in the top of the core to the tube and lay in your carbon cap. Fair it in and you are done.


T.D.

[rdwoebke]

Other planes that used CF cloth as you described. Addiction, Compulsion, bagged Psyko, Fusion, 2m Laser, etc.

Nuevo,

I don't think this is correct for the Psyko. I have two psykos, and the layup is as you describe (carbon from le back to right in front of hinge line, then kevlar from there) but the carbon on my Psyko is a uni type carbon. Not a bi directional cloth (it might have a few pieces of "holding in place" carbon strands but it is definitely not a ballanced carbon cloth). I think, but am not sure, that the kevlar is oriented 90 degrees with span not on bias.

Ryan

[nuevo]

Ryan, You are correct on the Psyko CF cloth. My error. The cloth was not balanced cloth but mostly UNI with regularly spaced cross fibers.

The meat of my comment is that cloth is traditionally oriented along the span/chord axis, not bias 45-degrees.

I didn't comment on how the kevlar was oriented. Only a recommendation that it be placed on a 45-degree bias.

[rdwoebke]

The meat of my comment is that cloth is traditionally oriented along the span/chord axis, not bias 45-degrees.

Yeah, that is correct. TD makes a good point that the 5.7 cloth will probably work just fine, but the stuff going cord wise is just extra weight.





I didn't comment on how the kevlar was oriented. Only a recommendation that it be placed on a 45-degree bias.

I have always been curious how the Kevlar is laid on the Psyko. From looking at it, I think it is not on a bias, but sometimes it is tough to tell fine weave Kevlar or glass by looking. The carbon is usually pretty obvious. :)

[T.D.]

"but the carbon on my Psyko is a uni type carbon"

It was for the most part 80/20 carbon uni with S-Glass at 90 degrees as was the layup on most if not all of the gliders mentioned.

"I think, but am not sure, that the kevlar is oriented 90 degrees with span not on bias."

If Phil Barnes laid those wings up which is highly possible the Kevlar is most likely at a +/-45 degrees which it how it should be used in this app.


T.D.

[rtbrowntrout]

Thanks for all of the replies. I think I will run some experiments attempting to pull out at least some of the fibers that would run chordwise to reduce the weight. Perhaps leaving some amount of the chordwise fibers in the fabric will help it retain its shape?

T.D., can you provide a bit more explanation of your wax paper/spray adhesive/low temp iron technique for removing fibers?

I agree with everyone that 5.7oz carbon is overkill for a 2m wing, but that is what is readily available, and it seems to be a lot cheaper than the lighter weights of carbon.

I appreciate all the comments.

[target]

Actually, I usually find that Uni Carbon is much cheaper than a balanced CF fabric.

I think that you may need to look around. I have noticed that one fabrics distributor in particular is seemingly very proud of their uni-carbon compared to some of the other places...
And the Uni seems easier to work with especially than the carbons that aren't plain weaved.
I'm butting in because I'm also getting the itch to bag my own Thermal wing sets.

Good luck on your project.

Target

[Phil Barnes]

You have gotten the correct answers to almost everything so I will mostly be simply confirming which replies are correct and adding a tiny bit of new information.

I did build all of the wing types mentioned except the Addiction and Compulsion which were Fred Sage models, I believe.

The carbon on the forward parts of the wings was indeed the type commonly referred to as "8020" fabric, although it was a lighter version than what most people are familiar with. The carbon was 12 strands of 3K carbon per inch, the cross fibers were 12 strands of 1K s-glass. The cross fibers are mostly just along for the ride and add little or nothing to the strength or stiffness of the wing. Your 5.7oz carbon fabric is very likely a balanced weave of 12 strands of 3k carbon in each direction. That means that it will give roughly equal strength and stiffness as the original 8020 carbon/s-glass since the spanwise carbon fibers will be identical. The cross fibers will be heavier since they will be 3K carbon bundles in place of 1k s-glass and so the wings would be heavier for no strength/stiffness gain.

The carbon part of the skin would run from LE to about 1/4" ahead of the hinge line at the root. This would taper towards the tip end such that the carbon would be less than 50% of the chord width. You do want to keep the carbon off of the hinge line if you want to make skin hinges.

The Kevlar was the 1.7oz variety (1.8oz is the same thing). It was always applied on a bias to increase torsional stiffness of the control surfaces. The bias layup would also add durability to the skin hinge.

You can remove some of the unwanted cross fibers in the carbon fabric. It is a very tedious job though. You do need to keep some cross fibers to hold the spanwise fibers in place. You would want to pull the cross fibers before spraying with 3M77. Any more than a light mist of 3M77 would make it nearly impossible to pull out cross fibers. I would recommend cutting a rectangle of fabric, taping that down with two strips of masking tape or packing tape with the tape running along the chordwise ends of the rectangle. Then pull out maybe 1/2 or 2/3s of the cross fibers. Then spray a light mist of 3M77 on wax paper, apply to the fabric and then remove the tape and lift from the bench. You could then cut that wax paper/carbon to size and apply to layup, wax paper side up, and then pull off the wax paper.

The Esteem and Pelican wings, during the time I started bagging them, used a 3.0oz uni-carbon on bottom with glass skins on top. That changed to the 8020 carbon on bottom with glass skins on top and finally changed to the layup described above for the other wings.

The carbon tube "spar" actually carries very little load and shouldn't be called a spar. It is primarilly a good place to put a joiner rod. The bending strength of your wings will primarilly depend on the amount of carbon that runs spanwise on the wings.

http://www.rcgroups.com/forums/showthread.php?p=6143620&highlight=bridge#post6143620

[rtbrowntrout]

Hi Target and Phil,

Target, I'm happy to say that I did find a source for some 3.5oz unicarbon. I hope you have success with bagging your thermal wings.

Phil, thanks for the information. It sounds like I could make my 5.7oz plain weave carbon work, but it will be a hassle. I'm going to try your technique for removing some of the chordwise fibers. If I struggle with it, I'll stick to using the unicarbon I just purchased. Also, thanks for the other information and the link. I had fun reading about your weblets/bucking experiments. With that information I'm convinced I'll want to install some weblets.

I've bagged DLG wings before (carbon rods with kevlar skin), but this will be my first attempt at a 2m wing, so I appreciate the help.

Ryan (rtbrowntrout)

[target]

Hi Ryan-

Glad you found some of the uni as it is very easy to work with. You'll like it.
I looked online at several of my previous sources, and couldn't find the deals like I spoke of... I was hoping to point you in the right direction. Can I ask you where you found the light uni and how much you had to give for it??

Also, if it were me, I would skip trying to make the uni out of the balanced CF. Why not just save it for some heavier project where you need it? Slope plane builders use it all the time; maybe you can sell or swap it?

Best,
Target

[rtbrowntrout]

Hi Again,

Target, I found the unicarbon at http://www.rcglider.com. He appears to be closing out his remaining stock of kevlar, fiberglass, and carbon, so the prices are VERY good. The unicarbon is the last one in the list. His price on 1.7oz kevlar are also very good.

Send Robert and e-mail. His e-mail address is on the website. He takes PayPal. He will work out all the details via e-mail. I haven't received my kevlar and carbon yet, so I can't speak to its characteristics.

I suspect once word get around about his closeout, the lighter weight stuff won't last long.

Thanks for heads-up on the plain weave carbon for slopers. I do a little bit of sloping from time to time, so I'll take a look at the slope soaring forum for making some wings for that.

Ryan

[target]

Ah ha, thanks, I had forgotten about Robert Cavazos.

Regards, Target