Wouldn't the exact effect depend on the relative areas
of the pot pitot and the usually very small holes in
the T.E. probe? The AAIB are normally very thorough
in their investigations, so I am happy to believe them,
and that this error was not the primary cause of the
accident. Neither am I recommending that you should
connect your instruments up in this way.

Derek Copeland

At 01:54 18 October 2006, Doug Haluza wrote:

Derek Copeland wrote:

T.E. probes produce a small amount of negative pressure
which increases with airspeed

Actually an ideal TE probe creates a 'negative' differential
pressure
exactly equal to the positive differential pressure
of the pitot tube
(relative to static). If the ASI was connected to Pitot
and TE (instead
of static) then the ASI would read 70% high, because
dynamic pressure
is related to airspeed squarred.

An ASI works by comparing pitot pressure with static
pressure, so reducing the static pressure will as
you
say increase the ASI reading. However the glider had
been flown in this configuration for some time, so
the pilot would have been used to any errors produced.

No way he compensated for a 70% high reading.

The AAIB actually set up a rig with the same configuration
and found that the errors where quite small. Presumably
the high pressure generated by the pitot was much
greater
than the low pressure generated by the TE probe.

This is not correct. Either the explanation is wrong
or there was a
problem with the test.

At 11:06 17 October 2006, Doug Haluza wrote:

Derek Copeland wrote:
The UK Air Accident Investigation Branch (AAIB) has
recently published a report on a fatal accident involving
a DG600 sailplane back in 2005.

The only anomaly found was that the ASI static was
connected to the Total Energy probe, which might
have
caused the ASI to misread. However tests showed that
this would only cause minor errors.

This seems completely wrong to me. The TE probe should
produce a
pressure below static equal to the dynamic pressure,
so the
differential pressure to the ASI would be doubled,
and the ASI would
read high by 70%. I would not consider this a minor
error!

I would seriously question the test results, and the
report's
conclusions based on this.