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Film on windshield after flying through light precip


DXB

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Something odd happened during my IPC today. My windshield appeared clean when we started.  We had a brief encounter with light rain, and a white hazy film remained on the windshield in the streaking pattern of the moisture  as it dried.  It was bad enough to mildly impair forward visibility.   I wondered if it was a little oil on the windshield, but it was not oily to touch.  We landed and found no oil on the cowl or evidence of a leak under the cowl.  I cleaned off the windshield with Zepp foaming cleaner (the only cleaner I have ever used, same I use it after every flight).  We entered rain briefly again on the next short leg and the same thing happened.  My instructor  has decades of experience and had seen nothing like it. Back at the hangar, I detected a similar film, though much lighter, on the side windows as well. 

Is this some kind of pollutant in the precip that leaves residue when it dries? Or maybe a pollen residue on the plane getting washed up onto the windshield in flight? Any related experiences?

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I always assumed it was back flow of oily water out of my cowl.  There is some reverse flow from the large cowl opening. I usually see some streaking on the upper leading edge of the cowl.  Also, I will occasionally wipe inside the starter ring/pulley.  I find it build a little oil residue over time, likely from very light weeping of the crankcase seal....  That said, I understand that you indicated it was not oily....so maybe it was some chem trail residue.

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Seeing that you always use the ZEPP product, Clean it with the ZEPP, let it dry then mist it with a water hose or squirt bottle and see if it fogs and streaks. I have used stuff on my windshield before that took quite a while to wash off with water while washing the plane. They look great after application because they have wax in them that coats the plexiglass and makes the scratches go away, but the wax can get foggy when wet.

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As for things that could be left on the windscreen after a flight in rain...

Any oil leaked or dripped inside the cowl has plenty of opportunity to make its way out of the front of the cowl to escape...

Any engine cleaner that may have been used at annual may be escaping as well...

The prop has opportunity to leak grease... but grease is typically too thick to spread out, unless the grease has started to degrade/separate...

Expect that there is so little to know what it is... but it will be incredibly well spread out...

PP thoughts only, not a mechanic...

Best regards,

-a-

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I’ve never used Zep but given it’s an aviation specific widow cleaner I doubt that it’s the problem. I think it more likely that residue from something that was used to wash the plane or engine is being released by the rain and depositing on windshield. 

If you want to try a different windshield product, All Kleer is the best I’ve ever used.

 

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Just to clarify - this is the identical plexiglass-safe cleaner (pictured below) I've used weekly for >4 years without issue, so I doubt it's residue from that.  $3 at Lowes or Home Depot.  I recommend it highly.  One can also buy the identical product for $8 from Skygeek to get the assurance of quality and safety provided by re-pricing it for the aviation market ;)

My two current oil/grease leak sources are well known to me and are watched closely (minor leak of liquifying Aeroshell #6 on back side of prop blades, also a small leak from the prop governor).  Neither had increased or has ever left even a hint of oil on the cowl. It seems unlikely that either of these got to the windshield without leaving any trace on the cowl.  In addition, there a similar film was left behind on all side windows to a lesser degree - I can't see how this would come from the cowl.   These observations led me to believe that there might have been an industrial pollutant suspended in the rain itself (e.g. is this acid rain residue?).  I tried to take a picture but it was impossible to capture the appearance on my phone's camera. I was just curious if there were any similar experiences out there.  I thought acid rain wasn't an issue any more given emissions controls.

 

Zep Foaming 19 fl oz Glass Cleaner

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  • 2 weeks later...

I’ve flown through clouds that smell like farts.   There is an area between Knoxville and Chattanooga where there’s some pretty big papermill..   the smell goes up into overcast layer.      I didn’t get foggy windshield, but definitely more than just H2O in those clouds.  

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5 hours ago, Browncbr1 said:

I’ve flown through clouds that smell like farts.   There is an area between Knoxville and Chattanooga where there’s some pretty big papermill..   the smell goes up into overcast layer.      I didn’t get foggy windshield, but definitely more than just H2O in those clouds.  

Light a match?

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