Help! What to do about covering film wrinkles.

[oipigface]

Bit specialised this. The tailplane in the photo is 11.5cm long, and 1.5mm thick. (i.e. tiny. The glider it belongs to has a wingspan of 60cm.) The picture shows my third attempt at covering it with clear uncoloured Oracover. The framework is balsa, with a spruce TE and diagonals of cf rod. The wood is all painted with Daler-Rowney System 3 acrylic paint. The problem is differential shrinkage between the open areas, and those where the film touches wood. As is clear in the picture, the film is taut in the open areas, but puckers wherever it is attached to the framework. I think is probably because the painted wood conducts heat away from the film at a greater rate than air does. I’ve tried ironing and I’ve tried using a heat gun. My iron is too big to enable me to iron the wood parts only, and repeated use of the heat gun leads to softened adhesive and detachment of the film at the LE, where the overlap of top and bottom films is necessarily very small. 
Anyone have ideas what I might try to solve this? Is it possible to get an iron that will iron a strip of wood 5mm wide or less?

[AnthonyB]

This first pick is what happens when you use Oracover on a light structure and then shrink it with a heat gun.

It is not really visible when normally looking at it. I should have used Oracover Lite as originally used.

It is a Maxa 4m tail, not a little one.

You really do need a Temp controlled iron. I set to 105deg and tack bits round the edges. Then seal all the way round edges.

Take the heat gun and DON'T fully shrink - Just make certain there are no big baggy bits. From there I have blown with the heat gun (bit at a time) and with 3 or 4 tissues folded in my hand, blow hot air and smooth, dab down. I then go up to 115 and iron all the ribs over. 

Just using the heat gun after doing the edges does not stick to the ribs - which I feel should be done. 

I don't think the temp read out is as good as you think, so I start as low as I can and slowly go up until it sticks. I know mine is 105, which is perfect. For the second stage it is 10deg hotter (115). 

I don't know the real name, but I call it blowing (because I think it gasses) - If you do that it will never be good again. 

Your photo looks like HobbyKing film, which I have blown a few times and will never go nice after.

AND - I have never used a sock, which I feel spoils your temp control. 

This film covering does also go "off" .... It has just got too old. I have done same as you with that as well.

Oh, and a month ago I read the instructions and they were good. (first time in 30 years)

[AnthonyB]

This is a roll of Oracover Pearl white. It was going to be an amazing pearl white and trans red scheme.

I put it on and it just would not go nice. No photos, because I had to take it all off.

I really thought it was me !  Then I did it with my normal trans white and it was a doddle.

As I said - Old stock !

[oipigface]

Thanks for this, although I don’t think your suggestions hit the spot. If it is old stock, then it’s been at the shop a long time, because they sent it to me only last week! It’s not Hobbyking, it’s Oracover, and the structure isn’t really ‘light’ for its size. I’m using a heat controlled iron (Prolux), which is fairly new. I have been using a sock. I’ve always found a tendency to damage the film without.

I’ve done a similar, although larger, structure in a similar way once before. That was clear transparent Oracover over a predominantly white structure. I had no trouble with that. I’m wondering if it’s not the black absorbing the heat.

[AnthonyB]

I realised after I wrote, that I am on much lighter structures than you.

I also didn't realise you are using the same Prolux as me.......... So start at 105deg.

Take it off for the third time and do a test bottom of a panel in a known good film. Oracover because it does not leave colour behind.

In the photo with the prolux iron on, that is really soft balsa and it is not marked without a sock. It is also Profilm Lite, so more delicate.

Half the planes I own are carbon edged ribs (and black) and that is not the problem.

By the way, my eyes prefer trans red - it is by far my best colour to see, but I also did fancy using a clear covering over balsa ribs. Though I thought it would look great doing the edge of the ribs with red felt tip.

It is not the black - I have done 40 or 50 over carbon / black - never a problem. This is done top and bottom all in 1 sheet.

[Phil.Taylor]

turn up the iron temperature a bit - should smooth things out - Profilm/Oracover will take quite a temperature range

Phil.

[oipigface]

15 hours ago, Phil.Taylor said:

turn up the iron temperature a bit - should smooth things out - Profilm/Oracover will take quite a temperature range

Phil.

