Getting shocked by late model J

[Ren B]

I posted this on another forum, Pilots of America but I figured it was worth re-posting over here because I got an interesting reply. The following quote is my original post.

 

 

Last night I went for an instructional flight in a Mooney M20J MSE. Fired up, took off and kept getting shocked through the controls of the airplane. In one lap of the pattern, I got shocked 6-7 times with varying intensity. It was a quick pulse shock, I could feel it through the yoke (metal yoke) but mostly my hand which was on the throttle. I would say it is similar to the type of shock delivered by a dog collar on a low setting. It was enough to make me flinch, it definitely hurt a bit and was very distracting. I kept thinking the panel lights were dimming every time I got zapped, but realized I was blinking. 

I turned the airplane in to the mechanic after one trip in the pattern. And of course on a later maintenance flight, no one got shocked. The only thing the A&P could think of that produced enough voltage to deliver a shock was something in the ignition or the strobes. Possibly a static issue, but he explained the grounding is so redundant on the airplane that it was a very remote possibility. In regards to that, it is worth mentioning that it was a warm night with the air saturated with moisture. Also worth mentioning that I got shocked after the landing rollout, turning on the taxiway.

Anyone have a similar experience?

 

 

 

 

[Ren B]

This is a response I received by another J model owner. Anyone experience this or heard of a similar issue?

 

 

Ren, I have had a similar problem for the 4 years with my 1990 J model. I only notice it on hot summer nights, when I'm sweating. I only notice it when the RPM is high, a few times on run-up, but more frequently on takeoff roll, usually the later part of it. It does feel like a light dog collar shock, enough to really get your attention. It's usually felt in my left hand on the yoke, sometimes right hand on throttle, and sometimes, right knee against the metal console (wearing shorts). It's been looked at numerous times, but no one can find anything. Since I've only noticed it at night, I can only assume it is related to the lighting. In the day, I only fly with the strobe on, at night, usually just strobe and nav lights. So, this leaves the possibilities with:

Recog lights
Taxi lights
Landing lights
interior glareshield lighting
interior instrument lighting


Since I cannot reproduce it at will on run-up, it's hard to narrow it down, I don't want to flipping switches around on take-off roll. At this point, I've stopped looking and just live with it. It's only summer nights for me.

If you can reproduce it in cruise, I'd be very interested in the results of turning off various lighting. I have some suspicion about my instrument lights since I've had other problems with them, but that has not been found either.

Please let know if you find anything. 

[fantom]

Could just be your racing heart from M20J MSE passion and love

 

But more likely a static electricity buildup.

[xftrplt]

Strobes or mag grounding I would guess, as they're the only source of high voltage in most GA aircraft.

[N601RX]

DME's and transponders are another source of high voltage.  Your best bet may be to turn one thing at a time off until it goes away.

[PMcClure]

DME's and transponders are another source of high voltage.  Your best bet may be to turn one thing at a time off until it goes away.

I would opt to turn off the mags last in hopes that it was something else! 

[PTK]

One or more of the 200 horses just didn't want to fly and was being temperamental. Their shadows must've startled them. Next time park the airplane with the sun in its face and enter very, very carefully! 

[Ren B]

I should mention I've flown this airplane a number of times during the day and have never been shocked since. The only time was on a muggy, warm night. I think the person who responded to my post is experiencing the exact same problem.

 

I would guess it might be panel lights. I turn all the other lights on for landing during the day (they are LED's so why not) and I have never been zapped then. 

[FloridaMan]

I wonder if it could be caused by the same sort of thing that causes Saint Elmo's fire or the orange lightning you see in ground fog. 

[Jamie]

Would it be accurate to assume both the yoke and the throttle are at ground potential? I mean, it seems like there's a lot of metal-metal contact in both of those, so I'd expect it.

 

If so, that means that either you or something other than (throttle, yoke, metal console) are not at ground potential. Do you get shocked just touching the yoke and nothing else? Or are you completing a circuit with the yoke and (throttle, metal console)? The bit about being sweaty is really important. I'm not a EE, but having stayed at a Holiday Inn Express recently, I feel like an expert. That lowers skin resistance a lot.

 

It'd be interesting to go flying in the right conditions with a multimeter in voltage mode, one probe on you (skin) and one on a place that usually causes a shock and watch the reading as you fly. Does it build slowly / quickly, etc. How much? With wet skin it doesn't have to be nearly as high as normal to cause a shock.

[johnggreen]

If it were my airplane, I would be very concerned.  Stray voltage of any kind could present problems.   

 

Is there some type of electric meter you could hook up to some of the metal that would identify the voltage/amperage?  I'm certainly not an electrician, but I would think that a meter that would record the current could point you in the right direction.

 

Surely there are electrical engineers here that could shed some light.

 

Jgreen

[AmigOne]

"The normal electrical conduction in the heart allows the impulse that is generated by the sinoatrial node (SA node) of the heart to be propagated to (and stimulate) the myocardium (Cardiac muscle). The myocardium contracts after stimulation. It is the ordered stimulation of the myocardium that allows efficient contraction of the heart, thereby allowing blood to be pumped throughout the body."

