FLARM.....for good, or evil??

On 10/27/2010 7:20 AM, wrote:
in "awareness mode", of course a led will indicate where the closer
glider is, but still alarms will only be triggered when a deviation
makes the collision a real possibility.

aldo cernezzi

Since the GPS accuracy is probably much poorer than 10 feet, when a
glider comes within 10 feet, I figure the FLARM should consider that a
collision, no?
I don't know what Flarm does in that case, but my guess is the
*relative* accuracy is much better than the *absolute* accuracy. If
that's true, then each glider might have position errors of much more
than 10 feet, but they'll have nearly the same errors, giving a more
accurate separation distance.

Maybe someone more familiar with GPS in this situation can jump in here
and tell us?

--
Eric Greenwell - Washington State, USA (change ".netto" to ".us" to email me)
- "Transponders in Sailplanes - Feb/2010" also ADS-B, PCAS, Flarm http://tinyurl.com/yb3xywl
- "A Guide to Self-launching Sailplane Operation Mar/2004" Much of what you need to know tinyurl.com/yfs7tnz

Having used Flarm for 2 years I have to agree, it is most effective in a
low density situation that is X/C and ridge flying which is what it was
designed for. Glider Highways where you are likely to meet another going
in the opposite direction at the same level Flarm will give you plenty of
warning. Almost all 95% + aircraft that I see at the same level are
gliders and if they all had Flarm that would please me. I am not sure how
useful the ADS and Transponder features will be, conflict with other
aircraft is thankfully unusual but if it picks up one power pilot with his
"head in the office" it will be worthwhile.

Dave

At 19:43 27 October 2010, Ramy wrote:
On Oct 27, 10:39=A0am, John Smith wrote:
Bruce Hoult wrote:
What do you consider dangerous in cross country flying?

I've lost three friends by midairs during leisure cross country
flying
but none during competition flying (all in Pre-FLARM-age). That's
just
my purely personal, anectotcal and irrelevant statistics.

Where I fly, there are "glider highways" which can be pretty crowded
on
thermally active weekends. With the difference that competition pilots
tend to be 100% awake, which cannot always be said of leisure pilots
on
an 8 hour leisure flight. Interesting is that one of the midairs
mentioned above didn't happen on such a highway, but out in the
nowhere
after the two gliders both had happily cruised along on a straight
track
for several minutes (as the logger file showed), until they happened
to
be in the same place at the same time. Again just my purely personal,
anectotical and irrelevant experience.

Back to the topic: I'm convinced that all three would still be alive
had
FLARM already existed.

I think these examples reinforces the notion that PowerFlarm should be
installed by all pilots and not just competition pilots.
And I am glad to report that many pilots in my area (Region 11)
already per ordered the powerflarm even though most of them are not
flying in contest.

Ramy

Having used Flarm for 2 years I have to agree, it is most effective in a
low density situation that is X/C and ridge flying which is what it was
designed for. Glider Highways where you are likely to meet another going
in the opposite direction at the same level Flarm will give you plenty of
warning. Almost all 95% + aircraft that I see at the same level are
gliders and if they all had Flarm that would please me. I am not sure how
useful the ADS and Transponder features will be, conflict with other
aircraft is thankfully unusual but if it picks up one power pilot with his
"head in the office" it will be worthwhile.

Dave

At 19:43 27 October 2010, Ramy wrote:
On Oct 27, 10:39=A0am, John Smith wrote:
Bruce Hoult wrote:
What do you consider dangerous in cross country flying?

I've lost three friends by midairs during leisure cross country
flying
but none during competition flying (all in Pre-FLARM-age). That's
just
my purely personal, anectotcal and irrelevant statistics.

Where I fly, there are "glider highways" which can be pretty crowded
on
thermally active weekends. With the difference that competition pilots
tend to be 100% awake, which cannot always be said of leisure pilots
on
an 8 hour leisure flight. Interesting is that one of the midairs
mentioned above didn't happen on such a highway, but out in the
nowhere
after the two gliders both had happily cruised along on a straight
track
for several minutes (as the logger file showed), until they happened
to
be in the same place at the same time. Again just my purely personal,
anectotical and irrelevant experience.

Back to the topic: I'm convinced that all three would still be alive
had
FLARM already existed.

I think these examples reinforces the notion that PowerFlarm should be
installed by all pilots and not just competition pilots.
And I am glad to report that many pilots in my area (Region 11)
already per ordered the powerflarm even though most of them are not
flying in contest.

