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Post by thevon on Jul 19, 2007 6:41:21 GMT 10
Guys, there is a fair bit of discussion around about variations to the normal 3M77 and filament tape method of preparing wings before covering. Some say that 3M90 is much stronger than 77 - but very different to use. It comes out like a foam and you squeegee it on. It sets dry, but apparently gives extra stiffness and coverings stick to it incredibly well. Also there's been a lot of experimentation about a method which seems to involve squeegeeing PU glue over the EPP and laying a fibreglass weave tape (Henry's Roofing Tape in the US, or HRT) - it's a bit similar to fibreglass flyscreen. Squashed flat to dry, then 3M90 squeegeed over the top of that, then covered with Monokote etc (or tape) makes the wings very stiff. And you can get a glassy smooth finish. From the discussion there's obviously a trade-off because stiffer gives high performance and limits minor damage, but on the other hand in a huge crash it won't flex and the plane might rupture more fatally! I haven't had any experience at all but picked up on it thru a discussion on the Maleny club group. This RCGroups thread links at the top to a series of articles which take some time to read thru, but are very interesting. www.rcgroups.com/forums/showthread.php?t=696829&highlight=3m90+coveringEzza have you had any experience with using these methods/ materials on your DS missiles?
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Post by ezza on Jul 19, 2007 9:46:07 GMT 10
I have not tried the PU/glass thing yet, but I do know Swoopdown (new memeber) is about to try it, so hopefully he will post the results?
I find that using Oracover or a new product called Toughlon (I think), as the final covering works best. They are basically a stronger or thicker version of solarfilm. It is so easy to iron or use the heat gun to get all the wrinkles out after a day of flying/crashing.
I put two layers of fibre tape with no overlaps on my last Reaper then coverered it with Oracover. I only use spackle under the fibre tape if there is large hole or crater as I find the tape covers them up so well. Always sand and wipe each layer with acetone, as the next layer or covering won't stick so well. I use 3M 77 between each layer as well. They come out real smooth and strong when using this technique. I have also put thinned goop on the fuse and wingtips however, I am not sure it has much benefit.
I built dad's Reaper with one layer of fibre tape and it seems to get less wrinkles from crashing. Mine weighs 200 grams more than his but will fly in just as light conditions. I just can't throw it around quite as much. I guess it depends on the type of flying you are doing. If you have large slopes with decent wind (15+ knots) a heavier plane is always going to fly better. A sea cliff with not much landing zone, lighter is probably better and more aerobatic.
I used to cover with colored packing tape which is fine but once they start getting wrinkly there is not much you can do to fix them, other than patch or recover.
I think it is good to have a way of adding ballast, that way you can build them lite and when you started getting blown back or having a hard time penetrating you can 'load up'. ;D
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Post by sean on Jul 19, 2007 11:41:00 GMT 10
Good find Andrew. It could work quite well but personally I'm not keen on sanding PU glue, it's very rubbery which I think makes it hard to sand to a good, flat surface. I used PU glue to strengthen and smooth out my Reaper's wingtips and the results are quite good, but sanding it is not fun, you have to be very careful that you don't sand down whatever is next to the PU coating (ie EPP or balsa) as the PU glue takes a lot of elbow grease to sand. The technique I used is described on the Ubercraft website ("Shaping Sharp Wingtips" PDF, available here: www.ubercraft.com/PAGES/UC-HowTo.html). It involves mixing a drop of water into the PU glue to thicken the glue and accelerate its setting. If you are patient this technique could be used on the whole wing, it would make for a good light weight and much stronger alternative to spackle, and the finish would be excellent. Ezza, at first I wasn't sure about the value of Goop either, but I've found that it adds a lot of toughness for really big hits, and Profilm (Oracover) sticks to it like nothing else. Without it I was finding that the fibre tape/covering would pull off my spackled foam with anything more than a moderate hit, and this needed a recover to fix. After applying goop over spackle the tape and covering have stayed stuck down in some huge hits.
