Rotating Wing Mast – theoretical discussion

Groper = For a long "tube" especially in a female tool most people start with a feed straight up the middle. What happens then is that the feed starts at one end and the resin has to flow along it and in the hoop direction. Usually the hoop flow at one end meets and slowly works its way to the other end. But this leaves small dry spots along the tube because the flowfront is not uniform. So the solution to this is to feed from the centre outward. This is because the vacuum is at the ends so the vacuum communication is good. So the feeder starts with a solid tube, turns into a spiral say 1/3rd in then back to a solid tube. Resin is feed from both ends. Sorry I'll have to do a diagram.

If you use perforated film the infusion stack comes out easy. If you use a light media you can leave it in. Cf laminates are very slow to fill. A 25mm thick laminate takes about 1 hr to soak through. You have to do tests with Ud to check it actually infuses. UD CF can pack very hard and not fill. If you hold it up to sunlight and can't see through it, it has a very good chance not to fill. I've done up to 30mm thick CF laminates using trialled materials. You can't see it wet out like glass. What i do is weigh the material as its stacked, divide the infusion into small chunks so you know the weight of Cf in each chunk. Then as you fill you can determine if that chunk is wet out by the correct weight of resin is consumed. Then move to the next chunk. Resins are getting thinner and the epoxy resin I was using for the 30mm thick had a 16 hour gel time. As soon as it was filled it was bunged into the oven!! Thick stacks can be interleaved with glass tissue or polyester scrim to keep the UDs from packing down. If possible stack Uds slightly off axis ie 2degs. -2degs etc so the alternate layers don't compact. Us a flow media that is very slow not the usual types that flow quickly. If you use one thats fast it flows straight across without soaking down. Cheers Peter S

 

Ok I'm with you on the flow front direction and shape..

If you have a 12m mast, and you only have 1/3 spiral in the middle, this means the resin has to travel 4 meters from the outer edges of the center spiral feeed to the base and tip of the mast laminate.... How do you get resin to travel that far?

 

Sigurd - To get your strength and stiffness your laminate has to be 70%UD and 30% DB. A majority 45 will be weak and low stiffness. If its a bolt rope you will have to rotate it to drop sail. If the bolt rope is cocked in the groove I don't think you will be able to drop it or raise it. I'll leave the CFD modelling to you. I recommned making a good mould I think you will be disappointed otherwise. Peter

You talked about bat cars earlier. Hmmm.. I'll leave that to you. I'll try and get your co ords into rhino or if you can sned me the section I'll run it. Peter

 

Good point, so in this case you need to know how far the resin can travel and this is the solid pipe length. Say 1 or 1.2m? I had a smaller part in mind when I wrote it. Peter

 

I haven't done one like this for a while but I just remembered the resin travels along the solid tube backwards from the centre along the bag "bridge" created by the tube. Make sense? If you put a tube under a vac bag it creates a little gap along its sides. Peter S

 

Yes the bag bridge makes sense... but now you have a feed that goes full length and your back to your uneven flow front you were talking about originally...

you didnt adress the issues I raised earlier about stripping the consumables from inside the mast if done in 1 shot and also the fibre lockout with thick CF laminates. .. any more elaboration on this?

 

But at least the ends are in contact with the vacuum. You pull the infusion stack out by undoing one end tying it in a knot, tying a rope to it and pulling it through. Recently I use Lavender CE white infusion media and leave it in. I do talk about filling and lockout earlier. Got to go will catch up tomorrow. . Cheers Peter s

 

Did I say bolt rope? I thought I had decided for bat cars, but I do not know if those will come down with the sail sideways. I'll send you a 3dm and a script that can import, and one that can export foils.

Here are the scripts : http://www.boatdesign.net/forums/sailboats/foiler-design-2447-33.html#post81021

I simplify most foils in xflr before I put them into Rhino. Then I use "line through points", under "polyline".

What did you mean about the luff tension?

 

For those interested in the maths - Heres a simplified approach to designing laminates. The gist of it is to do a "normal" engineering analysis. Assume the tension compression bending is supported by UD fibres, assume the torsion is supported by 45/-45 degreee fibres. So now you have two beams say one for the torsion one for the flexure. Then Interleave the two into a unified sensible laminate. This is conservative because the 45/-45 will take some of the bending,tension,compression etc and the sum is better then the parts. This is the same way as we design a concrete reinforced with steel structure by hand. Or you can look up the inertia transformation method. This does not help with buckling or exact stress analysis but it gets you closer then a guess. You can also look up Hart-Smith 10% rule thats good as well. Cheers Peter S

 

I doubt that would work peter, pulling the stack of consumables out with a rope... - have you actually done it on a long mast? I would predict it tearing and then nothing but small strips coming out the end, 90% of it remaining in there...

I cant find where you talk about fiber lockout RE: infusion of thick CF laminates, can you direct me?

 

In short yes, don't wait for a day for the epoxy to cure hard if you only use peel ply, it gets harder and harder to get out... Have you used perforated film before? It will come out very easily. But I'd probably use the white media from lavender CE and just leave it in. Have a look at #181 for thick laminates. Cheers Peter s

 

Ah, you must have edited and added that later, cheers. I know about the need to infuse slowly, what is the name of the infusion mesh from lavender? or do i just ask for the "white stuff"? Can you give an indication of how fast this particular media is for a given viscosity and temp etc? Also its resin consumption weight per/m^2?

How does including a permeable layer within the heavy CF laminate effect the global properties of the mast structure? does a resin rich interlaminar layer detract from the mechanical properties and does it need to allowed for or is its effect small enough that it can be ignored?

 

Hi Groper - When I was doing heavy carbon laminates they were replacing hand laminated Cf laminates and the customer didn't want to spend the money on actual tests. We knew the laminates were better so we didn't bother. There is an article in the second latest Proboat mag about including a scrim in the CF laminate. If I was doing this again I get tests done, but it must lower the properties. But on the other hand the properties are better then prepreg so will be interesting when or if I get the test results!! cheers Peter

 

Thank you very much Peter for the Spencer workpaper, it's exactly what I missed.
When it come to the 45° ply(ies), I would have a candid question.
Is it relevant to use carbon socks (when, of course, the appropriate size exists on the market). Or will the ratio fiber/resin be much lower than with 2 UD ply wrapped @45°
on each other ?
Socks could provide with the opportunity to pull a little bit?



Thanks in advance.
Erwan

 

Hi Erwan - Using a braided tube (sock) is good for making tubes. Yes you can stretch it out and it pulls down very well. The resin ratio will be correct for the process ie manual wet out, wet vacuum bagging or infusion. In order of decreasing Rw. Infusion should be about 28-30% Rw for carbon. In australia braids are very expensive so they are not used much. Alan Spencer was the first person I came across who knew anything about composites on a theoretical basis, I had been mucking about with them for a couple of years and talking to the material suppiers, but back then (+20 years ago) even they didn't know much. Only the aerospace industry was into it and they were using totally different materials to what we were using in boats. I was involved in the commercialisation of a pulwinder (a combination winder and fibre puller so it could lay 0deg fibres) that was made to produce high speed centrifuge tubes for plutonium processing. Mr Spencer worked for the Aust Atomic Energy Commisssion & designed the tubes and the machine. It was 3 stories high and our company decommissioned the machine at Lucas Heights and I rebuilt it at Goldspar with the intent to make CF masts. During that time I had very useful discussions with Alan. The machine never made a tube at Goldspar due the the huge start up requirements with material, solvents and we had to have the local substation upgraded to run the RF curing system!! All this was quite a challenge for a young engineer. Cheers Peter S