PLIGHT AT HIGH LIFT CONDITIONS 
It is frequently stated that the career Naval 
Aviator spends more than half his life “below 
a thousand feet and a hundred knots.” Re- 
gardless of the implications of such a state- 
ment, the thought does cunnute the relation- 
ship of minimum flying speeds and carrier 
aviation. Only in Naval Aviation is there 
such importance assigned to precision control 
of the aircraft at high lift conditions. Safe 
operation in carrier aviation demands precision 
control of the airplane at high lift conditions. 
The aerodynamic lift characteristics of an 
airplane are portrayed by the curve of lift 
coefficient versus angle of attack. Such a 
curve is illustrated in figure 1.15 for a specific 
airplane in the clean and flap down configura- 
tions. A given aerodynamic configuration ex- 
periences increases in lift coefficient with in- 
creases in angle of attack until the maximum 
lift coefficient is obtained. A further increase 
in angIe of attack produces stall and the lift 
coefficient then decreases. Since the maximum 
lift coefficient corresponds to the minimum 
speed available in flight, it is an important 
point of reference. The stall speed of the air- 
craft in level flight is related by the equation: 
V7.=17.2 J-- c w 
.ln2s 
where 
V.-stall speed, knots TAS 
W=gross weight, lbs. 
c Lnoz= airplane maximum lift coefficient 
csaltitude density ratio 
S= wing area, sq. ft. 
This equation illustrates the effect on stall 
speed of weight and wing area (or wing load- 
ing, W/S), maximum lift coefficient, and alti- 
tude. If the stall speed is desired in EAS, the 
density ratio will be that for sea level (u= 
1.000). 
EFFECT OF WEIGHT. Modern configu- 
rations of airplanes are characterized by a large 
percent. of the maximum gross weight being 
NAVWEPS 00-BOT-RO 
BASIC AERODYNAMICS 
fuel. Hence, the gross weight and stall speed 
of the airplane can vary considerably through- 
out the flight. The effect of only weight on 
stall speed can be expressed by a modified form 
of the stall speed equation where density ratio, 
c r,,,.,, and wing area are held constant. 
V _i_z- K 
J v.,- K 
where 
V*,=stall speed corresponding to some 
gross weight, WI 
V@a= stall speed corresponding to a dif- 
ferent gross weight, WP 
As an illustration of this equation, assume 
that a particular airplane has a stall speed of 
100 knots at a gross weight of 10,000 lbs. 
The stall speeds of this Sam: airplane at other 
gross weights would be: 
ll,W 100x 4, ‘&~=lO, 
12,ooO 110 
14,4al 120 
9mJ 95 
8,100 90 
Figure 1.15 illustrates the effect of weight on 
stall speed on a percentage basis and will be 
valid for any airplane. Many specific condi- 
tions of flight are accomplished at certain fixed 
angles of attack and lift coefficients. The 
effect of weight on a percentage basis on the 
speeds for any specific lift coefficient and angle 
of attack is identical. Note that at small 
variations of weight, a rule of thumb may 
express the effect of weight on stall speed- 
“a 2 percent change in weight causes a I per- 
cent change in stall speed.” 
EFFECT OF MANEUVERING FLIGHT. 
Turning flight and maneuvers produce an 
effect on stall speed which is similar to the 
effect of weight. Inspection of the chart on 
figure 1.16 shows the forces acting on an airplane 
in a steady turn. Any steady turn requires 
that the vertical component of Iift be equal to 
35