What am I seeing on the leading edge?
 

Last year I was cruising along at 12,500' in clear weather over Colorado and started seeing this shiny gray stuff on the leading edge. It kind of looked wet. Needless to say I was concerned, so I pulled my iPad - the one I was using to navigate - out of its mount and snapped this photo. The camera didn't focus properly, but hopefully someone will be able to guess at what I was seeing. Was it just an optical phenomenon or ice? The OAT at the time was 5C and there was no visible moisture (except in the far distance), so how could it have been ice? Could it have been a thin layer of "fog" due to the sudden decrease in pressure? The wing itself is white. What was going on?



I posed this same question on the Lancair forum last year but never got any meaningful responses. There is a lot more experience over here so I hope y'all won't mind...

Lighting?
 

From the mountains, looks like it could be shadow.... maybe it is effectively, a little moisture followed by shadow.

not a shadow
 

Thanks for responding. Yes, it does like a shadow in the photo but trust me, it wasn't the shadow of the top of the wing. Maybe it could have been a shadow of the condensation - that's a good idea. I don't know what the dewpoint was, but from the clouds in the background, it must have been close to the OAT. It seems like the "gray stuff" was located right where the pressure on top of the airfoil was at a minimum.

What i think
 

I have seen this before at a window seat om a airline. All i can think of is the water is starting to condense but instead of seeing a white cloud it is a reduction of light geting to the surface, like shadowing.

Did it look something like this?
 

Without the wingtip vortices, and viewed from the cockpit.


If your wing had rivets in it, this might not happen ;):D

Cheers, David

thank you
 

Thanks for confirming I wasn't hallucinating due to hypoxia. Yes, I was wearing my oxygen cannula.

no rivets (wink)
 

LOL! Nah, it's all glued together, but I must have built it straight and true because the gray area was pretty constant all along the span. If I ever see this again, I'll pull some G's and see if the gray area expands. It should, right? I was stupid because I had my Garmin Virb video camera mounted right next to my head. I could have easily removed it and video recorded the phenomenon.

It's a cloud;
 

just like a cap cloud on a mountain. Pressure drops as air passes over the wing and temperature drops below the dew point.

Cheers, David

That must have been what was happening. It looked for all the world like something wet was covering the leading edge. One correction, though. I took the photo near Grand View, ID, just past Mountain Home. I had spent the night in Brigham City and was on my way to Medford, OR. Man, that's some desolate country out there :eek:

Likely a very thin layer of ice is my guess. I've seen traces on my wing in clear air. On your picture there is some visible moisture (clouds) in the vicinity.