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

On 10/28/2010 11:32 AM, Mike Schumann wrote:


There's no question that FLARM or ADS-B based systems could have
easily prevented the Parowan mid-air. My question is how much you can
rely on this type of equipment to accurately warn you of collisions
when you are flying in gaggles.

Obviously knowing the relative position of other gliders in the gaggle
is helpful. I would be very skeptical, however, of putting my faith
in FLARM or any other system to accurately warn me of a collision with
another glider that was in the same thermal, near my altitude, that
was in my blind spot.
This situation is addressed at

http://www.gliderpilot.org/FlarmFlig...andPerformance

where it states that the human eye is better than Flarm. I don't think
anyone has claimed Flarm is better in every possible situation, and
users and Flarm itself repeatedly state you must still look outside to
have the best protection; however, I believe Flarm will indicate there
is a glider behind you, something a pilot might not always be aware of,
so it still has value in this situation.

Transmitting the project path of the aircraft is really only
beneficial if the equipment on board the transmitting aircraft has
some added information that is not available to the receiver on the
transmitting aircraft's intent.

With both FLARM and ADS-B systems, the initial visibility of the other
aircraft occurs way before there is any collision threat, so the
receiver should have no difficulty computing the project path of the
other aircraft. ADS-B actually transmits the category of aircraft
(i.e. glider, balloon, etc...) so the receiver can get a pretty good
hint on the type of maneuvers that can be expected.
I can think of three situations where the time involved can be reduced:

1) two gliders approaching head on. At 100 knots each - a 200 knot
closing speed - that's only 18 seconds or so to collision. How many
seconds of warning do you lose while collecting enough points to make a
good estimate of the projected paths - 5 seconds, 10 seconds? I don't
know, but I'd prefer to know sooner than later.

2) Ridge or mountain flying, where the transmissions are blocked by the
terrain. Once they round the corner of the ridge, there may not be
enough time to calculate a projected path.

3) shortened range due to signal blockage by the wings or fuselage.


--

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 10/28/2010 3:36 PM, Eric Greenwell wrote:
On 10/28/2010 11:32 AM, Mike Schumann wrote:


There's no question that FLARM or ADS-B based systems could have
easily prevented the Parowan mid-air. My question is how much you can
rely on this type of equipment to accurately warn you of collisions
when you are flying in gaggles.

Obviously knowing the relative position of other gliders in the gaggle
is helpful. I would be very skeptical, however, of putting my faith in
FLARM or any other system to accurately warn me of a collision with
another glider that was in the same thermal, near my altitude, that
was in my blind spot.
This situation is addressed at

http://www.gliderpilot.org/FlarmFlig...andPerformance

where it states that the human eye is better than Flarm. I don't think
anyone has claimed Flarm is better in every possible situation, and
users and Flarm itself repeatedly state you must still look outside to
have the best protection; however, I believe Flarm will indicate there
is a glider behind you, something a pilot might not always be aware of,
so it still has value in this situation.

Transmitting the project path of the aircraft is really only
beneficial if the equipment on board the transmitting aircraft has
some added information that is not available to the receiver on the
transmitting aircraft's intent.

With both FLARM and ADS-B systems, the initial visibility of the other
aircraft occurs way before there is any collision threat, so the
receiver should have no difficulty computing the project path of the
other aircraft. ADS-B actually transmits the category of aircraft
(i.e. glider, balloon, etc...) so the receiver can get a pretty good
hint on the type of maneuvers that can be expected.
I can think of three situations where the time involved can be reduced:

1) two gliders approaching head on. At 100 knots each - a 200 knot
closing speed - that's only 18 seconds or so to collision. How many
seconds of warning do you lose while collecting enough points to make a
good estimate of the projected paths - 5 seconds, 10 seconds? I don't
know, but I'd prefer to know sooner than later.

2) Ridge or mountain flying, where the transmissions are blocked by the
terrain. Once they round the corner of the ridge, there may not be
enough time to calculate a projected path.

3) shortened range due to signal blockage by the wings or fuselage.



The proper logic on unexpectedly seeing a new target close by without
have a chance to compute trajectory is to use a worse case scenario.
Granted, having the trajectory as part of the transmission would be
helpful in this instance.

--
Mike Schumann

On 10/28/2010 4:03 PM, Mike Schumann wrote:
On 10/28/2010 3:36 PM, Eric Greenwell wrote:
I can think of three situations where the time involved can be reduced:

1) two gliders approaching head on. At 100 knots each - a 200 knot
closing speed - that's only 18 seconds or so to collision. How many
seconds of warning do you lose while collecting enough points to make a
good estimate of the projected paths - 5 seconds, 10 seconds? I don't
know, but I'd prefer to know sooner than later.

2) Ridge or mountain flying, where the transmissions are blocked by the
terrain. Once they round the corner of the ridge, there may not be
enough time to calculate a projected path.

3) shortened range due to signal blockage by the wings or fuselage.
The proper logic on unexpectedly seeing a new target close by without
have a chance to compute trajectory is to use a worse case scenario.
Granted, having the trajectory as part of the transmission would be
helpful in this instance.
And which way do you turn, when you don't know where the threat is going?

--
Eric Greenwell - Washington State, USA (change ".netto" to ".us" to email me)

Mike Schumann wrote:
My question is how much you can rely on
this type of equipment to accurately warn you of collisions when you are
flying in gaggles.

In gaggles: Not at all. Period. Simply not possible - and not
necessairy, either.

Eric Greenwell wrote:
On 10/28/2010 7:29 AM, Mike Schumann wrote:

It would be interesting to get more detailed information on the exact
algorithms that FLARM uses in it's collision threat analysis

I tend to assume that if there is one thing that the developers want to
keep, then it's this algorithm. ;-)

But from real life experience, it seem's to work pretty well.

It would be interesting, informative, andentertaining if there was
a website or application that would let us runIGC files we select
in a simulation like this.

Entertaining... well... but educative indeed. And it would provide the
FLARM developers with a huge test crew for free.

On Oct 28, 2:14*pm, Eric Greenwell 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"

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 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"