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Helicopter Flight Question-see Video  
User currently offlineMirrodie From United States of America, joined Apr 2000, 7444 posts, RR: 62
Posted (7 years 7 months 2 weeks 2 days 3 hours ago) and read 2933 times:
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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
8 replies: All unread, jump to last
 
User currently offlineMeister808 From United States of America, joined Jan 2000, 973 posts, RR: 1
Reply 1, posted (7 years 7 months 2 weeks 2 days 3 hours ago) and read 2929 times:

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
User currently offlineCopter808 From United States of America, joined Dec 2000, 1138 posts, RR: 3
Reply 2, posted (7 years 7 months 2 weeks 1 day 21 hours ago) and read 2903 times:

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!"


User currently offlineBio15 From Colombia, joined Mar 2001, 1089 posts, RR: 7
Reply 3, posted (7 years 7 months 2 weeks 1 day 19 hours ago) and read 2895 times:

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 


User currently offlineHeliflyerPDC From Belgium, joined Sep 2006, 128 posts, RR: 0
Reply 4, posted (7 years 6 months 3 weeks 4 hours ago) and read 2591 times:

WOW, thats all I can say

Are there any other video's like this one ?

grtz PDC



grtz PDC
User currently offlineScooter01 From Norway, joined Nov 2006, 1214 posts, RR: 8
Reply 5, posted (7 years 6 months 2 weeks 6 days 15 hours ago) and read 2526 times:
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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]


"We all have a girl and her name is nostalgia" - Hemingway
User currently offlineIkramerica From United States of America, joined May 2005, 21590 posts, RR: 59
Reply 6, posted (7 years 6 months 1 week 2 days 4 hours ago) and read 2246 times:

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.
User currently offlineN231YE From , joined Dec 1969, posts, RR:
Reply 7, posted (7 years 6 months 1 week 2 days 1 hour ago) and read 2225 times:

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]

User currently offlineSprout5199 From United States of America, joined Feb 2005, 1855 posts, RR: 2
Reply 8, posted (7 years 6 months 1 week 2 days 1 hour ago) and read 2222 times:

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.

Dan in Jupiter


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