This is a video of the Mi-24 helicopter. The rotor blades appear not to be moving. Did the pilot and photographer sync the camera and helicopter to make this video and how? I do not know the true source but the video is remarkable.

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    $\begingroup$ I think this should go on video.stackexchange.com $\endgroup$ – user71659 Apr 28 '19 at 3:01
  • $\begingroup$ Closely related $\endgroup$ – Pondlife Apr 28 '19 at 4:19
  • $\begingroup$ Video is shot at fixed frame rate, so there's nothing the photographer can do to synch with the helicopter. $\endgroup$ – David Richerby Apr 28 '19 at 9:13
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    $\begingroup$ @user71659 Heh, OK. The question has come up for reopening but I didn't vote either way. $\endgroup$ – David Richerby Apr 28 '19 at 18:01
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    $\begingroup$ We've seen this effect in film/video for years, but what makes this so striking is that newer digital sensors are so fast that they can have an extremely high shutter speed. On an older video camera the blades would just blur to a far greater extent. $\endgroup$ – TomMcW Apr 28 '19 at 18:06

If the rotor is spinning at 360 RPM, typical of helicopters, that's 6 revolutions per second, and 5 blades go by each revolution. 6 x 5 is 30, so you have 30 blades passing point X in any 1 second period of time. Unlike film at 25fps, video is shot at 30 fps, in perfect sync with the blade passage, so the blades look stopped. If the rotor was going a little faster or slower, the blades would start to move.

The video camera is in effect working like a stop action strobe camera.

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    $\begingroup$ Video cameras generate the frame rate from a quartz oscillator, that is very accurate. I think the interesting aspect of this question is, how/why the rotor keeps the spinning rate that accurate. Is is just coincidence, or could such a video be reproduced any time? $\endgroup$ – bogl Apr 28 '19 at 9:13
  • $\begingroup$ @bogl yes and the helicopter faces directly at the camera at one point leads me to think the pilot may have fine tuned the throttle to the camera. $\endgroup$ – Muze Apr 28 '19 at 14:15
  • $\begingroup$ The fuel control system on a turbine helicopter regulates a pre-set rotor RPM. You apply throttle from idle to an operational setting that bring the RPM into the operating range, then fine tune the speed governor with blips of a toggle switch, setting the precise rotor RPM. When you pull pitch with collective the governor system will add whatever fuel is required to keep that RPM. That's why the RPM in the video is so consistent. $\endgroup$ – John K Apr 28 '19 at 14:50
  • $\begingroup$ so it is on the helicopter not the camera making this question on topic? $\endgroup$ – Muze Apr 28 '19 at 15:25
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    $\begingroup$ Well.. on topic enough for me. Some others are a bit more fussy. For me, it involves a flying machine. Good enough. $\endgroup$ – John K Apr 28 '19 at 17:09

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