Ramy

On 10/27/2010 3:48 PM, Eric Greenwell wrote:
On 10/27/2010 7:20 AM, wrote:
in "awareness mode", of course a led will indicate where the closer
glider is, but still alarms will only be triggered when a deviation
makes the collision a real possibility.

aldo cernezzi
Since the GPS accuracy is probably much poorer than 10 feet, when a
glider comes within 10 feet, I figure the FLARM should consider that a
collision, no?
I don't know what Flarm does in that case, but my guess is the
*relative* accuracy is much better than the *absolute* accuracy. If
that's true, then each glider might have position errors of much more
than 10 feet, but they'll have nearly the same errors, giving a more
accurate separation distance.

Maybe someone more familiar with GPS in this situation can jump in here
and tell us?

Even if the relative GPS position computed by each glider has 0 error,
you still have the problem that at 50 Knots, each aircraft is moving ~
75 ft / second. With FLARM (or ADS-B) only transmitting positions every
second, you can't rely on these technologies to protect you from random
course changes that the systems can't possibly predict, if you are in
close proximity.

--
Mike Schumann

On 10/27/2010 5:33 PM, Mike Schumann wrote:
On 10/27/2010 3:48 PM, Eric Greenwell wrote:
On 10/27/2010 7:20 AM, wrote:
in "awareness mode", of course a led will indicate where the closer
glider is, but still alarms will only be triggered when a deviation
makes the collision a real possibility.

aldo cernezzi
Since the GPS accuracy is probably much poorer than 10 feet, when a
glider comes within 10 feet, I figure the FLARM should consider that a
collision, no?
I don't know what Flarm does in that case, but my guess is the
*relative* accuracy is much better than the *absolute* accuracy. If
that's true, then each glider might have position errors of much more
than 10 feet, but they'll have nearly the same errors, giving a more
accurate separation distance.

Maybe someone more familiar with GPS in this situation can jump in here
and tell us?

Even if the relative GPS position computed by each glider has 0 error,
you still have the problem that at 50 Knots, each aircraft is moving ~
75 ft / second. With FLARM (or ADS-B) only transmitting positions
every second, you can't rely on these technologies to protect you from
random course changes that the systems can't possibly predict, if you
are in close proximity.
FLARM does more than transmit positions: it transmits the projected path
of it's glider. Here's what I understand will happen: when the pilot
makes a course change, a new path is calculated and compared to the
paths Flarm has received from nearby gliders. If this new path puts it
on a collision course with any of them, the pilot is warned
"immediately", meaning it does not have to wait one second. The new path
will be transmitted within one second, so the nearby gliders can update
the other glider's path in their database. It might actually be more
sophisticated than that, such as transmitting a new path sooner if the
amount of change is "large", but I don't know what the algorithms are.

This projected path is a key element to the system working properly.
Without it, each FLARM unit would have to calculate the path of every
nearby glider; with it, each unit only has to calculate one path - it's
own. Potentially, it could be using a much higher position rate than
once a second to calculate it's projected path. In any case, the result
is much better than you might think for a system that transmits once a
second.

Does ADS-B transmit a projected path, or just position?

--
Eric Greenwell - Washington State, USA (change ".netto" to ".us" to email me)
- "Transponders in Sailplanes - Feb/2010" also ADS-B, PCAS, Flarm http://tinyurl.com/yb3xywl
- "A Guide to Self-launching Sailplane Operation Mar/2004" Much of what you need to know tinyurl.com/yfs7tnz

On Oct 27, 8:16*pm, Eric Greenwell wrote:
On 10/27/2010 5:33 PM, Mike Schumann wrote:

On 10/27/2010 3:48 PM, Eric Greenwell wrote:
On 10/27/2010 7:20 AM, wrote:
in "awareness mode", of course a led will indicate where the closer
glider is, but still alarms will only be triggered when a deviation
makes the collision a real possibility.

aldo cernezzi
Since the GPS accuracy is probably much poorer than 10 feet, when a
glider comes within 10 feet, I figure the FLARM should consider that a
collision, no?
I don't know what Flarm does in that case, but my guess is the
*relative* accuracy is much better than the *absolute* accuracy. If
that's true, then each glider might have position errors of much more
than 10 feet, but they'll have nearly the same errors, giving a more
accurate separation distance.

Maybe someone more familiar with GPS in this situation can jump in here
and tell us?

Even if the relative GPS position computed by each glider has 0 error,
you still have the problem that at 50 Knots, each aircraft is moving ~
75 ft / second. *With FLARM (or ADS-B) only transmitting positions
every second, you can't rely on these technologies to protect you from
random course changes that the systems can't possibly predict, if you
are in close proximity.

