Aerodynamic phenomen when descending in Phantom

[havasuphoto]

I worked as a Commercial Helicopter Pilot for over 20 years, and have 1000 of flight hours in various aircraft.
I've flown my Phantom a few times in my backyard, but only at low altitudes.

Today, I went to our local Park and flew the Phantom up to about 100 feet. I was hovering there, and yawing/panning the camera. I then decided to descend, straight down, and discovered that the Phantom is effected by the same aerodynamic effects of a real helicopter. That effect is called "Settling With Power", or "Vortex Ring State"(you can google either for a textbook discussion).

In a real helicopter-if you descend at a rate of around 300 feet per minute, or more, straight down(assume zero wind), you will enter you own down-wash. This causes the aircraft to start yawing and rolling as it enters this disturbed air. If you add more power, the Helicopter, and the Phantom, will actually descend faster!!!

Now I had the blade guards on-and that probably doesn't help. But, what I did was to push forward on the stick and move the Phantom into clean air while it was descending.

My post is a warning to all you Drone Drivers-beware!!! Going straight up-not a problem. Coming straight down-big problem.
Try going forward/sideward/backward, while descending from higher altitudes to avoid this situation. You will also notice your descent footage is a lot smoother, as you are in clean air.

Now if you are flying in wind-note which direction the wind is coming from. It's still possible to enter this Vortex Ring State. For example-you're hovering high up in a head wind, and you decided to descent and go backwards-you could enter your own rotor down wash.

This only applies when descending, and only when descending at a speed faster than your down wash is blowing away from your aircraft. If you descend slowly-no problem.

Here's a link that will help describe this phenomenon;http://www.copters.com/aero/settling.html

And for those that don't think this is possible-it is. I know what it looks like, because I've been in it, many times. And Today, on descent, I was in it.

 

[OI Photography]

Excellent warning and explanation. And yeah it always seemed to appear sooner when I had the propguards on.

 

[havasuphoto]

Excellent warning and explanation. And yeah it always seemed to appear sooner when I had the propguards on.

Thanks. I actually noticed it in some people's video's. So, I went out in got into it on purpose...just to test my theory-and I was correct. And, when I added more power, it dropped a little faster and wobbled a lot more. But, just a slight push forward, and everything smoothed right out.

I also noticed that the Phantom goes into Effective Translational Lift at about 10mph. At this speed, the power required is reduced, to maintain a given altitude. You will notice this if you leave the throttle in a fixed position, and just go forward. If the aircraft starts a slight climb-you've got Translational Lift. IF, you are already flying in a 10mph wind-you've already got the effect, in a hover-so less power is required.

I plan on doing some more "experimenting" once I get more batteries(I'll end up with 10 shortly).

 

[OI Photography]

I also noticed that the Phantom goes into Effective Translational Lift at about 10mph.

I didn't know that was the name of it, but I've definitely played around with that as well. Still working on perfecting the "pitch forward/throttle back" combo to maintain even flight level at forward speed like that.

 

[havasuphoto]

I also noticed that the Phantom goes into Effective Translational Lift at about 10mph.

I didn't know that was the name of it, but I've definitely played around with that as well. Still working on perfecting the "pitch forward/throttle back" combo to maintain even flight level at forward speed like that.

Good luck with that.......LOL
I'm only on my 6th flight or so......so, I'm still working on a lot of things
1 of the things I want to do-and haven't figured it out yet(I tried CL and HL), is to move forward in a straight line at a set speed, and yaw slowly 360 degree's, while maintaining course and altitude.

 

[Driffill]

The vortex ring effect has been mentioned on here before, while relevant, with a multi rotor it's harder to purposely induce this effect (as a posed to a standard helicopter), with that said, I still try to descend while moving in another direction too, mainly to avoid the propwash!

These types of things are still handy to know, with the amount of phantoms flying around out there now, I'm sure people have had the vortex bring them down.

 

[Dave Pitman]

Yes, pretty well known that descending straight down is the least stable. Worth repeating though.

