MAKING CANOPY
FOR
LARGE SCALE AEROPLANE

You broke a canopy on your scale aeroplane, and no replacement is available?

You are building a large aeroplane and search for a cheap and simple way to make the canopy?

You have no vacuumforming equippment?

Here is how I made my large canopies-the simple way!

I use a styrofoam block, and carve a canopy shape.  At its edges, I made that shape (lets call it »positive mold«) larger  for about 2,5 cm (1inch) so we could later trim the finished canopy to proper size.
Shaping of the positive mold starts with transfering outer contour to sides of the styrofoam block and cutting it. You can use very sharp knife (beware, not to cut yourself!!) using motions as knife was a saw. You can use hot wiring bow, going carefully over the drawn lines, or over prepared templates, made from hard paper, masonite, or other apropriate material. Now we should refine the shape, to give it proper shape (oval cross sections). We can use some cross section templates, to check our progress. I usually cut away the edges at approx 45°.  Afterthat I cut again all edges. Now the canopy positive mold is comprised by about 9 surfaces.  We use sandpaper or sanding block, to smooth the positive mold surface.

 

When satisfied with the shape, we must cover the surface with some kind of filler, that can be later easily sanded.  If we intend to use this mold many times it is not a bad idea to strengten its outer surface. You can use glass laminate and filler if you are master in this technology.

My prefer method is more low-tech. I use white carpenter glue thinned with a water and small pieces of newspaper to cover the surface. I pour allmost milk-alike glue in a pan and troughly soak paper pieces in it. I apply about 3 layers of paper over the mold surface, and leave over night in very warm place so water from glue could evaporate. Well, somethimes take two days for evaporating the moisture from the paper skin.

 

Now I sand the surface a bit, and apply filler. I use a filler that is made for wood and can be sanded easily. After each layer I leave to harden and then sand. I repeat this process for about  3 times, or until get satisfied result. I use fine grade sandpaper.

 

We can use that positive mold already, but we can also paint it to get smoother surface, and find out possible areas, where more filler should be applied.

And now to the making of our canopy!

 

I use a 0,4mm thick thermoplastic foil. I clamp two sides between a pair of wooden sticks and use woodscrews to tight them together.

I insert a nail on each of four ends , cut their heads off, and bent it to a hook shape.

I heat the kitchen owen and insert the plastic in. I hook those bended nails into side rails of the owen, so plastic will be hanged nicely in the available space.

I  look into the owen trough a windoow in the owen door. The plastic will soon starts to be soft. You will notice, that it shakes a bit under the air circulation inside the owen. The plastic will became soft and it will starts to streech under its own weight, which is visible by its lower side slowly sinking down. Plastic can also starts to look foggy. Dont worry, it will became clear later on the process by itself.

Now open the owen and grab both wooden ends (HOT!! Use  safe kitchen gloves!!! Dont burn yourself!!) take it out from the owen and put over your canopy mold. Be careful and place it properly! Now push both wooden parts down. The plastic will strech and follow the mold shape. Dont ease on the down pressure.

  Pulling down against the mold. (here I use a mold from pure styrofoam, and resulted canopy get inprint from foam structure. I recomend to use filler on the surface!)

 

  This picture show making canopy on the mold that has prepared outer surface with filledr and paint. This will brings much better results! I recoment this way to do it!
 
 

Now a helper should cool the canopy surface with a wet piece of cloth. Now you can stop pulling down.

Carefully remove your plastic canopy from the mold.

If canopy looks well, cut it on the proper size and install it on the model.


 

Canopy frame in front, broken canopy in center, and newly finished canopy in rear. Trimmed with scissors.

 

 

New canopy on the model! It is allmost hard to believe, that this canopy was made using above described simple technology.

Some aditional info:
Once I coat the mold with a thin layer of grease, so the plastic can streech over the mold without unnecessarry friction. That way, the thicknes of finished product is more even. The result was very well.
 
Once, when pick up the plastic from owen, it fall down on the floor from my hands, as I was clumsy with gloves. When I finally pick it up from the floor and try to streech it over a mold it was already not hot enough. I was thinking, that I destroyed the plastic. But I return it into owen and repeat the process. I made a perfect canopy second time.  So, dont be affraid if it will not goes at very first attempt. You can use the same plastic again, even if looks used...

And that is all you need to do!

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