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Post by ezza on Jul 19, 2007 13:13:37 GMT 10
Great tips Sean! How is she coming along? Sounds like you are more than ready to introduce her to the darkside. I have used the goop trick on all my foamies so I don't have anything to compare, but I will keep doing it.
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Post by thevon on Jul 19, 2007 18:40:43 GMT 10
All very very interesting. For final covering I"ve only used Solafilm (much too thin and easy to melt, and doesn't stick) and Monokote (seems great, it's incredibly strong, I wonder if you even need fibre tape with it!).
Do you guys think Oracover/ Profilm/ Toughlon is better than Monokote? If so I have a fair amount of Monokote for sale .... !
I'm really impressed with using a strip of Clearshield Urethane Paint Protective film over the LE. It's not cheap but you don't use much. I reckon it's much more practical than gooping and extremely rip proof. They use it to protect car paint from stone chips, which is a tough job. Hard to poke a hole in it with a screwdriver. It's pretty much invisible when it's on.
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Post by GotrekGurnisson on Jul 19, 2007 20:29:18 GMT 10
Mark used Toughlon on his recently rebuilt Bat. He likes it but personally I don't see much benefit in it. It looks like Swiss cheese after the first landing - sticks and rocks puncture it very easily.
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Post by sean on Jul 19, 2007 21:08:18 GMT 10
Hi Ezza, The Reaper's coming along very nicely, I've been working on it again these last few days. I can't wait to get it in the air actually, it should be brilliant on the darkside! I reckon I'll go the single layer of tape option to save some weight behind the CG. I can see the advantage of two layers of tape for huge speeds but I can't see myself going that quick, at least for a while anyway . I'll update the build thread when I get a chance. Andrew, I used Monokote on balsa models many years ago and it is a good film, much better than Solarfilm but IMO not as good as Profilm (which is also sold as Oracover and Ultracote, both of which are the same product). I believe it requires a higher temp than Profilm which makes it less suitable for foamies. Basically though I think Profilm is the duck's guts, it's strong, the colour doesn't come away when you unstick it, it shrinks brilliantly around compound curves, it's the easiest to iron down without wrinkles, you can iron it over itself with only minimal or no bubbles forming, and if you're building a balsa model it wrinkles less in the sun than the other two. BTW I have no financial interests in this product! The urethane paint on the LE sounds like a good idea!
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Post by thevon on Jul 19, 2007 21:52:21 GMT 10
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Post by thevon on Jul 30, 2007 8:25:28 GMT 10
I borrowed the "Say No to Tape" DVD from Jeff at Burpengary. I felt pretty low yesterday not only being in the shed fiddling with planes, but also having the shed TV playing a glider-building DVD! Very, very sad.
I was almost the boringest video I've watched, but the 3M90 technique with fibre mesh looks interesting. So I'm gonna get some and start to play around with it.
The big benefit seems to be that it sets totally dry within a short time (less than an hour?) and then it's not sticky, making it easy to work with. He hates 3M77 and tape - says it's gooey and soft. Also you can iron Monokote onto the dried finish and with the heat activation it sticks extremely well.
The difficult part is that you have to work it in with a flat spatula at just the right time, ie it's a bit like concrete - once it's going off, you can't work the bumps out any more.
I was also relieved that this guy loves Monokote and won't use anything else.
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Post by ding on Jul 30, 2007 12:23:18 GMT 10
I can't speak for these methods but I must say I love monokote too!
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Post by thevon on Aug 1, 2007 20:23:38 GMT 10
Just logging my investigations into better covering methods!
I bought some 3M90 and tried it out. It's very different to using 77 - it really blasts out and is very cold, and it really tacks up gooey in a minute or so, but then proceeds to take many hours to really cure. I tried squeegeeing it over a piece of flyscreen mesh just to see how it went and it didn't really work for me first time. I was surprised that it stays very rubbery even a day later - I mistakenly thought it went hard. So the Chris Klique method with 3M90 and Henry's roof tape really relies on the fibreglass tape to provide the rigidity. I can see why other guys have tried using PU glue instead since it dries rigid.
