How is this helicopter flying if the blades aren't spinning?

[alsenior]

the main rotor and the rear rotor are usually connected via a shaft in most copters. the rear ones are spinning so i assume the main rotors are aswell

[floppybootstomp]

Its the new Hind Emohawk, powered by harvested teenage angst.

Obviously

[Nick]

No, it's just proving that old saying that helicopters can't actually fly, they're so ugly the earth repels them.

[Marcos]

Video frame rate making the rotors look stopped

didnt think of that one

[Marcos]

No, it's just proving that old saying that helicopters can't actually fly, they're so ugly the earth repels them.

thats good

[hsncool]

u fools, im suprised no1 was thinking on the same wavelength as me.

i thort that the helicopter got to a high enough height, and then stopd the blades spinning, and just dropped. another chopper was beside it (where the filming was done) and just dived down, level with it, so they cud take the footage. hence the heli's noise.

all you can see behind is cloud, which isnt going to realy change that much during the drop....and towards the end of the film, the filming chopper was lower, and having to film upwards.......makes perfect sense to me.

[JPreston]

It's clever. I wouldn't have thought that the frame rate could have been matched so closely to the rotors (strictly; the number of frames per second has to divide the rotations per second, not match it exactly) because surely the speed of the rotors varies by quite an amount in normal flight due to wind etc, it just seems to work too well.

But I don't think helicopters look like that when they are autorotating, plus the hassle of organising a second one to film from and the shakiness of filming from a second helicopter, so it must be the frame rate

[iranu]

Having worked for a company that produces helicopter main rotor and tail rotor gear boxes, there is absolutely no way that a tail rotor would continue to spin normally whilst the main rotor remained stationary.

This is an optical illusion caused by camera framerate as suggested by others here. Well spotted. You will also notice the slowed tail rotor RPM in the film. Again no helicopter will produce such a slow tail rotor speed.

The manouverability shown by the helicopter could not possibly happen with a static main rotor.

The main rotor noise picked up by the camera's microphone gives the game away.

[jamin]

u fools, im suprised no1 was thinking on the same wavelength as me.

i thort that the helicopter got to a high enough height, and then stopd the blades spinning, and just dropped. another chopper was beside it (where the filming was done) and just dived down, level with it, so they cud take the footage. hence the heli's noise.

all you can see behind is cloud, which isnt going to realy change that much during the drop....and towards the end of the film, the filming chopper was lower, and having to film upwards.......makes perfect sense to me.

Helicopters main rotors will autorotate if in an unpowered decent mate. So you would see them spinning at a slower speed, its a technique chopper pilots are taught to use if the engine fails. The chopper is basically brought back to the ground in a unpowered controlled decent and then just above the ground the rotors are feathered to give more lift and slow the decent, hopefully landing the chopper without too much of a bump.

Looks like a clever or lucky stroboscopic effect caused by the framerate. Same as when it looks like alloy car wheels are spinning backwards, even though the car is moving forwards on TV.

[chicken]

u fools, im suprised no1 was thinking on the same wavelength as me.

i thort that the helicopter got to a high enough height, and then stopd the blades spinning, and just dropped. another chopper was beside it (where the filming was done) and just dived down, level with it, so they cud take the footage. hence the heli's noise.

all you can see behind is cloud, which isnt going to realy change that much during the drop....and towards the end of the film, the filming chopper was lower, and having to film upwards.......makes perfect sense to me.

This is the conclusion I came to. I, like everyone else thought to begin with that it would just be the framerate matching the spin, but as has been said there is no variation, and surely banking and the like would alter the spin speed enough to send it way out of sync.

Another factor is that the blades are quite detailed in some shots, they don't appear to switch places ever so the sync would have to be perfect, and how are they not blurred? Yes you may match sync but even the fraction of a second taken to capture a frame is going to involve a lot of movement on the blades of a flying helicopter, they would surely be blurred, not crystal clear.

