Tissue over Doculam covering for undercambered wings

[John T]

I'm planning to make an enlarged version of the old Keil Kraft Chief glider for my next build, and in order to keep the original appearance I intend to use a tissue finish.

I've recently built a couple of small models using tissue doped over Doculam and I've been really impressed by how much stronger the result is, so I'm tempted to do the same on the Chief. However, these other models don't have under cambered sections. The KK Chief has a very pronounced under camber (NACA 6412) and I wondered if the Doculam has sufficient adhesion to prevent it pulling away. Has anyone tried doing this, and if so are there any tips to help?

[extra slim]

cover the undercamber first, then from the uncovered top, run glue along all touchpoints

[John T]

Nice idea. I've used this method years ago using Nylon covering. I'm not sure what glue would work with Doculam though...

[Tim Hooper]

My Cambrian 'Answer' has very pronounced undercamber., and is doculam/tissue covered. It's several years old now, and still in pretty good condition.

I used Balsaloc to secure the doculam, and on the wing underside, I started in the middle and worked outwards.

Tim

Edited By Tim Hooper on 20/07/2020 21:28:11

[Outrunner]

I tissued over doculam earlier this year when I refurbished my Junior 60. I brushed on thinned Balsaloc along all the ribs, leading and trailing edges. Stuck perfectly even after shrinking.

Phil

[PatMc]

I built a Amigo 2 three years ago & covered it with with tissue over doculam. The wings are more undercambered than the KK Chief, I found no need for any extra adhesive at all.
OTOH I covered my KK Chief with tissue over mylar several years ago using Balsaloc to stick the mylar to the wood, the wings periodically have needed to have an iron run across the ribs underside & spar to re-stick the mylar since a couple of months after being covered. I intend refurbing the Chief & fitting a small motor sometime when I'll be stripping the mylar off & replacing it with doculam.

Edited By PatMc on 20/07/2020 22:59:36

[John T]

Thanks for the replies. Following the example of PatMc I think I'll try without any extra adhesive, but I'll add cap strips to the ribs so that the Doculam has a bit more area to stick to.

[Nigel Dell]

As I have used Doculam for both models and it’s intended use, to get the best out of it just do some samples onto balsa structure using different heat settings of your iron, when laminating using the proper laminator the heat range generally was between 130C and 150C but that was on that machine and dependant on lam thickness and area also we had to take into account too much heat would curl the sheet etc. But to get the best out of the adhesive just run a few tests and get the optimum.

I use the lightest I have (48mic) on small rubber powered free flight, adds very little to the overall weight and only use 2 thinned coats of dope, a Junior 60 was done with 125mic and although I thought this was a little too much has proved to be very strong in use and much lighter than Solartex and about on par with normal film.

[John T]

Nigel, I take your point about running a few test samples. This is the stuff I've got.

The wing is a 30" span "Wee Snifter" before I applied the tissue with a couple of coats of thinned dope. If anything, I think it may have ended up lighter than just tissue and dope alone as I didn't need so much dope.

[Nigel Dell]

Hi John

I am not surprised it seems lighter, dope can defiantly add a lot of weight like all things if used too much🤭 it only has to hold the tissue onto the film, I used to like a glossy finish when I was a kid, can’t remember how many coats I gave them, looked nice but I didn’t know any better!

That looks the ideal weight of film, the 48mic is a bit too light and can be difficult to apply, if you want some to try PM me your address I I will send some over.

Cheers

Nige.

[John T]

Thanks for the offer Nige, it's very kind of you.

However, I think I'll use the film I've got, now I know how to apply it and what iron temperature seem to work ok. I don't want add more variables into the mix.

[Engine Doctor]

Have look at the Matt finish laminating film . It gives a very tissue like appearance and is incredibly strong .Its a bit difficult to stretch around compound curves and a lot of heat is required .

[PatMc]

Posted by Nigel Dell on 21/07/2020 11:53:08:

Hi John

I am not surprised it seems lighter, dope can defiantly add a lot of weight like all things if used too much🤭 it only has to hold the tissue onto the film, I used to like a glossy finish when I was a kid, can’t remember how many coats I gave them, looked nice but I didn’t know any better!

That looks the ideal weight of film, the 48mic is a bit too light and can be difficult to apply, if you want some to try PM me your address I I will send some over.

Cheers

 

Nige.

