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

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 Oct 28, 4:54*pm, SoaringXCellence wrote:
On Oct 28, 1:40*pm, "Wayne Paul" wrote:



"Darryl Ramm" wrote in ...
On Oct 28, 8:47 am, Andy wrote:

Just to give a flavor ADS-B data-out systems as mandated for 2020 in
the USA for power aircraft (basically where a transponder is required
today) will put out the following data

Aircraft ICAO ID (can be made anonymous for a UAT on VFR flight)
Aircraft callsign/flight number (not required for VFR flight)
Time of applicability
GPS Lattitude
GPS Longitude
GPS altitude
Airborne/on-surface status
Northbound ground velocity component while airborne (from GPS)
Eastbound ground velocity component while airborne (from GPS)
Heading while on the surface
Ground speed while on the surface
Pressure altitude
Vertical rate (may be pressure or GPS based)
GPS uncertainty/integrity (which needs information form a fancy TSO-
C145 class WAAS GPS)
Ident (equivalent to transponder ident/SPI)
Distress/Emergency status
ADS-B data-in/display capability
TCAS equipage/status

This is a simplified list and there is various other status/validity
data as well. There is also the concept in ADS-B messages of an
estimated position, and even estimated velocity. But AFAIK this is not
intended for fancy manoeuvrings predictions - it is more intended to
allow different parts of the ADS-B infrastructure to project position
or velocity updated to a single time of applicability. There is space
for future expansion and as an example there is long-term work
underway to look at an ADS-B based replacement for TCAS that could
well utilize extra data transmission than that above, but think well
post 2020 for this to actually happen. My brain hurts enough thinking
about ADS-B as is.

---

BTW my suspicion is given that the FAA currently requires a STC for
any installation for ADS-B data out that it is currently not possible
to install any ADS-B data-out system in the USA in any certified
aircraft (including gliders) that only meets a subset of the 2020
mandate requirements (ie. does not include all the stuff above). Which
I expect the FAA would also require fully TSO-C154c/DO-282B (UAT) TSO-
C166b/DO-260B (1090ES) and with the corresponding TSO-C145 level GPS.
Experimental aircraft are another question since an STC cannot apply
to them. This STC restriction hopefully is short-term as its is going
to have a chilling effect on ADS-B data-out adoption in general
aviation and gliders. Besides some more complex issues you can start
to see even simple installation concerns that are probably causing
this current STC requirement, such as squat switch/or other on-ground
detection, needs to have a single squawk code and ident button across
any installed transponder(s) and ADS-B data-out devices, ability to
transmit a distress/emergency code, ability to turn off the ADS-B
transmissions if requested, etc.

Darryl

The following is not directed at any individual, it is simply an observation.

Even the old Garmin 12XL provides a lot more information in it's NMEA sentences the most of us realize. *It is data output sentences are fully compliant with NMEA 0183 ver 2.0. *The following link give an example of the data provided by "GPS engines" to software developer thus minimizing the amount of calculation required in display devices.http://www8.garmin.com/support/pdf/NMEA_0183.pdf

As I watch these PowerFLARM discussion it is apparent that many assume that things provided by the GPS must be created by the FLARM software.

Let us accept the fact that the PowerFLARM is just an upgrade of previous units that have been proven effective in increasing glider flight safety..

Respectfully,
Wayne

There have been several comment regarding the need for an STC to
install an ADS-B system in a certified aircraft.

This is not unlike the original situation with the installation of IFR
certified GPS systems, in the early 1990s. *I was involved in several
installations and most of the concerns were about the placement of
antenna and the effect of spurious signals on navigation.

Today if you get an IFR GPS installed in an aircraft the manufacturer
has a detailed description of antenna placement, cable routing and
possible interaction. *This data was collected during the earlier STC
period and as experience with more installations was gained, the FAA
changed the requirements from an STC to a 337, if installed in
compliance with the manufacturer's instructions.

I expect that the STC requirements for the ADS-B will follow the same
path over time.

Mike

Agreed completely. However, note that 1090 MHz
ADS-B (1090ES) uses the existing transponder antenna.
Much simpler than the early GPS situation.
However, UAT...

