sonic67
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Russian Levitating Technology

Sun Nov 04, 2007 5:57 pm




Apparently the Russian government is working on new Levitating device seen being tested on a MI-24 Hind helicopter in the video above. Can anyone shed some light on what is going on?  biggrin 
 
highlander0
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RE: Russian Levitating Technology

Sun Nov 04, 2007 6:03 pm

If I remember correctly- the frame rate of the camera is a multiple of the rotor revolutions.


I think
 
sonic67
Posts: 284
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RE: Russian Levitating Technology

Sun Nov 04, 2007 6:42 pm

I think your right it is just freaky to see the rotors not spinning.

This is another crazy video.

 
OlegShv
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RE: Russian Levitating Technology

Mon Nov 05, 2007 2:07 pm

Quoting Highlander0 (Reply 1):
If I remember correctly- the frame rate of the camera is a multiple of the rotor revolutions.

In scientific terms that's called aliasing (when the sampling frequency is not high enough, high frequency phenomena would often look like low frequency phenomena).
 
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moo
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RE: Russian Levitating Technology

Tue Nov 06, 2007 9:15 am

Quoting Sonic67 (Reply 2):
I think your right it is just freaky to see the rotors not spinning.

This is another crazy video.

What films that from?
 
F27Friendship
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RE: Russian Levitating Technology

Tue Nov 06, 2007 6:36 pm

Quoting Highlander0 (Reply 1):
If I remember correctly- the frame rate of the camera is a multiple of the rotor revolutions.

if that was the case we should still see somewhat of a disc. The helicopter maneuvres in different ways, where the relative motion can never be corresponding to the framerate all the time.

What we are seeing is a complete still rotor.
 
Dakar
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RE: Russian Levitating Technology

Wed Nov 07, 2007 2:23 am

Complete still rotor? I don't think so! How does it fly? Alien technology? Does it have a giant magnet inside it? If it is a still rotor why is the tail rotor moving?

Highlander0 is correct. The camera catches every blade at the exact same spot. The tail rotor, being geared higher, spins, although seen slower than normal due to the frame capture speed.

Nick
 
Stealthz
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RE: Russian Levitating Technology

Wed Nov 07, 2007 8:33 am

Quoting F27Friendship (Reply 5):
if that was the case we should still see somewhat of a disc.

Not really,

The combination of a highish "shutter" speed and a frame rate of 24fps will give you the effect shown.
At 24fps the effect shown will be visible at a rotor speed of 288rpm,at 25fps (PAL TV) or 30fps (NTSC TV) the RPM would vary a little.
I am no expert on helicopter rotor speeds but 288rpm seems entirely plausible.
If your camera sends text messages, that could explain why your photos are rubbish!
 
checksixx
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RE: Russian Levitating Technology

Wed Nov 07, 2007 2:26 pm

Quoting F27Friendship (Reply 5):
What we are seeing is a complete still rotor.

My God I hope your just joking...
 
UH60FtRucker
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RE: Russian Levitating Technology

Wed Nov 07, 2007 2:46 pm

Quoting F27Friendship (Reply 5):
What we are seeing is a complete still rotor.

You can't be serious??!?  crazy 

-UH60
Your men have to follow your orders. They don't have to go to your funeral.
 
FighterPilot
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RE: Russian Levitating Technology

Wed Nov 07, 2007 3:50 pm

Quoting F27Friendship (Reply 5):
What we are seeing is a complete still rotor.

 rotfl 

Cal  airplane 
*Insert Sound Of GE90 Spooling Up Here*
 
knoxibus
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RE: Russian Levitating Technology

Wed Nov 07, 2007 6:30 pm

The spooky thing is that even the shadows of the blades can be clearly seen against the fuselage.

Furthermore, the video quality (or me being tired Big grin) does not allow me to see if there is a pitch change in the blades AoA, or even the blades moving up or down at all!

Should be the case when the helo is doing some vertical manoeuvers only neh?
No matter what anybody tells you, words and ideas can change the world.
 
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scbriml
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RE: Russian Levitating Technology

Wed Nov 07, 2007 6:51 pm

Quoting F27Friendship (Reply 5):
What we are seeing is a complete still rotor.

So what's making all the noise on the video? wink 
Time flies like an arrow. Fruit flies like a banana!
There are 10 types of people in the World - those that understand binary and those that don't.
 
Marcus
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RE: Russian Levitating Technology

Wed Nov 07, 2007 9:53 pm

Quoting Scbriml (Reply 12):
So what's making all the noise on the video?

