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08-14-2012, 09:14 PM
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Join Date: Aug 2010
Location: Marshall TX (KASL)
Posts: 1,783
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Thanks Tony! I stand corrected! If I was doing mine over I would definitely seal the holes with silicone as I was installing the screws, and cover the bottom edge and one-half inch or so of each side of the window from the edge with metallic tape - all of the window hidden behind the skin. If someone has access to scrap pieces of this lexan, some TESTS would really be good! Would tape like that make a difference? Or silicone in screw holes? Why sometimes 2 spills until crazing? Does it craze more or less If the piece is under a bending load? Does the roughness of the edge make a difference (I.e. different sanding grits.) Is the edge flame polishable? Does it make a difference? (THAT is probably a mod that steps over the bounds though! But it would be interesting to know, that treatment could weaken it - would need to look that up.) What about those films mentioned i.e. typical auto window tinting film? Mogas vs. 100LL? Would make a neat little research project and all that is needed is a bunch of scrap.
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08-14-2012, 09:22 PM
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Join Date: Jan 2005
Location: Arlington, TX (DFW)
Posts: 1,164
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Quote:
Originally Posted by Bill_H
Thanks Tony! I stand corrected! If I was doing mine over I would definitely seal the holes with silicone as I was installing the screws, and cover the bottom edge and one-half inch or so of each side of the window from the edge with metallic tape - all of the window hidden behind the skin. If someone has access to scrap pieces of this lexan, some TESTS would really be good! Would tape like that make a difference? Or silicone in screw holes? Why sometimes 2 spills until crazing? Does it craze more or less If the piece is under a bending load? Does the roughness of the edge make a difference (I.e. different sanding grits.) Is the edge flame polishable? Does it make a difference? (THAT is probably a mod that steps over the bounds though! But it would be interesting to know, that treatment could weaken it - would need to look that up.) What about those films mentioned i.e. typical auto window tinting film? Mogas vs. 100LL? Would make a neat little research project and all that is needed is a bunch of scrap.
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Bill and/or anyone in our group:
I'll gladly supply ALL the acrylic and polycarbonate scrap pieces you could ever want, if someone wants to do some testing. I'd gladly volunteer to do some tests myself, but between work, family, and everything else, I'm doing good just to find the time to work on my -12.
Please, if anyone has the time to devote to testing various 'barriers', etc., let me know. I'll FedEx you'll boxes of scrap for your testing. In the end? I'll bet we will ALL benefit! Just let me know if someone wants to devote the time to try.
__________________
Gary Robertson
Arlington, TX
RV-12 Built / Sold / Flying
Currently Flying: Cessna Skyhawk 172
Rebuilding a true barn find J-3 Cub
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08-15-2012, 07:06 AM
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Join Date: Oct 2010
Location: La Feria Texas
Posts: 3,822
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If one wanted, they could make supports inside to replace the strength lost from changing rear window material, perhaps even strengthening the structure more than the window does..
Quote:
Originally Posted by skydiverlv
I hope to never have an extremely hard landing but it has happened to pilots much superior than myself. I have seen Cessnas bounce off the runway because of wind currents. With my upper harness connected to the tailcone I would want the highest level of integrity available to me if an event should occur. I'll have to trust someone else for this one even though I do not like the thought of replacing an affected window. Maybe a solution will be found before my window gets mounted.
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08-15-2012, 10:07 AM
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Join Date: Aug 2010
Location: Marshall TX (KASL)
Posts: 1,783
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Well, I really stepped in it by opening my big mouth...
I'll do some testing if you send me a bunch of scrap! I do not intend to text plexiglas, no one has ever said that fuel crazes that and I do not intend to do any structural strength testing or otherwise open that can of worms!
So just pieces of the existing material in the rear window - in that thickness. From only a few minutes thinking about it, I'll need a bunch of pieces about a foot long in one dimension, maybe 6 inches in the other. Yeah, those would be good. Even some larger like 12" x 12". Tiny pieces like 4"x4" might not be much use. I could cut those from bigger ones if I needed them
I may use a vise and a wood jig to slightly bend the pieces as they are tested so they are under a similar load curvature to the installed piece. In some I will drill holes and attach scrap aluminum (simulating the fuselage) and the sames screws/nuts/washers use to attach the existing window. This allows testing of the silicone-filled-holes idea - plus figuring out a way to introduce the silicone effectively and non-messy. (Maybe a hypo needle?)
In fact upon thinking further - to simplify my work it would be really great to get a bunch of 12"x6" pieces. Do you have the saw or setup to make a bunch of those easily from your scrap? I am thinking of building a jig to hold the test pieces and a uniform size would be much easier for that. Don't worry about dressing the edges because I intend to use several grits for that.
