PowerFLARM questions

On Nov 2, 1:05*pm, Greg Arnold wrote:
On 11/2/2010 12:52 PM, Grider Pirate wrote:





I don't have FLARM, but I have a TT21 transponder. I WILL be talking
on 123.5 on the Whites!
Let me get this straight. *FLARM uses GPS altitude. My transponder
uses Pressure altitude.
FLARM will see my transponder (assuming I'm interrogated) much as a
PCAS.
FLARM will look at its GPS altitude, and maybe not worry about me
because it thinks we have 1000' vertical separation. *Too bad for us
if it's a smokin' day, and the tranponder pressure altitude show
16,800 when the GPS altitude shows 18,000!

B2016373615714N11540384WA *05179 *05561 *000076000000
B2016413615718N11540296WA *05202 *05585 *000072000000
(just an example of a 1,256 difference between pressure and GPS alt,
spaces added for clarity)

The difference between cabin and static is trivial compared to the
difference between pressure and GPS.

Also, we just learned that the altitude of other gliders displayed by
SeeYou for Flarm purposes is absolute, not relative. *So we will be
comparing the GPS altitude of other gliders with the pressure altitude
on our altimeter. *This seems like a problem.- Hide quoted text -

- Show quoted text -

My understanding from Urs's talk is that Flarm is using pressure
altitude, not GPS altitude. It does not make sense otherwise as other
pointed out. While GPS altitude is more accurate as an absolute
altitude (if you took a tape measure), the actual difference between
GPS altitude and pressure altitude can indeed be over 1000 feet, and
the accuracy of gps altitude relies heavily on reception and can
jitter a lot. Since all we need to know is relative altitude to
another aircraft carrying a flarm or transponder, pressure altitude
makes much more sense to me. Did I miss something?

Ramy

On Nov 2, 12:52*pm, Grider Pirate wrote:
On Nov 2, 11:20*am, Darryl Ramm wrote:
[snip]

I don't have FLARM, but I have a TT21 transponder. I WILL be talking
on 123.5 on the Whites!
Let me get this straight. *FLARM uses GPS altitude. My transponder
uses Pressure altitude.
FLARM will see my transponder (assuming I'm interrogated) much as a
PCAS.
FLARM will look at its GPS altitude, and maybe not worry about me
because it thinks we have 1000' vertical separation. *Too bad for us
if it's a smokin' day, and the tranponder pressure altitude show
16,800 when the GPS altitude shows 18,000!

B2016373615714N11540384WA *05179 *05561 *000076000000
B2016413615718N11540296WA *05202 *05585 *000072000000
(just an example of a 1,256 difference between pressure and GPS alt,
spaces added for clarity)

The difference between cabin and static is trivial compared to the
difference between pressure and GPS.

James

Thanks for using a transponder!

You are asking a different question than I was talking about. flarm-
flarm collision avoidance radio links uses GPS altitude and does not
involve pressure. I did not say th PowerFLARM does not use pressure
information elsewhere.

PCAS systems today can suffer from altitide errors (esp if the PCAS
eqiupped glider does not have a local transponder to pick up an
accurate altitude). PCAS systems sniff the local transponder altitude
or use ambient cockpit pressure to sense their relative altitude to a
threat and I assume PowerFLARM will do similar. What exactly the PCAS
does I am not sure, then there are parts of the Zaon MRX that I don't
understand either. And I'm not losing any sleep over it given how
obviously the difference between encoder altitude and GPS altitude can
be (so pressure data is needed) and from conversation with these guys
over related issues where they clearly are smarter than your average
bear on this stuff.

I know you know this but the PCAS warning from a PowerFLARM or Zaon
MRX on the White Mountains to your Trig TT-21 will be a lot less
useful that the flarm-flarm link between two PowerFLARM units. I've
flown the whites with PCAS (and a Mode C) and on busy days you get too
many alerts with too little time to work out where the threat is. On
quiet days it is handy for letting you know somebody else is in the
area.

If you have a Trig TT21 in an experimental glider today you may want
to consider connecting a GPS and transmitting 1090ES data-out in
future. And before anybody asks - ADS-B data-out systems are required
to transmit GPS altitude _and_ pressure altitude.

Darryl

On 11/2/2010 1:28 PM, Darryl Ramm wrote:


You are asking a different question than I was talking about. flarm-
flarm collision avoidance radio links uses GPS altitude and does not
involve pressure. I did not say th PowerFLARM does not use pressure
information elsewhere.


So PowerFLARM uses GPS altitude to avoid collisions, but also broadcasts
pressure altitude, and this is what shows up on the SeeYou screen next
to other gliders?

On Nov 2, 1:39*pm, Greg Arnold wrote:
On 11/2/2010 1:28 PM, Darryl Ramm wrote:



You are asking a different question than I was talking about. flarm-
flarm collision avoidance radio links uses GPS altitude and does not
involve pressure. I did not say th PowerFLARM does not use pressure
information elsewhere.

So PowerFLARM uses GPS altitude to avoid collisions, but also broadcasts
pressure altitude, and this is what shows up on the SeeYou screen next
to other gliders?

I was saying PowerFLARM is a PCAS *receiver* it just needs to know the
pressure altitude for that to work - it does not transmit anything.
Same for ADS-B since it is only a receiver.

Flarm and PowerFLARM have to be 100% compatible and Flarm does not use
pressure altitude in its collision avoidance protocol. And I want to
qualify that as far as I know PowerFLARM does not transmit pressure
altitude, but it might, I dont know. And if anybody ever wanted to use
that it might break things so I'm not sure it would ever be a good
idea. See my other post in this thread on how SeeYou Mobile does what
it does which I think will address these concerns.