It's the cameraman making funny noises...........when you were a kid did you play with toy airplanes or toy cars?....remember making the noises of those machines when playing?....this is the exact same thing.
Kids!....we are going to the happiest place on earth...TIJUANA! signed: Krusty the Clown
 
highlander0
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RE: Russian Levitating Technology

Wed Nov 07, 2007 11:13 pm

Quoting Knoxibus (Reply 11):
The spooky thing is that even the shadows of the blades can be clearly seen against the fuselage

But they'd be rotating at the same speed no?
 
Dakar
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RE: Russian Levitating Technology

Thu Nov 08, 2007 12:04 am

Of course, Highlander0, they would.

Think of it as a flip-style stick-figure cartoon. The figures are drawn doing motions that look very disconnected if flipped slowly, but the faster it is flipped, the more connected and "real" it looks.
 
sonic67
Posts: 284
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RE: Russian Levitating Technology

Fri Nov 09, 2007 3:05 am

Quoting Dakar (Reply 15):
Think of it as a flip-style stick-figure cartoon.

If you look close enough you can see a cable or string when the light hits just right.



Quoting Scbriml (Reply 12):
So what's making all the noise on the video?


If you listen to the sound it is not the engine noise of a MI-24 Hind it has much more of a raspy growl to it. The sound is smooth closer to the sound a Eurocopter such as the Dauphine would make. It must have been daubed in later.
 
UH60FtRucker
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RE: Russian Levitating Technology

Fri Nov 09, 2007 3:29 am

Quoting Sonic67 (Reply 16):
If you look close enough you can see a cable or string when the light hits just right.

 rotfl 

Yeah... this is a video of someone using a clear string to hold up a model aircraft.... a model aircraft that has a working tail rotor and fully operating landing gear!

Some of you are just too funny!

-UH60
Your men have to follow your orders. They don't have to go to your funeral.
 
F27Friendship
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RE: Russian Levitating Technology

Fri Nov 09, 2007 5:57 pm

Quoting Checksixx (Reply 8):
My God I hope your just joking...



Quoting Checksixx (Reply 8):
You can't be serious??!?

lol! no worries guys! I'm not saying the vid is real! I'm saying that they must have used some kind of trick, because the rotor is clearly still in the vid (hence, what we are seeing, doesn't mean that it actually happend like this)

Quoting Knoxibus (Reply 11):
The spooky thing is that even the shadows of the blades can be clearly seen against the fuselage.

indeed, they must have edited the vid pretty profesionnaly. Let me underline I'm not high and did not mean to say the vid was real, just that the whole framerate story is unlikely. Another explanation must be found.
 
2H4
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RE: Russian Levitating Technology

Fri Nov 09, 2007 9:53 pm

Quoting F27Friendship (Reply 18):
that the whole framerate story is unlikely. Another explanation must be found.

There's nothing unlikely about it at all.

Imagine you have a flipbook that shows a bicycle wheel spinning around at one revolution per second.

Now, as you're flipping through the flipbook, keep your eyes closed, and open them once per second.

Provided your timing is accurate, you'll only ever see one position of the wheel. It will appear to be stationary. That is what's happening with this video.

The framerate explanation is far more likely than the idea that someone would go to such great lengths to doctor a video like this in the hopes that people think a helicopter is magically levitating.....

2H4
Intentionally Left Blank
 
UH60FtRucker
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RE: Russian Levitating Technology

Fri Nov 09, 2007 11:08 pm

Quoting 2H4 (Reply 19):
There's nothing unlikely about it at all.

Imagine you have a flipbook that shows a bicycle wheel spinning around at one revolution per second.

Now, as you're flipping through the flipbook, keep your eyes closed, and open them once per second.

Provided your timing is accurate, you'll only ever see one position of the wheel. It will appear to be stationary. That is what's happening with this video.

The framerate explanation is far more likely than the idea that someone would go to such great lengths to doctor a video like this in the hopes that people think a helicopter is magically levitating.....

2H4

Exactly.  checkmark 

I really cannot believe we're having this discussion!

There are plenty of videos out there that prove this concept. Hell, how many private pilots post videos looking out the front of their Cessna, and the main propeller appears to be at a dead stand still?? I'm just amazed that some people rather believe this was a giant hokes! That someone would create a model aircraft with a working tail rotor, and fully operating landing gear... hang it from a string.... and video tape it!!!

Yes, and the same person who pulled this stunt, also shot Kennedy from the grassy knoll, blew up the WTC with C4, and has the Roswell spaceship in his garage!!!  rotfl 

Check this video out: the plane propellers appear to be completely stopped. It's the same damn concept.



