At 01:36 29 September 2007, Mike Borgelt wrote:
The real problem with all TE varios at present is that
horizontal gusts will
cause spurious readings. The problem gets worse with
the square of the
TAS(See our website article). If you slow the vario
response to get rid of
the problem you get rid of good information about vertical
air motion
changes too. I've been going around in a thermal with
a PZL and a B21 in a
customer's glider and seen the B21 show 1 knot on
one side of the thermal
with peaks of 6 knots while the PZL sat on close to
2 knots all the way
round. Re centering on the B21 got me 5 knots on the
averager. This was an
unusually smooth thermal and it was hard to tell by
feel. A reasonably fast
responding vario is an advantage but there is a high
workload in mentally
filtering the horizontal gust 'noise' from the vertical
'signals'
This may change soon.
Mike Borgelt
Borgelt Instruments
Maybe sooner than you may think! This is the main problem
that Dr Ludek Smolik's Yaw-Free probes are designed
to combat. for those who did not see my last post on
it, here is his answer to my query again, along with
links to probe info and a youtube video link showing
the swiveling action that makes these probes resistant
to yaw/gust errors (particularly the 2 and 3 way probes,
for reasons described below):
http://www.eaglebrandproducts.com/TE...rices_2006.pdf
and the Youtube video:
http://youtube.com/watch?v=OpN9sYHF_yc
I am still awaiting the performance plots, and will
post
them when I get them.
Paul Hanson
Dear Mr. Hanson,
many thanks for your mail which reached me here in
Europe across New Zealand.
ItŽs very pleasant for me to serve you some information
on my project.
The probes are manufactured in Germany in a more or
less individual manner according to the pilots wishes.
The major step forward is the yaw-free pressure measurement
of all three important pressures at same place and
time. Time to time there are discussions on web or
in articles in magazines about the yaw dependence of
the so called TE-pressure, which is normally taken
as a velocity dependent under pressure due to the
vorticity behind an particular object like e.g. a small
tube.
But such discussion is just a half truth ! ItŽs obvious
that beside the TE-under pressure the static and total
pressure are very sensitive for �yawing�
too. The new probe improves the measurement by rotating
around the yaw axis significantly.
If you are interested on results, I can provide plots.
But the tenor is: if a standard TEK-probe has an spread
in the probe coefficient of 10 or 20% due to yaw angel
or air turbulences, for the new probe such spread is
0%.
It is hard to make meaningful photographs of the probes
because they all are black and look boringJ) Therefore
I send you a short video where the functionality and
the free rotatability around the yaw axis is demonstrated.
The two prongs of the �Y� shape are
the tubes for the TE-measurement and the orifices
for total and static pressure are mounted in the small
antennas in the forward direction.
Of course , the probes fit to all standard adapters
or if desired to a new type of 3 way adapter, where
all the sealing o-rings are mounted and accessible
on probe itself.
One word to the results, in principle itŽs difficult
to compare probes really meaningful simply using a
flume. Normally the flume does not simulate either
real air conditions nor the glider influences and last
not least the individual pilots behaviour.
For this reason only a measurement on the same place
and at the same time on one glider with a same type
of electronics can provide the best and direct comparison..
For this purpose I made a probe with 2 x 3 independent
orifices. 3 orifices build a standard probe the other
3 orifices are build like the yaw-free probe. Feeding
the data to two independent vario circuits and logging
the results one obtain a flight �seen�
from two different probes. This experiment is still
in preparation and is foreseen for next spring.
I hope this short overview gives some helpful information
Best Regards
Ludek Smolik