Windscreen replacement

[Gary]

I have searched the Hanger forum looking for information on replacing my windscreen. All I find is the long post about a "dumb question" about the debate of straps or no straps. I purchased an LP Aero replacement windscreen at Oshkosh this year and it arrived last week. Does anyone have photos of their replacement process? I have questions about using screws or rivets on the lower retaining bracket and about what sealant to use that won't harm the glass. Does one have to completely remove the lower retaining bracket, or can it be partially removed? Some of the rivets there on my 170B have been replaced with screws, so it looks like the windscreen has been replaced in the past. I see from the AP Aero instructions that I will have to remove the top retaining bracket and install the new one provided by AP Aero. I plan to use rivets for this install. Maybe I'm just missing the info already on the forum, but I sure can't seem to find it. Any redirect would be very helpful. Gary

[Bruce Fenstermacher]

Gary, it's been about two years but I installed the LP Aero strapless windshield in my A. It's the same as a B.

Our lower bracket was already held in with screws and that is how we reinstalled it. We also used screws on the top bracket and I'm glad we didn't attempt rivets The screws were bad enough.

For sealant we used the LP green strip sealant that comes in a roll. We also used the felt supplied.

You will need to fit the windshield by trimming it at the wing root. Trim a little, fit it, trim a little more.

I can't recall what tool worked to trim the best. I have a small hand held air driven belt sander which I probably used to finish and probably a small die grinder with a 2" abrasive disc to cut it.

[c170b53]

Gary try different search terms such as windshield; plus other terms as windshield will return quite a few pages. ie windshield replacement. I know I've commented on the topic and I wasn't alone. Miles has a good story on his replacement with pics.

[Gary]

Thank you Bruce. I wonder why just some of my lower bracket are screwed in place. Seems that only about 6 or 7 on each side have been replaced with screws. I will start the project and will learn as I go along. Projects always seem like they are overwhelming before getting into it. I'm also replacing both door glass and rear seat glass. The pilots door window has had the hinge pins removed and replaced with fast pin's like the door hinges. So that side will be easy to remove the window. However, the copilots side has the original hinge pins. Looks like one or both ends of the hinges are crimped. How do I remove these? Guessing I would use pliers to undo the crimp and punch the pins out? Any leads on what gasket to use on edge of the door window glass or the seal to use to seal the closed window? Thanks for your response. Gary

[c170b53]

What you may find is on the cabin side, some brackets (to attach interior furnishings) are fastened by the same rivets which attach the lower windshield retaining strap. These may have been replaced and screws used in lieu of rivets. Then again maybe whomever removed the windshield before just couldn't handle a drill and now the holes are oversized.
Basically when working on planes most will adopt a standard practice when approved data is missing. Since there's no real maintenance manual for the 170, repairs likely will use standard practices as the basis of approval. What most do is what makes them feel comfortable and legal of course.
As an example I would use rivets where rivets were. Bruce chose to use screws as many have. I'm thinking (and I'm wrong most of the time) using screws at the bottom strap, no problem, screws at the top for the top retaining strap? Those screws will be attaching the top of the front carry through-spar cap fwd edge. So if you can find a structural 1/8" screw, great. It's something to think about when you tear into something.

"

[Bruce Fenstermacher]

Hard to undo the crimp on the those window hinges. You'll probably find you just need to carefully drive the pin out.

[Metal Master]

Gary,
Here is one windshield replacement topic.
http://www.cessna170.org/forums/viewtop ... =24&t=4526
I have replaced numerous Cessna single engine windshields. Installing rivets back in or using screws are both complicated due to access to the back side due to installed equipment the glove box etc. complicating the access and challenging the skill of the person on the inside bucking the rivets. Some may find jacking the tail easier on a tail dagger so the the bucker is more level while laying on their back. As commented in the attached post on my 170 it was less complicated because at the time I performed the operation the fire wall was removed. That being said. I used screws and nuts and nut plates as outlined below because it had already been done on my airplane before. (not the nut plate strips)

The only reason I replaced the windshield was due to it getting cracked during transport on the truck trailering the aircraft from Beegles Aircraft in Greeley Colorado back to Burien Washington.

