using CRP 1 to calculate average wind from spot wind chart??
Thread Starter
Joined: Jan 2008
Posts: 691
Likes: 0
From: Yorkshire
using CRP 1 to calculate average wind from spot wind chart??
How do I use the wind side of the computer to interpelate between say 4 different wind speeds and directions from F214?
I understand there is a way of drawing on the speeds then turning the slide until it gives you the average heading and average speed for the wind from the 4 spot winds.
The instructions for this are not in the booklet.
Thanks
Liam
I understand there is a way of drawing on the speeds then turning the slide until it gives you the average heading and average speed for the wind from the 4 spot winds.
The instructions for this are not in the booklet.
Thanks
Liam
Joined: Nov 2008
Posts: 67
Likes: 0
From: norf of inngland
No , I generally only ever use the two spot wind boxes rather than four and a quick interpolation is usually reasonably good . The wind after all is never quite what it seems so you are not gonna lose too much accuracy doing it that way .
Thread Starter
Joined: Jan 2008
Posts: 691
Likes: 0
From: Yorkshire
thanks for your replies.
I am right in thinking that averaging 4 wind directions by dding up and dividing by 4 will give a completely incorrect answer arnt I?
I just thought that sometimes 2 boxes just wont cover the larger routes...
I am right in thinking that averaging 4 wind directions by dding up and dividing by 4 will give a completely incorrect answer arnt I?
I just thought that sometimes 2 boxes just wont cover the larger routes...
Joined: Nov 2008
Posts: 67
Likes: 0
From: norf of inngland
Really depends how far you are flying if you are going from lands end to norfolk then maybe you need to look at different boxes but a qxc flight two should be adequate .
YOu will probably find that the answrr wouldnt be too far removed in any case . try it and have alook
I only ever used two for cpl and never had much of an issue . Just remember it is never so accurate that you can rely on it totally . Once airborne you can assess how accurate it is .
YOu will probably find that the answrr wouldnt be too far removed in any case . try it and have alook
I only ever used two for cpl and never had much of an issue . Just remember it is never so accurate that you can rely on it totally . Once airborne you can assess how accurate it is .
Joined: May 2005
Posts: 1,170
Likes: 0
From: Abroad
Technically, you could do bilinear interpolation of the four corners, or use a 1/distance squared weighted average of any number of spot readings near your point of interest. Two interpolations in each case, for either the rho and Phi (if using a polar reference system), or the U and V components (if using a rectangular system).
Or in practice, you eyeball it.
Or in practice, you eyeball it.
Joined: Jun 2003
Posts: 13,787
Likes: 0
From: EuroGA.org
I think LH2 has the right answer, but the real Q is what is the exam paper looking for?
To be practical, the Winds Aloft forecasts are almost never right. Errors of 30-50% in the wind speed are pretty common, especially at the low levels (say 2000ft) at which GA pilots are asked to demonstrate their dead reckoning prowess.
Averaging the direction (heading) figure is also the right thing to do, if the variation is small, say 30 degrees. The problem is if one spot shows 090 and the other one shows 270. The average is then 180
What this tells you is that there is a frontal system lying between the two, or something like that, and you need to apply different winds to different segments of the route.
To be practical, the Winds Aloft forecasts are almost never right. Errors of 30-50% in the wind speed are pretty common, especially at the low levels (say 2000ft) at which GA pilots are asked to demonstrate their dead reckoning prowess.
Averaging the direction (heading) figure is also the right thing to do, if the variation is small, say 30 degrees. The problem is if one spot shows 090 and the other one shows 270. The average is then 180
What this tells you is that there is a frontal system lying between the two, or something like that, and you need to apply different winds to different segments of the route.
Joined: May 1999
Aviation Qualifications: ATP+Mil
Posts: 27,402
Likes: 858
From: Quite near 'An aerodrome somewhere in England'
Ah - an analogue problem which digi-yoof do seem to find so very hard.....
Just interpolate between 2 values at the same latitude and obtain a figure, then the other 2 at the other latitude. Then interpolate between your 2 results to obtain the 'middle of the box' value.
Or just look at the figures and use the TLAR technique.
Just interpolate between 2 values at the same latitude and obtain a figure, then the other 2 at the other latitude. Then interpolate between your 2 results to obtain the 'middle of the box' value.
Or just look at the figures and use the TLAR technique.
Thread Starter
Joined: Jan 2008
Posts: 691
Likes: 0
From: Yorkshire
I think LH2 has the right answer, but the real Q is what is the exam paper looking for?
To be practical, the Winds Aloft forecasts are almost never right. Errors of 30-50% in the wind speed are pretty common, especially at the low levels (say 2000ft) at which GA pilots are asked to demonstrate their dead reckoning prowess.
Averaging the direction (heading) figure is also the right thing to do, if the variation is small, say 30 degrees. The problem is if one spot shows 090 and the other one shows 270. The average is then 180 What this tells you is that there is a frontal system lying between the two, or something like that, and you need to apply different winds to different segments of the route.
To be practical, the Winds Aloft forecasts are almost never right. Errors of 30-50% in the wind speed are pretty common, especially at the low levels (say 2000ft) at which GA pilots are asked to demonstrate their dead reckoning prowess.
Averaging the direction (heading) figure is also the right thing to do, if the variation is small, say 30 degrees. The problem is if one spot shows 090 and the other one shows 270. The average is then 180
What this tells you is that there is a frontal system lying between the two, or something like that, and you need to apply different winds to different segments of the route.thanks for all your replies, most helpful. I have passed the exam bt wanted to know the "real world" way of doing it which is going to actually help my flying and navigation
Thread Starter
Joined: Jan 2008
Posts: 691
Likes: 0
From: Yorkshire
yes I meant using the spot wind chart but inputting the figures into a CRP 1 somehow to get the average. But the other replies show that this does not work and there are better methods out there.
