On Oct 28, 7:32*am, Andreas Maurer wrote:
On Thu, 28 Oct 2010 06:53:27 -0700 (PDT), Brian
wrote:

I hadn't really considered how the projected flight path system works
before. But after thinking about it for a bit it has a lot of
potentional. How much the Flarm actually uses I do not know.

Flarm uses ONLY projected flight paths to calculate a collision
probability.

Even without that I
can see that gliders could get very close but have potential flight
paths that would make colliding impossible and as a result would not
create a collision alarm.

This is exactly how Flarm works.
Flarm doesn't care about distances - as long as Flarm doesn't detect a
potential collision cource, you can fly very close to each other
without getting a warning - even if you are circling.

Andreas

I think that's the secret for how you make it useful in thermals - if
the system knows you are circling it can do a better job predicting
your curved flight path and potential threats along that path. I
presume that if you assume the full maneuvering envelope of each
glider you'd generate a lot of warnings, so it would make sense to
assume something more limited that strikes a balance between false
positive warnings and missing potential maneuvers that could create a
threat with little advanced notice. Think of a glider pulling up into
a thermal as a good example. I assume that Flarm does all this based
on the following explanation where an expanding projected flight path
envelope is depicted:

http://www.gliderpilot.org/Flarm-WhatDoesItDo

As to ADS-B - without some algorithm for projecting flight paths the
only warning you can realistically generate is a proximity warning.
Even warning only for declining separation distance is a crude form of
relative path prediction, just not a very useful one - particularly
for glider operations with multiple targets and circling flight.

9B