How do glass panels compute wind vectors?

[MSPAviator]

Ok, I fly standard 6 pack steam gauges 99% of the time.


I got a chance to ride in a Cirrus, glass panel of course. It had synthetic vision and it had a little wind vector arrow that showed which direction and how fast the wind was blowing from.

How exactly does the computer figure that out?

I wish I had one of those in my plane. I still use the E6B for WCA and hand fly everything.

 

[Jim Logajan]

I got a chance to ride in a Cirrus, glass panel of course. It had synthetic vision and it had a little wind vector arrow that showed which direction and how fast the wind was blowing from.

How exactly does the computer figure that out?

It needs to know the direction and magnitude of the ground velocity vector and the true air speed vector. The vector difference between the two is the wind vector.

It may get the ground velocity vector from two or more GPS or VOR/DME readings.

It may get the true air speed vector from the indicated airspeed (pitot) reading, corrected for outside air temperature and altitude setting (barometric pressure.)

That's how I would program it - but I have no idea if that is what those systems actually do - I'm assuming the above is the most likely mechanism.

 

[fszczerba]

Yep. The GPS calculates your ground track and ground speed, the AHRS knows your magnetic heading, and the ADC knows the outside air temperature, pressure altitude, and IAS. The EFIS is programmed with the corrections table to get CAS, so it can use that and the other info from the ADC to calculate TAS. After that, it's just the same wind triangle problem you do on the E6B.

 

[PittsDriver]

How exactly does the computer figure that out?

It's good at math.

 

[jasc15]

I have no idea how it does it, but the simplest and most straight forward way would be what has been said so far. When you use your whiz wheel, you have the wind vector and your airspeed vector which you use to compute the groundspeed vector. With the gps, it has your airspeed vector and groundspeed vector, and uses those to calculate the wind speed vector.

 

[JeffDG]

It's good at math.

Bingo.

It has all the information being fed to it constantly, and does precisely the same calculations you would, just with more accuracy, speed, and frequency.

 

[HPNPilot1200]

It crunches all of the numbers together. I presume the calculations done in the ADC uses Groundspeed, Actual Ground Track, Heading, and True Airspeed (the ADC calculates and displays this usually). In the Cirrus and the Phenom we get wind vectors if all of these components are present.

 

[gismo]

It crunches all of the numbers together. I presume the calculations done in the ADC uses Groundspeed, Actual Ground Track, Heading, and True Airspeed (the ADC calculates and displays this usually). In the Cirrus and the Phenom we get wind vectors if all of these components are present.

Close enough. The raw data includes Indicated Airspeed, OAT, and pressure altitude to compute TAS which is subsequently used along with magnetic heading, magnetic track, and groundspeed to deduce the wind.

And FWIW, while two DME measurements and the location of the DME ground stations is sufficient to determine groundspeed and track, no GA Air Data Computer does it with that, all use GPS instead.

 

[flyingcheesehead]

I got a chance to ride in a Cirrus, glass panel of course. It had synthetic vision and it had a little wind vector arrow that showed which direction and how fast the wind was blowing from.

How exactly does the computer figure that out?

Well, there's a couple of little gremlins in there with miniature E6B's that spend the entire flight computing and re-computing the winds aloft.

(Actually, Jim's answer is pretty good.)

 

[denverpilot]

How exactly does the computer figure that out?

There's a really tiny person inside the box with an E6B. Make sure you don't feed them after dark.

[Edit: Aww crap, Kent beat me to it.]

 

[denverpilot]

Bingo.

It has all the information being fed to it constantly, and does precisely the same calculations you would, just with more accuracy, speed, and frequency.

Until you fly over the North or South Pole, then the box crashes since all headings (from the North Pole) are 180 degrees.

The algorithm barfs. Well, it does in Boeing 777's anyway. (There's a "no-fly" box directly over the Pole because the math falls apart in the FMS.)

 

[flyingcheesehead]

Until you fly over the North or South Pole, then the box crashes since all headings (from the North Pole) are 180 degrees.

The algorithm barfs. Well, it does in Boeing 777's anyway. (There's a "no-fly" box directly over the Pole because the math falls apart in the FMS.)

The G1000 also has a no-fly area over the poles that's actually quite large. Some pretty big chunks of northern Canada are in the no-fly area.

EDIT: I guess you can fly there, but you'll lose the Heading indicator. Nav signal on the HSI will still be displayed, but the heading portion will be tagged "GEO LIMITS."

Here's the blurb from the manual which describes the affected area:

WARNING: Because of anomalies in the earth’s magnetic field, operating the G1000 within the following areas could result in loss of reliable attitude and heading indications. North of 70° North latitude and south of 70° South latitude. An area north of 65° North latitude between longitude 75o West and 120o West. An area south of 55° South latitude between longitude 120o East and 165o East.

 

[gismo]

The G1000 also has a no-fly area over the poles that's actually quite large. Some pretty big chunks of northern Canada are in the no-fly area.

EDIT: I guess you can fly there, but you'll lose the Heading indicator. Nav signal on the HSI will still be displayed, but the heading portion will be tagged "GEO LIMITS."

Here's the blurb from the manual which describes the affected area:

You'll lose more than the heading indication, without usable magnetic heading the AHRS will lose attitude information as well (says so in the text you quoted too). So if you're going to fly your fancy glass panel airplane north of about 60° lattitude, you'd best bone up on your "partial panel" skills (partial panel being stuck with a mechanical attitude gyro).

 

[Baron2PG]

The wind vector may simply be from the XM Weather forecast winds aloft and not an actual calculation. My Garmin 530W displays just such a vector based on the XM weather download and the GPS altitude.

My handheld Garmin 396 will give you the wind vector if you enter the information previously discussed; thus, there is no reason a "glass panel" couldn't do the math provided it had all of the variables.

 

[skidoo]

Well, there's a couple of little gremlins in there with miniature E6B's that spend the entire flight computing and re-computing the winds aloft.

(Actually, Jim's answer is pretty good.)

The Intel 4004 was released in 1971. I haven't used an E6B since 1975...

The wind display box in the G1000 is a great feature! It is really interesting to see 20 kts on downwind, and then drop to < 8 kts just prior to touchdown. No way would I be trying to calculate winds at those times.

 

[CJones]

Well, there's a couple of little Tonys in there with miniature E6B's that spend the entire flight computing and re-computing the winds aloft.

(Actually, Jim's answer is pretty good.)

Fixed that for ya'...

Seriously.. Have you seen the guy use an E6B? My fingers won't move that fast, much less the thought required to understand what I'm looking at at that speed...

 

[tonycondon]

Fixed that for ya'...

Seriously.. Have you seen the guy use an E6B? My fingers won't move that fast, much less the thought required to understand what I'm looking at at that speed...

its just a slide rule...

 

[gismo]

The wind vector may simply be from the XM Weather forecast winds aloft and not an actual calculation. My Garmin 530W displays just such a vector based on the XM weather download and the GPS altitude.

My handheld Garmin 396 will give you the wind vector if you enter the information previously discussed; thus, there is no reason a "glass panel" couldn't do the math provided it had all of the variables.

I think you're talking about the wind vector weather overlay that shows a bunch of arrows in lines on the map page and if so that's definitely XM derived. But IIRC that requires you to select an altitude for the wind data and doesn't show up in a data field like the ADC generated wind vector does on the 430/530/Aspen/G1000/G500 etc.