Hope that helps clarify the (not simple) situation,
Best Regards, Dave "YO electric"

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"

On 10/28/2010 5:15 PM, Darryl Ramm wrote:
On Oct 28, 1:54 pm, wrote:
On Oct 28, 1:40 pm, "Wayne wrote:



"Darryl wrote in ...
On Oct 28, 8:47 am, wrote:

Just to give a flavor ADS-B data-out systems as mandated for 2020 in
the USA for power aircraft (basically where a transponder is required
today) will put out the following data

Aircraft ICAO ID (can be made anonymous for a UAT on VFR flight)
Aircraft callsign/flight number (not required for VFR flight)
Time of applicability
GPS Lattitude
GPS Longitude
GPS altitude
Airborne/on-surface status
Northbound ground velocity component while airborne (from GPS)
Eastbound ground velocity component while airborne (from GPS)
Heading while on the surface
Ground speed while on the surface
Pressure altitude
Vertical rate (may be pressure or GPS based)
GPS uncertainty/integrity (which needs information form a fancy TSO-
C145 class WAAS GPS)
Ident (equivalent to transponder ident/SPI)
Distress/Emergency status
ADS-B data-in/display capability
TCAS equipage/status

This is a simplified list and there is various other status/validity
data as well. There is also the concept in ADS-B messages of an
estimated position, and even estimated velocity. But AFAIK this is not
intended for fancy manoeuvrings predictions - it is more intended to
allow different parts of the ADS-B infrastructure to project position
or velocity updated to a single time of applicability. There is space
for future expansion and as an example there is long-term work
underway to look at an ADS-B based replacement for TCAS that could
well utilize extra data transmission than that above, but think well
post 2020 for this to actually happen. My brain hurts enough thinking
about ADS-B as is.

---

BTW my suspicion is given that the FAA currently requires a STC for
any installation for ADS-B data out that it is currently not possible
to install any ADS-B data-out system in the USA in any certified
aircraft (including gliders) that only meets a subset of the 2020
mandate requirements (ie. does not include all the stuff above). Which
I expect the FAA would also require fully TSO-C154c/DO-282B (UAT) TSO-
C166b/DO-260B (1090ES) and with the corresponding TSO-C145 level GPS.
Experimental aircraft are another question since an STC cannot apply
to them. This STC restriction hopefully is short-term as its is going
to have a chilling effect on ADS-B data-out adoption in general
aviation and gliders. Besides some more complex issues you can start
to see even simple installation concerns that are probably causing
this current STC requirement, such as squat switch/or other on-ground
detection, needs to have a single squawk code and ident button across
any installed transponder(s) and ADS-B data-out devices, ability to
transmit a distress/emergency code, ability to turn off the ADS-B
transmissions if requested, etc.

Darryl

The following is not directed at any individual, it is simply an observation.

Even the old Garmin 12XL provides a lot more information in it's NMEA sentences the most of us realize. It is data output sentences are fully compliant with NMEA 0183 ver 2.0. The following link give an example of the data provided by "GPS engines" to software developer thus minimizing the amount of calculation required in display devices.http://www8.garmin.com/support/pdf/NMEA_0183.pdf

As I watch these PowerFLARM discussion it is apparent that many assume that things provided by the GPS must be created by the FLARM software.

Let us accept the fact that the PowerFLARM is just an upgrade of previous units that have been proven effective in increasing glider flight safety.

Respectfully,
Wayne

There have been several comment regarding the need for an STC to
install an ADS-B system in a certified aircraft.

This is not unlike the original situation with the installation of IFR
certified GPS systems, in the early 1990s. I was involved in several
installations and most of the concerns were about the placement of
antenna and the effect of spurious signals on navigation.

Today if you get an IFR GPS installed in an aircraft the manufacturer
has a detailed description of antenna placement, cable routing and
possible interaction. This data was collected during the earlier STC
period and as experience with more installations was gained, the FAA
changed the requirements from an STC to a 337, if installed in
compliance with the manufacturer's instructions.

I expect that the STC requirements for the ADS-B will follow the same
path over time.

