de-icing equipment than rime ice. Since it is transparent, clear icing may go undetected
until it is too late for de-icing equipment. Clear ice on an airfoil is depicted in Figure 1-9.
Figure 1-9 -- Clear ice.
Rime ice is a rough, brittle, milky opaque deposit of ice formed by the instantaneous
freezing of small super-cooled water droplets. Rime ice usually occurs at a lower
temperature than does clear ice.
Unlike clear ice, rime forms as drops freeze upon striking the airfoil trapping air, giving
the ice its opaque appearance and making it porous and brittle. The resulting deposit is
tiny pellets of ice frozen together in a spongy mass. Rime ice on an airfoil is depicted in
Figure 1-10 -- Rime ice.
The conditions that favor the formation of rime ice are:
Very small water droplets such as are found in stratiform clouds
A relatively small number of water droplets that are found in clouds that are not
Temperatures far below freezing