Just think of all of the other stuff that is well known about quads already. Just waiting for you to either discover on your own, like the guy who just splashed $1300 worth of equipment because he didn't read about the other "well known" information available, or do some reading and not have to learn everything on your own, good and bad.

Have fun.

 

[miskatonic]

A warning about the prop guards. If you remove the prop guards make sure you put the Phantom's original screws back in place. DO NOT PUT THE PROP GUARD SCREWS IN PLACE WITHOUT THE PROP GUARDS! What happens is the prop guard screws are long enough to pierce the motor windings; you will find yourself with stuttering and broken motors.

 

[miskatonic]

Also you don't want to come straight down because in some cases this means that you are putting less than 10% on the throttle. The motors will cut off and you will find that the Phantom will drop like a stone.

 

[PhantomFan]

I always transition forward or circle around (to the left mostly, don't know why) while I descend for just that reason. The wobble can be fierce if you don't. As an added bonus, when you are up high, you always know where the "forward" end of your craft is if you are moving rather than simply hovering...which I find anxiety provoking given my background as a pattern plane flier.

The only time I like to hover my Phantom is at the time of landing...otherwise that puppy is moving in one direction (at the very least!) or another. :lol: :lol: :lol:

PF

 

[havasuphoto]

I always transition forward or circle around (to the left mostly, don't know why) while I descend for just that reason. The wobble can be fierce if you don't. As an added bonus, when you are up high, you always know where the "forward" end of your craft is if you are moving rather than simply hovering...which I find anxiety provoking given my background as a pattern plane flier.

The only time I like to hover my Phantom is at the time of landing...otherwise that puppy is moving in one direction (at the very least!) or another. :lol: :lol: :lol:

PF

Spoken like a true fixed wing flier
I can remember instructing fixed wing guys, and they would always tense up the first time we were at 1000 feet above the ground, and the air speed bled off to zero.....just made them nervous. I learned in fixed wing before helicopters-and had the same feeling the first time I saw it.......

 

[PhantomFan]

Yeah, man, you KNOW it!!! Years of fixed wing flying has caused me to break out into a cold sweat whenever any craft I'm flying slows to a crawl. This hovering thing...very weird and hard to get used to!!! :lol:

I have to admit though, I once built a balsa, ply and shrink-skin biplane that - in any decent headwind - you could slow to a walk and it would fly just fine. I remember one day landing it directly into a stiff breeze blowing straight down the runway (YEAH, we had a runway!). When I landed it had zero ground speed. Just set it down in place and watched it bounce on the tires. Friggin' hysterical.

Quite the opposite of my pattern planes with their symmetrical wings. Those I brought in HOT every time despite their balsa covered foam wings and fiberglass fuse. To tell the truth, I just like to fly FAST. Once I got into pattern flying, everything else was ho-hum. Gimme a plane with on-board fuel pumps, wicked screaming OS engines, and tuned pipes that'll go vertical until out of sight. That's what makes MY heart go thumpa thumpa!!! :lol:

PF

 

[havasuphoto]

Yea, I understand completely. The Phantom, to me is just a platform to hold the camera in a certain position....basically for film making. It's a tool.
I've had my share of fun with both fixed and rotary winged aircraft, and lived to tell all the stories.
Now, I can sit in my comfy chair, with my FPV and the Phantom, and just fly around and get the shots I need to get.

 

[PhantomFan]

That's why I'm in the midst of a scratch built PVC v-tail racing/acrobatic quad. Painted up the frame blood red this morning and mocked up the motors this evening. I have everything I need except the flight controller, which is going to be a KK2.1. It left China 11 days ago, and I can't WAIT to have it in-hand and start the setup process.

After it's built I'm going to set up some pylons (flags) in my back yard and start doing circuits...faster, and faster, and faster. Then after I get it all dialed in and or make whatever mods are necessary, I'm going to make the same machine out of carbon fiber or kevlar (not sure which) to make it super light, and dope it up with 30A Simonized ESC's and some Tiger motors (using Sunny Skies 980kv motors currently for the initial testing).

Can post a couple of pix if you are interested.

