Outer Windshield Center Strip

How to keep the Cessna 170 flying and airworthy.

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dstates
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Outer Windshield Center Strip

Post by dstates »

I’m in the process of replacing the windshield of my 170A with an original style windshield (not the STC, I’ve already purchased the windshield so no need to talk me into the STC versions). I have found I need to make a new outer center strip (PN 0510000-23). The center strip that was on my plane looks like it was previously repaired. I’m making an assumption that the original center strip was one piece. Can anyone verify this?

Here is the strip I removed. It has a second short piece at the top that looks to be spot welded to the long piece. The long piece has had two cracks in the corners stop drilled. The short piece now has small cracks in the corners as well. I will round the corners more on the piece I make. Do I just make a one piece center strip or does it need the doubler at the top?

Thanks, Doug
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N1235D - 1951 170A - SN: 20118
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GAHorn
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Re: Outer Windshield Center Strip

Post by GAHorn »

All three models IPCs seem to show a multi-piece strap. However, my own “restored” airplane has a one-piece strap. Hope that helps. :roll:
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dstates
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Re: Outer Windshield Center Strip

Post by dstates »

GAHorn wrote:All three models IPCs seem to show a multi-piece strap. However, my own “restored” airplane has a one-piece strap. Hope that helps. :roll:
George, I saw that line at the top of the parts catalog image as well. The spot welding makes me think it is original, but found it odd that the cracks on the bottom (invisible when installed) were stop drilled. I guess they might have stop drilled through just one sheet and hoped to stop before going too deep. It is hard to tell.
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Bruce Fenstermacher
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Re: Outer Windshield Center Strip

Post by Bruce Fenstermacher »

Doug, it is very difficult, maybe impossible, to find a shop and/or person with the tools and knowledge to spot weld anything let alone the material of that strap. So I'd say yours is not a repair. And I doubt you'll be able to have it repaired by spot welding.

I would make a new top piece and flush rivet rather that spot welt it together. Of course the flush side will have to be down so you will see the shop head. I don't think that to intrusive.
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Re: Outer Windshield Center Strip

Post by dstates »

Bruce Fenstermacher wrote:Doug, it is very difficult, maybe impossible, to find a shop and/or person with the tools and knowledge to spot weld anything let alone the material of that strap. So I'd say yours is not a repair. And I doubt you'll be able to have it repaired by spot welding.

I would make a new top piece and flush rivet rather that spot welt it together. Of course the flush side will have to be down so you will see the shop head. I don't think that to intrusive.
Bruce,

I was thinking that might have to be my plan. I’m not excited about the looks of shop heads being visible. Maybe I can find one from someone who has switched to the thicker window.

Doug
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Re: Outer Windshield Center Strip

Post by edbooth »

dstates wrote:
Bruce Fenstermacher wrote:Doug, it is very difficult, maybe impossible, to find a shop and/or person with the tools and knowledge to spot weld anything let alone the material of that strap. So I'd say yours is not a repair. And I doubt you'll be able to have it repaired by spot welding.

I would make a new top piece and flush rivet rather that spot welt it together. Of course the flush side will have to be down so you will see the shop head. I don't think that to intrusive.
Bruce,

I was thinking that might have to be my plan. I’m not excited about the looks of shop heads being visible. Maybe I can find one from someone who has switched to the thicker window.

Doug
Hi guys, it’s been my experience over more years than I can count, that with most of the 170s out there this strip is either broken or has been repaired and/or replaced. Because the windshield just kinda floats around due to temp variations, vibration and movement during landings and taxi, that solid attachment at the top is going to break sooner or later. With the thicker windshield STC eliminating this center strip, there are usually four screws going through enlarged holes at the top of the new windshield so it can float around in the channel and still do the job of securing the windshield from popping out. I have replaced several windshields over the years, and they would probably not pop out even with that strap broken, but it’s just another precaution……. Just my two cents.
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Re: Outer Windshield Center Strip

Post by c170b53 »

I’m in Ed’s camp. Obviously the IPC is an artist’s rendition of what could be there. Maybe countersink both rivet hole ends and use 3/32 “ if you desire to have a flush look on your doubler. Are you going to keeping the mast support or deleting it ? Prior to going to a strapless window my plane had a non original single piece strap which had seen many years of service. I would repair it in a fashion that would make you happy as your solution likely will last for sometime.
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Re: Outer Windshield Center Strip

Post by hilltop170 »

Doug-
My 170 had a one-piece T-shaped top strap that overlapped the straight windshield strap and attached to the top windshield strap screw and front and back side of the spar carry-thru hat channel. No hidden rivets or spot welds.

