Originally Posted by
theFirstDave
Then I measured the length of the fuselage and marked off that distance increments to the later frame image. I did not account for the later image being closer and that will skew things a very small amount.
Images from Twitter video
That method would work if the plane was flying directly across the field of view but not in this case where it is approaching at an angle.
Just imagine the answer it would give if the flight was directly towards the camera?
So I'd say you need to multiply your answer by 1/sin(45 degrees) to allow for the angle (guessed at 45 degrees)
which would give 92 x 1.414 = 130 knots
Also the fuselage is 1.5 times as long in the second image as the first, so the skew may not be negligible.