My home-brew winter project has reached the stage where the woodwork is essentially complete, bar some final gluing up, and it’s time to cover the model. Since the aeroplane is a sports design I’ve decided to use an eye catching scheme in a bright iron-on film. Now, before applying any covering I always perform a trial installation of the radio and engine, including all control runs, as it’s all too easy to damage a covered model during this process. Also, it’s very much easier to cover components whilst they’re still flat objects on the bench. Trust me, it’s murder to neatly cover a fin and tail in situ with iron-on film.
Horses for courses
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As a bog standard builder, I seem to return to the same old covering favourites. I only use dope and tissue for smaller and / or classic models, or sometimes on scale fuselages as a painting substrate, whilst for sport and scale aircraft I tend to use Solartex since it looks good and is so convenient to apply. What’s more, it’s tough and there’s no mess. Truth is, the process is so much easier than the dope and nylon days of yore and, I confess, I like the finished result. However, I find the newer products like Solarfilm Supershrink, Profilm, and Toughlon are just great for brightly coloured sport models. But, no matter which brand I buy, or how well I pre-treat the underlying wood and film joints – or even epoxy coat the firewall / film overlap – my models eventually seem to succumb to a little fuel seepage. Take heart though, you have not failed as human being if your film overlaps lift over a period of time. Look at any expensive professionally-covered ARTF and witness exactly the same phenomenon.
In the swing
So, I’ve just spent a happy week of evenings covering my model with iron-on high-shrink polyester film. It’s been awhile since last I burnt my fingers with a heat gun, so I was a bit rusty. Let me state straight away that I am not a natural Solarfilmer, Toughloner, or Profilmist. Film covering is one of those blacke artes that seem to take me almost as long as the wood work. Truth be told, I have an irrational dread of cocking it all up. I know that any bad overlaps or folds on the wing tip will be there forever to mock me as a silent reproach. And so, I usually put the task off. However, when I finally tackle it, I’m always pleasantly surprised just how deeply satisfying it is and how enjoyable. Even my tubby, gluey, overweight own-designs look just about okay in the right covering. However, this is only because I’ve learned the hard way. So, here’s my clutch of idiot proof workarounds, sub-techniques and gadgets that speed me on my covering tasks. Fear not however, none of it is rocket salad.
Workaround 1 – Polyester. If you try nothing else from this list of suggestions, move on to polyester films! These more expensive high tech products such as Solarfilm Supershrink Polyester, Toughlon, and Profilm (Oracover) really are worth the extra money over the basic product. They’re very difficult to fry and they shrink faster than an MP’s reputation. If, like me, you dread covering double curvatures, wing tips and cowls, these newer products make it almost foolproof. Most importantly, before you start, read the destructions which come with every roll. Each brand has subtly different heat requirements and cock-ups can only be avoided if you’re wise to the variations.
Workaround 2 – Panels. When you’ve finished your model’s woodwork look for all the natural panel lines e.g. the lines of underlying sheeting and longerons, tailplane halves, fin, hatches, cockpit edges, and so on. Take note of their positions. Since you can’t stick film down to fresh air, you need an underlying hard point. With these located, make your choices and apply film in the most convenient panels that you can confidently handle. Don’t be afraid to break it down into smaller bits. I long ago realised that a man on his galloping horse is not going to notice that I cheated and covered my demanding fuselage turtle decking in two halves rather than a single patiently shrunk sheet. This means taking a bit of time to plan the panels and their overlaps. In my case, I usually make simple card templates first (see Workaround 8). By the way, the leaflet that comes with all films will give you the order in which to apply the main covering panels, so it’s good to read that first.
Workaround 3 – Overlaps. I found out the hard way that you should allow a minimum 1/4” overlap on all joins. Allow more on bigger panels if you can get away with it. All too often I’ve applied a panel of film over, say, the open area of a built up wing and ribs, only to find that when shrinking, it has lifted and come away due to too small an overlap at the edges.
Workaround 4 – Marking. Rather than try to guesstimate each separate film overlap, I use an off-cut of 1/2 x 1/4” balsa to mark the line of an overlap on the underlying balsa frame. I then match the film to the scribed lines as I stick it down. No more skewwhiff edges!
Workaround 5 – Masking tape. Use cheap Pound Store masking tape to hold the film to its marks whilst you iron it down. You can iron through cheap masking tape which will allow the film to adhere to the underlying balsa, yet the tape will still peel away with ease.
Workaround 6 – Backing film. I only remove the backing film immediately before I’m going to apply heat. This stops the covering from being accidentally damaged and marred by sticking to itself.
Workaround 7 – Scalpel cuts. I cut my film with a scalpel, reserving the scissors for rough cuts, and for non-critical nicks around protrusions. Hang the expense, fit a brand new scalpel blade just for the task of covering and change it frequently – it’s all too easy to nick, bunch up, and tear polyester with a bad blade.
Workaround 8 – Templates. I make card templates for all odd shapes and panels that need to be cut from film. Kellogg’s grade is good, but light A4 card from the stationer’s is better since it’s already cut nice and square. For example, when I wanted to wrap a panel of film from below the wing’s leading edge, all the way around to the limit of the top wing sheeting, rather than attempting to measure it, I just made a card template. This stops guesswork and wastage of film and you can instantly see that it’s right or wrong as you trial fit it around the wing. This done, I lay the template on the film and cut to size. Since most of my basic panel cuts are straight-edged, an A4 size card allows me to accurately mark out each end of a much larger panel, then cut it square in the straight edge machine (see 14 below).
