Making a canopy
 

I have an old Jemco Hellcat that needs a new canopy and so far I can't find anyone that sells one for that size, 1/9 scale, plane so I need to know how to go about making one for it. I have the old canopy still on the plane but it is cracked in several pieces.
So my question, how do I go about forming a new one, what materials and sizes do I use, etc.? I need to know everything there is to making one from scratch.
Thank you,
Larry

RE: Making a canopy
 

Well Then - Where to start

Is it a one piece canopy made from clear plastic?
If so, the easiest way to make a new one would be to vacuum form it.
Assemble the old one (Using tape etc to hold it together) in the correct shape. apply some release wax (such as "Traffic wax" floor polish) Then make a "plug" by pouring some plaster of paris inside of it.
Once set the plug will need to have any flaws filled in and/ or sanded out of it as any flaws will show up in the final product.

A sheet of thin PVC, Acrylic, Polycarbonate or PETG (around 0.25 - 0.5mm thick) will be needed to make the new canopy. Your local plastic supplier can probably advise you on what is available and what temperature you should form it at.
This sheet will need to be at least 3 times the width of the original and at least 1.5 times the length.
Make a simple 2 piece frame to hold the sheet. The frame will consist of 2 rectangles that clamp the sheet between them.

Mount the plug on a solid base (Such as a 3/4" or 1" thick 25mm piece of wood) that will fit neatly inside the frame mentioned above (I use small "G Clamps to hold the 2 frame halves together). Before you mount the plug on the wood - cut a hole in the centre of the base board large enough to insert a pipe from your vacuum cleaner.

Mount the plug on the board with a gap between the plug and the board (I usually mount them on some thick washers - say 1/8" thick.).

Now for the easy bit

Insert (and seal) the vacuum cleaner hose in the "mold".
Mount the mold on a frame so that you can press the frame over the base plate
Switch on your oven to the forming temperature (try around 250 degrees F)
Get some gloves ready to handle the item (Oven gloves or welding gloves).

Once the oven is hot - place the frame in the oven until the plastic "droops" well. - switch the vacuum on before this time
Take the frame with the plastic in it out of the oven and press it over the mold - the plastic will form to the shape of the plug

Hold it there until it is cooled enough to hold its shape

I is that simple but buy a few pieces of plastic because the chances of a perfect job on the first attempt are slim - everybody has a slightly different technique.

This link is one of many that explain this

[link]http://www.marvin3m.com/vacuum/index.htm[/link]


Edited to correct the temperature Range (F not C)

RE: Making a canopy
 

Thanks for the info supplied now I,ve got a fair idea about how to attack my next job ,your bloods worth bottling matey Next question what can you tell me about United hobbies I do believe they in your part of the world and are there any other worth while places where us poor Kiwis can order stuff with confidence ,,sorry to be a pain in the butt take care Paul

RE: Making a canopy
 

Aussiesteve,
that was great, just what I was looking for.
Thank you, Larry

RE: Making a canopy
 

I have ordered from United Hobbies ( also reffered to as Hobby City ). I have found their prices to be excellent, especially when compared to most online places. The products I have received (Motors, ESC and LIPO ) have all been very good.

I have no problems recommending them.

RE: Making a canopy
 

That explination oughta become a "stickie"! Thanks from me too! Q.[8D][8D][8D]

RE: Making a canopy
 

No Worries guys
I haven't actually ever dealt with United Hobbies but from the accounts I've heard they are pretty good.

I used to be in the plastics business - GRP, Epoxy manufacture, Vacuum forming, Infusion molding etc. It's generally an easy business - just time consuming to make one offs. (I sold the business and decided to concentrate on design work instead - more money and easier to manage the business:D).

RE: Making a canopy
 

I have seen people use clear plastic cola bottles, 2 liter, 1 liter, 20 oz. etc.

RE: Making a canopy
 

Yep - That plastic works well - it's PETG!
Actually, the 2lt and larger bottles are a good cheap source of it for home projects - cut the ends off, split them along the middle and you have basically a shee tof it that is large enought to form

RE: Making a canopy
 

Your narrative is great, except that I think you really meant 250F not 250C. I'll bet you would have lots of bubbles in the plastic at 250C.

RE: Making a canopy
 

Just testing
Yep - it would be a fast heat and short soak at that.:D

Reminder to self - Bad Fingers - Must check before posting[&o]

RE: Making a canopy
 

I won't have a chance to form my canopy for a while yet but I was thinking, do you need to use a "wax" in the orginal canopy before I pour for a mold and will I have to use the same "wax" over the plug I make from the mold when I press the hot plastic sheet down?
Larry

RE: Making a canopy
 

The wax in the original canopy is only to stop the Plaster of Paris from sticking to it. Some people use a layer of food film inside the original to do the same job but there is a risk of "Crease Marks" from the film that you will need to fill and sand out.

