Fun With Film (How to Move On from Solartex)

Chris Williams

For many years, when it came to finishing a model, I had a well-practised routine that involved using copious amounts of Solartex and paint. Then came the day when ‘Tex was no longer available, which also coincided with the fact that I wasn’t getting any younger, and models seemed to be getting heavier and harder to launch. So, a new World Order came into being and I started to use film on the flying surfaces and some of my dwindling stock of ‘Tex on the fuselages. This meant that models were getting lighter and I could start feeling like I used to when I was only a lad of eighty-nine. It was then that HobbyKing brought out their new clear matt film and a whole new covering experience was born.
A quick bit of context here… It was fashionable in the 1930s to cover gliders with the usual doped fabric, but to leave the open structure areas clear-doped, with only the plywood-sheeted parts painted in trim colours.

scale soaring fun with film chris williams

The Glory of see through coverings.

Thus, in the same way, that the trailing edges on a seagull’s wings glow in the sunlight, the flying surfaces of these old gliders would glow in a similar way, causing those through whose veins the juice of aviation runs to get all misty-eyed and heave a heartfelt sigh. It is also a fact that a model glider with translucent surfaces is much easier to spot at height when the glare of the sun otherwise reduces visibility.
So, what are the advantages, or otherwise, of this new material…? Despite a recent 50% price rise, this film is way cheaper than ‘Tex, to which you can also add that it is also a heck of a lot lighter. On the downside, it’s a lot more see-through than fabric, which means that if you are cutting your own parts, it’s best to try to hide the part numbers as best you can. There’s your calculation then: not as scale as fabric, but cheaper & lighter…
When it comes to the trim colours, these are not, as many assume, painted on, but rather applied as a secondary (or thirdly) film covering.
Right, then…let’s get to the nitty-gritty.

Applying film over film is complicated by the fact that bubbles are likely to raise their shiny heads, so in order to avoid this; the clear film is applied over the open structure areas only, with a 20-25mm overlap. Then the trim colours are ironed on and only the overlapped edges will need to be de-bubbled, as it were.

A quick look at the tools that are required for the job: A domestic iron, a heat sealing iron, a scalpel, a heat gun, a long straight-edge, and some sheets of thin card.

scale soaring fun with film chris williams

The tools used for this job.

scale soaring fun with film chris williams

Starting the process: the clear film cut to size with suitable overlaps.

Now we come to the most critical aspect of film covering…temperature. The clear film needs to be initially applied with the iron hot enough to melt the adhesive, but not so hot as to bring about any shrinkage. I’d like to be specific about temperatures, but my domestic iron only has a series of dots on the dial, and the heat sealing iron has a temp control that’s so small it’s hard to get an accurate reading.

But if we take 140 degrees Celsius as a baseline, this seems to be a good setting to activate the adhesive without causing shrinkage. (What follows is the process of covering the flying surfaces of my current project, the reduced scale version of my Rhonadler 35 design.)

scale soaring fun with film chris williams

Removing the backing film with the help of masking tape.

Having applied the clear film to the open structure areas, we rebuff the strong desire to shrink it taut because of the danger of it pulling away from the edges as it shrinks. Rather, we’ll wait until the trim colours have been added, as they will assist with the total adhesion. Now, you may have noticed that glider wings tend to be long, but accurately applying trim colours over long distances is fraught with difficulties, so I have always found it best to have a join somewhere around halfway along the wing.

The same applies to the top and bottom surfaces: trying to do this in one piece would not be easy, so it’s best to do the bottom surface first & overlap it at the LE with top surface trim. For consistency between the two wing panels, I have always found it best to make up a card template for the various areas and use this to cut out the parts for each wing.

Here’s another pointer…make it so that all the overlap edges are arranged in such a way that the slipstream won’t get under them and lift them up. This means that you work from the back of the wing forward, applying the D-box trim last of all.