Doesn’t work Phil

 

[MikeE]

Hi John, I suggest that you,

Tack lightly onto each corner of the frame.

Tack along the LE and TE, start by tacking at Central points. Trying to get the film on square and wrinkle free with no shrinkage taking place.

Tack the tip and root, again without shrinking the film.

When all edges are stuck down, shrink the film all over as lightly as possible with either the iron held an inch or so away from the film or a gently heat gun. Get the whole structure warm in a even manner.

Rub it all over with a cloth. 

In you picture it looks like you have ironed along the ribs, I would suggest that you don't do that. Or if you do it's a last job when all is shrunk and smooth. Then only do it just enough.

[AnthonyB]

Previously I said HobbyKing film is horrible. It does not have the temp variability of Profilm. BUT at £6 or £7 for 5m it is really worth a go.

If you “blow” it – it will NEVER go good again.

Here is one I did.

It can NEVER go better. If you try to shrink the wrinkles, it will pull off the inside of a concave surface. Imagine I have to live with this ! Once blown there is not enough adhesion to hold the solid surface, but it can still be shrunk, but it will pull off the surface. Profilm is far better for this.

Try covering a 100% Depron model, that is about temp control – one mistake and it is ruined.

Also, after 3 covering attempts there will be a build up of blown adhesive and you need a strong tissue and a hottish iron. Iron the tissue on and when you pull it off, some adhesive comes off.

That was about HK film, but my reasoning is that old Profilm is exactly the same. Degraded Profilm adhesive gets poor thermal qualities.

 

Is your film firmly attached to the backing it came on ?

 

[mikef]

My experience is that you need to get the film on as wrinkle-free as you can and then use just enough heat to tighten it.  If you over heat it you can have it wrinkle more later - especially on hot days.

[oipigface]

4 hours ago, AnthonyB said:

Is your film firmly attached to the backing it came on ?

No, not really. Is this a marker for old stock? I just ordered some clear Oralight hoping that it might perform better.

And on the question of black: I was comparing like with like, that is, wood painted white with wood painted black. White gave me no problems, black is giving me lots. The wing (which I have covered with the same stuff) is not nearly as bad, because the film is attached to carbon fibre rods almost everywhere except the edges of the ribs. These are 0.5mm plywood, so there’s not much of them to cause a problem, but nonetheless, there is slight puckering visible on all of them. The CF leading edge and the CF spar, both black, cause no problem at all.

4 hours ago, AnthonyB said:

Also, after 3 covering attempts there will be a build up of blown adhesive and you need a strong tissue and a hottish iron. Iron the tissue on and when you pull it off, some adhesive comes off.

This isn’t an issue. I’ve rubbed down the surfaces with dry 400 grit, and repainted after each attempt.

4 hours ago, AnthonyB said:

Try covering a 100% Depron model, that is about temp control – one mistake and it is ruined

Been there, done that! Never again.

[oipigface]

5 hours ago, MikeE said:

In your picture it looks like you have ironed along the ribs, I would suggest that you don't do that.

I’ve only ironed along the ribs in an attempt to get rid of the puckering! I don’t normally. 

[AnthonyB]

I have NEVER filmed over a painted surface. I have done a lot of black, because of carbon fibre. (I have "gassed" kevlar D-box, which gave a whitish look, but no real problems)

White paint and black paint must have different pigment (same brand). I would think paint would give off vapour when heated. You do take paint off doors with a heat gun.

I would paint something with the black paint and then test it after a couple of days.

I had the pearl white and it has all fallen off. I bought 2m of carbon effect Profilm, which had also fallen off the backing paper. It was for a solid wing, but the edges did not stick well, but then I just used the heat gun to shrink the lot (with some tissues to rub down) These were bought mail order from places I don't normally use - they had it ! (maybe for a long time)

I have trans red and semi trans white Profilm both perfect - on the backing and to use. I have the same in Profilm Lite fully on backing, both perfect........ All from Hyperflight. These need the 2 pieces of tape to separate.

Never had a problem ironing ribs - I used a lot of S4083 (undercamber).

It just has to be old film or paint solvent. Please try Prolux at 105deg with no sock, and clean any adhesive off the iron if it stops sliding smoothly.

