Wind Drift Calculations
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Wind Drift Calculations
I have a simple question that will hopefully receive a simple answer. I've had a go at a search and not come across the answer that I'm after.
I was initially taught "wind up", I teach "wind down", and when I'm off out and about by myself I just calculate "max drift" and then make calculations along the way.
I've spent this morning with an exceptionally argumentative student who is determined to use the "wind up" method. Not really a problem. I've just been trying to prove, to no avail, that the "wind down" method is more accurate.
So my question is, why is the "wind down" method often the preferred method? I've got a funny feeling that it may become more accurate with an increase in TAS. Therefore more suitable for anyone considering a career as a commercial pilot.
Thank you for any responses.
I was initially taught "wind up", I teach "wind down", and when I'm off out and about by myself I just calculate "max drift" and then make calculations along the way.
I've spent this morning with an exceptionally argumentative student who is determined to use the "wind up" method. Not really a problem. I've just been trying to prove, to no avail, that the "wind down" method is more accurate.
So my question is, why is the "wind down" method often the preferred method? I've got a funny feeling that it may become more accurate with an increase in TAS. Therefore more suitable for anyone considering a career as a commercial pilot.
Thank you for any responses.
It is the preferred method because that's how it was designed to be used. The writing on the device matches what it does. Thats the way it was always taught in the RAF. It is only solving a vector triangle so you will get the same result whichever way you use it, right way up or upside down. As Murphy said if anything can be used back to front it will be.
Why do it if it's not fun?
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I don't believe there is any difference in accuracy between wind-up and wind-down.
The difference is that wind-down can be used for a number of different problems, not all of which can be solved with wind-up, for example (I think, if memory serves me correctly) calculating wind speed and direction given heading, TAS, groundspeed and track. Because of this, it is the preferred method for wannabe CPL students who will have to solve problems like this for the ATPL written exams. But for a PPL who is not intending to take commercial exams, the wind-up method is slightly easier to use.
FFF
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The difference is that wind-down can be used for a number of different problems, not all of which can be solved with wind-up, for example (I think, if memory serves me correctly) calculating wind speed and direction given heading, TAS, groundspeed and track. Because of this, it is the preferred method for wannabe CPL students who will have to solve problems like this for the ATPL written exams. But for a PPL who is not intending to take commercial exams, the wind-up method is slightly easier to use.
FFF
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Thank you for the initial responses.
Whopity I've just had a look at the wind side of the flight computer. Like you say, it quite clearly states at the top that the indication given shows drift. Therefore the "wind down" method would appear to be the one to use. Thank you.
FlyingForFun The "wind up" method can certainly be a little bit quicker. If memory serves me right there are questions in the PPL examinations that involve making calculations backwards to come out with wind speed and direction, etc. I'll have to pull out my computer at work and have a play when I get the chance.
Whopity I've just had a look at the wind side of the flight computer. Like you say, it quite clearly states at the top that the indication given shows drift. Therefore the "wind down" method would appear to be the one to use. Thank you.
FlyingForFun The "wind up" method can certainly be a little bit quicker. If memory serves me right there are questions in the PPL examinations that involve making calculations backwards to come out with wind speed and direction, etc. I'll have to pull out my computer at work and have a play when I get the chance.
Wind up is as accurate as wind down. Speed is irrelevent - it's the same vector triangle
The advantage of wind up is that for the most common problem - find HDG & GS given W/V & TAS/TRK - the jiggling of the compass ring is eliminated. The disadvantage is that it's a bit of a one-trick pony. If you wish to use the data for other problems you have to redraw using the wind down method.
Still, if all you wish to do is obtain HDG & GS and wish to save a little bit of mucking around, use the wind up. If you have trouble remembering which method to use for which problem, stick to wind down.
Or give slide types the flick & use a CR type instead and avoid the whole argument while gaining something that is smaller & more convenient without sacrificing accuracy...
The advantage of wind up is that for the most common problem - find HDG & GS given W/V & TAS/TRK - the jiggling of the compass ring is eliminated. The disadvantage is that it's a bit of a one-trick pony. If you wish to use the data for other problems you have to redraw using the wind down method.
Still, if all you wish to do is obtain HDG & GS and wish to save a little bit of mucking around, use the wind up. If you have trouble remembering which method to use for which problem, stick to wind down.
Or give slide types the flick & use a CR type instead and avoid the whole argument while gaining something that is smaller & more convenient without sacrificing accuracy...
