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Post by thevon on Jun 12, 2008 19:48:31 GMT 10
Pij, the leading edge has a very flexy fibreglass rod, not carbon. That's my point ... I really think that external stiffeners should be f/g, not c/f which shatters.
But I do agree, it's too expensive and far too much work for the average build. As the kids say, "I'm OVER IT!!" It's finished now, yeehah! ... I'm sick of building it!
Yes the bits are expensive for a foamie, and it's far too much work to justify. I'm not suggesting this build for your average foamie use. My motivation for this build is that my previous Bat was a great all-round well behaved DS'er that I threw out to sus out a site or wind direction. As such it met the earth spectacularly and often. Yes, the extra bits cost more but if it means that the Bat survives its crashes and serves its purpose for longer, postponing a rebuild or replacement, then it's worthwhile.
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Post by thevon on Jun 12, 2008 20:15:46 GMT 10
I wanted to stick the approximate amount of balance lead into the nose before covering, so I “mocked up” the finished plane by sticking the fin, elevons and other bits on … plus some bits of covering over the back end. It took 280gm of lead to get it to balance at around 122mm. I cut a hole in the nose, and used the soldering iron to neaten it up. I like the way the melted EPP makes a more solid wall. Then gently pushed 2 layers of aluminium foil into the cavity to make a mold. It’s very easy to rip the alfoil, but tiny holes aren’t a problem. Then melted 280gm of lead in a tin. You need a very hot flame – the kitchen stove will take forever but a good camping stove or soldering torch works well. Avoid breathing the fumes. Not good for you, apparently. I tilted the mold so the top was level, and poured the lead into it. When it was solid I dunked it in cold water. It took a bit of beating and bending to make a really snug fit, then it was permanently and heavily Shoe-Goo’ed in. When the Goo was set, I cut a piece of EPP to shape and glued it onto the lead with Super 77, and whittled and sanded it to shape. At this point the airframe weighed 933gm with ailerons, but with no spackle, Goop, tape or covering! I mixed up some spackle with PU glue. I just guess the mix at around 5:1. I mixed it with a couple of spatulas, which was OK since it had more working time with the weather being cooler but it’s faster to mix it with a plastic fork. I smoothed it on with a spatula so there was no excess. I only applied it where there were holes or rough patches – didn’t try to cover the whole wing with it. If it had been a cut EPP wing I would have done the whole thing, probably twice. But the molded foam doesn’t need it and it doesn’t stick well to it anyway. You can see it foaming up a bit. I sanded it after a couple of hours when it was still a bit soft. Don’t use the mesh sander for this as it clogs. Then left it to set more and despite rain all night, it was really hard in the morning.
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Post by thevon on Jun 12, 2008 20:29:25 GMT 10
I applied a coat of thinned Goop which was mixed ages ago, a nice honey consistency. I didn’t use a brush – just wore gloves, dipped a finger in the Goop and smeared it all over the wing. It works well, coats it quicky and quite evenly. Then I hung it up by a wire to dry. As it dried off I applied another couple of coats around the LE and tips. I also applied it thickly to the balsa fixed elevons at the tips, which helps make them more rubbery - they’re going to take a pounding. Hung it up to dry. I mixed up more Goop for later. Worth noting here that the Goop in this tube was rather stiff and dry-ish, but it’s not a problem as Goop never really “sets” – it can always be reconstituted with solvents (even when it’s been hard for ages, apparently). So I added the Xylene and allowed a few hours before using it, mixing it every now and then. Not sure if these photos show it well, and you’ll laugh, but this is now a favourite trick of mine. I sliced and diced a grid pattern well into the EPP of the nose, top and bottom, then got some Shoe Goo and really worked it into the area. This is because I’ve honestly found that when my foamies’ noses get pulverized and I repair them with Goo, they are stronger and last longer than when new! As I said before, you can’t have too much Goop around the nose! I had to let this set for at least half a day. I covered the tips with tape, right around the fixed elevons. At this stage, believe it or not, I still couldn’t make up my mind whether to cover it with Profilm or Burrly. So I applied a mixed diagonal pattern of strapping tape, similar to what I’ve used on the Bat successfully before. But a few less strips and none on the LE. I sanded or acetone wiped the anti-stick off after applying each strip. Then applied another coat of thinned Goop over the whole thing, and hung it up to dry.