That was all removed as well as the ADF sense antenna mast support bracket when the new windshield was installed without the center strap.

Since you're not using an STC, you could always add the 4 additional fasteners of the STC on top of the windshield just for insurance.

Use a thicker grade of material for the new T-strap and make the fillet radius as large as possible in the new T-strap. I would use countersunk rivets with the heads against the windshield and the upsets up but that is just me. Hard to see on top of the wing from the ground and parasitic drag at 100 knots is negligible. :wink:

Or, just let the top windshield attach screw carry the load by itself without any other rivets between the windshield strap and new T-strap since it is backed-up by the inside strap as well as the outside strap.
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Re: Outer Windshield Center Strip

Post by Karl Towle »

I've not had a lot of experience with this strap, but of the two I've thrown away, both had cracks to varying degrees.

I'm not a fan of drilling holes in windshields if I don't have to. I know it's a pain to accomplish, but the locking strip Cessna came up with really holds the top of the windshield in. You're going to be drilling out 52 (as I recall) rivets. You'll either be setting the same number, or replacing them with #6 screws, washers & locking nuts. But, if done right, that windshield will not come out, and it can still wiggle around some.

For the legal minds out there, I'm guessing you either go back in with a center strap (and the principle of owner produced parts applies) or you go with one of the two STC concepts out there. I'm also guessing any mixing of the three methods would place one in a legal quandary? BTW, thinking about the rivet question, has anyone tried forming the shop head of a flush rivet, with a round-head rivet set? I'm wondering if you could create anything that looked like a normal rivet head opposite the flush head. I'll have to try this one myself.
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Re: Outer Windshield Center Strip

Post by dstates »

Karl,

Unfortunately (or maybe fortunately) I’m no longer in need of a center strap. After I was all done trimming and drilling my new windshield and making a new center strap I went to pick up my new windshield to move it 3 inches closer to the right position and it cracked at my hand. It didn’t crack at a hole and I hadn’t even trimmed the side that cracked. After dealing with the center strap and getting everything to line up I decided to go with the STC for the thicker windshield and the later model Cessna retention piece at the top. LP Aero was super about it and did give me a discount on the second windshield I ordered from them. I’m hoping that a thicker part, warmer temps and being smarter about how I pick it up will lead to a successful install in the future. I now have another 4 weeks to procure a compass to mount on my glare shield.

I also now have to decide if I’m going to rivet the retention piece in place or use #6 screws (per the STC and also per the 172 service manual). If I rivet it, I would likely try to do that after fitting and trimming the windshield, but before the final install of the windshield. I’m hoping it wouldn’t be to difficult to pry the retention piece down to get the lip of the windshield past it.

Doug
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Bruce Fenstermacher
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Re: Outer Windshield Center Strip

Post by Bruce Fenstermacher »

Doug, we did the screws. Don't recall it being a problem slipping the plexi into place. I always liked the look of the center strap and never considered it to block my vision. I was shocked how nice it was not having it and never looked back.
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Re: Outer Windshield Center Strip

Post by dstates »

Bruce Fenstermacher wrote:Doug, we did the screws. Don't recall it being a problem slipping the plexi into place. I always liked the look of the center strap and never considered it to block my vision. I was shocked how nice it was not having it and never looked back.

