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National Advisory Committee for Aeronautics, Technical Notes - Icing and De-Icing of a Propeller with Internal Electric Blade Heaters

An investigation has been made in the NAGA Cleveland. icing
research tunnel to determine the de-icing effectiveness of an
experimental configuration of an internal electric propeller-blade
heater. ‘I'wo aunospheric icing conditions and. two propeller operat-
ing conditions were investigated in experiments with unheated blades
and. with heat applied to the blades both continuously and. cyclically .
Data are presented to show the effect of propeller speed, ambient-
air temperature and liquid-water concentration, and the duration of
the heat-on and cycle times on the power requirements and tie-icing
performance of the blade heaters.

The extent of ice-covered area on the blades for various icing
and operating conditions has been determined. The largest iced
area was obtained at the higher ambient-air temperatures and at low
propeller speed. The chordwise extent of icing in practically every
case was greater than that covered by blade heaters.

Adequate de-icing in the heated area with continuous appli-
cation of heat was obtained with the power available but a maximum '
power input of 1250 watts per blade was insufficient for cyclic
de-icing for the range of conditions investigated._ Blade-surface
temperature rates of rise of O.2° to 0.70 1' per second were obtained
and. the minimum cooling period for cyclic de-icing was found to be
approximately 2;.- times the heatim period.

Several methods of obtaining icing protection for propellers
have been proposed including the use of alcohclor other freezing-
point depressants, the external electric blade heaters (reference 1) ,
authepaseageofahetwthroughahollowblade (reference 2).

The recent development of hollow steel propeller blades con-
structed with a thin sheet-metal outer skin has permitted the instal-
lation of an electric heater within the blade. Such a heater instal-
lation does not impair the aerodymic performance of the blade and
is free from abrasion damage. Theoretical analysis (reference 5)
and flight investigations (reference 4) of heat requirements for ice
prevention with continuous heating have indicated that the electric
power needed is excessive for current aircraft. An investigation
concerned with both continuous and cyclic heating systems was there-
fore conducted at the NACA Cleveland laboratory to determine the
icing protection provided by an experimental configwation of an
internal electric prepellernblade heater and the effects of several
icing, heating, and propeller operating conditions on the heater
performance.