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Carbon Fiber Control Surfaces

dtw_rv6

Well Known Member
Has anyone ever built carbon fiber control surfaces for an RV? I was wondering if there are any reasons a set of CF flaps wound't help us guys with aft CG tendencies. It might also make for an easy way to reflex the flaps above the fuselage with some trick geometry that wound't be so easy in aluminum.

I realize other control surfaces might need some serious test flying due to altered harmonics and flutter characteristics - nonetheless, it might also make it possible to reduce overall weight and improve handling qualities.

Along the same lines, I wonder if the commonly available accelerometer chips out there might be installed on control surfaces to detect the onset of flutter before it becomes dangerous.....

Don
 
Interesting idea. You are talking about the entire structure being made of carbon fiber except the fittings, right? Maybe the elevators would be an even better way to save weight in the back. I am too close to flying to do it myself but am sure interested in how it would work.

If you go with it, keep me up to date.
 
Interesting idea. You are talking about the entire structure being made of carbon fiber except the fittings, right? Maybe the elevators would be an even better way to save weight in the back. I am too close to flying to do it myself but am sure interested in how it would work.

If you go with it, keep me up to date.

I don't see CF parts saving weight on control surfaces. Think about the weight added in the finishing process. Also, consider the thinness of the skins on the control surfaces. Aluminum is tough to beat there. Compound curves, pressurized vessels, maybe. But simple control surfaces? Gonna be tough.
 
You are right Kyle. More of a Lancair type process. I was thinking some of the ribs and other parts may be unnecessary with the stiffness of the carbon skins. I have a Catto carbon fiber spinner and it is as cool as it gets!
 
Many high performance aircraft (e.g warbirds) use fabric covered control surfaces for weight reduction. Well researched and cheaper than CF.
 
Carbon

I think a Kitplanes article discussed Dave Anders using carbon on the rudder?? of the RV4.
The Sukhoi SU29 uses a combination of composite with metal ribs on all tail surfaces. I saw a SU29 that hit a turkey buzzard on the tip of the horizontal stabilizer. The airplane was going somewhere around 270 statute. The damage was minimal. It appeared the outboard skins "ballooned" out and then returned to more or less normal. I personally don't believe a metal structure would have survived that incident.
 
You are right Kyle. More of a Lancair type process. I was thinking some of the ribs and other parts may be unnecessary with the stiffness of the carbon skins. I have a Catto carbon fiber spinner and it is as cool as it gets!

My memory says column loading (think compression on thin skins) goes unstable around an L/T of 24 meaning buckling can and is likely to occur. Ribs or internal structure are needed to address the "T" or thickness part of the equation. I'm sure the Lancair folks took that into account of course.

I'm with Kyle. I think making a lighter than aluminum surface will be a challenge due to minimum materials needed for common construction techniques available to homebuilders. Making one same weight with higher stiffness due to higher carbon modulus more likely in my opinion.
 
I'm definitely thinking of a foam core construction like the Long-EZ. Could this be sufficient to handle the L/T concern, or do I need to think about true ribs internally?

How about flutter detection? Is it possible to detect it electronically prior to actual structural damage?
 
I'm sure the Lancair folks took that into account of course.
Well yeah. Our control surface skins are a 1/4" thick sandwich of glass/foam/glass which are fairly stiff. Rather than pre-punched aluminum, we got pre-molded fiberglass skins. This is my horizontal stabilizer, but the control surfaces use the same technique. You can see where the foam core ends near the leading edge.

PjVYKW.jpg


Frankly, I don't think the idea of going to carbon fiber control surfaces makes sense unless you want to build the molds and set up a vacuum autoclave in your garage.
 
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Well yeah. Our control surface skins are a 1/4" thick sandwich of glass/foam/glass which are fairly stiff. Rather than pre-punched aluminum, we got pre-molded fiberglass skins. This is my horizontal stabilizer, but the control surfaces use the same technique. You can see where the foam core ends near the leading edge.

PjVYKW.jpg


Frankly, I don't think the idea of going to carbon fiber control surfaces makes sense unless you want to build the molds and set up a vacuum autoclave in your garage.

Snopercod: what are those white cords that are glassed into the skin on a diagonal?
 
Snopercod: what are those white cords that are glassed into the skin on a diagonal?
Those are Nylon tubing. Originally I had the great idea of installing a VOR antenna inside the horizontal stabilizer. Unfortunately, the ends of the tubing are so far back in the tailcone now that there's no way to reach them. Oh well, it seemed like a good idea at the time :rolleyes:
 
CF Control Surface

The cause of the F-117 accident was not due directly to aileron flutter. Four of 5 one-inch bolts holding the outer wing panel were missing. There is no reason a CF aileron or flap cannot be designed, built, and tested successfully for an RV. Instead of layups, epoxy, and autoclaves, build it out of CF and make the structure very similar to aluminum. Mechanical fasteners can be used where they make sense, and either epoxy or structural adhesive can be used where that makes sense. Impossible is temporary.
 
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CF aileron question ?

I replaced badly fabricated ailerons on my -3 with new construction. They work VERY well. I like to tinker with composites and considered rebuilding the bad ones with CF skins and either CF ribs or foam. Without getting into a lot science above my pay grade, would a counter balanced aileron, like elevators, eliminate concern for flutter ?
 
I am sure you can make balanced composite control surfaces for your RV. But it would be so much more work than the aluminum ones that one has to ask why bother? You would have to make tooling (molds etc). Whereas an RV aileron can probably be made in a week of evenings and it would be ready to fly. There is no guarantee that a composite one would be any lighter.
 
i once considered CF empanage control surfaces. after running the numbers for composite construction the weight would be about the same as the current RV aluminum ones. i wanted them for possible increased stiffness not necessarily being lighter. the RV ailerons are not a flutter problem if they are connected through the control surfaces and have good hardware. believe it or not some have forgotten control tube rivets. the flutter range for the wing and control surfaces is far above the empanage and with generally good construction techniques it isn't what you need to be worried about. i followed ken kruegers' suggestions for increased stiffness for my rudder and elevators. since then i have had no cracking or any apparent problems with them. this was my 3rd set and they still look as good as the day i made them probably 1500 hrs ago. the certain thing about aluminum surfaces is you can KNOW how good they are made and how strong they were intended to be, not so easy with composites. you really need to know what your doing when making CF surfaces.
 
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