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Author Topic: How is the wind vector calculated ?  (Read 237 times)

jcomm

  • Join date: Dec 2011
  • Location: Portugal
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How is the wind vector calculated ?
« on: Thu, 12 Jul 2018 08:20 »
I wonder how the wind vector displayed on the ND is actually determined.

I guess it's not "exactly" instantaneous, but rather based on an average over a dt, and... is it true or magnetic ( should be magnetic, thus adapted to the local magvar ?, even more if the data coming from the ADIRs is already magnetic which I really don't know if it's the case...  ).


G-CIVA

  • Join date: Dec 2009
  • Location: Adelaide, South Australia
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Re: How is the wind vector calculated ?
« Reply #1 on: Thu, 12 Jul 2018 08:59 »
I wonder how the wind vector displayed on the ND is actually determined.

FCOM Vol 2 Ch 11 Sect 20 .....



With regard to the determination of the presentation of heading reference information ....



(Although I suspect the actual presentation of the Wind Vector Symbol Data on the ND does not change ... over to the astronauts & engineers for that one)
Steve Bell
aka The CC

jcomm

  • Join date: Dec 2011
  • Location: Portugal
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Re: How is the wind vector calculated ?
« Reply #2 on: Thu, 12 Jul 2018 12:07 »
Thx Steve,

so I can assume all of the data used for computing the vector display comes "ready to use" from the IRS.

Hardy Heinlin

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Re: How is the wind vector calculated ?
« Reply #3 on: Thu, 12 Jul 2018 12:50 »
There are no ADIRs on the 744 so far; IRUs and ADCs are separate boxes. According to the left and right pilot's onside IRS source selector and ADC source selector, the related IRU gets TAS data from the selected ADC source. The IRU senses current track, heading, groundspeed. And with the received TAS value it computes the current wind data, and sends this data to the FMCs which send the data via the onside pilot's selected FMC source to the onside ND. If the pilot's onside FMC source is inoperative, the IRU wind data goes directly to the ND (in CDU standby navigation mode, each CDU is linked with one IRU -- CDU L with IRU L, CDU R with IRU R etc.). The display on the ND refers to the current MAG/TRU mode. To avoid on-off flicker, the wind display includes a hysterisis: It disappears below 4 kt windspeed, and re-appears above 5 kt. The ADC filters its airspeed data for smoother flight instrument behaviour by using a small artificial inertia. However, this is recorrected during takeoff acceleration to avoid delays, and it's still fast enough to see windshears. You can use the wind display to check for fast windshear trends. Of course, the aircraft track has a great inertia, and the computed wind data always depends on that as well.

jcomm

  • Join date: Dec 2011
  • Location: Portugal
  • Posts: 1049
Re: How is the wind vector calculated ?
« Reply #4 on: Thu, 12 Jul 2018 16:56 »
Thx HH!