On Wed, 21 Apr 2004 00:39:14 GMT, "Bill Daniels"
wrote:


"Mike Borgelt" wrote in message
.. .
On 16 Apr 2004 03:27:43 -0700, (Robert) wrote:

Hello! Can someone tell me which compensated varios do not need a
total energy probe? (no electronic compensation) Thanks a lot! Robert

While some people report good results with pitot/static TE your
results may differ. I wonder if thy've tested two identical varios
capable of being on pitot/static or TE side by side on the same
sources then on the different sources side by side. I've done this
with TE probes mounted in different places on the ship and got
interesting results.The gear doors are a good location for a TE probe.

I have one pitot/static TE vario (With dedicated static ports.) and one TE
probe vario (B40)

Generally pitot and static probes/ports are much more sensitive to
sideslip than are good TE probes.(Good TE probe = Irving type two hole
probe )

True, it's easily observed.


You may have timing issues due to the distributed flow resistance and
capacitance of the sailplane plumbing.

Yep, the TE probe vario is about 0.25-0.5 sec slower than the pitot/static
vario at the onset of lift. Mike, do you think this is due to the long
tubing run to the fin mounted TE probe?

May be, particularly the capacity with small holes at the probe.
You may also be seeing the g effect when you enter lift. The probe is
about 1 meter above the instrument. Add g load due to entering lift
and the vertical pressure gradient in the glider plumbing in the fin
increases. As the pressure at the probe holes hasn't increased this
means the B40 sees increased pressure i.e. sink while the G is
increasing which will have to effect of slowing the response to lift.
This is one advantage of pitot static TE when using nose pitot and
fuselage nose statics. Also why a TE probe sticking out of the nose
ahead of the glider is better than a tail mounted probe.
There is also an effect of the rotation of the glider when pitching
with pressure sources a long way from the C of G.



What pitot/static positions are you using? I presume nose and sides
of the nose. Some people run pitot static TE off tail fin mounted
pitot static probes which are no better than a TE probe on the fin and
maybe worse fro the above reasons and the one below.

If you do pitot/static TE you want the pitot to be twice as far from
the C of G as the static port and on the same side. This avoids
pressure transients due to atmospheric pressure gradient during pitch
manouvers. Stig Oye pointed this out to me 20 years ago.

The B40 has electrically adjustable instrument time constant. See the
manual but VERRRY gently on the adjust please! Try about 20 degrees in
the faster direction if you like on the 180 deg trimpot. These are
factory set at the midway position and I haven't seen any reason to
change mine nor have I had people complain about the factory setting.


Mike Borgelt




Remember for pitot/static TE you are measuring two large signals and
subtracting them. Minor timing differences in the signals and small
non linearities in the measurement show up as large unwanted
transients on your vario.

Hmm, they seem to track together most of the time but there are differences.
I trust the B40 the more.

Thanks for the comments, Mike.

Bill Daniels