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Ring vortex...more of a problem in calm air??

Discussion in 'General Discussion' started by usaken, May 29, 2014.

  1. usaken

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    I was just thinking, if you are flying your bird in say a 5 mph wind, and the bird is standing still and descending quickly, it must be flying through the moving air at 5 mph to hold position. Is that enough to counter ring vortex? Clearly, this is more of a problem in still air? Thanks
     
  2. Gotcher6

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    Re: Raring vortex...more of a problem in calm air??

    Yep, it's all about air speed. If you're hovering and descending in 5 mph wind, it's like flying your drone forward at 5 mph while descending with 0 wind.
     
  3. N017RW

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    Re: Raring vortex...more of a problem in calm air??

    Think of it like a smoke ring, you may have seen, but horizontal or parallel to the ground and encompassing the rotor blades.

    Always combine lateral motion in any direction with your descent unless there is a breeze which can essentially have the same effect and always try to land facing the wind.

    Google the Vortex Ring State and you'll find tons of information, graphics, and videos illustrating the phenomenon.

    Or go here: viewtopic.php?t=7923&p=64487.
     
  4. QYV

    QYV

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    regardless of how it happens, you'll know you're experiencing a VRS if the Phantom begins to drop out of the sky like a stone straight down and throttle commands don't do anything (like you're pushing up and it just keeps falling). The only way out of it if you can remember in time, is to slam the LATERAL movement stick in any direction. The disturbed air that you can't generate lift in is directly below you, so moving laterally is your best chance for getting back into "good" air.
     
  5. JRapt

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    In the situation you mentioned you will have 5mph airspeed and 0 groundspeed so you're correct.

    Hope this helps guys!

    The following combination of conditions is likely to cause
    settling in a vortex ring state in any helicopter:
    1. A vertical or nearly vertical descent of at least 300
    fpm. (Actual critical rate depends on the gross weight,
    rpm, density altitude, and other pertinent factors.)
    2. The rotor system must be using some of the available
    engine power (20–100 percent).
    3. The horizontal velocity must be slower than effective
    translational lift.
    Some of the situations that are conducive to a settling with
    power condition are: any hover above ground effect altitude,
    specifically attempting to hover OGE at altitudes above the
    hovering ceiling of the helicopter, attempting to hover OGE
    without maintaining precise altitude control, pinnacle or
    rooftop helipads when the wind is not aligned with the landing
    direction, and downwind and steep power approaches in
    which airspeed is permitted to drop below 10 knots depending
    on the type of helicopter.
    Reference: http://www.faa.gov/regulations_policies ... h_ch11.pdf
    JRapt Posts: 8
     
  6. N017RW

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    There is tons of info and study on this with regards to 2 rotor aircraft (main and tail) but none that I could find with regards to multi-rotor.

    Therefore I'm not convinced that anyone knows how VRS and related phenomena may be enhanced or reduced by the configuration of multi-rotor a/c and if traditional methods can be used to escape from it.

    Compared to my Trex 450, the Phantoms seem much more prone to it (FWIW).
     
  7. Big Ben

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    There's also an essential difference between helicopters and our quads most likely making the do's and don'ts for VRS recovery different too.

    Helicopters have variable pitch rotors and our birds have fixed pitch rotors. Since VRS is caused by (partially) stalled rotor blades 'pulling up' is the wrong thing to do in helicopters since that increases collective pitch and increases the Angle Of Attack of the rotor blades which aggravates the stall. When we increase throttle the speed of the blades increases which should decrease the AOA and reduce/resolve the stalled state. But the four props will undoubtedly influence each others air dynamics and when it starts to wobble the aerodynamics are likely to be complex.

    I would be interested in any work done on this subject with computer simulations. If real-life behaviour could be reproduced in such simulations then these could probably be used to better understand and help prevent VRS in multirotors and the recovery from it.
     
  8. N017RW

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    Yes to your last paragraph and how the prop guards interact as well.
     
  9. Kelso Kubat

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    i had VRS on my first flight, and was very windy. 25-35 winds. gusts over 40+
    hooked it hard left and corrected really hard and immediately went into VRS.
    hasn't happened since but WTF... :shock:
     
  10. N017RW

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    With those kind of winds I'd guess you were in a down-draft.
     
  11. d4ddyo

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    LOL... you should know not to be flying in winds over 25 mph. Are you a storm chaser or something? LOL
     
  12. ORPER

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    Nice to know now why the P2V+ behaved like it did and how lucky I was because mine must have fallen through the Ring Vortex since it stabilised again but the downward speed was to great for it not to hit the ground quite hard but on a relatively soft surface and just full speed up again.

    Got very surprised but the phantom is all ok even acted that and now i know.

    Sent from my Nexus 7 using Tapatalk
     
  13. Airmotive

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    FYI, that was certainly not a VRS event.
    I don't know what was around you in your immediate flight area, but I would hazard to guess that there were structures, trees etc that caused near-ground-level rotors, that were beyond the control capabilities of your Phantom.
     
  14. CarlJ

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    I'm a freak and like to watch mine hover. I've noticed that changes in air pressure either over or under the Phantom will cause changes in altitude. I'm thinking flying in high wind is problematic.
     
  15. AndysAdventures

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    I read that line 5 times to help me remember. :)

    My first few flights yesterday went really well. Although I didn't go very high or very far.

    I did remember to not descend while hovering. I always started descending while flying slowly back to my home point.