A very unusual canopy

Slowly working on my P35 Seversky, I am going to need help with the canopy. It is a long, curved structure of greenhouse design; maybe a job for Bill Sawyer. Question: If I carve the 'buck' from balsa, what is the best mat'l to use for the framework surrounding the plexiglass panes? As the canopy is the most visible part of this airplane, I would really like it to be transparent, not painted. Any ideas?
Thanks, guys

Well, it labor intensive, but I use an old Coca Cola can. I cut the aluminum strips to the scale size of the frame and AC'd them to the buck. They came out quite nicely, but after three canopies things came unstuck. Luckily I only needed one, but made two spares. Worth a try.

LAST EDITED ON Nov-29-04 AT 01:33 PM (CST)
 
>Slowly working on my P35 Seversky, I am going to need help
>with the canopy. It is a long, curved structure of
>greenhouse design; maybe a job for Bill Sawyer. Question: If
>I carve the 'buck' from balsa, what is the best mat'l to use
>for the framework surrounding the plexiglass panes? As the
>canopy is the most visible part of this airplane, I would
>really like it to be transparent, not painted. Any ideas?
> Thanks, guys

Well you could carve the buck and set it up about 5 inches on a post. The make a frame out of wood about 10 inches square. Attach clear Lexan to the frame. Heat in toaster oven till soft. Pull over mold buck. Good luck.. Takes practice

LAST EDITED ON Nov-29-04 AT 01:22 PM (CST)
 
Hi Mike,
I have used strips of masking tape and 1/8th blue 3M, 1/32-1/64 ply and balsa strips. Just about anything that you can shape to the proper configuration.
I seal it all with Z poxy finishing resin, which I sand smooth.
Bill <><

EDIT: I have also masked off the panels after the canopy has been mounted, and finished the "frame" as I do the rest of the plane. All my Classic planes I have done like this when using a Sig Canopy. Filler and paint leaves a nice thin framework that is scale like.

>Slowly working on my P35 Seversky, I am going to need help
>with the canopy. It is a long, curved structure of
>greenhouse design; maybe a job for Bill Sawyer. Question: If
>I carve the 'buck' from balsa, what is the best mat'l to use
>for the framework surrounding the plexiglass panes? As the
>canopy is the most visible part of this airplane, I would
>really like it to be transparent, not painted. Any ideas?
> Thanks, guys

Ron B.
F4Fguy

The simplest way I've found for "greenhouse" canopies is to pull a second canopy over the first while it's still on the buck. Then cut out the window areas from the second and glue it in place over the first.This ensures a good fit and, while still labor intensive,is neater than trying to glue individual strips in place. This also allows painting and adding detail off the model.All my Macchis and Wildcats were done this way.

My Zero canopy was vac formed with the framing in place. I don't think it's as satisfactory. It's a trade off in labor,you have a LOT of masking to do. It's also not nearly as "crisp", since you can't get good definition vac forming on a male buck. One bit of advice;use at least .040 material for the main canopy.You can sometimes get away with .030 but, most of the time,it will eventually deform in the flatter areas. For the second, framing pull,use any thickness you like.

LAST EDITED ON Nov-29-04 AT 08:53 PM (CST)
 
How much definition do you need? Actually less is better because the frames on real airplanes are made to be as level with the window area as possible because of wind flow
This canopy was made on a mold I carved from a 4 X 4 X 12 block of mahogany

>How much definition do you need?
Ron B.
F4Fguy

A lot more than that. By definition,I mean sharpness,not height. Most WWII and earlier canopy framing was anywhere from .063"to .125" aluminum* and was not flush with the surface.Typically very little was done to the edges except deburring.This is simulated very well by pulling a thinner sheet over the main one and cutting as described.It gives clean,sharp frame edges with no radius from the frame to the pane.