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Tinstaafl I can now see/ remember why I was taught to use "wind up" while learning (after a fashion) to fly in the USA and then later changed to "wind down" for both the CAA examinations and then teaching in colleges offering integrated ATPL courses. I'll still need to have a little play on the computer to prove to myself the differences. Thank you.
I've now played with the computer. I'm now uncertain of my earlier thoughts.
I've now played with the computer. I'm now uncertain of my earlier thoughts.
Last edited by Esperanza; 25th Feb 2008 at 21:30. Reason: Change of opinion
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By draw the wind vector down to the ctr both Hdg and G/S and w/v problems can be solved. The other problem that sometimes crops up has to be solved by drawing wind vector down from centre. (Possibly one question on ATPL exam ).
At least wind vector down to centre can be explained easily from first principles and when computer is placed on map wind, track etc. appears in its logical relative positions.
All this jiggling around is nonsense.
At least wind vector down to centre can be explained easily from first principles and when computer is placed on map wind, track etc. appears in its logical relative positions.
All this jiggling around is nonsense.
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It's now late and my brain may be malfunctioning. I've pulled out an old computer and had a look at calculations where I've given myself a heading, TAS, ground speed and wind drift angle. From these calculations I can calculate the wind direction and speed by using either method. What am I missing? I dare say that this will all seem clearer tomorrow.
I can see that Whopity's answer makes sense. As do BigEndBob's comments about first principles and vector triangles.
I can see that Whopity's answer makes sense. As do BigEndBob's comments about first principles and vector triangles.
Last edited by Esperanza; 25th Feb 2008 at 21:22.
The use of the Dalton computer has now become rather academic, what many don't realise is that the primary use for this device was to actually calculate the wind. Before the days of sophisticated weather forecasting (The Met Office was developed to do this for the RAF) crews on long range flights had very limited wind information to work on.
Flying three different headings and measuring the drift by looking vertically downwards through a drift sight (ideally over the sea) drift lines could be plotted on the computer to give a 3 drift wind and from that ground speed could be deduced.
With the advent of doppler radar in the early 60s by plotting Heading/TAS and Drift/GS the local wind could be determined and then used for the next 20 minutes.
In all these cases, and when calculating an Air Release Point for objects dropped by parachute, the resultant wind is downward.
In most cases the Dalton was only used to calculate actual winds along a route so that they could be given the met man at the end of the flight. It was not used for preflight planning; a much simpler tool was available called a Drift and Wind Component Template that was calibrated for the aircraft TAS
Flying three different headings and measuring the drift by looking vertically downwards through a drift sight (ideally over the sea) drift lines could be plotted on the computer to give a 3 drift wind and from that ground speed could be deduced.
With the advent of doppler radar in the early 60s by plotting Heading/TAS and Drift/GS the local wind could be determined and then used for the next 20 minutes.
In all these cases, and when calculating an Air Release Point for objects dropped by parachute, the resultant wind is downward.
In most cases the Dalton was only used to calculate actual winds along a route so that they could be given the met man at the end of the flight. It was not used for preflight planning; a much simpler tool was available called a Drift and Wind Component Template that was calibrated for the aircraft TAS
Last edited by Whopity; 26th Feb 2008 at 08:18.
You're not missing anything. Wind up & wind down both work to obtain solutions. It's just that it's usually considered easier to use wind down for most of the problems.
I prefer wind up if all I wish to do is find HDG & GS. No reason other than not having to jiggle the ring a bit. I have no problem with wind down either and switch to that method without fuss.
Of course that's if I use a slide type (rare. Very). I choose to use CR types if I have to use whiz wheel. That was the case for my Australian IR & ATPL, US ATP, & UK ATPL. Last time I needed to use a slide type for anything much was my Oz CPL & when I used to instruct if a student wanted to use a slide.
I prefer wind up if all I wish to do is find HDG & GS. No reason other than not having to jiggle the ring a bit. I have no problem with wind down either and switch to that method without fuss.
Of course that's if I use a slide type (rare. Very). I choose to use CR types if I have to use whiz wheel. That was the case for my Australian IR & ATPL, US ATP, & UK ATPL. Last time I needed to use a slide type for anything much was my Oz CPL & when I used to instruct if a student wanted to use a slide.
In my ATPLs, I used wind up to calculate heading from track/wind (the one you want most often in real life).
For the odd question where you had to work out something useless like wind from track and heading, I used wind down. It's so back to front doing it backwards, I found it no harder to mix the two methods.
If that makes sense...
For the odd question where you had to work out something useless like wind from track and heading, I used wind down. It's so back to front doing it backwards, I found it no harder to mix the two methods.
If that makes sense...
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Can we now wind this up?