FLARM does more than transmit positions: it transmits the projected path
of it's glider. Here's what I understand will happen: when the pilot
makes a course change, a new path is calculated and compared to the
paths Flarm has received from nearby gliders. If this new path puts it
on a collision course with any of them, the pilot is warned
"immediately", meaning it does not have to wait one second. The new path
will be transmitted within one second, so the nearby gliders can update
the other glider's path in their database. It might actually be more
sophisticated than that, such as transmitting a new path sooner if the
amount of change is "large", but I don't know what the algorithms are.

This projected path is a key element to the system working properly.
Without it, each FLARM unit would have to calculate the path of every
nearby glider; with it, each unit only has to calculate one path - it's
own. Potentially, it could be using a much higher position rate than
once a second to calculate it's projected path. In any case, the result
is much better than you might think for a system that transmits once a
second.

Does ADS-B transmit a projected path, or just position?

--
Eric Greenwell - Washington State, USA (change ".netto" to ".us" to email me)
- "Transponders in Sailplanes - Feb/2010" also ADS-B, PCAS, Flarmhttp://tinyurl.com/yb3xywl
- "A Guide to Self-launching Sailplane Operation Mar/2004" Much of what you need to know tinyurl.com/yfs7tnz

That's my understanding as well - the Flarm algorithm looks at a range
of potential paths that the glider might maneuver to and calculates
potential collisions on the basis of all potential paths within that
maneuvering envelope. I expect within a couple of seconds the path
assumes a fair amount of potential maneuvering while over a longer
period of time it would limit extreme maneuvering assumptions to be
closer to an extrapolation of the current path/turn rate. Because it
understands your trun rate it works well in thermals.

I have not heard anything about similar capabilities for ADS-B and I
am confident that it doesn't extrapolate with a glider performance
envelope in mind, since it isn't designed explicitly for gliders. I
would think ADS-B would be particularly challenged in predicting
likely collisions in thermals - much more so than Flarm.

9B

On Tue, 26 Oct 2010 18:03:50 -0700 (PDT), John Cochrane
wrote:


"Idiot" is perhaps a bit strong, and I may have been hasty in applying
it to a fellow pilot. On the other hand, he did pass 10-20 feet over
the top of my glider in a large gaggle.


One pilot who I know very well told me that during a WGC when he was
competing for the first place (he was in the lead), one very-well
known competitor flew maneuvres that this pilot could only classify as
attempts to produce near-misses. Within half an hour they had two
near-misses with less than fifteen feet, both provoked by the same
pilot.

Then the pilot in question lost his nerves and broke off the flight.
The attacking pilot won the WGC.



Andreas

On Oct 28, 1:11*am, Andy wrote:
On Oct 27, 8:16*pm, Eric Greenwell wrote:





On 10/27/2010 5:33 PM, Mike Schumann wrote:

On 10/27/2010 3:48 PM, Eric Greenwell wrote:
On 10/27/2010 7:20 AM, wrote:
in "awareness mode", of course a led will indicate where the closer
glider is, but still alarms will only be triggered when a deviation
makes the collision a real possibility.

aldo cernezzi
Since the GPS accuracy is probably much poorer than 10 feet, when a
glider comes within 10 feet, I figure the FLARM should consider that a
collision, no?
I don't know what Flarm does in that case, but my guess is the
*relative* accuracy is much better than the *absolute* accuracy. If
that's true, then each glider might have position errors of much more
than 10 feet, but they'll have nearly the same errors, giving a more
accurate separation distance.

Maybe someone more familiar with GPS in this situation can jump in here
and tell us?

Even if the relative GPS position computed by each glider has 0 error,
you still have the problem that at 50 Knots, each aircraft is moving ~
75 ft / second. *With FLARM (or ADS-B) only transmitting positions
every second, you can't rely on these technologies to protect you from
random course changes that the systems can't possibly predict, if you
are in close proximity.

FLARM does more than transmit positions: it transmits the projected path
of it's glider. Here's what I understand will happen: when the pilot
makes a course change, a new path is calculated and compared to the
paths Flarm has received from nearby gliders. If this new path puts it
on a collision course with any of them, the pilot is warned
"immediately", meaning it does not have to wait one second. The new path
will be transmitted within one second, so the nearby gliders can update
the other glider's path in their database. It might actually be more
sophisticated than that, such as transmitting a new path sooner if the
amount of change is "large", but I don't know what the algorithms are.

This projected path is a key element to the system working properly.
Without it, each FLARM unit would have to calculate the path of every
nearby glider; with it, each unit only has to calculate one path - it's
own. Potentially, it could be using a much higher position rate than
once a second to calculate it's projected path. In any case, the result
is much better than you might think for a system that transmits once a
second.

Does ADS-B transmit a projected path, or just position?

