This video, going around the Internet lately, was allegedly shot with the shutter speed synchronized to the helicopter's blade speed. I thought that shutter speed is a function of still shot cameras, so maybe it's really synchronized to the frame rate. Photographers, please educate us. via Urlesque
Anyway, film cameras have shutter speed, also. I can't speak for digital, although I assume it's the same there... assuming this is a standard film camera, the blades are probably spinning at some multiple of 24FPS (framerate of the camera) / 5 (number of blades).
I'm guessing the camera wasn't actually synched to the chopper, unless this is some kind of flight testing, but its framerate and the chopper's RPM just happened to hit the right combination of awesome.
MarcZero: that would be one hell of a detailed toy.
Now, shutter speed is the speed of the shutter thus controlling how long the sensor will be exposed for each frame. Now, in video cameras, synchronizing the shutter speed to the speed of the coppter's blades will produce this effect in the video since the camera will see the blade in the same position for each frame, thus it appears that it doesn't move... although, it is actually moving, at very high speed actually. The sensor is exposed to see each frame every time the blade is the same position...
http://www.neatorama.com/2007/07/28/video-effect-of-helicopter-in-flight/
the shadow moves with the blade so if the blade doesn't appear to be moving, neither does the shadow.
This is the same effect that you occasionally see in cars that have been filmed and because of the framerate of the camera, the wheels appear to move backwards. Or for that matter, why under artificial lighting (with and alternating current) your wheels seem to turn backwards. It's a strobe effect. Turn off the lights and wave your hand back and forth rapidly in front of your monitor. If you get the right speed, your hand will appear stationary as well.
the shadow moves with the blade so if the blade doesn't appear to be moving, neither does the shadow.
This is the same effect that you occasionally see in cars that have been filmed and because of the framerate of the camera, the wheels appear to move backwards. Or for that matter, why under artificial lighting (with and alternating current) your wheels seem to turn backwards. It's a strobe effect. Turn off the lights and wave your hand back and forth rapidly in front of your monitor. If you get the right speed, your hand will appear stationary as well.
"The blades are turned off. No camera has a shutter speed that fast and it's a video, not a camera. It's a military helicopter--they take them up and turn it off to test the helicopter if it were to happen for real and to test the back blades. Really cool to watch in person."
I'm not sure what to believe, but she has actually seen it in real life, so this could be the truth...?
I can imagine they do turn off the rotors in drills and testing, but this video doesn't represent that.
Either she lied to you or she's a complete idiot.
I recall that when this video went around on the net a couple of years ago, it was proven to be just a toy model with some bullshit back-story to go with it.
Like others have said it is the framerate that has been matched with the blades and it clearly isn't a toy.
That the frame rate was just right, I can only imagine to be coincidence, because it would be a huge amount of math just to compute the needed rate.
Very impressive video though, even if it is "as old as dirt" as someone commented.
The frame rate of the camera in the video is a sub-multiple of the revolutions per minute of the rotors. We may not be seeing the same blade in the same position each time - we are seeing a different blade caught in the same place. Since the blades are visually the same, we do not notice any movement.
The more blades there are to the rotor, the more likely it is that the speed will synchronise in this way.
Amanda 949 your friend the military wife as they say in Dutch -loosely translated- has heared a bell sounding but she hasn't got any idea where to look for the clock that made it sound. Explanation is done by several others here.
:-D
Set the shutter speed too low (long exposure) and you'll get blur but you won't see it because of the over exposure white out, set the shutter speed higher and you'll get stopped or worse, "bent blades".
Most consumer level cameras just don't have enough of an arpeture setting (f-stop) to balance out the long exposure.
@amanda
"they take them up and turn it off to test the helicopter if it were to happen for real and to test the back blades", your friend is very very confused.
All helicopter pilots are trained in the event of engine (or gearbox etc) failure to autorotate, that is, the rotors disconnect from the engine and "free-wheel", it is the free wheeling that creates sufficient lift to get you to the ground somewhat under control.
Autogyros (gyrocopters) in fact use this autorotation as the primary means of lift, an autogyro's rotor is not connected to the engine in flight at all, the engine uses a propellor to push the aircraft along and the rotors free-wheel to quite a speed and generate the lift to rise, and arrest descent.
If the rotors just STOPPED like the video in real life, you would have a large splat, preceeded by several seconds of terrified screaming and a whooshing sound as you plummet directly downwards uncontrollably to the earth at unsurvivable speeds.
