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 How Is Tailwind And Headwind Measured?
 YokoTsuno From Singapore, joined Feb 2011, 372 posts, RR: 0Posted Tue May 24 2011 06:55:29 UTC (5 years 1 week 1 day 11 hours ago) and read 10471 times:

 How is tailwind and headwind actually measured? You can't possibly derive that from the forward pointing pitot tubes alone, can you?
 boeingfixer From Canada, joined Jul 2005, 578 posts, RR: 0 Reply 1, posted Tue May 24 2011 08:34:55 UTC (5 years 1 week 1 day 9 hours ago) and read 10444 times:

 Quoting YokoTsuno (Thread starter):How is tailwind and headwind actually measured? You can't possibly derive that from the forward pointing pitot tubes alone, can you?

It's done with Inertial Reference Units(IRU's). This is the heart of most modern airliners and provides attitude and direction information to the pilot and flight management computers. In simple terms it knows the aircrafts position, speed, heading, drift, course etc. and can extrapolate wind information from this data.

Cheers,

John

 Cheers, John YYC
 be77 From Canada, joined Nov 2007, 455 posts, RR: 0 Reply 2, posted Tue May 24 2011 10:52:30 UTC (5 years 1 week 1 day 7 hours ago) and read 10381 times:

 Quoting boeingfixer (Reply 1):t's done with Inertial Reference Units(IRU's).

..or on the windspeed / wind component page of most Aviation GPS machines, especially if they are tied into the airspeed and external air temp data.

Old school is by taking the groundspeed calculated by time between two points or between navigation beacons (VORs, NDB;s etc), calculating true airspeed from airspeed, temp, and altitude data, then adding in the correction for drift required to maintain the desired track, then plotting all that on the wind side of the whiz wheel, and voila, it's done. Pre GPS some of us could actually do that fast enough for the answer to be relevant to the current flight. Of course, I also remember using a slide rule, rotary telephones, leaded car gas, and a whole truckload of other stuff I DO NOT MISS!

 Tower, Affirmitive, gear is down and welded
 Mir From United States of America, joined Jan 2004, 22868 posts, RR: 53 Reply 3, posted Tue May 24 2011 23:36:50 UTC (5 years 1 week 18 hours ago) and read 10201 times:

 Pure headwind or tailwind is just groundspeed minus true airspeed. If you get a positive number it's a tailwind, a negative number is a headwind. So if you're flying at 450 knots and your groundspeed is 480 knots, you've got a 30 knot tailwind. But since the wind is rarely directly on the nose or the tail, other factors like heading and track start to come into play. The formula for headwind and tailwind still works, but the 30 knot tailwind would now just be a component of the total wind. -Mir
 7 billion, one nation, imagination...it's a beautiful day
 B747FE From Hong Kong, joined Jun 2004, 230 posts, RR: 4 Reply 4, posted Wed May 25 2011 01:55:47 UTC (5 years 1 week 16 hours ago) and read 10168 times:

 Quoting YokoTsuno (Thread starter):You can't possibly derive that from the forward pointing pitot tubes alone, can you?

No, you can't. boeingfixer got it right...the IRS/GPS or INS in old birds take care of that.
However when in long flights in the middle of nowhere and boredom kicks in, nothing like cross-checking your instruments with a good old CR3.
Wind triangle, anyone?

Regards,
B747FE.

 "Flying is more than a sport and more than a job; flying is pure passion and desire, which fill a lifetime"
 Starlionblue From Greenland, joined Feb 2004, 17668 posts, RR: 65 Reply 5, posted Wed May 25 2011 02:45:47 UTC (5 years 1 week 15 hours ago) and read 10150 times:

 Quoting YokoTsuno (Thread starter):You can't possibly derive that from the forward pointing pitot tubes alone, can you?

Quite. That only gives you indicated airspeed. Aerodynamically, the aircraft doesn't care if it is in in a tailwind or a headwind. It just cares about airspeed.

 "There are no stupid questions, but there are a lot of inquisitive idiots."
 YokoTsuno From Singapore, joined Feb 2011, 372 posts, RR: 0 Reply 6, posted Wed May 25 2011 07:02:17 UTC (5 years 1 week 11 hours ago) and read 10091 times:

Thank you very much for the anwers

 Quoting be77 (Reply 2):rotary telephones, leaded car gas

Are you referring to these?

http://en.wikipedia.org/wiki/Rotary_dial

Really? So you dial the guy who does the calculation for you .

 sprout5199 From United States of America, joined Feb 2005, 1866 posts, RR: 1 Reply 7, posted Thu May 26 2011 06:59:15 UTC (5 years 6 days 11 hours ago) and read 9948 times:

 Quoting be77 (Reply 2):Of course, I also remember using a slide rule, rotary telephones, leaded car gas, and a whole truckload of other stuff I DO NOT MISS!

or having to get up and change the channel on the TV. When I was young, I asked my Dad to buy a TV with a remote, his answer "we already have one, I just have you change the channel for me"

Dan in Jupiter

 be77 From Canada, joined Nov 2007, 455 posts, RR: 0 Reply 8, posted Thu May 26 2011 12:18:12 UTC (5 years 6 days 6 hours ago) and read 9866 times:

 Quoting YokoTsuno (Reply 6):Really? So you dial the guy who does the calculation for you

Heh heh - yes, one of those. I even spent a summer job fixing / refurbishing them at the local phone co warehouse.
Problem with your idea of calling someone to do the calculation though is that as strange as it sounds, we didn't have cell phones either. Does anyone know if there is an Iphone app to let you dial using rotary movement, hopefully with the clicking sounds and all?

 Quoting sprout5199 (Reply 7):or having to get up and change the channel on the TV. When I was young, I asked my Dad to buy a TV with a remote, his answer "we already have one, I just have you change the channel for me

How on earth did I not remember that...of course, we only had two channels (CBC English, and CBC French), we we only had to walk over to the TV to turn it on or change the volume. (And yes, it was uphill both ways through 6 feet of snow to get to school!).

 Tower, Affirmitive, gear is down and welded
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