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Author Topic: Home brew canopy for profile?  (Read 1399 times)

Online Tim Wescott

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Home brew canopy for profile?
« on: September 30, 2018, 07:19:59 PM »
Looking for suggestions & advise.  I'm trying to decide between vacuum-forming a canopy or painting one on.  It's for a profile scale Ercoupe.  Pdf attached.  It'll be about 11 inches long, 3 1/2 inches tall, and just 3/4 inch thick -- is this possible?  Reasonable for Beginner's First Vacuum Form? Or is such a deep, narrow vacuum form going to be impossible?

Alternately -- can it be done by shrinking a bottle over a form?  I've seen this done elsewhere, and tried it once or twice without huge success -- but as far as this particular building technique goes, I put the "rank" in "rank beginner".

Dunno if the attached PDF will clarify or obfuscate -- but here it is.
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Offline Howard Rush

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Re: Home brew canopy for profile?
« Reply #1 on: September 30, 2018, 09:10:04 PM »
Paint it on and make TUTs.
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Offline Mike Haverly

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Re: Home brew canopy for profile?
« Reply #2 on: September 30, 2018, 09:53:38 PM »
Howard could print one for you!
Mike

Offline Curare

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Re: Home brew canopy for profile?
« Reply #3 on: September 30, 2018, 10:23:05 PM »
I think you'll struggle to get that to happen with an conventional vacuum former - the draw is quite deep, and I dare say you'll get a lot of webbing (where the plastic doesn't conform to shape and sticks to itself) because of it.

Paint would probaby be easier, or perhaps two parts?
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Offline Trostle

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Re: Home brew canopy for profile?
« Reply #4 on: October 01, 2018, 12:47:20 PM »

(Clip)

Alternately -- can it be done by shrinking a bottle over a form?  I've seen this done elsewhere, and tried it once or twice without huge success -- but as far as this particular building technique goes, I put the "rank" in "rank beginner".

(Clip)


I have  had success using the process to shrink a plastic bottle over a form.  My experience suggests that you would have a problem using this method for the canopy you want.  The main problem is the length.  Your state your dimensions are 11" long, 3 1/2" tall and 3/4" wide.  You would need to find a bottle long enough to contain the 11" long form after you have removed the bottom section of the bottle. 

I have only worked with 32 oz or 1 liter bottles. The longest form that I think can be used with one of these bottles is maybe 7" or 8" long.  Maybe you can find some larger containers that would work.

An alternative would be to do a forward section and an aft section of your canopy.  Then bond them together with a thin metal strip (like 1/8" wide brass, something around .010" thick or thinner) to strengthen the joint.

Another problem is the height of the form.  Again, a larger bottle than the 32 oz size may be needed to accomplish this.  The problem will be compounded by the narrow width.  It will be difficult to get a satisfactory canopy without getting some signs of creases or lines in the final shape that would really make it unsatisfactory.  However, with a much larger bottle, you might be able to get something, but you will be asking for a lot of shrinkage and there is a limit to how much this material will conform to the form.  Would be an interesting exercise though.  If it works, it would impressive.  One thing about the material used in these bottles is that it is fuel proof, will not distort when exposed to heat/sunlight, and you can simulate a canopy frame by building up epoxy over the canopy after the clear sections have been masked off.  They are really more durable than the typical vacuum formed plastic canopies.

Keith

Online Tim Wescott

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Re: Home brew canopy for profile?
« Reply #5 on: October 01, 2018, 01:48:35 PM »
<snip>

I have only worked with 32 oz or 1 liter bottles. The longest form that I think can be used with one of these bottles is maybe 7" or 8" long.  Maybe you can find some larger containers that would work.

<snip>

The last time I was in a store looking for water there were some 1-liter containers of fancy water that were tall, skinny, and smooth.  I may be misremembering just how tall -- I noticed them before I got this urge to put a clear canopy on the plane -- but if they're as tall as I remember they'll do a good job.

