Page 25 - Understanding Flight

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12 CHAPTER ONE

The Pitot Tube

P total measured here
(Pitot tube)

Flowing air

P static measured here
(static port) P dynamic measured here
(Differential pressure gauge)
Fig. 1.10. Measurement of pressures with the Pitot tube.

During WWII the length of a belt not changed. Thus the total pressure has increased. The moral
of 50-caliber machine gun bullets of this story is that when someone refers to air pressure of
was 27 feet. When a pilot moving air they are probably referring to static pressure
emptied his guns into a single (though they may not know it). It is also wrong to think that
target, he was giving it the just because air is flowing faster the (static) pressure has
“whole nine yards.” decreased. This topic is covered in more detail in the Appendix.

The Pitot Tube
As mentioned previously, the tube measuring the total pressure in Figure
1.10 is called the Pitot tube, which, along with static pressure, is used for
measuring the airspeed of an airplane. Several Pitot tubes can be seen on
the front of the large jets at the airport. A single Pitot tube can be seen
protruding (or hanging) from the wing of small airplanes. The hole that
measures the static pressure of the air is the static port. This port is usu-
ally on the side of the airplane fuselage near the front, though it is also
occasionally placed on the side of the Pitot tube itself. In an airplane
there is a gauge that measures the difference between these two
devices and is calibrated in speed. This is the airspeed indicator.
In 1908, a French woman named
Since the dynamic pressure measured is related to the dynamic
Therese Peltier became the first
pressure, there is also a correction made by the pilot for the
woman pilot.
reduced density of the air at altitudes above sea level.