NXi : two questions

[Dominique_K 10,149]

The long time lover of steam gauges that I was, appreciate more and more a good glass cockpit and no doubt that the excellent Nxi serves well the Milviz Porter.  It is a great help in hand flying this bird including visual approach in the boonies.

Two questions : 

- An useful tool is the wind direction and strength thingie specially in a sim with a poor (understatement) weather UI. They show  only when the aircraft is aloft and flying. Couldn't it work on the ground too ?  I suppose that the data come from some aircraft sensors ? 

- There is no indication of airport altitude in nearest airports or other procedure tables. If I remember well, my F1 G750 had them in P3D. Is it the way the real Nxi works or something which may come later ?

Edited November 25, 2021 by Dominique_K

[ronmarks 13]

Quick reply to question 1

Wind direction and velocity (wind vector)is generated in the air as the difference between true airspeed vector and ground speed vector. That mechanism would not work in real life on the ground.

[ark 1,291]

TAS is a calculated value (based on parameters such as calibrated IAS, altitude, pressure, temperature, air density). The GPS of course measures your ground speed. So if you taxi fast enough on the ground to get a IAS value you will get a wind display unless the a/c systems detects you are on the ground (e.g., weight on wheels sensor) and inhibits the wind display.

Al

Edited November 25, 2021 by ark

[jrw4 624]

13 minutes ago, ark said:

TAS is a calculated value (based on parameters such as calibrated IAS, altitude, pressure, temperature, air density). The GPS of course measures your ground speed. So if you taxi fast enough on the ground you will get a wind display unless the a/c systems detects you are on the ground (e.g., weight on wheels sensor) and inhibits the wind display.

Maybe in MSFS, but not the real world. This is true only if the wind is coming straight down the runway, at which point the wind speed is nominally the difference between the TAS and the GS. So long as the wheels are in contact with the ground, the aircraft's ground speed vector points in the direction of the runway. Once airborne, @ronmarks has it right.

PS For a while at least (and maybe even today), the MSFS G1000 incorrectly gave you a readout of the wind direction on the ground. All that told us was that it wasn't actually doing the calculation, but just pulling the numbers from the sim.

Edited November 25, 2021 by jrw4
PS

[ark 1,291]

25 minutes ago, jrw4 said:

Maybe in MSFS, but not the real world. This is true only if the wind is coming straight down the runway, at which point the wind speed is nominally the difference between the TAS and the GS. So long as the wheels are in contact with the ground, the aircraft's ground speed vector points in the direction of the runway. Once airborne, @ronmarks has it right.

That's why I said the readout may be inhibited by the a/c systems. You may get a wind readout on the ground, but since the wind is not influencing your direction of movement or ground speed, that readout will not be accurate. Currently the sim G1000NXi does provide a wind readout on the ground. I don't know what the G1000NXi does in the real world. Light a/c likely don't have a weight on wheels sensor, but many do have a gear up sensor so the G1000NXi could use that input. I guess with fixed gear a/c the wind display could be inhibited until some minimum IAS is measured.

It would be interesting to know what the G1000NXi wind display does on the ground in some real world a/c. The simplest approach would be just to assume the pilot knows the wind info is not accurate on the ground.

Al

EDIT: Regarding the wind display window, the G1000NXi manual says: "When the window is selected for display, but wind information is invalid or unavailable, the window displays NO WIND DATA". So the question is how does the G1000NXi determine the wind info is invalid?

Edited November 25, 2021 by ark

[SAS443 1,723]

6 hours ago, Dominique_K said:

An useful tool is the wind direction and strength thingie specially in a sim with a poor (understatement) weather UI. They show  only when the aircraft is aloft and flying. Couldn't it work on the ground too ?  I suppose that the data come from some aircraft sensors ?

For what it's worth: I don't fly with the G1000 NXi but with the Garmin G3X package (dual 10 inch displays) in a B23 IRL.

I 've seen "No Wind data" even at 500ft AGL on the PFD after takeoff. Not quite sure of the exact logic but in the tech course they mentioned the Garmin unit compares heading / TAS vs GPS track / groundspeed  and calculates wind velocity+ direction.
After landing, I usually get "No Wind Data" as I decelerate from 30kts to normal taxi speed.

 

[Bert Pieke 7,585]

8 hours ago, Dominique_K said:

There is no indication of airport altitude in nearest airports

The MFD Nearest page does give you that Info.

[Dominique_K 10,149]

A lot of useful infos, thank you guys, appreciated. 

In my first departure, after this thread, the wind indicator became alive indeed at 30 knots while taxiing on the runway downwind to the the starting point( MV Porter). 

And the  wind velocity is indeed obviously a computation from TAS and GS. I still don't entirely get how it computes the direction (head and cross wind) but what are insomnias for 😉 ?

18 minutes ago, Bert Pieke said:

The MFD Nearest page does give you that Info.

Okay ! I saw a Nearest soft key only on the PFD not on the MFD. But after checking the on-line manual I see that you have to access the FMS  that I have never used. I used only the basic functions. Good to know, thanks.

[ark 1,291]

53 minutes ago, Dominique_K said:

I still don't entirely get how it computes the direction (head and cross wind)

The G1000NXi crosswind info is particularly useful when landing.  At an airport with a tower the tower will typically give you the wind speed and direction, but without 'smart' avionics it is up to the pilot to resolve that tower's wind info into the crosswind component (and headwind if so desired). 

It may also be worth mentioning that while the wind direction from the tower is Magnetic, wind direction in a METAR or TAF is True. Usually 'spoken' wind direction is Magnetic, 'written' wind direction is True.

Al

Edited November 25, 2021 by ark

[martinboehme 492]

1 hour ago, Dominique_K said:

And the  wind velocity is indeed obviously a computation from TAS and GS. I still don't entirely get how it computes the direction (head and cross wind) but what are insomnias for 😉 ?

It knows your heading and your track as well as TAS and GS. From that, it can compute wind direction and velocity -- this is essentially the inverse of the computation you would do when flight planning to compute your wind correction angle from the desired track and the wind.