CONCLUSIONS

The variation of the aerodynamic characteristics of the related airfoils with the geometric characteristics investigated may be summarized as follows:

Variation with thickness ratio:

1. The slope of the lift curve in the normal working range decreases with increased thickness, varying from 95 to 81 percent, approximately, of the theoretical slope for thin airfoils (2 (pi) per radian).
   

2. The angle of zero lift moves toward zero with increased thickness (above 9 to 12 percent of the chord thickness ratios).
   

3. The highest values of the maximum lift are obtained with sections of normal thickness ratios (9 to 15 percent).
   

4. The greatest instability of the air flow at maximum lift is encountered with the moderately thick, low-cambered sections.
   

5. The magnitude of the moment at zero lift decreases with increased thickness, varying from 87 to 64 percent, approximately (for normally shaped airfoils), of the values obtained by thin-airfoil theory.
   

6. The axis of constant moment usually passes slightly forward of the quarter-chord point, the displacement increasing with increased thickness.
   

7. The minimum profile drag varies with thickness approximately in accordance with the expression
   
   
   
   where the value of k  depends upon the camber and t is the ratio of the maximum thickness to the chord.
   

8. The optimum lift coefficient (the lift coefficient corresponding to the minimum profile-drag coefficient) approaches zero as the thickness is increased.
   

9. The ratio of the maximum lift to the minimum profile drag is highest for airfoils of medium thickness ratios (9 to 12 percent).
   

Variation with camber:

1. The slope of the lift curve in the normal working range is little effected by the camber; a slight decrease in the slope is indicated as the position of the camber moves back.
   

2. The angle of zero lift is between 100 and 75 percent, approximately, of the value given by thin-airfoil theory, the smaller departures being for airfoils with the normal camber positions.
   

3. The maximum lift increases with increased camber, the increase being more rapid as the camber moves forward or back from a point near the 0.3c position.
   

4. Greater stability of the airflow at maximum lift is obtained with increased camber if the camber is in the normal positions (0.3c to 0.5c).
   

5. The moment at zero lift is nearly proportional to the camber. For any given thickness, the difference between the experimental value of the constant of proportionality nod the value predicted by thin-airfoil theory is not appreciably effected by the position of the camber except for the sections having the maximum camber well back, where the difference becomes slightly greater.
   

6. The axis of constant moment moves forward as the camber moves back.
   

7. The minimum profile drag increases with increased camber, and also with a rearward movement of the camber.
   

8. The optimum lift coefficient increases with the camber and for the highly cambered sections a definite increase accompanies a forward movement of the camber.
   

9. The ratio of the maximum lift to the minimum profile drag tends to decrease with increased camber (above 2 percent of the chord) and with a rearward movement of the camber (for the highly cambered sections).

LANGLEY MEMORIAL AERONAUTICAL LABORATORY,

NATIONAL ADVISORY COMMITTEE FOR AERONAUTICS,

LANGLEY FIELD, VA, December 20, 1932.

Table of Contents | Summary | Introduction | Description of Airfoils | Apparatus and Methods | Results | Discussion | Supplementary Airfoils | Conclusions | Appendix | References