I like your idea of a two-piece canopy.  That would play well with your suggestion of painting on a canopy frame, and with the contour of the Ercoupe canopy -- I could bond the halves together and then paint over the joint, and the transition from the fixed to the moving section of the Ercoupe canopy has a distinct step.
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The problem with electric is that once you get the smoke generator and sound system installed, the plane is too heavy.

Offline Dave Hull

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Re: Home brew canopy for profile?
« Reply #6 on: October 01, 2018, 09:12:30 PM »
Tim,

The biggest profile canopy I have managed using either the 1.25 or the 2 liter soda bottles is 8" long by 1-5/8" tall. My form is actually 8-1/2" long, but I could not work out the last of the wrinkles at the back end. So I just trimmed the canopy once off the form. The shape is the standard looking WWII bubble canopy with flat windscreen. I used beech for the form and when stuffed into the 2-L, I used a 2-1/2" filler board under it that looked like I had added a section of fuselage to the form. Something I did not do, but would try next time is to get the form into the bottle and then use 3 or 4 sheet metal screws thru the opposite side of the bottle into the bottom of the filler. It would make things much more manageable.

The bottles have at most about 8 - 9 inches of usable height. If you find a better bottle, I'd sure like to know about it!

I agree with Keith--the stuff is really rugged after you have it formed.

Good luck with your project,

Dave

Offline Randy Powell

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Re: Home brew canopy for profile?
« Reply #7 on: October 02, 2018, 03:02:27 PM »
Aren't you supposed to be building a killer PA plane to thump us all with?
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Online Tim Wescott

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Re: Home brew canopy for profile?
« Reply #8 on: October 02, 2018, 03:06:09 PM »
Aren't you supposed to be building a killer PA plane to thump us all with?

And getting a TUT done that does data recording, yes.  I actually am working on the Legacy: here's the logic:

  • I plan on putting the data recording TUT into the Legacy, so construction is on hold until I get that software written
  • While that was happening, my shoulder went out.  In despair, I started working on a CL scale Ercoupe, because I can fly the weenie Scale maneuvers left-handed (duck and cover, Tim!!)
  • I have a personal rule about putting projects aside, so dammit, I'm finishing the Ercoupe.  Besides, I'm going to use it for a practice piece on nice dope finishes -- so it's really part of getting the Legacy done

So, as you see, it's perfectly logical that making a canopy for a profile scale model is actually working on getting a CLPA stunt plane done.
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The problem with electric is that once you get the smoke generator and sound system installed, the plane is too heavy.

Offline Randy Powell

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Re: Home brew canopy for profile?
« Reply #9 on: October 02, 2018, 03:09:37 PM »
A nice a piece of convoluted logic as I've seen in awhile. Good job.
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Offline Gerald Arana

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Re: Home brew canopy for profile?
« Reply #10 on: October 02, 2018, 03:27:37 PM »
And getting a TUT done that does data recording, yes.  I actually am working on the Legacy: here's the logic:

  • I plan on putting the data recording TUT into the Legacy, so construction is on hold until I get that software written
  • While that was happening, my shoulder went out.  In despair, I started working on a CL scale Ercoupe, because I can fly the weenie Scale maneuvers left-handed (duck and cover, Tim!!)
  • I have a personal rule about putting projects aside, so dammit, I'm finishing the Ercoupe.  Besides, I'm going to use it for a practice piece on nice dope finishes -- so it's really part of getting the Legacy done

So, as you see, it's perfectly logical that making a canopy for a profile scale model is actually working on getting a CLPA stunt plane done.

Tim,

Go to Costco and get a (pumpkin-my favorite!) pie, enjoy it and use the cover for your canopy. It measures 12" square and so what if you screw it up? You get to eat pie and you can always get another one!

Jerry

Offline Trostle

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Re: Home brew canopy for profile?
« Reply #11 on: October 02, 2018, 03:32:22 PM »
The last time I was in a store looking for water there were some 1-liter containers of fancy water that were tall, skinny, and smooth.  I may be misremembering just how tall -- I noticed them before I got this urge to put a clear canopy on the plane -- but if they're as tall as I remember they'll do a good job.

