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National Advisory Committee for Aeronautics, Technical Notes - Correlations Among Ice Measurements, Impingement Rates, Icing Conditions, and Drag Coefficients for Unswept NACA 65A004 Airfoils

An empirical relation has been obtained by which the change in drag
coefficient caused by iCe formations on an unswept NACA 65A004 airfoil
section can be determined from the following icing and operating conditions:
icing time, airspeed, air total temperature, liquid-water content, cloud
droplet impingement efficiencies, airfoil chord length, and angles of
attack. The correlation was obtained by use of measured ice heights and
ice angles. These measurements were obtained from a variety of ice for-
mations, which were carefully photographed, cross—sectioned, and weighed.
Ice weights increased at a constant rate with icing time in a rime icing
condition and at progressively increasing rates in glaze icing conditions.
Initial rates of ice collection agreed reasonably well with values pre-
dicted from droplet impingement data. Experimental droplet impingement
rates obtained on this airfoil section agreed with previous theoretical
calculations for angles of attack of 4° or less. Disagreement at higher
angles of attack was attributed to flow separation from the upper surface
of the experimental airfoil model.

Over the last several years considerable information about aircraft
icing characteristics and the resultant aerodynamic penalties has been
vauired. This information now generally permits: (1) calculation of
cloud droplet impingement rates for a variety of body shapes and flight
conditions, (2) prediction of the area of a body on which ice formations
will occur and the general nature of the ice (rime or glaze), and (5)
for several airfoils, estimation of aerodynamic penalties due to ice
formations acquired during exposure to a variety of specified icing
conditions. Unfortunately, very little direct correlation has been shown
among these three facets of the icing problem. The impingement calcula-
tions do not quantitatively foretell size, shape, or even weight of ice
that will form under given conditions, nor are the published aerodynamic
penalties related to the actual ice size and shape, except in a gross way.
Furthermore, it is difficult to estimate aerodynamic penalties in icing
conditions different from those specifically investigated for a particular
airfoil.