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Post by thevon on Jun 12, 2008 20:30:32 GMT 10
Finally, at the last minute I decided to go for the Burrly covering, mainly because I just want to try it. You can always remove Burrly completely and go back to a Profilm covering, but not so easily the other way round. The Bat has a multipanel wing, and I expected that the Burrly wouldn’t fit the shape, and I’d have to do it in several sections. But as it turned out, it fitted really well using one whole piece on the top and on the bottom. It seemed to work itself really well to the shape, with only a couple of thin V’s taken out of the top piece. This is a big advantage as the full one – piece coverage will make it stronger. I decided to have the bottom piece wrap up over the front and back edges and overlap onto the top – that way there are no joins to crack apart on rough landings. (later comment – that’s assuming it hits the deck right-side-up, which is a big “if” for me!) The Burrly is only 300mm wide so it won’t cover the back tip of the centre fixed elevon, but that’s OK. I marked some dots on the wing with a marker pen, then positioned the Burrly so that it only just covered the nose, and marked an X on the Burrly over the dots, as locating points for later. The most critical thing was to get really neat sharp bends around the dragspar, so the hinge line stays good. This can be a problem if the bends are rounded or wavy. So with the film carefully held in the right position, I pinched and pushed it around the dragspar in different spots till it had made some marks. I then highlighted them with a pencil, carefully pressed it into a fold, and ran a steel edge back and forth along it to really make a sharp bend. Note you have to do this for both top and bottom edges, so you have to do it in a couple of stages for one side. Then it will have a nice square fold like this: Fit it on tightly, then make sure the Burrly is tight and accurate, then do the other wing. At this point it would be best to do a crease similarly for the leading edges – I forgot. I started ironing the Burrly on from the dragspars forwards. It stuck down well. Keep pulling it hard and snugly onto the dragspars while you do this. I ironed it all along the back edge, up the middle, and working out and forward all the way to the LE. I found it useful to have a wet handtowel nearby, and after ironing a bit I’d hold it in place and sponge it to cool it and make the glue on the back of the film set hard. It was very nice how it seemed to fit the shape perfectly! I had to cut slits away in the excess sheet in front of the LE to get it to curve nicely, which it did, so I kept ironing it all the way to the LE… then remembered that I’d forgotten to do the crease. Oh well. But it ironed around the LE pretty tightly anyway. Then I ironed a piece right over the top, letting it overlap the rolled edges of the bottom sheet by a cm or so. Same process to iron it. Then I got a sharp X-acto knife and cut the top sheet really carefully next to the edge of the bottom sheet (easy since it’s clear) so it was a butt-join. Ezza did it this way and covered the join with clear tape. I thought I’d be clever and use some thin strips of bi-di strapping tape, for more strength. But it backfired a bit because despite acetone-rubbing it, the paint I later used didn’t stick to the strapping tape – it comes off easily. As recommended by Ezza, I left some of the sheets overlapping at the TE’s of the fixed elevons, as done for the elevons. It welds itself together solidly this way, and the plastic edge is at least as stiff as an ice cream container. By the way, I left some of the top and bottom sheets overlapping the wingtips, and cut and creased it around the end of the tip and ironed it. Not sure if this is a good idea because the top and bottom overlaps won’t stick well to each other and it will surely get daggy. It might be better not to cover the very tip and just layer it with Goop. I noticed Shane had done this with his new highly modified Reaper when I saw it on his bench. But I’ll try this way first, and wrap insulating tape over the overlaps.
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Post by thevon on Jun 12, 2008 20:31:27 GMT 10
Next step was to fit the elevons. Having used silicon hinges on balsa elevators covered with thin laminating film, I was really looking forward to using it here! As a matter of fact it was one of the main reasons I was keen to experiment with Burrly. Silicon hingeing is simple and really effective. Align the pieces perfectly, stick them together with plain masking tape (on the flush, non-hinge gap side). Then turn it over and open up the gap, and syringe a thin bead of silicon into the gap. Then cut a little spatula out of plastic and trowel the silicon along the V. You can smear it with your finger too. Don’t use too much. Easy!! But it didn’t work!!! Initially, anyway. The silicon just peeled off really easily. Two possible reasons: 1) the coating on the Burrly is different to the thinner film I’ve successfully used, or 2) the new tube of silicon doesn’t work as well. It’s important to use “RTV” silicon. I couldn’t find a tube at Bunnings which said RTV, but this one was for windows and glass and was acetic based, so it should have been OK. Anyway I went back to my old tube, and also sanded the Burrly over the hinge lines thoroughly. This time it worked much better. You can see the light through the hinge line. I set up the horns, control rods and stuck a coreflute fin mount on using Super 77 (double sided tape doesn’t stick well to Burrly. Nothing does!). At this point the whole thing in flying condition weighed 1.246kg!!! I was pretty disappointed with the weight, but I should have expected that. I’ve pretty much doubled up with this thing – using spars and taping like a solid build for conventional covering, but then I’ve covered with the very heavy Burrly. But I like the experiment. I’ll just need to hold back for strong lift days to fly it!