I like your idea of a two-piece canopy.  That would play well with your suggestion of painting on a canopy frame, and with the contour of the Ercoupe canopy -- I could bond the halves together and then paint over the joint, and the transition from the fixed to the moving section of the Ercoupe canopy has a distinct step.

Your comment above got me thinking.  (I do try to think sometimes, though nothing much ever seems to happen.)  My thought would be to join the two halves together where the surface would be flush.  (I have done this with two halves made from the soda bottles by backing the joint with a thin strip of metal, then using epoxy, build up the canopy frame which the joint is a part of.)

I think you are taking it a step further by overlapping the two halves and still use this joint as part of the simulated canopy frame.  This would be much more durable and easier to accomplish and in the end would still look really good.  Good idea.  I wish I had thought of that.

Keith

Online Tim Wescott

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Re: Home brew canopy for profile?
« Reply #12 on: October 02, 2018, 04:42:36 PM »
I think you are taking it a step further by overlapping the two halves and still use this joint as part of the simulated canopy frame.

Yup.  But it would only work on some airplanes.
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The problem with electric is that once you get the smoke generator and sound system installed, the plane is too heavy.

Offline billbyles

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Re: Home brew canopy for profile?
« Reply #13 on: October 02, 2018, 04:46:03 PM »
Looking for suggestions & advise.  I'm trying to decide between vacuum-forming a canopy or painting one on.  It's for a profile scale Ercoupe.  Pdf attached.  It'll be about 11 inches long, 3 1/2 inches tall, and just 3/4 inch thick -- is this possible?  Reasonable for Beginner's First Vacuum Form? Or is such a deep, narrow vacuum form going to be impossible?

Alternately -- can it be done by shrinking a bottle over a form?  I've seen this done elsewhere, and tried it once or twice without huge success -- but as far as this particular building technique goes, I put the "rank" in "rank beginner".

Dunno if the attached PDF will clarify or obfuscate -- but here it is.

3.4482???  As a mechanical engineer I have frequently gone to 4 decimals for machining parts from various metals but for a canopy?  (Just kidding, I know you are an engineer also so I know where you are coming from...)
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Online Tim Wescott

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Re: Home brew canopy for profile?
« Reply #14 on: October 02, 2018, 05:05:29 PM »
3.4482???  As a mechanical engineer I have frequently gone to 4 decimals for machining parts from various metals but for a canopy?  (Just kidding, I know you are an engineer also so I know where you are coming from...)

It's just what dropped out of LibreCad -- you mean I can't get that much precision from something bent out of a used soda bottle  ???
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The problem with electric is that once you get the smoke generator and sound system installed, the plane is too heavy.

Online MikeyPratt

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Re: Home brew canopy for profile?
« Reply #15 on: October 02, 2018, 06:05:05 PM »
Hi Tim,
While working for Sig I made about a dozen profile canopies using the best equipment and plastics that were availed.  Each one was really tough to get just right because the draft angle is so steep to be able to pull the plastic over the mold that far (2-1/2 in height is close to the max).  Now try to pull more than just one at a time and the plastic forms web's over all of the molds.  I was trying to make molded canopies for the Twister during production runs, what a pain in the butt.  I built six (aluminum filled epoxy) hollow canopies molds (exactly the same) and we could only get three canopies (reliable) per pull that were usable.  I also tried to produce a molded canopies for my Force when building the prototype, same thing happened.

I'm my opinion, it would be best to make them in two or three separate parts and glue them together and fill & paint the seams just like molding ABS cowls.

Later,
Mikey

Offline Will Hinton

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Re: Home brew canopy for profile?
« Reply #16 on: October 03, 2018, 11:38:45 AM »
Whatever you decide, Tim, don't give up on the canopy idea from a bottle.  Do a search  for my SBC 3 Helldiver build on here and look at the profile canopy I got from a one liter bottle.  It's roughly 8 inches long with a very deep draft on the sides.  It went really well and the end result was from the very first one.
You might find a 2 liter bottle of your favorite poison (pop) and try for a one piece from that.  You really need to block it tight on the interior to win the battle, but it's worth a try.
Of course, Keith's solution and yours sound good also.  Just don't give up on it, pleeeeeeeeaaaze. S?P
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Offline Randy Powell

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Re: Home brew canopy for profile?
« Reply #17 on: October 03, 2018, 02:35:00 PM »
I didn't know the LibreOffice folks had a CAD component. Now I'll have to go look.

