Flarm Range Analysis

Understood.

Along those lines, I recall in my AF jet, the transponder had an antenna
select switch - Top, Auto, Bottom. That would be nice for the Flarm.

On 6/8/2017 10:40 PM, wrote:
The problem is that the B antenna is receive only. So if the other guy is in you blind spot, he won't see you even if you can see him. A RF opaque glider needs at least two transmit antennas to get a full situational picture.

And as Mark points out, the range tool is a 2D projection of 3D data. So the good range shown could be based on a cone pointing up or down. It's possible your range is near zero on or near the horizon.

Maybe the range tool should provide several charts for different azimuths. But ti would still not be quite right because some hits would be while the glider is banked. So now the range tool should analyze the track and estimate bank angle.

Gets complicated pretty fast :-)

5Z

On Thursday, June 8, 2017 at 2:00:04 PM UTC-7, George Haeh wrote:
Both A & B antennae will be blocked by the engine and one or two bodies.

I'd look into placing the B antenna behind the gear in the tailcone.

On two Scout towplanes, I taped the dipole to a structural cross piece with
a
bit of balsa in between and connected to the A port. The B port got the
straight up antenna.

--
Dan, 5J

On Wednesday, June 7, 2017 at 9:55:56 PM UTC-4, wrote:
However, I would REALLY like to see a 3D view of my range. 2D is fine as far as it goes for the basic knowledge about horizontal coverage, but I think that better understanding of the vertical arena could be equally important, as thermaling in close quarters often puts other gliders in a blind spot for both parties.

I totally agree that Flarm should provide a side view, and front view analysis in addition to the top view. Or even better provide a 3D bubble if they wanted to delight their customers.

Has anyone asked them for this?

Chris

On Thursday, June 8, 2017 at 9:58:39 PM UTC-4, Dan Marotta wrote:
Here are those pictures you asked for:

https://www.dropbox.com/s/nd4z1itc0i...41.15.jpg?dl=0
https://www.dropbox.com/s/fxt1nog20c...23.34.jpg?dl=0
https://www.dropbox.com/s/banwv1ljv1...23.23.jpg?dl=0
https://www.dropbox.com/s/2bqq8ez1ag...22.30.jpg?dl=0

Hope that helps. I know it would help with my reception to place the B
antenna on the bottom of the aircraft, but that would be a pain in the
behind - hardware, cabling, convincing the IA to sign off the
installation, etc.

Dan

On 6/8/2017 8:42 AM, Dan Marotta wrote:
I'll try to remember to get a picture but here's a description:

The Flarm portable is mounted to the top center of the glare shield on
the Stemme. The B antenna is mounted through a grommet directly in
front of me (left side) and about 6 inches forward of the aft edge of
the glare shield. The A antenna is mounted in the same location on
the right side of the glare shield (right side) and the ADS-B antenna
is mounted about 6 inches in front of the A antenna. The GPS antenna
is mounted on top of the glare shield near the forward center. I cut
the coax cables to length and ran them along the under side of the
glare shield cover where they exit their own grommets a couple of
inches away from where the antennae are mounted allowing for a
perpendicular run of coax from the antenna before turning down under
the glare shield.


On 6/7/2017 7:21 PM,
Very good reception compared to most of what I've seen. I would love
to see a photo or detailed description of your antenna layout, in
particular the location, orientation, and separation of the FLARM A
and B antennas. I assume the former is mounted on the portable box
itself.

Chip Bearden


--
Dan, 5J

I would recommend to put the 2nd Flarm recieve antenna in a more diverse location - such as below the insturments and or below and behind the engine. This should provide more reception from people below you.
Chris

I'm pretty sure that the reason that Flarm does not provide 3D information revolves around the fact that the data available is very limited. You can get some sense for your antenna performance only by collapsing a data set into a single plane to get enough points to do some averaging. Even though collapsed into a plane, the data is still quite granular. Remember also that each data point is not a measure of own ship performance; it is the composite performance of own ship and target ship Powerflarm systems. So averaging results from multiple ships is fundamentally necessary to get meaningful information. There just isn't enough data.

