Windshield Replacement

How to keep the Cessna 170 flying and airworthy.

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Re: Windshield Replacement

Postby n2582d » Tue Nov 23, 2021 3:49 am

I found this Robinson video interesting. Why is it that the aftermarket windshield manufacturers aren't using this type of plastic on fixed wing aircraft?
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Re: Windshield Replacement

Postby GAHorn » Tue Nov 23, 2021 4:08 am

Vne of 102 kts might have something to do with it.
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Re: Windshield Replacement

Postby n2582d » Tue Nov 23, 2021 5:20 am

This polycarbonate windshield is used on the R22, R44, and R66. The R66 has a Vne of 161 mph. The C-170B's Vne is 160 mph. But you may be correct for Robinson says, "Tests were conducted at the Southwest Research Institute in San Antonio, Texas where a 2.2 lb (1 kg) bird, the FAA’s standard test weight, was used to simulate a bird strike. Tests demonstrate the R22’s windshield provides protection at impact speeds up to 90 knots, while the R44 and R66 windshields provide protection at impact speeds up to 100 knots."

Cost may be another factor. The price for a impact-resistant Robinson windshield is between $6600-$6800.
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Re: Windshield Replacement

Postby Bruce Fenstermacher » Tue Nov 23, 2021 10:42 am

I think, generally, planes do not fly at common altitudes of birds compared to helicopters. I wouldn't be surprised to find helicopters have more bird strikes than airplanes if there was such a survey anyway. In my 6-7 thousand hours of helicopter time I've had so many bird strikes I never counted them. In fact at one time it was considered routine and not even reported unless there was damage or you needed maintenance to help remove the carcass. I was lucky and never, to my knowledge hit a goose or vulture, at least nothing ever entered my cockpit though I've had friends not so lucky.

In contrast in my 3 thousand hours of fix wing time I've never hit anything in flight other than the few balloons launched specifically to be hit, and I've missed most of those.

Perhaps this is why it is worth the expense of a stronger windshield in a helicopter and most of them aren't going much more than 100 kts.

And BTW should you think that meat clever you have spinning on the nose of your aircraft would deflect or mince anything entering its arc you'd be wrong. I've had a balloon or two pass right through the prop arch and hit the windshield which can really scare the heck out of you.
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Re: Windshield Replacement

Postby ghostflyer » Wed Nov 24, 2021 12:23 am

Any helicopter parts have a zero tacked on a price of what a part is worth. I am not surprised at the cost of a Robinson windscreen. Some areas of a bell 206 windows [lower bubble area ] are made of carbonate material. I have always thought a Cessna 170 windscreen made of “Lexan” would be good alternate . I have lexan side windows in my aircraft . Thank goodness I did that because one day I was trying to refit my back seat [with the front seats still fitted] and we managed to slide it in to the rear of the aircraft but part of the upper seat back was against the rear window . It was distorted and badly marked . The front seats were then removed . If that side window was perplex it would have been broken .please note.. I haven’t researched the optics and distortion factor when these plastics are shaped in comparison of using perplex and lexan.
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Re: Windshield Replacement

Postby GAHorn » Wed Nov 24, 2021 12:21 pm

Google says the difference between Acrylic (brand name Plexiglass) and polycarbonate (brand name Lexan) is that Plexiglass can be shaped easier with heat, is clearer, more easily scratched, but capable of being polished. PLexiglas is also easily tolerated by the body if injured by it. (They make contact lenses and cataract replacement lens of it.)
Lexan is more impact resistant but cannot be polished, not as easy to shape (most commonly flat shaped unless exceptionally thin where it loses strength) and contains “Biphenol” which messes with your endocrine glands, growth, and may be a contributor to certain cancers. Lexan (Polycarbonate) is less tolerant of chemicals such as ammonia (glass cleaners)..and less tolerant of sunlight which can “yellow” it. (Maybe that’s why it’s often used on flat side windows beneath the wing.)

Chemistry makes advances all the time…. acrylic/plexiglas was first discovered/developed in the mid-1800s…. polycarbonate/lexan in the 1930s. Maybe the Robinson windscreens are a further development of poly. But whatever…. I hope I don’t have to replace my windshields anytime soon. The 170 was new in ‘97 and the 172 is of unknown age (I don’t think it’s original but I haven’t found a record of it having been replaced either.)
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