AnFI - I'm sure a little thread drift would be tolerated. The discussion included a g meter for the Apache, I was interested to find that this was fed to a cockpit instrument. If you recall you were the one who introduced sideslip "wot do they use lateral g for ? sideslip? dCL/da are you actually a helicopter designer?" empahsis was yours.
I have posted the BET equation for lift, that is sufficient for most to grasp the concept of inflow/induced flow and its impact on lift. I don't intend to get in to a deeper discussion on tip or wake models.
No, I can't measure distance from the video as there is nothing clear to refer the distances to.
It can't be done by analysing the frame, as there is no clear indication of the speed at which the frame is moving. If the frame was stationary then the aircraft itself could act as its own reference scale. With the aircraft and the frame moving it can't be derived as there are two unknowns. It can't be done by comparison to the background as the background is clearly a substantial distance away. This introduces, in essence, parallax. Without knowning the difference in distances this cannot be taken out. Further information is required, or gross assumptions made. The only thing that can be seen in plane with the aircraft is its downwash effect on the water. When this is evident there is much too short a clip to analyse without introducing large deviations in the measurement. This is why I asked you what you used as your points of reference.