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National Advisory Committee for Aeronautics, Technical Notes - Aerodynamic Effects Caused by Icing of an Unswept Naca 65A004 Airfoil

The effects of ice formations on the section lift, drag, and
pitching-moment coefficients of an unswept NASA 65A004 airfoil section
of 6-foot chord were studied. The magnitude of the aerodynamic penalties
was primarily a function of the shape and size of the ice formation near
the leading edge of the airfoil. The exact size and shape of the ice
formations were determined photographically and found to be complex
functions of the operating and icing conditions.

In general, icing of the airfoil at angles of attack less than 4°
caused large increases in section drag coefficients (as much as 550
percent in 8 minutes of heavy glaze icing), reductions in section lift
coefficients (up to 15 percent), and changes in the pitching—moment
coefficient from diving toward climbing moments.

At angles of attack greater than 4° the aerodynamic characteristics
depended mainly on the ice type. The section drag coefficients generally
were reduced by the addition of rime ice (by as much as 45 percent in
8 minutes of icing). In glaze icing, however, the drag increased at
these angles of attack. The section lift coefficients were variably
affected by rims-ice formations; however, in glaze icing, lift increases
at high angles of attack amounted to as much as 9 percent for an icing
time of 8 minutes. Pitching-moment—coefficient changes in icing condi-
tions were somewhat erratic and depended on the icing condition.

Rotation of the iced airfoil to angles of attack other than that
at which icing occurred caused sufficiently large changes in the pitching-
moment coefficient that, in flight, rapid corrections in trim might be
required in order to avoid a hazardous situation.

In evaluating the mission capability of an all-weather aircraft it
is necessary to determine its performance in icing conditions. Information
concerning the aerodynamic penalties associated with icing of airframe
components is therefore required. Research has been conducted by the
NACA to determine the drag penalties associated with icing of several
airfoils of thickness ratios from 9 to 12 percent (refs. 1 to 5).