Home Forums Air and Sea Air TU-95 Bear Propellers? (BBC)

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  • #18039
    Admin Test Account
    Participant

    The author of this topic requested their account be deleted.

    This topic has been kept by attributing the original post to an admin account, and replacing the initial wording by the now deleted user with this.
    To have deleted the topic in its entirety would also have deleted the replies of others, and it is not fair that their postings be effected.

    – Mike.

    • This topic was modified 3 years, 2 months ago by Mike.
    #18045
    John D Salt
    Participant

    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,

    John.

    • This reply was modified 6 years, 5 months ago by John D Salt.
    #18054
    John D Salt
    Participant

    …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.

    #18056
    Mr. Average
    Participant

    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.

    #18103
    Not Connard Sage
    Participant

    Tu-95s have contra-rotating propellers on the same shaft which amplifies the effect.

     

    watch this vid

     

    http://theaviationist.com/2015/02/15/bear-contra-rotating-blades/

    "I go online sometimes, but everyone's spelling is really bad. It's... depressing."

    #19841
    Jemima Fawr
    Participant

    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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