Jonathan writes:

It's funny how many pilots think that air flows down the pitot
tube. The fact of the matter is that it's a static pressure sensor inlet tube
and that all that happens is air pressure builds up and it transmitted down the
tube but is essentially a static column of air not unlike a spring. The problem
with inlets is that is the air does not hit is square on in gives variable
reading depending on the angle relative to the ambient airflow. It's very easy
to test by attaching a hose to the exhaust end of a vacuum cleaner and clamping
that blower nozzle down and hand holding the 6030 a safe distance away. By
changing the angle of the 6030 you can see immediately how this affects the
airspeed reading. Be sure to keep it a safe distance now.

What I've noticed about aircraft pitot tubes is that they all have an outside
bevel around the perimeter of the opening. I bought some 6x4mm plastic hose and
carefully cut a bevel around the perimeter so that it has a sharp edge around
the inlet. When I have tested this using the blower method while changing the
angle relative to the airflow I find I get far less variation. If I remove the
hose altogether is becomes very sensitive to even small variation in angle
relative to airflow.

The moral of the story is if you do not change the angle of attack of the inlet
of the 6030 relative to the airflow then you can dispense with the hose but will
still probably have to calibrate the pressure sensor regardless. It's rare that
these give correct TAS reading without some amount of compensation.

Steve Kroop at Flytec <<info>>
writes:

NMERider is spot on. The one thing that I would add is that there
is a divergence in the airflow around the instrument. At slower speeds this
airflow split is close to the instrument and should not effect the airspeed
reading without a pitot tube. As the airflow speeds up, the airflow split moves
forward, having a pitot tube allows the pressure to be sampled forward of this
divergence.

More important than the pitot tube is proper placement of the 6030. It needs to
oriented into the relative airflow AND it needs to be as far away from the
disturbed air around the pilot as reasonably possible. The cleanest convenient
airflow is out at the control frame corner bracket. A longer bracket arm or pod
gets the instrument out in front of the disturbed air around the pilot and
improve visibility at high speed.