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• January 29, 2017 Create Date
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National Advisory Committee for Aeronautics, Technical Notes - Experimental Droplet Impingement on Several Two Dimensional Airfoils with Thickness Ratios of 6 to 16 Percent

The rate and area of cloud droplet impingement on several.two-
dimensional swept and unswept airfoils were obtained experimentally in
the NACA Lewis icing tunnel with a dye-tracer technique. -Airfoil thick—
ness ratios of 6 to 16 percent, angles of attack from O0 to 12°, and
chord sizes'from 15 to 96 inches were included in the study. The data
were obtained.at 152 knots and are extended to other conditions by dimen-
sionless impingement parameters.

In general, the data show that the total and local collection effi—
ciencies and impingement limits are primary functions of the modified
inertia parameter (in which airspeed, droplet size, and body size are
the most significant variables) and the airfoil thickness ratio. Local
collection efficiencies and impingement limits also depend.on angle of
attack. Secondary factors affecting impingement characteristics are air—
foil shape, camber, and sweep angle. The impingement characteristics ob—
tained experimentally for the airfoils were within :10 percent on the
average of the characteristics calculated from theoretical trajectories.
Over the range of conditions studied, the experimental data demonstrate
that a specific method can be used to predict the impingement character-
istics of swept airfoils with large aspect ratios from the data for un—
swept airfoils of the same series.

Knowledge of the local and total rates of cloud droplet impingement
and of the surfacewise extent or limit of droplet impingement on bodies
is required for the design and evaluation of icing—protection equipment
for aircraft. These impingement characteristics are important factors
in determining the extent of the surface to be protected, the shape and .
location of some ice formations on aircraft components, the aerodynamic w
penalties associated with icing of aircraft surfaces, and the local and _
total requirements for various thermal and fluid protection systems.