windshield replacement

[33alfa]

Does anyone know if the strip on the front window needs to be removed all the way for installation. I want to do it right. Also i have seen some of them screwed in. Is this a good idea? and is it a 337 issue.

[N2865C]

You need to remove the strip. Mine had screws when I replaced it and it worked great. I think putting rivets back in there would be a real bear. I don't think a 337 should be needed as all the regular suppliers of windows have PMA and it's not a major repair. I think the 100 series service manual (1962 and prior) may show the correct way to do the installation.

[33alfa]

Thanks John. Looking under the panel it almost looked like those rivets hold the instrument and dash assembly so i was nervous about removing any more untill i asked someone. So my next question would be what kind of nut plates to use for install if i go that way? Thanks. Roger

[N2865C]

We just used locknuts and washers, mostly reusing what was there. It was a while ago and I don't remember the size.

[lowNslow]

The service manual says you can replace the rivets with screws and self locking nuts or screws and Rivnuts. It also says if you use #6 screws and "properly installed Rivnuts" no loss of strength will result. I used screws and self locking nuts, but if I do it again, I will install the Rivnuts.

The rivets on the sides of the windshield do support the side panel trim pieces located just forward of the doorpost (B model) so you will have open up that area as well. The channels and under the strip are one of the areas prone to corrosion, so you may also need to deal with that.

[GAHorn]

Don't use RTV or ProSeal or other adhesives (such as are used in some other makes of airplanes). The Cessna uses felt (which wicks moisture away) and allows the windshield to "float" in the frame.

[wingnut]

Just yesterday I replaced a windshield in a 150, without removing the retaining strip. I had heard others say it could be done, and this was a cheap windshield ($160) to experiment with. It worked well with 2 people and a long strip of metal to guide (shoehorn) the top in under the cabin top skin. No scratches, no cracks. Beginners luck?

Prior to this we've always removed the strip. We reinstall the strip with solid rivet which is a pain, but looks best. Rivnuts and screws are legal and work great for the next window change.

[c170b53]

I used rivets, did it by myself, would recommend the same until the holes open up, Also I used the felt and cessna sealant that remains flexable.

[Metal Master]

I always do things different. I guess it’s just the way I am. I was lucky when I fit my windshield because the fire wall was not installed. The rivets had already been replaced with screws & nuts by the previous installer. I manufactured .032 aluminum plates that fit against the skin. First I made templates from cardboard. Old cereal boxes worked fine. Then after picking up the original rivet (screw holes) I installed regular floating nut plates into the strips I had made. (The reason for this is that it makes maintenance easy in the future). You have not lived until you have had a riv-nut spin in a location like this. It can cause all sorts of expletives & damage trying to get a screw out of a spinning riv-nut. Having more than one is twice the fun. Then all I did was duct tape the strips I had made in place and when I put the screws in it took about 15 minutes to install the entire lower strips screws. If you are paying to have this done by a shop though it is going to cost you. I takes some time to fit counter sink & contour the strips to fit and then install all of the nut plates. But the next time the window has to come out it will be an easy job.
I have installed Many windshields back in with rivets and with two experienced techs it takes less time than installing them with screws. I have installed many with screws because the holes were made to large by the owner drilling out the old rivets. I have installed many with screws at the owner’s request. I have installed the nut plate strips as described above on my plane and on my friends 172 TD because to us time spent on our own planes is no object.

Other issues for windshields are the LP AERO STD’d replacement with no center brace windshield. It comes with a different upper strip which has to be riveted in. The original window installation had no L bend retaining lip over the edge of the upper windshield. The original windshield just slid into the retaining strip. It depends on the center strip to hold the wind shield in. Later Cessna’s that had no center strip had a strip of Plexi-Glass bonded to the upper edge and an L shaped flange (Similar to that mentioned above) on the upper retainer strip that clips over it to retain the wind shield. I understand that other so called “one piece” windshield STC’s use screws drilled through the upper flange to retain the windshield when the center strap is removed. I have never installed one of these and have not seen one. This last is not a good Idea to my way of thinking as the windshields are designed to float around. This would make a good place for cracks to start. Also you find places where this no center strip installation is referred to as a one piece windshield. All of the windshields on the 170s are one piece. The center strip installation just has holes drilled through it which you are going to have to drill when you fit the center piece. Make sure you have the correct type of drill bit to drill the holes. A regular none plexi-glass drill bit will crack the plexi-glass. Drill the holes slightly larger than the screws being installed. Chamfer the holes after drilling them. A uni-bit works great.

There are articles written about these issues in the copy of the Cessna 170 maintenance related articles. Which I assume must be out of print because I do not see it advertised on the home page any more.

It would surprise most people to find out that the windshield is actually in a negative pressure area. And if not properly retained can be sucked out. I can not remember where I read an article about a guy that decided to fly with a slightly cracked wind shield and then was surprised that it cracked the rest of the way it during flight and was sucked out instead of being blow in.

We had a Cessna 152 aerobat loose its windshield during a spin and it was sucked out. It blew the cabin door off from the pressure in the cockpit after the windshield left the airplane. The plane was flown to a safe landing by the surprised student & instructor. The word from the instructor was that they got into a spiral dive and exceeded VNE.