*.125" @ 1/8 scale =.015"(1/64")

If you vac form over a balsa mold with enough suction to produce frames, the grain of the wood will show. You might think you have the surface smooth but the suction will pull the plastic into the soft parts of the mold. If someone sends me a balsa mold I make one canopy and then produce a new mold with harder material that I can fill, sand and polish down to 2000 grit paper

Holy Crow! At least three avenues I hadn't imagined. Ty, the Coca Cola can sounds 'uncanny', but worthwhile, hadn't thought of that one. Shape is there, for starters. I like aluminum, but hate the sharp edges, and there are a LOT of panes (pains?) to this one.
Bill Little, I also like the masking tape idea.Possible to work with.
Sparky: I was fidgeting with the possibility of 'pulling my own'...
Ron B., a 'wildcat' venture is intriguing: NEVER would have thought of pulling a Second over the First! (When I think about it, that's the only way we could have financed the House Upgrades!)
Bill Sawyer: Thanks for the insight! Never having pulled a canopy over a balsa buck, I would have been in for a surprise with WOOD GRAIN VISIBLE! I've pulled Gee Bee wheel pants, but that was white, not windshield-stuff!
Thanks to you all! I am now armed.

>If you vac form over a balsa mold with enough suction to
>produce frames, the grain of the wood will show. You might
>think you have the surface smooth but the suction will pull
>the plastic into the soft parts of the mold. If someone
>sends me a balsa mold I make one canopy and then produce a
>new mold with harder material that I can fill, sand and
>polish down to 2000 grit paper

Ron B.
F4Fguy

I use balsa bucks exclusively. Grain read through can be eliminated easily by making the buck .030 smaller and pulling a .030 "cover" over it,then fastening it to the buck. No finishing required on the buck beyond 320 sanding.

I used a block of Bass wood to make my Gypsy canopy. For me the end result was just fine, but I did notice a bit of the grain of wood to show in the canopy. You had to look closely, but I could see it. I am interested in knowing what some of you guys use to finish the mold. I am concerned that whatever I use it will stick to the hot plastic when I pull it.

Hi Keith,
have you tried any finishing resin?
Or you could do like Ron and pull a "cover" left in place and then pull your final copy over that.
Bill <><

LAST EDITED ON Nov-30-04 AT 10:45 AM (CST)
 
Paint would be the most realistic and accurate depiction of canopy frames. Aircraft windows are not installed in raised frames like house windows. Aircraft windows have always been installed as near flush as possible to minimize drag. In fifty three years of flying, I have never seen any aircraft windows installed with anything other than the minimum exterior framing necessary to retain the windows.

I also make canopy molds, as necessary, to be as realistic as possible on my semi-scale airplanes. Paint framing is the only framing that would be a true presentation of how the real airplane looked.

Like Ron, on occasion, I have also used a layer of canopy material on the mold to obtain satisfactory mold finish. In the photo below, the Hornet canopy mold on the extreme right in the front row still has a plexiglas covering. Hornet canopies were pulled over that plexiglas finish.

Hi Al,
I thought I must be nuts when I wrote this above in reply #3:

"EDIT: I have also masked off the panels after the canopy has been mounted, and finished the "frame" as I do the rest of the plane. All my Classic planes I have done like this when using a Sig Canopy. Filler and paint leaves a nice thin framework that is scale like."

Seems to me the easiest way, but others know more about it than I do.

Bill <><

Right, but many of the prewar canopys were not as smooth. The Brewster Buffalo, TBD, SBD, early F4F-3 all had a definite "lip" or edge to the frames. The blown canopy came out in mid 43 and this helped make them flush with the frame. It did add a lot of speed to the aircraft also. I was really surprised when I saw the canopy on an BF-109 at an airshow. It was on a flat bed, no wings, and it sorry shape. Some really rich guy was going to restore it. That was in 81. I don't think he got very far!

