When I was revalidating my PPL some years ago on a 152 I was using more fuel from one tank than the other. I was told by my instructor that this was because I did not have the ball in the middle most of the time - wings not level.
Now, if I fly a 172 on 1 - 2 hour cross country in relatively calm air, mostly with the ball in the middle and little or no rudder required, I still find I sometimes use more fuel from one side than the other (selector on both).
Does this really mean that I have been flying badly? If so, how do I improve?
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"If you keep doing what you've always done, you will keep getting what you've always got"