LXNAV flarmMouse

On Monday, January 7, 2013 10:06:48 AM UTC-5, Tim Newport-Peace wrote:
As I recall, for FLARM to work properly, a pressure sensor is required.
FLARM without Pressure Altitude has too much 'jitter'. The altitude used
'FLARM to FLARM' is GPS altitude smoothed by pressure altitude.

Wrong.

As I recall, for FLARM to work properly, a pressure sensor is required.
FLARM without Pressure Altitude has too much 'jitter'. The altitude used
'FLARM to FLARM' is GPS altitude smoothed by pressure altitude.

Always interesting to read all those FLARM rumors No idea where
that particular one comes from, but it's definitely not the case.
GPS altitude is typically accurate to a few meters, more than enough
for collision avoidance. Check your IGC logs.

Many 'Classic' FLARM devices don't even have a pressure sensor.

PowerFLARM's pressure sensor is used to calculate relative altitude
between your own ship and XPDR equiped traffic (PCAS, sometimes ADS-B),
except for the 'Pure' variant.
Why ADS-B? There are indeed ADS-B installations which transmit baro altitude, GPS position, but no GPS altitude.

HTH
--Gerhard (dev mgr FLARM)

On Monday, January 7, 2013 5:40:22 PM UTC-5, Tim Newport-Peace wrote:
Dave Nadler writes
On Monday, January 7, 2013 10:06:48 AM UTC-5, Tim Newport-Peace wrote:
As I recall, for FLARM to work properly, a pressure sensor is required.
FLARM without Pressure Altitude has too much 'jitter'. The altitude used
'FLARM to FLARM' is GPS altitude smoothed by pressure altitude.

Wrong.

Justify.

As Tim should be well-aware from work with IGC loggers,
the cockpit static used by loggers (and FLARM) is
subject to large variations in indicated altitude
due to air-vent effects. Changing speed and/or fiddling
the airvent leads to big indicated altitude changes.
Not appropriate for collision avoidance...

Hope that helps clarify,
Best Regards, Dave

I have performed some measurements last season using a bmp085 sensor running at roughly 40Hz (I recall, no oversampling anyway).
In my Pilatus B4 I had it mounted behind my head, between the wings.

I could see an effect when I was rolling over the ground during winch launching, where pressure increased slightly.
I could also see perfectly when I opened my airbrakes, which made a very sharp drop of roughly 20 meters. When I closed them the value restored to the old
value again.

I have not yet tried a wide variety of speed ranges, nor have I been able to compare the reported altitude with a GPS receiver. That is planned for next
season.

But I would agree that Pressure Altitude itself for FLARM would not be

good.



Getting back to the original question, flarmMouse claims to produce an

IGC file and a true IGC file should have pressure altitude. Before

flarmMouse could get IGC approval, pressure altitude would need to be

recorded.


How accurate is the Nano then?

On Thursday, January 10, 2013 8:12:30 PM UTC-8, Dale Watkins wrote:


But I would agree that Pressure Altitude itself for FLARM would not be



good.







Getting back to the original question, flarmMouse claims to produce an



IGC file and a true IGC file should have pressure altitude. Before



flarmMouse could get IGC approval, pressure altitude would need to be



recorded.





How accurate is the Nano then?

42. Now what's your question?

Accuracy for what? GPS 2D Location? GPS altitude? (which ellipsoid? etc?) Pressure altitude? That nano includes both a pressure transducer and a GPS sensor and meets all the requirements for IGC approval. The need for a pressure transducer is for accuracy to a pressure datum that is required by the IGC. Without a pressure sensor its a non-starter for IGC approval.

Darryl