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Covering with SIG KOVERALL

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Shaun K26/03/2008 02:26:00
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192 forum posts
38 photos

Hi folks,
I'm building my first fully sheeted plane (the Tony Nijhuis 62" Spitfire) and I'm in a quandry over how to cover/finish it.

I've done a smaller plane with a more open frame with Solarfilm and that all went fine but that didn't need to be painted over - the Spitfire does. I've seen a few painted Solarfilm jobs at my club and they don't seem to stay looking good for too long.

My local hobby shop is selling SIG KOVERALL shrinkable cloth at a pretty good price compared to Solarfilm but I've never heard any feedback other than what the shop guy tells me. It's a non-glued shrinkable cloth that you essentially put on the same way as you would with tissue and dope, the difference being it can then be heat shrunk with an iron or heat gun and therefore tightened afterwards for a supposedly stronger, smooth finish.

If you can offer any feedback (good or bad) on SIG KOVERALL I'd be grateful. Also feel free to mention your preference for any alternatives like glassing, ye olde tissue and dope etc, bearing in mind that I'm building a warbird that will need to be painted.

Thanks in advance,
Shaun K.

Evan Pimm26/03/2008 06:38:00
146 forum posts

Sig Koverall is very nice stuff, on anything over 80 odd inch span. Your little Spit would be staggering under the weight just taxiing. You are looking at lightweight modelspan on all sheeted surfaces and lightspan or similar on the open structure areas. Sanding sealed and spray painted in the usual fashion, with the minimum amount of paint buildup possible, and you will be able to fly the thing. Light Spits fly, heavy ones might, but only once.

Evan. 

Andy Green26/03/2008 08:24:00
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2279 forum posts
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2 articles

Tissue & dope would be my choice. Seal the wood with a couple of coats of thinned dope. Wet the tissue and apply with thinners only (this will activate the dope previously applied).

The wet tissue will go around all the curves. You can then finish with a few more coats of thinned dope or one of the water based varnishes.

I still like to use dope if for no other reason than to see the look on family faces when I say "I'm off to get some dope"

Andy

Shaun K26/03/2008 10:32:00
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192 forum posts
38 photos

Thanks guys.

Evan - excellent point on heavy spits - just this weekend at my local club I watched a clubmate solo his Top Flite 1/7th Spit for the first time (the old hands did his first few take-offs and landings for him). To be blunt the thing weighs a ton for its size! The take-off and subsequent flight were lovely then as I watched him kill the throttle very early on finals, at about 6 feet off the ground it literally fell out of the sky! Neither wing dropped - it simply fell flat on its belly, breaking the U/C and engine mount. So I take your point - light =good.

However, having ogled a 5-yard pack of Koverall at the shop today it doesn't feel like it would be much heavier than 8 the-9 rolls of Solarfilm that would be needed to do the job.

I have actually put quite a bit of time into some sensible weight loss with lightening holes in wing ribs that don't play a part in mounting or U/C, through lack of availability of correct size, the sheeted fuse sides are done with sheet that's 0.5mm thinner than that in the plan (4mm vs 4.5mm) and I am making a built-up stab rather than a solid sheet as in the plan to save some weight there as well, so I think perhaps a little leeway is available if the covering job will give me a great result.

Shaun K26/03/2008 11:47:00
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192 forum posts
38 photos

Hi Evan - A Little More on weight

 I've just done some web crawling and calculating to compare relative weights of Koverall and Solarfilm as an example. Please don't take this exercise as a criticism - I'm genuinely trying to learn and find the right way to go so I'm trying to get all the facts. I work in IT - we like details...

SIG state that Koverall weighs 1.25 ounces per square yard. Converting ounces to grams and yards to metres that equates to around 42.4 grams per square metre (gsm).

The Solarfilm web site quotes "50 to 65 gsm", so on the manufacturers' claims even the lightest Solarfilm is heavier than Koverall. From Andy's suggestion though, I suppose if weight is a primary driver then tissue has got to be the lightest, I suppose???

So the question I have now is - is it the coats of dope added to the Koverall that give it an overall high weight or does dope weigh next to nothing once the liquid evaporates to leave the coating?

Evan Pimm27/03/2008 03:44:00
146 forum posts

By the time you have doped and painted the Koverall enough to hide the weave I would think that it would be little different in weight to Solartex, possibly heavier. The weight of the couple of rolls of film needed for the job would, by comparison, be negligable. Remember, the film is the finish, not just the start. On a model this size, lightweight tissue (Modelspan) is both likely to be the lightest, and certainly the best representation of the real surface, of all the finishing mediums so far discussed. With modern '2 pack' paints, or even just a final two part clear finish (Satin, of course) it is just as fuel proof as film, posibly better, and almost as easy to repair. You sound like you need to talk to an 'old' modeller and get the good oil on tissue finishes, and a bit of practical help.

Evan. 

Shaun K27/03/2008 12:23:00
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192 forum posts
38 photos

Thanks Evan, I think you're right re talking to the old folk. I know that our club president has done a slightly larger Spit in tissue & dope and if anything the finish looks too nice and smooth to look realistic.

Thanks also for clarifying that Modelspan is actually tissue - I've never heard of Modelspan before nor seen it in any local hobby shops. Out here in Australia the hobby shops are all totally dominated by the RC car world with a small corner allocated to aircraft and if we're lucky there's one guy who knows a little about planes. As such we only have easy access to the high-volume building materials.

Shaun K27/03/2008 12:28:00
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192 forum posts
38 photos

Alas, a quick search on both Google and ebay reveals no Australian suppliers of Modelspan...

