Mike Borgelt wrote:
On 5 May 2004 16:53:06 GMT, Derrick Steed
wrote:

I have driven many miles with an automobile test rig consisting of a
pitot, a static and a TE probe connected to a pair of side by side
U-tube water manometers. The manometers share the same static and one
uses the pitot signal while the other uses the TE signal. A properly
calibrated TE probe will cause exactly the same pressure difference as
the pitot, just with the opposite sign.

I understand we need the TE probe to generate the difference
static-dynamic because classical instruments are pure mechanical and
need the TE information to compensate the vario. But given electronic
devices/computers, do we really need the TE probe at all? The
information is given, when static and dynamic pressure are known. The
rest can be calculated. Wrong?
Eggert

Eggert, right. You are correct and some electronic instruments do just
that
- they take the pitot and the static (instead of static and TE) and
subtract
them electronically, and it's not just mechanical instruments which use
TE,
the B50 has three inputs: pitot, TE, and static.

A TE probe isn't the only way of compensating for airspeed changes,
ancient
glider pilots used diaphrams to achieve the same thing.

I sent some notes to Eckhard yesterday relating to how you might try and
achieve the calculation in Cumulus.

Rgds,

Derrick.


The B50 does not do electronic TE from the pitot/static. The TE probe
provides TE for the vario and the pitot/static measures airspeed for
the TAS/speed to fly/relative netto computation.

The reason for this is that is is *much* easier to get satisfactory TE
this way for the users.

The diaphragm compensator was one of the giant setbacks to the cause
of good glider instruments. Read any of the stuff by Moffat et al from
the 1960's and you will be treated to many stories of trying to get
good TE(and mostly failing). They only work properly at one altitude
too.

Althaus's revival of the venturi type probe in about 1969 was a great
improvement and they provide correct compenation at all altitudes.

It seems to me most TE probes are somewhat shorter than this thread!

:-)

Mike Borgelt
Borgelt Instruments

I should correct the impression given above - I wasn't trying to imply the
B50 did it electronically, but I did, although it seemed obvious to me when
I wrote my bit that if it took the TE input then it used it as just that in
the conventional way.

I cherish memories of a british army nationals pilot that I crewed for back
in '69 and '70 trying to repair his diaphram compensator with a sheet of
latex material cut from a male contractive - I think he might have got a lot
more pleasure from using it in the conventional manner.

I think the thread on high energy pull ups with or without water was longer
- there was just as misconception, bogus physics, and appalling arithmetic
there too!

Still, it's a good laugh innit?

Rgds,

Derrick.