Replacing or Repairing Broken Windshield Center Strap C170B

[dsyoung]

We have a broken windshield center strap, C170B. Looking for a recommendation on where a replacement strap could be ordered from or a repair solution.

[Bruce Fenstermacher]

Many of these are broken and have been repaired. Most of them I've seen break at the top. The purpose of the strap is to actually hold the windshield in at the top where it is riveted to the fuselage.

You might be extremely lucky to find a good one removed for a "one piece" windshield installation. But your looking for a needle in a hay stack. Your better bet is to find some like material and have a new strap fabricated. Or you could find some suitable material and rivet a patch over the end off your old strap and then attach the new piece to the fuselage with the screws.

[GAHorn]

Place a short doubler on top/over the break. Make it long enough to include the two lower holes and the first hole encountered at the lower portion of the windshield. No need even to rivet the doubler to the piece beneath.... let the screws do the work.

Trying to match all the holes with another part off a salvage airplane is likely impossible.

[Bruce Fenstermacher]

I like Georges idea. If you riveted, they would have to be flush underneath requiring the removal of all the screws to lift the strap far enough to cut the relief for the rivet head.

[dsyoung]

Thank you Bruce and George for your recommendations.
--Dave Young

[c170b53]

Well trying to be positive here, so I think it would be very easy to fabricate a new one for a tin man or not hard for someone with access to a shear, metal and a little oversight. At issue here is, it appears there’s near zero edge margin coupled with countersunk screws in a fairly thin piece. That’s a sign and not a very good one. The overall hardware doesn’t look too happy and seeing countersunk screws on the lower window outer retaining strap, well you could reason the use of countersinks and the parts involved are considered non airworthiness items but whomever did that lets hope they didn’t have a significant amount of touch time with your plane. In maintenance practices there should always be good, better and best approaches, in my opinion that mark has been missed here.

[c170b53]

Dave I should have welcomed you to the forums and to the association. I think this is your first thread, Is the plane new to you ?

[Kyle]

Hi Dave,

I have one in perfect shape. you can have it if you wish for the cost of shipping it to you from Cape Cod. let me know.

Kyle T.

[c170b53]

Here’s the one removed 22 years ago from my plane. I’ve always been told the outside strap’s purpose and haven’t really given much thought to it until this thread. It’s .025, real light with a single fastener on the top, two at the bottom. Hard to image that it would retain the window, if the window really wanted out. Certainly the airframe and window would have to flex a fair amount for the window to depart. Also consider the window to wing fairings on the top which would also resist the window’s escape attempt.
The inside retainer is much heavier, just a guess but I’d say .200-.250 thick and heavy in comparison to the outside strap. The inside vertical strap gives the window considerable strength against air pressure induced window flex and limiting impact damage, such as a bird strike. So I think the outside strap is used more to fasten the inside strap to the window than to hold the window in although I guess it’s one fastener doesn’t hurt.

[ghostflyer]

Having holes drilled through the windscreen and screws under tension would be a weak point or stress area for a windscreen crack , for When a bird strike happens. I have a no strap and a thicker windscreen and have hit a couple of birds or their remains And that windscreen really flexes when hit . That bang is over before you can think and all you have a white dust from the birds feathers all over the screen. I have hit 2 pelicans and a ibus . One hit the windscreen missed the prop ??? How?? The other hit the lower cowl and then the undercarriage leg [a bit of a messs] . The ibus hit the horizontal stab and elevator horn jamming the controls for a little while . Having no strap gives a great view .
Ps. Our runway is right on the coast and has salt water canals running down both sides of the runway . Full of bird life and fish.

[cessna170bdriver]

...I have hit 2 pelicans and a ibus . One hit the windscreen missed the prop ??? How?? ...

Pardon the off topic, but “how” is that a 170 with a two-blade propeller flying at 120mph at 2450rpm advances nearly 27 inches between blade passes. I’ve seen a balloon pass through my propeller disk unscathed. It’s just a matter of timing.

[c170b53]

Ps. Our runway is right on the coast and has salt water canals running down both sides of the runway . Full of bird life and fish.

I’m holding out hope to hear something about the fish .
Hanger neighbour had a bird strike two weeks ago at night which damaged (172L) his fibreglass nose bowl, he didn’t mention the prop.

[MoonlightVFR]

Could this broken strap just be welded by a skilled mechanic?

[DaveF]

2024 aluminum is not considered a weldable alloy. Seems like it would be a lot easier to fabricate a new strap. It's not that complicated.

[GAHorn]

AND... it would have to be removed for welding (might as well fabricate/replace it).... AND welding (IF it was a weldable alloy which it is not) would created a heat-spot stress point and likely embrittle it.

Don’t make this simple repair complicated. Either fabricate a doubler or fabricate a replacement.