]
If someone wants to donate me some window film or tapes for the testing, please send that as well. Otherwise I'll just go by a nearby auto window tint shop and beg for scraps, or get some cheap film from Wal-mart. The metal tape I am thinking about is the type that they use on metal HVAC ducts - peel and stick, a really SOLID stick.
Any other suggestions / ideas are WELCOME! I intend to take lots of pictures of the test setup and the results.
Gary - please email me at billhollifield AT iname DOT com for my address.
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08-15-2012, 11:30 AM
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Join Date: Jul 2008
Location: kansas
Posts: 330
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I will furnish some 3M paint protector film. Very durable stuff.
From what I have heard though it is the cut edges and screw holes that are introducing fuel penetration, allowing the rapid degradation of the Lexan to occur. I would assume a scratch on the main surface would have the same results. It is extremely difficult to mar this film and appears impervious to auto fuel.
__________________
Larry Vandegrift
ULPower 260is
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08-15-2012, 12:33 PM
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Join Date: May 2008
Location: Friday Harbor, Wa
Posts: 300
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__________________
MRT890
120042 RV-12
N112XP
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08-15-2012, 01:14 PM
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Join Date: Aug 2010
Location: Marshall TX (KASL)
Posts: 1,783
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That video looks applicable. It might be the ideal way to non-messily plug the screw holes. And, if the spilled gas never reaches the lower edge it can't cause crazing - except for surface crazing. BUT!!!
But when I remember the issues about actually installing the window and bending it and sliding it under the edges of the skins to line it up, I think that the example of the video isn't very realistic and it might be very difficult to keep the butyl rubber in place during that installation process. Someone should try this!
I still plan to do the testing and will get some of this to see the effect gasoline has on it as a barrier at the screw holes. But unless this installation is perfect in the area around the gas filler, spilled gas could seep past it to the window's edge. So I am still thinking that a tape covering on the edge might be useful.
Larry - thanks for the film offer, please email me for the address. billhollifield AT iname DOT com
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08-16-2012, 06:33 PM
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Join Date: Jan 2005
Location: Arlington, TX (DFW)
Posts: 1,164
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Gentlemen,
Sorry for my delayed response. I've been out of town and away from the computer. OK as I catch up on the thread, Bill H volunteered to do some testing, and others have offered some materials in addition to my plastics, so that Bill H can do some testing. But I may have another solution?
I received a message from David Hill (Delta Hotel on the forums). David is an A/P, IA, DME, pilot, and a professor at one of our local colleges. David teaches aviation courses at Tarrant County College, and has asked if he could take on the testing/project as a unique challenge for his students as an extra credit project! I think this offer is fantastic, and I believe we would all benefit from their findings. David is local and I could get him the plastic samples quite easily and quickly. Bill H, if you agree, I'll get the materials to David Hill and his students can begin tests. If you'd still like to do some tests on your own, I'll gladly still send you some plastic test pieces. Just let me know you thoughts on the proposal from Daivd and his college students, and/or if you'd still like to do some tests on your own.
Thanks!
__________________
Gary Robertson
Arlington, TX
RV-12 Built / Sold / Flying
Currently Flying: Cessna Skyhawk 172
Rebuilding a true barn find J-3 Cub
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08-16-2012, 08:08 PM
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Join Date: Aug 2010
Location: Marshall TX (KASL)
Posts: 1,783
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That is a great idea! Very practical for those students. One thing they will need is pictures of the crazing and event reports like in this thread and others. Can you be the clearinghouse and get the pics and info to them? They will also need some scrap aluminum and the plans instructions for the size of the holes, nuts and screws, etc. to do the simulation. I'll take some pics Saturday of my "event aftermath."
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08-16-2012, 08:38 PM
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Join Date: Mar 2009
Location: Austin, Texas
Posts: 306
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Steward Systems EverShield
As one data point, I queried the folks at Stewart Systems regarding their protectant, "Evershield", advertised as "An Easy-To-Apply Glass-Like Finish With Many Incredible Protective Properties For Almost Any Aircraft Surface." I thought that would be a really swell thing if it worked for the crazing problem.
They planned to obtain some scrap from Van's to test for crazing.
They never got back to me, so I asked them last year at Airventure... apparently they didn't have a positive (protective) result--so no magic cure there.
One question I have--are all polycarbonates created equal? Lexan, etc., as opposed to the brand that Van's uses???
Rob
__________________
Rob Reese
RV-12 #120332 N73HR
Austin, TX
TangoFlight Mentor
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