Frameless windshield

[gobrien]

Attached are photos of N4180V's windshield. There is no STC or 337 in her paperwork. There are no through bolts in this so I'm assuming/hoping this is the LP Aero STC. Can anyone confirm or deny?

Thanks

Gareth

[n2582d]

Gareth,
Although from the photo it’s hard to tell, I don’t see a bonded doubler attached to the top of your windshield. Here’s a screenshot from LP Aero’s website:

Click to Enlarge

My C-170B strapless windshield STC is SA3548NM from Del-Air. It uses a Cee Bailey windshield. Cee Bailey makes a windshield for the ‘48 but it appears they only offer the strapless STC for the170A and 170B. LP Aero, and Del Air also only offer a strapless STC for the A and B models. The only ones that I find that offers a strapless STC for the ‘48 is Great Lakes Aero Products and Jack Shannon’s STC — probably orphaned.

[gobrien]

Thanks Gary,

I had a look at that picture and hoped I was missing something. However ...

I have put a video online. It is a bit hard (motion sickness warning). It's from a tiny endoscope camera looking into the channel that the top of the windshield floats in. https://youtu.be/UjeLAgmA57A

It looks like the windshield is drilled with the 4 holes of the GLA (http://www.glapinc.com/instructions/index.htm#cessna) STC but there are no holes in the fuselage and no bolts through the windshield. Half the felt has fallen out.

Engineering-wise: 1. It's clearly been like this for years w/o problem. 2. I struggle to see what situation would cause the top of the windshield top to be forced forward against the airflow and pop out.

However, I'll be pulling it, at the very least to put new felt in.

Anything to watch out for while doing this? Has anyone done it or watched an A&P do a windshield removal and replacement especially with the GLA STC?

Thanks,

Gareth.

[n2582d]

... Engineering-wise: 1. It's clearly been like this for years w/o problem. 2. I struggle to see what situation would cause the top of the windshield top to be forced forward against the airflow and pop out. ...

Years ago I applied for a field approval to install a skylight on a BF12-65 Taylorcraft. The Designated Engineering Representative (DER) required a push test using a jack on a scale. I no longer remember how much pressure was required to pass the test but I do recall being quite nervous whether it would pass the test. It was a lot of pressure. I too wonder how the windshield could pop out of it's slot but apparently there is a lot of low pressure created there. In fact, back in 1947 Cessna had an issue with this very thing on the 120 and 140. Ya gotta love the way Cessna downplays the seriousness of this in their Service News Letter 7: "This condition will cause tail buffeting, and although it has never caused any serious trouble, it does cause a few moments of discomfort to the pilot concerned." This issue was serious enough that the FAA issued AD 46-44-03.

Service News Letter 7, Page 1 (Click twice to Enlarge)

Service News Letter 7, Page 2 (Click twice to Enlarge)

... Anything to watch out for while doing this? Has anyone done it or watched an A&P do a windshield removal and replacement especially with the GLA STC? ... .

I'd review Chapter 3, section 3 and 4 of AC 43.13-1B. Most of the windshield manufacturers also have advice on their websites: Cee Bailey, Great Lakes, Airplane Plastics, LP Aero.

[cessna170bdriver]

Cessna 170 cockpits are slightly pressurized in flight. If a windshield fails, it will go out forward. Before I converted to a strapless windshield years ago, I found a cracked strap bracket on mine when I noticed that my windshield rode about 1/8 inch further forward along the top in flight than it did on the ground. The only thing holding it in were the wing root fairings.

[ghostflyer]

I have fitted a new windscreen to mine a few years ago but do recall it was a thick one due to the affinity of me and bird strikes. Can’t remember the brand name but the top of the windscreen had 4 holes in it drilled by the manufacturer. However in each of these holes was a clear soft plastic plug with a hole drilled into it. The supplied screws and nuts fitted through these holes so the windscreen could move around . Plus a large tube of grease [brown in color] was supplied to be coating the new felt. However on top of the out side of the windscreen where the plastic and lip of the forward spar meet has been faired with the correct silastic . The silastic is smoothed on about 1.5 in down the windscreen and faired with top of the fuselage .
The reason being when flying through a tropical rain storm I used to get soaked from water in gestation from where the windscreen met the fuselage. However also with the silastic fairing I totally believe it aids in aerodynamic fairing. There is less noise and aircraft feels smoother when flying. NO I am not smoking those funny cigarettes.