Those of us who do high-speed flight photos know we have to set lower shutter speeds than expected so that we can get blurred propellers on planes to show movement. It take practice and patience.
On top of that, remember there are five blades. If the shutter speed is fast enough, it has about a 20% chance of making it look like it's frozen in time. That's a pretty easy to come by chance of making this kind of video.
As for Amanda's comment, she's somewhat right as well, but with different words being used. They do test emergency conditions during helicopter pilot training which involves shutting down all power to the rotors(not stopping the rotors). This is a way to test for the student's emergency training involving "autorotation." It is meant to stop the sudden descent of a helicopter without power, but does not mean that the blades have stopped, only the engine has stopped. See article: http://en.wikipedia.org/wiki/Autorotation_%28helicopter%29
Apr 28th, 2010 at 6:08 pm
"I thought this was common knowledge"
Commom knowlege like what a pigeon looks like??
Or common knowlege like where do babies come from??
Or common knowlege like Algebra??
http://en.wikipedia.org/wiki/Wagon-wheel_effect
You might also be able to see it on rotors/blades during start up and shut down and likely at certain speeds and angles. It's never as clean as this, which is why it's so rare and debatable.
A big helium filled radio controlled balloon.
That's my theory anyway.
: )
D
Shutter speed is like frame rate in that it takes a lot of light, even daylight would look darkened to match the speed of a helicopter. Plus a high shutter makes things look slo-mo or clicker. And that helicopter's blades would have to be moving at the same constant speed without any minor changes. FAKE.
If you were lucky, a person could "dial in" the camera to the right rotor speed. If the rotor speed did not change significantly (which is possible), then it would be easy (only problem would be with motion blur). Like what was posted, each frame could catch the rotor move by 1/5 of a rotation between frames. If 1/5 of a rotation is 1/30 of a second, then that means the blade is spinning at 6 revolutions per second. This quick calculation shows that this situation is not unreasonable.
Anyway, if you weren't lucky but were instead really clever, you be able to synchronize the "shutter" timing to be matched with something from the helicopter. Maybe you could use the "beat" sound of the blade. If it were possible, note that the beat sound would probably be out-of-phase of the actual rotor position (due to sound travel time), but this would make little difference as a change in phase would make the blades move to a different apparent position.
If you were unlucky and more bored than clever, since this is a fairly short video you could hand-pick frames from a high-speed camera to give the proper speed and little-to-no rotor movement. You could find the period of the rotor blade rotation and make a generalization.. e.g. "about 221 frames between regions of interest." It would be time-consuming, but hardly a week-long effort.
I'm not saying it's real, but it can't just be discarded as "impossible" or "FAKE" without being more thorough. Basically, saying it is impossible is saying that "I don't know how it would be done, so it can't be done"; that is just being arrogant. All I am saying is that there are ways that it *could* be done, so your premise is not conclusive.
D-uh.
If the helicopter was spinning in an opposing direction at 1 revolution in 17 seconds (which it appears to be doing), this would mean a change in 0.059 revolutions per second. If the rotor was spinning at 6 revolutions per second, we're talking about a 0.9% variance.
Anyway, watch the video particularly right at the end. Keep an eye on one blade and its position relative to the helicopter tail (the "back" two are a good idea). At one point, the tail bisects the space between the back two blades. The setup changes and then one blade is almost parallel to the tail. At the very end the helicopter rotates while the blades do not, returning the setup to the "bisecting" position.
Like I said, doesn't mean it's real, but the issues that have been pointed out are more subjective than objective.
Don't know if it's true, but would explain why the effect would continue with changes in the speed of the rotors.
"That the frame rate was just right, I can only imagine to be coincidence, because it would be a huge amount of math just to compute the needed rate."
No, because pro video cameras have variable shutter speeds (not frame rates), so you can just dial it in. As you do, you would observe the rotors "slowing down" until they "stop". As you went past that point, they would seem to begin to rotate in the opposite direction. The aforementioned wagon-wheel effect. I've done the same thing myself w/ hummingbird wings. You can dial it in where it just looks like it's floating with its wings stationary.
As to the comment of it being fake because it would be dark, ....uh, this is shot in broad daylight. There's plenty of light. You can hardly get a brighter setting. And why would someone invent a function on a camera that couldn't make a useable picture? Silly.
Based on this lack of understanding, people are willing to cede their liberty to a power-hungry political elite.