- 20/02/2015 at 14:34 #18039Admin Test AccountParticipant
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20/02/2015 at 16:21 #18045John D SaltParticipant
- This topic was modified 3 years, 2 months ago by Mike.
Tim, surely you’re old enough to remember watching Westerns on the telly where the wagon wheels appeared to be going round backwards?
This is the same thing. The sampling rate on the camera is small compared to the rotation rate of the blades of the airscrew. I believe the Bear’s engines drive the airscrew at about 750 rpm at cruising speed, and a fairly normal refresh rate for video might be 60 frames a second, so the camera would only “see” the blades about once every dozen turns.
You’ll also notice that on digital film spinning airscrew blades appear bent, I assume because digital cameras scan their pixels, whereas “wet” film sees the whole frame in a oner.
All the best,
20/02/2015 at 17:47 #18054John D SaltParticipant
- This reply was modified 6 years, 5 months ago by John D Salt.
…or, because minutes are not the same as seconds, once every fifth of a turn (3600 frames a minute, 750 revs a minute).
All the best,
John.20/02/2015 at 18:10 #18056Mr. AverageParticipant
It’s an effect common to Russian aircraft, whose engines seem to turn at rates comparable to the frame rate on many video cameras. The “stopped rotor” effect happens a whole lot in videos of the Hind. I’m sure it’s unintentional, unless it’s part of the Russian’s maskirovka, in which case he’s playing the very long game.21/02/2015 at 13:29 #18103Not Connard SageParticipant
Tu-95s have contra-rotating propellers on the same shaft which amplifies the effect.
watch this vid
"I go online sometimes, but everyone's spelling is really bad. It's... depressing."17/03/2015 at 07:21 #19841Jemima FawrParticipant
I took some film of a hovering Lynx (the helicopter, not your old recce runabout!) on my phone and the rotors appeared to be staying still – deeply odd! 🙂
My wargames blog: http://www.jemimafawr.co.uk/
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