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Uncontrolled descent, couldn't throttle up for lift

Discussion in 'Phantom 2 Vision Discussion' started by dbcch, Jan 11, 2014.

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  1. dbcch

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    So, I long ago noticed, as have many others I think, that descending too rapidly can cause flight instability. These days I descend fairly slow and try to give it a little directional momentum to keep it out of its own wake.

    Anyway, today I was flying the Phantom 2 Vision, descended just a bit, and it suddenly started dropping like a rock. I was about 30 feet off the ground, and despite my attempt to throttle up, it just kept falling until it got to the ground, at which time it finally got lift and softly 'bounced' off the grass.

    What happened?

    Was this being caught in its own wake? Maybe since it's heavier than the Phantom 1 it is more susceptible to descent problems?

    Or maybe a controller problem?

    Battery was fine, and I continued flying 10 minutes after bouncing off the grass.

    I do have a video of this event, though it's probably not too helpful.

    p.s. should I bother to update the RC firmware? Since I have to open it up, I have put that off.

    Thanks!
     
  2. W.A.R.

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    What was your battery percentage? I find this happens if I am below 25%. Otherwise it is not a problem.
     
  3. iDrone

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    Yes... If you're Vision is running v1.05 or later (v1.08 current) the controller needs to be upgraded to v1.0.2.22 2013-11-05. DJI advises upgrading only one may result in communication failures.

    iDrone
     
  4. Pull_Up

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    Sounds exactly like Vortex Ring state: http://en.wikipedia.org/wiki/Vortex_ring_state

    More power makes it worse. Reduce power and move out of your propwash. Always try and have a little lateral or spiraling movement when descending and you'll never encounter it again. Sounds like ground effect saved you from a harsh impact at the end. Phew! :)
     
  5. dbcch

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    Thanks guys!

    The Vortex Ring state is a reasonable explanation, and along the lines of what I thought. Thanks Pull_Up!

    The more I read about it, the more sure I am that this was it. More throttle just made it worse.

    And, yes, it was a very, very close call - if it didn't get *some* lift as it finally got to the ground it would have impacted much harder. It barely touched the ground, thankfully.

    I've not seen this happen again, though am being pretty cautious.

    I will go ahead and update the RC firmware.
     
  6. estahlhammer

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    This has happened to me 3 times. It is really disconcerting when it happens. It is NOT related to battery and has happened both at 8,000 ft and sea level. Throttle didn't work and I had zero control. Distance from transmitter wasn't really the issue either. each time I was I was about 80' away or less and had spend more than 20 min in that range without hiccup.

    I would buy vortex ring state but am going to see if I can cause it to happen and practice getting out of it a few times. Its pretty crazy to loose lift and not be able to recover.
     
  7. dbcch

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    Ah, glad someone else has seen this!

    Yes, battery for me was 70% or so, and I was within 20 feet when this happened. It certainly was no auto-landing or anything, nor did it lose power. I kept flying 10 minutes after it bounced off the grass.

    It was so noticeable and disconcerting because normally I *always* have precise control of the Phantom.

    Do let us know if you are able to force a Vertex Ring State. I have a DJI Phantom 1 w/o camera that I may also experiment with, though I need to add some weight to it to emulate the Phantom 2's flight characteristics.

    EDIT: A lack of wind probably would contribute to this problem, if the hypothesis is right. On the day this happened there definitely wasn't much wind, especially at my low altitude. With wind, I would imagine the wash gets blown away.
     
  8. DanCH

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    So if a Phantom goes into VRS, best fix would be to pitch down in a direction to get out, like a real Heli?

    Would be interesting to see what the "Dead mans curve" is for a phantom.
     
  9. dbcch

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    Being too lazy to clip and re-upload, you can see this incident from FPV perspective here:

    [redacted]

    Go to 1:30 to see. Not sure it'll be enlightening in any way, but you do see the very rapid uncontrolled descent.

    There is a second quadcopter flying around. Ignore it.
     