The 3M90 really does stick to the EPP much harder than 77. I compared 2 bits of mesh I stuck on and after 24 hours, the 77 one peeled off pretty easily but I really had to rip off the 90 one.
Also the 90 goes really dry (feels soft and rubbery but dry); but in 24 hours the 77 still feels tacky.
Thinking about all this, I'm sure there must be better methods. Klique obviously succeeds with 3M90 but it's a bit fiddly I reckon, and the 90's not cheap - $22 a tin like the 77, and you'd probably use most of a tin on a wing I think. Also the thick layers of 90 with the tape etc must make the wing thicker and seems like overkill to me.
There are so many products out there, I can't help wondering if there's some sort of cheap filler or adhesive that has the properties of being easy to spread on in a thin layer, sets quickly without shrink, is tough and doesn't crack, flexible but not too stretchy, etc. Plus it has to grip to EPP and Monokote has to grip to it!
Now that I write it like that it sounds impossible! But I have a couple of ideas. I've heard a lot of good things about Sikaflex - never used it myself - so I'm going to get some and try slathering some of it on EPP and see what happens.
If that worked (or something similar) I am going to get some organza - the incredibly fine nylon fibre mesh that they make wedding dresses etc out of. We use it in the lids of insect bottles at work. It's very very thin, very very tough and so light you can hardly feel it, plus it doesn't stretch. Wouldn't it be good if you could spread some Sikaflex and lay a sheet of organza on it and squeegee it with a credit card and let it set??
I know, I know, I'm getting ahead of myself and it probably won't work but you've gotta try!
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Post by thevon on Aug 8, 2007 18:08:48 GMT 10
EXPERIMENTS WITH COVERING MATERIALS Here are some more findings to add to the quest for new, simple and tough covering methods for EPP. Firstly EPP density. Have a look at this photo of scraps from 3 dif wing beds – the one on the left is really high density EPP, came with Scorpian from Zipper. Middle one is from Gerard’s Ozprey, right hand one from Wowings Duck. You can see (I hope) that the bead size is smaller on the left and bigger on the right. The low density one on the right is more open, has more holes etc. When you squeeze them the difference is very obvious. Apart from being far harder to squish, the very dense one has a "dry" feel to it whereas the low density one feels more slippery and plasticky. I think that the toughness of the EPP is a HUGE factor in wing toughness. I used the medium stuff for these experiments. I got 2 pieces of EPP, spackled them with Bostik lightweight filler (I’ve also used Spakfilla Rapid & was very happy with it too). When dried sanded, I compared the flex with a raw piece and found that the spackled pieces were definitely more rigid. So the spackling doesn’t’ just fill the holes … it adds to the rigidity of the build. Spackled and sanded 1) 3M90 and Organza Firstly I tried a method spraying with 3M90, smoothing it with a spatula made from ice cream lid, laying some organza over it, spraying and smoothing again. Then when dry, resprayed and laid a 2nd layer of organza obliquely. When dry, sprayed and smoothed again and in a few minutes, ironed Monokote on. This was all surprisingly easy and the 3M 90 is nice to work with since it sets dry and doesn’t stick to things. With one layer of organza on 2 layers on and more 3M90 glue sprayed on top This sounds fiddly but was quick and easy to do. I was happy with the end result. It had a lot of body to it, stiff but rubbery, felt very light, and when I crunched the corner onto the bench it wrinkled it but would be easy to iron straight again. None of the deep wrinkling you get when it’s covered in bi-di tape. It was smooth and the Mono didn’t want to peel off. I think this method has potential! It wouldn’t be anything like as stiff as using PU glue but on the other hand far, far less mess, no sanding and it won’t smash up on impact. Combined with good spars it should be great. It will get harder tomorrow as the 90 cures. 