loo. ................. l.lm 1.30 20.00 
110 .................. ,826 1.24 15.P 
17.0 .................. ,694 1.04 12.7’ 
lY) .................. .444 .61 8.20 
200 .................. 230 .38 4.6’ 
MO. ................. ,111 .I7 2.10 
4&l. ................. .c453 .o!J 1.10 
30.7. ................. ,040 .06 .T= 
600 .................. .028 .04 .5O 
Note that for the conditions of steady flight, 
each airspeed requites a specific angle of attack 
and lift coefficient. This fact provides a fun- 
damental concept of flying technique: Angle 
of attack is tbs primary Control of airspeed in steady 
flight. Of course, the control stick or wheel 
allows the pilot to control the angle of attack 
and, thus, control the airspeed in steady flight. 
In the same sense, the throttle controls the 
output of the powerplant and allows the pilot 
to control rate of climb and descent at various 
airspeeds. 
The teal believers of these concepts ate pro- 
fessional instrument pilots, LSO’s, and glider 
pilots.. The glider pilot (or flameout enthusi- 
ast) has no recourse but to control airspeed by 
angle of attack and accept whatever rate of 
descent is incurred at the various airspeeds. 
The LSO must become quite proficient at judg- 
ing the flight path and angle of attack of the 
airplane in the pattern. The more complete 
visual reference field available to the LSO 
allows him to judge the angle of attack of 
the airplane mote accurately than the pilot. 
When the airplane approaches the LSO, the 
precise judgment of airspeed is by the angle 
of attack rather than the rate of closure. If 
the LSO sees the airplane on the desired flight 
path but with too low an angle of attack, the 
airspeed is too high; if the angle of attack is 
too high, the airspeed is too low and the ait- 
plane is approaching the stall. The mirror 
landing system coupled with an angle of attack 
indicator is an obvious refinement. The mit- 
tot indicates the desired flight path and the 
NAVWEPS WOT-BO 
BASIC AERODYNAMICS 
angle of attack indicator allows precision con- 
trol of the airspeed. The accomplished insttu- 
ment pilot is the devotee of “attitude” flying 
technique-his creed being “attitude plus 
power equals performance.” During a GCA 
approach, the professional instrument pilot 
controls airspeed with stick (angle of attack) 
and rate of descent with power adjustment. 
Maneuvering flight and certain transient 
conditions of flight tend to complicate the 
relationship of angle of attack and airspeed. 
However, the majority of flight and, certainly, 
the most critical regime of flight (takeoff, ap- 
proach, and landing), is conducted in essen- 
tially steady flight condition. 
AIRFOIL LIFT CHARACTERISTICS. Air- 
foil section properties differ from wing or 
airplane properties because of the effect of the 
planform. Actually, the wing may have vati- 
ous airfoil sections from root to tip with taper, 
twist, sweepback and local flow components 
in a spanwise direction. The resulting aeto- 
dynamic properties of the wing are determined 
by the action of each section along the span 
and the three-dimensional flow. Airfoil sec- 
tion properties are derived from the basic shape 
or profile in two-dimensional flow and the force 
coefficients are given a notation of lower case 
letters. For example, a wing or airplane lift 
coefficient is C, while an airfoil section lift 
coefficient is termed cr. Also, wing angle of 
attack is Q while section angle of attack is 
differentiated by the use of 01~. The study of 
section properties allows an objective consider- 
ation of the effects of camber, thickness, etc. 
The lift characteristics of five illustrative 
airfoil sections are shown in figure 1.12. The 
section lift coe&icient, c,, is plotted versus 
section angle of attack, olO, for five standard 
NACA airfoil profiles. One characteristic fea- 
ture of all airfoil sections is that the slope of 
the various lift curves is essentially the same.