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Best way to scrub altitude?

Discussion in 'General Discussion' started by Diesel31, Jun 18, 2014.

  1. Diesel31

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    Move back and forth, never straight down.
     
  2. varmint

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    What he said. If you go straight down with too little lateral or longitudinal velocity, you can introduce vortex ring state which can potentially ruin your day. DJI attempted to address this by capping the maximum vertical decent rate at 2M per second in the last firmware update, but even that can be too fast depending on conditions. Personally I'd rather make my own caps, and I have no idea why they didn't just set that as the default rate and allow you to modify it (within reason) via the assistant.

    Anyway, just make sure you're moving horizontally (relative to the air mass) when you descend. Wind alone will not protect you, since the unstable air you create under your pops is moving WITH you if you unless you have your own velocity.
     
  3. wkf94025

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    Two answers to your two questions. Some would say best is to learn how to fly Manual mode, enable it briefly (perhaps using momentary switch if your radio has one) and let motors idle. You will scrub altitude in a hurry that way. Then some safe distance before impact, switch back to ATTI or GPS mode, and let Naza save your ***, perhaps with upwind right stick to get out of the down elevator.

    The above method is by no means the safest. Safest is to move upwind at several meters per second, and pull left stick down until you're descending at 1 meter per second or so. If you don't have enough battery left, your f*cked. In which case branch to best method above.

    Best to avoid flying above 200m AGL until you have mastered the above.

    Kelly
     
  4. wkf94025

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    Also, heard some great stories this weekend from a buddy who trained Chinook pilots in Afghanistan. The brown trowser moments for rookie pilots when one rotor entered/exited clean/dirty air and the other rotor had not. Check out the possibilities with the beast with two rotors:

    [youtube]https://www.youtube.com/watch?v=laYw9YFRZa8[/youtube]
     
  5. chuddly

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    I am by no means a pro and maybe someone will pipe up and tell me how i am doing it is wrong (and thats fine). But when space is tighter and i need to scrub some height I go down in a spiral pattern. Kind of like if you were circling something and decending at the same time. Only reason i think this is better than straight down is because by the time my quad gets back around to a fixed location in the circle that it has already been I am now MUCH lower and plenty of time has passed so the air should be cleaner(at least in my mind). Dont know if its right or wrong but it has worked for me thus far.
     
  6. Jebus

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    If a person is moving forward fairly quick (say right stick up all the way - or close) and down (left stick down), can a person descend quickly that way? I'm thinking kind of how chuddly explains - going in a downward spiral.

    My thought is that as long as you're moving forward and descending, you should be out of your prop wash - right? Then you could hopefully descend fairly quick without having to worry about VRS. Would this work ok - or is there a good chance it would still get caught up in it's prop wash and fall from the sky?
     
  7. wkf94025

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    I agree with Chuddly that the corkscrew down is a good technique in tight quarters. My instincts are that straight-ahead descents are safer, and I sometimes slide forward and backward while descending. However the corkscrew is helpful at times. Also, by playing with amount of forward right stick during the corkscrew, and/or amount of yaw, I can do non-circular descents that bring me closer to home while bleeding altitude (i.e., tigher turns when facing away from home, more open turns when within 90 degrees of straight home).

    Re Jebus' question, in my experience it depends substantially on your All Up Weight. If you're flying heavy, I would be cautious about the corkscrew or descent rates greater than 0.8m/sec. Unless you find VRS fun, which I do but only at altitude.

    Kelly
     
  8. chuddly

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    I agree that straight line or something other than "The corkscrew" (we have a new term now LOL) is safer by far. I was only throwing that in for the tight quarters scenario and a majority of the time I do use straight line decent.
     
  9. Jebus

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    My Phantom v1.1.1 weighs in at around 1200g and I usually descend around 2m/s (sometimes I notice I'm going quicker - more like 3m/s) and haven't had any issues - even coming straight down at those speeds. I can't say for sure what speeds I've reached descending while going forward, but I'll have to watch for that now. Luckily I haven't had to deal with VRS yet!
     
  10. wkf94025

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    Try adding 200g somewhere on your P1, and I think you'll have some exciting descents at those rates! ;)
     
  11. Jebus

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    That doesn't sound fun! haha
     
  12. GreenMarine

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    Very glad do see someone else promoting the proper rotary-winged flight :)
     
  13. wkf94025

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    The stories from Afghanistan are separate from the impressive flying of the Chinook test pilot. Agree the vid is impressive. Just helps one imagine what a rookie pilot might experience when his ship unexpectedly goes nose way up or way down in a hurry as a function of one rotor suddenly seeing very different air than the other.

    Kelly
     
  14. wkf94025

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    I pulled my GoPro and H3-3D off my P2 and put on a Fatshark 600TVL pan & tilt camera ($80 from getfpv.com) for some Manual Mode experimental flying today. Short summary is that switching briefly into Manual Mode as a method of dropping altitude in a hurry works very well. I started at 200 meters and tried brief forays into Manual Mode, from a stabilized GPS hover, and with no stick inputs other than in/out of Manual Mode. Descent rates ranged from 5 to 10 m/sec, and NAZA seemed good at recovering stable hover upon flicking mode switch back into GPS. Note however those descent rates are without GoPro and Gimbal. I would expect higher descent rates with a fully loaded bird, and somewhat less chances of a successful recovery. Of course one can always nibble at Manual Mode, a few seconds at a time. I went for several 10 second drops, losing between 50 and 90 meters each time.

    I only switched into Manual Mode by accident once, at a fairly low altitude, and that convinced me that having a 3-way switch for GPS/ATTI/Manual is just plain dangerous. (I am used to GPS/ATTI/ATTI on that switch.) I saw a post elsewhere where a Futaba pilot used the SH momentary switch for Manual Mode. I think that's an excellent idea: stay in Manual Mode only so long as you actively hold that switch in the up position.

    Video of the descents and recoveries soon. Oh and BTW, I did at least 4 inadvertent barrel rolls with the stripped-down P2, which weighs 1070 grams when free of GoPro and Zenmuse. I also wired the pan and tilt functions on the Fatshark camera into unused channels and switches on the Futaba 14SG radio and R7008b receiver, but that's OT here.

    Kelly
     
  15. Jebus

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    I'm not sure what speed the Phantom's fail safe descends at, but I would guess it's probably around 2m/s. I assume that if VRS was that big of an issue descending straight down at that speed, you'd hear about it more often.
     
  16. Wedeliver

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    I went looking but I could not find a thread where I think it said that DJI was releasing new props to help with the issue you speak of above. It was maybe a 1 week ago but I searched and I just don't remember what the subject was where this was mentioned. I think we all have an interest in this especially if we like to fly loaded.
     
  17. OI Photography

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    This one: viewtopic.php?f=4&t=20292

    Looks to be very soon too, since they're already putting them in the retail packaging :)
     
  18. Timtro

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    Weather (air temp, humidity - air density) may be playing a part (?)
     
  19. scottro

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    I'm always afraid that I'm going to turn the motors off while descending. Will the motors shut off if you are pulling straight down on the throttle while moving forward with the other stick?