 

[oipigface]

 

Well, it’s finally finished. I must have used up about 10 times the amount of film that has actually finished up on the tailplane, and I’m still not very happy with the result. It’s nowhere close to AnthonyB’s excellent work. I did buy new film: Oralight Clear this time. The adhesive on this appears to be less sticky than on the Oracover, which added an additional problem: the film very easily came unstuck at the edges (only 2mm thick) during shrinking. It still suffers from the original problem of puckering over the wooden framework. I phoned Siegfried at Oracover, to see what he had to suggest. His advice amounted to “sort out your technique and use masks for shrinking”.  So that’s what I tried to. I was very careful to keep the film flat while tacking it to the framework, and I decided after the second instance of unstuck edges to use some extra adhesive as well as a mask. The result you can see is OK but far from perfect. It won’t show in the air. The ruddervators are still covered in Oracover Clear.

Here’s the whole plane. Almost ready to go!

 

[AnthonyB]

I said use 105deg, because that works for me (no cover on iron).

You pull it to all corners, then right round the edges.

Then you shrink it. I use a heat gun and heaven only knows the temp, but certainly more than 105deg. I will also up the iron temp and iron on the ribs.

 

At 105 it melts the adhesive enough to stick it down – so it goes soft at 105deg.

If you then use 110, 115 or 120deg – it is hotter than the original 105deg and so will melt the adhesive again. The additional heat will also shrink the film – enough to deform a carbon edge. If it will deform the carbon, it will certainly pull the film along / off the edge you previously ironed to.

Above is the red film round a carbon trailing edge – I said I did that all in one sheet. I do feel you have to. Failing that you have to wrap round the back, so that the heat cannot melt the adhesive as you shrink. I have been known to then pull the part round the back off and trim to the edge.

 

I don't think old film or film on a painted surface sticks as well or (the glue) has the same properties. As soon as you have a hinged surface, you cannot go round the back, which makes it worse.

I think you had 2 or 3 different things adding up to your problem – really frustrating.......... But don't beat yourself up (I know I do !)

I do like the effect you were going for.

[oipigface]

The puckering is caused by a difference in the rate of shrinking between open parts and the frame. What could cause this? It seems to me that since the heat sources I use are uniform in temperature, there must be something about the film, or the frame, or some kind of interaction between the two. All parts of the frame are painted, but the puckering only occurs on parts which are either balsa or plywood edges. I had no problem with the wing TE, which is the face of plywood, or with carbon. I think there may be some difference in the conductivity of balsa and plywood end-grain relative to air, which isn’t shared with plywood face or carbon. Perhaps these surfaces absorb more paint, which somehow conducts the heat away?

12 hours ago, AnthonyB said:

Above is the red film round a carbon trailing edge – I said I did that all in one sheet. I do feel you have to. Failing that you have to wrap round the back, so that the heat cannot melt the adhesive as you shrink. I have been known to then pull the part round the back off and trim to the edge.

The leading edge of my wing is a 1mm carbon rod. Fortunately, it is glued to the edge of a 0.8mm plywood false LE, onto which the ribs are slotted. I did think of trying to do this all in one sheet, and if it had been straight I would have done. As it is, I folded the bottom covering around the carbon, and ironed it onto the top of the false LE between the ribs. This required loads of snipping! The top film I ironed onto the bottom film as usual. 

When I bought this kit, I thought it would be a quick build. Well, I wasn’t wrong, but I hadn’t reckoned with spending almost two weeks covering it!

[MikeE]

You may find it useful to use a light dusting of Scotch 77 adhesive spray along the edges. Using the spay allows the film to be layed onto the frame and lightly pulled into place without applying any heat. This can be useful as tacking with heat can cause some shrinkage as you do it.

If you can get it all in place with no shrinkage then iron along the edges carefully without any local shrinkage, it's then an easier task to lightly sharing all over.

 

[oipigface]

3 hours ago, MikeE said:

You may find it useful to use a light dusting of Scotch 77 adhesive spray along the edges…..

 

I’ll try that the next time I build a minuscule slope soarer!
I did brush some Balsaloc on the edge before putting on each piece, which helped stop the edges separating, as did the masks I made. Problem of puckering isn’t solved though.

It’s all ready to go now, bar 2.2g of lead in the nose, and a bit of programming.