Kind of hard to answer your question unless one has done exactly as you say and compared the two......I have never done the 2 layers of veil but I have done both one layer of med. silkspan on a set of flaps and one layer of .2 oz. veil on another set of flaps both attached with nitrate dope. I find that they are very close in strength. I recently did flaps on a 51 inch wingspan, 1/4 in. thk. with Z-Poxy (finishing resin) and .5 oz. fiberglass cloth and it was far and away stronger than either of the previous methods. Hope this is helpful....

It is not the material that makes for stiffness in my thinking.  Backin the day when trying to make fibre glas fuselages, we tried different glas cloth thicknesses.  The resins were polyester and eposly.  Only choice we had then.  Epoxy made for the stiffness.   Polyester was very pliable.  We learned that using a fibre glas mat cut ito squares flaking off thin layers made for some strong landing gear mounts in the fuse shells.  We also learned that using slo cure epoxy also made for light parts as the roll of toilet tissue was used to daub out the excess epoxy.  The resin with any of the carbon cloth or glas is what makes the stiffness.

 I purposely built a profile fuse from punk light 1/2" balsa...rare I know in that thickness but I found one. I covered it in CF veil and finish cure epoxy..one to apply, one final and sanded well in between and after. Straight to color dope for finish and If i had clear coated it would have been perfect. It lasted 9 years of fairly heavy use and is still the lightest and strongest I ever built. Im getting ready to do it again except this time it will be for an entire built up and sheeted foam structure. I like it this way but hate applying it with dope...not enough stiffness  and doesnt stick as well. Sands to almost gone and unless you silkspan over it loses the strength. With epoxy it fills well but does not lose much of its original intended purpose to the sand block. Worked before over the years for me and it is definitely lighter than glass.

John, Phil,

Could one of you describe your method for applying the CF with epoxy?

Thanks,

Alan,

Could you please briefly describe what your vacuum bagging equipment consists of.   I'm familiar with the basic process, but it sounds like a rather large commitment to invest in.  If you could post a photo of your setup, it would be helpful.

Question:  How are the EDGES of the flaps handled in the vacuum bagging process?

TIA

Cheers.

Warren Wagner

                 

Phil,
I appreciate the detailed description.  So this technique if for flaps or other relatively thin pieces that can be secured flat during the application of the matte?  How about built-up fuselages?  Would you need to process each piece before assembly, or would that leave the sides, for example, too rigid to pull together at the tail?

Warren,
Vacuum bagging parts can be done pretty cheaply.  Aerospace Composites sells a small vacuum unit that consists of a diaphram pump that is designed to run continueously during the bagging operation.  The whole kit sells for about $140.  It includes the pump, bagging film, breather cloth, release ply and mylar for other types of bagging operation.  I got mine from someone who got it and never used it.  Works like a charm.
Alan

Stiffness is only good in the areas where it is needed. Any kind of stiffening near the tips are of no use and to some degree detrimental to model's performance(read extra weight). If one were to measure surface tension of a stab, he would find that majority of force is centered near the middle. The tips experience almost zero surface tension. With that in mind, may I suggest looking stiffenning the middle third of the stab. Why middle third? Middle third covers enough of the span to provide more than adequate stiffness. In reality you need a lot less area since balsa near the surface soaked in dope provides a lot of tension resistance plus silkspan(the lightest one) also increases the stiffness a LOT.

There are many ways to increase stiffness and I'll start with the simplest ones:

1) apply extra layer of silkspan on both sides of the stab near the middle third. Use thinned dope for the first layer or two to allow it to soak into the wood.
2) Glue 1/65th birch plywood to cover the middle third. Keep it 1/4 from the leading edge to help with feathering it into the stab. some people sand the feather but I just apply light filler.
3) get a strip of .005 thick 1" wide carbon fiber laminate(http://www.cstsales.com/carbon_Laminates_36.html) and glue it on both sides of of the stab with CA. Position it anywhere on the stab. Personally, I like it right up against the trailing edge so that I only have to use filler on one side when feathering. This is my preferred method.

I am not sold on using carbon veil on stabs. Carbon veil is good for providing stiffness against twisting forces such those applied to flaps and fuselage in flight. It will do a fine job on a stab as well(if applied BEFORE the stab is glued into the fuse) but it is not designed to provide directional rigidity which is exactly the kind forces are acting on a stab in flight.