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Post by ding on Oct 20, 2007 6:17:14 GMT 10
Ah, yes, I understand - yes, each of the broken spars was broken like a crease, but the break was still held by strands, if you know what I mean. Lkke breaking a green stick - it snaps but the fibres are still holding the 2 pieces together. I had to cut thru the break to open it up. Therefore it looked like flexing under compression. I think a break under tension would have torn it up differently. That's it then... compression. Hopefully I'll get to talk to you about it at sometime soon. Basically, you need something solid to tie the two spars together on each side of the wing to stop this. I'm reluctant to mention the I-word though... LOL At any rate, I'm not sure how it can be done effectively but we can think about it. A ribbon at the front and the rear of the spar that goes through the wing would be ideal.. but I'm not sure the glue joint could be made effectively and then profiled to wing thinkness. The way you've repaired it will move the problem to either end of the repair. It might not happen till the next big one though
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Post by ding on Oct 20, 2007 8:33:12 GMT 10
Just a thought... perhaps a 3 or 4 mm spruce through the wing over about 50% of the wing to join the two carbon strips together. You could try putting a V either end of the spruce to limit the load at it's end. Otherwise you'd have problems at the end of the spruce. You'd also have to glue it with something serious... ie pu or epoxy. I reckon that would be seriously strong though.
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Post by thevon on Oct 20, 2007 12:07:38 GMT 10
Steve I think the performance of the current setup is excellent and I reckon it's fine as it is. It's withstood lots of hard prangs at high speed with no damage but it only broke in a really huge impact with a tree! To have survived with so little damage is a minor miracle I think. The impact forces have to get dissipated somewhere and if we beefed this up it could just mean that the I beam centre spar cracks too, requiring much more surgery to fix. The flat spars are easy to get to on the outside skin so if they break to dissipate the impact it's not a huge drama to repair so you're back in the air quickly.
I'm keen to develop better building techniques for foamies but apart from stiffness, the other aims are to keep it simple and make it prang-proof so it's least build time and max fly time. You're dead right that a strong brace between the 2 would be more rigid and might stop the spar cracking in some cases but it'd be beyond most of us to slice the wing up to do it, and would be hard to repair. So far my evaluation of this Bat's system of flat spars, still a prototype, is that it's a great technique and a great result.
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Post by ding on Oct 20, 2007 12:54:06 GMT 10
Good stuff Andrew. As a general rule there is no solution that isn't a compromise! IE even the best is usually a compromise on cost/design/build. Like you say... you've got to find somewhere in between.
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Post by jase on Oct 22, 2007 18:20:57 GMT 10
got a question regarding fibreglass tape.. i was at the Hypermarket today and they had some polyfiler Fibreglass tape.. not like the stuff that comes with the model kits, but more just mesh of 2mm squares which you use a separate filler to glue it all together..
i almost bought it but thought i'd ask first... does anyone know what i'm talking about and has anyone had any success with it...
i was thinking about using this instead of the tape the instructions indicate to use and then spackle over this..
suggestions???
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Post by callun on Oct 22, 2007 22:23:14 GMT 10
I'd use tape. The stuff you're talking about is supposed to be used with the two-part fibreglass composite. I would speculate that filler alone wouldn't do a dam thing. Spackle/Filler's not meant to be a glue, and it's not meant to be thick, so it's seeming to me like a bad idea.
Having dabbled once or twice with it, I think Shoe Goo MAAAY work, but even so, it's not really the kind of thing that mesh you're talking about is designed to work with either. Maybe if it were applied unthinned, but it just sounds like far more work than it's worth. Unthinned shoe goo isn't a terribly easy medium to work with.
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Post by sean on Oct 22, 2007 22:39:19 GMT 10
I'm with Callun, you'd need a strong thick plasticky coating to bond with that tape. PU would probably work but it would be a nightmare to sand afterward. I don't think Goop would work, it dries really thin and spackle definitely wouldn't work as it has no bonding ability. Best to stick with good ol' strapping tape stuck on at 45 deg for torsional strength (which is really important for a DS wing), it does a really really good job I think.
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Post by thevon on Oct 23, 2007 7:17:20 GMT 10
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Post by thevon on Nov 11, 2007 13:35:09 GMT 10
Sorry I meant to put this on a while ago. After the first sessions I realized the Bat needed ballast to DS better. So I made a mould in a piece of wood and poured 4 lead blocks. Each block is 70gm and you can put either one or 2 pieces on each side, therefore 140 or 280gm ballast. I also made up some dummy bits of EPP to fill the trenches when not using the ballast. Then cut trenches in the wings, smeared 5min epoxy all around them to make them tougher. It really works. Sorry that the Bat looks so crappy - I took the photos after yesterday's DS session when I'd taped a rip in the wing from hitting Ezza's Reaper, and the ugly yellow/black tape was used as a temporary cover when changing the nose weight.
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Post by callun on Nov 11, 2007 18:20:09 GMT 10
Hey Andrew, a neat ballast solution. I'm intrigued - what do you use to melt up your lead? And what are you using to melt down? What's your "ore"?
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Post by thevon on Nov 11, 2007 18:44:41 GMT 10
I just use any scraps of lead I have from sinkers etc lying around. Initially I used the kitchen gas stove to melt the lead in a tin can, but it was sooo slow! I have one of those little bushwalking gas stoves that screws into the top of a throwaway gas canister and man, it pumps out incredible heat so I tried that, and it was excellent. Just put the lead in an old tin, hold it with some vice grips over the flame. If you're making it for the nose you can make up a good mould by pushing layers of alfoil into the cavity, carefully lift it out, and pour the lead into it. For the ballast I got a hammer and chisel and cut a rectangular hole in a bit of hardwood- makes a great mold.
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Post by callun on Nov 11, 2007 19:48:40 GMT 10
Bushwalking gas stoves... Got any pictures of the rig?
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Post by jase on Nov 11, 2007 21:44:41 GMT 10
andrew, are they the ones that bolt ontop of the gas cylinder
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Post by sean on Nov 11, 2007 22:04:48 GMT 10
I've been wanting to do this too, is there something super cheap that can bolt onto the top of a gas cylinder to turn it into a blowtorch or stove?
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Post by ding on Nov 12, 2007 2:52:45 GMT 10
I think supercheap have little gas stoves that would do this job for about $20.
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