So off to the old club folk it is to get the local knowledge on tissue covering, starting with where to get it!

Evan Pimm28/03/2008 03:57:00
146 forum posts

Airsailmodels .co.nz are purveyors of fine modelling material and offer a web based 'online shop' where such things as Modelspan and Jap tissue of various grades/colours may be purchased. And not so far from you either.

Evan. 

Shaun K28/03/2008 13:12:00
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192 forum posts
38 photos
Thanks Evan - that's a great help.
Shaun K23/06/2009 15:27:20
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192 forum posts
38 photos
It's been a long time since I started this thread, but I thought it worth reporting back on the result. All parts are now covered and I'm in the final stages of sanding back preparing for paint.
 
I've read, consulted, listened and read some more and decided in the end to give the Sig Koverall a go.
 
I'm really pleased with the results and I'm happy to report that the weight gains expected don't appear to have happened. I don't think she's obese at all... At every step I've been sparing with the dope and been extremely thorough with the sanding block, taking all the filler back to leave only what's required to fill the weave and nothing more.
 
Some lessons learned on my first attempt with Koverall:
- It's REALLY easy to work with the iron and heat gun. Much easier than Solarfilm etc.
- It's super tough. I dropped a wing radiator from the Spitfire while sanding it and it fell right onto the edge of a hard plastic crate on the floor. Not a mark on it! It's as tough as nails.
- It's sooooo time consuming compared to Solarfilm! I've no doubt the end result will be great, but I am so sick of sanding.
 
It's all part of the learning experience though.
Shaun K24/06/2009 04:16:39
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192 forum posts
38 photos
Some more things I didn't mention in the last post.
 
Why did I choose Koverall? I'm really hoping that this plane lasts a long time (assuming that the only things that touch the ground are the wheels!) and I've seen many models at the local club with either paint flaking off their Solarfilm base or even worse, painted Solarfilm peeling off. Hence I decided to use something more permanent that provides a good base for painting camo.
 
Filling and Sanding - I read many forum comments on this site and others about how to fill, what to use and so on. The most common, recurring theme was the traditional thinned dope and talc (mixed 1/3 dope, thinner and filler each by volume), however it seems its impossible these days to get unscented talc (no oils) so I used some glass micro balloons I already had in the shed.
 
I read some forum comments claiming that glass micro ballons are much heavier than talc, however I'm sure that in practice the difference in weight is insignificant. Consider this - the entire bottle of glass microballoons I bought weighed 42gm net. I only used about 2/3 of the bottle on the entire airframe, the vast majority of which actually gets sanded off again. So I'd be surprised if I have more than 10gm of filler on board. That equates to around 0.25% of the total completed weight of the aircraft. I can't see that making a real difference.
 
There is one downside to using the glass microballons though - it sands quickly and easily but even the best wet&dry sandpaper is worn smooth in no time flat. I've been through three sheets (cut into 6 pieces per sheet for the sanding block) on a 62" airframe.
 
My last lesson to share - even though our winter weather down under is probably still warmer than half the summer days in the UK, I'm finding that waiting 2 days before sanding the dope/filler gets a much nicer result than sanding any sooner.
 
Hope this helps anyone else who's struggling with covering decisions...
Klippy24/06/2009 07:19:46
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755 forum posts
13 photos
Hi Shaun, just 'fell' over your thread, is your Spit electric or IC? What power train? I'd be interested to know the comparison between the plan AUW and yours. Any chance of some pictures?
Shaun K24/06/2009 16:01:44
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192 forum posts
38 photos
Hi Tony,
I'm very much from the Alex Whittaker school of thought - if the engine doesn't go 'bang' a few thousand times a minute it's just not a real plane. 
 
I'm using the same ASP/Magnum .61 4 stroke that Tony Nijhuis used in his prototype. I just happened to have one when Tony's plan came out and it looked like a perfect use for it.
 
I'm still not quite finished with the final building yet, so as soon as I can tell you the final weight I'll report back. I'm really keen to do the comparison because I've made a few minor changes in an attempt to manage the weight a little better. I've extended the nose by 30mm to reduce the need for balast and through lack of availability of the right thickness the fuse sides were made with 0.5mm thinner balsa than shown on the plan.
 
My one little luxury that I know adds weight will be on-board glow.
 
I've got some pictures of her 'in the nude' here in my gallery.
Sir John22/10/2010 10:58:16
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33 forum posts
Hi All,
I also would like to use Sig. Koverall to cover my model, can anyone give me some advice on how to exactly how to use it.
Many thanks in advance,
Sir John
Shaun K22/10/2010 13:24:27
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192 forum posts
38 photos
Hi Sir John,
 
Koverall is fantastic to put on - very easy, gets a great result but it is very time consuming!
 
There's plenty of good info elsewhere on the net if you google "koverall how to", but in short you need the Sig Stix-it heat activated glue, which you paint on the air frame as needed, let it dry then iron on like any other heat-shrink covering.  Remember that where you're puting one layer over the top of another you need to put a line of glue over the edge of the first layer to make sure the top layer has something to stick to.
 
Any cutting has to be done with your best, sharpest scissors to prevent fryaing or snagging the weave.
 
I found it easier to work than Solarfilm but that's only part of the complete finish.
 
Where Koverall takes more time the Solarfilm etc is the filling and sanding stage. If you have the patience the finish you can get is just fantastic, but the filling & sanding phase takes a lot of time. If time's not an issue go for it.
 
Good luck!

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