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National Advisory Committee for Aeronautics, Technical Notes - Investigation of a Thermal Ice Prevention System for a Cargo Airplane - IX - The Temperature of the Wing Leading Edge Structure as Established in Flight

As part of an investigation of a thermal ice—prevention system
for a cargo airplane the NACA has completed flight measurements of
the structure temperatures prevailing in the wing outer panel of the
airplane. Sections of the wing panel were altered to represent three
commonly employed types of thermal ice—prevention systems.

Temperatures of the structural components of the forward por—
tion of the wing were‘ obtained for various normal operating condi-
tions of the airplane at 5000, 10,000, and 15,000 feet pressure
altitude. Controlled tests were made to determine the effects of
heated—air temperature, heated—air flow rate, airspeed, and altitude
on the structure temperatures.

The structure temperature data have been compiled in a table
which should provide an indication of the structure temperatures
that prevail in a typical air—heated wing:

The data obtained indicate that the structure temperatures
which prevail in a thermal ice—prevention system are sufficiently
high to merit some consideration in the design of stressed members.
The variables controlling the structure temperatures were analyzed,
and the heated—air temperature was established as the dominant vari—
able. The structure temperatures increased in almost direct propor—
tion to increases in heated—air temperature, but were much less
affected by changes in air flow rate, airspeed, and altitude over
the test range.

The conclusion is reached that‘the most direct method for
increasing deficient surface temperatures is to increase the tem—
perature of the heated air with the understanding, however, that
this method will result in a larger rise in structure temperature
than would occur if the surface temperature were raised by increas—
ing the heatedrair flow rate.

As part of an investigation of a thermal ice—prevention system
for a typical transport or cargo airplane, the NACA has undertaken
an examination of the possible deleterious effects resulting from
the circulation of heated air adjacent to the airplane structure.
This problem was not treated during the initial stages of the de—
velopment of thermal ice-prevention equipment for airplanes by the
NACA (references 1 to 8) as it was considered to be of secondary
importance.