aerdingus
Topic Author
Posts: 2667
Joined: Tue Dec 05, 2006 8:58 pm

Hi everyone,

Say if I'm on a heading of 230, & there's a wind of 40kts on a heading of 247, would my speed increase that much? Or would I have to be on the exact heading?

Thanks
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JohnKrist
Crew
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Joined: Sat Jan 22, 2005 11:54 pm

It wouldn't increase that much no, it would increase 38 knots, pretty close since the heading of the wind almost is equal to your heading.
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aerdingus
Topic Author
Posts: 2667
Joined: Tue Dec 05, 2006 8:58 pm

Thanks for that man, now I am DIABOLICAL* at maths, can I ask where does the 38kts come from?

Cheers

* And evidently also at spelling: "Qusetion"?! wtf?!

[Edited 2010-11-10 13:40:03]
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Fly2HMO
Posts: 7187
Joined: Sat Jan 24, 2004 12:14 pm

 Quoting aerdingus (Thread starter):would my speed increase that much?

WHAT speed? Groundspeed? True Airspeed? Indicated Airspeed?

TAS and IAS would not change (not instanteneously at least). Groundspeed would increase a bit.

 Quoting aerdingus (Reply 2):can I ask where does the 38kts come from?
http://www.csgnetwork.com/e6bcalc.html

Mir
Posts: 19291
Joined: Mon Jan 05, 2004 3:55 am

 Quoting aerdingus (Thread starter):Say if I'm on a heading of 230, & there's a wind of 40kts on a heading of 247, would my speed increase that much?

Unlike your airplane's heading, wind is read in the direction it's coming from, not the direction it's going to. So if you're on 230 and the wind is reported at 247, it's a headwind, and your speed will decrease instead of increase.

 Quoting aerdingus (Thread starter):Or would I have to be on the exact heading?

No, the wind can be way off your course and still give you more of a headwind/tailwind component than crosswind component.

 Quoting Fly2HMO (Reply 3):Groundspeed would increase a bit.

If by "a bit" you mean 39 knots, then yes.

-Mir
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JohnKrist
Crew
Posts: 1741
Joined: Sat Jan 22, 2005 11:54 pm

Aerdingus, it's an easy formula that uses COS where COS(0)=1(equals tailwind) and COS(180)=-1. (equals headwind), and as Fly2HMO indicates, this is only true for ground speed.
So in your case your relative heading to the wind is 17 degrees (230-247) you get COS(-17)=approx 0.95. That factor is then multiplied with the windspeed, in this case 40kts gives the result of approx 38kts.

Hope I made it clear, I am not a teacher
5D Mark III, 7D, 17-40 F4 L, 70-200 F2.8 L IS II, 50mm 1.4, EF 1.4x II, EF 2x III, SPEEDLITE 600EX-RT

aerdingus
Topic Author
Posts: 2667
Joined: Tue Dec 05, 2006 8:58 pm

 Quoting Mir (Reply 4):Unlike your airplane's heading, wind is read in the direction it's coming from, not the direction it's going to. So if you're on 230 and the wind is reported at 247, it's a headwind, and your speed will decrease instead of increase.

Ohhhhhhhhhhhhh this makes so much more sense now......

 Quoting johnkrist (Reply 5):Hope I made it clear, I am not a teacher

Cheers John

Thanks everyone
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