I have a question that has been bothering me for some time. I am need of replacing the windshield on a 172K. I have seen other 172's after they are done and they have removed the strip at the base of the windshield. They have been re-attached by using screws or rivnuts.
I talked to another 172 owner recently who said he replaced the windshield without removing the strip. He has the Cessna service manual and apparently it describes the procedure for replacing the windshield by popping out the old, trimming the replacement and popping in the new window. I wonder when the aircraft was new if the windshield was popped into place or was the bottom strip rivetted afterward?
If the windshield is popped into place is there more of a chance that it would leak??? Any information would be appreciated.
Ron,
I am highly suspicious of anyone who claims that the windshield can be replaced with out removing the bottom trim as that is the clamp that holds the windshield in. if that is in fact possible I would really like to have him come to my shop and demonstrate it as it might save me some time on the next one.
the best way to reattach the clamp is with the same AD rivits that the factory used when installing it at the time of assembly Kansas. however due to the lack of accessibility to the underside of the fuselage in that area in most airplanes it is acceptable to use alternate methods. screws and nuts are commonly used by persons not comfortable or experienced in riviting but again you still have the problem of access to the back side. the easiest way is using cherry max rivits. I dont recommend the use of rivnuts as they arent considered to be adequate for structual use and the windshield clamp is an important part of the structure. consider what would happen if the rivnuts pulled loose inflight. the other problem using rivnuts would likely cause is water and air leaks.
when I get to work on Monday I will try to remember to look up the replacement instructions and see what is said.
mark
Clay,
nutplates are a great idea and one that I personally wish Cessna would have thought of. Piper uses nutplates on their windshield clamps.
the installation of nutplates however runs into the accessibility issues previously discussed. if its something that a person really wants to undertake it is recommended that it be done when the airplane is undergoing a complete rebuild or when the entire instrument group is being upgraded/replaced. you wouldnt necessairly need to remove the windshield to install the nutplates.
mark
I did some more research on the pop out and in windshield replacement. The plane in question is a 172N. The replacement windshield came from Leavens Bros. in Toronto and it was the standard thickness and manufactured by Great Lakes Plastics.
I have a photocopy of the page from the Cessna service manual that describes how to remove and re-install without drilling out the bottom strip. Removal is done by two people pushing out the old with their feet from the inside. The new one is trimmed to be the same as the old. The windshield has the felt applied to the edges and put in the bottom track. It is started into the side tracks and then popped into the top. Cessna describes making a tool out of sheet metal to "shoe horn" the windscreen in at the top.
The person I know says that changing the front windshield was easier than doing the sides or the rear. I don't think the method would work with a thicker windscreen.
I wonder how Cessna installed the windscreen originally. I would bet that they used this method on the assembly line since it sounds fast if done correctly.
Regardless I am going to give it a try when I do a paint and plastic replacement on my plane.
I'm currently replacing the windshield in my C150L. The manual says the original rivets can be drilled out and replaced with nuts and screws--with regard to the clamp. It took two of us about 2 hours to remove the last installed screws and nuts...I laid on the floor and worked looking up. Removal of the turn coordinator and the glove box made access to the nuts fairly simple.
About the windshield--I don't think popping the windshield in is a sound solution. With my clamp removed I'm still having trouble getting the newly trimmed unit to fit well and it is taking trial and error fitting. I can't imagine popping it in and having to take it out again to do more trimming for proper fit. I made a paper duplicate of the old unit and trimmed the new unit to old size. One friend said using a towel wrapped across the windshield with one person at each end and pulling would help to get the windshield to insert completely on the sides and top. This is with the clamp off--if anyone knows why it won't simply slide in - I'd appreaciate some advise. I believe the problem is the seal I'm using--zinc chromate putty is what was removed, nobody sells it anymore and the seal I have now isn't as pliable as the old putty.
hey, im near toronto.. and have a '74 206 that needs a new windshield.. would you pass my message along to the guy that just "pops" them in and ill get him to come and do mine!!
thanks
