When the runway edge 'touches' the bottom of your headset, start the flare. When it reaches the middle of your ears, you're down.
Troy, interesting - but what about on a grass field, when there is no clearly defined runway edge? Especially if eyesight less than perfect
Also, does the width of the runway have any effect? I can't visualise it myself, hence the question.
Finally, would there be a difference for different sizes of individuals in different aircraft types - e.g. tall & short people in say a Europa vs C172? Or is the variation actually fairly insignificant?
Is this something best "calibrated" by an individual student in the aircraft they usually fly - noting the "flare" position while the instructor demostrates the correct height?
FBW