Question stuck with on Nav in Air Pilots manual
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whoswho and DaveD, one of the fundamental skills when using the "wizz-wheel" (or any other computer for that matter) is to have some idea of the answer yourself to use as a rough check. It is as much part of the skill in evolving the answer as using the equipment itself.
In this case, it should be obvious that there will be an element of headwind component. From that, it should be equally obvious that the TAS must therefore be greater than the G/S required. So, if you get an answer where TAS is less than the required G/S, you will know you have made an error.
If you want to get on (and survive) in aviation, live defensively - if you don't check it, no one else will ...
JD
In this case, it should be obvious that there will be an element of headwind component. From that, it should be equally obvious that the TAS must therefore be greater than the G/S required. So, if you get an answer where TAS is less than the required G/S, you will know you have made an error.
If you want to get on (and survive) in aviation, live defensively - if you don't check it, no one else will ...
JD
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thanks for all answers. I cannot believe one PPL Nav question can get so many different replies!Anyway I have learned the wind down method up to now for all the other types of calculations so would like to stick to this method rather than mixing and matching.
So am I right in adapting whoswho's method as someone pointed out it was wrong and do it the following way:-
1. Spin the rotating part (inner scale) so index points to 90 (wind direction)
2. Set the centre blue dot (wind index) over the 100 speed arc.
3. Mark (down the way) the wind speed in at 80 (80 because 100-20(wind speed) = 80)
4. Rotate the inner scale to set the true track, 180 (180 under index)
5. Move the vertical rectangle part down (in this case) until the mark you made sits on the 80 line. (80 because that's the groundspeed that you need to maintain)
6. Now you need to apply the drift, in this case it is right drift by 14 so rotate inner scale right by 14. Index now is 166. (you could've just done 180-14 also). The drift is shown as that's where your put the mark (step 3)
7. True heading is 166
8. NOW MOVE THE CARD UNTIL YOUR WIND DOT (THE MARK YOU MADE WITH YOUR MAGIC MARKER) UNTIL IT IS BACK OVER THE GS OF 80KTS, THIS WILL REVEAL YOUR TAS OF 83KTS.]
So will this "wind down" method work for any calculations of this type, i.e find TAS and true heading whilst maintaining a particular groudnspeed taking into account a specfic wind...
?
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So will this "wind down" method work for any calculations of this type?
If you stop at the first iteration, you might get the heading wrong by even 10°, which is probably enough to fail the question, if not the actual navigation. Try with TR/GS = 300°/80 kt and W/V = 160°/40 kt, to see what I mean.
Deeday
Last edited by Deeday; 9th Mar 2009 at 17:04. Reason: typo
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Yes, it will work, if properly executed, but the wind-down method doesn't finish there. You should care to check (Step 9) that the drift resulting at Step 8 - indicated by the wind mark - is the same as the drift correction that you initially used. In this particular case it's almost exactly the same, but in general it won't, and you'll have to repeat steps 6 to 9 with an appropriately adjusted value of drift, and do so until the value of drift at Step 8 matches the one used at Step 6.
If you stop at the first iteration, you might get the heading wrong by even 10°, which is probably enough to fail the question, if not the actual navigation. Try with TR/GS = 300°/80 kt and W/V = 160°/40 kt, to see what I mean.
Deeday
If you stop at the first iteration, you might get the heading wrong by even 10°, which is probably enough to fail the question, if not the actual navigation. Try with TR/GS = 300°/80 kt and W/V = 160°/40 kt, to see what I mean.
Deeday
Just done it using wind down method and it took a lot of adjusting and fiddling about to do that one.
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Nope, sorry. You can tell that it's wrong, because if you put 265° under the index and 59 kt under the centre dot, the wind mark gives you a right drift of 30°, which means that you are tracking 265° + 30° = 295°, instead of 300°.
This is how I did it with the wind-down, initially putting 300° under the index:) and the result is the same.