  10. theSelf

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    I'm a full scale helicopter pilot- and yes it does sound like vortex ring state- commonly known as 'settling with power'- where the helicopter settles into its own downwash/unstable air and adding power actually increases the descent rate- very dangerous for real helicopter pilots and and can end up damaging your RC aircraft which is still upsetting.. best option if this occurs (if altitude permits) is to regain forward airspeed (nose forward) and reduce power a little-forward airpseed adds what is known as 'translational lift' (from the airflow over the rotor airfoils from forward movement above a certain airpseed- it demands more power to stay in a hover with no forward airpseed than it does to fly forward (or backwards etc)- not only when descending vertically at too high a rate settling with power can especially also occur if descending at a steep angle, whilst moving forward with a tail wind (the tail wind will blow the downwash vortices into the path of the aircraft, equally causing instability/reduced lift- so best option is to always avoid descending at too high a rate in forward motion with the wind behind the aircraft and avoid descending vertically at too high a rate..always in these circumstances descend as slowly as you can, particularly if in a hover or at low airpseed- note you can have zero ground speed whilst having some airspeed- ie. when in a hover with the nose of the aircraft into a fairly strong wind- ie. the wind's airflow over the rotors creates the transitional lift forward airspeed creates
     
  11. dcoski

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    Looks like you flew into the other "Drone's" prop wash.
     
  12. dbcch

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    No. Did you just say that or what? It was nowhere near the other quadcopter.
     
  13. dbcch

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    After doing some more research, I've learned that other people have seen this as well - one having commented here in this thread. They experienced the *exact* same condition.

    Again, since someone will ask, this is not a battery charge or communication issue. It's a flight control issue. It loses altitude rapidly and can't be stopped even with full throttle. If it ever happens again, I'll try to steer forward/left/right to see if I can get out of it.

    The best video of the problem I've attached below:

    [youtube]http://www.youtube.com/watch?v=fXhqkvROlOM[/youtube]

    Vortex ring state? Who knows. This particular video is of a Phantom, not a P2V.. but apparently he added a good bit of weight to his Phantom, so maybe that made it behave similar to what I've seen with the P2V.
     
  14. Jerrygrubbs

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    I have experienced two vertical descent crashes with total loss of control. The first was about 60 feet in the air coming down vertical and hit the ground bounced upside down. Battery was at 60%. Second vertical descent crash occurred about 5 feet above the ground while in hover mode with 35% battery. Quad copter dropped and crashed. Both times the quad copter hit hard enough it bounced and landed upside down and when located the props were still trying to turn. Once it was picked up it went to full power. Both instances created total loss of control. I was not able to give it power or have it move in any direction. I sustained prop brakes on both crashes. This was certainly no automatic landing. Neither crash occurred after the initial 30% battery warning. Both crashes occurred within 100 feet of the transmitter. Conditions at the time of both crashes was light wind. During the first crash the quad copter firmware was 3.0. The second crash occurred with firmware 3.04. Calibration test had been run on the transmitter and the quad copter just prior to the second crash. Prior to these two crashes the quad copter had flown approximately 40 times without incident. I would appreciate any help or advice someone might be able to give me to solve this problem. My application involves flying over some bodies of water and I would like to resolve this problem before I lose the quad copter in an uncontrolled descent into water.
     
  15. dbcch

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    It happens. Nothing to do with calibration or battery.

    I have seen many other reports.

    I believe this is why they keep lowering the maximum descent rate, hoping to mitigate these occurrences. When it happened to me I wasn't even descending, had just come to a stop. However, even when you are NOT descending, the craft can start to descend just a little, and if you throttle up (natural reaction) it will exacerbate the situation.

    It's not happened to me again, knock on wood .. maybe because I now am very careful to add lateral movement whenever I see such a condition as a possibility. Or maybe newer firmwares have helped, or maybe I've just been lucky. Actually, it only happened to me with the P2V, not seen it with the P2V+ (though others have).

    It did forever change my confidence in flight though, I'm always aware that this could happen, so fly accordingly (even though it never has again, like I said). I still fly over water and such, this doesn't limit me... it's more about flying over people, I don't do that. I figure the moment you put a craft into the air you have to accept the risk of losing it.. but the trick is to make sure you don't injure or damage anyone else's property.

    EDIT:
    As I just said, it hasn't affected my confidence over water (sorry, love to share ;p). Video not relevant to isssue
    [youtube]http://www.youtube.com/watch?v=vhAaOuOqQ9o[/youtube]
     
  16. Kelso Kubat

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