Nigel, I take it the label in the photo John posted indicates the weight of film. Am I missing something obvious ? What is the weight & how can you tell ?
AFAICS the label indicates 20" wide by 200' length but what's the 1" ?

The film I have is a 12" wide roll of 34 micron (IIRC). I found it reasonably easy to apply, the overlaps stick down very well, are near invisible & disappear completely under the tissue. I think the film is easier to apply than Solarfilm etc.
It can certainly stand much higher temperatures than any model film I've used. When covering the Amigo wings I made a pigs ear of a balsa covered section near the root of one wing resulting in some unsightly wrinkles. I managed to smooth it using a heat gun & iron over it several times. I didn't realise how much the heat was building up until I noticed that I'd actually scorched the wood under the film !! The film was undamaged.

John T, this thread in RCG contains some info that you may find helpful.

Edited By PatMc on 22/07/2020 00:07:41

[Nigel Dell]

Hi Pat

Labelling on these rolls can be confusing, as Doculam is a US product they use feet and inches, the CR confused me at first, not sure where the CR came from but would welcome enlightenment! In fact they use thou for this measurement which is usually down as mil to add further confusion!😳🙄 the 20” is width and 200’ is length of roll as you say the 1” is the core size of the roll, our machines used a 32mm Core, the 1.5 CR (mil) equates to 38micron (mic) most laminating film supplied here is in metric ( which is why I can get confused🥴 thickness being in microns.

the film I have that I thought was 48mic is actually 42mic (I went to find a roll) and is a Matt laminate, it is very easy to use and as you say the joins can be hidden well, what I meant to say is it can be sensitive to too much heat, turn the heat up to stretch or form around complex curves but if you are not careful it can drag over sheeted areas and cause creases which basically stick together far too well! I like the 75mic on larger models as it is easier to use, obviously on bigger areas but is not so sensitive to excessive heat and is more stable due to it being heavier weight wise.

Cheers

 

Nige

P.S. It might be of interest, but application of this film is designed to be applied through a slowish moving machine through a pair of heated rubber rollers under pressure, they can be turned off so only one side heats up ( causes curling issues unless speed, heat and tension are optimum but mostly we used a two roll machine which did both sides, it was not really manufactured to be applied as we do, so I suggest on flat sheeted areas, to hold plenty of tension and I have used kitchen roll laid over to Iron on to stop dragging the film to good effect.

 

Edited By Nigel Dell on 22/07/2020 01:24:46

[John T]

Interesting link PatMc. Slightly off topic, but I was interested to see "Eze Dope" or "WBPU" mentioned. Although I quite like the smell of dope it might be worth a few extra brownie points if I could use Eze Dope instead

I'll perhaps give it a go on an old wing to see what it does.

[PatMc]

Posted by Nigel Dell on 22/07/2020 00:52:02:

Hi Pat

Labelling on these rolls can be confusing, as Doculam is a US product they use feet and inches, the CR confused me at first, not sure where the CR came from but would welcome enlightenment! In fact they use thou for this measurement which is usually down as mil to add further confusion!😳🙄 the 20” is width and 200’ is length of roll as you say the 1” is the core size of the roll, our machines used a 32mm Core, the 1.5 CR (mil) equates to 38micron (mic) most laminating film supplied here is in metric ( which is why I can get confused🥴 thickness being in microns.

the film I have that I thought was 48mic is actually 42mic (I went to find a roll) and is a Matt laminate, it is very easy to use and as you say the joins can be hidden well, what I meant to say is it can be sensitive to too much heat, turn the heat up to stretch or form around complex curves but if you are not careful it can drag over sheeted areas and cause creases which basically stick together far too well! I like the 75mic on larger models as it is easier to use, obviously on bigger areas but is not so sensitive to excessive heat and is more stable due to it being heavier weight wise.

Cheers

Nige

P.S. It might be of interest, but application of this film is designed to be applied through a slowish moving machine through a pair of heated rubber rollers under pressure, they can be turned off so only one side heats up ( causes curling issues unless speed, heat and tension are optimum but mostly we used a two roll machine which did both sides, it was not really manufactured to be applied as we do, so I suggest on flat sheeted areas, to hold plenty of tension and I have used kitchen roll laid over to Iron on to stop dragging the film to good effect.

Edited By Nigel Dell on 22/07/2020 01:24:46

Thanks for the info, Nige.