>Paint would be the most realistic and accurate depiction of
>canopy frames. Aircraft windows are not installed in raised
>frames like house windows. Aircraft windows have always
>been installed as near flush as possible to minimize drag.
>In fifty three years of flying, I have never seen any
>aircraft windows installed with anything other than the
>minimum exterior framing necessary to retain the windows.
>
>I also make canopy molds, as necessary, to be as realistic
>as possible on my semi-scale airplanes. Paint framing is
>the only framing that would be a true presentation of how
>the real airplane looked.
>
>Like Ron, on occasion, I have also used a layer of canopy
>material on the mold to obtain satisfactory mold finish. In
>the photo below, the Hornet canopy mold on the extreme right
>in the front row still has a plexiglas covering. Hornet
>canopies were pulled over that plexiglas finish.
>
>Al

Ron B.
F4Fguy

Al:

Very nice! As is all your work,but,unlike the blown Mustang canopy the "greenhouse" canopies of pre-WWII and earlier,were made up of individual panes, and the framing was much thicker as it carried most of the mechanical loading.In the attached full scale BT-13 pics you can see the very well defined edge relief and the thickness of the frames. This is much more typical of A.C.such as the P-35.

LAST EDITED ON Nov-30-04 AT 04:19 PM (CST)
 
Even so, the BT-13 canopy shown has relatively thin frames probably no thicker than .040. Much of the apparent thickness is the lapping of sliding panels. This was a trainer, not intended to go anywhere and certainly having no need for speed. In this case simplicity of construction would be more important than drag. Still if you look closely you will see attempts to flush intersections and use minimal frames as would be required to make some concessions to drag. The forward sliding panel is also flush with the windscreen and fuselage sides. While drag wasn't a paramount consideration on this trainer it certainly wasn't ignored either.

The P-35 was a different animal altogether. Jackie Cochran raced the p-35 and the airplane competed in the 1935 pursuit competition for a fighter manufacturing contract. Drag was a major consideration. It sorta depends on your photo, but in the photo below of Jackie's P-35 (actually a SEV-1, which was the prototype of the P-35), it appears there was considerable effort to flush the windows in an attempt to minimize drag. There just doesn't appear to have any shadows on most of the windows. Allowing for fairly crude frames, I still doubt that at a model size of fuselage length of 3 1/2', an exterior scale framing would probably be in the neighborhood of .009". Who said "coke can"?

Frames 1/16" would be ridiculously oversize. I'd still go with paint, and if I really wanted to go to the nth extreme, I'd use paint and a simulated sliding canopy which lapped the rear sections of glazed canopy. It should be flush with the fixed forward windscreen. Flush framing existed long before 1943 bubble canopies.

>Even so, the BT-13 canopy shown has relatively thin frames
>probably no thicker than .040. Much of the apparent
>thickness is the lapping of sliding panels. This was a
>trainer, not intended to go anywhere and certainly having no
>need for speed. In this case simplicity of construction
>would be more important than drag. Still if you look
>closely you will see attempts to flush intersections and use
>minimal frames as would be required to make some concessions
>to drag. The forward sliding panel is also flush with the
>windscreen and fuselage sides. While drag wasn't a
>paramount consideration on this trainer it certainly wasn't
>ignored either.
>
>The P-35 was a different animal altogether. Jackie Cochran
>raced the p-35 and the airplane competed in the 1935 pursuit
>competition for a fighter manufacturing contract. Drag was
>a major consideration. It sorta depends on your photo, but
>in the photo below of Jackie's P-35 (actually a SEV-1, which
>was the prototype of the P-35), it appears there was
>considerable effort to flush the windows in an attempt to
>minimize drag. There just doesn't appear to have any
>shadows on most of the windows. Allowing for fairly crude
>frames, I still doubt that at a model size of fuselage
>length of 3 1/2', an exterior scale framing would probably
>be in the neighborhood of .009". Who said "coke can"?
>
>Frames 1/16" would be ridiculously oversize. I'd still go
>with paint, and if I really wanted to go to the nth extreme,
>I'd use paint and a simulated sliding canopy which lapped
>the rear sections of glazed canopy. It should be flush with
>the fixed forward windscreen. Flush framing existed long
>before 1943 bubble canopies.
>
>Al

Ron B.
F4Fguy

Al:

Not to be contentious ,but, who said anything about 1/16"? I said full scale thicknesses of .060"to .125" which I'll stand by.At 1:8 scale thats .0075" to .015". The BT was very close to 1/8" main (vertical) frames.The drop from section to section is close to 1/2". I took these pics myself ,and had good access to the A.C.I've also been up close and personal with an SBD-5 Dauntless which had similar canopy structure.

