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  #1  
Old 12-30-2011, 11:13 AM
Toobuilder's Avatar
Toobuilder Toobuilder is offline
 
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Default Flat Wrap Conversion - Photo Highlights

There are a few "flat wrap" -8's out there, but in case I'm the only one who converted a flying airplane from the bubble to flat, here's a few pictures of the process.



This hole caused by a few inconsiderate birds got the process rolling.



Since this airplane had two prior windshields, I welded up the roll bar to seal the holes.



I used a straight edge to see where the line drawn from the canopy bubble would fall on the boot cowl. On this canopy, a straight line tangent to the canopy radius falls on the boot cowl 24 inches from the front of the roll bar. Rough cardboard template cut to fit



Since the "E-AB" category is all about education and learning new things, I decided I'd learn how to make a heat formed windshield. I made a buck using the roll bar as a loose pattern.



Buck was skinned with thin ply, finished with filler and covered with felt.



Since I couldn't find an oven big enough, I made my own out of plywood. I upped the thickness of the plexi to .250"



Rough cut the windscreen using the cardboard template. There is a lot of trimming and fitting after this step!
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WARNING! Incorrect design and/or fabrication of aircraft and/or components may result in injury or death. Information presented in this post is based on my own experience - Reader has sole responsibility for determining accuracy or suitability for use.

Michael Robinson
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Harmon Rocket II -SDS EFI
RV-8 - SDS CPI
1940 Taylorcraft BL-65
1984 L39C
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  #2  
Old 12-30-2011, 11:15 AM
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With the base of the windscreen this far forward, the baggage door need to be notched and fixed structure added to the boot cowl. I decided to make things difficult by making a cut following the windscreen radius.




I had to de-skin the door and move some structure around inside.




With my decision to follow the windshield , I set myself up for a compound curve on some of the edge structure. Fortunately, my shrinker/stretcher made short work of that.



It's serviceable... I'm still kicking the idea of doing a new one in composite with a hidden release latch.



While I was at it I decided to fix the area around the skirt. I had to do some surgery and pull in the canopy frame tight to the fuselage. These fairings smooth things out big time. No more gaps!



New shape windshield means new glareshield cover. This is black canvas with pockets for charts and pens sewn on. Also has a big strip of velcro for any of the antennas needed in the future. The 430 antenna is permanent, of course.



With such a rakish angle on the windshield, the transition needs to lay down pretty well against the boot cowl. There is only one mechanical attachment on the boot, and it is a small clip right on centerline. It is buried under the fiberglass. The clip was there mainly to keep things from moving around while the tank sealant and glass cured.


I still have a bunch of bodywork to go before it's ready for final paint, but it's plenty good enough for the time being. All gaps are very tight, and I was even able to incorporate a nice foam seal. The canopy closes like a bank vault.




So overall it's been an interesting modification. It took just under 2 months of weekends to get it flying again. Certainly, if I had purchased the windscreen I would have saved myself a ton of time, but E-AB's are for education and experience and I already know how to write a check...
The modification added 4 pounds to the airplane and it is noticeably quieter. The drumming of the prop is the biggest reduction. And, yes, I have done some limited speed testing to see if it picked up anything... I have not noticed any increase in speed both flat out, nor in long distance cross country cruise. Of course, I had hoped that all my cleanup would pay off in speed, but I did the modification for increased birdstrike protection. While I am confident that I have achieved that goal, I'm not about to test it.
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WARNING! Incorrect design and/or fabrication of aircraft and/or components may result in injury or death. Information presented in this post is based on my own experience - Reader has sole responsibility for determining accuracy or suitability for use.

Michael Robinson
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Harmon Rocket II -SDS EFI
RV-8 - SDS CPI
1940 Taylorcraft BL-65
1984 L39C
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  #3  
Old 12-30-2011, 12:17 PM
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Nice work Mike!

See, contrary to popular belief there are real homebuilders in the modern Vans community
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  #4  
Old 12-30-2011, 01:59 PM
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Looks good Mike! Nice work!

If you've seen my bird you'll know I am obviously a fan of the sloped windshield.
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  #5  
Old 12-30-2011, 02:14 PM
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Thanks Dan... I do like figuring stuff out on my own. Learning the hard way, I think they call it.

And yes, Brent, yours was an inspiration!

Anyway, I forgot to address the oft asked question about how to get the top of the canopy to line up with the thicker windscreen. I struggled with this one as well, and what I came up with turned out to be pretty simple. Once I got the holes in the roll bar welded up and dressed and the windshield sitting on top (no spacers), I found that the outer surface of the 1/4 inch windshield was riding about 1/8 of an inch high relative to the canopy right at the centerline (butt line 0). All other areas were flush or low relative to the canopy. My fix was to simply raise the entire canopy frame off the rollers by the 1/8 inch to line up with the windshield. Once the basic position was established, then I simply had to figure out the spacers that would be needed at the screw hole locations in the roll bar. Including the single hole at the center line, I had 4 other fasteners on each side (total of 9 screws on the roll bar). At each of these locations I welded a small tab of 1/8 steel. Each of these tabs was ground and finished to bring the windscreen perfectly flush with the canopy. I figured a permanent spacer would be easier to keep track of during installation as well as providing a bit more material to cut the threads into.