Thanks, Tim.
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Online Tim Wescott

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Re: Home brew canopy for profile?
« Reply #18 on: October 03, 2018, 04:06:02 PM »
I didn't know the LibreOffice folks had a CAD component. Now I'll have to go look.

I think it's a separate effort.  It's an OK CAD system, although it is clunky around the edges.  Save your work often -- one of the "clunks" is that it occasionally crashes for no reason, usually when you're trying to do something Really Impressive.
AMA 64232

The problem with electric is that once you get the smoke generator and sound system installed, the plane is too heavy.

Offline Steve Helmick

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Re: Home brew canopy for profile?
« Reply #19 on: October 04, 2018, 12:28:19 AM »
Tim needs to visit a set of Barnstormer plans.  y1 Steve



In 1944 18-20 year old's stormed beaches, and parachuted behind enemy lines to almost certain death.

In 2015 18-20 year old's need safe zones so people don't hurt their feelings.

"Be polite, be professional, but have a plan to kill everybody you meet." General Mattis.

Online Tim Wescott

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Re: Home brew canopy for profile?
« Reply #20 on: October 04, 2018, 08:36:40 AM »
Tim needs to visit a set of Barnstormer plans.  y1 Steve

I'm not sure how the shoelaces would fly with the judges, though.
AMA 64232

The problem with electric is that once you get the smoke generator and sound system installed, the plane is too heavy.

Offline Randy Powell

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Re: Home brew canopy for profile?
« Reply #21 on: October 04, 2018, 01:26:47 PM »
I checked. It seems to be part of the LibreOffice system. The interface is similar. And you're right, it's not ready for prime time yet. Hasn't crashed on me but I'm using it on a linux system so the unix version may be more stable. Or not.
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Online Tim Wescott

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Re: Home brew canopy for profile?
« Reply #22 on: October 04, 2018, 02:51:43 PM »
I checked. It seems to be part of the LibreOffice system. The interface is similar. And you're right, it's not ready for prime time yet. Hasn't crashed on me but I'm using it on a linux system so the unix version may be more stable. Or not.

My experience is entirely with using it under Linux.
AMA 64232

The problem with electric is that once you get the smoke generator and sound system installed, the plane is too heavy.

Offline Steve Helmick

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Re: Home brew canopy for profile?
« Reply #23 on: October 04, 2018, 06:21:00 PM »
I'm not sure how the shoelaces would fly with the judges, though.


It's a PROFILE, so no appearance points. Alternatively, you might mold each side and the top "flange". Join the two parts together by overlapping the top flanges, maybe, with "clear glue". The Gorilla has a "clear glue" that they're advertising on the TeeVee a lot. Two flat sides connected with a strip of clear plastic might also be viable, if it doesn't come apart in the air. With the three slabs of plastic suitably buried in the fuselage, it shouldn't be a problem.

Even just a single slab of 1/8" Acrylic or Polycarbonate would be ok and not terribly heavy. Since you have the drawing in CAD, you could find the area and then derive the weight, and make it thinner if deemed necessary. This version would make a dandy skid for inverted "landings", just in case. :P Steve
In 1944 18-20 year old's stormed beaches, and parachuted behind enemy lines to almost certain death.

In 2015 18-20 year old's need safe zones so people don't hurt their feelings.

"Be polite, be professional, but have a plan to kill everybody you meet." General Mattis.

Online Tim Wescott

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Re: Home brew canopy for profile?
« Reply #24 on: October 04, 2018, 10:10:18 PM »

It's a PROFILE, so no appearance points.

It's profile SCALE, so appearance points.
AMA 64232

The problem with electric is that once you get the smoke generator and sound system installed, the plane is too heavy.