Mike

Absolutely right (and antenna issues are one of the concerns with this
STC requirement as well). Its a matter of when the STC process
migrates to a 337/Field approval. Given the complexity of ADS-B I
wonder what the time frame will really be. And the FCC has stated that
clearly but the STC requirement still seems to have come as a bit of a
surprise to some developers--and maybe regulators where there are
questions if the cost of this was included in disclosures. I see no
way for now but for this to freeze a lot of adoption--but I suspect
from the FAA viewpoint it is needed. I do worry that smaller
manufacturers won't be able to develop many STCs and I am doubtful
you'll see folks willing to develop STCs for gliders. My purpose of
promoting the STC issue is just nobody seemed to be aware of it in
the glider community yet there are (a few) owners starting to look at
install of ADS-B data-out. Some of those owners have experimental
gliders and are in a better position. Those with certified gliders
need to have a discussion with vendors about STCs. In a practical
sense as well most vendors are busy finishing off their "-B" rev data-
out products (e.g. Garmin, Trig and others) and getting TSO approval
on those. And I see that as a gate to STC approval, but clearly they
could be overlapping TSO approval and STC development. And larger
companies beside having lots of STC approval experience may also be
able to leverage past ADS-B STC developed for trails, such as the
GOMEX ADS-B trials.


Darryl

I find it difficult to understand the "complexity" involved in ADS-B.
This is basically the same technology as FLARM (UAT) or Mode S
transponders (1090ES). The main difference between FLARM and UAT is the
frequency and power level of the transmitter. (Yes I know that UAT
doesn't include any of the collision detection logic of FLARM).

At some point, the FAA will figure this out or the whole ADS-B exercise
will come to a dead end.

--
Mike Schumann

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 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, 9:47*am, Andreas Maurer wrote:
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

Aha! Finally, somebody came out with the truth!

In my first post when I asked, "Are you thinking what I am
thinking?" THAT was what I was thinking!

Cookie

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)

On Oct 28, 3:57*pm, Mike Schumann
wrote:
On 10/28/2010 5:15 PM, Darryl Ramm wrote:







On Oct 28, 1:54 pm, *wrote:
On Oct 28, 1:40 pm, "Wayne *wrote:

"Darryl *wrote in ...
On Oct 28, 8:47 am, *wrote:

Just to give a flavor ADS-B data-out systems as mandated for 2020 in
the USA for power aircraft (basically where a transponder is required
today) will put out the following data

Aircraft ICAO ID (can be made anonymous for a UAT on VFR flight)
Aircraft callsign/flight number (not required for VFR flight)
Time of applicability
GPS Lattitude
GPS Longitude
GPS altitude
Airborne/on-surface status
Northbound ground velocity component while airborne (from GPS)
Eastbound ground velocity component while airborne (from GPS)
Heading while on the surface
Ground speed while on the surface
Pressure altitude
Vertical rate (may be pressure or GPS based)
GPS uncertainty/integrity (which needs information form a fancy TSO-
C145 class WAAS GPS)
Ident (equivalent to transponder ident/SPI)
Distress/Emergency status
ADS-B data-in/display capability
TCAS equipage/status

This is a simplified list and there is various other status/validity
data as well. There is also the concept in ADS-B messages of an
estimated position, and even estimated velocity. But AFAIK this is not
intended for fancy manoeuvrings predictions - it is more intended to
allow different parts of the ADS-B infrastructure to project position
or velocity updated to a single time of applicability. There is space
for future expansion and as an example there is long-term work
underway to look at an ADS-B based replacement for TCAS that could
well utilize extra data transmission than that above, but think well
post 2020 for this to actually happen. My brain hurts enough thinking
about ADS-B as is.

---

BTW my suspicion is given that the FAA currently requires a STC for
any installation for ADS-B data out that it is currently not possible
to install any ADS-B data-out system in the USA in any certified
aircraft (including gliders) that only meets a subset of the 2020
mandate requirements (ie. does not include all the stuff above). Which
I expect the FAA would also require fully TSO-C154c/DO-282B (UAT) TSO-
C166b/DO-260B (1090ES) and with the corresponding TSO-C145 level GPS..
Experimental aircraft are another question since an STC cannot apply
to them. This STC restriction hopefully is short-term as its is going
to have a chilling effect on ADS-B data-out adoption in general
aviation and gliders. Besides some more complex issues you can start
to see even simple installation concerns that are probably causing
this current STC requirement, such as squat switch/or other on-ground
detection, needs to have a single squawk code and ident button across
any installed transponder(s) and ADS-B data-out devices, ability to
transmit a distress/emergency code, ability to turn off the ADS-B
transmissions if requested, etc.

Darryl

The following is not directed at any individual, it is simply an observation.

Even the old Garmin 12XL provides a lot more information in it's NMEA sentences the most of us realize. *It is data output sentences are fully compliant with NMEA 0183 ver 2.0. *The following link give an example of the data provided by "GPS engines" to software developer thus minimizing the amount of calculation required in display devices.http://www8.garmin.com/support/pdf/NMEA_0183.pdf

As I watch these PowerFLARM discussion it is apparent that many assume that things provided by the GPS must be created by the FLARM software.