Even though I used screws instead of installing riv-nuts which can spin after installation frustrating even the best of mechanics. Imagine getting most of the screws installed all of the sealant in and then having one of the last few Riv-nuts spin in its hole while installing the screw. Back off comes the retaining strip. Also with riv-nuts a much larger hole must be drilled into the skin to allow the installation of the Riv-nut.This is the way the factory installed the center windshield strip on AH-1G Cobras. Replacing one of those make installing a Cessna windshield look like a breeze.

I have in several installations and even on my 170A instead made aluminum strips (about six not one continuous strip) that I cut and curved to fit. Then installed regular aircraft nut plates on them on the work bench outside of the airplane. First getting the strip roughly cut to size and the clecoing it into place and finish drilling the holes. Then remove the strips to drill and fit the regular nut plates on the work bench. Then trim and finsh the edges of the strip. I did not use floating nut plates although it may be helpful. Then when installing the windshield all one has to do is hold the nut plate strip up and the person outside installs the screws.

I find that installing regular rivets back in the windshield lower strip much faster and easier than any other method and if working on a customer aircraft is my preferred method to keep costs down for the customer. However for future maintenance installing nut plates as I outlined here or just using screws and nuts makes it easier to remove and install the windshield if it ever comes to that. Guess how I know that. Drilling out the rivets from and an initial replacement windshield the debris of falling buck tails causes a big FOD mess be sure to locate all debris from drilled out buck tails. Using screws and nuts on a later removal and installation causes a similar FOD issue. Using the nut plate strips as I have outlined here removes about 90 percent of the FOD problem. The down side being labor to make the strips and the cost of the nut plates. The up side is that it is amazingly easy to remove and install the screws and nut plate strips once they are made.

Concerning the upper retaining strip the rivets between the door post are fairly easy to get to and buck and is the way I have always installed them. I have a lot of special bucking bars I have made to allow me to install rivets in the outer part of the windshield upper retaining strip but because of other fasteners in the area sometimes they will not even work and require removing the bolts through the wing attachment brackets through the carry through spar is an issue. So I have resorted to using screws and self locking Cherry rivets in the areas above the door posts. There is often an issue directly above the flanges of the outboard door post bracket complicating any method be it screws rivets or Blind rivets. Be careful drilling out fasteners in the area because it is easy to make drill marks in the structure below the retaining strip if you run the drill in to far. Any way you choose they are much easier job when the wings and fire wall are not installed. I am sure you would not want to do that just to remove the windshield. But just thinks of the opportunities you would have to fix other things you would find.

A final note after getting the windshield finally fit and cut to size be sure to polish the edges. I have seen many windshields propagate cracks from the rough edge left by the installer.

[c170b53]

That last post pretty much nails it and the more you have things apart the easier it is to do the work but the creation of less work is something to think about when you're trying to buck in a tight spot and other thoughts come ro mind

[Gary]

Medal Master, thanks for the information. Sounds like the nut plate strips is the ticket. What kind of nut plates did you use, and how are they attached to the strips? Flush rivets? I'm going to the plane today and will look long and hard under the panel for access to the back side of the forward retaining stip. To my understanding, the new retaining strip at the top is installed before the new windscreen goes in. So can't a rivet squeezer be used for most of those rivets?

[n2582d]

Medal Master, thanks for the information. Sounds like the nut plate strips is the ticket. What kind of nut plates did you use, and how are they attached to the strips? Flush rivets? ...

I installed MS21047-06 nutplates to my boot cowl with NAS1097AD3 rivets. They have a reduced size head which works great for attaching to thin sheet metal. Great idea to fabricate nutplate strips. Wish I would of thought of that ...

The floating nutplates are MS21059-06.

