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Thread: Windshield install

  1. #1
    Birdseyeview's Avatar
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    Default Windshield install

    The cutout on my series 6 windshield seems to be "dented" on the left side at the top of the forward door frame. The right side in this area seems perfectly aligned but the "dent" is causing a tight fit across the top of the door frames. It's so tight I don't dare stretch it too much more for fear of cracking the acrylic somewhere in this key area. Is it possible to heat up the acrylic to reshape it to a better fit and relieve the stretching tension across the door frame?

    IMG_7939.jpgIMG_7940.jpg

    The left picture shows the "dent" on the left side and the right picture shows the "normal" right side for comparison.
    Larry Olson
    Kitfox Series 6 - 1st Flight Oct 2021
    Tri-gear, smooth cowl
    912 ULS

  2. #2
    Senior Member efwd's Avatar
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    Default Re: Windshield install

    Larry, I think you may have removed more material from the right side. I noticed how tricky it is to notice this myself in my build but it was on top. Looking at your photos I see in the right photo that it appears that you trimmed into the window approx three times the distance compared to the left side. The left side appears to begin the radius at only about 1/4" from the window edge, maybe 1/2". It seems that if you trim deeper and then radius the same degree, you will trim out the dent. Maybe?
    Eddie Forward
    Flying
    SS7, 912iS, Garmin G3X

  3. #3
    Birdseyeview's Avatar
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    Default Re: Windshield install

    Eddie, Thanks for your input. I actually haven't trimmed the right side at all yet and I did some trimming on the offending left side. I have reread some of the past issues that others, including yourself, have had in the past and it seems that my vintage windshield did have a history of some molding issues. I'm hopeful that as I trim this problem area some more, and as I reposition the front leading edge inside the front door frame, that the tight fit will be reduced or eliminated (time will tell). My real question is still if heating the windshield in the problem area with a heat gun or hair drier will have a chance of relieving any stress in the acrylic due to a less than perfect fit, or does too much heat cause other problems? One of the past comments in the forum hinted that since acrylic has a "memory" heating of the formed acrylic can "return it to its original flat state". I just don't know how hot it can stand without some unforeseen damage. One would think that heating would tend to reduce forming stress but it may be that localized heat may induces additional stress in adjacent areas. I don't have access to a large furnace to evenly heat the entire screen and that proposition seems tricky at best. I guess I'll try an experiment with some localized heating and bending with some of my scrap pieces that I trimmed off the windshield.
    Larry Olson
    Kitfox Series 6 - 1st Flight Oct 2021
    Tri-gear, smooth cowl
    912 ULS

  4. #4
    Senior Member rv9ralph's Avatar
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    Default Re: Windshield install

    My real question is still if heating the windshield in the problem area with a heat gun or hair drier will have a chance of relieving any stress in the acrylic
    Acrylic products always have stresses which result in propagation of cracks at the worst time and place. Heating or cooling can cause cracks. I have heard of RV8 canopies cracking in flight at altitude due to the cold air.

    Heating a portion of your windscreen will result in stresses in other areas due to expansion. You would have to heat the entire canopy to reach the required temperature to reshape that area of your canopy. If I remember correctly, the required temperature is between 325 to 380 to be able to reshape.

    I hope this helps.

    Ralph

  5. #5
    Birdseyeview's Avatar
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    Default Re: Windshield install

    Ralph, Thanks for the confirmation of it being a bad idea to heat the windshield to make it fit better. I thought that this might be the case so I'll drop that idea. It turns out that as the installation of the windshield progressed today and I repositioned the vertical edges of it inside the front door frames it all fit much better, and with less bending of the acrylic to make it fit up close to the mating door frame surfaces. I also accomplished some more trimming of the cutout area near the forward wing attachment pins and this seemed to help reduce the acrylic bending in that area that I was initially concerned about since that area has been known to be crack prone. Although I must have taken the windshield off and on many times while trimming the vertical edges little by little, it all began to fit better and better with each trimming iteration. I finally got it all to fit as it should with the fuselage and with the upper cowl and I successfully match drilled all the attachment holes per the build manual (all without any acrylic cracking). After reading some of the past horror stories about cracks I'm breathing a sigh of relief that my experience went better than some in the past.