Darryl

Darryl

On 11/2/2010 2:02 PM, Darryl Ramm wrote:


Flarm and PowerFLARM have to be 100% compatible and Flarm does not use
pressure altitude in its collision avoidance protocol. And I want to
qualify that as far as I know PowerFLARM does not transmit pressure
altitude, but it might, I dont know.


It must transmit pressure altitude, as otherwise the altitude reading
displaying on SeeYou next to another glider is GPS altitude. I can't
compare that to the altitude on my altimeter.

On Nov 2, 1:05*pm, Greg Arnold wrote:
On 11/2/2010 12:52 PM, Grider Pirate wrote:



I don't have FLARM, but I have a TT21 transponder. I WILL be talking
on 123.5 on the Whites!
Let me get this straight. *FLARM uses GPS altitude. My transponder
uses Pressure altitude.
FLARM will see my transponder (assuming I'm interrogated) much as a
PCAS.
FLARM will look at its GPS altitude, and maybe not worry about me
because it thinks we have 1000' vertical separation. *Too bad for us
if it's a smokin' day, and the tranponder pressure altitude show
16,800 when the GPS altitude shows 18,000!

B2016373615714N11540384WA *05179 *05561 *000076000000
B2016413615718N11540296WA *05202 *05585 *000072000000
(just an example of a 1,256 difference between pressure and GPS alt,
spaces added for clarity)

The difference between cabin and static is trivial compared to the
difference between pressure and GPS.

Also, we just learned that the altitude of other gliders displayed by
SeeYou for Flarm purposes is absolute, not relative. *So we will be
comparing the GPS altitude of other gliders with the pressure altitude
on our altimeter. *This seems like a problem.

Having never flown with SeeYou Mobile and Flarm I'll admit to not
being sure exactly what is shows for altitude on the Flarm radar
screen. But that does not stop some reverse engineering...

Some other Flarm 3rd party display products only show relative height.
But lets assume SeeYou Mobile shows absolute altitude not differences.
But that does *not* automatically mean it is showing pressure altitude
(corrected for QNH) or GPS altitude of those other gliders?

The altitude data presented to SeeYou Mobile or any other application
that connects to a Flarm is only ever *relative* altitude between the
remote gliders flarm GPS and your flarm's GPS. The dataport interface
document is on Flarm's web site and is great quick bedtime read.
SeeYou Mobile would have to add your GPS altitude to the difference to
get the absolute GPS altitude of the other glider. Now if SeeYou
Mobile knows your pressure altitude I would hope it works with that
and all the other Flarm targets are show with pressure altitudes.
That would be consistent with the general handling of altitudes in
SeeYou Moble but I'll let Andrej or others confirm what they do.

BTW anybody else got an idea that Flarm folks working on this know
what they are doing? :-)

And to be clear to others in case they are worried about the absolute
altitude description - when you get a pop-up Flarm alert in SeeYou
Mobile the altitude displayed is always relative. The Flarm "radar"
display also has user settable color bands to show it the other
aircraft are near, above or below your altitude.

You know for a large map/radar display I'd personally rather see
absolute altitudes - especially as we eventually forward to ADS-B and
may see people over hundreds of miles. Ultimately having a choice of
relative/absolute would be best. Now somebody tell us that SeeYou
Mobile shows relative altitudes now and we can all go back to
sleep :-)


Darryl

On Nov 2, 2:15*pm, Greg Arnold wrote:
On 11/2/2010 2:02 PM, Darryl Ramm wrote:



Flarm and PowerFLARM have to be 100% compatible and Flarm does not use
pressure altitude in its collision avoidance protocol. And I want to
qualify that as far as I know PowerFLARM does not transmit pressure
altitude, but it might, I dont know.

It must transmit pressure altitude, as otherwise the altitude reading
displaying on SeeYou next to another glider is GPS altitude. *I can't
compare that to the altitude on my altimeter.

Greg,

O ye, of little faith. Wanna bet a case of good San Ynetz area wine?

Darryl

On 11/2/2010 2:25 PM, Darryl Ramm wrote:


You know for a large map/radar display I'd personally rather see
absolute altitudes - especially as we eventually forward to ADS-B and
may see people over hundreds of miles. Ultimately having a choice of
relative/absolute would be best. Now somebody tell us that SeeYou
Mobile shows relative altitudes now and we can all go back to
sleep :-)

This morning Andrej told us it is absolute.



Darryl

On 11/2/2010 2:29 PM, Darryl Ramm wrote:
On Nov 2, 2:15 pm, Greg wrote:
On 11/2/2010 2:02 PM, Darryl Ramm wrote:



Flarm and PowerFLARM have to be 100% compatible and Flarm does not use
pressure altitude in its collision avoidance protocol. And I want to
qualify that as far as I know PowerFLARM does not transmit pressure
altitude, but it might, I dont know.

It must transmit pressure altitude, as otherwise the altitude reading
displaying on SeeYou next to another glider is GPS altitude. I can't
compare that to the altitude on my altimeter.

Greg,

O ye, of little faith. Wanna bet a case of good San Ynetz area wine?

Darryl

No, I will decline that bet.

Originally Posted by Greg Arnold[_2_]

Will the PowerFLARM logger record pressure altitude, or only GPS
altitude? Will it record engine noise level?

Yes, I think. It will record it.