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National Advisory Committee for Aeronautics, Report - Icing Protection Requirements for Reciprocating Engine Induction Systems

Despite the derelop-ment of relatirely ice—free fuel—metering
systems, the widespread use of alternate and heated—air intakes,
and the use of alcohol for emergency tie-icing, icing of aircraft-
e-ngine induction systems is a seridas problem. Investigations
have been made to study and to combat all phases of this icing
problem. From these in-restigations, criterions for safe opera-
tion and for design of new induction systems have been estab-
lished.

The results were obtained from laboratory investigations of
carburetor-supercharger combinations, wind-tunnel i-ntestiga-
tions of air scoops, multicylinder—engine studies, and flight
inrestigations. Characteristics of the three forms of ice, impact,
throttling, and fuel eraporation, were studied. The ejects of
sereral factors on the icing characteristics were also studied and
included (I) atmospheric conditions, (fl) engine and air-scoop
configurations, including light-airplane systems, (3) type of
fuel used, and (4) operating rariables, such as power condition,
use of a manifold pressure regulator, mixture setting, carburetor
heat, and water-alcohol injection. In addition, ice-detection
methods were investigated and methods of prerenting and re-
moving induction-system ice were studied. Recommendations
are given for design and operation uith regard to induction-
system icing.

Ice formations within an aircraft—engine induction system
are serious hazards because: (1) the critical areas may be
sufiiciently restricted to reduce considerably the flow of
combustion air to the engine; (2) the fuel—metering process
may be upset and cause erratic engine operation; or (3) the
movable parts, such as the throttle or the heat damper, may
freeze and become inoperative.

The symptoms associated with induction-system icing are
not. always discernablc and recognition of icing conditions
usually requires considerable operational experience and
judgment. This type of icing is not. necessarily a cold-
weather phenomenon, but may occur at temperatures far
above the normal ambient freezing level.