Applying trim colours over large areas needs a cool-ish iron of laying the film down without undue wrinkling. Another quick tip: at 140 degrees, the sealing iron will scale soaring fun with film chris williamsshrink the clear film without pulling it away from the edges if you limit it to the areas where the edges of the trim film will meet the clear. , and this is where the domestic iron comes in. Using a temperature that only just melts the adhesive, the large area of the iron makes easier work of laying the film down without undue wrinkling. Another quick tip: at 140 degrees, the sealing iron will shrink the clear film without pulling it away from the edges if you limit it to the areas where the edges of the trim film will meet the clear.

scale soaring fun with film chris williams

Then, the LE trim is applied, after which, the clear can be heat-shrunk.

So, you now have a wing, or tailplane, wherein all the film has been added, but now needs final shrinking. At the aforementioned 140 degrees, the sealing iron will shrink all the clear film, maybe increasing by a few degrees for any stubborn areas. The trim film is ironed down, but maybe still has a few stubborn wrinkles. Now for some tension & drama…The heat gun I use costs about £11 or so from Screwfix, and is probably designed for stripping paint. Even at the lowest setting, it’s still pretty hot, so it goes without saying that a certain amount of care will be needed here. The thing is, if you keep it moving and get it right, you can see the wrinkles magically disappear, but don’t make the mistake of thinking it might work just as well on your hair!

scale soaring fun with film chris williams

Here, the tail feathers have been finalised.

AILERONS

If your ailerons have mostly straight edges (this won’t work for elliptical TE’s) you can cover them in one piece of clear film, thus avoiding joins at the TE. Seal one edge along the LE, wrap the film along the lower surface and over the top and seal over the LE again. If the TE curves at the tip, slice along the film until you reach a straight part, then iron the lower part of the film over the TE after trimming off the excess, followed by the upper. Finishing off the root should be pretty straightforward. In this instance, the heat gun is the ideal tool for performing the shrinkage as it will allow both upper and lower areas to best adjust to the new regime.

scale soaring fun with film chris williams

Heated square brass tube is ideal for the hinge cutouts.

scale soaring fun with film chris williams

The Clear film is added to the wing in discrete panels with a 20-25mm overlap.

What about the undercamber, you might be thinking…? I usually make the cap strips a bit wider over the more cambered areas at the root, making them around 6mm in width. I don’t use Balsaloc, as the film seems to adhere quite successfully. The trick is to iron the film down to the rib cap, following along with a finger wrapped in a handkerchief to press it down as the adhesive cools down.

That just leaves the odd bubble on the areas where the trim and the clear overlap. Pricking them out with judicious use of a pin and then ironing flat will improve matters here, and now you have it: a translucent wing of which any seagull would be proud.

STRESS-REDUCING TIPS

Getting the backing film off the mat clear is a son-of-a-female-dog affair. It took some time, but I finally realised that a short strip of masking tape applied to the underside of the film makes it much easier to pull the backing material off…

The film has a very annoying tendency to keep rolling into a cylinder: a long straight-edge laid on it whilst you mark out your panels will help to keep it in order.

Be VERY careful when marking out your panels to limit the use of the humble biro. I can tell you from experience that a biro mark on the clear film will show through the trim colour causing much in the way of angst & teeth-grinding. One way to avoid this is always to mark out on the backing film side, remembering, of course, that the piece will be a mirror image of the template!

There it is, then, a way of highlighting all that hard work on the airframe, with eye-catching results. In the unlikely event that the manufacturer ever reads this piece, how nice would it be if all the colours were made available in the same matt finish…?

Note: Since the pandemic, HK film has been no longer available, but with the reintroduction of the HK UK warehouse, we hope for better things…

scale soaring fun with film chris williams

Now the wing is ready for the trim colours.

scale soaring fun with film chris williams

Card templates make it easier to cut out trim panels more quickly and accurately.

scale soaring fun with film chris williams

Once again the trim is added from the rear forward.

scale soaring fun with film chris williams

On the Rhonadler, an enormous template is needed for the red trim.

scale soaring fun with film chris williams

Wing panel covering now completed. At this angle, the translucence is not so obvious.

scale soaring fun with film chris williams

The Rhonadler filmed and painted.

scale soaring fun with film chris williams

1/4 Scale Habicht with HK film flying surfaces.

scale soaring fun with film chris williams

5th scale Petrel with HK film flying surfaces.