Carbon Fibre

[Jay]

Hi guys

Building a Noble and laying down Carbon Fiber on solid blocks.  So far is it coming out great.
What I need to know is, do I carbon the whole plane?  I plan on using Polyspan on the open bays and silkspan on the fuse and tail.

Thanks for your help.

Jay

[Howard Rush]

I do it because people tell me I should, but I think it's a waste of time.

[phil c]

If the plane can handle the bit of extra weight, putting carbon veil over everything stiffens up the balsa considerably.  Much less hangar rash in the long run, compared to silkspan and dope.  If you've ever built a stick and tissue plane, like a Guillow's, you could see just how much a little twisting from flight loads can run through the airframe.  If you stiffen one area the torque just goes further on to a softer area and shows up there.

[Brett Buck]

I do it because people tell me I should, but I think it's a waste of time.

   My graphite-mat-covered airplane handled minor dings much better than my silkspan-covered plane. It didn't help much when I dorked it into the ground over by the Team Race circle, though.

    Brett

[Bill Johnson]

Is this a unidirectional cloth or some type of Kevlar/carbon fiber hybrid? I know on 1:1 aircraft, we use cloth that is directional and multiple layers, oriented in different directions, has to be used. The hybrids are tougher but weigh more. Also, where do you get this cloth and what type resin is used?

[Dave_Trible]

Is this a unidirectional cloth or some type of Kevlar/carbon fiber hybrid? I know on 1:1 aircraft, we use cloth that is directional and multiple layers, oriented in different directions, has to be used. The hybrids are tougher but weigh more. Also, where do you get this cloth and what type resin is used?

Bill this is a carbon tissue, random fiber that looks like black silkspan.  It's put on with clear dope.  I get mine (.2 and .5 weights) from CST composite sales off the web.  Aircraft Spruce has it too I think.

Dave

[Serge_Krauss]

You can use epoxy resin too, squeegied in thin. This creates the best stiffness and surface finish.

[Avaiojet]

Which offers less weight when applied with dope?

Which offers greater strength when applied with dope?

Silkspan, CF veil or silk?

Charles

[Dave_Trible]

Which offers less weight when applied with dope?

Which offers greater strength when applied with dope?

Silkspan, CF veil or silk?

Charles

Charles I'm sure carbon is far more stiff.  I use it a lot but am thinking about backing off some because I also think it stores more dope/weight which I'm struggling with.  Silk is OK until the dope gets hard and brittle then it shreds like tissue.  Quality silkspan which is hard to come by now is hard to beat.  Jap tissue works too if you get the hang of using it.

Dave

[peabody]

Winfred pointed out to me that silkspan shrinks and puts the surface into tension.
For an incredibly hard, durable finish, try silkspan stuck down with water based polyurethane thinned with rubbing alcohol.
Thanks to Brad Walker and a bunch of Texans for that.

[Jay]

Winfred pointed out to me that silkspan shrinks and puts the surface into tension.
For an incredibly hard, durable finish, try silkspan stuck down with water based polyurethane thinned with rubbing alcohol.
Thanks to Brad Walker and a bunch of Texans for that.

Looks like silkspan is a thing of the past.  It is no longer found online and I would love to get some.  Point me in the direction where I can order some.

Jay

[Jay]

Here is how far I am along.  Had a busy day so really didn't do much on the Nobler.  I laid some of the CF in patchwork so there is a little overlapping.  I plan to sand them smooth.
Going to do the wing and fuse next.

Jay

[john e. holliday]

Now Rusty Brown told me when sanding the carbon, do not blow the dust off.   It makes great filler in the thin areas.   

[David_Stack]

May want to seriously consider wearing a mask if you intend to sand into the carbon veil enough to generate dust, there has been much discussion about the inhalation dangers associated with carbon fiber.

r/
Dave

[Howard Rush]

To wit, black boogers.

[Jay]

For those who are still looking for SGM Silkspan.  I found a link and looks like it is still in stock.  Shipping is a killer but still might be a good deal for those that need it.

http://www.hobbyfever.com/shop/product_info.php?products_id=28418

Jay

[john e. holliday]

A person should wear a mask anytime they are sanding a plane.   

[Randy Cuberly]

I do it because people tell me I should, but I think it's a waste of time.

Yeah...I've done it and am convinced it's a waste of time and money!

I use fiberglass (.5 oz on the nose and wheel pants) 1 oz FG on the flaps...and silkspan on everything else... Polyspan on the open bays.  The fiberglas cloth is much stiffer on the flaps and the weight difference is negligible.  Easier to finish also.  Glass is applied with Nitrate Dope.

I'm and unpaid spokesman and your results may vary.

