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Andy Klie

Anyone hand lay their own carbon fiber spars?

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Hi Y’all,

I have extensive experience hand laying fiberglass and carbon fiber using epoxy resin. I was wondering if anyone has made their own spars? If so what weight cloth/tape, what weave and did you use epoxy or Phenolic resin?

I am think about experimenting with different weaves, cloth and lay up schedules and making a one piece LE spar for local flying.

 

 

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I really wish I could respond but I have zero experience in that area.. I'll volunteer to test anything you come up with though..

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The initial setup cost would exceed the cost of 12 complete quad frames, and that's just one size of tube. Unless I was planning to go into commercial manufacture there's no reason to do so. It would be like building your own textile mill so you can make some Icarex sail material. 

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The initial setup cost would exceed the cost of 12 complete quad frames, and that's just one size of tube. Unless I was planning to go into commercial manufacture there's no reason to do so. It would be like building your own textile mill so you can make some Icarex sail material. 

 

I am not sure what your level of expertise is with carbon fiber or fiberglass but there is not much of an investment at all when hand laying.

The majority of the cost is in the materials. A frame set for a Rev is $90. I could purchase all supplies for 4-6 frames at a minimum for that amount.

When you are thinking of high cost you are probably thinking of vacuum bagging and a special mandrel set up. It does not have to be that complex.

Using a rod with the outside diameter the same as want the inside diameter of the finished spars serves as a mandrel. Cover it with mold release and hand wrap the carbon fiber cloth or tape like a candy cane in one direction and the if desired in a different direction. The schedule/layup plan will determine the characteristics of the spars. No, they will not come out perfect but as long as the carbon fiber cloth is wound tightly and not over saturated in resin the some detail sanding will even out any sags or runs in the resin. Sections would then be weight matched.

Benefits would include the fun of building (I love building stuff) the ability to make very stiff or flexible spars and the ability to add in Kevlar or other composite materials to gain positive characteristics.

I over simplified the above a little but I am going to get some materials and give it a go. I will add pictures along the way.

 

 

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Indeed, please share your experiences here.. Looking forward to it.

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Much interesting project. You ( @Andy Klie ) mentioned sanding to even out the tube. Do you intend to use heat shrink tubing or perhaps heat shrink ribbon (since you are not using vacuum bagging)? In that case all or most of the sanding might be redundant.

Heat shrink tubing:

https://www.youtube.com/watch?v=jwExI_vnchE

Heat shrink "tape"/ribbon:

https://www.youtube.com/watch?v=wOZRALnsmwU

I have only some experience of carbon fibre or fibre glass repair of kite spars and stand offs using heat shrink tubing for electrical insulation (because that was what I had available). I’m sure that was far from perfect, but it reduced much sanding afterwards because the resulting surface was smoother. It also squeezed out excess epoxy.

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23 hours ago, Andy Klie said:

 

I am not sure what your level of expertise is with carbon fiber or fiberglass but there is not much of an investment at all when hand laying.

The majority of the cost is in the materials. A frame set for a Rev is $90. I could purchase all supplies for 4-6 frames at a minimum for that amount.

When you are thinking of high cost you are probably thinking of vacuum bagging and a special mandrel set up. It does not have to be that complex.

Using a rod with the outside diameter the same as want the inside diameter of the finished spars serves as a mandrel. Cover it with mold release and hand wrap the carbon fiber cloth or tape like a candy cane in one direction and the if desired in a different direction. The schedule/layup plan will determine the characteristics of the spars. No, they will not come out perfect but as long as the carbon fiber cloth is wound tightly and not over saturated in resin the some detail sanding will even out any sags or runs in the resin. Sections would then be weight matched.

Benefits would include the fun of building (I love building stuff) the ability to make very stiff or flexible spars and the ability to add in Kevlar or other composite materials to gain positive characteristics.

I over simplified the above a little but I am going to get some materials and give it a go. I will add pictures along the way.

 

 

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Yes, I was definitely thinking of mandrels and ovens and such. I have had "parts" for various projects machined for me and on small batches the cost per unit is very steep. I have four custom endcap sets for Revs that fit inside the spar that were CNC'd that cost about $90 per set/6.

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Any small batch of custom parts from a shop will be expensive. In the case of CNC work you are primarily paying for the time and expertise to write the program to make your part and of course time to mill the part.

Making composites can be pretty DIY friendly. It gets expensive quickly if you are trying to produce quantity. Just fooling around here and there it is not bad at all.

The heat shrink idea is interesting and I am going to look into it.

Right now I plan on building a fixture out of some scrap wood that will enable me to lay up 10 sections/2 frames at a time and another fixture that allows me to use a standing drill press to turn/sand the spar. Then each one will be cut to length.

Right now the only special tools I have that I am planning to use are the drill press and abrasive chop saw.

When laying up a project I like to be able to see the whole thing to make sure it is evenly wet out so I am not sure about the shrink tube idea. If I can find carbon fiber fabric sleeve for a decent price that will also assist in uniformity

 

 

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The heat shrink material appears advantageous when doing a read up. Apart from the sanding issue, the strength to weight ratio should increase when the excess epoxy is squeezed out. This because of two factors. First getting rid of excess epoxy leaves a higher fraction of fibres remaining which is the major contributor of strength in the fibre/epoxy (or vinyl ester resin) matrix. Second it should allow to use more epoxy during the wetting of the carbon fibres (which are more tricky to determine if wetted than for glass fibres) which should reduce the risk of not wetting the fibres properly everywhere (we don’t want any weak spots in a load-carrying beam).

Written heat shrink instruction:

http://www.sollercomposites.com/MakingShafts.html

The heat shrink material also appear to be advantageous for reducing the bubbles: “If you are not using shrink tubing... many people complain about bubbles when epoxy is drying” ("drying"? - rather hardens/cures I believe). Vacuum bagging seem to be the next step more expensive way of removing some more epoxy: “You can vacuum bag the shaft to achieve a slightly lighter shaft at a great expense.”

From the discussion in:

https://www.rocketryforum.com/threads/using-heat-shrink-tape.69266/

It appears like overheating also can lead to bubbles.

Sorry if providing some obvious info above – I do part of the above read up to teach myself. As I said before my experience is limited to using electrical insulation heat shrink tubing for spar and stand off repair purposes.

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I watched the video and looked at the articles you mentioned. I agree. The only problem is that I could not find the shrink tubing on their website. I will definitely give it a try if I can find it. I may make a vacuum bag set up, I have done it before.


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