Ultimately, all 9 of these holes were opened up in the plexiglass to 1/4 inch and lightly countersunk/polished. The 1/4 inch size allows the #6 screws and countersunk washers to act as a spring type clamp without fear of stressing the hole (a #6 screw has plenty of room in a 1/4 inch hole). During the install, the holes were filled with tank sealant and the screws installed wet. Time will tell, but the tank sealant should allow the windshield to move around on the structure just enough to prevent a local stress riser anywhere. So far, it's happy in the cold of winter but we'll see how it likes the 110+ summer sun.
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WARNING! Incorrect design and/or fabrication of aircraft and/or components may result in injury or death. Information presented in this post is based on my own experience - Reader has sole responsibility for determining accuracy or suitability for use.

Michael Robinson
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Harmon Rocket II -SDS EFI
RV-8 - SDS CPI
1940 Taylorcraft BL-65
1984 L39C

Last edited by Toobuilder : 12-30-2011 at 02:17 PM.
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  #6  
Old 12-30-2011, 03:31 PM
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Ironflight Ironflight is offline
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Nice write-up Michael! I really like seeing photo essays of "pure fabrication" - going outside the kit box is something that many folks are afraid to do, and seeing techniques that work is great.

Paul
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  #7  
Old 12-30-2011, 04:01 PM
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Toobuilder Toobuilder is offline
 
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Thanks Paul. I took about a million pictures of this stuff, so obviously I just touched the high points here. If this thread generates any follow up "how to" questions, I likely have the answer in picture form.
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WARNING! Incorrect design and/or fabrication of aircraft and/or components may result in injury or death. Information presented in this post is based on my own experience - Reader has sole responsibility for determining accuracy or suitability for use.

Michael Robinson
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1984 L39C
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  #8  
Old 12-30-2011, 05:03 PM
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Quote:
Originally Posted by Toobuilder View Post
..... If this thread generates any follow up "how to" questions, I likely have the answer in picture form.
Nice writeup Mike. Forming a windshield from raw Plexiglas stock the way you did is an impressive feat. You put a lot of distance between yourself and the average tab A into slot B kit assembler. Where does one buy the required Plexiglas stock? What temperature was required to warm the .250 thick material and for how long? What type of heating was used in your homemade oven and how did you control the output? Does the Plexiglas give off an "aroma" while in its softened state? After forming, how long was the cooling process before you felt comfortable removing the windshield from its buck?
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  #9  
Old 12-30-2011, 06:21 PM
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Thanks Rick. I'll try answer your questions the best I can, but be forewarned that forming plexiglass is not my forte'... All I know is from internet research and this experience.

That said, plexi can be found at a local window/glass shop, but your best deal is going to be a plastics supplier. Most large cities have them. Also, like anything else, quality varies significantly. The stuff you want is cast acrylic ("plexiglass" is a brand name, and it's cast). There is also "continuous cast", which I think is one step down in quality, and then you have "extruded" sheet. This is the junk you get at Home Depot. I'm not sure if the protective backing is an indicator of quality or not, but I'd stick to paper (vs. plastic) backing.

Temperature is fairly critical. You want to get the material uniformly up to 275 - 300. This is a major pain if you are using the Rube Goldberg contraption I did. In fact, I got a hotspot in my first attempt and instantly turned it into a pattern. I simply made a plywood box and loaded it with every heat producing item I had laying around, including a couple oven heating elements, quartz work lights, space heaters (with the thermal switches bypassed, of course) and even a heat gun or two. All told I was pumping 7000 watts into that box. You will also need to keep the air circulating in there, which is another problem - the metal fan I had in the box gave up right at the critical temperature. I monitored temperature with a thermometer inside and a IR surface thermometer to spot check the surface. Very crude, and very risky to the material. Ultimately, I simply placed the flat sheet over the form and shoved the whole mess in the oven. After a while the ends started to droop and it draped over the form. I had to clamp the free ends to the sides at the very end to make sure it went the rest of the way. Though I left it clamped over night, the stuff cools very quickly and could probably be removed from the form in just a few minutes. It does smell a bit while cooking, but it's not like cutting foam with a hot wire or anything.

Now, with all that said, the windshield I have now has a very slight wave in it down in a corner because I was too conservative and didn't quite get it hot enough to really lay down everywhere. So that's 2 "non perfect" windshields, and it's easy to see that if you're just looking at dollars, I'd be ahead buying one from a windshield specialist. But I'm stubborn, and this will not be the only windshield (or airplane) that I ever build, so I was happy to pay for the education. Based upon this experience, I think if I had access to the right oven, I could crank perfect windshields out all day long.
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WARNING! Incorrect design and/or fabrication of aircraft and/or components may result in injury or death. Information presented in this post is based on my own experience - Reader has sole responsibility for determining accuracy or suitability for use.

Michael Robinson
______________
Harmon Rocket II -SDS EFI
RV-8 - SDS CPI
1940 Taylorcraft BL-65
1984 L39C
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  #10  
Old 12-30-2011, 06:45 PM
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N941WR N941WR is offline
 
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Very nice job Mike, along with great photos and write-up!

BTW, with the thicker material and the angle, you are correct in that the chances of a bird coming through the windscreen vs. glancing off should be significantly improved. Let’s just hope you don’t have to test it!
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