In order to obviate some of the problems 
of a deficiency of airspeed at takeoff, usual 
result can be an excess of airspeed at takeoff. 
The principal effect of an BXCBJS takeoff air@pssd 
is the greater takeoff distance which results. 
The general effect is that each 1 percent excess 
takeoff velocity incurs approximately 2 per- 
cent additional takeoff distance. Thus, excess 
speed must be compared with the additional 
runway required to produce the higher speed. 
In addition, the aircraft tires may be subject 
to critical loads when the airplane is at very 
high rolling speeds and speeds in excess of a 
basically high takeoff speed may produce 
damage or failure of the tires. 
As with the conditions of landing, excess 
velocity or deficiency of velocity at takeoff 
is undesirable. The proper takeoff speeds and 
angle of attack must be utilized to assure 
satisfactory takeoff performance. 
GUSTS AND WIND SHEAR 
The variation of wind velocity and direction 
throughout the atmosphere is important be- 
cause of its effect on the aerodynamic forces 
and moments on an airplane. As the airplane 
traverses this variation of wind velocity and 
direction during flight, the changes in airflow 
direction and velocity create changes in the 
aerodynamic forces and moments and produce 
a response of the airplane. The variation of 
airflow velocity along a given direction exists 
with shear parallel to the flow direction. 
Hence, the velocity gradients are often re- 
ferred to as the wind “shear.” 
The effect of the vertical gust has important 
effects on the airplane at high speed because 
of the possibility of damaging flight loads. 
The mechanism of vertical gust is illustrated 
in figure 6.5 where the vertical gust velocity 
is added vectorially to the flight velocity to 
produce some resultant velocity. The principal 
effect of the vertical gust is to produce a change 
in airplane angle of attack, e.g., a positive 
(up) gust causes an increase in angle of attack 
NAVWEPS DD-BOT-BD 
APPLICATION OF AERODYNAMICS 
TO SPECIFIC PROBLEMS OF FLYING 
while a negative (down) gust causes a de- 
crease in angle of attack. Of course, a change 
in angle of attack will effect a change in lift 
and, if some critical combination of high gust 
intensity and high flight speed is encountered, 
the change in lift may be large enough to 
cause structural damage. 
At low flight speeds during approach, land- 
ing, and takeoff, the effect of the vertical gust 
is due to the same mechanism of the change 
in angle of attack. However, at these low 
flight speeds, the problem is one of possible 
incipient stalling and sinking rather than 
overstress. When the airplane is at high 
angle of attack, a further increase in angle of 
attack due to a gust may exceed the critical 
angle of attack and cause an incipient stalling 
of the airplane. Also, a decrease in angle 
of attack due to a gust will cause a loss of lift 
and allow the airplane to sink. For this 
reason, any deficiency of airspeed will be quite 
critical when operating in gusty conditions. 
The effect of the hori<oonral gust differs from 
the effect of the vertical gust in that the im- 
mediate effect is a change of airspeed rather 
than a change in angle of attack. In this 
sense, the horizontal gust is of little conse- 
quence in the major airplane airloads and 
strength limitations. Of greater significance 
is the response of the airplane to horizontal 
gusts and wind shear when operating at low 
flight speeds. The possible conditions in 
which an airplane may encounter horizontal 
gusts and wind shear are illustrated in figure 
6.5. As the airplane traverses a shear of wind 
direction, a change in headwind component 
will exist. Also, a climbing or descending 
airplane may traverse a shear of wind velocity, 
i.e., a wind profile in which the wind velocity 
varies with altitude. 
The response of an airplane is much de- 
pendent upon the airplane characteristics but