Workaround 9 – Cutting board. Even an apparently flat and clear bench top will have hidden debris and bits of glue and chippings to mar the finish of your film as you cut it. Work on a cutting board laid on your bench top that’s both flat and free of debris. I use a plywood off-cut that measures about three feet long by two feet wide
Workaround 10 – Padding. Once you’ve finished cutting your film and are moving on to the ironing stage, clear your bench completely and pad it with plastic foam, a towel or something equally soft and forgiving. This will save your carefully sanded virgin balsa airframe from dings as you wield it about. Rolled polystyrene will also do as a worktop padding, although the grey foam that goes under laminate flooring is better, and its dirt cheap from B&Q. It folds nice and flat for storage, too.
Workaround 11 – Put a sock on it! – Despite its sole’s Teflon coating, your covering iron may pick up messy adhesive, especially with the non-polyester films. If not noticed and cleaned this can transfer to new film, marring the whole job. Go to the model shop and buy a cloth iron sock which will also reduce scuffing. At the first sign of marring, buy another one – they’re less than a fiver.
Workaround 12 – Edge puller. Sometimes you need to pull an edge or overlap of film quite hard whilst simultaneously applying full heat with the heat gun. This can seriously singe your finger tips! My solution is to use a big bulldog clip (its jaws lined with scrap balsa sheet) to give an insulated handle to help you tug the film around a curve or over an edge. Where the bulldog clip is too bulky to use, masking tape is also useful as a film edge puller for a small square edge of a panel.
Workaround 13 – Backing lifter. Sometimes the damned backing film defies all your attempts to peel it off. In this instance, just dab on some masking tape to lift it clear. It works like magic!
Workaround 14 – Straight cuts. I use a metre length of aluminium carpet kicker extrusion (from B&Q) taped to the cutting board as a cutting guide / straightedge. The clever bit is using masking tape to secure it to the bench top at each end allowing you to slip your covering underneath the extrusion and align it exactly square for that all-important cut. The raised extrusion saves your fingers from the scalpel, too. This is also a brilliant way of cutting chequered panels so that the finished check blocks are ‘open’, and do not display a thin visible line.
Workaround 15 – Overlap cutter. The SLEC Crafty Cutter costs about a quid and is the cleverest film tool on the planet. It’s unbelievably efficient at cutting neat exact overlaps in film. Say, for example, that you wish to cover an aileron with a neat but tiny film overlap, parallel to the trailing edge. Just nick it into the film and pull it along the edge that you want the overlap. It cuts like a laser and the overlap is utterly consistent. Use one and you’ll never want to be without.
Workaround 16 – Damp dabber. When sealing down film edges that may require a bit more heat than normal it sometimes helps to have a pad of cool damp tissue or kitchen roll handy. Once the edge is sealed dab it with the cool pad and this light chilling will tend to set the film’s adhesive. Then, when you apply full shrinking heat the panel has a better chance of staying on. It works.
Workaround 17 – Balsa fillets. It’s poor practice to expect film to stick to film without an underlying balsa framework to adhere to. If you’re planning a complicated film scheme with contrasting panels, you may find that in one or two places you need to glue in an extra bit of underlying balsa sheet (or perhaps a fillet) to which the film may positively stick. I found this out recently when I wanted a join line in the film to fall on the hollow of a built up wing tip. Here, then, I just knocked up a couple of balsa fillets and glued them in place. Then, when I came to iron on the film overlap its adhesive had a secure base on which to bite. Mind you, Sod’s Law decrees that you will not realise this necessity until you’re either finalising a complex film design or ‘mid shrink’!
Workaround 18 – Temperature. So obvious that I almost hesitate to mention it to you, but do set the temperature of your iron to exactly match the manufacturer’s suggestions. For example, it’s better to begin tacking down and sealing edges at the lower setting suggested by the manufacturer than rushing straight to the mid range. In the past I’ve made a complete Horlicks of covering balsa sheeting simply by getting the film far too hot, whereupon it attempts to shrink and adhere all in one go. The magic temperatures are written on the instruction sheet supplied with the film. If your heat controlled iron doesn’t have a temperature dial you can buy a film thermometer. I have an American Coverite item that works extremely well.
Workaround 19 – Spring thing. Modern polyester film takes up quite a ‘spring’ when it’s rolled up at the factory and is very hard to keep flat whilst you handle or cut it. Admit defeat; you do not have enough hands to both hold it down and cut it! Just tape it to the bench with masking tape as you cut it with your straight edge machine. Don’t use Sellotape! You’ll never get it off.
Workaround 20 – Double trouble. Finally, have you tried heating the film with the heat gun as you simultaneously smooth it flat with the iron? It may sound tricky but practice a bit and you’ll find it works well with polyester films. When ironing film to sheet balsa, say a fuselage or wing leading edge panel, with a little practice a two handed technique really can pay dividends. The usual problem with sheet is getting the film laid flat without trapping air under it. Polyester films are better than the original films for this task and I’ve found that being bold and gently heating the film ahead of the advancing iron really does work. Admittedly it takes a bit of bottle but try it with a spare panel when next covering a sheeted wing and you may be pleasantly surprised. Happy wrapping!
