Carbon Veil

Apply it with dope but be careful when brushing. It tends to come apart with excessive brushing.

Except over open bays.

Denny,
Most recent use of the material (.02 oz/sq.yd) was for fillet repairs on a Sig Magnum. I had cleaned(read:gouged out/jack-hammered)the old silk-span off, down to the wood, and needed something to both fill it's spot (read: low spot), and something to rebuild strength in the wing root area, ..enter C.F.

I doped it into place with Brodak clear. Layered the material approx. three layers deep in spots, not so much for the extra strength, but because that's how the pieces overlapped is all. Did not worry about butt joints or seams, once doped in place the clear/thinner/cornstarch filler mix leveled it off with no seams to be seen, ..there's hardly a bump in the seams anyway as this stuff is so thin.

For compound curves I just cut the wrinkles out where ever they came up, and layered another piece in to cover the gaps if any. Clear dope unto itself does a fair job of leveling any joint/seams/layers, it seems to me.

This airframe finally made it into base color coats this afternoon, after 13 years in construction/re-construction. No sign of the C.F. or joints from it.

Also used it with thinned epoxy to but a little muscle on the Magnums cowl (interior areas), which is thin and "was" fragile in a couple of key spots, ...Not any more thanks to C.F.

Other use includes as mentioned by the Steve's. Only difference is that I use the .02 oz material for a stiffener also. I've never tried the .05 oz material for this, but can only imagine that it would do a dandy job.

Second build, Super Turcano, uses the material (at this stage) to stiffen the rudder which is quite tall, and was flexible until the C.F. dope treatment. Major improvement with just one layer either side. The rudder will be hinged for adjustment, so little help from the vert Stab was forth coming. This whole airframe will be covered in the .02 oz material. The wing is balsa sheeted, fuselage is profile build. Try it, your gona love it!!!!

How to put it on, what I did: 1)Three coats of dope to airframe, light sand between each. 2)Cut C.F. to size, or over size, whatever works, and then dope into place with dope again. I think some thin the dope a bit at this stage so it attacks the under coats for a good glue effect. Let this dry. 3) Sand with fine paper at an angle to the edges to cut the C.F. to final size of the item in question. More dope to seal the edge as required. Apply more coats of dope as needed to fill the weave. I normal only put one post install coat on, then go into the clear/thinner/cornstarch filler mode. This mixture is as used by "the Man" himself GMA. 1/3 clear, 1/3 thinner, the rest cornstarch to what ever the liquid medium can stand or float, ..use a volume of your choice. The more corn you get in it the easyer it is to sand, ..and boy does it sand when the mix is right. Be sure to be outside while sanding the filler mix. 5) You should sand back down until you can see the C.F. again, but don't sand through it. You only want to fill the weave, not hide the material. 6) Obtain smooth seamless fill, then prime or prep as you normally would for finish coats.
At least this is what has worked for me, ..any other techniques fellas?
Tony

How would the stuff work out sandwiched between balsa layers, for tail surfaces, fuselage bulkheads, maybe even profile fuselages themselves? What sort of adhesive would work best for that?

How would it do in critical, often broken, areas like Ringmaster trailing edge joints?

What thickness is Brodak's veil?

For a super strong spar, make it of three layers of balsa (widthwise): The inner third, approximately, of the spar is made up of three widths, the next third, approximately, of two widths, and the last third of one width. Then glue the .007 carbon fiber between the layers as you assemble them.

Doing this, the extra weight and strength remains in the center, rather than keeping the same structure all the way out. You can sandwitch the carbon fiber between two pieces to make up a trailing edge for the wing or stabilizer this way, too, and do the same for the leading and trailing edges of the flaps and elevators. This makes a nice center line edge, but on the hinged surfaces makes it more difficult to cut the slots for the hinges.

On the hinged pieces, if you make them up of three layers with carbon fiber between the layers, you will add additional stiffness and strength, while leaving balsa in the center to cut out for the slots.

