Report on Ice Formation on Aircraft Page: 4 of 22
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iT.A.C.A. Technical Memorandum No. 919
CHAPTER I
ICE FORMATION ON AIRPLANiES IN FLIGHT
This coating. of ice is formed on certain parts of an
airplane when flying through clouds in a temperature
ranging in general between 00 and -lO0.
The clouds which we see in the atmosphere, are said
to be formed of extremely small water droplets suspended
in the air. Water vapor also exists in greatly varying
amounts, but it is absolutely invisible; it is precisely
this water vapor which by condensing into water brings
forth the microscopic droplets which constitute the clouds.
This phenomenon of condensation presents certain very
important oarticularitios brought out in particular by the
works of the Torwegian physicist, Hilding Kohler, titled
"n the Water in Clouds," Goefysiske Publikosjoner, vol. 5,
no. 1 - C-irondahl and Sons, Oslo, 1928.
TWhecn an air mass containing water vapor is suffi-
ciently cooled, this vapor condenses partially to drops
of wateCr, which form condenstion nuclei. These condensa-
tion nuclei arec generally conceded, after much research
,and many experiments, to be constituted of grains of mi-
croscopic dust in suspension, or else ions or, preferably
of particles of hygroscopic salts of magnesium chloride
and sodium chloride, according to Kohler, with particles
of sodium sulphate.
The first two are, according to Kohler, the result
of evaporation of sea spray; sodium sulphate comes from the
combustion of sulphur,which is present in coal and coke.
These hygroscopic salts in the presence of water vapor,
even if at pressure lower than its maximum pressure for the
existing temperature, have the quality of becoming deli-
quescent on condensation with water vapor and to change to
a more and more diluted solution, thus forming a liquid
drop.
It seems to be ' definitely shown by Kohler~ as well
as by U.S. investigations (Don MacNeal - Journal of the
Aeronautical Sciences, January 1937) that the water vapor
contained in the air of a cloud is generally at a pressure
lower than the saturation pressure; it furthermore appears
that a cloud mass in the atmosphere can be rarely consid-
ered as being in a state of equilibrium.3
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Report on Ice Formation on Aircraft, report, November 1939; (https://digital.library.unt.edu/ark:/67531/metadc63229/m1/4/: accessed April 25, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.