T

the4ork

Member
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?
 
Read about Aluminum and Carbon Fiber at this link:

http://stinet.dtic.mil/oai/oai?verb=getRecord&metadataPrefix=html&identifier=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/community/showpost.php?p=58481&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/community/showthread.php?t=8992
 
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.
 
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
 
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.
 
using Carbon Fiber

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'? :eek:
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.
 
DGlaeser said:
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'? :eek:
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.
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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
 
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
 
RV6 Empennage?

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)
 
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.
 
I'd echo what others said. The exception might be for something like cowls, where instead of making the part from a relatavely thick bit of glass, you could use two thin carbon skins, and some really light weight ally h/c core. It might not even end up lighter, but it'd be a stiffer, prettier part, that wouldn't flap about in the wind as much.....not that it matters.
 
Lightning & carbon fiber?

Just this last week at our local EAA meeting, we had a speaker who did a lot of carbon fiber work on rods for a Wright replica. From what I heard; I'm under the impression that "straight" carbon fiber will blow to bits, if hit by lightning. Any comments?

L.Adamson
 
I checked on some CF cloth about a year back and it was hyper expensive :eek:......... anyone checked cost lately?
 
MatthewD said:
I checked on some CF cloth about a year back and it was hyper expensive :eek:......... anyone checked cost lately?
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It's just getting more expensive thanks to the Airbus and Boeing... it's hard to get because these guys are sucking all of it. We are building experimental planes, so if you look for challenges and fiberglass is piece of cake, this is route to take. :rolleyes:
 
jsharkey said:
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)
Click to expand...

Just checked the weights of my empennage - itwas built a long time ago - total unpainted but with untrimmed weights in elevators and rudder is 53lb. At best you could probably save 20lb with carbon but more likely 15lb or even only 10lb. That could translate into more fuel or baggage while staying within the aft cg limit - but is it worth it. Possibly for education and recreation purposes. It's the challenge of home building:D
Jim Sharkey
 
My horizontal stabilizer, elevator, rudder, and ailerons are carbon fiber.
Total weight savings was about 20 pounds. Helped a bit with CG but in retrospect was not worth the extra $ and was a bit more difficult to work with than fiberglass.
 
I have a hangar neighbor who uses CF extensively - built his Lancair cowl from it, his Moni cowl and ailerons as well from vacuum bagged CF layups. Resultant weight savings apparently, for him, were worth it, and in particular his ailerons were much stiffer and more responsive than the aluminum originals.
Downside is the care and attention needed to layup, vacuum bag and cure, and then you have to fill and sand.......although if you prepare a female mold (as he did for the cowls) the resultant finishes were exceptional, and very stiff and strong.

Expensive? I think 6oz CF is about $50/yd x 38" wide, equivalent FG about $10 or less, and all this is weave and weight/type dependant. However, the comparison of stiffness between a CF and FG part is incredible - CF is way more stiff and strong, so I presume you could use less........

Allan
 
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N395V said:
My horizontal stabilizer, elevator, rudder, and ailerons are carbon fiber.
Total weight savings was about 20 pounds. Helped a bit with CG but in retrospect was not worth the extra $ and was a bit more difficult to work with than fiberglass.
Click to expand...

So my estimate wasn't to far off the mark:D
Jim Sharkey
 
jsharkey said:
So my estimate wasn't to far off the mark:D
Jim Sharkey
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I suspect you were close but bear inmind I am not talking about an RV.

For similar weaves I use 1 layer of CF for every 3 called out in the layup. It is especially useful as a corner laminate in a difficult to get at location. Unlike glass layups where you can see the voids and bubbles you cannot see them in the CF. CF also is sometimes difficult to tell if it is fully wetted out and the edges seem to fray a lot easier than glass even when wet. fill and finish is also a real pain.
 
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