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altitude drop in a hover while landing

Discussion in 'General Discussion' started by spitfire44, Aug 19, 2014.

  1. spitfire44

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    I might be missing some pertinent info describing this, so please let me know if you need more details.

    I am flying my P2 with H3-3D, gains are stock except I am running at 200/200 on the attitude rather than 240/240.

    Flight mode was in GPS mode.

    Several times yesterday in low to mod winds 5-10 mph, but sometimes flat, as I came in to land the P2 would start to drop but recover. I was descending around .3 - .5 meters per second, what I think is not an extreme descent rate. This happened twice at an altitude of about 10 - 12 meters. First time, the bottom dropped out, I released the sticks and the P2 recovered. Second time, same thing, but the P2 didn't recover fast enough and had a hard landing. No damage incurred except a chipped prop.

    What can I do to determine the cause of this and avoid it in the future.

    as a side note, I have about 4 - 6 hours of flight experience on this none of which are in ATTI mode.

    Thanks in advance,

    Eric
     
  2. ProfessorStein

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    You were descending into your own prop wash, otherwise known as Vortex Ring State. Happens in all modes, and to every type of rotor craft. You can read more about it by searching in these forums, but basically the easiest way to avoid it is, as you're descending, always make sure you're applying a little bit to the other stick so you're also moving laterally. You're basically skirting out of the bad air that forms under your Phantom before it has a chance to affect lift.

    I'll typically come down in a zig zag pattern. Others prefer a spiral.
     
  3. spitfire44

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    Prof, Thanks for the insight. Just to add some info to those following. There was NOT any wiggle on the P2 before it lost lift AND I have props guards on which after looking through the forum I noticed might be a bad idea aerodynamically. Any thoughts on that?

    Eric

     
  4. N017RW

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    I know many of these type videos have been posted but here's one involving the V-22. Unfortunately loss of life occurred and this appears to have been produced for the investigation(s).

    Note:This contains is animation only.


    https://www.youtube.com/watch?v=wddpsnvu0PM
     
  5. ProfessorStein

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    I would say a wiggle is a common symptom of oncoming VRS... but it's not necessarily ALWAYS present.

    The only other thing that could cause a drop like you describe would be if you momentarily lost power to all four motors... but since easing up on the throttle brought recovery, and since you did not indicate that there was any oddness in the sound of the motors (ie - sudden loss), it's a reasonable assumption that it was not power loss but VRS.

    Some people say the prop guards heighten VRS, some disagree. But, really, for me, prop guards are a bad idea to fly outside anyway, since they can so easily snag on things.
     
  6. bgb1996

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    Prop guards are the best way to break props if your copter tilts on take off or landing. I had the same problem at a moderate speed. Got about 50 feet from landing and it kept descending, tried reversing thrust and nothing. Thanks for the advice about dirty air.