People this is not a conspiracy! It's a well known event. No one "faked" this video! Put the tinfoil hats away!

-UH60
Your men have to follow your orders. They don't have to go to your funeral.
 
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moo
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RE: Russian Levitating Technology

Fri Nov 09, 2007 11:12 pm

Quoting F27Friendship (Reply 18):
indeed, they must have edited the vid pretty profesionnaly. Let me underline I'm not high and did not mean to say the vid was real, just that the whole framerate story is unlikely. Another explanation must be found.

Its not hard to do if you know your way around cameras - it would take a few minutes experimentation with the framerate, and you would have the above video as a result.
 
ferrypilot
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RE: Russian Levitating Technology

Sat Nov 10, 2007 12:19 am

Can't believe you guys are so taken up with the helicopter video. ...Check out the two fishermen and the Catalina in the video supplied by SONIC67 at reply2. ...It's 10 times as much fun" ...I've watched it three times already.
 
F27Friendship
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RE: Russian Levitating Technology

Sat Nov 10, 2007 9:49 am

Quoting 2H4 (Reply 19):
There's nothing unlikely about it at all.

Imagine you have a flipbook that shows a bicycle wheel spinning around at one revolution per second.

Now, as you're flipping through the flipbook, keep your eyes closed, and open them once per second.

Provided your timing is accurate, you'll only ever see one position of the wheel. It will appear to be stationary. That is what's happening with this video.

The framerate explanation is far more likely than the idea that someone would go to such great lengths to doctor a video like this in the hopes that people think a helicopter is magically levitating.....

2H4



Quoting UH60FtRucker (Reply 20):
There are plenty of videos out there that prove this concept. Hell, how many private pilots post videos looking out the front of their Cessna, and the main propeller appears to be at a dead stand still?? I'm just amazed that some people rather believe this was a giant hokes! That someone would create a model aircraft with a working tail rotor, and fully operating landing gear... hang it from a string.... and video tape it!!!

my point is, those examples are 2D, this vid here is a chopper rotating, generating all kinds of relative motions for the observer (camera) which would make it difficult to exactly match it with the framerate, as it would have to vary.

Nevertheless, the other vid you posted made me think if my assumption is in fact true.
 
rwessel
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RE: Russian Levitating Technology

Sat Nov 10, 2007 11:25 am

Quoting F27Friendship (Reply 23):
my point is, those examples are 2D, this vid here is a chopper rotating, generating all kinds of relative motions for the observer (camera) which would make it difficult to exactly match it with the framerate, as it would have to vary.

Larger helicopters essentially all have mechanical systems for maintaining a constant rotor RPM under normal conditions, and those track the nominal "100%" RPM quite closely. Smaller helicopters require the pilot to fiddle with the throttle to maintain rotor RPM as the other flight controls are manipulated.

The trick is finding a helicopter with a rotor RPM that's a nice multiple of your frame rate (or conversely adjusting your frame rate appropriately - which can be done on the better camcorders). The CH-47, for example, runs the rotors at 225rpm, which doesn't match standard frame rates very well, so you'd have to fiddle at the camera end pretty hard. A 288rpm rotor would match a 24fps video well, 250rpm would match 25/50fps, 300rpm 30/60fps (and other combinations are possible as well, especially as the rotor or propeller gets larger or smaller).
 
David L
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RE: Russian Levitating Technology

Sat Nov 10, 2007 11:45 am

Quoting Moo (Reply 21):
Its not hard to do if you know your way around cameras - it would take a few minutes experimentation with the framerate, and you would have the above video as a result.

While I agree in principle, I'm not sure many cameras will let you adjust the frame rate. I suspect it's just a case of the rotor RPM being "just right" on that day.

Back to shutter speed, my camcorder allows shutter speeds down to 1/8000th of a second. While I'm unlikely ever to be able to use that, even at 1/500th of a second there must be a fair chance of "freezing" the main rotor on a helicopter.

Any helicopter experts ( * ahem *  Smile ) want to give us a ballpark figure for the main rotor RPM?
 
F27Friendship
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RE: Russian Levitating Technology

Sat Nov 10, 2007 1:22 pm

Quoting Rwessel (Reply 24):
The trick is finding a helicopter with a rotor RPM that's a nice multiple of your frame rate (or conversely adjusting your frame rate appropriately

my point is, this would apply when you film the rotor directly from above or below. In this case there are several angles and the helicopter is moving around. Thus the RELATIVE motion changes.
 
