Plexi Wrap-around Canopies

[dmar836]

Appears 1/8" is mostly used for this. If anyone has done it, did you form it? To relieve stress from my fairly flimsy canopy frame, I figured that I might, at minimum, curve it and heat it either in a box with a heat gun or two or in an oven. I have seen no locations where straps across the canopy frame had been so hoped to have it somewhat pre shaped. I'll likely add a front and rear strap to keep it nice and tight. Overthinking it all?
Dave

[Supervee]

Overthinking...Not at all, a strong and light canopy is a very important structure. I know of at least one fatality in formula one because the canopy came off.
I will send you some pictures of the canopy I built for V-Witt #33…Very light, and strong, and great visibility.
We have done it both ways….On our cassutt, we made a plug, or form. To it we glued felt. We then got the 1/8" plexiglass cut out , larger than needed all around, and clamped it to the form, top center and bottom center. We then took it to American Aviation and put it in their oven…Back then getting access to a big oven was a big deal…but today, with the gigantic powder coating industry, large ovens are all over the place…As the plexi got hot, it draped down and assumed the shape of the plug.
On other airplanes, and on #33, I used .093" Polycarbonate sheet (Lexan)…..I love working with it…it can be sheared, bent in a brake, drilled, riveted, etc. Just don't get fuel on it…
I will send those pictures…Most people don't know I did a good portion of building on Jim Vliet's #33 'Chasin' Rainbows'...

[dmar836]

Great! Then that begs the question why Jim's vertical wasn't to plan. Ever discussed?
Dave

[Supervee]

Package has been dropped in the mail…..
Heres the history on #33 V-Witt……Jim had bought the plans, and it was Jim who drew the long wingtip drawing for Wittman, and about that time, he negotiated to buy a V-Witt Project in wisconsin. It was , I believe, one of three welded up under Steve Wittman's guidance. This one originally was destined to have a mercury boat engine in it, but the project we got delivered to my shop had already fabricated cowl parts for the VW installation. I rejuvenated the silver dope, built a new cowl, built canopy, covered ailerons/flaps, hung engine, designed and built intake system and baffles, built instrument panel, fitted wheel pants, and painted the whole thing. I took it to my hangar and put it together and started rigging it, when I discovered that one wing was skinned with a twist in it, so…the whole project ended up going to Jim's in New Jersey, where he ended up re-skinning one wing. Charlie Terry test flew it.
Jim always regretted not having me put the bigger stock fin on it. everyone who flew it remarked about how it had less than good yaw stability...

[chuckerf14]

Back to the light but sturdy issue.

The wrap-around I want to build is very highly raked. I am considering using less than .125" acrylic. The next size down at Aircraft Spruce is .080". When I did the trigonometry, the .080" is thicker (as seen by flying object passing through the prop arc) than a normal .125" windshield. However, I don't know if there is a problem with turbulence and the lifting force on the canopy. Just trying to watch the grams.

Any thoughts?

[chuckerf14]

Ed,

Can you tell us more about the accident? What let go? Was it struck? Was it a design problem, a building problem, or a material problem? How did that result in a fatality?

Thanks,
Chucker

[Supervee]

Are you asking about the Cassutt accident? If so, he was on the first flight, and the canopy opened, and pivoted at its hinge, so it disturbed the airflow over the whole tail, and it PIO'd till finally striking the ground. Can't tell you if it was a material problem, I would assume it was a latch design deficiency. I have simple safety latches on all my little airplanes.