Windshield Replacement

How to keep the Cessna 170 flying and airworthy.

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dstates
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Windshield Replacement

Post by dstates »

I'm working on my list of maintenance and improvements I'll be making this winter while there is snow on our grass runway. One of the main projects is to replace my windshield. I asked the representative at LP Aero at Airventure if temperature at installation is a concern. He didn't think so, but wasn't confident with his answer so now I'm asking the TIC170A brain trust. If it is 30 degrees in the hangar when I'm fitting and installing the windshield (with LP heaters on) are there any concerns or special steps to take?

Thanks,
Doug
N1235D - 1951 170A - SN: 20118
DWood
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Re: Windshield Replacement

Post by DWood »

Aero Plastics.png
This from their website.
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GAHorn
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Re: Windshield Replacement

Post by GAHorn »

Sunlight will degrade the protective coating and make it exceedingly difficult to remove, so keep it indoors and away from sunlight.
'53 B-model N146YS SN:25713
50th Anniversary of Flight Model. Winner-Best Original 170B, 100th Anniversary of Flight Convention.
An originality nut (mostly) for the right reasons. ;)
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dstates
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Re: Windshield Replacement

Post by dstates »

Thanks for directing me to the additional instructions at the manufacturer's web page. It makes sense that the acrylic can handle more at 80 degrees vs. 30.

My main question is based on an assumption I have that the windshield will expand and contract at different temperatures. If I have to do some trimming to get a good fit at 30 degrees in my hangar (the aircraft is at 30 degrees too), will I have any fit issues at 100 degrees in the summer?

Doug
N1235D - 1951 170A - SN: 20118
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ghostflyer
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Re: Windshield Replacement

Post by ghostflyer »

Windscreens cop a abusive life . When fitted they sit in the sun all day and heat up to over 50degs C and when in flight have cold air at minus 20 C trying to bend them and rip them out of the mounts. Plus the odd bird impact. So when in storage I would support all surfaces and keep dust away. They do gain a “set” in shape if left for long periods without support. Be wary of leaving that protective paper on the surface of the windscreen for long periods as it’s a real pain to remove.
I was told the other day [haven’t tried it yet] but pouring beer over the hard to remove paper protection helps to remove it.
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GAHorn
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Re: Windshield Replacement

Post by GAHorn »

These windshields “float” in the frame and that requires a somewhat loose fit. (Felt is used as a gasket.) When some shops use proseal or other sealant in an attempt to make them absolutely waterproof at their juncture with the frame ….they end up cracking the windshield as the frame flexes in flight and on rough strips.
Pipers often use a zinc-chromate type of “putty” as a sealant and that allows a degree of movement, and I’ve been told by some mechanics they’ve had success using it in Cessnas. My windshield is set in felt (and in heavy rain in-flight it bubbles-up inside the cabin) but it dries-out quickly also because the felt “wicks” the moisture away and allows the seams to drain. (Sealing the frame to the fuselage may actually contribute to corrosion by retaining moisture.)
'53 B-model N146YS SN:25713
50th Anniversary of Flight Model. Winner-Best Original 170B, 100th Anniversary of Flight Convention.
An originality nut (mostly) for the right reasons. ;)
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wingnut
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Re: Windshield Replacement

Post by wingnut »

ghostflyer wrote:I was told the other day [haven’t tried it yet] but pouring beer over the hard to remove paper protection helps to remove it.
Sorry to inform you, you were told wrong. It's repurposed beer that removes the paper. Let me see if I can remember how this works.

First, you drink the beer. Then you wizz on the paper. Attempt to peel the paper off. If it's still stubborn, repeat the previous steps. Quantities and times may vary. Wash hands before opening the next beer.
Del Lehmann
Mena, Arkansas
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dstates
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Re: Windshield Replacement

Post by dstates »

Got a little off track....

Maybe I'll ask the question a new way... Would any of you replace a windshield in an unheated hangar with the temperature 30 degrees Farenheit?? I'm worried that I get it to fit nice during installation, but it might have issues on a 100F day.
N1235D - 1951 170A - SN: 20118
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Re: Windshield Replacement

Post by GAHorn »

dstates wrote:Got a little off track....

