When you perfectly match a video camera’s frame rate to the rotation of a helicopter’s rotors as it takes off, it looks like it’s magically floating away on the breeze. Here’s an older video of the same effect that I probably posted back in the day. Here’s an explanation of the effect:
Since each frame has to ensure the blade is in the same position as the last it therefore needs to be in sync with the rpm of the rotar blades. Shutter speed then needs to be fast enough to freeze the blade without too much motion blur within each frame.
Here the rotor has five blades, now lets say the rpm of the rotor is 300. That means, per rotation, a blade is in a specific spot on five counts. That gives us an effective rpm of 1500. 1500rpm / 60secs = 25.
Therefore shooting at 25fps will ensure the rotor blades are shot in the same position every frame. Each frame then has to be shot at a fast enough shutter speed to freeze the blade for minimal motion blur.
This is basically the same technique used by John Edmark for his strobe light sculptures.