carbon fiber parts?

[the4ork]

lets take an Rv-4 kit for example,

out of curiosity what would be some good components to replace with carbon fiber with the build?

a thought crossed my mind of building some pieces from carbon fiber, if i recall its stronger and lighter than aluminum correct?

i was thinking in terms of leading edge skins (woulnt get beat up from hitting bugs i would think) and would be lighter?

what about flight control surfaces? ailerons/flaps/elevators/rudder?
they could easily be manufactured from sheets of pre-made carbon fiber trimmed to fit... only i dont know if its possible to flush rivet them...

anyone thought of this at all? ever been brought up before?

[RV6_flyer]

Read about Aluminum and Carbon Fiber at this link:

http://stinet.dtic.mil/oai/oai?verb=...fier=ADA300630
From the above link:"...carbon fiber/epoxy resin composite materials are joined with high-strength titanium alloys, aluminum alloys, lCrl8Ni9Ti stainless steel, or other structural materials, galvanic corrosion and crevice corrosion take place on the contact boundaries."

Here is one on this forum:
http://www.vansairforce.com/communit...81&postcount=7

From the above link:
"...carbon fiber and aluminum don't like each other, with aluminum being the loser." ..."As long as you prevent contact of the aluminum with the carbon, you should have no problem. Otherwise, you have a galvanic battery with corrosion of the aluminum at an unacceptable rate."

The above link was in this thread: http://www.vansairforce.com/communit...ead.php?t=8992

[airguy]

It's doable, yes, but not practical. The steps you would have to take to prevent galvanic corrosion are no where near worth the gains.

[PJSeipel]

Not to mention that you're going to change the weight/balance, especially if you're talking about control surfaces. If you don't plan it out pretty carefully you could end up with flutter problems or an airplane that's unflyable because of its CG envelope.

PJ Seipel
RV-10 #40032

[RV505]

The airliners use metal bond. It requires sip metal, aluminum honeycomb and a autoclave. Most graphite flight controls are made with prepreg. Not to mention that it must be kept frozen along with the glue untill used and that must be kept in a monitered freezer. If you use carbon you have to use Titinaum fasteners or it will corrode.. I would just go with fibreglass.. the weight saving isn't worth the pain and trouble.

[DGlaeser]

I designed composite (glass and carbon fiber) aircraft parts for 'a number of years' for Boeing and (the former) McDonnell Douglas.
Preventing corrosion is fairly easy by putting a layer or 2 of glass on the surface where the contact occurs.
Prepreg is used in production environments for ease of manufacturing and repeatable quality purposes. For the small size and number of parts being discussed, CF cloth can be layed up using the same kind of methods as you would for FG.
Aluminum rivets in a CF skin is a problem - can you say 'battery'?
The real reason I wouldn't bother is that the weight savings would be negligable for such small parts, especially skins. If you were to really design the part for the strength required and minimum weight, the skins would be very thin and easily damaged. When you thicken them up, and/or add glass (we even used Kevlar) to make them operationally acceptable, and buid up as required for attachments, etc. the weight savings pretty much goes away. When the structures get bigger, it gets easier to truly save weight in a practical design.

[RV505]

Originally Posted by DGlaeser

I designed composite (glass and carbon fiber) aircraft parts for 'a number of years' for Boeing and (the former) McDonnell Douglas.
Preventing corrosion is fairly easy by putting a layer or 2 of glass on the surface where the contact occurs.
Prepreg is used in production environments for ease of manufacturing and repeatable quality purposes. For the small size and number of parts being discussed, CF cloth can be layed up using the same kind of methods as you would for FG.
Aluminum rivets in a CF skin is a problem - can you say 'battery'?
The real reason I wouldn't bother is that the weight savings would be negligable for such small parts, especially skins. If you were to really design the part for the strength required and minimum weight, the skins would be very thin and easily damaged. When you thicken them up, and/or add glass (we even used Kevlar) to make them operationally acceptable, and buid up as required for attachments, etc. the weight savings pretty much goes away. When the structures get bigger, it gets easier to truly save weight in a practical design.

Kevlar is even worse.. I can't tell you how many panels we had to repair ( Boeing and Airbus) because Kevlar wicks water into panels and blows them out.. The panels are then very heavy with water. Even the smallest kevlar thread will wick water into a panel.

Preventing corrosion is fairly easy by putting a layer or 2 of glass on the surface where the contact occurs. That is true unless you have chaffing

Prepreg is used in production environments for ease of manufacturing and repeatable quality purposes. For the small size and number of parts being discussed, CF cloth can be layed up using the same kind of methods as you would for FG.

However it takes more plys to get the same strenth as a prepreg layed up and cooked in a autoclave. Damge repaired to autoclaved parts were usally to 2 wet layups to 1 damaged prepreg autclaved ply/layer

[videobobk]

My slider is all CF and considerably lighter than the "standard." I don't believe it would be strong enough (without the tube frame) if done in FG. If it had to have the steel framework, it wouldn't be any lighter, or perhaps only a little. We are talking 8 pounds lighter for the CF! Of course, it isn't in contact with aluminum at all, only contacting through teflon guides and vinyl seals. No corrosion problems to worry about. To me, that seems to be the key. I would think weight and balance on CF control surfaces could be dealt with, and they also could be isolated from AL structure. Just my $.02, and I admit to knowing very little about composites of any kind.

Bob Kelly

[jsharkey]

I have considered developing a carbon composite empennage for the 6 in order to increase useful load and move the cg forward however the factory design is incredibly simple, economical and robust and would be a hard act to follow.

A benefit or carbon composite is that it is roughly 60% of the density of aluminum and 90% of the density of fiberglass. In a practical and affordable form, such as standard modulus fabric, the carbon is probably at least as strong as aluminum and fiberglass but not nearly as strong as steel. Also although stiffer than fiberglass it will be less stiff than aluminum and much less stiff than steel. It does tend to be less prone to fatigue than metal but can be sensitive to minor damage when fabricated in the thin gauges likely to be used on a light aircraft.

Fabrication techniques would be different than aluminum and probably rely on bonding which can be difficult to control and verify for strength in a home shop. Similarly adhesive application variance can have significant effects on weight.

Hard points for attachment of control surfaces and to the rest of the airframe could be problematic and in a practical and robust form would erode some of the overall weight benefits. Similarly with parasitic fiberglass plies used for galvanic protection at metal faying surfaces. And as an earlier poster commented any benefits dwindle to nothing for small or minimum gauge parts.

Carbon comes in to its own when you can make use of its directional properties, e.g. use unidirectional plies for predominantly axially loaded spar caps and +/-45 deg plies for shear webs. Treating it like black aluminum doesn't realize it's full benefit.

When I get my 6 flying a carbon empennage might be a good project to keep me busy!

Jim Sharkey
RV6 ? Still Wiring!!!!
(day job ? General Manager, www.vtcomposites.com)

[szicree]

I think a real sweet canopy frame on a -4 could be made of CF. Maybe the skirts too while you're at it. I'd get on this, but I've already got 9 years into this project and would really like to see it fly while I'm still above ground.