brakes does not produce the maximum coefi- 
cient of friction. The incipient skid condi- 
tion will produce the maximum coefficient of 
friction but this peak is difficult to recognize 
and maintain without an antiskid system. 
Judicious use of the brakes is necessary to 
obtain the peak coefficient of friction but not 
develop a skid or locked wheel which could 
cause tire failure, loss of control, or consider- 
able reduction in the friction coefficient. 
The capacity of the brakes must be sufficient 
to create adequate braking torque and produce 
the high coefficient of friction. In addition, 
the brakes must be capable of withstanding 
the heat generated without fading or losing 
effectiveness. The most critical requirements 
of the brakes occur during landing at the 
maximum allowable landing weight. 
TYPICAL ERRORS OF BRAKING TECH- 
NIQUE. Errors in braking technique are usu- 
ally coincident with errors of other sorts. For 
example, if the pilot lands an airplane with 
excessive airspeed, poor braking technique 
could accompany the original error to produce 
an unsafe situation. One common error of 
of braking technique is the application of 
braking torque in excess of the maximum 
possible rolling torque. The result will be 
that the wheel decelerates and locks and the 
skid reduces the coefficient of friction, lowers 
the capability for side force, and enhances the 
possibility of tire failure. If maximum brak- 
ing is necessary, caution must be used to 
modulate the braking torque to prevent lock- 
ing the wheel and causing a skid. On the 
other hand, maximum coefficient of friction is 
obtained at the incipient skidding condition 
so sufficient brake torque must be applied to 
produce maximum friction force. Intermittent 
braking serves no useful purpose when the 
objective is maximum deceleration because 
the periods between brake application produce 
only slight or negligible cooling. Brake 
should be applied smoothly and braking 
torque modulated at or near the peak value 
to insure that skid does not develop. 
NAVWEPS OD-BOT-80 
APPLICATION OF AERODYNAMICS 
TO SPECIFIC PROBLEMS OF FLYING 
One of the important factors affecting the 
landing roll distance is landing touchdown 
speed. Any excess velocity at landing causes 
a large increase in the minimum stop distance 
and it is necessary that the pilot control the 
landing precisely so to land at the appropriate 
speed. When landing on the dry, hard surface 
runway of adequate length, a tendency is to 
take advantage of any excess runway and 
allow the airplane to touchdown with excess 
speed. Of course, such- errors in technique 
cannot be tolerated and the pilot must strive 
for precision in all landings. Immediately 
after touchdown, the airp1ar.e lift may be 
considerable and the normal force on the 
braking surfaces quite low. Thus, if excessive 
braking torque is applied, the wheel may lock 
easily at high speeds and tire failure may take 
place suddenly. 
Landing on a wet or icy runway requires 
judicious use of the brakes because of the re- 
duction in the maximum coefficient of friction. 
Because of reduction in the maximum attain- 
able value of the coefficient of friction, the 
pilot must anticipate an increase in the mini- 
mum landing distance above that applicable 
for the dry runway conditions. When there 
is considerable water or ice on rhe runway, an 
increase in landing distance on the order of 40 
to 100 percent must be expected for similar 
conditions of gross weight, density altitude, 
wind, etc. Unfortunately, the conditions 
likely to produce poor braking action also 
will cause high idle thrust of the turbojet 
engine and the extreme case (smooth, glazed 
ice or heavy rain) may dictate shutting down 
the engine to effect a reasonable stopping 
distance. 
REFUSAL SPEEDS, LINE SPEEDS, AND 
CRITICAL FIELD LENGTH 
During takeoff, it is necessary to monitor 
the performance of the airplane and evaluate