Why does a prop ice up so apparently readily?

You are assuming that you are getting your calculated aero heating even
though the air is full of supercooled water.

Mike
MU-2

"Peter" wrote in message
...

Brian Whatcott wrote

...and did I not account for aero heating, using the figures given by
you?

Yes, but I don't think icing works that way. The reason is that
supercooled water won't (generally) exist below about -15C to start
with, so if the aerodynamic heating increment exceeds 15C one doesn't
get ice.

So, if e.g. the SAT is -25C and the aero heating is 20C, the airframe
part will be at -5C but it won't ice up because there wasn't liquid
water in the -25C air to start with. Any water would have been in
solid (frozen) form, as in e.g. cirrus clouds, but a -5C airframe
flying through that won't accumulate ice because the crystals don't
have time to melt and convert themselves into drops of liquid which
could stick.

That's my understanding, anyway.