Page 235 - Understanding Flight

CH08_Anderson 7/25/01 9:02 AM Page 222

222 CHAPTER EIGHT

Fig. 8.21. Trailing cone on 737-700. (Used with
the permission of the Boeing Management
Company.)

placement of the static port is called position error. A flight test must be
performed to determine the amount of the position error. To do this the
pressure must be measured free from aircraft interference. One method
used by commercial airplane manufacturers is to use a drag cone to pull
a probe far to the rear of the airplane, as shown in Figure 8.21. The drag
cone is deployed and then retracted with a winch in the tail of the
airplane.
On many military tests, flight testing for position error is
In 1955, “Tex” Johnston became
measured on a probe mounted on a long spike on the nose of
a legend at Boeing when he
the airplane as shown in Figure 8.22. The difference between
rolled the Boeing 707 prototype
the true air pressure and that measured by the static port can
at an air show in front of many
be translated into an altimeter error, which must be published
airline executives.
for the airplane.