Video: Motionless Helicopter Rotor Illusion


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The blades of the Russian MI-24 Hind helicopter in this video are perfectly in sync with the “shutter” of the videocamera filming it, making it appear as if the blades are not moving at all. [via Dan's Data]

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11 Responses to Video: Motionless Helicopter Rotor Illusion

  1. Anonymous says:

    Video cameras don’t have shutters but they still have a frame rate.
    That’s why the word shutter is in quotes.

  2. Anonymous says:

    That is absolutely astounding. I’ve never heard of anything like that before. Great video.

  3. Anonymous says:

    Yep, the last guy’s right – this video comes up time and time again and everyone always gets all ‘smart’ about either how its all CGI or really flying without spinning the blades.

    Some helos have constant RPM blades (for safety [constant rotor energy in case of engine fail] and efficiency [turbines don't like to change speed much]), it happens to be synched with the sample rate of the camera which is for sure rare and odd but not impossible. Also the lack of blur isn’t surprising:
    – big helos like this don’t actually spin their blades that fast; the bigger the blade length the slower angular speed they spin at since it’s not sensible to have the tips going very supersonic
    – it’s a bright day so the camera’s not sampling the sensor for very long

  4. Anonymous says:

    Some observations

    1. Shutter speed, probably best dicribed as light sample period. There is no problem for a modern camera handling the tip speed. Speed of sound is around 350 mps and there’s plenty of clear footage of planes breaking the barier. To my knowledge rotor tips don’t exceed the speed of sound.I’d say the operator had it on manual settings though as point and shoot probably will shift up and down even on clear well lit days
    2.The tail rotor is blured as it’s rotating at a different rpm.
    3.There appears to be 5 blades when I think these heli’s may have only 3,this has to do with how digital cameras actaully work. They playback at only 25 (ish) frames ps but display every second line of each image or greater. To explain, say you had 500 still images and wanted to annimate them you could just flick through them above 16fps and you would see motion ok. Digital cameras do it a little differently by splitting the images into parallel lines and displaying different parallel lines of multiple images at the same time. Blending them together to form a frame which is the dislayed at the frame rate. Each frame is NOT one full image, its slices of many. Thats why you have five blades.
    4. Because the blade is captured at the same or near location (angle to the fuselarge) each time by the camera, the angle of attack would not be expected to change. It is changing as it rotates but it’s returning to same postion relative to it’s requirement by the gyro as each sample is taken by the camera.
    5. If you look closely you will see the tail rotor’s blur varies, and it’s relative to the rotation being applied to the heli’s body. The rotor is either slowing or quickening to initiate body spin and you can see this blur change is in sync with the spin. I work with computer nerds all the time and i’d never find one prepared to go to that detail to fake something as detailed as the tail rotor blur. Possible though doubt it.
    6. There is no eveidence the heli is inreasing altitude, it may just appear that way relative to the angle back to the lens. There could also be zoom + – by the operater.

    Anyway, i just bored myself by typing this.. and i know i cant spell but dont care.

  5. Anonymous says:

    The lack of blur is unreasonable. Even at 1/1000 shutter, the rotor is still turning too fast for the edges of the blades to be perfectly clear. Also, the blade pitch never changes, which is also unrealistic.

    While in an alternate universe it might be possible to have a transmitter on the chopper that transmits the RPM’s to a camera that varies its shutter, the lack of pitch change is a dead giveaway.

  6. cautionyou says:

    Mod Converter can convert the .mod files recorded by most popular digital camcorders.

  7. Anonymous says:

    Only a fool would believe this is a video of a real helicopter (it’s CG). The trick becomes obvious at 00:27 when the helicopter begins executing several quite dangerous and counterclockwise spins with no tilt to its blades.

    The other tip is that video cameras don’t have shutters.

  8. Anonymous says:

    any non archaic video camera, just like any non archaic ccd camera, will have a “shutter speed”. It’s the amount of time the light levels are summed before dumping the summed values to memory. And if you notice, a few slight rpm changes do happen…that’s why the blades appear to go forward and backwards slowly…they become slightly out of sync.

    And, heli’s always run at full power/rpm. You don’t change the engine speed to go up and down, you change the pitch of the blades (collective). and, since you probably know that the maximum effective angle of attack for a wing is around 30 degrees before stall. He’s not doing any high speed or high force maneuvers, so he needs *very little* pitch change.

    my grandpa flew in vietnam and said the only time the crazy ones would back off the engine was during landing cause they were so damn noisy and attracted lots of little pieces of metal from the local northerners…but they would go as far as stalling the engines completely then build rotor speed and use only its momentum to quickly land the plane.

    always amazed me how people that don’t understand how things work seem unintelligent. hrmm.

    so here, go learn something about what you’re talking about.
    helicopter controls:
    http://en.wikipedia.org/wiki/Helicopter_flight_controls

    ccd’s:
    http://en.wikipedia.org/wiki/Charge-coupled_device

  9. dculberson says:

    Oh jeez, I was thinking I should put up an “OMG FAKE LOL u n00b” comment but decided it was too close to what someone would actually post on the average site. Unfortunately, it turned out I was incorrect in thinking people wouldn’t post that (at least seriously) here. Oh well.

  10. Anonymous says:

    this is pretty cool and very possible!

    “video cameras don’t have shutters” get a grip! Every type of camera has a shutter of some sort! They have to to trap light…

  11. Anonymous says:

    I would agree that the video is a fake. Helicopters are constantly changing their rotor speed in order to balance their lift vs. the pull of gravity. In the last part of the video, when the helicopter is flying upward, it would have had to increase rotor speed in order to do that.

    Also, the rotor blades aren’t blurred at all. On any camera, each single frame still takes time to let enough light in to record, so even if the blades were in sync with the camera, they would still be blurred.

    Still a cool video, I would like to see if something similar ever actually happened…

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