For the final one no wax will be required. If you want to be absolutely certain you can seal the "Plug" with furniture varnish. (I use Shellac - the stuff used for French Polishing that is made from dead beetles).

RE: Making a canopy
 

Well,
I gave it a try and only ended up ruining one large sheet of plastic. I use PETG, 020". I had enough to try three times. First one I had it in the oven where it was drooping down some, then put it over the plug with the vacuum on. I ended up with a piece that had folded in a couple of place in the front of the canopy and wasn't quite formed all the way. Next sheet I tried, I let it droop to much and it got on the tin foil in the bottom of the oven. Third and last sheet I raised the frame with the sheet higher, let it droop more then tried that. When I went to put it on the plug, it again folded is several places. Seems it will fold nice over the top of the canopy but won't around the front of it. Any ideas??? I ordered more plastic, I won't give up to easly.

Larry

RE: Making a canopy
 

The vacuum is causing your problem. Basically too much suction. For a simple shape like a canopy, you really do not need the vacuum suction. Mount the canopy mold high off the base using a rod, then genly pull the frame containing the plastic sheet down over the mold until the mold is completely covered.

RE: Making a canopy
 

With the bottle, you make a plug that is a force fit in the bottle and then use your heat gun to make the plastic shrink around your plug.

RE: Making a canopy
 

hi,
been reading this thread, I have an ESM P-47 with the bubble canopy, they are a fairly hard material of some kind, it is .5mm thick, I have rung a few plastic suppliers, for Vacuum forming, the word is PETG the stuff they use for soft drink bottles, comes in a 2400 x 1200 sheet, Aus, $25 plus GST. (Grand Scale Theft)

the P-47 canopy took a bit over 1kg of plaster of paris, I gave the inside of the canopy a light spray of "INOX" then wiped it out, the plug came out without any problems.

HINT, if you get the chance, make a frame to hold the canopy in, I didnt and have a flat spot, can be fixed.

BTW if you use a good Tupperware container to mix the Plaster of Paris belonging to "you know who" MAKE SURE TO WASH IT OUT BEFORE IT SETS.

I am still building my model, the canopy has not been fitted, decided to make a plug. Just in case I break one.

happy flying. Oldtimer.

RE: Making a canopy
 

Larry,

I believe I've encountered the problems you mention, and found the solution that worked for me. On my build thread, I document my attempts with a brand new vacuum forming machine I built . . .itdiscussesthe less than successful results (complete with pictures so you can see if this was the same type of problem you were experiencing), and what I learned in order to fix those problems. If you are interested, follow this link (below), andscroll downto Post #189 forthe likely solution.

http://www.rcuniverse.com/forum/m_96..._8/key_/tm.htm

I hope this may be of help. Either way, don't give up. There's a learning curve to everything in this hobby that is worthwhile. My first true success was pretty exhilarating, and madethe initialfrustrationsall worth it.

Ollie

(Oops! After I posted all this, I looked back and realized that although others posted more recently, Larry's post that I responded to is pretty ancient. Oh well, I tried.)

RE: Making a canopy
 

Good stuff here, I'm marking this as a reference, since i've avoided building models allready due to the fact of eventually haveing to make a canopy!! I've figured out that i'll attempt the canopy before spending the time building the model & not haveing a canopy for it. Thanks for the posts.....Gene;)

RE: Making a canopy
 

Many times, the front of the canopy needs to be elevated relative to the rear of the canopy so that the 'folds' (webbing) don't occur. This occurs because the PETG isn't being stretched locally. Imagine wrapping a sheet of paper over your knee. In the oven the PETG should sag then retract a 'smidge' indicating it is ready for the forming process. Another thing that is helpful is to 'deepen' your plug with something like balsa. Glue your mold to it then 'fair' the extra material as if it were an extension of your plug. That reduces webbing. I have a small vacum former (10x14) but am going to build a bigger one because I am building bigger airplanes, now. I speak from experience and not anecdotally!

I fixed the spelling from the 'fair' to then 'fair'...

RE: Making a canopy
 

Mixing plaster of paris. If you take one of the kids 8" diameter soft plastic balls, cut it in half, and use that; then when the plaster dries you can massage what is left in the ball and it will break out solid with not mess. Don't wash it down the drain, it will accumulate in the trap, and you will have problems.

Les