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National Advisory Committee for Aeronautics, Technical Notes - Investigation of Effectiveness of Air Heating a Hollow Steel Propeller for Protection Against Icing - I - Unpartitioned Blades

An investigation to determine the effectiveness of icing protec-
tion afforded by air-heating hollow steel unpartitioned propeller
blades has been conducted in the NACA Cleveland icing research tunnel.
The propeller used was a production model modified with blade shank
and tip openings to perndt internal passage of heated air. Blade-
surface and heated-air temperatures were obtained and photographic
observations of ice formations were made with variations in icing
intensity and heating rate to the blades.

For the conditions of icing to which the propeller was subjected,
it was found that adequate ice protection was afforded with a heating
rate of 40,000 Btu per hour per blade. With less than 40,000 Btu per
hour per blade, ice protection failed because of significant ice
accretions on the leading edge. The chordwise distribution of heat
.was unsatisfactory with most of the available heat dissipated well
back of the leading edge on both the thrust and camber faces
instead of at the leading edge where it was most needed. A low
utilization of available heat for icing protection is indicated
by a heat-exchanger effectiveness of approximately 47 percent.

As the demand for all-weather protection on aircraft for unimr
paired and continuous commercial and military service developed,
the detrimental effects of propeller icing on airplane performance
became increasingly important. Early attempts toward some means
of propeller icing protection centered around the use of anti-icing
pastes and slinger-ring arrangements for distributing anti-icing
fluids on the propeller-blade surfaces. More recently, electric
de-icing systems using external rubber-clad electric heating elements
have been employed with a comparative high degree of success (refer-
ence l). Attempts have also been made to use internal electric
heaters, which inherently eliminate the possibility of erosion damage
and preserve the aerodynamic performance of the blade surface.