If I could ask AnFI and Crab to go back a few posts, and edit out (each of you) the bits where you both play the man and not the ball for the last few pages, there would be less FOD in the thread and the points you are each making would be clearer. For example, Crab's last post is mostly content ... but in the past page this back and forth attracted more turbulent flow over the discussion's airfoil than laminar flow.
AnFI: my question on speed calculation, if your use of measurement is valid, will be modified. If we presume the camera to not be moving (which I don't, since I saw the whole video and the camera moved with the aircraft) you are measuring ground speed with the nose to tail technique.
From the earlier video of the Apache accident, my estimate of the breeze from what I saw is that the air (based on the motion of the water) was not moving much, but you might want to account for maybe 5-7 knots. (I'd not guess any higher). That would make for a delta between entry and exit airspeed for the helicopter between 10 and 14 knots if he started into the wind and finished down wind or vice versa. If, on the other hand, there was a gentle cross wind more or less perpendicular to the flight path, that should wash out.
To restate my earlier question regarding your 90 kts estimate:
Is that based on 90kts (in a X axis) with an unknown vertical speed (down) in the Y axis, or, based on your measurement method, is the 90 knots estimate more or less "along the path of flight" and thus the hypotenuse of a triangle with X and Y being horizontal and vertical components?
The triangle we could be constructed by superimposing a grid on the frame and tracing the flight path/hypotenuse and the constructing a right triangle legs from that. I realize that this bit of video does not give us gnat's arse precision, but I am interested as much in method as anything else. The last five seconds of video are not "level flight" but a nose down descent.
The other problem that arises to resolve is the dynamic nature of the event.
The Apache attempts to decelerate (and let's say he started somewhere around 90 knots as a baseline). The pitch isn't oriented in a purely Y or X axis direction: it's a bit of both.
His "nose up" at the end takes him from nose down to a bit above level, if not level, but he was surely in transition, not steady state, in those last two seconds.
Edited upon a second review of the video.
Last edited by Lonewolf_50; 20th Oct 2016 at 18:48.