[Whiternoise]

This is the conclusion I came to. I, like everyone else thought to begin with that it would just be the framerate matching the spin, but as has been said there is no variation, and surely banking and the like would alter the spin speed enough to send it way out of sync.

Another factor is that the blades are quite detailed in some shots, they don't appear to switch places ever so the sync would have to be perfect, and how are they not blurred? Yes you may match sync but even the fraction of a second taken to capture a frame is going to involve a lot of movement on the blades of a flying helicopter, they would surely be blurred, not crystal clear.

Why would there be variation? I think you'd be pretty buggered in a helicopter if the blades changed speed randomly I would imagine that the rotors are powerful enough that the drag does not affect them very much. Plus, i imagine that the blades are controlled to spin at a set rpm so there's probably a computer auto adjusting to counteract the turn.

The shutter speed of the camera doesn't have to be exact - otherwise the blades would be perfectly still (and you can see them rotating very slowly). If you had a camera taking shots at 50fps, that would be 3000fpm so it's possible.

Ever seen standing waves on a bit of string? You get a stroboscope and make it flash at the same frequency as the one of the harmonics of the string. You can make the string move slowly or stand still, the strobe flash is usually a bit out but the string is still clear.

[chicken]

A strobe is an much greater amount of light in a much shorter burst in comparison to normal daylight. It doesn't matter if your camera takes shots at 50fps and matches a harmonic, a blade moving 60x the speed is very unlikely to appear crisp and not blurred in every frame, yet you can still see the blades clearly.

For the variation part, the helicopter quite clearly changes angle and direction several times, appearing* to rise towards the end. If that doesn't cause a variation in rotor speed then something very strange is going on.





(Edit: I say "appearing" to rise because if this is the falling scenario then it's actually the effect of the cameraman decending faster than the subject)

[TeePee]

The rotor speed does change a little, which is why the blades appear to move a small amount.

But, there's no reason it necessarily would change the rotor speed. Blades speed is maintained largely regardless of engine power by altering blade pitch, as with a constant speed propeller.

[BUFF]

For the variation part, the helicopter quite clearly changes angle and direction several times, appearing* to rise towards the end. If that doesn't cause a variation in rotor speed then something very strange is going on.

but the pilot should be feeding in more throttle as well as increasing the angle of attack of the blades (increases aoa = more lift= more drag so needs more power) so you should have a fairly constant rotor rpm

[chicken]

Fairly constant though doesn't really cut the mustard with 47 seconds of footage and staying so closely sync'd to the camera. No-one's touched on the clarity of image side yet.

All in all I'd say I just can't watch this and believe it is just camera sync, there's too much wrong with it. The blades move slowly sometimes, but remarkably in accordance to how a free-turning thing would in relation to an object rotating and banking underneath it. The last shot where the helicopter appears to fly up and over the viewer just doesn't look right to me either. Unfortunately I can't really explain it but it feels like the viewer goes under it rather than the helicopter goes up and over. Also, where is the horizon? The whole shot is nothing but clouds & sky. It would be so much easier to make sense of if you only saw a tree-top or a building.

[Nick]

I reckon they've got a model of a chopper suspended on a string and they pan around under and past it... Very much like Spielberg did to give the impression the Millenium Falcon was zipping past the camera. The slight blade rotation is as they turn the model...

Zooming in and out to give the impression of movement is a lot easier than actually moving sideways to give the impression of rotation, depending how far you are from the subject you have to move faster and faster the further away you are.

So they either zoom or move the camera in to give depth (probably the latter as we get an almost underneath shot), then pull out and rotate the model to give the impression of turning.

Notice that the blades rotate slightly when the main body of the chopper turns, which would say to me that their is a small amount of friction and free play between the body and rotor with the rotor initially resisting the turn due to inertia.

Of course, this could have been a test shot of a bloody great film rig... it's not unknown for those guys to have massive rigs of stuff like choppers, Harriers etc.