PC12Fan
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RE: Russian Levitating Technology

Sat Nov 10, 2007 2:54 pm

Quoting F27Friendship (Reply 26):

I think you are putting waaaay to much thought into this. Just remember the old saying: the most simple explanation is the most logical one.
Just when I think you've said the stupidest thing ever, you keep talkin'!
 
2H4
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RE: Russian Levitating Technology

Sat Nov 10, 2007 3:28 pm

Quoting F27Friendship (Reply 23):
my point is, those examples are 2D, this vid here is a chopper rotating

This vid here is 2D, as well. It's a series of images represented on a flat screen.

Quoting F27Friendship (Reply 26):
Thus the RELATIVE motion changes.

That's probably why the main rotor position changes very slightly. The relative motion that occurs as a result of the helicopter flying closer to and further from the camera isn't very significant. It's not as though the helicopter is flying a half mile away, turning around, and then flying back.

Quoting PC12Fan (Reply 27):
I think you are putting waaaay to much thought into this.

 checkmark  checkmark  checkmark   yes 

2H4
Intentionally Left Blank
 
David L
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RE: Russian Levitating Technology

Sat Nov 10, 2007 3:57 pm

Quoting F27Friendship (Reply 26):
my point is, this would apply when you film the rotor directly from above or below. In this case there are several angles and the helicopter is moving around. Thus the RELATIVE motion changes.

No it wouldn't. Each part of the blade makes the same percentage of a revolution in a given time. The tip of the blade rotates at exactly the same RPM as a point 1 inch from the hub.

Every one revolution, each part of each blade is back in exactly the same place relative to the helicopter. If the rotor has n blades, all of which appear identical, then it looks as if each part of each blade is back in the same place every 1/n sec, 2/n sec, 3/n sec, ... , n-1/n sec, n/n sec, n+1/n sec... and so on.

The angle from which you view it has no effect whatsoever.

Read about the Wagon Wheel Effect here:

http://en.wikipedia.org/wiki/Wagon-wheel_effect

http://www.newton.dep.anl.gov/askasci/gen01/gen01404.htm
 
F27Friendship
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RE: Russian Levitating Technology

Sat Nov 10, 2007 4:28 pm

Quoting PC12Fan (Reply 27):
I think you are putting waaaay to much thought into this. Just remember the old saying: the most simple explanation is the most logical one.

Sorry, I'm trained not to do that  Wink

Quoting 2H4 (Reply 28):
This vid here is 2D, as well. It's a series of images represented on a flat screen.

you don't understand what I mean. The vid on the screen is 2D yes, but it;s a transformation of a 3D event happening. What happens in 3D changes how it is perceived in 2D

Quoting 2H4 (Reply 28):
That's probably why the main rotor position changes very slightly. The relative motion that occurs as a result of the helicopter flying closer to and further from the camera isn't very significant. It's not as though the helicopter is flying a half mile away, turning around, and then flying back.

Didn't really notice the slight rotor movement.

Quoting David L (Reply 29):
No it wouldn't. Each part of the blade makes the same percentage of a revolution in a given time. The tip of the blade rotates at exactly the same RPM as a point 1 inch from the hub.

Again, you don't understand my point. I'm talking relative to the observer. There are relative angular velocites towards the observer, when the angle of the rotor disc towards the observer changes. I could get into advanced dynamics but I rather not (as it's been a while for me as well)
 
David L
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Joined: Tue May 18, 1999 2:26 am

RE: Russian Levitating Technology

Sat Nov 10, 2007 7:02 pm

Quoting David L (Reply 29):
every 1/n sec, 2/n sec, 3/n sec, ... , n-1/n sec, n/n sec, n+1/n sec... and so on.

Damn! I went out shortly after I posted that and alomost immediately realised I'd typed "sec" when I meant "rev".  banghead 

Quoting F27Friendship (Reply 30):
I could get into advanced dynamics

I wish you would because I don't see how that would affect the well known Wagon Wheel effect. As long as each blade does (almost) exactly as the previous one, the potential is there.
 
fumanchewd
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RE: Russian Levitating Technology

Sat Nov 10, 2007 9:26 pm

Its all trick photography.

Of course the only one who can levitate aircraft is Bob Hoover. ;-}

In the time of chimpanzees, I was a monkey...
 
ferrypilot
Posts: 623
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RE: Russian Levitating Technology

Sat Nov 10, 2007 11:47 pm

Quoting Fumanchewd (Reply 32):

Of course the only one who can levitate aircraft is Bob Hoover. ;-

That eight point slow roll at the start looks very cool. But there's a point a bit later in that landing trick and in the second contact where he slips quite heavily on to his left wheel and clearly nearly takes the tire off the rim. I don't see finesse it looks ragged to me although he is of course right out on the edge of the envelope. ...It's also possible to see very significant sideways stress going through the undercarriage leg, arguably enough to damage or even collapse it. ...He's undoubtedly an ace handling pilot, but even the aces aren't perfect all the time.
 
