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Post by callun on Aug 7, 2007 20:41:18 GMT 10
Well, I just went and had a look at my experiment. The implement used to test the two, was a rather pointy letter opener.
Goo over filler went on super smoothly and relatively thick using the "spatula" that came with the filler. I covered only a small area of probably 10 square centimetres with goo, and then went on to the bare foam.
The goo over bare EPP didn't go on as well as I mentioned previously. It was having to do the job of the filler first, and it pulled on itself and peeled it away from sections, so it would therefore require a second coat (more weight) to get it as strong as filled then goo'd.
The filled goo'd area resisted side-angled stabbings well because of its glassy smoothness, as well as only allowing a very slight dimple from the tip of the opener.
The goo'd bare EPP stood up much less favourably, penetrating quite easily through the thin goo, almost gouging off flakes of foam. Straight stabbing allowed the opener to penetrate a few milimetres - almost the same result as bare un-goo'd EPP.
I would be interested to see how thinned goo goes onto bare foam, and realise this isn't really a fair comparison because of the uneven application of goo, but I'm pretty well sold on filling first, almost purely because the filler was/is a piece of cake to use comparatively and much faster.
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Post by thevon on Aug 7, 2007 21:21:39 GMT 10
Callun I'm like you, the thought of thinning the Goop seems a lot of bother. I haven't done it. I have only used it smeared neat on areas like the nose, or in the nose lead or battery bay to toughen them up. But when you smear it on neat it goes rough. I sometimes let it sit overnight and sand it but it's a rough job really. Everybody recommends the thinned Goop so I think I'll get around to it next time.
However I'm also playing around with using 3M90 and I'd like to try it on the spackled surface - much easier to use and quite rubbery.
Also if you look at that thread I started about new methods for EPP building, there are some interesting articles. Down the page further he mentions a new method using a 2-pack clear coat like they put on timber bar-tops. Interesting. I'd like to find a quick but tough method.
Just saw your next post ... re: the filler, for some reason I reckon the filler adds strength and toughness. You wouldn't think so 0- it seems so chalky but I think it has some paint acrylic in it and perhaps that does it? When I've used it the end result seems very rigid and has a much more woody feel than taped EPP. The Scorpian of Zipper's is realy tough - man that thing can bounce. (but also it's very high density EPP and that makes a big diff too)
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Post by thevon on Aug 8, 2007 18:54:28 GMT 10
Here are some pics of the Clearshield film I've mentioned a few times before. It's a urethane paint protective film which car shops that do window tinting etc can put on new cars to protect the paint from stone chips. I had some sitting around, left over from when we used it to protect expensive racing bike frames. When I got back into foamies and people were talking about gooping wing leading edges I remembered it and tried using strips of it to protect the LE. This shows it along the LE of the Scorpian. As you can see it's very clear. On car paint or bike frames it's basically invisible. I've only recently realized that you can stretch it around a curved wingtip, and it will shape itself to the curve with no wrinkles!! This wing has had a couple of repairs hence the joins where I've replaced bits. It sticks well, but when a bit gets damaged I can easily rip it off and replace it. It's sort of stretchy, but hard to tear or puncture (a bit like Goop!). After using it for a while now on 3 planes, I think it's great. When the LE gets a big hit, it might scuff up the Clearshield or even tear it a bit, but the damage is much more limited than before. I've even crashed into barbed wire fences and hardly torn it. I also put bits of it under the belly or any place that's going to get scuffed up badly. It's thick-ish tape, but I don't think it makes a bee's doo-dah of difference to the performance. It's not cheap. I bought it from Premier Industries at Hendra, ph 3268 8444 and it cost $72 for 1 square metre, but that's enough to last about 10 years of foamie DSing.
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Post by jase on Sept 2, 2007 22:03:07 GMT 10
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Post by thevon on Sept 6, 2007 12:58:24 GMT 10
I've found when cutting EPP, using one of those trimming knives with the blades that you can break along the score lines, that it's a huge help to sharpen the knife on a sharpening stone. I was changing blades a lot, and they seemed to go blunt after only a few cuts. Seems weird when EPP is only plastic, but they do seem to go blunt quickly.
But if you give the blade a touch-up on a fine stone, it works even better than new. Maybe it roughens up the edge a bit, like the way a serrated tomato knife works. Only takes a sec, you can keep using the blade for ages, and it cuts really straight and easily.
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Post by thevon on Oct 9, 2007 21:09:41 GMT 10
It's amazing how often I find that elevon control horns have got loose. You do them up snug when you build the plane, but with use and time the balsa squashes down under the pressure of the screws squeezing the horn and backing plate together. Causes elevon slop which is your enemy. If your plane's been behaving like a dog for no good reason it might be loose horns. Check them and make them snug again. When building it's probably a good idea to reinforce the horn mount area with a bit of CA glue dribbled into the balsa before you cover them.
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Post by callun on Oct 9, 2007 23:10:13 GMT 10
Bill had a similar issue on Sunday, sort of. He wasn't getting any up elevator response, because the hinge had worked itself loose. Down elevator worked because as the elevon was pushed away, the slop in the tape hinge was taken up, but pulling up elevator pushed the hinge-side of the elevon downwards from the leverage of the horn resulting in no elevator.
Did that make any sense?
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Post by ding on Oct 9, 2007 23:15:59 GMT 10
And lets not forget Callun, you were suffering from reduced control effectiveness because your aileron was broken at the aileron horn
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Post by thevon on Oct 10, 2007 8:33:41 GMT 10
Yeah Callun that makes sense. It seems to have happened with almost all of my planes at some point, but particularly after the initial build. I reckon it's partly why a plane feels so snappy when you've just built or rebuilt it! Part of the problem is using the small Dubro horns - they crush in easily. It's better to use the bigger ones, which have a bigger footprint. The other benefit of using bigger horns is that you can hook the control rod higher on the elevon horn, which reduces the effect of any slop in the upstream linkages (servo slop, rod slop, rod bend etc). Particularly applicable for fast pitch sensitive plank wings.
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Post by sean on Oct 10, 2007 10:14:57 GMT 10
It's amazing what you can get away with. I DSed my Bat to about 100 half a dozen times with a broken elevon who's horm was CAed into mangled balsa . CA really works!
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Post by callun on Oct 10, 2007 17:29:19 GMT 10
And lets not forget Callun, you were suffering from reduced control effectiveness because your aileron was broken at the aileron horn That's a design feature see... you wonder why I've never stripped a servo gearset - there's your answer ;D
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Post by sf2 on Jan 10, 2008 17:11:51 GMT 10
If you spray the wings with a little water and then spackle, you are garunteed to get it filled, probably with less spacke.Also things like spars if you water, the spackle gets in deeper and is less likely to shrink and dip into the spar groove, unless of course you put 1/4 inch spakle over the top, love sanding tho'
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