PF

 

[Peter Patricelli]

"the Phantom goes into Effective Translational Lift at about 10mph. At this speed, the power required is reduced, to maintain a given altitude. You will notice this if you leave the throttle in a fixed position, and just go forward. If the aircraft starts a slight climb"

This brings up an issue I think DJI should consider as a flying mode....like CL or HL, ATTI, GPS, Manual. Seems to me that at neutral throttle position...the correctly set up bird hovers at that altitude. I'm not sure whether that altitude stability is based on GPS position or negative accelerometer input....but it holds its altitude just as well as its "over ground" position. Obviously these position locks UNlock as soon as the sticks move for roll (L-R) or pitch (F-R). Clearly the altitude lock UNlocks when the throttle position is advanced or lowered....DUH.....but ALSO seems to me that it UNlocks with YAW rotation. WHY??

When I fly out, stop in a holding hover, or drift, then yaw (rotate) to turn around, the bird usually drops up to 4-5 feet which I have to correct with throttle. I assume this is because whatever lock exists UNlocks AND LIFT is reduced by the motor variations necessary to YAW. (Or, I have wondered, did I ALSO move the throttle?) I can correct and survive this, obviously, and watch for it. But seems to me there would be serious value and advantage in an ALTITUDE (not ATTITUDE, ATTI) lock flying mode. That is, as long as the throttle is in neutral position the bird uses GPS/accelerometer/whatever to correct itself and maintain altitude established when the throttle went into neutral. Sooooo.....if one lifts off and then hovers at, say, ten feet off the ground.....on a perfectly flat field.....one could then maneuver and yaw all over the field with the bird maintaining, as closely as it can, ten feet off the ground, instead of climbing with Effective Transitional Lift or dropping with Yaw Lift Loss.

I love to do video at high speed close to the ground but the altitude Instability currently inherent in the bird keeps me higher up for safety and buffer altitude than I want for video.

And if I am missing something or mis-interpreting the bird's actions....then I am about to learn something.

 

[PhantomFan]

That shouldn't happen. It certainly doesn't happen with either my Phantom or my F450 which is also NAZA-based. I sling my F450 in yaw and have it spin like a top and it doesn't drop an inch. if the trim is out it may translate a foot or so left or right, but drop?? Nope.

Go into the NAZA Assistant and check your vertical gain. Bump it up to 140 or possibly more. Is your bird overweight??? If so, you may need to go up to 150! Max is 200 IIRC.

PF

 

[Hiway]

I noticed this phenomena but didn't have a term or official definition for it- I compensated by doing the slow forward or side movement by experience- glad to know my instincts are spot on.

I have never flown anything with a motor... but I have plenty of time in the air on a kite... instructed and hung around Kitty Hawk Kites along the NC OBX for a spell back in the mid 90's

...I know a little about thermals, but without a fold out delta wing option on my Phantom I think my skill set is moot.

 

[hurseyc]

Also you don't want to come straight down because in some cases this means that you are putting less than 10% on the throttle. The motors will cut off and you will find that the Phantom will drop like a stone.

There's a setting for this right? Mine is set for "intelligent control" or something like that and as long as the thing is moving in space I can have the throttle at 0% and it doesn't turn off.

 

[havasuphoto]

Also you don't want to come straight down because in some cases this means that you are putting less than 10% on the throttle. The motors will cut off and you will find that the Phantom will drop like a stone.

There's a setting for this right? Mine is set for "intelligent control" or something like that and as long as the thing is moving in space I can have the throttle at 0% and it doesn't turn off.

Are you sure? You might wanna try that when you're very close to the ground.
I'd like to know the results. I do know that after I land, and the throttle is full down-the engines don't shut off for 3 seconds.

As for the; more power required to maintain altitude while yawing. Not sure what you can do to "fix" this. It's normal for any rotorcraft to either descend or ascend while yawing, and altitude compensation is with Power(throttle).

 

[IAP]

Ah, thanks for explaining this.

I experienced that effect on my 5th flight. Was bringing her down (max rate) from 400 feet. At about 200 feet the PV wobbled, I just thought it was a cross wind / turblance, but not from its own thrust. Makes sense now.