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National Advisory Committee for Aeronautics, Technical Notes - An Investigation Utilizing an Electrical Analogue of Cyclic De-Icing of a Hollow Steel Propeller with an External Blade Shoe

A study has been made of the heat requirement for the cyclic de-icing
of hollow steel propellers fitted with external blade heating shoes.
Solutions to the equations for the heat flow in cyclic heating of propel-
lers were obtained, using an electrical analogy. The study shbwed how the
energy requirement for propeller de-icing with existing blade shoes could ‘
be decreased, and illustrated the effect of blade—shoe design on the
energy requirement. It was demonstrated, for example, that by increasing
the heating intensity and decreasing’the heating period from those cur-
rently used the energy requirement could be decreased in the order
of 60 percent. In addition, it was shown that heating requirements could
be decreased further, by as much as 60 percent, through proper design of
the shoes. The investigation also showed the energy requirement to
increase with decreasing liquid-water content and air temperature. Uncer-
tainties as to the exact values of convective heat—transfer coefficient
prevailing over the surface of the blade and ice layer resulted in uncer—
tainties of approximately proportional magnitude in the values of required
heating intensity.

Propeller ice protection for aircraft is generally provided by
electrical heating. In the development of external heating shoes, emphasis
was placed primarily on the determination of the heating intensity
required. Preliminary tests indicated power requirements for continuous
heating to be so large that cyclic operation, with attendant pOWer savings,
was almost mandatory. Subsequent tests (reference 1) included some varia-
tion in cyclic time and other pertinent factors, but were mainly concerned
with heating pattern and heating intensity for one blade and shoe config-
uration.

Tests of cyclically operated propeller blade shoes have been too
limited in scope to provide a comprehensive picture of the effects of
various parameters on blade-shoe performance. Electrical simulation of
the flow of heat from the heating element of a blade shoe during cyclic
operation offered a means for obtaining more complete data on cyclic
de—icing. By use of an electrical analogy, a large range of configura—
tions and operating conditions could be covered readily. Such a study
of a similar problem was first made by Tribus (reference 2). This work
was limited in its scope, reproducing portions of the data obtained in
reference 1 and covering only the general aspects of the problem.