F27Friendship
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RE: Russian Levitating Technology

Sun Nov 11, 2007 1:02 am

Quoting Fumanchewd (Reply 32):
Of course the only one who can levitate aircraft is Bob Hoover. ;-}

what a great guy! This is fantastic! There's a bunch of people I gotta show this vid!

Quoting David L (Reply 31):
I wish you would because I don't see how that would affect the well known Wagon Wheel effect. As long as each blade does (almost) exactly as the previous one, the potential is there.

Right, below you find a rather simplified picture of what I mean



On the left you see a rotordisc which has an angular velocity around axis z. on the right the disc is tilted under angle alpha. The angular velocity can be expressed around the purple axis (as you can express is around any axis you please) is cos(alpha) times the original angular velocity.

In the case of the chopper, it moves around many axes, thus the relative speeds of the rotor perceived by the camera vary all the time. The vid simply doesn;t look like classic wagon wheel, it's too clean.

[Edited 2007-11-10 17:03:39]
 
fumanchewd
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RE: Russian Levitating Technology

Sun Nov 11, 2007 7:42 am

Quoting Ferrypilot (Reply 33):
I don't see finesse it looks ragged to me although he is of course right out on the edge of the envelope.

With the engines stopped?!
In the time of chimpanzees, I was a monkey...
 
David L
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Joined: Tue May 18, 1999 2:26 am

RE: Russian Levitating Technology

Sun Nov 11, 2007 11:26 am

Quoting F27Friendship (Reply 34):
The vid simply doesn;t look like classic wagon wheel, it's too clean.

That's entirely down to shutter speed. I'm forever forgetting to slow the shutter when photographing helicopters and props. The result is an unpleasing freeze of the props and, on a bright day, you get a very "clean" freeze on a helicopter's main rotor.

Quoting F27Friendship (Reply 34):
In the case of the chopper, it moves around many axes, thus the relative speeds of the rotor perceived by the camera vary all the time.

I still don't see how that's relevant. All you need to compare are blade 1 at point X with blade 2 at point X a fraction of a second later. You don't need to compare what's happening at the left side of the disc to what's happening at the right side of the disc.

Strobe lighting is used frequently in industry to "freeze"rotating machinery while it's operating and it doesn't need to be used from directly above or below:

http://en.wikipedia.org/wiki/Strobe_light
 
F27Friendship
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RE: Russian Levitating Technology

Sun Nov 11, 2007 12:36 pm

Quoting David L (Reply 36):
I still don't see how that's relevant. All you need to compare are blade 1 at point X with blade 2 at point X a fraction of a second later. You don't need to compare what's happening at the left side of the disc to what's happening at the right side of the disc.

it does, because due to the changing relative angular velocity, blade 1 at point X, shows up at point Y after the helicopter has moved around it's axes, where you would have expected it at point X, which would cause a blur with constant FPS.

I think they did the following:

-Film the chopper with a high-speed digital camera (lot's of fps)
-In the computer delete all frames where the rotor is in a different position
-Convert it to a normal framerate.
 
David L
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RE: Russian Levitating Technology

Sun Nov 11, 2007 1:29 pm

Quoting Dakar (Reply 40):
Why is it so difficult to believe? Why is F27Friendship the only one who is skeptical?

I admit I'm really only assuming a camcorder could have a fast enough shutter speed in those lighting conditions and if someone can show that it's not likely I'll think again. However, I'm afraid all this "angular velocity" and "relative motion" versus frame rate just doesn't do anything for me.  Smile
 
David L
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RE: Russian Levitating Technology

Sun Nov 11, 2007 4:16 pm

Quoting F27Friendship (Reply 37):
it does, because due to the changing relative angular velocity, blade 1 at point X, shows up at point Y after the helicopter has moved around it's axes, where you would have expected it at point X, which would cause a blur with constant FPS.

Blur can only be controlled by shutter speed. i.e. how much the tip of the blade moves while the shutter is open. If the shutter is only open long enough for the tips to move a few centimetres, it won't necessarily be noticable on a YouTube video. That's why I was looking for a typical helicopter rotor RPM (and rotor diameter, of course). Frame rate has no bearing on that.

