A great instrument for hang gliding and paragliding.
The Hall Airspeed Indicator is a simple, reliable way to keep track of your
airspeed while flying. An airspeed indicator will help you to fly at the appropriate
speed for a given situation and when compared with variometer readings yields a wealth of
information about the performance of your wing. Whether you're applying speed-to-fly
theory to your inter-thermal glides or trying to get the most out of the house thermal, the
Hall Airspeed Indicator will help.
The design of the Hall type airspeed indicator involves using a ram air versus
static pressure differential to raise a disc in a tapered tube against the force of the weight
of the disc. Because of this the ASI has certain operating limitations:
a) It is only accurate in one G
flight. If you are turning at a bank angle of more than 30 degrees, the ASI will read artificially
low as a result of the G loading of the turn. Reliance on the ASI for limiting airspeeds in
high banked sustained spiral maneuvers will likely cause you to exceed the placarded speed
limitations of the glider and will compromise your safety.
b) It is only accurate when within
15-20 degrees of the vertical orientation.
From the Wills Wing Fusion Owner's Manual:
Speeds to Fly and Using Your Airspeed Indicator
The Wills Wing Hall Airspeed Indicator has been specially designed
to help you fly your Fusion at the proper speeds for optimum safety and performance.
There are four color coded bands on the ASI:
White: This is the range from 18
m.p.h. to 28 m.p.h.. This is the normal thermalling speed range for light to moderate thermalling
conditions. Try to keep your speed within this range when thermalling in light to moderate
conditions. Very strong or turbulent conditions will warrant a faster flying speed.
Green: The top of the green region
represents the placarded maximum rough air and maximum maneuvering speeds. This speed of 48
m.p.h. should not be exceeded except in smooth air, and no abrupt large control deflections
should be used above this speed. In significant turbulence it is recommended that you keep
the airspeed "in the green" for best control and stability and best structural margin
at all times.
Yellow: This region represents
the upper speed range between maximum rough air / maximum maneuvering speed and the speed
never to exceed. You should fly in this range only in smooth air as described above.
Red Line: This is your never to
exceed speed. At no time should you fly faster than this speed.