You will appreciate the Jacobson Flare … when the penny drops
After more than 100 years, pilots are still being taught to land by guesswork. Triangles have been around a lot longer and work much better.
Since flight instruction started to become more formalised during and following World War One, pilots have pursued the consistently perfect landing. ‘What’ to do is generally understood; the ‘where’, ‘when’ and ‘how’ involved in landing an airplane has been far more elusive.
The conventional wisdom on landings has been that it just takes indefinite hours of practice to finally ‘get the hang of it‘. And many of us did get the hang of it – some faster than others. Many others didn’t and gave up, or were ‘scrubbed’ off a flying course.
Sadly, many have died in the process – and still do, to this day.
For those who did get to first solo and beyond: What then? How did you go on your next airplane type conversion? Or in a decent crosswind? Or at a different airfield? Or at night? The only conventional and honest answer is … ‘by trial and error and with difficulty’.
The Jacobson Flare technique is the quantifiable explanation of what pilots have been trying to achieve by repetition, feel and guesswork, with varying results, for over 100 years.
Apart from the simple and logical solutions to determining where to aim and how to aim (at an appropriate initial aim point on the runway), how much to flare and how fast to flare (i.e., the flare rate), the unique key to the Jacobson Flare is the eclipsing of a longitudinal flare point, short of the initial aim point by the airplane’s windscreen lower visual cut-off angle.
This flare cut-off point is easily derived for any fixed-wing airplane that flares for landing; it can even be applied to the autorotation manoeuvre in helicopters. The essential thing to understand is that while the flare is still commenced at the optimum flare height, that height is visually recognised by the flare cut-off point ahead, on the ground, which corresponds to that height.
Triangles have had 3 sides for a very long time and to this day and, historically, we only ever used 2 of them: the hypotenuse (slanting) side represents the pilot’s eye path and the opposite(vertical) side represents the flare height.
The adjacent (horizontal) side was simply ignored. If the flight path angle had been drawn more accurately at around 3º, instead of the typical 25-30º, it would have been recognised that the adjacent side is approximately 20 times larger than the opposite side. This means that any vertical error, made in guessing flare height, compounds 20 times longitudinally along the runway, greatly increasing the landing footprint. Moreover, the vertical side is invisible to the pilot.
In contrast, using a longitudinal flare cut-off point in determining a visual fix means that any error made in assessing the flare cut-off point position, in relation the the initial aim point, is reflected by only 1/20th of that error, vertically, making the flare initiation point much more accurate. Moreover, the flare point, not to mention the entire landing flare manoeuvre, is fully visible to the pilot and tolerant of error, making the Jacobson Flare eminently suitable for unmarked gravel and grass airstrips.
The flare point calculation is only made once, for each airplane type (or variant) and the technique actually self-compensates (geometrically) for variations in flight (approach) path angle, runway slope and landing flap angle. The vertical height illusions, encountered when landing on an un-familiar narrower or wider runway can be discounted with a consistent and fully visible, longitudinal flare cut-off point, rather than a conventional guess of flare height.
So triangles and their structure work much better than antiquated guesswork.
When the penny drops, your ‘aha moment‘ will make you smile and that’s when the value of the Jacobson Flare will be appreciated.
Wishing you many safe landings
Captain David M Jacobson FRAeS MAP
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