Windshield installation questions

[Bruce Fenstermacher]

Getting close to installing a new windshield in my 170A. We decided to go with Lp Aero "One Piece" windshield which requires a new top lip to catch and hold the windshield.

The LP installation instructions say to use felt AND sealing compound or sealing tape on ALL edges of the windshield. I bought the LP recommended Cessna (Presstite) No. 579.6. The instructions say to refer to fig. 2 of the LP instructions which is the same essentially found in the Cessna '62 and Prior Service Manual. The Service Manual (which of course is trumped in my case by the LP STC'd installation instructions) shows the use of felt and calls for the use of sealer (Presstite or C-1202 Tape (10) ) on all edges where felt is used.

Here is my problem none of the figures shows where to put the sealer. It is not pictured at all. The instructions just say to use it everywhere the felt is used.

I've looked at Mile's window install pictures a few times and I see he used the (green) Presstite sealer on the bottom strip on the inside and out but unless I'm misstaken Mile's didn't use sealer other than the felt on the side and top. Mile's didn't install a LP Aero shield but for all intent and purpose as far as sealing goes they are the same in the use of felt and or sealer.

I just can't really figure out how one uses both the felt and sealer on the same window edge as called out int the LP instructions and the Service Manual.

How have others done it?
Do you put the sealer over the felt?

All the instructions call for sealer (in addition to felt) on the sides AND the top. I always thought the top of our Cessna windshields needed to float. They certainly will float inside just the felt but if you also use sealer well, I'm afraid the windshield with be pretty much stuck in place and not float.

I will most likely call LP for their guidance but I'm just wondering exactly how others have installed their windshields lately.

[c170b53]

I installed this window but its been too long to remember exactly what I did. I did follow the instructions and used the felt and sealant that you've mentioned. I believe I used the sealant sparingly and I have not had water problems. The top retaining strip is a pain and although I re-riveted the bottom retaining strap, I'd use screws and nuts next time.

[Bruce Fenstermacher]

But Jim I must be missing something. Do you put the sealant ON the felt? It doesn't appear from the illustrations one can do otherwise. Which begs the question, why use the felt at all?

Our window was already replaced 10 years ago and the bottom lip held on with screws and that is how this one will go in. As for the new retainer on the top we will see how hard it is to squeeze the rivets. If to difficult we will use screws there as well as allowed and mentioned by the instructions.

[c170b53]

Thks, your right, I believe the felt acts as the cushion so I used more felt when there was space and less where its tight and I used the sealant to seal the edges but did not cover the felt in sealant only the edges of the felt that are on the weather side. I used rivets, I've seen screws on the top but I don't think it was the norm when I did it. That top is the front spar cap so I couldn't find structural screws at the time maybe something is available now. That top strip will test your patience.

[Bruce Fenstermacher]

Jim, as for the screws used for the top retainer which is held in place with the rivets for the from spar cap, the instructions call for MS 35218-28 screws or equivalent to be used instead of rivets if desired. The MS35218-28 is an aluminum 6/32 screw and are expensive. I thought I might substitue a AN stainless 6/32 as it would be stronger.

I guess I need a picture. If you use felt and sealant aren't you defeating the purpose of the felt?

[KS170A]

Must be time for windshield replacements...I am also replacing mine with the LP Aero unit and going through the same screw problem. The STC instructions do state "or equivalent hardware" so I'm looking at the MS35206-231 screws (same length & diameter). Yingling Aviation lists them on their web site at $0.06 a piece, minimum of 100. Felt all the way around, sealer along the bottom strip. Be sure to seal both sides around the screws so no water leaks through the screw holes. Removed my old one today, will fit the new one tomorrow, hopefully fly this weekend.

[c170b53]

I think the sealant remains somewhat gooey, when I get to my hangar next Monday I'll check as I think I still have a half tube of that sealant. I suspect it will still be pliable.

[Bruce Fenstermacher]

Must be time for windshield replacements...I am also replacing mine with the LP Aero unit and going through the same screw problem. The STC instructions do state "or equivalent hardware" so I'm looking at the MS35206-231 screws (same length & diameter). Yingling Aviation lists them on their web site at $0.06 a piece, minimum of 100.

Well you will need 48 screws if your plane has the same amount of rivets that my plane has. You'll probably drop a few so @ $6 your probably OK.

Felt all the way around, sealer along the bottom strip. Be sure to seal both sides around the screws so no water leaks through the screw holes. Removed my old one today, will fit the new one tomorrow, hopefully fly this weekend.

The placement of felt verses sealer or both may become obvious when I can finally get around to changing out this windshield and look at it closer first hand.

[Bruce Fenstermacher]

Jim the Cessna (Presstite) No. 579.6 is a tape like product not a liquid form in a tube. This is maybe why I'm so perplexed why one would put on both felt and sealer in the same place. Of course the felt won't seal like the sealer will but felt will allow some give give but the sealer not so much.

[c170b53]

Sorry to mislead you Bruce but what I used was a windsheild sealant recommended and sold at the Cessna dealership here in YVR. I thought we were talking about the same stuff but obviously we're not. So I went into my records and found the bill from Cessna for PRC sealant from June 99. This stuff is dispensed from a caulking gun that you'd use around the house. It's a single stage sealant that didn't seem to cure hard but rather was soft. When I get a chance I'll go to the hangar and ID the stuff.

[Bruce Fenstermacher]

Jim, the Cessna Service Manual lists another product as well as the Presstite green seal tape I've meantioned. While they don't say it in the specific installation instructions in LP Aero's catelog, they recommend a few different sealants for sealing windows including 100% Silicone. So clearly there are several that are exceptable and work well depending on if your talking to brand X window company or brand Y airplane manufacturer.

[KS170A]

The stuff ("sealer") I have is, for lack of a better metaphor, like string putty almost. It's not PRC or the sealer that Jim mentioned. It's rolled up just like "tape" would be, then you unroll it to apply it to the airframe. I'll take a picture or two when I'm at the hangar today. And yes, it should become more obvious when you start the project!

[GAHorn]

Be very suspicious of any recommendations to use RTV or "silicone" type sealants on winshields or plexiglas/acrylics.

Most RTV type products emit ammonia while they cure, and most everyone knows that ammonia will embrittle and craze plexiglas. Dont even use the stuff near a window, is my recommendation.

Bruce, I cannot confirm this because of lack of response, but I seem to recall that the Presstite tape is applied to the window edge, then the felt is overlaid that to allow the entire assy to shift within the framework. The felt "wicks" moisture away from the seam.

Unfortunately, if used alone, the felt may allow driven-rain to bubble through the seams into the cockpit when flying in heavy rain..... and the sealants, if used alone, may contribute to cracking of the plexi as the airframe distorts during rough-filed operations.

I'll try to get my factory contact to give us an answer, but I'm not having luck with my old Cessna respondant.

[FredMa]

The putty type tape you are talking about is called BUTYL tape. It is widely used on campers and R.V.s to install windows onto the aluminum siding of R.V.s. It looks just like what came with my CeeBailey window. It is available from Lowes and Home Depot for around $5 a roll.

[GAHorn]

Piper uses zinc chromate putty.
http://www.emedco.info/rtk/common/wcd00038/wcd0389d.htm