Photo 2421 shows a pretty standard technique for measuring takeoff performance. Known points on the ground would be surveyed, and could be used to calibrate info in the picture. Before the test run some junior test engineer got to carry a 50 foot pole down the runway center line while pictures were shot, so the vertical axis was calibrated as well. Thus you can accurately determine the lift off point, and the point at which the aircraft passes 50 feet altitude. Knowing the starting point, you then have the 2 important take off distances. Knowing the frame rate, you can also determine aircraft ground speed at any point during the take off (distance between frames / time between frames = speed), and acceleration. The same basic method can be used for landing distances.
The basic technique is often called "the screen method", since sometimes a transparent screen with a grid marked on it is placed in front of the camera for the calibration shots and the test runs.
When I started doing this in 1976, we used a Super 8 movie camera, and projected the film frame by frame on the design office wall, in the evening, with all the lights out. I used a tape measure to locate the aircraft in each frame. I also got to carry the pole down the runway. I bet Grumman had a bigger test budget than we did, and probably used a more sophisticated data extraction method
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Bill Walker
Canadian Military Aircraft Serials
www.ody.ca/~bwalker/
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