traveling is just as important, if not
more so, than knowing how fast a car
is moving. However, the measurement
of an aircraft' s speed is a bit more complex than the speedometer on an
automobile. In this article we will
discuss the various types of air speed
and how they are measured. Pilots speak of several types of air
speed. When read directly off the air
speed indicator, the value is called
indicated air speed (IAS). Indicated air
speed has several factors that must be
corrected in order to determine the actual speed of an aircraft over the
ground. To determine the aircraft' s indicated air speed, two pressures are
measured. A pitot tube is positioned
on the exterior of the aircraft so that
the air molecules of the atmosphere
" ram" into it. The faster the aircraft is traveling, the greater the ram
pressure. As an aircraft climbs, the
atmospheric air pressure decreases, as
does the ram pressure. To account for
this, the aircraft has a static air
pressure port that is also connected to the air speed indicator. The greater the
difference between the ram and static
pressures, the greater the indicated air
speed.