Interesting you mention matt laminate, "Sundancer" (George Stringwell) on RCG has been using a matt film &, on some small scale models, painting directly on to it instead of using any tissue. The results have been very good & long lasting.

[Nigel Dell]

Glad it was of interest Pat, I will have a look over on RCG as I have not been on there for a longtime now, and George inspired me on some of my designs with his construction articles years ago, I will be interested is what he does with the Doculam.

Cheers

Nige.

[PatMc]

Posted by John T on 22/07/2020 12:22:30:

Interesting link PatMc. Slightly off topic, but I was interested to see "Eze Dope" or "WBPU" mentioned. Although I quite like the smell of dope it might be worth a few extra brownie points if I could use Eze Dope instead

I'll perhaps give it a go on an old wing to see what it does.

 

Hi John, I used a water based floor varnish instead of dope on a test spare tailplane & Wilco's water based clear satin varnish on the fuselage of my Amigo.

The above links are to threads in this forum.

Edited By PatMc on 23/07/2020 00:14:49

[PatMc]

Posted by Nigel Dell on 23/07/2020 00:04:08:

Glad it was of interest Pat, I will have a look over on RCG as I have not been on there for a longtime now, and George inspired me on some of my designs with his construction articles years ago, I will be interested is what he does with the Doculam.

Cheers

Nige.

Nige, George is a regular on RCG's "Vintage & Old Timers" section, in fact he's a prominent contributor to the thread I linked to in my earlier post. He's been an advocate of tissue over doculam for some time & has posted details of his methods several times.

[John T]

Love the Amigo Pat. I'll definitely try the Wilco varnish at some point, although I think I'll use cellulose dope on the Chief, mainly because I've got a tin open and I know it turns a bit murky if you leave it too long.

I'm guessing you need to use a reasonably high wet strength tissue such as Esaki or Model Span with these water based varnishes. I've had trouble in the past using Eze Dope on cheaper tissue as it just disintegrates.

[Malcolm Fisher]

I resurrected an old Chief not very long ago and used some paper designed for use with inkjet printers or other machines. I used PVA as adhesive and sprayed the paper with water before applying it. When dry I used a water based satin clear varnish as at the time i didn't have any dope. I am pleased with the result and the "varnished" paper seems pretty tough. Haven't yet managed to get it to my favourite slope site so don't know how well it will stand up to that.

The original model was for single channel rudder but I added an elevator when I acquired a two channel radio. For me that made a huge difference in my ability to control the model.

Malcolm

[John T]

Interesting comment about using paper designed for inkjet printers Malcolm. A couple of months ago I recovered an old model, again using tissue over Doculam. Inspired by Pat's posting I used Wilco quick dry satin varnish for the tailplane and fin, and used cellulose dope on the wing for comparison. I used what I think was some old lightweight modelspan for the wing and tailplane, while the fin was covered with JP Accessories lightweight tissue.

The first thing to say is that I found it easier with dope, but then it was a process I was used to.

My first attempt with the varnish was a bit of a disaster. I tried using it slightly watered down, but when I tried to brush it through, the tissue just disintegrated. At least it was easy to remove.

For my next attempt I used a shallow tray with the varnish watered down about 30%. I quickly floated the tissue across the surface, removing the excess on the edge as I lifted it out. I then draped it over the surface, starting from one end to try and chase the air bubbles out. I found I could lift it and re lay it if I was careful, but the tissue was very easy to rip when wet.

After it had dried it was much stronger. I bushed on subsequent coats with no problem, and I was quite pleased with the finished result.

I have since flown the model a few times, including a few times when it got damp. There has been no sign of the tissue slackening off in the damp, which does happen on a couple of my other models that are covered in tissue and Eze dope but without Doculam.

[Ned Watts]

Does the balsa surface need to be prepared, or can the doculam be ironed directly onto the raw balsa?

VERTI-GO SIDES OFFSET.HEIC

[PatMc]

Same prep as any other film cover material sand & vacuum or tack cloth to remove dust. Don't use supplementary adhesive - such as Balsaloc either on the bare wood or film overlaps.   

[John T]

I've found that Doculam adheres really well to raw balsa and  itself when overlapped, though I don't know whether other laminating films are as good. Perhaps anyone else that's used them can comment.

What's the size of the model you're building Ned? Its nice to see a rubber model design on these pages.