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Drift question

  • Nicoll
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Nicoll created the topic: Drift question

Hi all,
I’m working through the IREX study guide and on page 38 it has some questions about drift and I’m getting quite confused with the first three.
It’s saying we’ve kept a constant heading on the DG and the ADF is pointing to the left or right of the nose.
I need to know if the ADF needle is 10 degrees to the right (010), what is the drift?

I think if the ADF swings to the right by 10 degrees while tracking to the station, I am experiencing left drift. The wind has pushed me to the left.
But the answer is saying that it is right drift.
Please help. I’m starting to lose my mind.
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  • John.Heddles
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  • ATPL/consulting aero engineer
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John.Heddles replied the topic: Drift question

Your problem, on this occasion, is that you are misreading or misinterpreting what the question is trying to tell you.

Especially when something is a bit new to you, it often helps if you draw (on paper or in your mind's eye) a picture so that you can "see" what the basic idea is and what is happening. It doesn't matter whether we are playing with a fixed card ADF or an RMI, it's all the same philosophy.

In fact, until you become a very experienced and proficient instrument pilot, the easiest and most reliable way to "fly" the ADF is to run a constant orientation picture in your mind of what is going on. Where are you, where are you pointing, and where is the station located .. from which you can figure out how to set up intercepts and so forth and then monitor your navigation progress.

After you have a squillion hours using the ADF, it all becomes a pretty straightforward doddle and you don't have to think much about orientation as your mind does that automatically without your even realising it. But, until you get to that stage, it's all about orientation, orientation, orientation.

For this problem (keeping in mind that I don't have the book so I am filling in some gaps along the way), the following things are pertinent -

(a) it is a steady situation with a constant heading AND a constant ADF indication on the needle (called a "relative" bearing). In this case the ADF needle is pointing 10 degrees right of the aircraft nose and staying there. That can't be a case of the wind's having pushed you somewhere to the left .. which would mean the needle indication would be changing rather than indicating a steady relative bearing.

(b) by definition, the needle points to the radio station's location relative to the aircraft position and heading (that's all nice in theory but wait until you are out and about on a dark and dirty night full of thunderstorms ...). The picture tells you that the station is somewhere ahead and to the right of the aircraft nose by 10 degrees and, more importantly, that the orientation is remaining unchanged.

(c) let's forget the IFR thing for a minute and think visual flying. Here you are flying along, maintaining a constant heading. The ADF needle told you that the radio station was ahead of the aircraft and 10 degrees to the right of the nose.

On this CAVOK day, you LOOK out the window, 10 degrees to the right of the nose and you can see the station (that's the big aerial somewhere off in the distance there). You maintain the heading and you observe that the position of the radio station out the window doesn't alter.

Forgetting all about the ADF, what does the visual story tell you ? Right, you have set the aircraft up to track direct to the station, maintaining a drift angle of 10 degrees TO THE RIGHT.

Now, where did your problem arise ? You made the comment

I think if the ADF swings to the right by 10 degrees while tracking to the station, I am experiencing left drift. The wind has pushed me to the left.

Points to note -

(a) the needle didn't swing to the right while you were tracking to the station. Rather, you had manoeuvred so that the aircraft ended up on a heading of whatever with a relative bearing of 010R and that was maintained as a constant track to the station. The wind is from your left and would, if you let it, push you to the right.

(b) had the wind been from the right, and you were maintaining a constant heading generally pointing at the station to start with .. then the wind would have pushed you to the left and the needle would swing around to the right, progressively and fairly steadily, while pointing at the station.

Suggest you draw the picture in your mind and then figure out what it all might mean from the point of view of the navigation solution.

PS .. don't worry too much about having some difficulties getting on top of this IFR stuff .. we all started off from the same point of confusion .. the only difference for we old chaps is that we started off a long time ago.

Engineering specialist in aircraft performance and weight control.
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The following user(s) said Thank You: Nicoll, calejoh

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  • Nicoll
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Nicoll replied the topic: Drift question

Light bulb moment (The needle is steady at 010R). Thank you.
I'll sleep tonight now


(a) the needle didn't swing to the right while you were tracking to the station. Rather, you had maneuvered so that the aircraft ended up on a heading of whatever with a relative bearing of 010R and that was maintained as a constant track to the station. The wind is from your left and would, if you let it, push you to the right.
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calejoh replied the topic: Drift question

I’ve been struggling with this too. Your explanation was like a bolt of clarity. Thank you so much for your thoughtful reply John. And thank you Nicoll for asking the question.
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