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Safe descent speed for straight-down descent

Discussion in 'General Discussion' started by Prime12, Feb 5, 2015.

  1. Prime12

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    Having crashed my RC helis before twice due to VRS, I try to avoid coming straight down whenever possible. However, sometimes it just has to be done for one reason or the other.

    So I was wondering, up to what kind of speed is it generally ok to descend straight down? I try to not descend any faster than 1m/s (most of the time half that really), but it's kind of slow.

    Let's assume it's a Phantom 2, fully loaded with gimbal, gopro, fpv, and iosd (1300-ish grams).
     
  2. p fandango

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    as long as your in gps the software limits the descent speed anyway. I normally do all my flying at low level, but go straight up & straight down for high shots & never had an issue
     
  3. Meta4

    Meta4 Moderator
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    The Phantoms originally could descend at 6 m/sec.
    Dji changed that to 4 m/sec and then to the current snail's pace 2 m/sec to reduce the VRS risk.
    I've been descending straight down at the full 2 m/sec on a hundred or more flights without problem.
    As long as you don't have prop guards, I wouldn't worry.
     
  4. Prime12

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    Hmm, so maybe I'm overly worried about this.

    6 m/s?! Sounds about right for a cinder block in free fall :eek: .
     
  5. crash1sttime

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    I regularly go upto 1000ft for the views, then just hold the stick down to descend, never had any issues with VRS
     
  6. Meta4

    Meta4 Moderator
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    Six metres/sec was fine as long as you had some forward component.
    Now we all have to fly with trainer wheels.
     
  7. TMAN1985

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    Wtf is VRS??
     
  8. Mako79

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    its herpes for phantoms/multirotors.. its not contagious but avoidable if you vaccinate with firmwares 3.0 and up.
    Its essentially gravity being a *****. The phantom creates Vortexes under each prop. There is "dirty air" in the vortexes. If it slips into the "dirty air" it can no longer "grip". This lack of grip is the Vortex Ring State (VRS), basically getting caught in its own prop wash. To prevent, don't throttle, just move fwd or any other direction than up to grip the clean air.

    The Prop guards don't help (yet to be proven), but adding weight makes it more difficult to recover from a prop wash/VRS.
     
  9. TMAN1985

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    Thanks!
     
  10. KMW

    KMW

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    Still new here. Is what I'm seeing when my 1.1.1 is coming straight down and I hear the motors start going crazy changing speeds and it starts wobbling like crazy? I still have the prop guards on, by the way. I kind of accidentally found that just giving any horizontal input gets it smoothed right out.
     
  11. mendezl

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    Phantom software limits descent speed to 2meters/sec. This is pretty slow and easily keeps you out of VRS. When flying high always remember it takes 3 times as long to come down. You can fly up at 6m/sec.

    Now in manual mode there is no descent speed limits.
     
  12. Happyflyer

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    Straight to the ground and: SPLAT! :shock:
     
  13. SteveMann

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    Vortex Ring State. It's why helicopter pilots don't like to hover at low altitudes. The props on your quad are blowing a lot of air downwards to stay aloft. If you descend into this column of air that is already going down, then you are going to go down a lot faster. If you add throttle, all you do is to increase the speed of the column of air below the props, increasing your speed down. To avoid VRS, don't descend into this column of air that your props are generating. Move laterally so that you are descending into undisturbed air.
    http://www.copters.com/aero/settling.html
     
  14. msinger

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    If I must descend straight down, I find it best to descend no faster than 2-3 ft/second (that's about half throttle down). I realize that's extremely slow, but it hasn't failed me yet.

    I've tried full throttle down a few times and noticed my Phantom would sometimes wobble a tiny bit or the pitch of the props would change. Neither happens when I slow down to 2-3 ft/second.
     
  15. Hughie

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    I dont mind the max decent rate for normal use, but where I fly there are plenty of helicopters/light aircraft who see to think it is fine to fly in the 250' to 500' layer. If I end up being obliged to get out of the way quickly my only real option is to CSC into a crash landing. I dont really want or need manual mode for 99% of what I do, but what I wouldnt mind would be an option to set the decent rate in the Assistant when under ATTI.

    They could still limit it to 2 or 3 times what it is, it would all help, I would prefer to have more capability to drop down on a glidepath quickly rather than have to drop the quad in the lake from a CSC.
     
  16. crash1sttime

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    Gonna ask a question , if I'm up at 1000ft and I do a CSC, the quad will drop, would there be enough time to do another CSC to catch the fall and would it auo level or would it need power?

    Time for the mathamaticians to get their calculators out :lol:
     
  17. dirkclod

    dirkclod Moderator
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    Only one way to know for sure bro ;) Report back :D
     
  18. Hughie

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    I'm no mathematician and no aerodynamisict but, some finger in the air calculations.

    If you say that the Phantom can reach a maximum of 50mph in free fall
    See discussion here viewtopic.php?f=4&t=30834&p=284666&hilit=terminal+velocity#p284666

    And assume for the sake of argument that it reaches that pretty quickly, than means it falls 22m per second.

    1000 ft = 305m that means you would freefall for 13s. Which seems like plenty of time :eek:

    Plenty of time maybe ..... but I am not going to be trying it :D

    Here is one attempt, but the pilot did not allow enough time for the quad's thrust to arrest the rate of descent. It's not just about getting the engines started on time, its about thrust overcoming momentum.
    https://www.youtube.com/watch?feature=p ... BvmIJ6mE1U

    Edit: although this "save" appears to be settled in under 100'
    https://www.youtube.com/watch?v=bMbvA2xyPL8
    12:20 to 13:25
     
  19. crash1sttime

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    Not sure that i want to find out, however i may try it one day and will film it.


    I got up to 1600ft this evening, im trying to find out the range of this bloody amazing piece of kit, so far i can get 1612ft FPV at 248ft elevation when running a GS mission,



    and around 1000ft when im just flying LOS, i have switched over to FCC mode and doing the math 500m = 1640ft, so i set my vertical height limit to 1600ft and let it go up, and i lost FPV at 1655ft but not the control signal , which suggests that had i had the FPV i may have gone higher (seemed pointless without the telemetry as i couldnt see if i was going up)

    I just need to get an RE700 now (getting ordered on payday) and i will be changing the height limit to 2000ft and see if i can get that high
     

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  20. wkf94025

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    Manual mode descent at 10m/sec is a LOT of fun and less risky than CSC. Never tried CSC and can't imagine why I ever would.