Using Filming Principles to Make a Helicopter Fly With Its Propeller Seemingly Not Turning
Image: Pexels
A clip of a helicopter taking off is circulating online. In this video, the helicopter lifts off, yet the propeller on top of it is not turning. It looks as if the helicopter has been pulled into the air without power by an alien beam, as in a movie. However, this is neither post-production nor magic, and certainly not alien technology. It is purely a matter of the principles of photography.
The video was shot by a YouTuber, Chris Fay. It shows a helicopter taking off with its rotor blades apparently not moving at all. Although the blades look stationary in the video, the helicopter is of course lifted by the lift the rotor generates, and the sound in the video clearly shows the rotor running normally. Nor is this "stationary propeller" an effect created in post-production.
The moving videos we usually watch are made by capturing and playing back many images per second. This illusion occurs because the camera's frame rate happens to be in sync with the speed at which the propeller turns. In other words, every time the camera captures a frame, the propeller has just reached the same position. When the footage is played back, this is the result.
Besides helicopters, you may sometimes notice a similar effect with car wheels when watching films or TV shows featuring cars. The speed, and even the direction, in which the tyres appear to turn does not match the speed at which the car is travelling. This is also an illusion caused by the frame rate. Keep an eye out for it next time you watch.
https://ccc.technews.tw/2017/03/07/helicopter-propeller-did-not-turn-to-fly-the-film/
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