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Post by thevon on Jun 12, 2008 20:32:07 GMT 10
I had also got another couple of colours of the Tile Spray Paint, on sale at Bunnings. This is the only paint that seems to stick to Burrly (apart from grey auto primer, says Zipper). I did a quick job with the paint and didn’t try to make sharp edges. It has a strange behaviour. It is supposed to be gloss, but it really sets as matt. Also a milky colour appears as it’s drying. BUT: the weird thing is that over any solid parts such as the lead in the nose, ballast tube, and servos, the paint looks perfectly glossy and solid!! Really weird! How can it do that?? Anyway I found that it looked better if you keep shaking the tin almost every few seconds. I applied a few more light coats here and there. The paint only added 20 grams to the total weight, even after more coats. Here’s the final result … not bad for an experiment, really! And it was nice to find that it balances right on the mark! The silver tape is covering the ballast port. There’s black insulating tape on the wingtips. The actual colour looks better in real life - the photos make it look too patchy. I’m hoping to maiden it Saturday!
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Post by Vanders on Jun 12, 2008 21:17:49 GMT 10
Its so true what you guys have been saying, foamies are a lot of time consuming work. Mate you've done really well with this & we should all appreciate the fact that you've experimented with all these ideas & now know what works, what doesn't & some little tips on other little parts of the build.
Nice effort!!!!
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Post by Pij on Jun 12, 2008 21:38:53 GMT 10
Looks nice. Interesting and very detailed build report, thanks Andrew. I hope you get big weather for it.
I did wonder about your silicon hinges - could the Burrly perhaps have been strong enough to act alone as hinge tape?
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Post by thevon on Jun 12, 2008 22:03:07 GMT 10
Pij, yes, and I think that's what Ezza did with his Reaper. You use the top sheet to cover the wing and right across the elevon. (like live hingeing with fibreglass). It doesn't stick well enough to itself to use it as a stuck-on hinge between 2 bits.
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Post by felix on Jun 12, 2008 22:10:18 GMT 10
andrew that is looking like a real weapon there mate,well done. also a big thanks for the great descriptions/photos....will definately use some of the methods when i get back to the slope ;D
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Post by thevon on Jun 15, 2008 22:27:56 GMT 10
Well, it’s not great news … I had a bad time trying to maiden it and have now stripped the Burrly off completely and recovered it, using thinner laminating film. Plus I have to say with some shame that when Karl says NO reflex on the fixed elevons, he means it! I headed out yesterday to make use of the much-anticipated winds, expecting some (for me) serious DSing and good conditions to maiden the Bat. But it turned out to be light and flukey. But after sussing it out with the Minij, I got the nerve to put the Fazer up, and the lift got a bit better. I had a lot of fun flying and light-air DSing the Fazer, then when a mate arrived we maidened his (beautiful) Duck. Then I decided that I had to achieve the big aim of maidening the Bat. So I stuck a hook on it and rigged up the Hosemonster bungee. It spun and fluttered madly on launch and crashed pretty hard. Obviously CG back too far. So I stuck some lead on the nose. Same result. Four launches, more and more lead, and more and more crashes. Maybe a bit of improvement, but still not flying. We had to travel to a different site to get some lift, and I added quite a bit more lead to the nose and this time it flew, (more or less like the space shuttle “gliding”) and I brought it back for its first “landing”. Next time I shot it high enough to do a dive test and it pulled out reasonably firmly, so I started thinking the CG could go back … but as I looped it and went to roll out at the top, it spun and I couldn’t recover it, and it went a long way down! So after a long walk we actually stuck a bit MORE lead on and next launch it seemed a lot more stable, but I crashed it into a tree on the edge of the slope requiring a fairly risky tree climb to get it back! One of the silicon hinges had torn away. I was fairly sick of this plane by now. Which wasn’t really fair, because when I got home and checked the CG, I found I’d made a mistake. I thought it was set up perfectly to a CG of 122mm, but it wasn’t. Even with all that lead on the nose it was at 119mm. When