mirrodie
Posts: 6789
Joined: Wed Apr 19, 2000 3:33 am

Helicopter Flight Question-see Video

Sat May 19, 2007 9:09 am

http://www.filecabi.net/video/ufochopper.html

Is this an optical illusion on the part of the video camera or am I seeing what I think I am seeing? If its not an illusion and the rotors are going, what is keeping this chopper afloat?
Forum moderator 2001-2010; He's a pedantic, pontificating, pretentious bastard, a belligerent old fart, a worthless st
 
meister808
Posts: 924
Joined: Sat Jan 01, 2000 11:45 am

RE: Helicopter Flight Question-see Video

Sat May 19, 2007 9:23 am

That would be what happens when the frame rate of the camera matches the rpm of the rotor blades. Fairly spectacular effect, though.

-Meister
Twin Cessna 812 Victor, Minneapolis Center, we observe your operation in the immediate vicinity of extreme precipitation
 
copter808
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Joined: Sat Dec 30, 2000 1:14 pm

RE: Helicopter Flight Question-see Video

Sat May 19, 2007 3:09 pm

Wow! That's some really cool photography--and careful monitoring of the rotor rpm.

As said above, the frame rate matches the rpm, or a harmonic of it.

If the rotor was not turning, you would notice more coning, (blades bent upward) and a much higher (vertical) rate of descent!!!

...followed by a "Splat!"
 
bio15
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Joined: Fri Mar 23, 2001 8:10 am

RE: Helicopter Flight Question-see Video

Sat May 19, 2007 5:18 pm

Every time the camera snaps a video frame the blades have turned an angle equal to the angular separation of the blades amongst themselves, or twice that angle, or three times,... It depends on the camera framerate and rotor RPM. What seems as one stationary blade is actually blades 1, 2, 3, 4 & 5 caught in the same position by the camera in fractions of a second. It is also noticeable on the tail rotor which seems to turn very slowly when it really isn't.

Wonderful video, that's a nice effect!  thumbsup 
 
heliflyerPDC
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RE: Helicopter Flight Question-see Video

Wed Jun 13, 2007 7:35 am

WOW, thats all I can say

Are there any other video's like this one ?

grtz PDC
grtz PDC
 
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Scooter01
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RE: Helicopter Flight Question-see Video

Wed Jun 13, 2007 9:01 pm

Quoting HeliflyerPDC (Reply 4):
Are there any other video's like this one ?
Check out the video in reply #6 by TRVYYZ in the "AC777-300 Engines" topic in the Civ.Av forum.

The white spiral on the black spinner seems to be moving a lot slower than it actually does during take-off and watch it change again when climb-power is increased.

Scooter

[Edited 2007-06-13 14:08:10]
There is always a good reason to watch airplanes
 
ikramerica
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Joined: Mon May 23, 2005 9:33 am

RE: Helicopter Flight Question-see Video

Mon Jun 25, 2007 8:17 am

It's not just framerate but also shutter speed. This must be a high shutter speed or the rotors would be blurred anyway. The rotor is going at 6-7 Hz, or 0.14 sec per rotation. So, I'd imagine a shutter speed of 1/1000 second or so could give this effect, matched with a multiple of the fps to keep it from moving too much.

408 rpm would do it, which is a viable rotation speed for a rotor. Or 400 rpm if the footage is from 25fps video or film and not 24 fps film. Both are viable.
Of all the things to worry about... the Wookie has no pants.
 
N231YE
Posts: 2620
Joined: Tue Jul 25, 2006 9:24 am

RE: Helicopter Flight Question-see Video

Mon Jun 25, 2007 10:43 am

I think there is (or was) a thread going in Civ Av about this. The illusion is created by the shutter speed of the camera, and/or the framerate mirroring that of the speed of the rotors. Great illusion!

[Edited 2007-06-25 03:49:50]
 
sprout5199
Posts: 1681
Joined: Sat Feb 26, 2005 8:26 am

RE: Helicopter Flight Question-see Video

Mon Jun 25, 2007 10:53 am

Quoting N231YE (Reply 7):
I think there is (or was) a thread going in Civ Av about this. The illusion is created by the shutter speed of the camera, and/or the framerate mirroring that of the speed of the rotors. Great illusion!

NOPE, there was a lot of birds in there flapping their wings just after it took off from a conveyor belt.

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