[Metal Master]

Medal Master, thanks for the information. Sounds like the nut plate strips is the ticket. What kind of nut plates did you use, and how are they attached to the strips? Flush rivets? I'm going to the plane today and will look long and hard under the panel for access to the back side of the forward retaining stip. To my understanding, the new retaining strip at the top is installed before the new windscreen goes in. So can't a rivet squeezer be used for most of those rivets?

Gary,
It is Metal Master no medals included. Which is another story. I was under the instrument panel today re-routing the gyro plumbing from the venturi to the newly installed vacuum regulator. And I used both fixed non floating nut plates and floating nut plates. So much for memory I did this back about 2004. I used 6-32 nut plates like this: http://www.aircraftspruce.com/catalog/h ... ckkey=4515 and floating 6-32 nut plates like this: http://www.aircraftspruce.com/catalog/h ... ckkey=4515 I used 2024 T-3 .032 alclad aluminum to make the strips. I riveted them on with AN426 AD 3- what ever rivets countersinking the .032 aluminum strips. And I installed the windshield strip with stainless steel screws.
Regards,
Jim

[cessna170bdriver]

Hi Gary, I'm the Miles that Jim McIntosh referred to earlier. Here's the thread I posted when I replaced my windshield 5-6 years ago.

http://cessna170.org/forums/viewtopic.php?f=24&t=7897

[c170b53]

I took the windsheild out of my 172 xp today and thought about this post again. The XP m/m says you can remove the window by drilling out the bottom strip and if you have to by drilling out the rivets along the top of the center cabin roof. It also says and is specific, the rivets can be replaced with number six screws along the bottom but then unfortunately it's a bit vague about the specification of the top fastner replacement.
The collective hangar thoughts around this airport are install window with screws all around. So looking at the top of the window, I decided to explore the other side of " if you have to" as I didn't want to drill out the rivets. Well it's not that hard to extract the window without drilling the top (this method works best with a wing off). Using a strip of .032 inch bent 90 degrees, from one side of the cabin, the metal strip is tapped across the window inside top doubler, across the cabin which deflects the top retaining strap, allowing the window to be pushed out. Pretty simple, so I hope the new one goes back in (I know it will be a fight) with minimal blood loss.
The window had been installed from the factory with felt strips on the edges and sealed in place with a pliable sealant. The sealant, 36 years old now has the consistency of warm putty and has remained fairly sticky.
To sum up if your replacing your window, a stock window has vertical metal exterior and interior retaining straps in the center of the window which led to it being referred to as the two piece window (a one piece with holes in the center for the straps to be secured together). The original windows are positioned at the cabin tops by a metal strip which forms a U- channel. On replacement the window just slides in to the channel at the top and the vertical straps hold it in place.
If your planning on replacing your window with a STC'd aka" one piece" window then the top U-channel strip is removed and a retaining strip (supplied with the new window) must be fastened to the top of the cabin. The new top retaining strip which takes the place of the old vertical retaining straps, holds the window in place with a formed hook edge. The new window at the top inside surface will have a 1" wide plastic doubler strip which the the hook grabs and prevents the window from being liberated. To attach the new hook retaining strip, the forward rivet row of the forward center carry through spar cap must be drilled out. Many are using screws to attach the parts together but rivets can also be used.
If you have a STC'd window installed and you need to replace the window again, then I would use the metal strip technique to remove the window if it's retainer is riveted in place. Likely with effort, the metal strip could be made into sections and tapped into place inside the cabin if the wings are installed.

[bat443]

I have replaced a windshield with a one piece from Great Lakes Aero Products, Inc, it uses the original top retainer strip but adds 4 screws at the top. Different STC's use different methods when replacing the center retaining strip. I only had to remove the lower strip and of course the center strip.

Tim

[c170b53]

I left that out as I didn't think it popular as they say " my bad". I had a look at their website and that method, is the window thicker? I've also helped long ago install a window that used 4 plexi screws (large diameter) from the inside top to hold the window. Maybe that's the same window as yours but I thought that method also used a hook strip. So your right there are other ways's to do it. I do like the LP product for fit but fit also is influenced by the cabin I guess.