NAVWEPS OO-80T-80 
OPERATING STRENGTH LIMITATIONS 
CHANGE IN LIFT 
AIRPLANE VELOCITY, V 
GUST 
VELOCITY RESULTANT VELOCITY 
KU 
figure 5.2. Effect of Vertical Gust 
e.g., if in level flight before encountering the 
gust, a final load factor of 1.0+1.61=2.61 
would result. As a general requirement all 
airplanes must be capable of withstanding an 
approximate effective f30 ft. per sec. gust 
when at maximum level flight speed for normal 
rated power. Such a gust intensity has rela- 
tively low frequency of occurrence in ordinary 
flying operations. 
The equation for gust load increment pro- 
vides a basis for appreciating many of the 
variables of flight. The gust load increment 
varies directly with the equivalent sharp 
edged gust velocity, KU, since this factor 
effects the change in angle of attack.’ The 
highest reasonable gust velocity that may be 
anticipated is an actual vertical velocity, U, 
of 50 ft. per sec. This value is tempered by 
the fact that the airplane does not effectively 
encounter the full effect because of the response 
of the airplane and the gradient of the gust. 
A gust factor, K (usually on the order of 0.6), 
reduces the actual gust to the equivalent sharp 
edged gust velocity, KU. 
The properties of the airplane exert a power- 
ful influence on the gust increment. The lift 
curve slope, m, relates the sensitivity of the 
airplane to changes in angle of attack. An 
aircraft with a straight, high aspect ratio 
wing would have a high lift curve slope and 
would be quite sensitive to gusts. On the 
other hand, the low aspect ratio, swept wing 
airplane has a low lift curve slope and is com- 
paratively less sensitive to turbulence. The 
apparent effect of wing loading, W/S, is at 
times misleading and is best understood by 
considering a particular airplane encountering 
a fixed gust condition at various gross weights. 
If the airplane encounters the gust at lower 
than ordinary gross weight, the accelerations