At 12:35 PM 23/05/2014, you wrote:
The newer generation Varios still use TE but
have inertial sensing as an adjunct to TE to assist with gust filtering.
Regards,
John Orton
Mob: 0429357439
The inertial versions do (ie. ones that donât use a TE tube).
One other valuable feature I think is a good Artificial Horizon.
I agree though that I would rather use external
device (I use XCSoar) for glide computer (final glide, navigation etc).
Scott
You don't need a TE tube to do a total energy
vario based on pressure measurement but there are
many problems introduced by this which is why
most varios that offer this also can use a TE
probe. The main problems are that you are taking
the difference between two large signals and if
they don't arrive at the vario at the same time
you get large transient false indications. The
other problem is that a pitot and static source
on a glider are far more sensitive to yaw and
pitch changes than is a good TE probe. You may as well just use the TE probe.
The so called "inertial" varios no doubt have
the 3 axis accelerometer/gyros and magnetometer
built in (same kind of thing as in your iPad and
maybe even the same device, they are only a few
dollars) but whether or not anything useful is
done with them is another matter. They may be
there for advertising purposes. I was advised to
put them in the B600/B800 and advertise that but
not do anything with the data. If you buy a vario
with inertial sensors ask what exactly is done.
It is a good bet that you will get some
figurative arm waving and talk of "Kalman
Filters" without an actual good explanation.
It is fairly easy to build a variometer (not TE
compensated) using the inertial techniques but a
total energy variometer is far more difficult. Or
at least one that is a *good* vario with low zero
point drift, like all modern pressure transducer
varios. The MEMS (Micro Electro Mechanical
Systems) accelerometers are pretty good but the
gyros are fairly horrible. They look good when
you sit them on the bench and integrate the
output to get attitude (they measure *rate* of
roll, pitch and yaw you need to integrate these
to get attitude changes from the start attitude)
but are terrible when moved around due to
something called cross axis coupling and output
noise (no, the noise doesn't average out to zero). Been there, done that.
Inertial measurement units that will work are
still quite expensive, of the order of USD10,000
for the bare sensor and even then by the time you
do all the reference frame transforms and put it
in a dynamic flight vehicle (read glider) you'll
probably find the error budget has got out of hand.
A human pilot filters out horizontal gusts by
"seat of the pants" i.e. the vario is now showing
lift but did I feel the vertical acceleration?
The problem is that sometimes the onset of lift
is very gentle and your push or pull on the stick
can mask it easily. Sure it is simple to use an
accelerometer to detect vertical acceleration but
how do you remove the pilot inputs on the stick?
Removing them is what total energy varios are
about but by measuring the airspeed you make the
vario respond very well to small rapid changes in
airspeed caused by horizontal gusts as well as
small rapid changes in vertical motion of the
air. This makes the vario more difficult and tiring to interpret.
Anyway, our upcoming Dynamis system solves all
these problems and can be added to B600 or B800 variometer systems.
Mike
Borgelt Instruments - design & manufacture of
quality soaring instrumentation since 1978
www.borgeltinstruments.com
tel: 07 4635 5784 overseas: int+61-7-4635 5784
mob: 042835 5784 : int+61-42835 5784
P O Box 4607, Toowoomba East, QLD 4350, Australia
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