If the frame rate is just very slightly out of sync with the rotor, you'll see what looks like a slow forward or backward rotation of the rotor. Again, the amount of blur would still depend on the shutter speed. As the helicopter turns and as power alters slightly, you can see the frozen rotor appear to rotate slightly forwards or backwards.
 
2H4
Posts: 7960
Joined: Tue Oct 19, 2004 11:11 pm

RE: Russian Levitating Technology

Sun Nov 11, 2007 4:21 pm

Quoting F27Friendship (Reply 37):
I think they did the following:

-Film the chopper with a high-speed digital camera (lot's of fps)
-In the computer delete all frames where the rotor is in a different position
-Convert it to a normal framerate.

Despite what you may want to believe, a known, proven, and common technical occurrence is far more likely than your elaborate conspiracy theory...

2H4
Intentionally Left Blank
 
Dakar
Posts: 70
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RE: Russian Levitating Technology

Sun Nov 11, 2007 5:22 pm

Quoting 2H4 (Reply 39):

+1

Why is it so difficult to believe? Why is F27Friendship the only one who is skeptical?
 
ferrypilot
Posts: 623
Joined: Mon Sep 11, 2006 1:19 pm

RE: Russian Levitating Technology

Sun Nov 11, 2007 10:56 pm

Quoting Fumanchewd (Reply 35):
Quoting Ferrypilot (Reply 33):
I don't see finesse it looks ragged to me although he is of course right out on the edge of the envelope.

With the engines stopped?!

I don't doubt he had pulled that trick off cleanly on previous occasions. I am just saying that on that occasion he didn't pull it off so well as the aircraft is slipping like hell out of the second turn and so makes a very unhealthy looking contact with the runway as the consequence. Undercarriages are not ever for landing going sideways on. It looks like crap to an aviator and nearly bust the aeroplane. I'd have been walking in red faced and sweating if I had been him.
The guy can fly for sure and actually I respect "RAW HANDLING SKILL" far above all else in a pilot, but even outstanding pilots must be seen to temper their skill with caution and good judgement. I am afraid I have formed the opinion that Bob Hoover has a history of going too far, pulling dangerous on the limits stunts that could all too easily go wrong and this video reinforces that opinion. ...You can read as much in Chuck Yeager's book all the way back in the 1940's.
And think on this, he is not trying to impress the thousands of average guys at an airshow audience with those stunts and who are unable to relate to the degree of difficulty, far more likely is that he has always been trying to put one over on his pal's, ...those other guys with big reputations as aviators like Yeager.
 
F27Friendship
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RE: Russian Levitating Technology

Mon Nov 12, 2007 7:45 pm

Quoting David L (Reply 38):
Blur can only be controlled by shutter speed. i.e. how much the tip of the blade moves while the shutter is open. If the shutter is only open long enough for the tips to move a few centimetres, it won't necessarily be noticable on a YouTube video. That's why I was looking for a typical helicopter rotor RPM (and rotor diameter, of course). Frame rate has no bearing on that.

If the frame rate is just very slightly out of sync with the rotor, you'll see what looks like a slow forward or backward rotation of the rotor. Again, the amount of blur would still depend on the shutter speed. As the helicopter turns and as power alters slightly, you can see the frozen rotor appear to rotate slightly forwards or backwards.

That could be an explanation as well. I have no knowledge at all about camera's etc. Just was thinking over in my head what could have happened else, since all other wagonwheel footage I saw looked very different. I can't believe this vid could have been made without a high speed digital camera.

Quoting 2H4 (Reply 39):
Despite what you may want to believe, a known, proven, and common technical occurrence is far more likely than your elaborate conspiracy theory...

2H4

If that suits you, fine. Some people like to think further. When being wrong when doing so, that's not a shame, you actually learned something. Nevertheless, I still think my theory is the most plausible: high speed camera, then edit it on the computer.
 
rwessel
Posts: 2448
Joined: Tue Jan 16, 2007 3:47 pm

RE: Russian Levitating Technology

Tue Nov 13, 2007 11:18 am



Quoting F27Friendship (Reply 43):
I have no knowledge at all about camera's etc.

But our whole point is that this is a fundamental part of the way cameras take pictures and record movies. And the effect happens all the time, sometimes deliberately, sometimes not. Just because you don't understand how cameras work doesn't make alternative explanations reasonable.

Let me try to break this down.

