Canopy options
You usually end up with a canopy in one of three ways:
- Kit part. Plastic kits include a clear canopy, often moulded in several pieces. Handle it carefully, since scratches and fingerprints show badly.
- Replacement or aftermarket part. Useful if the original is lost or damaged.
- Home-made. When you build a flying or scale model from plans, there is usually no canopy supplied, and you need to form one.
Without a vacuum-forming machine, there are two simple methods that hobbyists commonly use: plug moulding, where a male form is pushed through heated plastic, and drawing heated plastic over a form.
Making a canopy by plug moulding
The steps below follow the approach described by builders of small flying scale models. Practice on scrap first, because the first attempt often needs repeating.
- Carve the plug. Shape a block of medium to hard balsa into the canopy form, checking it against the model and a copy of the plan. Sand through progressively finer grits, around 600 grit, for a smooth surface. Bare balsa is usually enough for this method, because the plastic is pushed rather than sucked into the surface.
- Add a base plate. Glue a thin plate (about 1/8 in) to the underside of the plug, extended where the canopy meets the fuselage with steep edges. This gives a clean edge to trim along and reduces thinning at sharp corners. A small handle on the underside helps.
- Make a female jig. Cut a hole in a piece of scrap balsa sheet, leaving a small clearance (about 1/16 in) around the plug, and round the entry edge so the plastic leads in smoothly.
- Choose the plastic (see below).
- Heat the plastic gently until it goes soft and slightly floppy but not discoloured or bubbled. A grill or oven at low heat is commonly used; never leave it unattended, and keep your hands protected, since the plastic and the tray get hot.
- Push the plug through the heated sheet in one steady motion, hold it briefly while it cools, then release.
- Trim the result along the base plate line.
If you use a kit canopy as the plug, fill it with putty, epoxy, or plaster first. Otherwise heat may distort it, which can ruin both the kit part and your first attempts.
Materials
- Clear acetate or PET sheet. Packaging blisters and clear binding covers are popular for scrap-bin forming. Builders often recommend around 0.3 to 0.4 mm thickness for small canopies, because the sheet thins as it stretches.
- Avoid unknown plastics when heating. Some packaging is PVC, which can give off unpleasant fumes when heated. If you are unsure what a piece is, ventilate well or use a known material.
- Allow for thickness. A canopy formed over a plug ends up slightly larger than the plug by roughly the plastic thickness, which is rarely noticeable on a small canopy, especially one shown open.
Trimming and fitting
- Cut slowly with sharp scissors or a fresh blade, then sand the edge on a flat sanding block until it sits tight against the fuselage.
- Test fit repeatedly. Gaps are much easier to fix before painting.
- Rubbing the edge with fine abrasive gives a better bond surface for glue.
Masking and painting frames
For most scale models, the frames are painted rather than moulded. Options include:
- Masking tape or pre-cut masks cut to follow the frame lines.
- Liquid mask brushed on, for curved shapes.
- Strips of thin foil or tape used as frames on a home-made canopy.
Paint the interior color first if the frames are visible from inside, then the exterior color. Remove masks carefully so the paint edges do not lift.
Attaching and sealing
- Use a clear-drying canopy glue or white PVA-type glue. These dry clear and are forgiving, and any excess can be cleaned with a damp swab before it sets.
- Avoid cyanoacrylate (super glue) near clear parts. Its vapors can leave a white frosted film on clear plastic. If you must use it, use a minimal amount and allow ventilation.
- Plastic cement can melt or craze clear plastic, so avoid it on canopies unless it is formulated to be safe.
- Hold the canopy in place with tape or clamps until the glue is fully dry.
Polishing and clarity
- Light scratches can often be polished out with a fine polishing compound used sparingly.
- Many modelers dip clear parts in an acrylic floor polish to restore shine and fill tiny marks. Check that the product is compatible with your plastic and paint, and allow it to dry in a dust-free place.
- Keep fingerprints away by handling the canopy by the edges.
Troubleshooting
- Plastic wrinkles or webs: the sheet was too hot or the clearance too tight. Try again with slightly less heat and a smoother entry edge.
- Canopy too thin at the top: use thicker plastic or heat more evenly.
- Cloudy canopy: often glue fumes or overheated plastic. Replace it, or polish lightly if the haze is only on the surface.
If you are building a flying model, the canopy is only one part of the finish. For the airframe itself, see our model airplane covering guide.