At 19:49 26 July 2012, Darryl Ramm wrote:
On Thursday, July 26, 2012 8:32:41 AM UTC-7, John
Galloway wrote:
At 13:34 26 July 2012, JohnDeRosa wrote:
On Jul 26, 3:33=3DA0am, John Galloway wrote:
Flarm themselves have made the same point since
the
beginning. =3DA0See their PP presentation from
2005:


http://www.flarm.com/files/basic_presentation_en.ppt

At 22:22 25 July 2012, John Trezise wrote:

On Jul 25, 11:14=3D3DA0am, Darryl Ramm
=3DA0wrote:
And if I was religious I'd thank God G made it
out=
=20
OK.

Darryl

Having with at a "flarm mandatory" club for over
4=
=20
years,
my view is
that flarm is of little use where there are a
significant
number of
gliders in a gaggle (ie contest/regatta situation)
as=20
the
alarms are
set of very frequently, but there is not the time to
identify whether
the cause is the glider you can see or someone
else.

John

Slide numbers that seem to relate to gaggling; 12, 17

I might be wrong but I don't see that the FLARM
PPT=20
mentions anything
if their device is good, bad or indifferent during
gaggling.

Did I miss something?

- John

=20
The diagrams in Slide 12, "Situation in Gliding",
indicate=20
the scenarios in which Flarm was predicted to give=20
improvement on See and Avoid and the one that it
can't -=20
i.e. "identical circling".
=20
John G.

As I think "Flarm" (Urs?) is already trying to say in this
thread. This
may=
well change with use of the second flarm antenna in
PowerFLARM -- if it
is=
mounted to the rear/underside of the glider. We'll need
to see how many
ow=
ners do that with PowerFLARM and how it works out in
practice.

My personal worst scare in a thermal was a clueless pilot
entering the
ther=
mal in the opposite direction, coming straight at me while
I was busy with
=
a few other gliders above and below me, something I
expect flarm would
have=
totally alerted me to before I saw him. OTOH there are
probably lots of
ti=
mes I was aware of other gliders thermalling close by in
the same
direction=
and never saw them.

We all need to remember that saying: perfection is the
enemy of good. We
do=
n't need to be seeking perfection, but no argument that
understanding
pract=
ical limitations is important.

Darryl


To clarify, Darryl, I am a strong proponent of Flarm and co-
wrote the Scottish Gliding Union trial report on Flarm in
2007. It has long been known, for the exactly the
reasons that John Trezise pointed out, that when there
are several gliders in close proximity in thermal gaggle
then the pilot is not easily able to interpret which glider is
"flarming" him when a collison alert sounds. This isn't to
do with poor Flarm reception etc. Partly it is due to the
fact that the (unavoidable) Flarm altitude buffer is greater
than the height separation that pilots will happily accept in
a gaggle. Partly it is due to the fact that Flarm is
calculating a collision alert up to around half a circle ahead
- impossible for a pilot to do with several other gliders in a
close gaggle.

We did various trial collision scenarios for our report.
With only 2 trial gliders in a thermal sometimes an alert
would sound and I would wonder why as there was no
obvious imminent collision risk. If no corrective action was
taken it would become apparent that Flarm was in fact
right and the extended circular paths would intercept
(within the Flarm software criteria) eventually.

In the UK most pilots I speak to regard Flarm alerts in a
gaggle as a general reminder to keep the head swivelling
inside and outside the circle - especially looking for gliders
that may be joining the gaggle. A few pilots regard these
alerts as "false alarms", which is unfortunate.

John Galloway