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Urs,
Very helpful
explanation.
Thank you.
----- Original Message -----
Sent: Tuesday, October 25, 2005 5:07
PM
Subject: Re: [Aus-soaring] Zaon Flight
Systems collision avoidance
Hello,
Let me comment the video DG-video:
http://www.dg-download.de/Videos/flarm-rennes.wmv.
0:06
Flarm correctly warns of a aircraft ahead (warning leven 1)
0:08-0:10
Pilot pulls up and rurns right, alarm stops immediately
0:11-0:16
Pilot turns back back onto collision
course
0:18 Flarm
warns of aircraft ahead and below (warning level 2)
0:19-0:24 alarm
continues as other aircraft is very close and on opposing
track
The
reason for the 2-3sec alarm delay at 0:18 is that Flarm calculates a
"motion prediction" and this algorithm assumes that the left turn
initiated
at 0:11 continues. As the pilot stops his turn at 0:16 Flarm
calculates new
trajectories and issues an alarm for the straight
flight...
Please also note that this display is set to "alarm only"
mode. Most pilots
prefer the "nearest" mode, which not only shows alarms
but also the position
of the nearest aircraft (with steady light and no
beeping). So in this video
the PIL could have tracked the relative
position of the other aircraft
during his maneuvers if he had left it on
"nearest" mode (default).
>I found it interesting that based on the
latter part of that video, it
>would be
>possible to be at the
same height and flying towards (but a tad behind)
>that
>other
glider ... and not get any warning unless the tracks intersect or
>converge
>..and if the other remains unseen it would be possible
to tighten the turn
>and converge to get a warning just as they
collide.
Flarm uses a combination of time-to-impact on the predicted
trajectory and
absolute distance for issuing alerts.
But there will
always be a tradeoff between too many and too few alarms...
Based on
the feedback of pilots and many hours of logged flights we
regularly
improve the alarm algorithms. Updates (of the firmware and the
obstacle
database) can be done by the user with a standard IGC loggercable,
the
same setup is also used to read out flight logs (IGC format, but NOT IGC
approved flight recorder).
For the 2005 devices we also added a
barometric sensor, to improve the
prediction of vertical seperation. It is
however not yet used in the 2005
firmware.
> It just proves that
Flarm is certainly useful but it is an aid to the
> "see"
>of
see-and-avoid, but there can never be any guarantees even if
all
>aircraft are equipped.
Absolutely! Flarm is an aid for VFR
flights and only improves safety if the
pilots do not change flight
tactics.
However we have noted that pilots actually become fore careful
with Flarm as
they come to realize how many close "visits" they had and
did not even know
about.
>How does it indicate proximity as per
your 2nd last para?
Proximity (actually time-to-impact) is indicated with
the flash frequency
and buzzer tone hight.
>Does anyone know
what frequency FLARM transmits on, please?
Australia: 921 MHz /
Europe 868.2 MHz. Can be configured by our free
software
Hope this
helps
Urs -
Flarm
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