Airspeeds – Get to Know the Operation and Manufactures
How it works
Pitot pressure is forced into the diaphragm causing it to expand like a balloon. Static pressure is contained within the indicator case and surrounding the diaphragm. As the static pressure changes it, will either cause the diaphragm to compress, as the aircraft loses altitude or allow it to expand as the aircraft gains altitude. This expansion and contraction of the diaphragm is mechanically linked to the pointer causing it to move around the dial thereby displaying the speed of the aircraft as a function of the difference between the Pitot and static pressures.
Range Marks
Range marks are a reminder to the pilot of the aircrafts basic operating envelope as it pertains to airspeed. Typical range marks found on an air speed dial are:
White Arc – VFE – This is the maximum speed at which the aircraft can operate safely with the flaps extended.
Green Arc – This is the normal operating range
Yellow (Orange) Arc – Caution
Red Radial – VNE – Never exceed speed
Blue Radial – This is the minimum operating speed using one engine on a two engine aircraft.
Note: Maneuvering speed is not marked on the dial, it is normally on a placard, which is located on the instrument panel.
Manufactures
The following companies all have manufactured air speed indicators and are the most common that you will see:
United Instruments
Kollsman
Aerosonic
Aeromarine
McCleod
UMA
Garwin
Edo-Aire
