Page 274 - Planning and Design of Airports

Geometric Design of the Airfield 235

the shape of a spiral, thus the reason for suggesting a compound
curve. The following pertinent conclusions were reached as a result
of the tests [13]:
1. Transport category and military aircraft can safely and comfort-
ably turn off runways at speeds on the order of 60 to 65 mi/h on
wet and dry pavements.
2. The most significant factor affecting the turning radius is
speed, not the total angle of turn or passenger comfort.
3. Passenger comfort was not critical in any of the turning move-
ments.
4. The computed lateral forces developed in the tests were sub-
stantially below the maximum lateral forces for which the
landing gear was designed.
5. Insofar as the shape of the taxiway is concerned, a slightly
widened entrance gradually tapering to the normal width of
taxiway is preferred. The widened entrance gives the pilot
more latitude in using the exit taxiway.
6. Total angles of turn of 30° to 45° can be negotiated satisfac-
torily. The smaller angle seems to be preferable because
the length of the curved path is reduced, sight distance is
improved, and less concentration is required on the part of
the pilots.
7. The relation of turning radius versus speed expressed by the
formula below will yield a smooth, comfortable turn on a wet
or dry pavement when f is made equal to 0.13.

R = V 2 (6-4)
2 15 f
where V is the velocity in mi/h and f is the coefficient of friction.
8. The curve expressed by the equation for R should be pre-
2
ceded by a larger radius curve R at exit speeds of 50 to 60
1
mi/h. The larger radius curve is necessary to provide a grad-
ual transition from a straight tangent direction section to a
curved path section. If the transition curve is not provided
tire wear on large jet transports can be excessive.
9. The length of the transition curve can be roughly approxi-
mated by the relation

L = V 3 (6-5)
1 CR
2
where V is in feet per second, R is in feet, and C was found
2
experimentally to be on the order of 1.3.