How is this Helicopter flying?

I think I know the answer, but haven't looked at any yet. Via that big site that doesn't need our via.
Farhad2000says...

Optical camera effect captures blade positions in one position each time. Makes it look like the blades are still when they are not, this is why you see them moving one and then another direction, the camera is basically capturing an instance each time (this is also why the video is so ridiculously sharp). The tail rotor moves at a constant speed because usually it's twice as fast as the main rotors to counter the want of the helicopter to go into an uncontrollable spin.

This is something you learn when you try to model rotary motion in 3D, the most obvious thing would be to just create a main rotor and spin it, however this doesn't give that washed out blade spin you see in real life. So instead of that you create two layers, one of the main rotors and another of a flat 2D texture for the actual helo rotor motion then animate a switch between both.

Next time you fly a chopper in BF2, look at the blades prior to and after take off. You will see the same effect.

gluoniumsays...

that's it. its the same as when you look at wheels on a car at night as it accelerates. the freqency of the flickering yellow sodium lights goes in and out of sync wth the spokes of the wheel and it makes it look like its going reaaaaly slow or stopping altogether or even going backwards. if you can only see the wheel (or whatever) at certain points during its rotation AND it is an object that has perfect radial symmetry then the illusion is complete!

BoneyDsays...

lol no, no.. It's large scale-model on a very thin string. I imagine hung from a crane or the like. Because:

1) optical effects you mentioned would be true only if it was stationary and the blades remained at the EXACT same rate of rotation, assuming the camera had somehow magically found the precise shutter speed to match the positions of the blades. This is not true as the Hind is yawing/pitching and gaining/losing height - this would require changes in the throttle, hence changing the speed of rotation and de-synchronising it with the camera shutter speed.

2) Notice how the model seems to swing right to left, then right again, as though from a point high above. It's not until it comes to a stop that the 'crane' is raised.

Very impressive model though! It must be huge... and even comes with retractable landing gear!

gluoniumsays...

If this is a model Boney then someone REALLY, I mean REALLY REALLY did thier homework. In addition to the very convincingly real retractable landing gear, why is the tail rotor moving at the correct speed that you would expect if it were an actual flying heli and why are the blades of the main rotor TILTED UP from center to tip, like they are providing lift? They would be tilted down in a non-flying heli and probably not noticeably tilted at all in any model. This fact would also appear to rule out the possibility that it is being lifted by another helicopter, as the blades would not be rotating or providing lift there either. the simplest explanation is video frame rate sync using a LARGE aperture lens capable of using extremely fast shutter speeds, possibly even a high speed video camera whose video was later sped up.

deathcowsays...

I'm telling ya, I had this 3D model as early as 1992 off the great ViewPoint Datalabs CD. This is rendered. No shutter speed freezes things like this, especially with the radical velocity at the rotor tip. Rendered... rendered... rendered....

Sketchsays...

Yeah, there's no way that's an optical effect. I agree with garsh and BoneyD. There would be major blurring on the blades, and the rotation would be pretty obvious and steady as the throttle changes, like it does when you look at wheels on a car.

However, I'm don't know if I buy the other options proposed... I'm going with Magneto having a fun day.

gluoniumsays...

look at this other video he uploaded http://www.youtube.com/watch?v=HZJJK-XAnso&NR=1 model? rendered? no way. this is the best model hoax I have ever seen if that's the case. look at the specular glints off the small windows at :26 complete WITH oversaturated CDD bloom! you never see that kind of absurdly high attention to detail with any rendered video. I'm still not convinced the main rotor tips can't travel slow enough with a fast camera to eliminate the blur. I think at sufficiently slow speed using a very high speed camera, they can.

dagsays...

Comment hidden because you are ignoring dag.(show it anyway)

My theory was the shutter timing too, but DC has made me think again. There is something a little bit modelish about it - plus the jerky camera and good sound lends it a lot of undue credibility.

Solmedsays...