Offline Steve Helmick

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Re: Home brew canopy for profile?
« Reply #25 on: October 05, 2018, 12:22:17 PM »
It's profile SCALE, so appearance points.

Oh, so it is. Well, then make it out of balsa and paint it with transparent paint, except for the roof and framework. Alternatively, plead with Mrs. Wescott to knit one from clear yarn.  y1 Steve
In 1944 18-20 year old's stormed beaches, and parachuted behind enemy lines to almost certain death.

In 2015 18-20 year old's need safe zones so people don't hurt their feelings.

"Be polite, be professional, but have a plan to kill everybody you meet." General Mattis.

Offline 944_Jim

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Re: Home brew canopy for profile?
« Reply #26 on: October 05, 2018, 04:44:58 PM »
I've done two profile canopies using water bottles. Granted, mine are smaller given they are 24"-27" WS models.

Both planes "landed" inverted a couple of times each...or you could say I ran out of headspace and timing, so the canopies made great friction brakes. The glue (E6000) never let go. My youngest boy's Scientific Typhoon needed some engine work. E6000 held the cowl on. I destroyed the cowl removing it.

I just wanted to add that E6000 is clear, and glues the soda bottle plastic to the fuselage just fine. I also agree for the larger plane, go in pieces. E6000 will be your friend!

Offline Steve Helmick

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Re: Home brew canopy for profile?
« Reply #27 on: October 06, 2018, 09:02:57 PM »
Why didn't we think of having Howard or Mike print one from clear plastic?  D>K Steve
In 1944 18-20 year old's stormed beaches, and parachuted behind enemy lines to almost certain death.

In 2015 18-20 year old's need safe zones so people don't hurt their feelings.

"Be polite, be professional, but have a plan to kill everybody you meet." General Mattis.

Offline Dave Hull

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Re: Home brew canopy for profile?
« Reply #28 on: October 29, 2018, 11:53:12 PM »
Just made up another canopy on my profile form. Good over the 8" length. Using the sheet metal screws into the form before shrinking helped anchor the bottle "blank."  Had a bit of trouble with a wrinkle near the front. If I can make that go away, I think I can routinely get almost 9" out of a 2-liter bottle. I also made up a wider wedge which helped, too.

Dave

Offline Trostle

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Re: Home brew canopy for profile?
« Reply #29 on: October 30, 2018, 08:31:26 AM »
Using the sheet metal screws into the form before shrinking helped anchor the bottle "blank." 

Dave

Using at least two good sized clamps from the hardware store also works to stabilize the bottle around the form during the shrinking process. 

Keiith

Offline Paul Smith

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Re: Home brew canopy for profile?
« Reply #30 on: October 30, 2018, 11:40:16 AM »
I was able to vacuum form a canopy for my profile scale Bearcat.  Note the wrap-around picture frame.  A key element in the process.

As mentioned by others, you need to start thick because it draws down thin.

But it pays off in the end.  Judges that know their business will give more points for actual cockpit detail than a painted-on canopy.
Paul Smith

Offline Dave Hull

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Re: Home brew canopy for profile?
« Reply #31 on: October 30, 2018, 07:30:29 PM »
I have used C-clamps in previous iterations. They definitely help. Where do you put them, Keith?

This time, I found it was helpful to put one screw thru the bottle and into the form backer right on the centerline (below where the windscreen ends up) right at the bottle neck. I could not get clamps up there. The advantage is that with that point anchored and the back end too, the rest of the blank will pull, such that all of the shrinkage at the front (with the highest curvature) does not all have to happen locally. Hopefully that makes sense. Since I had the box of screws out, I used them instead of clamps this time to pull in the plastic at the open end (tail of the canopy). They work ok there, but no real advantage over the clamps except the thing is less bulky and easier to work with. That matters only in that I like to hold the assembly up to the overhead lights so I can see from the reflections. When the material is starting to shrink I can stop when I see the ripples disappear. And it gives a good indication before you melt thru anywhere...which is also important.

