Wobble during fast descent

[gogowanda]

Hi,

I was flying my phantom 2 w/ gopro attached. When I was doing a fast descent it started to wobble left and right. I pull it up and it stabilized. So I figured what was the issue, i moved it to a grass area and tried fast descent again and this time i couldn't pull it up. It started pulling with wobble and hard bounced off the land (thank god it was just grass!).

Is this common? My stick was almost all the way to the bottom, but i don't understand why it will wobble so violently.

thanks

Daz
a new p2 pilot

 

[canadavenyc]

were you descending straight down, or was there some lateral movement in addition? If straight down, could it have been due to vortex from your own props?

 

[gogowanda]

were you descending straight down, or was there some lateral movement in addition? If straight down, could it have been due to vortex from your own props?

It was straight down. it's not spinning but just violent left/right swing. I can pull it up if i catch it early.

 

[canadavenyc]

Try some lateral movement while descending...see if that's smoother. I'm putting my money on descending into your own "prop wake turbulence", as it were.

 

[DaveTown]

were you descending straight down, or was there some lateral movement in addition? If straight down, could it have been due to vortex from your own props?

It was straight down. it's not spinning but just violent left/right swing. I can pull it up if i catch it early.

Do a search of the forum for "vortex ring state" or "settling with power". You are descending into your own propwash.This can be avoided by moving forward, backward, or to either side while you are descending.

 

[gogowanda]

thanks guys! i'm gonna give it a try today.

 

[QYV]

DaveTown nailed it. rotary wing aircraft, when descending straight down can descend into their own prop wash (disturbed air) causing loss of lift. if you understand the physics involved, simply giving it lift/thrust doesn't fix it - you NEED to move the other stick ( go forward/backward/left/right ) to get into "good" air and get lift back.

one thing I didn't see mentioned is that in Firmware version 2 or 3 they put in a "rate limited descent" to help guard against it. They made the max descent rate I believe 3 meters per second which is still enough to bonk pretty hard on landing, but if you're up in the air having that limited rate of descent should avoid a vortex ring state

knowledge is power, spend 2 minutes watching this video for visualization

 

[gogowanda]

DaveTown nailed it. rotary wing aircraft, when descending straight down can descend into their own prop wash (disturbed air) causing loss of lift. if you understand the physics involved, simply giving it lift/thrust doesn't fix it - you NEED to move the other stick ( go forward/backward/left/right ) to get into "good" air and get lift back.

one thing I didn't see mentioned is that in Firmware version 2 or 3 they put in a "rate limited descent" to help guard against it. They made the max descent rate I believe 3 meters per second which is still enough to bonk pretty hard on landing, but if you're up in the air having that limited rate of descent should avoid a vortex ring state

knowledge is power, spend 2 minutes watching this video for visualization

watched the vid, feel like I can ace a highschool physics test now