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Post by Pij on May 26, 2008 14:54:04 GMT 10
Feel free to post your glider reno's here too. My Duck is only a few weeks old. Though I'm reluctant to admit it, it might be time to give it a make-over. There are only minor rips, 3 or 4mm, in the covering, from encounters with sharp trees. But there is more tape on it than it was first built with, from securing loose edges, surgery on the switch and receiver area, replacing servos etc. If it was just the covering, I'd tape over the problems again and keep on flying. But it's time for an equipment upgrade too. The $15 servos, 2 sets, have served me well for the learning stages. First set lasted a couple of days, then the next set (which got damaged in the first couple of days but kept working) have gone on for a few weeks, and still work well within their actual flying range. But today my Hitec HS-65HB servos arrived from USA, and my servo covers from UK. I went out and bought some lead flashing, so I can re-balance the Duck more efficiently - flatter lead, so I can put more of it in the forward-most position, should be able to use a little less, and have no bulging lump from trying to squeeze sinkers in where they don't want to go. And over the weekend I made up the charging jacks. The one with the LED is destined for the Duck, I think. Though it'll cut the brightness, I think I'll mount the jack and LED below the surface so some clear tape can cover them, or a clear plastic window taped down. So, I'll be able to get rid of the plastic-spooƱ lump on top, too. I'd really rather be going out to the cliffs this afternoon again, but, sigh... it might be time. On the bright side, the winds should be even better in a couple of days. If I get it all fixed up by then, I'll have a new-looking and -feeling Duck to fly! If there's anything else I should be doing while the Duck's naked, please tell me. I'll take some BEFORE photos prior to stripping the Duck.
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Post by Pij on May 26, 2008 21:02:57 GMT 10
Here's the before pics. There was a bit more damage than I thought, once I looked closely at each part. The damaged fin was a surprise to me. Not shown are about 10 little holes in the covering, and rips near the ends of the hinges and at the TE near the fins. Also impact "bruises" near the tips and of course along the LE. I removed 79g of lead while stripping it down. Calculations show that the half (or so) of the covering removed must have weighed 34g. That's more than I thought the tape would be. BTW the bottom right photo is a "during" shot, with layers of tape removed, showing surgery scars from replacing servos previously. I drove to a nearby home-based signwriter, who kindly gave me a small bit of 3mm coreflute, just enough to replace the fins.
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Post by felix on May 26, 2008 22:08:34 GMT 10
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Post by felix on May 27, 2008 20:00:05 GMT 10
thought i'd post a progress shot of the electra wing.rebuilt it flat,capped the ribs,cut the ailerons and added false ribs,sheer webbing done and servos installed.next is a good sanding and covering (not looking forward to that! it's a 6 1/2 foot wing ) s281.photobucket.com/albums/kk209/14FELIX2/?action=view¤t=Picture.jpgoh excuse the disgraceful state of my "lab".....it's not normally that clean ;D
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Post by Pij on May 27, 2008 20:09:33 GMT 10
Had a sneak peek at your Bee pics too. Aahh, isn't a Bee supposed to have tip fins? But that certainly LOOKS great with the single fin. How will it fly? And, what's sheer webbing? I have some progress shots too. Naked Duck. Well, almost. Last look at the old switch, box, plug and servos before they come out. Extra taping to give strength to the fixed-trailing-edge tips, and to help remove some excess reflex. Surgery scars have cut across some of the original taping, but I still want to be able to access the servo leads. So, I'm putting angled taping across the centre join, on the underside, but still leaving the servo leads clear. The taping also reinforces the join between EPP sub-trailing-edge centre and fixed-trailing-edge centre, to match the taping on the top side. Full-length hinge taping. There was a little play in the elevons, twist-wise, where the strip hinges allowed the inner end to rise up a tiny bit. This should help. I also want to do something about the tear-zone near the inner end of the elevon. It has only shown up as a tear in the covering, but I can see that there is a stress on everything at that point.
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Post by Pij on May 27, 2008 20:32:16 GMT 10
My new charging jack and LED is a little too deep for the wiring box area. If I was building from scratch I'd put it further up front, where the EPP is deeper. As it is, I've hollowed all the way through the EPP, but still the jack sits a little proud of the surface. I'm shaping ahead and behind with some thinned depron to smooth the bump. It also gives me a chance to fill in a dip in front of the top-rear spar, caused in initial construction by the spar refusing to sit in place round a compound curve.
