On Fri, 27 Nov 2015 11:27:06 -0800, jfitch wrote:

On Friday, November 27, 2015 at 11:15:40 AM UTC-8, Martin Gregorie
wrote:
On Fri, 27 Nov 2015 09:31:17 -0800, jfitch wrote:

James mentioned false alarms while diametrically opposed in thermals.
That is highly unlikely to be due to wind drift.

... which is something I've never experienced, but maybe I've never
shared a thermal with an idiot since I've had FLARM fitted. That said,
at my club there was one collision in a thermal between two
FLARM-equipped gliders. AFAICT from talking to the pilots, one of them
was far from being on the diametrically opposite side of the thermal
and then misread the intentions of the other pilot. Under these
conditions FLARM won't help because the time between its warning being
triggered and the collision is likely to be too short for either pilot
to do anything about it.


--
martin@ | Martin Gregorie gregorie. | Essex, UK org |

The short warning you get in thermals is a limitation of Flarm.
Mitigated by a very good tactical screen of which there are
unfortunately few examples. One of the compromises that appear to have
been made to eliminate false alarms in thermals is a very short warning
distance. I have flown close to other gliders in thermals (yes they were
aware) to see just when the alarms occur. I'm not criticizing Flarm for
this, something I think they had to do. Too many extraneous alarms is as
bad as no alarms at all.

Yes - agreed. I wasn't criticising FLARM at all for this. IMO the reality
of thermal gaggles is that everybody *must* maintain situational
awareness in a multiply occupied thermal. Thinking about it a bit
further, if everybody at more or less the same height in a thermal flies
sensibly, the time to go from safe to collision takes enough time to make
avoidance fairly easy. It would take at least one pilot to be grossly out
of position to make a collision imminent (think leaving by blasting
across the centre or getting too close behind or below another glider).
FLARM will spot a dangerous joining manoeuvre but whether the warning
would do you any good may depend on where the other glider(s) in the
thermal are, i.e. do you have an escape route that doesn't endanger
anybody else.


--
martin@ | Martin Gregorie
gregorie. | Essex, UK
org |