--
Eric Greenwell - Washington State, USA (change ".netto" to ".us" to email me)
- "Transponders in Sailplanes - Feb/2010" also ADS-B, PCAS, Flarmhttp://tinyurl.com/yb3xywl
- "A Guide to Self-launching Sailplane Operation Mar/2004" Much of what you need to know tinyurl.com/yfs7tnz

That's my understanding as well - the Flarm algorithm looks at a range
of potential paths that the glider might maneuver to and calculates
potential collisions on the basis of all potential paths within that
maneuvering envelope. *I expect within a couple of seconds the path
assumes a fair amount of potential maneuvering while over a longer
period of time it would limit extreme maneuvering assumptions to be
closer to an extrapolation of the current path/turn rate. Because it
understands your trun rate it works well in thermals.

I have not heard anything about similar capabilities for ADS-B and I
am confident that it doesn't extrapolate with a glider performance
envelope in mind, since it isn't designed explicitly for gliders. I
would think ADS-B would be particularly challenged in predicting
likely collisions in thermals - much more so than Flarm.

9B- Hide quoted text -

- Show quoted text -

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. But it
would be possible for the Flarm to actually learn the possible flight
paths for a given glider and dynamically adjust it's algorithm for
where the glider might be able to go from that. 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.

Brian

On 10/27/2010 11:16 PM, Eric Greenwell wrote:
On 10/27/2010 5:33 PM, Mike Schumann wrote:
On 10/27/2010 3:48 PM, Eric Greenwell wrote:
On 10/27/2010 7:20 AM, wrote:
in "awareness mode", of course a led will indicate where the closer
glider is, but still alarms will only be triggered when a deviation
makes the collision a real possibility.

aldo cernezzi
Since the GPS accuracy is probably much poorer than 10 feet, when a
glider comes within 10 feet, I figure the FLARM should consider that a
collision, no?
I don't know what Flarm does in that case, but my guess is the
*relative* accuracy is much better than the *absolute* accuracy. If
that's true, then each glider might have position errors of much more
than 10 feet, but they'll have nearly the same errors, giving a more
accurate separation distance.

Maybe someone more familiar with GPS in this situation can jump in here
and tell us?

Even if the relative GPS position computed by each glider has 0 error,
you still have the problem that at 50 Knots, each aircraft is moving ~
75 ft / second. With FLARM (or ADS-B) only transmitting positions
every second, you can't rely on these technologies to protect you from
random course changes that the systems can't possibly predict, if you
are in close proximity.
FLARM does more than transmit positions: it transmits the projected path
of it's glider. Here's what I understand will happen: when the pilot
makes a course change, a new path is calculated and compared to the
paths Flarm has received from nearby gliders. If this new path puts it
on a collision course with any of them, the pilot is warned
"immediately", meaning it does not have to wait one second. The new path
will be transmitted within one second, so the nearby gliders can update
the other glider's path in their database. It might actually be more
sophisticated than that, such as transmitting a new path sooner if the
amount of change is "large", but I don't know what the algorithms are.

This projected path is a key element to the system working properly.
Without it, each FLARM unit would have to calculate the path of every
nearby glider; with it, each unit only has to calculate one path - it's
own. Potentially, it could be using a much higher position rate than
once a second to calculate it's projected path. In any case, the result
is much better than you might think for a system that transmits once a
second.

Does ADS-B transmit a projected path, or just position?

I'm not an expert on either FLARM or ADS-B. I believe that ADS-B
currently only transmits absolute position. Future enhancements might
transmit trajectory, which would be most useful for aircraft with Flight
Management Systems where the trajectory is well defined and could be
used by the ATC system for airspace management.

Regardless of whether or not the trajectory is transmitted, a
sophisticated receiving system (either FLARM or ADS-B based), can
remember each aircraft's position data and compute it's current
trajectory. While a glider might be moving 75 ft / sec, this is
obviously in a relatively forward direction.

Neither the transmitting nor the receiving FLARM or ADS-B system can
predict an abrupt change in course that a pilot flying manually might
command. However, every aircraft has physical limits on roll rates,
etc. that restrain the potential change in direction that can occur
within the one second update interval of these systems. As a result,
the systems can, theoretically, compute a pear shaped threat envelope
for each aircraft and limit collision warnings to those situations where
these envelopes intersect.

It would be interesting to get more detailed information on the exact
algorithms that FLARM uses in it's collision threat analysis and compare
this to the actual unit performance in situations where gliders are
flying at close distances in formation or in gaggles. This could also
help pilots understand the limitations of these systems so they don't
develop a false sense of security in situations where these systems are
not reliable.

--
Mike Schumann

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