The problem with this so-called experiment is that it is not a valid experiment. They were attempting to determine the altitude loss in a 360 degree gliding turn. In a gliding turn, there are 4 independent parameters that can be varied. They are (1) air density - altitude (2) Aircraft weight (3) Bank angle (4) Angle-of-attack The purpose of the experiment was to determine the effect of the bank angle on the altitude loss. If you perform that type of experiment you must keep the remaining 3 parameters constant, otherwise the experiment is flawed. If you work through the 4 parameters and carefully review the video, you will note that: (1) The initial altitude varied by a few hundred feet - air density is essentially constant (2) The weight of the aircraft was essentially constant- slight variation in weight due to fuel burn (not much, so weight is essentially constant) (3) The bank angle utilized was 15, 30, 45 and 60 deg. This was the experiment. (4) The angle-of-attack was not fixed. In order to fix the angle-of-attack for each bank angle, you must fly at a speed that is a specified percent above the accelerated stall speed for that bank angle. They flew almost the same speed for all four bank angles. That means the angle-of-attack could not be the same, which means there were two parameter varying and not one. Thus, the conclusions that are drawn from this experiment are flawed. One really needs to understand basic aerodynamics of the turnback maneuver if you want to perform a valid flight experiment. Sorry to burst your bubble.