Carbon Fiber Leading Edge?

[Kelpy]

I am at the point where I’ll be fitting the leading edge fiberglass on my STI wings. Is there any reason that they can’t be made out of carbon fiber. They seem like a lot of weight that could be shaved down. Is there a stiffness issue or otherwise preventing the use of carbon fiber?

Just trying to shave off a bit of weight where practical.

Thanks

[patrick.hvac]

The carbon with direct contact on the aluminum spars would be a galvanic corrosion problem wouldn't it?

[taff]

The carbon with direct contact on the aluminum spars would be a galvanic corrosion problem wouldn't it?

Galvanic reaction (or corrosion) occurs when two dissimilar metals come in contact with each other.
Like steel touching aluminum. Add a little humidity / water and the reaction starts.
Carbon fiber contacting aluminum should be Ok.

Don't know what Kitfox sells today. When I built my Classic IV, It come with plastic leading edges that I had to glue on with 3M structural adhesive.

[jiott]

There is a corrosion problem with carbon contacting aluminum; that's why the builder's manual says NOT to mark aluminum with a pencil, use a fine sharpy instead.

[DesertFox4]

What Jim said.

[taff]

This could be of some interest

https://flightsafety.org/amb/amb_nov-dec89.pdf

[patrick.hvac]

https://youtu.be/yRpMZaU8zKw
Dark Aero did a good carbon aluminum corrosion video as well as Mike Patey.

This is a great application for S-Glass and a good resin I would think.

[PapuaPilot]

This could be of some interest

https://flightsafety.org/amb/amb_nov-dec89.pdf

What part of it? It is a 16 page document with about 40 articles.

Here is a document from the FAA that covers that topic at hand:
http://www.tc.faa.gov/its/worldpac/techrpt/tctn17-42.pdf

The bottom line is you don't want to use carbon fiber where it touches aluminum, especially to such a critical part of structure like the spar. There are several other ways to save weight.

[jrevens]

There was a company here in Colorado making a carbon fiber airplane patterned after something like a Swift or maybe a Falco... I don’t remember. It was a vey impressive and sophisticated design. Our EAA chapter had a tour of their factory. It was a first class operation and involved several engineers as I recall. Anyway, the point is that they went to great lengths in the design to keep aluminum and carbon fiber structure conductively separated to prevent corrosion. They even used very expensive special fasteners (titanium?) almost exclusively, as well as special coatings. It was quite a few years ago. The linked article stresses scratching of the aluminum surface by a pencil, but the graphite that can remain on the surface, even microscopically, is definitely also an important issue regardless of any scratching.

the Kitfox wing is relatively flexible and carbon fiber isn’t. That might or might not be an issue. One of the advantages of making the Laker leading edge out of a thin fiberglass laminate is flexibility. Making it in 2 separate pieces as they do probably helps to accommodate that, as well as thermal expansion and contraction. Of course it makes it easier to ship (& possibly manufacture as well?). The Laker leading edge is so thin that I wonder how much of a weight factor it would be compared to a carbon fiber one.

The Dark Aero video was very good!

[taff]

What part of it? It is a 16 page document with about 40 articles.

Here is a document from the FAA that covers that topic at hand:
http://www.tc.faa.gov/its/worldpac/techrpt/tctn17-42.pdf

The bottom line is you don't want to use carbon fiber where it touches aluminum, especially to such a critical part of structure like the spar. There are several other ways to save weight.

Sorry about that.
This was my response to Jim (post # 4). He mentioned the pencil not to be used to mark aluminum.
My focus is not the corrosion but the scoring damage to aluminum that a pencil can cause.
Of coarse If you score aluminum with fiberglass, the same damage can occur.

[taff]

My conclusion.
This has been a very interesting thread. And looked deep into the subject of pairing up two base materials.
Great feedback!

Kelby, what are you going to use as the leading edge?
From my earlier post, I mentioned that Skystar provided a plastic leading edge. Does away with all the incompatibles, and keeps movement with any potential flexing of the spar.
What is being provided these days?

[alexM]

We blend dissimilar metals (steel and aluminum) in several places on this plane, and all we do is add some micro balloons to the Hysol. Wouldn't that work in this situation? It is mostly bonded to the short sections of PVC you bond to the forward spar, and up onto the wood cap strips. It only comes into contact with the aluminum spar at the tangent points.

I weighed my Laker leading edge pieces. Ten pounds before cutting or bonding anything. Not trivial in my book.

[PapuaPilot]

I weighed my Laker leading edge pieces. Ten pounds before cutting or bonding anything. Not trivial in my book.

If you are trying to save weight the lightest option would be to not install the Laker leading edge or carbon fiber . . . ;)

[alexM]

If you are trying to save weight the lightest option would be to not install the Laker leading edge or carbon fiber . . . ;)

I should have been more clear. I'm at that cross road right now, being that I have the parts to go either way.

[Maverick]

I should have been more clear. I'm at that cross road right now, being that I have the parts to go either way.

If you have the Laker leading edge the weight penalty is not that much, assuming you are not going LSA. If you are going experimental the aesthetics are nice but if you haven't purchased them yet, consider that there are allot more Kitfoxes flying out there without them than with them and we who do not have them are happy and having a great time. Even though LLE are thin material, it will stiffen the wing some due to the D-cell structure it creates. Not like Carbon Fiber would but still it is there.
Fred