Low cost air speed indicator.

  Not compensated for temperature or altitude.

  Useful in the back seat of a tandem aircraft without
  a rear instrument panel.

  It is a simple water manometer 20 inches high.

  Paul Lamar

will it work as well with antifreeze liquid? i am thinking of wintertime...
Yvon Cournoyer

It will work but it may be off slightly as antifreeze is slightly
less dense than water. It can be calibrated or recalculated
once one determines the exact density of anti freeze.
The water calculations are based on 65 pounds per cubic foot.

Paul Lamar


My reference for ethylene glycol gives a weight of 69.5 lbs/cu ft.
Propylene glycol would be safer and is 64.675 lbs/cu ft. A 50% mix with H2O
would be a negligible difference.


Dale Davies

50 50 would be half way between 69.5 and 65 :)

Paul Lamar