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

On 10/28/2010 6:14 PM, Dave Nadler wrote:
On Oct 28, 2:14 pm, Eric wrote:
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.

...
You may be underestimating the value of transmitting the projected path.
When another glider is first detected, your unit has only one position
report and can not determine the flight path from that single point, and
it will take several more precious seconds to determine the flight path
of the potential threat; however, because the projected path is
transmitted every second, your unit immediately knows it.

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.

I'm sure the developers have tested their algorithms with thousands of
simulations using IGC files from gliders in many situations. The Parowan
accident simulation at

http://www.gliderpilot.org/Flarm-Par...dairSimulation

shows what can be done. It would be interesting, informative, and
entertaining if there was a website or application that would let us run
IGC files we select in a simulation like this. I'm curious about how
Flarm would react in a few situations I've encountered. Doing
simulations on a pilot's own files might be more persuasive of the value
of Flarm than even the most well-written explanations, and much more
easily understood than the algorithms themselves.

If you watch the Parowan simulation carefully, you will see that
the collision alarm sounds BEFORE the straight-line trajectories
intersect. This is because one of the gliders is circling, and the
projected trajectory (circling) shows a collision SECONDS
before the straight-line trajectories intersect.

These additional seconds can be a life-saver.

Hope that helps clarify,
Best Regards, Dave "YO electric"

I totally understand the advantage of using the expected trajectory in
computing the collision threat. The Parowan situation is an example of
a case where an ADS-B based system, with a sophisticated trajectory
algorithm in the receiving system would have been just as effective as
FLARM. Note: I am aware that such a system probably doesn't exist yet,
so let's not start a flame war over that issue.

--
Mike Schumann

On Oct 28, 4:07*pm, Mike Schumann
wrote:
On 10/28/2010 6:14 PM, Dave Nadler wrote:





On Oct 28, 2:14 pm, Eric *wrote:
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.

...
You may be underestimating the value of transmitting the projected path.
When another glider is first detected, your unit has only one position
report and can not determine the flight path from that single point, and
it will take several more precious seconds to determine the flight path
of the potential threat; however, because the projected path is
transmitted every second, your unit immediately knows it.

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.

I'm sure the developers have tested their algorithms with thousands of
simulations using IGC files from gliders in many situations. The Parowan
accident simulation at

http://www.gliderpilot.org/Flarm-Par...dairSimulation

shows what can be done. It would be interesting, informative, and
entertaining if there was a website or application that would let us run
IGC files we select in a simulation like this. I'm curious about how
Flarm would react in a few situations I've encountered. Doing
simulations on a pilot's own files might be more persuasive of the value
of Flarm than even the most well-written explanations, and much more
easily understood than the algorithms themselves.

If you watch the Parowan simulation carefully, you will see that
the collision alarm sounds BEFORE the straight-line trajectories
intersect. This is because one of the gliders is circling, and the
projected trajectory (circling) shows a collision SECONDS
before the straight-line trajectories intersect.

These additional seconds can be a life-saver.

Hope that helps clarify,
Best Regards, Dave "YO electric"

I totally understand the advantage of using the expected trajectory in
computing the collision threat. *The Parowan situation is an example of
a case where an ADS-B based system, with a sophisticated trajectory
algorithm in the receiving system would have been just as effective as
FLARM. *Note: *I am aware that such a system probably doesn't exist yet,
so let's not start a flame war over that issue.

--
Mike Schumann

Actually I don't think that's necessarily true Mike. There potentially
is a difference in some critical situations between each aircraft
estimating the other aircraft's projected path and having each
aircraft send the other it's on-board estimated path. In the first
case there is no way to close the loop on path estimation differences
between the two aircraft - that is, my estimate of where you are going
can differ from your estimate of where you are going, and vice versa.
It may in fact be better to exchange projected paths to take the
biases out of the system. There also may be lag effects on projected
flight path changes due to maneuvering. It's quite possible that my
onboard system will be faster to include maneuvering effects on the
projected path than trying to piece it together from simple GPS
location and velocity transmissions.

