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HeadsUp
Regular Member

Joined: 06/12/2009
Location: Australia
Posts: 43

Posted: 09:36am 08 Dec 2009

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KarlJ said Conductivity of CF for the most part is negligible.
Resin does not conduct electricity at all

Thus strike could be an issue.

Im also thinking that at these dimensions 3m+ you would be better off with a rougher airfoil that has twist and taper....ie the cheap chainsaw solution, or just buy some big blades suitable for chinese 10KW+ mill.

Throwing technology at 3m blade sections is all fine and beaut but you are then working towards the infinite number of blades, at small sections which as 'tules has said before is getting spectacularly complex to build.

at 3m+ if you were really into this blade section I'd be looking into pulling a mould off one and making the whole thing from Carbon, not as hard as you would think and you could do some cheating and make a wood or foam core to cut down on material costs as the bit up the guts is doing stuff all anyway.

Its a pity as I just threw away about 50KG of 10oz carbon cloth (was offcuts but large none the less)

yeah i would call that a pity or a waste

that would have sold on ebay any day of the week

could have kept some keen young creative student busy for months

pm me next time you have some ;)

KarlJ

Guru

Joined: 19/05/2008
Location: Australia
Posts: 1178

Posted: 12:17pm 09 Dec 2009

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Every time the kids got into it, it broke my heart, HUGE mess and putting it back together was getting tough, I folded it up best I could but after you have handled it a few times the tows are all over the place and furry edges and missing tows just make it impossible to use.

They were offcuts from 787 dreamliner, dry fabric for resin infusion and unfortunately for boeing cutting efficiency due to the shapes lucky to top 50% and lots of less than perfect material. EG defect 1cmx1cm throw out 1m either side of a 60" wide roll. roll 300' long 15 defects = 200' long roll with stops and starts which for a lot of parts was throw away as you needed 33' long pieces to cut a ply.

Certainly well and truly unethical to sell it as proprietary / controlled material and at the end of the day I paid nothing for it...

Luck favours the well prepared

HeadsUp
Regular Member

Joined: 06/12/2009
Location: Australia
Posts: 43

Posted: 12:41pm 12 Dec 2009

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for low risk experimental projects it would suit me fine

sell it to me as garden mulch if you have to

lol

i dont even know what its worth to buy new per roll , but if some of my Electric vehicle door linings end up being scrapped in the bin then a cheap CF price suits my budget just fine.

:)

Gizmo

Admin Group

Joined: 05/06/2004
Location: Australia
Posts: 5124

Posted: 11:53pm 19 Dec 2009

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Gordon Haverland sent this to me via email.......

I've read a few things on your website over the last few days.

I've no idea what design life you assume, or should assume. Looking at a table of suggestions, the best guess I got was 50 years, as some towers supporting windmills are lattice structures. If windmills get up to 600 or more rpm (10+ rps), I can see total cyclic stress rates being a bit higher than that. One of your readers suggested 100 cycles per second. I believe 100 cps and a 50 year lifespan comes out as 1.6E11 cycles per lifetime. I have yet to run across aluminum design data which goes past 5E8 cycles. Extrapolating 2.5 orders of magnitude is not a good thing.

Wind farm accuracy data - I started with one of the wind farms you point at (only 1?), anyway, from the numbers in the article, they consistently produce more power than they are capable of. I then looked up a wind farm at Swift Current, Saskatchewan, Canada. Looking at their average power production and total capacity, they are producing just a shade under 25% of possible power production (assuming best wind conditions all the time). Maybe that is about true everywhere? Anyway, it seems that a 50 year life is still about a factor of 80 more than the limit one sees in aluminum design data.

A person can weld PVC (and not the solvent welding the plumbers do), and it is thermoplastic. If you had multiple cross sections available (chord of 200mm, thickness = 5mm), chord of 190mm, chord of 180mm, and so on; you could "weld" the cross sections together, put the welded assembly inside a form, and with a little heat and hydraulic pressure (hydroforming), come up with a tapered airfoil. It might be that solvent welding might work, but it was never intended for anything like that.

If people are going to be glueing polymers to metals, you are looking for a polymer which has a large extension to failure value. Epoxies don't normally do that. There are some urethane glues which do. There are also some methyl methacrylate glues which do. It is rumoured (I haven't verified it) that some methyl methacrylates are relatively insensitive to imperfect cleaning of the oils often found on the surface of metals (for forming or machining).

Thanks Gordon

Glenn

The best time to plant a tree was twenty years ago, the second best time is right now.
JAQ

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