Let us accept the fact that the PowerFLARM is just an upgrade of previous units that have been proven effective in increasing glider flight safety.

Respectfully,
Wayne

There have been several comment regarding the need for an STC to
install an ADS-B system in a certified aircraft.

This is not unlike the original situation with the installation of IFR
certified GPS systems, in the early 1990s. *I was involved in several
installations and most of the concerns were about the placement of
antenna and the effect of spurious signals on navigation.

Today if you get an IFR GPS installed in an aircraft the manufacturer
has a detailed description of antenna placement, cable routing and
possible interaction. *This data was collected during the earlier STC
period and as experience with more installations was gained, the FAA
changed the requirements from an STC to a 337, if installed in
compliance with the manufacturer's instructions.

I expect that the STC requirements for the ADS-B will follow the same
path over time.

Mike

Absolutely right (and antenna issues are one of the concerns with this
STC requirement as well). Its a matter of when the STC process
migrates to a 337/Field approval. Given the complexity of ADS-B I
wonder what the time frame will really be. And the FCC has stated that
clearly but the STC requirement still seems to have come as a bit of a
surprise to some developers--and maybe regulators where there are
questions if the cost of this was included in disclosures. I see no
way for now but for this to freeze a lot of adoption--but I suspect
from the FAA viewpoint it is needed. I do worry that smaller
manufacturers won't be able to develop many STCs and I am doubtful
you'll see folks willing to develop STCs for gliders. My purpose of
promoting the STC issue is just nobody seemed to be *aware of it in
the glider community yet there are (a few) owners starting to look at
install of ADS-B data-out. Some of those owners have experimental
gliders and are in a better position. Those with certified gliders
need to have a discussion with vendors about STCs. In a practical
sense as well most vendors are busy finishing off their "-B" rev data-
out products (e.g. Garmin, Trig and others) and getting TSO approval
on those. And I see that as a gate to STC approval, but clearly they
could be overlapping TSO approval and STC development. And larger
companies beside having lots of STC approval experience may also be
able to leverage past ADS-B STC developed for trails, such as the
GOMEX ADS-B trials.

Darryl

I find it difficult to understand the "complexity" involved in ADS-B.
This is basically the same technology as FLARM (UAT) or Mode S
transponders (1090ES). *The main difference between FLARM and UAT is the
frequency and power level of the transmitter. *(Yes I know that UAT
doesn't include any of the collision detection logic of FLARM).

At some point, the FAA will figure this out or the whole ADS-B exercise
will come to a dead end.

--
Mike Schumann

ADS-B and its implementation and role in NextGen and all the different
players looking at this beast from all different angles and trying to
solve all sorts of different problems makes this is one of the most
complex undertakings ever in aviation.... and that includes everything
from the details of the data transmitted on up (e.g. the GPS chip in a
Flarm likely costs a few tens of dollars at most, a GPS box or module
for an ADS-B data-out TSO'ed product currently costs thousands of
dollars). All that extra stuff and bureaucracy that make it cost that
much really has no practical benefit for glider-glider collision
avoidance but has benefits to others.

Lets see, ADS-B data-out, ADS-B data-in, 1090ES, UAT, ADS-R, TIS-B,
FIS-B, surface surveillance, terminal surveillance, en-route
surveillance, essential services, critical services, TSO-C166b/
DO-260B, TSO-C154c/DO-282B, TSO-C145a/TSO-C146a WAAS GPS, SIL, NIC,
STCs, ... if this does not make your head ache you may not be thinking
about it hard enough. Most people just don't need to worry since this
is all years away from being interesting for them. Years away when FAA
ground services, ADS-B products, product cost, fleet adoption and
market awareness all start to line up.

And this applies to the ADS-B receiver part PowerFLARM as well -
especially its dependence on having ADS-B out for ADS-R and TIS-B to
work. There is a lot more the FAA and its providers have to do and
there is a lot more we all have to do to understand all this
technology and how best to use it moving forward - given that by 2020
a significant part of the entire USA aircraft fleet will be ADS-B data-
out equipped. But again I'm not trying to hawk ADS-B as being at all
ready for our market now, but I've very happy to see products like
PowerFLARM providing a path to include that in future.

Darryl

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