The thing I found particularly impressive about the Parowan
demonstration was how both Flarm units gave nearly identical,
complementary warnings. I'm not sure that would have been the case
using ADS-B on-board estimations of the other glider's path. It's even
worse if the two ADS-B systems use different algorithms. Flarm and
PowerFlarm solve this problem.

9B

On Oct 28, 9:19*pm, Andy wrote:

Also, to clarify, ADS-B does no path estimation of its own. That
function either would have to be added into an ADS-B unit by the OEM,
similar to the way Flarm does today - unlikely to be done in a glider-
specific way IMO - OR, it would have to be done by a separate external
device, perhaps a navigation computer/software like Oudie, WinPilot,
SN-10. For it to be effective manufacturers would all have to agree to
use the same algorithm, which also seems unlikely, unless they all
adopt the Flarm algorithm. That seems somewhat unlikely too, since I
don't think Flarm would want to start splintering how their algorithms
get used by splitting out the Flarm link technology from the collision
algorithm (which would have to be modified to accommodate the
differences in how path estimations get generated - with unpredictable
results). PLUS the external device OEM's would have to adapt to using
ADS-B inputs - another standards issue.

No matter how hard I try, it seems highly improbable that you will be
able to stitch together a satisfactory collision avoidance system for
gliders using ADS-B technology developed for general aviation. You'd
have to be satisfied with the simple functionality offered by ADS-B -
which would be fine if you generally come into conflict with GA and
airliners more often than other gliders, but there are a bunch of us
for whom the opposite is true. Then the problem becomes some gliders
using Flarm and others using ADS-B, you lose some of the Flarm
benefits of path estimation for the non-Flarm gliders.

9B

9B

On 10/29/2010 12:51 AM, Andy wrote:
On Oct 28, 9:19 pm, wrote:

Also, to clarify, ADS-B does no path estimation of its own. That
function either would have to be added into an ADS-B unit by the OEM,
similar to the way Flarm does today - unlikely to be done in a glider-
specific way IMO - OR, it would have to be done by a separate external
device, perhaps a navigation computer/software like Oudie, WinPilot,
SN-10. For it to be effective manufacturers would all have to agree to
use the same algorithm, which also seems unlikely, unless they all
adopt the Flarm algorithm. That seems somewhat unlikely too, since I
don't think Flarm would want to start splintering how their algorithms
get used by splitting out the Flarm link technology from the collision
algorithm (which would have to be modified to accommodate the
differences in how path estimations get generated - with unpredictable
results). PLUS the external device OEM's would have to adapt to using
ADS-B inputs - another standards issue.

No matter how hard I try, it seems highly improbable that you will be
able to stitch together a satisfactory collision avoidance system for
gliders using ADS-B technology developed for general aviation. You'd
have to be satisfied with the simple functionality offered by ADS-B -
which would be fine if you generally come into conflict with GA and
airliners more often than other gliders, but there are a bunch of us
for whom the opposite is true. Then the problem becomes some gliders
using Flarm and others using ADS-B, you lose some of the Flarm
benefits of path estimation for the non-Flarm gliders.

9B

9B


You are probably correct that no one is going to beat FLARM in an
optimized collision avoidance solution for high density glider
environments. That's obviously their focus and they are good at it.

However, most recreational, non-contest pilots, primarily need a system
that will reliably alert them to other aircraft in their general
vicinity. If I enter a thermal and know that there are 3 other aircraft
in the area, and I only see two, I'm going to abort and go elsewhere. A
contest pilot obviously wants more data.

What is interesting about the Parowan situation is that this was not a
gaggle of gliders. It was two gliders who apparently did not have a
proper appreciation that they were near each other. A simple graphical
display that showed their relative positions, with a very simple
collision avoidance algorithm, or some form of auditory announcement
could have prevented this accident. That's not to say that the FLARM
simulation was not impressive.

--
Mike Schumann

On Oct 28, 10:29*am, Mike Schumann
wrote:
I'm not an expert on either FLARM or ADS-B...
--
Mike Schumann

Finally, something we can all agree on ;-)
See ya, Dave "YO electric"