There are two important variables. First is the frame rate, second is the shutter speed. The camera takes one picture at each interval as specified by the frame rate. So at 24fps, it takes a picture 24 times each second. This picture is completely independent of the preceding frame, and completely independent of the following frame. It's as if you pressed the shutter button on your (still) camera several times, and looked at the resulting sequence of picture (although you obviously can't push the shutter release that rapidly). If that rate is appropriately synchronized with the rotor, the rotor will appear to stand still since it will be in the same position (taking into account that there are several symetrically identical positions for a rotor) for each image. It does not matter from what angle you see the rotor, it will be photographed in the same position for each frame. It doesn't mater if you're moving relative to the rotor either, at least so long as the speeds involved are well short of the speed of light. If the helicopter turns, while maintaining a constant RPM, you'll see the whole rotor image turn with the helicopter, and you do see a bit of that.

The shutter speed is the second important variable. In some cases the imaging sensor, be that the CMOS or CCD array in a digital camera, or the bit of film that represents a single frame, is exposed for the entire interval (or nearly so given the need to physically move the film between frame) specified by the frame rate. So for a 24fps movie, you'd have the sensor exposed for 1/24th of a second. Assuming a 288rpm rotor, this would allow the rotor to turn 1/5th of a rotation while the image was being taken. Which, for a five bladed helicopter, like the one in the video, would result in a continuous blur for the rotor (actually five blurs of 72 degrees each, one for each blade, which forms a complete circle). If you had a four bladed rotor with those conditions, you'd see four wedges of 72 degrees, with 18 degree empty wedges between them.

Now shutter speed is very important, since it's the primary way exposure is controlled. In short, and somewhat simplified, each sensor has some range of light exposure that it can measure. For example, typical film can measure a range of about 1000:1 - IOW, the brightest area that can contain any details is 1000 times brighter than the darkest area containing details. Any brighter or darker areas will record as flat white or black.

For film, the range is more or less fixed by the manufacturing of the film - so an ASA100 film is half as sensitive as a faster ASA200 film. You can adjust than somewhat by playing with the development (IOW you can make a given film act as if it were a faster film by overdeveloping it by leaving it in the soup for longer - although image quality suffers). In the case of electronic sensors, the range varies some with the technology, and the exact "speed" of the sensor can be varied to some extent by playing with the biasing voltage on the sensor or similar things. But the total range at any given speed is still in that same ballpark. Note that *printed* images have a much narrower range that they can reproduce (actually about 15-20:1), so a picture that looks good in a slide projector or on a monitor, can still have washed out shadows and highlights when printed.

To take a good picture you need to adjust the exposure so that you more or less hit the middle of the range the sensor can record. The way that's accomplished is by varying the shutter speed. Depending on the type of camera, you might have an actual mechanical shutter that stays open for a given amount of time (film cameras), or you might just read out the electronic sensor after the appropriate interval. The correct shutter speed depends on the amount of light, and the speed of the sensor (plus the amount of light actually transmitted through the optics, but we can consider that a constant for now). The more light, or the faster the sensor, the faster the shutter speed has to be to maintain the correct exposure.

Just to put some numbers on it, with a f/16 lens (a measure of how much light goes through the lens - f/16 being a fairly "slow" lens), in daylight, you'd need an exposure of 1/100th of a second with ASA100 film (moderately slow), or 1/800th with ASA800 (fast) film.

If you set a shutter speed of 1/1000th of a second, which you could do in daylight with a (four times faster, but still slow) f/8 lens, and ASA125 film (or some other combination of sense and lens speed that works out the same way), you'd still have 24 independent images taken each second, but now each would only record 1/1000th of a second, not 1/24th of a second. In that case the rotor would move less than 2 degrees during the picture, and would result in a vary narrow blur - and two degrees in the same order of magnitude as the rotor blade itself.

Nor is 1/1000th of a second particularly fast. Some low end camcorders use only the electronic adjustment of the sensor, but all the better ones support "real" shutter speeds. And speeds down to 1/12000th of a second are common on semi-high end gear. FWIW, a 1/12000th shutter speed would result in our hypothetical rotor being "blurred" about a 1/7th of a degree. A 1/12000th of a second exposure could be done in daylight with an f/4 lens and ASA400 film.

Here are a few pictures from the library illustrating the effect. These are all S-76's in flight, running at the same rotor RPM, with different shutter speeds (from fast to slow):


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Click here for bigger photo!

Photo © Diego Ruiz de Vargas - Iberian Spotters




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Click here for bigger photo!

Photo © Ralph Duenas - Jetwash Images




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Click here for bigger photo!

Photo © Harri Koskinen



And while this one is not in flight, it nicely illustrates the "wedge" effect:


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Click here for bigger photo!

Photo © Phil Vabre



Notice that in the first image, the shutter speed is fast enough to almost stop the much faster tail rotor too (although because it is faster, the blur makes a bigger arc).

