smartt1982
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Wind Speed/track On ND Display

Sun Jan 06, 2013 3:50 pm

With two operating IRSs’ I can on the IRS Display Unit (ISDU) select WIND and it will display the present inflight TRUE wind direction and wind speed in Knots (I am aware that the selection may differ to aircraft type).
For EFIS/Glass cockpit aircraft do you require an FMC to be able to have that wind info to display correctly on your Map/ND display?
My understanding is that there is an inbuilt Mag converter in the IRS in order to be able to display the Wind info in relation to Magnetic North.

But I have also heard that the FMC averages out the wind information that it receives from the IRS.
What would be the case if you have Dual FMCs, would each FMC average out the wind info it gets. I always wondered if that was the reason on a Dual FMC setup that the wind info displayed on the NDs was very slightly different for a quick moment.
If the FMCs fail, would that wind info on the ND be accurate or would you need to refer to the direct readout from the ISDU?
 
tdscanuck
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RE: Wind Speed/track On ND Display

Sun Jan 06, 2013 8:29 pm

Quoting smartt1982 (Thread starter):
But I have also heard that the FMC averages out the wind information that it receives from the IRS.
What would be the case if you have Dual FMCs, would each FMC average out the wind info it gets. I always wondered if that was the reason on a Dual FMC setup that the wind info displayed on the NDs was very slightly different for a quick moment.

My experience is all with Boeing aircraft, which have dual or triple FMCs and dual IRSs. On those systems, the wind is an output of the IRSs (difference between inertial velocity and air velocity), not the FMCs, so you will get wind displayed whether or not the FMCs are running.

The difference between sides, at least on those aircraft, is due to the different cockpit displays being driven by different display computers that aren't perfectly in sync.

Tom.
 
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Starlionblue
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RE: Wind Speed/track On ND Display

Mon Jan 07, 2013 12:52 am

Quoting smartt1982 (Thread starter):

With two operating IRSs’ I can on the IRS Display Unit (ISDU) select WIND and it will display the present inflight TRUE wind direction and wind speed in Knots (I am aware that the selection may differ to aircraft type).
For EFIS/Glass cockpit aircraft do you require an FMC to be able to have that wind info to display correctly on your Map/ND display?

How do you define FMC? Certainly you don't need an airliner style FMC. The Cessna 172 Nav III (G1000 glass cockpit) can display true wind direction and speed on the PFD. I think all you need is a GPS, an inertial platform, an air data computer and a computer to crunch the math.

Here's an example, 29 is the wind speed and the arrow shows the direction. You can also display it with the direction "written out" or as two components, headwind and crosswind.

The little magenta diamond on the top of the HSI is where the nose needs to be pointed in order to stay on track while compensating for the wind. Extremely useful for hand flown approaches.

http://blog.adamfast.com/wp-content/uploads/2012/05/IMG_0848.jpg
"There are no stupid questions, but there are a lot of inquisitive idiots."
 
Pihero
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Joined: Mon Jan 31, 2005 5:11 am

RE: Wind Speed/track On ND Display

Mon Jan 07, 2013 1:18 pm

Quoting tdscanuck (Reply 1):
with Boeing aircraft, which have dual or triple FMCs and dual IRSs. On those systems, the wind is an output of the IRSs (difference between inertial velocity and air velocity

Same on the Airbii. The info comes from the ADIRS, the digital direction is "True", the green arrow is "Magnetic".

Quoting Starlionblue (Reply 2):
The little magenta diamond on the top of the HSI is where the nose needs to be pointed in order to stay on track while compensating for the wind.

Unfortunately, your pic doesn't display the selected course, but I presume, IF the usual colour-coding of screen infos is valid on this, the course is 196... In this case, the diamond is not where it should be ( should be around 200° )...
I have a feeling that it is, as a matter of fact the actual Track derived from a heading of 190° and a wind around 200° / 29 kt
So the pilot action would be to fly a heading that would make the diamond coincide with the top of the course arrow ( which is a much more natural action than to follow the diamond )... That's how we fly the 'Bus, btw.

[Edited 2013-01-07 05:19:59]
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Starlionblue
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RE: Wind Speed/track On ND Display

Mon Jan 07, 2013 1:34 pm

Quoting Pihero (Reply 3):
Unfortunately, your pic doesn't display the selected course, but I presume, IF the usual colour-coding of screen infos is valid on this, the course is 196...

Agreed that is annoying about the pic.   And yes the course should be 196.

Quoting Pihero (Reply 3):
I have a feeling that it is, as a matter of fact the actual Track derived from a heading of 190° and a wind around 200° / 29 kt
So the pilot action would be to fly a heading that would make the diamond coincide with the top of the course arrow ( which is a much more natural action than to follow the diamond )... That's how we fly the 'Bus, btw.

Seems I had a total brainfart. I think the Christmas drinks have gotten to me. That is how it works in the G1000 as well.
"There are no stupid questions, but there are a lot of inquisitive idiots."

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