Maybe you have a "big heart" with similarly "big" electric impulses that in the emotion of flight get outside your body...  

[bumper]

I agree with fantom - - static electricity. I doubt that your symptoms would be caused by anthing in the avionics of plane's electrical system or ignition.

 

The airframe is becoming electrically charged due to friction between it, as well as the prop, and the moist air. As the electrical potential between it (i.e. the airframe is the reference point and a floating  ground in this case) increases, it does so until the potential difference reaches a point that it causes the air to ionize and an arc jumps between the airframe and you - this is the shock you feel. The arc discharge decreases or neutralizes the difference in potential between you and ground. All is good, but the charge in your body quickly dissipates and/or the airframe charge increases until again there is enough difference in potential to allow another arc between the airframe and you.

 

Static wicks would help as they allow the airframe to more easily discharge static to dissipate the charge into the air. Keeping your moist hand in continuous contact with a metal object that is well electrically bonded to the airframe would help as it would keep you and the airframe at the same potential. Unfortunately the yoke is painted or covered and so acts as an insulator, however poor. Thus holding the painted yoke, unless the paint is worn to bare metal, won't prevent the little shocks. 

 

When I'm using my bead blast cabinet I get the same thing - lots of friction between the glass beads, tubing, nozzle and air.  Have to ground myself and the cabinet to prevent lots of zaps!

 

And the comment on St. Elmo's fire is correct. It's essentially the same principal, sort of. The atmosphere being charged enought to ionize the air and discharge to ground through the pointed parts of a sailing ships rigging (yard arms, mast tips etc.).

 

bumper

Navy electronics tech and electrician - - though I sure wouldn't want to live in a house I wired, for although I have the license, never worked as an electrician.

[Ren B]

I agree with fantom - - static electricity. I doubt that your symptoms would be caused by anthing in the avionics of plane's electrical system or ignition.

 

The airframe is becoming electrically charged due to friction between it, as well as the prop, and the moist air. As the electrical potential between it (i.e. the airframe is the reference point and a floating  ground in this case) increases, it does so until the potential difference reaches a point that it causes the air to ionize and an arc jumps between the airframe and you - this is the shock you feel. The arc discharge decreases or neutralizes the difference in potential between you and ground. All is good, but the charge in your body quickly dissipates and/or the airframe charge increases until again there is enough difference in potential to allow another arc between the airframe and you.

 

Static wicks would help as they allow the airframe to more easily discharge static to dissipate the charge into the air. Keeping your moist hand in continuous contact with a metal object that is well electrically bonded to the airframe would help as it would keep you and the airframe at the same potential. Unfortunately the yoke is painted or covered and so acts as an insulator, however poor. Thus holding the painted yoke, unless the paint is worn to bare metal, won't prevent the little shocks. 

 

When I'm using my bead blast cabinet I get the same thing - lots of friction between the glass beads, tubing, nozzle and air.  Have to ground myself and the cabinet to prevent lots of zaps!

 

And the comment on St. Elmo's fire is correct. It's essentially the same principal, sort of. The atmosphere being charged enought to ionize the air and discharge to ground through the pointed parts of a sailing ships rigging (yard arms, mast tips etc.).

 

bumper

Navy electronics tech and electrician - - though I sure wouldn't want to live in a house I wired, for although I have the license, never worked as an electrician.

 

 

It could be static. Just to respond to a few things you talked about:

 

I got shocked through both the yoke and the throttle. Usually it was through the throttle, but sometimes I felt the shock through both yoke and throttle.

 

The yoke is painted but the paint is a little worn where I usually hold it.

 

The airplane has static wicks. At least three on each aileron. I think there are a few on the elevator as well. 

 

When I got zapped, it was about 65F and the dew point was about 63F. Was worried about fog forming but it didn't happen. Very humid.  I got shocked lightly once or twice during run-up. Then I really got shocked a few times after I was airborne. I also got zapped shortly after landing roll-out. But not during taxi after. 

 

The club mechanic happened to be on-duty so I discussed this with him. An instructor and I flew the plane shortly after (same night) to see if we could replicate and isolate the problem. Neither of us got shocked. 

[bumper]

Okay, one thing not discussed was "warning shots".

 

To test for this, stand outside and hold your arm high over your head with index finger extended. Yell, "Damn, Damn, Damn". If you get zapped, that explains everything.

 

bumper

[FloridaMan]

Okay, one thing not discussed was "warning shots".

 

To test for this, stand outside and hold your arm high over your head with index finger extended. Yell, "Damn, Damn, Damn". If you get zapped, that explains everything.

 

bumper

 

http://en.wikipedia.org/wiki/James_Otis,_Jr. 

 

Otis died suddenly in May 1783 at the age of 58 when, as he stood in the doorway of a friend's house, he was struck by lightning. He is reported to have said to his sister, Mercy Otis Warren, "My dear sister, I hope, when God Almighty in his righteous providence shall take me out of time into eternity that it will be by a flash of lightning".