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Thread: Hey copter folk.

  1. #1
    Join Date
    Jul 2008
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    Default Hey copter folk.

    Wheres the tail rotor?
    What kinda copter is it?
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  2. #2
    Join Date
    Nov 2002
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    Sitka, AK
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    Default Re: Hey copter folk.

    I've seen and heard of this type before. The main rotor appears to be driven by 'tip jets' at the end of the main rotor blades.

    The lack of a transmission between the front of the engine and the main rotor system is obvious. High pressure (and very hot at this stage) air is bled off of the turbine engine at the power turbine section of the engine, and directed up to the main rotor (I say main rotor, even though there is no tail rotor, so I could just say 'rotor') and ducted into the main rotor blades, down to their tips, and exhausted towards the trailing end so the main rotor spins just like it was driven by a transmission.

    In a standard helo, the high pressure air at the power turbine section would be used to turn the power turbine wheels mechanically connected to the main rotor via the main transmission.

    The ability to eliminate the tail rotor is due to the main rotor not being driven through a transmission, hence no torque generated in that axis. I suspect there is still some torque generated because the main rotor is still connected to rest of the helicopter by flight controls and rotor mounts, which will impart some torque. That torque may be small enough to be countered at the end of the tail boom via airfoils reacting to the rotor wash from the main rotor flowing over them in a hover, then airflow during forward flight.
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  3. #3
    Join Date
    Jan 2005
    Location
    Deepest Darkest Wales
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    19,518

    Default Re: Hey copter folk.

    The Fairey Rotodyne also used tip jets...

    Here's a different approach.

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  4. #4
    Join Date
    Jan 2003
    Location
    New Zealand's Far North
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    7,908

    Default Re: Hey copter folk.

    Brian, thanks for that explanation.
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  5. #5
    Join Date
    Oct 2008
    Location
    Walney, near Cumbria UK
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    40,127

    Default Re: Hey copter folk.

    Quote Originally Posted by BrianW View Post
    I've seen and heard of this type before. The main rotor appears to be driven by 'tip jets' at the end of the main rotor blades.

    The lack of a transmission between the front of the engine and the main rotor system is obvious. High pressure (and very hot at this stage) air is bled off of the turbine engine at the power turbine section of the engine, and directed up to the main rotor (I say main rotor, even though there is no tail rotor, so I could just say 'rotor') and ducted into the main rotor blades, down to their tips, and exhausted towards the trailing end so the main rotor spins just like it was driven by a transmission.

    In a standard helo, the high pressure air at the power turbine section would be used to turn the power turbine wheels mechanically connected to the main rotor via the main transmission.

    The ability to eliminate the tail rotor is due to the main rotor not being driven through a transmission, hence no torque generated in that axis. I suspect there is still some torque generated because the main rotor is still connected to rest of the helicopter by flight controls and rotor mounts, which will impart some torque. That torque may be small enough to be countered at the end of the tail boom via airfoils reacting to the rotor wash from the main rotor flowing over them in a hover, then airflow during forward flight.
    I suspect that the exhaust from the engine flowing over that large rudder also contributes.
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  6. #6
    Join Date
    Sep 2010
    Location
    UK
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    933

    Default Re: Hey copter folk.


  7. #7
    Join Date
    May 2005
    Location
    Bradford, VT
    Posts
    6,110

    Default Re: Hey copter folk.

    While on the subject, how does the regular Help transmission work to gear down a tens of thousands RPM turbine to the rotor speeds?
    And gas turbine driven ships too, for that matter?

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