What am I seeing on the leading edge?

[sblack]

OAT sensors read TAT (total air temp). This needs to be converted to SAT (static air temp) but it is TAT that determines whether or not you are at risk of ice sticking to the airframe. I was involved in certification trials in natural ice on the CSeries and we had to fly as slow as possible in the icing cloud to get the TAT down low enough for the ice to stick to the plane. It woulf form, but then break off right away.

You have to be in some serious cloud to get ice on the airplane. I can't tell much from your photo but I suspect it is a reflection from condensation. You had the sun at just the right place to see it.

[sblack]

Originally Posted by BobTurner

Lower, yes. 5 C (9 F) lower? Unlikely.

I have seen ice form on the outside of a carb during a run-up on an 80 deg day. That's a 50 deg drop. A carb has a pressure drop just like a wing. We have all seen water droplets coming off fighters in turns on humid days. The temp drop can be massive!

[BobTurner]

Originally Posted by sblack

I have seen ice form on the outside of a carb during a run-up on an 80 deg day. That's a 50 deg drop. A carb has a pressure drop just like a wing. We have all seen water droplets coming off fighters in turns on humid days. The temp drop can be massive!

Most of the temperature drop in a carb (which, as you note, can be large) is due to the evaporation of fuel. Not directly comparable to airframe icing.

[BenNabors]

Here is a good example:
https://www.youtube.com/watch?v=az7pt58J1KE