High altitude decent

Most of my flights so far have been done in fairly windy conditions. In GPS mode doing a straight down descent then is equivalent to flying with a horizontal speed equal to the wind speed. When I descended fast I usually gave some extra stick in the direction of the wind. I think it's a safe habit to make the Phantom fly into the wind when you descend more rapidly. You'll avoid high ground speeds that way.

If there is no reason to do otherwise it might also be a good habit to set Course Lock orientation facing the wind. That way you can always compensate wind drift in CL giving forward stick and do the same when descending rapidly.
 
havasuphoto said:
...and, you were descending without power. Basically, you need to be using around 15% of available power, and descending at least 300 feet per minute, or more, with near zero airspeed, or going backwards into a tailwind.
.....
I would have thought it would be good to go backwards into a tailwind as the propwash would be blown forwards and away from the Phantom .....
 
@pault. Watch some YouTube videos "settling with power" or "helecopter vortex ring state" it's interesting they show some training videos with real helis of putting their self in that predicament and how to recover out of it.
 
pault said:
havasuphoto said:
...and, you were descending without power. Basically, you need to be using around 15% of available power, and descending at least 300 feet per minute, or more, with near zero airspeed, or going backwards into a tailwind.
.....
I would have thought it would be good to go backwards into a tailwind as the propwash would be blown forwards and away from the Phantom .....
That's true-to a point. Doesn't matter which way you go, as long as you flying into the wind. Try to visualize your down wash.
 
I was able to do a fast descent with the P1, but I believe now with P2 and the new style props, there is a greater surface area creating more propwash, more chance of vortex ring state.

This actually happened on my 650 quad with 15" props. I was yawing in a big circle and it just started dropping out of the sky. Lucky for me I was surrounded by 3 feet of snow.... but very scary.
 
I should note that my P2 might be heavier than some ie. has a Zenmus H3-2D Gimbal, GoPro3, a AVL58 VideoLink Transmitter and a Clover Leaf Antenna, see attached photo. After several more flights since the crash, even in high wind, as long as I make angled descents I have no issues.
 

Attachments

  • My Phantom Loaded.jpg
    My Phantom Loaded.jpg
    88.3 KB · Views: 483
I found this video about the physics of SWP quite interesting.

[youtube]http://www.youtube.com/watch?v=HrsGM0PzQFo[/youtube]

It shows how the upward airflow relative to the helicopter exceeds the downward thrust from the blades creating an upward airflow through the rotor disk starting from the centre where the blades have a lower airspeed and create less downward thrust. This will lead to an increase of the AOA of the airfoil eventually leading to a stalled state. This is compounded by the additional vortex created by the stalled inner blades increasing the upward flow of air in the centre causing this area to 'grow' towards the tip of the blades. When this expands outwards with increasing downward speeds as shown an increasing surface of the blade is stalled and does not generate lift anymore.
 
Yea...now multiply that by 4. And, if you have Vision props, you have 40% more down wash than with 8" props. So you can see that multi-rotor systems are not without their faults. VRS is a big one.
 
Checked out some videos of R-22 and R-44 helos recovering from different scenarios, very interesting stuff,,,i saw one video of an instructor describing the ground going by as a conveyor belt,,,keep it rolling towards you when on approach,.i thought that was a cool training aide...from coming into this as a former RC airplane hobbyist (reigniting my passion again with the P2V after 11 years with no sticks on my fingers) i tend to fly it like an airplane, so i guess that may work in my favor, i feel i have alot to learn with the multi-rotor and need the confidence to fly it over water and offshore , lots of good advice on this topic...i know wind and weather play a roll as well with VRS, so the more info we get the better, keep it coming.,,,if this occurs 500-1000 feet from home point and over water it could become a submarine very quickly....i often fly over water and it scares the #^%@ out of me...
 
I had the death wobble happen to me yesterday, funny thing is before I read this thread I always came straight down in a line with no issues, yesterday I thought I wouldn't risk it and came down while moving forward and I got the death wobbles twice, with the second one about 15m off the ground and as you can see in the video I backed off the throttle and had enough altitude to only bump the ground. I did come down too quickly though but have done so in a straight line numerous time before. Here is the video:-

[youtube]http://www.youtube.com/watch?v=x0SbkjRExt4[/youtube]
 
Mattycee said:
I had the death wobble happen to me yesterday, funny thing is before I read this thread I always came straight down in a line with no issues, yesterday I thought I wouldn't risk it and came down while moving forward and I got the death wobbles twice, with the second one about 15m off the ground and as you can see in the video I backed off the throttle and had enough altitude to only bump the ground. I did come down too quickly though but have done so in a straight line numerous time before. Here is the video:-

[youtube]http://www.youtube.com/watch?v=x0SbkjRExt4[/youtube]

The difference between a helicopter and a plane is that the plane will always fly with a minimum speed relative to the air if it wants to remain airborne and not stall and fall out of the sky. A helicopter doesn't have to do that. When hovering stationary above the ground (GPS mode) the wind speed will be the helicopter's airspeed. Descending straight down when there is wind is therefore usually safe.

The concept 'forward' for a helicopter is very different than for a plane. If you're facing downwind 'forward' relative to the ground starting from a fixed ground position will not increase the speed relative to the air but will decrease it. You didn't tell whether you were moving downwind (which you preferably shouldn't do when descending) or upwind or...

It also depends on the flight mode. GPS mode will have your bird hovering stationary above the ground with centred sticks causing 'forward' downwind to decrease the airspeed. If you're hovering with centred sticks in ATTI mode your airspeed will be zero and 'forward' WILL increase your airspeed. Moving downwind will then result in (much) higher groundspeeds than when moving upwind and at some time you'll want to lose that kinetic energy and speed again. The high kinetic energy gives the Phantom the potential to do damage to itself or to whatever it might hit. Flying with high groundspeed near the ground is therefore an increased risk factor.
 
Big Ben said:
The difference between a helicopter and a plane is that the plane will always fly with a minimum speed relative to the air if it wants to remain airborne and not stall and fall out of the sky. A helicopter doesn't have to do that. When hovering stationary above the ground (GPS mode) the wind speed will be the helicopter's airspeed. Descending straight down when there is wind is therefore usually safe.

It also depends on the flight mode. GPS mode will have your bird hovering stationary above the ground with centred sticks causing 'forward' downwind to decrease the airspeed. If you're hovering with centred sticks in ATTI mode your airspeed will be zero and 'forward' WILL increase your airspeed. Moving downwind will then result in (much) higher groundspeeds than when moving upwind and at some time you'll want to lose that kinetic energy and speed again. The high kinetic energy gives the Phantom the potential to do damage to itself or to whatever it might hit. Flying with high groundspeed near the ground is therefore an increased risk factor.

Thanks, that makes sense. I also realised I had knocked the switch into ATTI mode as well afterwards, it seems I was lucky to just get away with just a little bump. It's school boy errors like that that cause crashes and fly aways (Not all of them obviously!)
 

Recent Posts

Members online

Forum statistics

Threads
143,066
Messages
1,467,352
Members
104,933
Latest member
mactechnic