As to Jackie's A.C.,it wasn't stock SEV-1 either. It was heavily modified and cleaned up, including a lowered and flushed canopy.

Ron,

Well at least we agree about realistic frames depth where the frames are on the surface. I said .009 which agrees pretty well with your .0075-.015. No problem there.

As for Jackie's airplane, it might have had some "clean up" but I don't see any difference in the canopys between Jackie's SEV-1 and this photo of a "real" P-35. What makes you think the canopy was "flushed"?

Why are we worried about how far canopy frames stick out, on (roughly) 1/7 or 1/8 scale stunters that are semi-scale in the first place? (And Al, I acknowledge that your models come closer to the real thing than almost all other stunters).

But this isn't an AMA Scale event. If the builder wants to accentuate the "greenhouse", let the frame stick out more. If not, make it less.

Currel,

To answer your question, if you know airplanes, you might find outrageously thick frames visually offensive. It sugggests the builder doesn't know or doesn't care what a real canopy would look like.

>Why are we worried about how far canopy frames stick out, on
>(roughly) 1/7 or 1/8 scale stunters that are semi-scale in
>the first place? (And Al, I acknowledge that your models
>come closer to the real thing than almost all other
>stunters).
>
>But this isn't an AMA Scale event. If the builder wants to
>accentuate the "greenhouse", let the frame stick out more.
>If not, make it less.
>
>Currell

Ron B.
F4Fguy

Currell:

If there's no consideration of full scale practice,why so much effort on cartoon renditions of cockpit interiors and/or carefully painted frames around blank painted canopies? If what you imply is so,why canopies at all? Why not just powder coat the airplane and buff it out?

Ron B.
Ron B.

>Ron,
>
>Well at least we agree about realistic frames depth where
>the frames are on the surface. I said .009 which agrees
>pretty well with your .0075-.015. No problem there.
>
>As for Jackie's airplane, it might have had some "clean up"
>but I don't see any difference in the canopys between
>Jackie's SEV-1 and this photo of a "real" P-35. What makes
>you think the canopy was "flushed"?
>
>Al

Ron B.
F4Fguy

Al:

After correcting for the slight difference in the photo size and angle,compare the canopy height of the Cochran and USAAF A.C.. The cochran A.C.is considerably lower.All the sources I have indicate this was an AP-7,considerably modified and cleaned up.In '39 it was further modified to AP-9 spec with inward retracting gear similar to the P-43,and a further cleaned up canopy with a blown rear section with no framing.

As to the P-35,the attached photos show that the canopy framing was much more like the BT-13 than the P-51.These are of an original AP-1 in the Swedish Air Museum.

Gee Bee: Aside from the canopy frame, tell us something about your P-35. Thanks. Currell

Al, I don't know about the canopys, but the pilot in the first photo is nearly perfect!

Ion (dumb joke) Muniz

LAST EDITED ON Dec-05-04 AT 11:28 AM (CST)
 
