NAVWEPS 00.401-80 
BASIC AERODYNAMICS 
Thus, a sea level airspeed (or EAS) of 100 
knots would provide the dynamic pressure 
necessary at maximum lift to produce 14,250 
Ibs. of lift. If the airplane were operated at a 
higher weight, a higher dynamic pressure 
would be required to furnish the greater lift 
and a higher stall speed would result. If the 
airplane were placed in a steep turn, the greater 
lift required in the turn would increase the 
stall speed. If the airplane were flown at a 
higher density altitude the TAX at stall would 
increase. However, one factor common to 
each of these conditions is that the angle of 
attack at C,,,, is the same. It is important to 
realize that stall warning devices must sense 
angle of attack (a) or pressure distribution 
(related to CL). 
Another important fact related by the basic 
lift equation and lift curve is variation of angle 
of attack and lift coefficient with airspeed. 
Suppose that the example airplane is flown in 
steady, wing 1eveJ flight at various airspeeds 
with lift equal to the weight. It is obvious 
that an increase in airspeed above the stall 
speed will require a corresponding decrease in 
lift coeflicient and angle of attack to maintain 
steady, lift-equal-weight flight. The exact 
relationship of lift coefficient and airspeed is 
evolved from the basic lift equation assuming 
constant lift (equal to weight) and equivaIent 
airspeeds. 
derived from study of the basic lift equation 
and the typical wing lift curve. One impor- 
tant fact to be appreciated is that the airplane 
shown in figure 1.11 stalls at the same angle 
of attack regardless of weight, dynamic pres- 
sure, bank angle, etc. Of course, the stall 
speed of the aircraft will be affected by weight, 
bank angle, and other factors since the product 
of dynamic pressure, wing area, and lift co- 
efficient must produce the required lift. A 
rearrangement of the basic lift equation de- 
fines this relationship. 
L = c&Y 
using q =$ (I’ in knots, TAX) 
solving for V, - 
V=17.2 & J L,J 
Since the stall speed is the minimum flying 
speed necessary to sustain flight, the lift co- 
efficient must be the maximum (CL,,,,). 
Suppose that the airplane shown in’ figure 
1.11 has the following properties: 
Weight = 14,250 lbs 
Wing area=280 sq. ft. 
C &=1.5 
If the airplane is flown in steady, level flight at 
sea level with lift equal to weight the stall 
speed would be: 
,- 
V.= 17.24&$ 
where 
V.= stall speed, knots TAS 
W= weight, lbs. (lift = weight) 
va= 17.2 J (I.&4E;280) 
= 100 knots 
C‘ v, p -= - C %n.* 0 V 
The example airplane was specified to have: 
Weight = 14,250 lbs. 
C L,,,=lS 
V,= 100 knots EAS 
The following table depicts the lift coefficients 
and angles of attack at various airspeeds in 
steady flight. 
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