air traffic control (ATC)...

Read the forum code of contact

Member for

18 years 6 months

Posts: 2,343

I have just bought a book ('How Airliners Fly: A Passengers Guide' by Julien Evans), and am currently reading the chapter on communications, but I am confused by what is said...

Here is a brief passage from the book:

When Tower cleared the aircraft for take-off, the controller also gave the surface wind, which was blowing from direction 280° (magnetic) at 12 knots. Since runway 33 by definition points approximately in the direction of 330° magnetic, the aircraft will have a headwind component for this take-off, and also a crosswind from the left.

Can anyone please help to explain this to me, or point me in the direction of a good source that might be able to...

Thanks in advance.

Original post

Member for

21 years

Posts: 1,004

the runway (and aircraft!!) will be pointing towards the postion on a compass that equates to 330 degrees... the wind will be comming fromthe direction of 280 degrees... rather than the ideal situation of the aircraft takign off directly in to the wind, the wind will be comming from the lefthand side at an angle across the runway... pilot will want to be aware of this so he can take it in to account during the take off run (or landing)..
Neil.

Member for

20 years 7 months

Posts: 2,623

Indeed, if the wind was coming from a direction of 240 or 060 the headwind component is zero as it is all crosswind, if you imagine the wind coming towards you in a diagonal direction you can see that you have headwind and crosswind, a quick rule of thumb to work out crosswind component is think of a clockface with 15, 30 & 45 minutes on it, if the wind is 15 deg off of runway heading the crosswind component is ¼ of the windspeed, if the wind is 30 deg off runway hdg then the crosswind component is ½ the wind speed, and for wind that is 45 deg off runway heading the crosswind comonent is ¾ the windspeed, if it is 60 deg off runway heading then you assume maximum crosswind, the remaining speed once crosswind component is worked out is the headwind component

Hope this helps

Dean

Member for

24 years 2 months

Posts: 6,968

Probably not very well explained but I'll have a go until one of the aircrew come up with a definitive answer.

Imagine you have a compass directly in front of you. 0 or 360 degrees at the top. If you look to the left and find 330 degrees and then line that up with the compass needle. Now find 280 degrees and that will be 50 degrees to the left. Transfer all that onto paper and you get the diagram below.

You will see that as the aircraft is heading at 330 degrees along the runway the wind is coming from the left, 280 degrees. The wind, coming almost directly from the left is the crosswind component. But the angle of the wind will also affect the aircraft's take off because it is coming slightly from in front, this is the headwind component. If the wind was coming from 90 degrees to the left of the aircrafts direction of take off, there would be no headwind. The effect of the headwind increases the nearer the wind direction is to the aircrafts direction of travel

Hope that helps till someone can explain more fully.

Edited to add someone beat me to it!

Regards,

kev35

Attachments

Member for

18 years 6 months

Posts: 2,343

Thanks kev35, you could of just posted the diagram, as that has helped to explain it.

The thing I was getting confused with was the direction of the wind speed and runway...got them the wrong way round :o , but thanks anyway for all your help.

At least I can continue to read the chapter... :D