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



  Since one is most interested in accurate airspeed when on final, would
  the errors tend to cancel out changes in aircraft performance due to
  temperature or altitude?

  If the air was denser, the manometer/altimeter would read a higher
  airspeed (correct??), so the pilot would unknowingly allow the aircraft
  to fly slower to "normal" indicated airspeed.  But when the air is
  denser, the aircraft will also fly slower/ground effect will increase/
  etc, and the pilot should be able to make a safe "normal" landing.

  Or am I thinking backwards here?

  Robin B


  I am not sure I understand what you are saying "changes in A/C
  performance".
  Do you mean stall speed? I have heard of a small airline pilot in
  Mexico that would stall the old twin piston engine airliner (at
  altitude) just
  before landing on a short dirt strip to make sure he landed it as
  slow as possible.
  Paul Lamar


  "Stall speed"?  Basically ... Yes.  My old CFI kept hounding me about
  landing too fast.  Even if I greased  a landing (but still had too much
  speed) he would pull back on the yoke and force the aircraft to lift
off
  the ground again to demonstrate that I had come in too fast.  (I think
  it mostly had something to do with the fact that the old C150 he
used to
  rent to me for $11/hour had a nose-wheel that would almost shake off at
  speeds above 30kts :))

  So if you make a landing using one of those manometer airspeed
  indicators on the approach, and it happens to be a cold day, the dense
  air will push the water in the manometer higher, indicating a higher
  airspeed.  The pilot will then force the aircraft too lose more
airspeed
  and land the aircraft at a lower true speed (But the aircraft can
handle
  it, because it will not stall before touchdown because the air is
colder
  and denser on this day.

  Conversely ... On a hot day the aircraft will not fly as well, the air
  is less dense.  On approach the manometer airspeed indicator will not
  read as high due to the light air; the indicated airspeed will be lower
  than actual. The pilot will adjust power/attitude to keep the indicated
  airspeed at what he thinks is correct but is actually above desired
  airspeed, but in the light/thin air more airspeeed is required for a
  safe landing, so everything works out fine.

  Make sense??

  Robin B

 Is the manometer air speed indicator any different to any other air
 speed indicator, except those with a adjustable backround to adjust for
 temperature and altitude, the number of air particules impacting the
 water collumn or diaphragm of the air speed indicator, varies with
 altitude and/or temperature.

 John Burey


Right..  And you could just as easily have a sliding scale on the side
which does the same thing as the rotating dial on an aviation airspeed
instrument.


Matt-


One does not need accurate "true airspeed" on final as the airspeed as
seen by the airspeed indicator is what the allows the aeroplane to fly.
    John Burey