Maybe I'll ask the question a new way... Would any of you replace a windshield in an unheated hangar with the temperature 30 degrees Farenheit?? I'm worried that I get it to fit nice during installation, but it might have issues on a 100F day.
No, I would not do that. I would pay someone else to do that. :lol: (Sorry…couldn’t resist… but don’t think it would be a problem.)
'53 B-model N146YS SN:25713
50th Anniversary of Flight Model. Winner-Best Original 170B, 100th Anniversary of Flight Convention.
An originality nut (mostly) for the right reasons. ;)
DWood
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Re: Windshield Replacement

Post by DWood »

Doug:
Acrylic does expand with temp and humidity. It also is more flexible at higher temperatures. Based on the manufacturers warnings I would not trim or drill at colder temperatures. You might get lucky at the colder temps but why chance it. I personally would want the windshield to stabilize at 60 to 80 degrees for several hours and maybe even a day before trimming or drilling. I did mine at normal room temp without any issues and installed the center strap. Use the drill bit(s) designed for acrylic. I also believe the instuctions I followed recommended that the windshield is allowed to float as it is held in place by either the center strap or by the top mounting if the center strap is eliminated.
Dan
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Re: Windshield Replacement

Post by c170b53 »

Its not a hard job, maybe a pain but not hard. As Dan mentioned, the windshield will be less pliable but should not be a problem as long as you handle it carefully. There’s different styles of window retainment. Original just fits into a channel on the sides and top and is retained on the bottom by an inner fuselage lip and outer strap riveted to the fuselage or replaced rivets with screws. The centre strap is held in with screws and large countersunk washers as the holes are enlarged to allow movement. Felt is used on all edges which allows the window to “move”. The heavier centre strapless is retained on the top with either a replaced upper channel which has lower bend in the bottom which grabs a doubler (comes bonded to the window) on the top inside of the window which spans the front spar (This is the “ modern Cessna window retainment method”.) There’s another style which uses plastic screws and holes drilled into the existing lower channel at the top of the windshield. (might be Great Lakes windows) to hold the top in.
Regardless of which window you use, I’d bet the fit will be close right out of the box. Areas to fit; top is going nowhere, no trimming there, trim to fit window’ s top lower bulges to lower wing surface thus having the wings on are a must or at least have those points marked on the fuselage if for some reason the wings are not on. The area that needs to be trimmed will be bottom aft corners to fair the window to the wings ( you’ll notice those fuselage corners are fixed whereas all other areas allow the window to float) and to allow the window to drop down around front bottom and sides, the aft vertical bottom edges again to fit the bottom. I bet you might have to trim the bottom of the sides just enough to allow the lower strap to fit.Likely you will be working in 1/8’s if you need to trim or in other words no need for neurosurgery.
Just my opinions and experiences here, go for it.
Jim McIntosh..
1953 C170B S/N 25656
02 K1200RS
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dstates
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Re: Windshield Replacement

Post by dstates »

Ok, I think I’ve decided on just replacing my original window with a direct replacement with the center support and not going with the thicker options. One of the main reasons is that my compass currently hangs from the center strap. I don’t see the need to pay extra to figure out a new method to mount my compass or pay for a new one and the bonded mounting block. I’d be more willing to replace or move my compass if it was something that I actually used.

Thoughts? Am I “crazy” to not go for the upgrade to remove the center strap?
N1235D - 1951 170A - SN: 20118
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Re: Windshield Replacement

Post by c170b53 »

Nope, center strap is classic plus no fuss.
While you’re at it there’s been a few threads where the top attachment for the outside strap has cracks, best to just renew it while you’re in the vicinity.
Jim McIntosh..
1953 C170B S/N 25656
02 K1200RS
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Re: Windshield Replacement

Post by ghostflyer »

This just a thought , the less holes you have in a flexing piece of plastic the less chance of stress risers forming around holes . Another point is if contact with a bird while in flight it’s the weakest point is where a crack or break will start . So if you have holes drilled in the center of the windscreen for a strap this will weaken the windscreen. Unfortunately where we fly there a lot of bird life and birds have hit me in all sorts of places . I do not really know if it was a pelican or ibis that hit my windscreen but as I ducked on impact ,I glanced up and was alarmed at how it flexed without breaking . The “bang” of the bird hitting the aircraft also scarred the hect out of me . This windscreen is relatively new and is of the thickest available due to the last one being broken by bird life .
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GAHorn
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Re: Windshield Replacement

Post by GAHorn »

I take the opposite view from the ghost…. If holes were drilled for no particular purpose I suppose the w/s would be weakened. … Except that the holes are drilled to accommodate a braced-Strengthened windshield…. Strengthened by a full-length center-strip.
'53 B-model N146YS SN:25713
50th Anniversary of Flight Model. Winner-Best Original 170B, 100th Anniversary of Flight Convention.
An originality nut (mostly) for the right reasons. ;)
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