I took the lead off it was at about 128mm. Really dumb thing to do. Maybe in the rush I checked it without the tail fin on. I think I have CG dyslexia. But I just wasn’t happy with it. With the 125gm nose weight required to make it fly, the AUW was now a whisker off 1400gm! And that’s without ballast. We just don’t get many days with enough wind to fly a 1400gm Bat! Plus, it was obvious the large centre fixed elevons (FE’s) section had too much reflex. Again, another dumb thing to do. In flying trim, the elevons were a 1 or 2 mm below the inner FE section. The outer ones were a pretty good match to the trim, but the large inner section was obviously having a big elevator effect. There were also now some substantial wrinkles in the Burrly covering too. So I stripped off the Burrly, which was really easy to do. It mostly ripped off quite cleanly, but I also used a heat gun to ensure I didn’t tear the foam. I replaced a few bits of tape, sanded it a bit, cut and re-set the center FE section with NO reflex and smeared a layer of thinned goop on. I wrapped the elevons with tape, sprayed the hinge areas with Super 77 and hinged with strips of tape. I had some Profilm and Monokote on hand, but I decided to use some thin (75 micron) laminating film, mainly because it’s really light but so tough. I tried poking a screwdriver through it, and it was much, much harder to puncture than Profilm / Mono. It was really easy to apply. Took about an hour. I covered right over the elevons including the hinge gap, too. Getting late now … screwed the horns back on, set the CG at around 118mm, weighed it at 1188 gm so it’s lost over 200gm. Slapped a couple of strips of dark tape underneath and some fluoro tips on top. The kids were beside themselves with excitement and trying to help … not because they give a stuff about the plane but because I’d been promising to take them to the park for at least 2 hours! So finally we got there and while they threw Frisbees and pushed the go-kart, I hooked up the bungee, gave it a mighty launch, and it flew! Quite nicely actually. It flew very fast and stable, and might be able to have the CG back a bit yet, but I’ll wait till I can slope it before deciding. The park is ringed by tall trees, and the highlight was zooming down and doing a couple of fast big circles with the wingtip about 2 or 3 metres off the ground, staying neatly at the same height and bank angle. All seemed well with the world again as I packed the Bat, the bungee and the kids back into the van. Even without the Burrly I think this thing is going to be an awesome DS workhorse. In these pics you can see the hook bolted through a piece of a plastic ruler. This is a great way to make a hook - so easy to tape to the plane. The silver tape is holding on the extra nose weight.
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Post by Pij on Jun 16, 2008 6:56:16 GMT 10
Lots of dramas, Andrew. I'm glad it seems OK now, but after all that trouble!
It will be interesting to hear how the lighter laminating film works out.
That was fortunate, having a park that suited you and the kids both.
Do you expect the CG to be staying around the 118?
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Post by sean on Jun 16, 2008 11:02:36 GMT 10
Hey Andrew,
Shame to hear about the first flight troubles, but glad to hear you have it flying well now. The new weight sounds just right to me.
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Post by chamm37 on Jun 16, 2008 11:08:32 GMT 10
hey andrew..... where are you buying your tape from. the straping tape that is
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Post by thevon on Jun 21, 2008 20:36:08 GMT 10
I got to fly the Bat in proper slope lift out near Dayboro today and it was really, really great. It was fast, it was stable, it had no bad habits. It loved being inverted, had a great roll rate (I had to cut back the aileron throws) and it DS'ed really well. It tracked nicely as it carved around and oh, did I say it was fast?? Well, in case you missed that point, it was fast! The only hassle was that after a couple of radio glitches on the first flights we had a major dropout and a long walk to get it, undamaged, so we decided that the aerials buried in the foam were getting blocked by the carbon dragspar. So I cut in and pulled out the aerial ends on each side and spliced some extra wire on so it dangled out under and behind the elevons. That's one plus about the see-thru covering - you can find the gear! There was no further problem.
I couldn't be happier with its performance. It's smooth and slick and nice to fly. The fluoro wingtips give great visibility.
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