Or, you can get more creative and use 1/64 plywood for the center layer, and cut it out before hand for the hinge slots. (Or, if you are using thicker hinges, use 1/32 balsa.) This way the pieces are preslotted as you build. You must, of course, use care to make sure everything lines up properly, but you do that anyway, don't you?

Carbon veil can be glued between two widths for fuselage sides, and you can dispense with plywood doublers. Just cout out the area for the motor mounts and attach them directly to the veil (which is epoxied in.) For profiles, the fuselage can be made up of two pieces with the carbon veil sandwitched between. On both profiles and built up fuselages, use a double layer (on the outside) around the area of the fuselage by the trailing edge, around the leading edge, and anywhere you expect to find stress cracks.

Half ounce glass cloth or carbon fiber can be layered over the center section of the wing for additional strength and rigidity. Remember, the greatest stress is in the center of the wing, or right at the fuselage joint. So make three oval pieces, one 6-8 inches wide, one 4-6 inches wide, one 2-4 inches wide. Do not cut these off square, but leave the width ends rounded so there are no stress areas. Put the longest one down first, then the second, then the third, and the wing will not break in the middle no matter how hard you hit the corner (or the ground). It adds very little weight, but relieves the stress in the very center of the wing.

Applying any hi modulus material to the neutral bending axis will not take much advantage of the material to appreciably stiffen the panel. This material is particularly in this category since it is so thin. It WILL strengthen the panel for impact resistance but not bending.

If you apply carbon veil or cloth for the purpose of adding stiffness, then the best way to do it is to apply a layer on each side of a "core".

Examples of good and bad application, from a bending resistant/per weight standpoint, are:

Two plys of any wood with carbon in between--not good.

Single layer of wood (same thickness as above) carbon on each side--very good.

Additionally, one of the problems in a balanced core with very thin laminates on the surfaces, is the compressive (edgewise buckling) of the compression side of the panel. Any additional material that will prevent surface buckling will help prevent failure. (we're talking ultimate panel failure here) This is why applying a carbon or glass over a core panel and then applying a doubler over that, makes such a strong, stiff structure.

Leonards' Flap example, for instance, is an outstanding example of a well balanced, extremely stiff section: balsa or ply core, carbon on both sides, with balsa both sides over all.

Also, don't overlook Kevlar materials for reinforcement. It is MUCH tougher than Carbon. Less expensive, and nearly as strong and stiff in applications that we can create. (non-solid, non-woven, non-autoclaved). Also, .75oz glass cloth is VERY inexpensive and effective.

Finally, if using carbon for ultimate strength and stiffness, consider using end-grain balsa for the core. In a balanced composite structure, the core must withstand compression between the outer skins to prevent core crushing. Regular 4-6 lb balsa cannot do this well. One should consider using a foam core or end grain balsa to resist this core crush. The tensile and compression in the panel skins is more than ably handled by the carbon or glas material without assist from the core in that direction.

Finally, Finally--and as everyone can attest, I have learned the hard (heavy) way, it is EASY to go overweight with carbon skins. The problem is the resin or other material (dope, CyA, etc.) we use to hold the material down is alot heavier than the carbon.
And, this material is "un-naturally" strong. At tensile strengths around 400Kpsi, our natural instincts for "how much is enough" get out of wack.

Great stuff but it will make you think alot about how and where you apply it.

FWIW

I have used the kevlar/carbon mixed fabrics a few times and like them alot. The kevlar adds some bulk and thickness and so adds a bit of stiffness. Kevlar does have other issues but its strength/weight is very good and it improves the "explosive" failure nature of impact damage--not so relavent in our apps but much so in many full size areas.

>A couple more questions...
>
>How would the stuff work out
>sandwiched between balsa layers, for
>tail surfaces, fuselage bulkheads, maybe
>even profile fuselages themselves?
>What sort of adhesive would
>work best for that?

I'd be hesitant to use a single layer between balsa. Think of how your gypsum wallboard (sheetrock) is constructed. The inner gypsum core is thick, heavy and fragile. The paper on either side adds a smooth finishing surface and stiffens the material considerably.

For your bulkheads, I'd go CF/balsa/CF.