For what it’s worth. The first image is with the engine stopped. The threads flutter and swing back and forth in the air stream and the camera freezes them in whatever position they are in when the exposure is taken. From what I saw first hand, the center of the thread flutter and swinging was straight back from the tape holding the thread at all test points. The aircraft is a modified Tower kit built Kaos 40 powered with an Irving 53 ABC.

Your test results may differ depending on aircraft size, etc.