Uncontrollable wobble descent with "Battery Comm Error"

[CGPhoto]

I was descending rapidly and near the ground when my aircraft developed a severe, uncontrollable wobble. As it was descending, I had the alert that says "Battery communication error", with the bold letters "MC". I do not take off with less than six satellites (Icon blue), and calibrate the compass before EACH flight. The bird would not respond to the controller. A screen shot shows 4 satellites in an area where I normally get 12.

What happened? It flew normally after I recovered...no harm done. But this is alarming.

Did I descend too fast and hit "dirty air" the way a full size helicopter does, causing the wobble? Then the battery was stressed?

I need input on whether to send it in to check its systems.

Thanks.

 

[Dirty Bird]

The uncontrollable wobble was likely VRS, and probably unrelated to your battery error. On the battery, check the two small battery contacts and their related pins in the Phantom. The pins are spring loaded. Make sure they are moving freely in and out, and they are not bent. Verify the contacts are clean. You might want to apply some DeoxIT on the pins and contacts to ensure a good connection.

http://www.amazon.com/gp/product/B003D8EA7A/ref=gno_cart_title_1?ie=UTF8&psc=1&smid=A1UMBRA5ZTBCX8

 

[Tony99982]

What is VRS?

 

[jaxbert]

"Dirty Air" as stated above, same thing happens to big helicopters...

Also known as Settling with power, this is a condition where the helicopter begins to settle in its own downwash.

The general cause of this condition will likely be a combination of high gross weight while landing in a down wind condition. Although VRS can occur while landing into the wind, it is not nearly as common.

There are three conditions required to be present to get into settling with power, I call this the 1,2,3, rule. You must have airspeed less than ETL (many teach 10-knots or less airspeed), you must be using 20-percent or greater power, and you must have a sink rate of 300-feet per minute or greater. These are minimums; I teach my students to maintain not less than 30-knots in the primary descent. Most importantly, the sink rate must be reduced to less than 300 fpm before airspeed is reduced to less than 30-knots.

Awareness requires that pilots know their gross weight especially where the power will be limited, and they must also be very aware of the direction of the wind. Never should a helicopter be landed in a downwind approach that will terminate in the downwind. If a downwind approach is necessary, the airspeed should be maintained above 30-knots (a good safety margin) until the helicopter is turned into the wind, and the sink rate is reduced.

Settling with power will be recognized by a vibration of the main rotor system, quickly followed by a rapidly increasing sink rate that can reach 6000 fpm. You don't want to be close to the ground when that happens!

The recovery procedure will be to input forward cyclic to fly free of the vortices, and simultaneously decrease the collective pitch reducing the size of the vortices (decrease power).

Avoidance requires that you remember that all three of the conditions stated above in the 1-2-3 rule must be present, so you only need to keep one of those conditions absent to avoid that phenomenon, and consequently you need only eliminate one to get out or the phenomenon of settling with power (VRS).

It is also important to note that although teaching that 10-knots is all that is necessary to avoid settling with power is correct by most published information, I feel that it is not sufficient airspeed to safely avoid the condition. If you are flying at 10-knots, all you need is a slight wind shear to put you in the condition, and if that occurs near the ground, look out.

Always be cautious.

 

[CGPhoto]

I was hoping to hear from Dirty Bird! I was thinking that I caused this by my rapid descent, and maybe the G forces caused the pins to retract, thereby giving me a clue, but a battery issue did not cause the problem. I bet that is the direction the thread will take. Please explain what VRS is. I will descend more slowly now, and stair step. Any other suggestions. I do not mind suggestions, how else will I learn?

 

[pyrophantom]

VRS - Vortex Ring State.

All helis and rotor aircraft small or large can suffer from it. In basic terms its the dirty turbulent air that forms under the rotors when in hover (mostly) which can lead to lack of lift and if you read about this in detail there are little vortices that can form midway along the top of the blades....but thats for anoraks like me who like to know why things happen lol

Basically when you are descending try to do it slower and on a shallow angle so your props are mostly going to be going through "clean" air and retain lift.

 

[Zinnware]

Please explain what VRS is. I will descend more slowly now, and stair step. Any other suggestions. I do not mind suggestions, how else will I learn?

Thanks jaxbert for a great explanation of avoiding VRS (Vortext Ring State) which can also be described as "Dirty Air". Here is another description on the wiki.
http://en.wikipedia.org/wiki/Vortex_ring_state

CGPhoto, here are a few other suggestions:
- Be careful while hovering in places where there are updrafts, like canyons, or along mountain sides.
- Do not descend straight down, especially in calm air. Come down at an angle.
- If you experience the VRS and wobble, then move the craft forward and clear of the dirty air and into clean air. Trying to go up could just increase the VRS or dirty air.

 

[Dirty Bird]

What is VRS?

Vortex Ring State - The air under your props becomes unstable and loses lift. Usually happens in rapid, straight down, descents. If you get in that situation, do NOT apply more power. Use the right stick in ANY direction to slide off of the dead air zone beneath. Do you have prop guards on your bird by chance? They seem more susceptible with prop guards installed.

 

[CGPhoto]

Thanks everyone...the more I learn the more I feel I caused this myself...and the G forces pulled the pins away for a fraction of a second. I was flying on a private airfield (with owner's permission) in the middle of nowhere just to learn the limitations of my airplane. I am a private pilot that has spent some time in helicopters...I have not had training to that detail but it all makes perfect sense. I had detected a wobble during a fast vertical descent, but I did not know that it would make the aircraft unstable. I do now! (I do not normally fly this way...but I was in a HUGE open field with no people or structures or objects to harm...so I could experiement safely.)

 

[CGPhoto]

Thanks to each and everyone for answers that are on point, and with background information. I'm flabbergasted by the speed of responses as well as the depth. I do understand my little helicopter is a real airplane that has to deal with the laws of physics just as I do with a full size airplane.

 

[Navman]

Very informative info on settling with power guys!

We hired a helicopter to set a 7,000 foot bridge into a canyon for the Pacific Crest trail system years back

They'd taken all the weight off the Sikorski they could and flew with minimum fuel

Always wondered, how is it a helicopter can sit in one place with a heavy load and not induce this state.

 

[sar104]

Always wondered, how is it a helicopter can sit in one place with a heavy load and not induce this state.

Because in a hover, with no external downdraft, the disturbed air remains below the rotor. The problem only arises when the aircraft sinks into the disturbed air.

 

[CGPhoto]

I do not have prop guards. Also, I rarely fly in still air. IF this ever happens again (should be easy to prevent) I will apply right stick. Easiest thing to do is to come down at an angle. I will do my best to pass this wisdom along.