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National Advisory Committee for Aeronautics, Technical Notes - The Effect of Ice Formations on Propeller Performance

Measurements of prepeller efficiency loss due to ice formation are
supplemented by an analysis to establish the magnitude of efficiency
losses to be anticipated during flight in icing conditions. The measure—
ments were made during flight in natural icing conditions; whereas the
analysis consisted of an investigation of changes in blade—section aero—
dynamic characteristics caused by ice formation and the resulting pro-
peller efficiency changes. Agreement in the order of magnitude of effi—
ciency losses to be expected is obtained between measured and analytical
results. The results indicate that, ingeneral, efficiency losses can
be expected to be less than 10 percent; whereas naximum losses, which
will be encountered only rarely, may be as high as 15 or 20 percent.
Reported losses larger than 15 or 20 percent, based on reductions in
airplane performance, probably are due to ice accretions on other parts
of the airplane.

Blade—element theory is used in the analytical treatment, and cal—
culations are made to show the degree to which the aerodynamic charac—
teristics of a blade section must be altered to produce various propeller
efficiency losses. The effects of ice accretions on airfoil—section
characteristics at subcritical speeds and their influence on drag—
divergence Mach number are examined, and the attendant maximum efficiency
losses are computed. The effect of kinetic heating on the radial extent
of ice formtion is considered, and its influence on required length of
blade heating shoes is discussed. It is demonstrated how the efficiency
loss resulting from an icing encounter is influenced by the decisions of
the pilot in adjusting the engine and propeller controls.

It has long been recognized that one of the hazards of flight in
icing conditions is the formtion of ice on propellers. The presence
of ice on propeller blades causes a decrease in the operating efficiency
of the propeller and a corresponding decrease in the airplane performance.
There has been much disagreement as to the actual magnitude of efficiency
losses experienced. in icing conditions. Measurements have been made of
propeller efficiency losses with simulated. ice formations (references 1
and 2) and in natural icing conditions (reference 3). The measured losses
were low when compared with those generally expected; however, reports
of very large apparent losses, deduced from decrease in airplane perform-
ance, persisted.