On Tuesday, June 13, 2017 at 9:35:33 AM UTC-4, Steve Koerner wrote:
I'm pretty sure that the reason that Flarm does not provide 3D information revolves around the fact that the data available is very limited. You can get some sense for your antenna performance only by collapsing a data set into a single plane to get enough points to do some averaging. Even though collapsed into a plane, the data is still quite granular. Remember also that each data point is not a measure of own ship performance; it is the composite performance of own ship and target ship Powerflarm systems. So averaging results from multiple ships is fundamentally necessary to get meaningful information. There just isn't enough data.

That is why is makes sense to concatenate several flight recordings together. There seems to be a limit of ~4mb (~10hours) but I would suggest that flarm should allow you to put about 50-100 hours of flight data into one analysis to get the required information.
Plus collapsing into the top view plan is just as arbitrary as any other plane, they should provide the option to collapse into side view plane also.

In my Arcus I have the receive and transmit aerial where fitted by the factory on top of the rear glare shield, and the receive only aerial on the belly in front of the main wheel.

I raised all of these issues with FLARM years ago. The typical statistics from a flight do not support the range analysis very well at all. I asked for the ability to upload multiple files but was completely blown off by FLARM. I wrote some code to add together many IGC files and it was quite instructive. Their tools work quite a bit better. The problem is that people really don't understand how to read these plots. What you are really getting is the mean range. The problem with that is that contact is really a statistical problem. Really there should be three range rings: Mean range, mean range plus one standard deviation, and mean range minus one standard deviation. I suggested this as well but was completely blown off again.

To get a minimum range with a reasonable contact probability from a safety standpoint, you really should look at the mean minus one standard deviation.. Those are the conditions under which you would have a reasonable confidence interval and know that you will hav a good signal. I suspect that in a large majority of cases, this may actually be a negative number. Unfortunately, people rely on this tech to alert them to a potential collision and the reality is that there is a relatively high probability that it will not do so. People use anecdotal evidence to support unreasonably long contact distances, "the other day I saw XX on my FLARM display from 15km away!", so they assume that is the norm but it is really probably mean plus multiple standard deviations. Unfortunately, they think that is normal when it isn't.

FLARM is hampered by several technological problems. Low power transmitters, poorly placed and poorly performing antennas, and low power cpus with insufficient horsepower to handle lots of targets in close proximity. It will never work right.

ADS-B uses high power transmitters, reliable position reporting and good antennas that are well placed. ADS-B targets can be easily tracked from 50 miles out. For an anti collision system, I want something that will give me good advanced notice that something is nearby and be compatible with all the other air traffic because it doesn't matter whether I hit another glider or a power plane, it's going to hurt either way.

FLARM is a highly flawed product and I won't have it in my aircraft.

FLARM is a highly flawed product and I won't have it in my
aircraft.

Interesting post Mike but I'm glad you don't fly in the same
airspace as me! Perhaps you should fit Flarm, try it for a
season, then post your conclusions? I've yet to meet anyone
who purposefully removed a Flarm; it may not be perfect but
it's a LOT better than nothing.
You might also ask yourself why the French mandate Flarm?
Dave Walsh

Unfortunately, the lower receive-only antenna may have nothing to
receive if the upper transmit-receive antenna is blocked by the fuselage
and does not ping the approaching aircraft behind/below.

On 6/13/2017 6:34 PM, waremark wrote:
In my Arcus I have the receive and transmit aerial where fitted by the factory on top of the rear glare shield, and the receive only aerial on the belly in front of the main wheel.

--
Dan, 5J

On Wednesday, June 14, 2017 at 2:20:49 PM UTC-4, Dan Marotta wrote:
Unfortunately, the lower receive-only antenna may have nothing to
receive if the upper transmit-receive antenna is blocked by the fuselage
and does not ping the approaching aircraft behind/below.

On 6/13/2017 6:34 PM, waremark wrote:
In my Arcus I have the receive and transmit aerial where fitted by the factory on top of the rear glare shield, and the receive only aerial on the belly in front of the main wheel.

--
Dan, 5J

Hi Dan. The flarm doesn't work as an interrogator/response system like a transponder. From flarm.com : "Each FLARM system determines its position and altitude with a sensitive GPS receiver. Based on speed, acceleration, track, turn radius, wind, altitude, vertical speed, aircraft type, and other parameters, a precise projected flight path can be calculated. The flight path, together with additional information such as a unique identification number, is encoded before being broadcast over an encrypted radio channel twice per second."

So the lower antenna doesn't "ping" the other flarm - it receives the signal which is transmitted twice per second by any flarm within its view.

Another Dan