CSC Questiom

Meta4 · Mar 8, 2016

Zzyzx said:
The second point was clarified above in the thread, yes, it's not a good idea to touch down at the max descent rate (2m/s in the current firmware). Not only is it really hard on the bird (pretty much a crash), but you'd probably experience some VRS (Vortex Ring State

The Phantom 3 is immune to VRS at the maximum descent speed which is 3 m/sec. .. (that is without prop guards)
Many P3 pilots have tested this many times with no ill effects at all.
The DJI design engineers offset the motors to reduce VRS and set an appropriate max descent speed so that VRS is not a problem with the P3.
You can descend straight down at max speed from 300 metres in still air and not encounter VRS.

GunnyPapa · Mar 8, 2016

Now I'm confused from the experts.
Guess i been doing it all wrong. When I want to land I use left stick down the whole time, with a few adjustments from right stick at about 5ft or so. Then I just drop left stick smoothly until aircraft touches ground. If I continue to hold left stick the motors shut off as normal. If I am doing a "touch and go" I will do the same, without holding the left stick down, let it idle a minute or less, than just take off as normal.Never had any problems or Vortex Rings or Propwash(When I was in the Marine Corps we used to send young Marines from unit to unit and supply looking for Prop Wash and Size 3 Vortex Ring Tools)

N017RW · Mar 8, 2016

Zzyzx said:
True, VRS doesn't get worse closer to the ground, and ground effect will create a cushion of air to help slow the descent.

But ground effect for a Phantom won't kick in until it's really close to the ground. I don't recall the formula but I believe ground effect kicks in within something like the diameter of the rotor, which for a Phantom is only 6 inches. So, we'll still be subject to VRS even a couple of feet off the ground, close enough that we can easily run out of room to react.

But I was also conflating VRS with close-to-ground turbulence. I don't know what it's called, but the prop wash close to the ground seems to make my Phantom unpredictably drift laterally. If I'm coming in fast, that drift can be the difference between landing where I want vs. on top of clump of grass that makes it tip over.

Anyway, this is getting geeky, I think we can probably agree that a landing at full down throttle is usually a bad idea.

Yea, landing is a skill.

Check this out re: geeky & GE...
http://dynlab.mpe.nus.edu.sg/mpelsb/AEG/2007UAV/ATSIndoorUAV.pdf

Specifically pages 10 -13 for a MR GE experiment(s).

(Spoiler alert: It may be more than a meter above ground).