Randy Cuberly

[FLOYD CARTER]

I really don't think the point of using silkspan, carbon veil, fiberglass, etc., is for strength.  I use carbon veil over balsa to prevent grain showing later- after the dope has aged.  Carbon veil is easy to apply with clear dope, and it is so light that it would be hard to measure any weight gain.

Floyd

[Bill Johnson]

I've been pondering this myself. In aircraft structural design and repair, carbon fiber is used as a replacement for aluminum. To attain stiffness, fibers must be oriented 90 degrees to the bending force. So on a spar, the fibers run the length of the spar. To carry twisting loads, as seen on surfaces like wings and flaps, bidirectional cloth is used. These cloths are available from the same distributors but it's probable that sufficient layers to obtain the required stiffness would negate any weight savings.

It's possible to test the difference in stiffness. Build 2 faux flaps, maybe 24" X 2" (over-large to make measurement easier), one covered in carbon fiber and the other in a traditional material. Mount them on a piece of wood the same as they would on an aircraft with hinges. Lock one end in place where the control horn would be and attach a spring scale to the opposite trailing edge. Measure the force required to twist the flap perhaps 1/4". You should be able to see some difference if there is a difference in stiffness.

[Don Hutchinson AMA5402]

I ran a series of tests comparing silkspan covered 1/8 sheet balsa to the carbon fiber veil. The results were published in Stunt News a number of years ago. I found the results almost exactly the same for both materials. I tested for bending, torsion and breaking strength. The big advantage I find in the carbon is when used on the leading edge sheeting, one gets much less sagging of the sheet between the ribs and it finishes very nicely.
Publishing of the article garnered zero response, so much for testing!
Don

[Robert-Jan]

Don,

which month I can't remember  read it. (aging?)

Greetings Robert-Jan

[FLOYD CARTER]

Don.  I did pretty much the same testing, but in a more unofficial way--not scientific!  So the issue comes down to ease of application.  The CF veil seems to stick much better at edges.  Once down, with clear dope, it stays down.  CF veil is thinner than silkspan, so overlapping the pieces is easier to sand level and even.

I didn't do any testing on "filling" the weave.  I usually spray clear dope until it "looks finished".  So I don't count coats, or volume of dope used.

Floyd

[Randy Cuberly]

I ran a series of tests comparing silkspan covered 1/8 sheet balsa to the carbon fiber veil. The results were published in Stunt News a number of years ago. I found the results almost exactly the same for both materials. I tested for bending, torsion and breaking strength. The big advantage I find in the carbon is when used on the leading edge sheeting, one gets much less sagging of the sheet between the ribs and it finishes very nicely.
Publishing of the article garnered zero response, so much for testing!
Don

Hey Don,
I remember that article and it even prompted me to do some similar tests that yielded about the same results as your so I didn't consider publishing it...I do think it was a very valuable piece of information for me at least and I appreciated your effort.
It is the main reason that I stopped using the carbon veil because I think the light fiberglass finishes better and fills eaiser the the carbon.  It also doesn't suddenly get full of little holes when trying to fill it with dope like the carbon sometimes does.  I found the 1 oz glass cloth on flaps to be much stiffer in torsion than the carbon and with a total weight gain of about 1/4 oz per both flaps.

Randy Cuberly

[Brett Buck]

To wit, black boogers.

  And black stuff underneath your fingernails, too. But perhaps I have said too much.

    Brett

[dennis lipsett]

I also use 1/2 ounce fiberglass cloth in my finishing process. Water based urethane is the adhesive and if it is 1/4 ounce heavier I can live with it. I have just started to use a heavier weight cloth for high stress areas..

Dennis

[Avaiojet]

I said eons ago fiberglass was the best choice.

Had to correct that, I said silk at first.

Charles

[phil c]

I ran a series of tests comparing silkspan covered 1/8 sheet balsa to the carbon fiber veil. The results were published in Stunt News a number of years ago. I found the results almost exactly the same for both materials. I tested for bending, torsion and breaking strength. The big advantage I find in the carbon is when used on the leading edge sheeting, one gets much less sagging of the sheet between the ribs and it finishes very nicely.
Publishing of the article garnered zero response, so much for testing!
Don

When you are using carbon fiber the fiber provides the strength.  The matrix(dope, polyurethane, epoxy) binds the fibers together.  Dope is a flexible, soft plastic when dry.  It won't stiffen anything much.  The water-based polyurethanes are mostly floor finishes and tend to dry very hard, very quickly, but they still are relatively weak plastic.  Epoxy, like something from West Systems, provides 2-3 times the strength, plus it's fairly hard.  It's also at least twice the density of a dope finish.

Don't sand the applied carbon fiber matte, other than to knock off goobers.  You're just sanding through the surface fibers and weakening it.  .2oz matte is already almost nothing.  Instead apply a couple of coats of nitrate dope to protect the carbon fiber, and then a very dry coat of sandable primer and sand almost all of it off without cutting into the carbon matte.