So when you combine the fast shutter speed (almost required in bright daylight), with a frame rate closely synchronized with the rotor's rotation, you end up with a seeming stationary rotor, with little apparent blurring.
 
F27Friendship
Posts: 1098
Joined: Sat Jul 14, 2007 11:45 pm

RE: Russian Levitating Technology

Tue Nov 13, 2007 6:43 pm



Quoting Rwessel (Reply 44):
But our whole point is that this is a fundamental part of the way cameras take pictures and record movies. And the effect happens all the time, sometimes deliberately, sometimes not. Just because you don't understand how cameras work doesn't make alternative explanations reasonable.

It's just dynamics and mathematics I'm applying; it's not alternative, it's how the world is explained in general terms.

I appreciate your long and elaborate eplanation of how camera's work; nevertheless, I'm not an idiot nor from another planet. I understand how a camera physically works, and also quite some bit on digital camera's (from a space point of view). My point was: it's not my hobby, so I wouldn't call myself an expert on camera's (maybe I overstated this a bit)

Quoting Rwessel (Reply 44):
There are two important variables. First is the frame rate, second is the shutter speed. The camera takes one picture at each interval as specified by the frame rate. So at 24fps, it takes a picture 24 times each second. This picture is completely independent of the preceding frame, and completely independent of the following frame. It's as if you pressed the shutter button on your (still) camera several times, and looked at the resulting sequence of picture (although you obviously can't push the shutter release that rapidly). If that rate is appropriately synchronized with the rotor, the rotor will appear to stand still since it will be in the same position (taking into account that there are several symetrically identical positions for a rotor) for each image. It does not matter from what angle you see the rotor, it will be photographed in the same position for each frame. It doesn't mater if you're moving relative to the rotor either, at least so long as the speeds involved are well short of the speed of light

this does not contradict my theory. If the RPM is the same, but if the angles change, the relative motion to the observer changes.

Quoting Rwessel (Reply 44):
If the helicopter turns, while maintaining a constant RPM, you'll see the whole rotor image turn with the helicopter, and you do see a bit of that.

I can accept the wagon wheel effect including the above, as that would come from what I explained. Nevertheless I guessed this effect would be much more visible than the slight nudge de rotor makes in this vid.

Again, I only own a simple digital camera to make snapshots, but if I would want to trick such a film, I'd do it with a high speed camera (say 1000 fps)

Just to underline once more, I really appreciate the time you took to explain all this.
 
rwessel
Posts: 2448
Joined: Tue Jan 16, 2007 3:47 pm

RE: Russian Levitating Technology

Tue Nov 13, 2007 7:09 pm



Quoting F27Friendship (Reply 45):
this does not contradict my theory. If the RPM is the same, but if the angles change, the relative motion to the observer changes.

While true, it's not really a factor. The largest apparent motion will be from directly above of below the rotor disk. From any other angle, the apparent motion will be less, but it will still be consistent on a frame-to-frame basis if the speeds are synchronized. Imagine a one bladed rotor (so the ride is a little rough), where its rotation is synchronized to the camera speed so that the blade is always pointing forward relative to the helicopter when the picture is taken, and further assume that the helicopter is not turning. Now image how the view of that rotor blade changes as you move around the helicopter - no matter where you are, you'll snap the picture with the blade pointing forward. If the shutter speed is fast enough, it will appear to be still.

Quoting F27Friendship (Reply 45):
but if I would want to trick such a film, I'd do it with a high speed camera (say 1000 fps)

That would certainly work (although the required gear is not cheap – at least the CCD based high speed cameras are a *lot* less expensive than the old high speed film stuff), and would produce basically the same result. But what you're basically doing is applying the synchronization after the fact.
 
F27Friendship
Posts: 1098
Joined: Sat Jul 14, 2007 11:45 pm

RE: Russian Levitating Technology

Tue Nov 13, 2007 7:24 pm



Quoting Rwessel (Reply 46):
no matter where you are, you'll snap the picture with the blade pointing forward. If the shutter speed is fast enough, it will appear to be still.

sure it will be, but if it's in a slightly different position, placing those pictures after each other will produce a film with a blade moving back and forth a bit (as can be seen in the vid, but just slightly)

Quoting Rwessel (Reply 46):
That would certainly work (although the required gear is not cheap – at least the CCD based high speed cameras are a *lot* less expensive than the old high speed film stuff), and would produce basically the same result. But what you're basically doing is applying the synchronization after the fact.

true, but I think you can do a better "cleaner" job this way.

I think we are somewhere in the middle now  Smile

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