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Erratic descending ...

Discussion in 'General Discussion' started by Dobmatt, Aug 21, 2016.

  1. Dobmatt

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    I've noticed that during fast descend (throttle stick fully down) both Inspire and Phantom exhibit the tendency to abruptly yaw side to side, no matter what wind conditions. It's a bit unpleasant behavior, like the bird is about to enter into infamous "toilet bowl" rotation. I can hear motors trying to compensate with desperation. Is it normal? All I know is switch to Atti Mode when such uncontrolled rotation happen. Still, it's "white knuckles" situation with this descending ...
     
  2. The Editor

    The Editor Moderator
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    It is because you are descending into your own prop wash which is turbulent air.
    Although there have been very few cases of VRS (Vortex Ring State) with the Inspire (which is why it's descent speed is limited) it can happen so be aware.

    You will never get completely smooth decent coming straight down because of the 'dirty' air from the props.
     
  3. Dobmatt

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    Aha, it makes perfect sense, wasn't thinking ... So, fast descent with horizontal movement should minimize the wobble ... Must practice that tomorrow. Thank you, Sir ...
     
  4. DennisR

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    I was always taught to descend at an angle to avoid prop wash if coming down fast.
     
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  5. lake_flyer

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    Throttle stick to neutral cancels VRS in any mode. After it has settled, bring it down with nose in wind, in a 'glide' slope. The more headwind, the shorter the final approach can be.
     
    #5 lake_flyer, Aug 22, 2016
    Last edited: Aug 22, 2016
  6. Dobmatt

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    Luckily I've never experienced VRS, but thank you for the advice. Some pilots recommend switching to Atti Mode after zeroing the throttle stick. However, just tested fast descend in cycled forward/backward (vertical zig-zag) style and it seems to work much better.
     
  7. Tubbyengineer

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    If you have to come down fast the safest way is to adopt a glide slope or "falling leaf" flight path, both of which avoid flying into your own prop wash and entering a VRS. Failing that you will just have to moderate your decent speed, a little bit of wobble can be compensated for by the flight controller but it's better to avoid if possible, I'm unsure how switching to Atti mode would help - unless it's come from pilots who have a tendency to "Bias" their flight slightly to one direction - in atti mode it would mean you would always experience a slight movement away from a directly vertical descent...
     
  8. Dobmatt

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    Thank you for advice ... For last few days I was practicing "falling leaf" technique and it works perfectly. Thing is I'm flying far and high recently, filming the beautiful mountain surroundings of Arrow Lake in BC. Far for me means 1km, still within LOS. For Inspire it's about 12-15 minutes flight, asking for fast return home from 250-300m altitude. So far so good ...
     
  9. Tubbyengineer

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    If you're decending from that height then you could always take an extremely steep glide slope, 5mph+ / above prevailing windspeed (If flying with a tailwind) should be enough to keep out of the propwash (something around a 70 deg angle)...
     
  10. Dobmatt

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    Yeah, that's what I do ... Usually make 2 or 3 takes until I get everything right (the flight path, speed, framing, aperture etc.), always doing fast and straight glide down home with at least 40% battery left ... If my math is correct that is about 30deg slope (from 900m away and 300m high)? Gee, I'm getting old ...
     
  11. lake_flyer

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    If you have a steady wind from one direction you can come straight down in GPS. As long as you have airspeed. Always keep the nose in the wind while descending, don't descent fast with a tail wind. Determine you landing area and possible approaches before take off. The wind direction can change. But if there's enough wind, just come straight down.
     
  12. AeroMirage

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    I always move forward slightly while descending for this reason. Works well.
    NEVER descend in reverse or the dreaded CSC could drop you like a rock!!
     
  13. lake_flyer

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    I never descend in reverse but turn it usually nose out prior to the final landing.
    Good point. The CSC position is not far away while descending at full pitch in reverse. But descending at full pitch, with throttle at minimum is not something I would do at all. Not even in forward.