As a side note, the MonoKote heat gun was sufficient for most of the shrinking and I never worried about melting the canopy. I had to work the center a little harder, and used a shop-type heat gun. Much hotter, and it helped with the last little bit of wrinkle. But be aware it definitely will melt thru the bottle material if held in one spot too long.

I believe that the bottle method actually increases the material thickness in most--if not all--the places compared to the original bottle. I wondered about that, but didn't make measurements last night. Tonight I will try to get a few. As Paul points out "pulling" a canopy in a vacuum forming operation does make the material thinner.

I can see where starting with a flat sheet and vacuum-forming avoids some limitations that bottles have. But when I need a canopy, there is usually a bottle in the trash. And you can have a pretty good canopy for 5 cents worth of a very rugged recycled material.

Dave


Addendum:

I just measured what I could of the unused portion of the bottle. All the measurements were between .008 to .009" thick.  The sides and edges of the formed canopy are between .013 and .016" thick. I don't have a large ball micrometer to measure the thickness at the top of the canopy, but I believe it would measure thicker than .008, not thinner. (I watched it shrink up to the mold, so logic tells me it has to be thicker....)
« Last Edit: October 30, 2018, 08:02:01 PM by Dave Hull »

Offline Trostle

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Re: Home brew canopy for profile?
« Reply #32 on: October 31, 2018, 12:03:49 AM »

I have used C-clamps in previous iterations. They definitely help. Where do you put them, Keith?

Dave


The canopy form is glued to a plywood base.  Of course, the plywood base is more narrow than any portion of the canopy.  The plywood base is "deep" enough so that it starts to need to be "jammed" into the bottle.  Then I use shims of different shapes to further "jam" the form into the bottle.  Then, use the C-clamps to hold the sides of the bottle very tightly against the plywood base.  These clamps help with the shrinking process and also become useful handles when you are using the heat gun over the form.  Hope this makes sense.   It really works.

Keith

Offline Dave Hull

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Re: Home brew canopy for profile?
« Reply #33 on: October 31, 2018, 03:17:42 PM »
Thanks, Keith. I'm doing pretty much the same thing.

I agree it works.

Dave

Online Tim Wescott

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Re: Home brew canopy for profile?
« Reply #34 on: December 02, 2018, 02:19:11 PM »
I read in this scale column that Zirolli models will pull canopies.  I'm going to give them a try -- they can always say no.  If they don't want to give it a whirl, or if they try and can't do it, then it'll be down to finding just the right soda bottle and trying that.

Mike Pratt -- I am listening to you!  But where you see getting three successes out of six tries as a failure, I see it as "woo hoo!  One canopy for one model, and two spares!!"  I figure that the Zirolli people will know if it can be done on their equipment.

Here's the plug.  It's currently untapered width-wise -- I'm assuming that it can still be convinced to come out of a part because of the fore-and-aft draft (and I may redo that back section if the Zirolli people say "yes, send in your plug").
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The problem with electric is that once you get the smoke generator and sound system installed, the plane is too heavy.

Offline Dave Hull

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Re: Home brew canopy for profile?
« Reply #35 on: December 02, 2018, 06:20:54 PM »
It will come out if they can pull it.

Dave

Online MikeyPratt

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Re: Home brew canopy for profile?
« Reply #36 on: December 03, 2018, 12:50:30 PM »
Hi Tim,
The sides of the canopy need draft as well, the for & aft draft is just fine.  I was pulling the canopy from .030 PPG plastic 20 square, six molds at a time.  A production run of 500 kits =30 sheets of plastic (without errors) so all canopies have to come out of the former in perfect shape.  Getting three per pull wasn't an option, what we were trying to do, improve and lower the cost of the kit.  I'm sure they could get a single pull out of a single sheet of plastic.

As a side note, apply finishing epoxy to your mold (when cured) and sand in the draft on the sides of the canopy.  Carefully check the amount of draft as you sand.  Apply more epoxy if needed and carry on until perfect.  Dust the mold with talcum powder before molding the plastic to help release the molds.  Sometimes a quick shot of compressed air can help the release the molds from the plastic.

Later,
Mikey


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