I was going to post this a few days a go, but ran out of time.
There are comments about making the plexiglas panels flush with the framing. This never happened, at least untill supersonic planes came into the picture. The subsonic stuff suffered with the framing over the plastic all through the years. The early F-84s with the birdcage canopies were built the same as the P-35. Planes with bubble canopies still had the windshield framing as exoskeletons. Remember, fighter planes, and combat planes, in general were built with the thought of ease of production as the forefront of their raison d'etre. The number two thing was to make them cheap. Flush canopies are more expensive and slower to build.
As far as molding a canopy to get crisp framing edges, it will be very difficult using a male mold. It would require a female mold and a lot of vacuum, and probably a harder plastic such as used in plastic models. The best way to get your required results is to use striping tape on the outside of the canopy. Using the tape on the mold, under the plastic, would give you a raised line, but it would be particularly crisp but would be decent of you don't try to make it too high.
A few more examples: Zero, Late Spitfire w/ Griffin, RF-84F, the one with the nose hook for the parasite thing, P-51A, P-40E, P-39, SB-2C Helldiver, and SBD Dauntless
Bare

Ron B.
F4Fguy

Barrie:

I still think it's easier to pull a second ,thinner canopy over the first,then cut out the framing.It gives crisper edges and perfect fits.

But you've certainly proved my point about early framing standing proud of the glazing. Thanks.

There are a number of canopy photos in the above post. Excepting overlapping canopy sections, there is very little visually detectable raised framing. Not enough to model with typical methods. In most, if not all the photos above, looking at the canopy external frames where you can see them edge on crossing the top of the canopies they nearly all appear hardly raised at all. If I knew how to repost these photos with superimposed arrows I'd make my point better. In any case the debate is as small as the framing edges.

The frames are ALL raised above the plexiglass. There is a strip under the 'glass and a strap over the glass, both with a them having layer of rubber under the strips to keep the pressure of the fasteners from cracking the plastic. The fasteners are either nuts and screws, or rivets. The average height above the plastic is about .090 +/-.030 inside and out. The inside strips may include flanges to stiffen the assembly. Granted, the height is a bit low to be depicted on a stunt model, but could be critical in a scale model. So how much fidelity do you want. Since our guy with the P-35 wants it, more power to him.
I'm still disgusted with the stunt fraternity's treatment of the guy with the near-scale Wildcat with the authentic paint job the was pushed to the back row during appearance judging at the Nats several years ago. Just because it wasn't shiny... You don't even want me to get into NASCRap mentality that I see here.
Bare

>The frames are ALL raised above the plexiglass. There is a
>strip under the 'glass and a strap over the glass, both with
>a them having layer of rubber under the strips to keep the
>pressure of the fasteners from cracking the plastic. The
>fasteners are either nuts and screws, or rivets. The average
>height above the plastic is about .090 +/-.030 inside and
>out. The inside strips may include flanges to stiffen the
>assembly. Granted, the height is a bit low to be depicted on
>a stunt model, but could be critical in a scale model. So
>how much fidelity do you want. Since our guy with the P-35
>wants it, more power to him.
>I'm still disgusted with the stunt fraternity's treatment of
>the guy with the near-scale Wildcat with the authentic paint
>job the was pushed to the back row during appearance judging
>at the Nats several years ago. Just because it wasn't
>shiny***... You don't even want me to get into NASCRap
>mentality that I see here.
>Bare

Ron B.
F4Fguy

***Thank you Barrie,that was me.

AL:

This is turning into "how many angels can..................". The original question had to do with the P-35 canopy. The AP-7 airframe is identical to the P-35 (it's simply an export designator).The Swedish Air museum photos are explicit and definitive. regardless of whether other A.C. were flush or not,the P-35 was not,visibly and conclusively. Interpreting this in model form is always a choice of the modeler and is ,to some extent,an aesthetic decision.My,personal,choice is to make the relief (subtly) obvious.Others may choose to make it go away.That it is there, on full scale aircraft of this era,and with this type of canopy, is irrefutable.

Al,
Thanks for posting the picture. I always liked the model!
Bare

LAST EDITED ON Dec-08-04 AT 03:29 PM (CST)
 
Ron B.
F4Fguy

Sorry to confuse you Barry,the Wildcat at the '88 Nats was mine,not Al's. Thats the #II one in post #28. They were essentially identical except for construction differences (carbon composite wing,1/20" molded sheet fuse).