    One additional question did come up during the installation and that is how much should the left and right outboard edges of the windshield overhang the mating butt ribs. I haven't trimmed either outboard side yet. The build manual indicates these edges should be trimmed flush with the outboard edges of the butt ribs. Unless there is a possibility of an interference with the adjacent wing rib it seems that some overhang might be beneficial to cover over the small gap between the butt ribs and the adjacent edge of the #1 wing ribs. Has anyone left such an overhang and if so, how much was it?
    Larry Olson
    Kitfox Series 6 - 1st Flight Oct 2021
    Tri-gear, smooth cowl
    912 ULS

  6. #6
    Senior Member rv9ralph's Avatar
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    Default Re: Windshield install

    The build manual indicates these edges should be trimmed flush with the outboard edges of the butt ribs.
    Follow the manual, the gap will be covered with the wing root cuffs.

    One note; when working with acrylic, it helps to have a warm workshop. Cold will make the acrylic brittle. Will cooler temps, just remember to keep things warm in the shop.

    Ralph

  7. #7
    Senior Member efwd's Avatar
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    Default Re: Windshield install

    Larry, I left a slight amount of overhang. Maybe 1/4 inch but probably less. Here is what I experienced as a result. I sanded the edge of the acrylic such that it has a 45 degree edge on it. I would recommend that the underside of the acrylic not bridge that gap. This helps the number one rib slip in and under the acrylic edge when the wing is swung and pinned to the airframe rather than the acrylic catching against the number one rib. When I opened the wings up at my condition inspection I found that my Oratex finish tape on the wing was bunched up due to the flexing of the wing where it contacted the acrylic. Thankfully all I had to do is heat up the finish tape and flatten it down again. I then needed to sand the acrylic a bit more so that the contact points were lessened. I had to fix only about three inches between the two sides. At 235 hours now, it all seems fine.
    Im not sure all this addresses anything whatsoever but I envisioned rain and hose water going right through that gap. I don't have any water make it through having done it this way.
    Eddie Forward
    Flying
    SS7, 912iS, Garmin G3X

  8. #8
    Senior Member Delta Whisky's Avatar
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    Default Re: Windshield install

    Far a diversity of options - some have left an overhang. Although this picture was taken for another reason, it shows what I did. As it turns out, I didn't have the butt rib quite high enough relative to the end rib and did have two very small locations where the overhang rubbed the wing. Since I don't and hopefully won't be swinging my wings it doesn't matter in my case. Observation - Eddie and I were typing at the same time. His idea to chamfer the edge makes a lot of sense.

    Butt rib to fuse closeout small.jpg

  9. #9
    Senior Member jiott's Avatar
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    Default Re: Windshield install

    Ditto what Eddie and Delta said. I also left about a 1/4" overhang but had the same issues. If you do an overhang you MUST make sure the bottom of the plexi does not scrape on the wing #1 rib (including several layers of covering fabric) when swinging the wings. In order to do this, it probably starts by planning for it way back when you set the height position of the butt rib. If you do all this and get it right, I think it is a good way to keep water out of that gap and it also looks nice. Pretty tough to do as an afterthought though.
    Jim Ott
    Portland, OR
    Kitfox SS7 flying
    Rotax 912ULS

  10. #10
    Birdseyeview's Avatar
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    Default Re: Windshield install

    An overhang was not planned from the beginning my project but I'm thinking that if I want an overhang now, as I'm installing the windshield, I could put a thin aluminum strip (lets say .016" thick) between the acrylic and the top of the butt rib to ensure that there is no rubbing on the top of the adjacent covered wing rib. With the size of the bolt holes in the acrylic there should be enough clearance to allow for such a spacer. I like the idea of having a small overhang and at the end of the day if it doesn't work I can always remove the spacer and trim back the overhang.
    Larry Olson
    Kitfox Series 6 - 1st Flight Oct 2021
    Tri-gear, smooth cowl
    912 ULS

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