Skin Deep – Pt.2

Skin Deep – Pt.2

Fig.1

Welcome back. In part.1 we looked at preparation so let’s get covering. 

PANEL GAMES
The wings, tail surfaces, and the fuselage can be covered using large sections of film, applied following the sequences shown in Fig.1&2. Start by covering the underside of the wing with half-panels, followed by similar panels on the upper surface. Move on to the horizontal and then the vertical tail surfaces remembering that with the latter you’ll need to treat the side opposite the exhaust blast first, as this will ensure that the exposed seams lie in such a way as to limit the ingress of combustion residues. Don’t forget to leave the tail-to-fuselage gluing areas free of film though.

The fuselage is covered as shown in Fig. 3, working from the bottom, up over both sides, and onto the top surfaces. Solarfilm strongly suggests that you don’t attempt wrapping a single piece of film around a fuselage or flying surfaces, and its a warning you should heed: until you’re very familiar with the materials characteristics, it’ll only lead to countless wrinkles, crinkles and distortions – trust me!

If there’s going to be a tricky moment, it’ll come in the shape of a compound-curve wing tip, canopy or fairing. If you follow Solarfilm’s advice, however, everything should go swimmingly.

Fig.2COMPOUND CURVES

Cut a film panel that gives you a three-inch margin all around the wing tip, then – covering the underside first – lightly tack the film along the outer edge of the tip. Now, gently pull the film span-wise and heat a small section at a time by hovering the iron over the film until you feel the film begin to give. You should be able to shape the film smoothly over the wings curvature. Using this technique, work across the wing tip from the mid-chord point out to the leading and trailing edges, pulling each section gently inwards, applying the heat, moulding the film to shape, and then tacking it in place.

When you’ve finished, the surplus film can be trimmed away from the outer and inner tip edges and the overlaps ironed down; you’ll need to slit the film edges on curvy tip rims to allow the overlaps to lie flat. When the tip is covered, bond it all over with the iron and pressing pad.

The topside of the tip is covered in the same way, except you’ll use the three-inch margin to pull the panel smoothly around the tip onto the lower surface and overlap the panel on the underside by half an inch. Once secure, you can trim the excess away and seal the edges.

Fig.3

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It’s also possible to cover a wing panel and its compound-curve wing tip with a single run of film. To do this, you begin by shaping, sticking and sealing the half-panel in place in the middle of the wing, and then work towards the tip. With care, it’s possible to produce an apparently seamless tip covering using this method.

The compound curves of a models nose are also covered using oversize film panels, which are lightly tacked along a corner line that flows into the contours of the main fuselage. Then, holding the film with your fingers, heat and pull it on either side of the tacked line to mould it to the required shape.

As with the wing tips, you’ll find it possible to cover the nose using an extended fuselage panel. Once again, leave yourself a three-inch margin around the section you’re going to cover, and get the main fuselage area tacked, sealed and trimmed before shaping the rest of the panel over the nose.

By comparison, curvy top decks and coamings are quite easy to cover, either by using two half-panels overlapped along the fuselage centreline, by shaping the fuselage side panels so that they extend up over the coaming, or by using a single panel cut to the tapered shape of the top deck.

ADVANCED SHAPES

When you’re ready for a challenge, try covering the built-in canopy base fairing on the centre-section of a wing. The trick here is to make a paper template of the upper wing sections curvature, and to transfer this shape to an oversize panel of film. The cockpit fairing can then be covered in two such half-panels, starting at the wing top / canopy base transition and working up to the fuselage centreline. You’ll find that using templates in this way will help you cover all sorts of seemingly complex shapes. However, when moulding and shaping Solarfilm, I can’t emphasise enough the importance of heating before you pull – get this right, and you’ll be able to produce well-camouflaged seams and ultra-smooth-looking curves.

OPEN STRUCTURES

Open frameworks require an equally light touch to get an even finish. Begin by cutting a panel of film to give a one-inch margin around the component you’re covering. Then, remove the films backing sheet and place the panel adhesive-side down on the airframe to give an even overlap all round. With the iron on a low heat, spot-tack the film to the framework; for wings and fuselages follow the sequences shown in Figs 4 and 5. If the film wrinkles during this process, whatever you do don’t press down. Instead, re-heat the affected area and tease out the wrinkles by pulling the film towards the edge of the framework.

Now, seal all the edges by gently running the sole of your iron around the framework. If you find that wrinkles form in front of the sole, use the iron to heat the area, without pressing down, and carefully pull the wrinkles out.

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Fig.4

Once you’ve fully attached the edges, use a scalpel or a new Stanley blade to trim away the surplus leaving a margin of half an inch. This is then ironed down to finally seal the edges, a job best done by working the iron out from the centre of the component to avoid lifting the film.

To save time when working on framework wings and tails, cover all the surfaces before moving on to the shrinking stage. Then, when you’re ready, turn the iron up to a medium heat setting and glide it gently just above the film; work slowly enough to allow the heat to take effect and for all wrinkles to disappear, but not so slowly that you risk overheating the surface and burning a hole.

The final stage is to bond the Solarfilm to the framework itself. To do this, crank up the iron heat a little more and move the sole over the film where it lies over the balsa structure but without actually touching it. With your other hand, press the heated film into contact with the wood using a soft cloth, tissue wad, or Top Flite’s Hot Glove. Start in the centre of a solid area and work outwards in all directions, taking care not to singe your airframe.

Fig.5IN A TWIST?

There’s always a risk, while shrinking the film around a lightweight framework, that it’ll distort the structure. You can usually correct any warp, however, by reheating the film, twisting the offending panel in the opposite direction to the warp and holding it until cool. You’ll be surprised just how far you may have to twist the structure, but all being well it’ll spring back to a centred position when you let go.

SOLID SURFACES

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The technique for covering wood-skinned airframes is much the same as for open structures: prepare oversize panels, spot-tack the edges, then shrink and bond the film in place working from the centre of the component outwards (Fig. 6).

If you constantly pull the heated film ahead of the iron it’ll help to prevent air bubbles forming and you’ll be able to tease out any wrinkles. Remember, don’t press the iron down on a wrinkle – that’ll only serve to iron it into a crease.

Fig.6Once you’ve achieved a smooth covering and trimmed and sealed the edges, go over the whole surface again with a slightly hotter iron and a pressing pad to bond the film to the wood. Again, work from the centre outwards and remove any air bubbles by pricking them with a modelling pin. Exercise great care when ironing film to solid sheet in this way, though, as its very easy to dent the timber with the sole of the iron.

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