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Post by felix on May 27, 2008 20:38:16 GMT 10
hey pij the cores on your duck look perfect! will make an easy reno.couple tips you may consider that i have found works- try coating the leading edge with watered pva,really seems to help the foam in bad impacts and second is the smoother you can make it the better and more efficient it will fly.like i stated before mine wieghs in at over 800g and will fly in as little as 8knots. yeah they normally have tip fins,mine i modified for a single fin.main reason being is that by sweeping my wings forward tip fins don't have enough moment arm! on looking at this wing before its current state i had tip fins and some of the area was actually in FRONT of my CG -not good.the other reason was for 2types of less drag.first being parasitic drag of one surface in the airflow instead of two and the other is induced drag caused by "toe in/out" of the fins in a turn. it flies fairly fast but only really comes alive in 15knts and anything less it is a wing that bites at every chance lol. shear webbing is filling the gap between the bottom spar to the top spar with verticle grained balsa.in the electras case it doesn't have a top spar but top balsa sheeting.basically it just stops the top surface buckling under compression in high g situations (something the electra was never originally designed for lol). the electra was my first scratch build (with my nephew).have a build log on rc groups i'll have to find. look forward to seeing your duck finished
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Post by Pij on May 27, 2008 21:00:28 GMT 10
Will the watered PVA work with the fibre tape still on? Because I decided not to strip it right down. The filament tape was in good condition, and in mostly the right places. I was thinking about the goop idea for the LE, but I don't have the funds to buy extra stuff right now. So it'll have to be something I have on hand, and which can go over the existing tape. I never thought of the toe-in/out before, but knowing how steering setups on cars are geometrically modified to turn properly, I see your point. www.rctek.com/handling/ackerman%5Fsteering%5Fprinciple.htmlThanks for the sheer webbing info. I actually built that way, on a spar that never got beyond being a spar, for a free-flight glider. I still have it around somewhere. It was a continuous-curve instead of polyhedral, and was intended to explore creating strength through opposing tensions. I needed the sheer webbing to stop the whole thing popping apart while it was sitting on the bench, let alone high-g turns! And bindings of carbon tow to hold it all together too. Did you see my suggestion for trapezoidal fillings between the top and bottom spars in the Joint Design thread? I suppose that was a minimised sheer webbing, too. I just didn't know the name, till now!
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Post by felix on May 27, 2008 21:41:42 GMT 10
pij the pva won't work over the tape...needs to wick through a porous material to bond the cells together.goop,like you mentioned may be the idea.i've never used it myself (i try to keep my hobby in a hobby budget) but i s'pose could always be done later. stoked you understand the toe in! funny how automotive principle and engineering can have so much in common with chunks of foam lol. i did notice the shear type webbing on your spar design.shows a very intuitive side to your thinking.much respect there mate! i have just made a composite spar as a testbed for my own design wing and at 25mm x 6mm and 1000mm long it supported 30kgs in it's centre with no visible bend and about 150kgs with heaps of bend but no breakage! will keep you posted on this one as the design progresses (if it ever gets off the drawing board lol).
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Post by Pij on May 27, 2008 22:00:23 GMT 10
I think you'd be interested in my composite spar. I would have to measure to remember the exact dimensions, but it was about 900mm long and 12 or so thick. Yes, we were working THIN at the time. Everybody told me it was a bad idea to deliberately lock in opposing forces, I referred them to pre-stressed concrete construction, but they didn't agree. I know it would go BOING in a nasty way if the bindings let go, but I don't think they will. I'll send you a pic of it if you like. I did consider stressing it to breaking point (when I decided not to finish the wing) to find out just how strong it actually was. The reason I discontinued was that I had been putting carbon-reinforced ribs on it, quite expensive, then calculated that I didn't have enough chord to achieve a glide-able wing-loading, so I retired it. It might be ok with no ribs, an EPP leading third, and maybe EPP back 2/3 too. Oops, forgot what I was here for. Here's the bump covering my new switch jack. First, with power disconnected, flash photo, then with the receiver battery doing its job, no flash, just the 30mA LED. This blue is the brightest of its colour changes and red the least bright. The 65HB servos fitted precisely in the slots from my eSky-ish ones. When I was testing my LMA and other gear, I discovered a metal-detector effect: the alarm's pitch would change dramatically when a tiny bit of metal (a small staple in a plastic bag) was brought near it. Now that my LMA is stuffed into my wiring box, with WIRING nearby, it makes some sick micro-squawks. I think the presence of thin metal ruins the effectiveness of the LMA much more than taping over it does.
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Post by felix on May 27, 2008 22:09:44 GMT 10
haha sounds like some sort of hand grenade! prestressed structures built right are an awesome thing (look at freestanding stone arches or bridges).send thru the pics,love to have a look!
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Post by felix on May 27, 2008 22:11:46 GMT 10
....that last pics looks like the little green men are coming :olol.well done.
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Post by Pij on May 27, 2008 22:26:46 GMT 10
I went down to my plane-room and found it in a box of balsa bits.
It's about 860mm long on the curve, 8mm thick, and weighs 18g.
Pics to follow.
OK, done. See "Composite Spar" thread.
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Post by Pij on May 28, 2008 13:02:37 GMT 10
More "During" photos: Ready to cover the underside. The greenish masking-tape covers areas I don't want to spray with the 3M-77. The black lines mark out an area to cover with black, including the servo lead scars, the servos, ballast box, battery, receiver, wiring box, switching jack, LED etc. The idea is that when I want to operate on any of those areas, I can remove some or all of the black tape, and only need black tape to put it all back together again. Covering the underside. The black zone on the underside. Ready to cover the topside. Covering complete, except for tips. Next, connect up the linkages, then do the tip fins.
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Post by Pij on May 28, 2008 18:06:05 GMT 10
Making the fins. The local signwriter gave me this piece of corflute, JUST barely enough to make the 2 fins. The double black line shows where I decided to extend the fins back by 5mm. By this time darkness was nearing, so I was in a hurry to do test chucks before nightfall. Therefore missing photos from the sequence. I fitted the fins in the normal way, but with more filament tape than usual. You can see in the fin pic, that I have CA'd a bamboo skewer (not skua) into the LE flute of the fins. After attaching them, I inserted another thinned skewer through about midway, and another further back. Of the 3, the LE skewer gave the most obvious improved stiffness. It also provides a rounder LE.
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