Deeday
This is how I did it with the wind-down, initially putting 300° under the index:
1) tentative drift = 19° --> heading = 281° --> new drift = 26°
Not good: old and new drift don't match, and indeed, if we steer 281°, we drift 26° to the right, that is we track 307°, instead of 300°. So let's try again with 7° more of drift correction:2) tentative drift = 26° --> heading 274° --> new drift = 28°
Almost there, but if we steer 274°, we drift 28° to the right, that is we track 302°. Let's repeat adding 2° more:3) tentative drift = 28° --> heading 272° --> new drift = 28°. Nailed.
The TAS then turns out to be 56 kt. I've double-checked with the wind-up method (in one step, of course ) and the result is the same.Deeday
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Don't you wish that 10% of the time wasted on teaching pilots how to use the stupid slide rule would be better spent teaching them how to fly from say Lydd to Le Touquet (which most new UK PPLs are incapable of)?
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Nope, sorry. You can tell that it's wrong, because if you put 265° under the index and 59 kt under the centre dot, the wind mark gives you a right drift of 30°, which means that you are tracking 265° + 30° = 295°, instead of 300°.
This is how I did it with the wind-down, initially putting 300° under the index:) and the result is the same.
Deeday
This is how I did it with the wind-down, initially putting 300° under the index:
1) tentative drift = 19° --> heading = 281° --> new drift = 26°
Not good: old and new drift don't match, and indeed, if we steer 281°, we drift 26° to the right, that is we track 307°, instead of 300°. So let's try again with 7° more of drift correction:2) tentative drift = 26° --> heading 274° --> new drift = 28°
Almost there, but if we steer 274°, we drift 28° to the right, that is we track 302°. Let's repeat adding 2° more:3) tentative drift = 28° --> heading 272° --> new drift = 28°. Nailed.
The TAS then turns out to be 56 kt. I've double-checked with the wind-up method (in one step, of course ) and the result is the same.Deeday
Give me another one to work out please.
Liam
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Hi All,
Here's a variation of the 'Wind Down' method that my instructor taught me, apparently it's an RAF method. It has always worked well for me - you might find it interesting to compare with other methods.
First set the wind dot, so set 090 on the wheel, move the slider to 0, go down the scale to 20 and draw the dot (or a + which I prefer)
Next set the Track, so turn the wheel to 180.
Now the unusual bit, your dot is now over somewhere to the right, take a straight edge and draw a vertical line downwards from it using the square section at the bottom of the slider to guide you.
Now push the slider so the wind dot is somewhere near the 80kt arc then turn the wheel until your vertical pencil line now lines up with the fan lines.
Finally make a couple of small tweaks, you will need to move the slider again to set the dot exactly on the 80kt arc and turn the wheel again to keep the pencil line lined up with the fan lines.
Now read off TAS 83kts at the centre dot and HDG 166 against the index.
I hope you find this useful!
Deeday - Thanks for nice clear explanations of the methods you use,
Liam and Whoswho - good luck in those exams!
Here's a variation of the 'Wind Down' method that my instructor taught me, apparently it's an RAF method. It has always worked well for me - you might find it interesting to compare with other methods.
First set the wind dot, so set 090 on the wheel, move the slider to 0, go down the scale to 20 and draw the dot (or a + which I prefer)
Next set the Track, so turn the wheel to 180.
Now the unusual bit, your dot is now over somewhere to the right, take a straight edge and draw a vertical line downwards from it using the square section at the bottom of the slider to guide you.
Now push the slider so the wind dot is somewhere near the 80kt arc then turn the wheel until your vertical pencil line now lines up with the fan lines.
Finally make a couple of small tweaks, you will need to move the slider again to set the dot exactly on the 80kt arc and turn the wheel again to keep the pencil line lined up with the fan lines.
Now read off TAS 83kts at the centre dot and HDG 166 against the index.
I hope you find this useful!
Deeday - Thanks for nice clear explanations of the methods you use,
Liam and Whoswho - good luck in those exams!
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Think rowing boat across river water flow = wind
Just for fun....Puzzle question
You have to row across a river - which is quicker to the far bank?
1. row at right angles to bank and arrive at far side a bit downstream
2. row upstream and arrive at the point right angles to departure point.
Just for fun....Puzzle question
You have to row across a river - which is quicker to the far bank?
1. row at right angles to bank and arrive at far side a bit downstream
2. row upstream and arrive at the point right angles to departure point.