It has nothing to do with shutter speed but Frames Per Second (FPS), you don't need a high shutter speed to capture the blades like that. If I were going to try this I would turn the FPS up as high as it will go and record. In editing I would adjust the FPS to create the effect of the blades not moving. I have a sneaky suspicion (and I'm not going to count) this video does not have a standard FPS, i.e. 24 or 29, but rather somewhat below that rate. As evidence to that fact look how jerky the clouds in the background are. Great trick though!

karaidlsays...

I saw this on Break and the explanation given is the same one that's been said. Break says that the FPS was perfectly in sync with the blades movements. Of course, that's just Break, so... you know.

Paybacksays...

The fact the Hind has 5 main rotor blades means it doesn't have to spin as fast.

This youtube movie shows a stroboscopic effect when filming a true Hind.
http://www.youtube.com/v/eLOXRQzkFCc

Using a high grain film or digital could produce what you're seeing on the above sift... unfortunately... when flying like that, the pilot would be changing the rpms personally, or at least the different air pressures would "turn" the rotor with respect to the camera shutter.

I say rendered using the soundtrack from the youtube movie I linked to. Nice one tho...

rensays...

no way is this a 3d model, no way in hell.
The angle of the blades clearly translate into the chopper's movement, my opinion its an optical effect caused by an intentionally synched camera.

jimnmssays...

There is an old joke in the aviation community that helicopters don't produce lift, they are so ugly that the earth repels them. This video could be used as evidence to prove that correct.

"Yeah, there's no way that's an optical effect. I agree with garsh and BoneyD. There would be major blurring on the blades, and the rotation would be pretty obvious and steady as the throttle changes, like it does when you look at wheels on a car."

Unlike the props on a plane and wheels on a car, the blades on a helicopter do not change RPM during flight. They stay at a constant RPM, and the rotor is tilted and the blade angle is adjusted for maneuvering.

You see this effect a lot on digital camcorders with a "sports" mode. I took a friend flying once and he brought his Sony camcorder. When he had it in normal mode, the props in the video were blurred, but when he switched it to sports mode, it recorded at a higher FPS and in the video the prop appeared to be slowly spinning backwards.

deathcowsays...

It's a friggin 3D model you blasphemous widget heads.

No camera in the world being casually handheld can freeze that kind of action with absolutely NO differential effects seen between the hub of the rotor and the far end.

It's a 3D MODEL WHICH HAS BEEN TRADED ON THE INTERNET SINCE THE EARLY 1990's:
http://images.google.com/images?hl=en&q=hind+24+3d+model&gbv=2

Additionally this whole thing would take about a day to make for someone with skills. Dont let the little specular effects and such fool you.

1) get HDR 360 degree panoramic image of the sky. If you dont have one, let Vue-6 render one for you automatically.

2) use the HDR image as the background, and also as the light source

3) place a specular "Sun" light somewhere matching up with the HDR location

4) take ancient moldy Hind 3D model from your most oldest ancient CDR on your most dusty bookshelf

5) use a flavor of hind paint scheme READY TO GO:
http://www.turbosquid.com/Search/Index.cfm?FuseAction=ProcessSearch&intStartRow=1&istSearchKey=hind&intMediaType=-1
(or roll your own)

6) flop it around in the viewport, render to small movie, apply sound effects

ReverendTedsays...

Despite what Solmed suggests, a high shutter speed WOULD be necessary to theoretically capture an effect like this, in addition to frames-per-second synchronization.
With a low shutter speed, each blade would move a significant distance while the shutter was open, resulting in a blurred (though apparently stationary) blade.
For the record, I believe it's entirely possible that this video is legitimate. As long as there is a (motion picture) camera capable of a high-enough shutter speed to capture the blade tips then the rest is academic.
It could be rendered, but I doubt it.
If you track down the original post there are actually two videos. The second includes a flyover of a crowded airstrip indicating that this probably took place at an airshow.

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