2) Concrete Sealer !!! Xylene is the thinner for Goop. It’s also the thinner for concrete sealer which you roll it thickly onto driveways and it self–levels and de-bubbles to leave an extremely tough skin which fills the porous holes. I wondered if the concrete sealer, might actually be like Goop?? I have some here so decided to give it a go. It’s thinner than the “warm honey” consistency that you aim for with thinned Goop. Also, my leftover sealer has been thinned with Xylene, so it’s even thinner than normal. It was easy to spread just using a piece of sponge. Initially I tried to put the organza on as I’d done for the 3M90 but it just won’t stick to the sealer,just lifts off. Maybe there’s a way, but I’m only looking for methods that are quick and easy, so I gave up on that idea. Decided to see whether it works like normal gooping anyway. Put a thick coat on and put it outside to dry. When you put it on it looks rough but sets to an even skin. In the pic you can see a daggy bit where I touched it with a sticky finger and pulled a bit of the skin off. I also thought I’d try just putting it onto a bit of plain cut EPP. It behaved quite differently than on spackled EPP. It took a long time to dry on the spackled (will need overnight to really dry) but on the raw EPP it felt completely dry in 15 mins. After about 40 mins the spackled one was tack dry, so I recoated it and the raw piece too. Again, the raw piece dried very quickly. You can see how different they look after 2 coats. Tomorrow I’ll spray the spackle/sealer piece with glue and Monokote it - see how it goes. In summary from Part 2), I’m definitely suspicious that concrete sealer might be a thinned version of the Goop chemical – seems to behave similarly I think. It’s obvious that my sealer gives a much thinner coat than gooping. However it seems to add a lot of toughness to the surface … it seems harder to tear a corner off the sealer-treated raw bit. If this works, it could provide a much easier and cheaper method than buying Shoe-Goo and thinning it.
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Post by thevon on Aug 9, 2007 12:44:11 GMT 10
A bit more ... I managed to get some Profilm so am looking forward to trying it and comparing with Monokote.
Morgan and Gav at Hobbyrama said that in the past they've covered foamie wings with "StickyBack" which is what is used to make lettering on yacht sails, available from marine shops. Apparently it's incredibly sticky, and tough, though a bit thick (not v light). Hard to work with but once it's on it's there for good and very strong, cut resistant etc. I had a look at the price of some 2pack polyurethane at Bunnings and it's really Xy. The super thick stuff (bar top coating?) is $50 for a couple of small bottles. The normal stuff used on sanded floors is $40 for the smallest quantity which I think is 2 x 500mL tins. So if anyone has some leftover floor 2-pack sitting around, let me know ... I'd love to try it on EPP.
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Post by sean on Aug 9, 2007 21:52:45 GMT 10
Looking good Andrew, I'm keen to have a look at that concrete sealer!
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Post by thevon on Aug 10, 2007 17:41:22 GMT 10
Nah, BUMMER - the concrete sealer's no good. It does provide a nice tough skin but when I sprayed it with glue then later ironed film onto it, then tried to pull the film off, the sealer peeled away in patches. Well really it looked like it was the spackle that was giving way, and since I haven't used Goop I can't compare. But from what I hear Goop sticks no matter what, so this didn't seem acceptable. Dang.
With no wind for a fly this arvo, I dived out and kept experimenting, but in summary I don't think I have a good (new) method. The organza fabric covering is nice, easy to apply. You can just let the glue dry and iron the gauze on - the heat melts it in well. Then spray again and put Monokote on. It gives a silky smooth finish and when it gets bent, it doesn't hold the wrinkles. I think it would be really good for a light model like a Weasel, but not much chop for a fast dunger.
The thing I don't like about strapping tape is that when it gets a big hit and gets badly wrinkled, the wrinkles seem to stay there. However it's very tough - when you do a puncture/ stabbing comparison it's much tougher than the other options I've tried.
So the only definite finding from my experiments so far is that spackling adds rigidity. I've done quite a few squares and the spackled ones have a different, stiffer feel than the plain EPP, no matter how I cover it. So although I'm suspicious of spackle being a weak layer in the covering, I'll keep using it. (might see if there's a tougher light spackle, or if you can mix something with it).
I've been talking to Chris Klique in the US (Ritewings) on RCGroups and he likes the 2-pack bar top epoxy, with fibreglass cloth but says he doesn't necessarily use it all over the wing.
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