Instrument Flying: Technique in Weather Page: 25
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T. O. No. 30-100D-1Procedures to be followed in avoiding icing con-
ditions in various types of weather will be treated in
section V. Avoid ice. If icing regions cannot be
avoided, flight through them should be made as short
as possible and should never be attempted unless ef-
fective de-icing equipment is available.
CARBURETOR ICE
Carburetor ice is not ordinarily classified as a
type of ice accretion, but because of widespread un-
familiarity with the subject it will be discussed here
briefly.
The prevention and elimination of carburetor ice is
an engineering problem. It has been solved by the en-
gineers. Procedures and methods to counteract car-
buretor ice have been developed to suit particular en-
gines and carburetors.
Carburetor ice is due to the refrigeration occurring
in the induction system of the engine. Ice usually
forms in the supercharger adapter or on the butterfly-
type of throttle valve and will eventually close off the
air passage. Since the fuel flow is "not interrupted,
the formation of ice in the carburetor venturi will be
indicated by a rapid increase in the fuel - air ratio,
resulting in power loss and eventual stoppage of the
Do not seek lower levels to avoidy -
equate ground clearance below.engine. The most evident indication of carburetor ice
will be a drop in the manifold pressure and, by keep-
ing close watch on the manifold pressure gage, car-
buretor ice may be eliminated before it becomes too
serious. Sometimes application of carburetor heat at
intervals will be sufficient, thereby allowing the en-
gine to develop its full power between applications.
On certain types of carburetors, ice may form on the
nozzle bar or on the nozzles themselves, partially
closing the nozzle openings and thus making the mix-
ture leaner. Either type of ice formation is dangerous,
and must be eliminated as quickly as possible by the
application of carburetor heat or by an alcohol or
anilol spray. Either of these procedures will remove
the ice by melting.
FREEZING AT 150C
Cooling of the air in the engine induction system
amounts to 100 or 150C in the average aircraft en-
gine. It is, therefore, possible to have ice form in the
adapter when the outside air temperature is as high
as 150C. The refrigeration is the result of the evap-
oration of the gasoline and the expansion of air through
the venturi and behind the throttle. If the cooling is
sufficient to produce condensation of water from the
inducted air, carburetor ice may form when the plane
1VI
iv~'
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Section 4
25
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Army Air Forces. Instrument Flying: Technique in Weather, book, January 1, 1944; Ashland, Ohio. (https://texashistory.unt.edu/ark:/67531/metapth873973/m1/31/?q=+date%3A1941-1945: accessed July 16, 2024), University of North Texas Libraries, The Portal to Texas History, https://texashistory.unt.edu; crediting National WASP WWII Museum.