Ground speed wrong in 750?

[Gregg_Seipp]

I was just flying the Turbine Duke at FL220.  I had a 51 knot headwind and showed a groundspeed of 301 knots.  That should not be possible.  The most I should see with that headwind is 230 to 240.  

Gregg

[thibodba57]

3 minutes ago, Gregg_Seipp said:

I was just flying the Turbine Duke at FL220.  I had a 51 knot headwind and showed a groundspeed of 301 knots.  That should not be possible.  The most I should see is 230 to 240.  

Gregg

I don't have the GTN. But I have seen I other add-ons that if you have True Airspeed selected in the simulator settings instead of Indicated by accident then you will see results like that.

[Gregg_Seipp]

3 minutes ago, thibodba57 said:

I don't have the GTN. But I have seen I other add-ons that if you have True Airspeed selected in the simulator settings instead of Indicated by accident then you will see results like that.

Indicated airspeed is selected.

[Gregg_Seipp]

Thought we'd have a response by now.  My suspicion is that it's a math error.  When I was 45 degrees off the headwind, my ground speed was 295-ish.  When I turned directly into the headwind, my ground speed actually increased.  There is a simconnect variable "GROUND VELOCITY" which should have the correct value.

Gregg

[RXP]

Hi Gregg,

This is the kind of question which couldn't bring an immediate answer, but requires deeper investigation! We are not done yet on this but we are looking.

Mind you, the GTN gauge uses "GROUND VELOCITY" simvar as source data indeed.

Now, can you please let us know 'where' you were reading the ground speed value?

Also, can you cross check what does it read on the Utilities | DALT / TAS Winds page (requires enabling Shadin Air Data input)?

[Gregg_Seipp]

2 hours ago, RXP said:

Now, can you please let us know 'where' you were reading the ground speed value?

Also, can you cross check what does it read on the Utilities | DALT / TAS Winds page (requires enabling Shadin Air Data input)?

Hi Jean-Luc,

Heck, it occurred to me you might have taken a deserved day off.  No worries.

I was reading the GS value from the bottom left of the 750.  The Turbine Duke can only hit 300 knots true under ideal situations so when I saw that with a headwind of 50 knots I knew something was up.  Today, I took a flight and had a 30 knot headwind at FL220.  I tuned my airspeed indicator for altitude and OT showing 292 KIAS true.  The GS value in the bottom left of the 750 was the same value plus or minus two knots.  I'd think the GS with a thirty knot headwind would have been 262 KIAS (292 - 30 knot headwind).  I'll try the other Utilities | DALT / TAS thing you mentioned as well.  Here's the thing, though, the problem may be the arrow next to the windspeed.  It was pointed down but, when I just checked the wind for Florida and it seemed to show the wind was from the south or southwest up there.  Here's the barbs at FL210.  I was at FL220.

[fppilot]

So an obvious question is whether you have your GPS display  track up, or if you have it north up?  May not be the answer to the issue, but worth asking.

[Gregg_Seipp]

45 minutes ago, fppilot said:

So an obvious question is whether you have your GPS display  track up, or if you have it north up?  May not be the answer to the issue, but worth asking.

Sure.  It was track up.  BTW, it's a pretty simple experiment to try so others could help investigate.  Pick an area that has good upper level wind and take a flight.  I flew the Turbine Duke which, at the moment, is the only airplane I have the 750 in.

[RXP]

So if I understand correctly, the wind arrow was pointing roughly 180º around what it was supposed to be (say the value internally interpreted as coming from instead of going to), or was it something closer to typically the local MAGVAR x 2 ?

I'm also asking for the DALT/TAS because the data source is not the same. The page 'computes' the wind from GS/TRK/HDG, whereas the MAP 'displays' the wind from the data input (typically our Shadin Air Data simulation embedded).

 

[Gregg_Seipp]

7 minutes ago, RXP said:

So if I understand correctly, the wind arrow was pointing roughly 180º around what it was supposed to be (say the value internally interpreted as coming from instead of going to), or was it something closer to typically the local MAGVAR x 2 ?

I'm also asking for the DALT/TAS because the data source is not the same. The page 'computes' the wind from GS/TRK/HDG, whereas the MAP 'displays' the wind from the data input (typically our Shadin Air Data simulation embedded).

If I recall, the wind was indicating from about 010 yesterday, so pointing down and a little left when I was flying north.  Today it was from straight north, so arrow pointing straight down when I was flying north.

[RXP]

6 minutes ago, Gregg_Seipp said:

If I recall, the wind was indicating from about 010 yesterday, so pointing down and a little left when I was flying north.

This one sounds right isn't it?

6 minutes ago, Gregg_Seipp said:

Today it was from straight north, so arrow pointing straight down when I was flying north.

This one sounds right as well isn't it?

[Gregg_Seipp]

1 minute ago, RXP said:

This one sounds right isn't it?

I'm suddenly confused.  If I'm flying track up, and the arrow's pointing down, it's indicating a headwind, no?  Yesterday a headwind of 50...today 30?

[RXP]

I don't know but I think I'm confused too LOL! Maybe it's time for me to really switch off this computer and sleep over it!

Nevertheless, arrow pointing in the direction the wind is flowing (wind vector like in math vector). So arrow pointing down in track up, means headwind. Arrow pointing down in north up view, while flying to the east, means side wind from the left. At least, this is what I can infer.

Now, the wind vector displaying on the map page is 'RXP' managed. We may have got the 'logic' wrong, and someone with a real GTN might certainly help with this. For example I'm wondering if the wind vector depends on the map 'up' setting (I guess so, otherwise this would be confusing).

During synthetic tests setting up wind layers in FltSim or XPlane, the wind vector was matching what was expected always.

Now all this wind vector discussion does not account for the G/S value you were reading. This is why I'd suggest you try with synthetic wind layers, instead of real-weather layers, just to make sure local wind is within known and controlled bounds.

[fppilot]

2 hours ago, Gregg_Seipp said:

I flew the Turbine Duke which, at the moment, is the only airplane I have the 750 in.

Do you need help? LOL!

[Gregg_Seipp]

Just now, fppilot said:

Do you need help? LOL!

Naw, not yet.  I just got on P3D a few weeks ago and enjoying my favorites.  I'll add more over time.

34 minutes ago, RXP said:

Now all this wind vector discussion does not account for the G/S value you were reading. This is why I'd suggest you try with synthetic wind layers, instead of real-weather layers, just to make sure local wind is within known and controlled bounds.

I'll do another test and confirm the wind...maybe take some screenshots.