Bruce,

I'm assuming that with the screws on the LP Aero STC windshield that you can put the retaining strip in after the windshield is in place. That should make it much easier than if you rivet the top retaining strip before the windshield is in place. Good to hear someone else has used screws, as I am considering it. I'll probably decide by putting the top strip in place with clecos to simulate it being riveted and see how difficult that is. I don't want to rivet it in with the windshield in place. It makes me nervous that I'd end up buying a third windshield and losing yet another month.
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Re: Outer Windshield Center Strip

Post by c170b53 »

I’ve done it both ways Doug. When I did it on the B, I riveted after everything was in place. It was not hard, maybe tedious due to taking care not to damage the glass and only difficult around the spots where there’s a proud metal lip from the side posts preventing perfect positioning on the bucking bar. The option to use screws to secure the retaining strip and close the centre section spar was not an option when I did mine and I’m much happier with rivets but that’s just me. I replaced the window on my xp (I regretfully no longer own), where the stock window is held in place with the same style retaining strip. So I didn’t have to drill out and replace rivets, I broke out the old window and pulled the window doubler retaining strips out from the sides. I then put a slight bevel on the new window aft trailing lower edge of the doubler windows strip and pushed the window aft into place. Only problem with doing this is the metal retaining strip is bent past its yield point and the metal retainer will not fully return to its original shape. Yes it will retain the window but its not perfect, and most of the time we like perfect :D .
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Re: Outer Windshield Center Strip

Post by dstates »

c170b53 wrote:I’ve done it both ways Doug. When I did it on the B, I riveted after everything was in place. It was not hard, maybe tedious due to taking care not to damage the glass and only difficult around the spots where there’s a proud metal lip from the side posts preventing perfect positioning on the bucking bar. The option to use screws to secure the retaining strip and close the centre section spar was not an option when I did mine and I’m much happier with rivets but that’s just me. I replaced the window on my xp (I regretfully no longer own), the stock window is held in place with the same style retaining strip. So I didn’t have to drill out and replace rivets, I broke out the old window and pulled the window doubler retaining strips out from the sides. I then put a slight bevel on the new window aft trailing lower edge of the doubler windows strip and pushed the window aft into place. Only problem with doing this is the metal retaining strip is bent past its yield point and the metal retainer will not fully return to its original shape. Yes it will retain the window but its not perfect, and most of the time we like perfect :D .
Jim,
That is the exact feedback I was looking for. Thanks!
Doug
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Re: Outer Windshield Center Strip

Post by Karl Towle »

Doug,

I went with the rivet option - originality and all - you know. Here is a way to do it and retain your sanity. Get yourself a decent number of Cleco clamps that have the wing-nuts on top; so you can pull the layers up nice and tight. At least 20 would be best. Trim and fit the windshield so it is ready to be installed. Now, with the windshield out of the airplane, Cleco the locking strip in place. Next, examine the holes out at the wing root ends, and drive the rivets that would be nearly impossible to get to once the windshield is installed. My recollection is you'll have about 4 on each side. Now, loosen the remaining Clecos, and cut some .016 aluminum strips to use for ramps to open the ends of the locking strip while you pull your windshield into place (or bevel the aft bottom edge as Jim did). If you need more persuasion, a cargo strap over the windshield, and back to the aft spar attach point can be used (connect the hooks to a rope loop tied around the aft end of the bolt/nut.) With the .016" ramp, the locking strip should flex enough to allow the windshield to snap into place. Now, tighten the wing-nut Clecos in every other hole, and start driving rivets in between. The remaining rivets should be easy to access. When you're done it will look like original. BTW, be prepared to put a slight bend in your trim piece that covers the front of the spar carry-through, to make up for the increased thickness of windshield/locking strip combination.
170CompassMount.jpg
Here's a picture of what I did with my compass (before I painted it). It's a fabricated bracket, that fits up against the trim strip along the front side of the carry-through. I took out the center push pin and installed a #10 riv-nut. I made a short stud out of a 10-32 brass screw, and threaded an acorn type nut with red Locktite on one end. The Pegasus Panel Mount compass is made mostly of plastic, so it is very light weight. The internal light is grounded under the #10 screw, and powered by a single #20 wire hidden behind the trim strip. The drum with the numbers is actually angled in such a way as to make it very easy to view from below. You'll note in the picture I made this mod before I changed out the windshield. It has served quite well for years.
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