existing on the surface. Of course, the ve- 
locity distribution, and resulting pressure dis- 
tribution, is determmed by the.shape or pro- 
file of the surface and the angle of a’track. 
Thus, any aerodynamic force can be repre- 
sented as the product df three major factors: 
the surface area of the objects 
the dynamic pressure of the airstream 
the coefficient or index of force determined 
by the relative pressure distribution 
This relationship is expressed by the following 
equation : 
F= C,qS 
where 
F = aerodynamic force, lbs. 
C,=coeflicient of aerodynamic force 
,iay;mic pressure, psf 
S=surface area, sq. ft. 
In order to fully appreciate the importance 
of the aerodynamic force coe&cient, C,, the , 
above equation is rearranged to alternate 
forms : 
In this form, the aerodynamic force coefficient 
Js appreciared as the aerodynamic force per 
surface area and dynamic pressure. In other 
words, the force coefficient is a dimensionless 
ratio between the average aerodynamic pres- 
sure (aerodynamic force.per ‘area) and the air- 
stream dynamic pressure. All the aerodynamic 
forces of lift and drag are studied on this basis- 
the common denominator in each case being 
surface area and dynamic pressure. By such a 
definition, a “lift coefficient” would .be the 
ratio between lift pressure and dynamic pres- 
sure; a “drag coefficient” would be the ratio 
between drag pressure and.:d.ynamic pressure. 
The use of the coefficient form of an aero- 
dynamic force is necessary since the force 
coellicient is: 
(1) An index 04 the aerodynamic force 
independent of area, density, and velocity. 
NAVWEPS m-60T-30 
BASIC AERODYNAMICS 
It is derived from the relative pressure and 
velocity distribution. 
(2) Influenced only by the shape of the 
surface and angle of attack since these factors 
determine the pressure distribution. 
(3) An index which allows evaluation of 
the effects of compressibility and viscosity. 
Since the effects of area, density, and velocity 
are obviated by the coefficient form, com- 
pressibility and viscosity effects can be 
separated for study. 
THE BASIC LIFT EQUATION. Lift has 
been dehned as the net force developed per- 
pendicular to the relative wind. The aero- 
dynamic force of lift on an airplane results 
from the generation of a pressure distribution 
on the wing. This lift force is described by 
the following equation: 
L=C& 
where 
L=lift, lbs. 
C, = lift coefficient. 
q= dy;:mic pressure, psf 
+p 
S= wing surface area, sq. ft. 
The lift coefhcient used in this equation is the 
ratio of the lift pressure and dynamic pressure 
and is a function of the shape of the wing and 
angle of attack. If the lift coefficient of a 
conventional airplane wing planfoi-m were 
plotted versus angle of attack, the result would 
be typical of the graph of figure 1.11. Since 
the effects of speed, density, area, weight, alti- 
tude, etc., are eliminated by the coefficient form, 
an indication of the true lift capability is ob- 
tained. Each angle of attack produces a par- 
ticular lift coefficient since the angle of attack 
is the controlling factor in the pressure dis- 
tribution. Lift coeflicient increases with angle 
of attack up to the maximum lift coefficient, 
c L,,,~., and, as angle of attack is increased be- 
yond the maximum lift angle, the airflow is 
unable to adhere to the upper surface. The 
airflow then separates from the upper surface 
and stall occurs. 
JNTERPRETATION OF THE LIFT EQUA- 
TION. Several important relationships are 
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