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


 I was thinking about the propylene mix.

Dale Davies

Most use ethylene.

Paul Lamar