Got shocked by the airplane

dell30rb

dell30rb

Final Approach
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Ren
This is really strange.

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?
 
Check the ignition and strobe leads for chafing, in think your guy is looking in the right place.
 
I would think the only way it could be static would be if your engine ground strap were completely disconnected but even then you've still got connections between engine and airframe like the throttle cable, mixture cable and primer line so it would be virtually impossible for a potential of that magnitude to build up.
 
Skylane81E said:
Check the ignition and strobe leads for chafing, in think your guy is looking in the right place.
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It sounded correct to me as well. Has anyone heard of this occurring though?

The A&P who works at the club seemed skeptical about my description of the problem, he suggested I have some sort of extreme sensitivity to such things. As someone who has been zapped a handful of times by various electrical forces, I don't think this is the case.

I have been shocked by a motorcycle magneto before and it felt similar
 
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It seems odd that it would happen, but electricity does some odd things
 
Try turning your strobes off next time and see if that fixes your problem. At least you can eliminate that problem or not
 
I had a dimmer switch that was installed in parallel somehow to my old MK-11 com. The hot wire had broken loose and was occasionally arcing behind the panel, and I'd get a zap once in a while. I cut the wire, wrapped the end in electrical tape and it's been good since. The MK-11 was replaced, so I'm pretty sure that wire isn't even hot anymore, but that's an issue I had.
 
EdFred said:
I had a dimmer switch that was installed in parallel somehow to my old MK-11 com. The hot wire had broken loose and was occasionally arcing behind the panel, and I'd get a zap once in a while. I cut the wire, wrapped the end in electrical tape and it's been good since. The MK-11 was replaced, so I'm pretty sure that wire isn't even hot anymore, but that's an issue I had.
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I think the mooney is 28 volts. What is the Comanche? Is that enough to provide this type of shock?
 
Jesse and I observed the 310 shocking us from the panel about a year ago. In that case, I recall only getting shocked with my hand on top of the panel, but I could be remembering incorrectly.

We were near some pretty intense electrical activity at the time, and I figured it was related to that and perhaps bad static wicks. So, I repplaced all the static wicks as they were old and in bad shape anyway. Hasn't happened since, but also haven't been near that level of electrical activity since.
 
It's possible the plane wasn't shocking you... you may have been shocking the plane. The Static build-up on your body from perhaps rubbing your feet on the plane's carpet or shifting around on the seat could cause you to discharge to the well grounded plane.
 
Mtns2Skies said:
It's possible the plane wasn't shocking you... you may have been shocking the plane. The Static build-up on your body from perhaps rubbing your feet on the plane's carpet or shifting around on the seat could cause you to discharge to the well grounded plane.
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It was just way too much of a shock, way too often for it to be that. Also it was a warm and humid day.
 
Even 28V shouldn't be enough to cause a perceptible shock. I'd also suspect it's related to the ignition, strobes, or some weird static thing (but I agree that's unlikely)
 
There's an old hangar yarn about a fellow who put long range tanks on his Supercub which gave it such endurance that he decided to fabricate himself an in-flight relief system out of a small plastic funnel and some tygon tubing. Story goes that the first time he tried to use it it drew a two inch arc off his pecker and he darn near crashed.

Now I'm not claiming it's a true story but it's kind of like the Darwin Award tale about the Chevy with the JATO rockets. Arguing that it's complete BS is like bringing a wet blanket to a slumber party because in our hearts we really want to believe it.
 
pericynthion said:
Even 28V shouldn't be enough to cause a perceptible shock. I'd also suspect it's related to the ignition, strobes, or some weird static thing (but I agree that's unlikely)
Click to expand...

12V will cause a perceptible shock. I found a bare wire behind the panel of the Frankenkota because it nipped me. Somebody had pulled a panel light wire out of it's socket and hadn't bothered to wrap it. Not a good way to do business.

Even 9V will let you know it's there - just put your tongue across the terminals of a 9V battery...
 
Clark1961 said:
12V will cause a perceptible shock. I found a bare wire behind the panel of the Frankenkota because it nipped me. Somebody had pulled a panel light wire out of it's socket and hadn't bothered to wrap it. Not a good way to do business.

Even 9V will let you know it's there - just put your tongue across the terminals of a 9V battery...
Click to expand...
For what it is worth a double a will do the same thing as a 9 volt, just not as strong
 
pericynthion said:
Even 28V shouldn't be enough to cause a perceptible shock. I'd also suspect it's related to the ignition, strobes, or some weird static thing (but I agree that's unlikely)
Click to expand...
28v or even 14v can deliver a fatal shock if your skin resistance is low enough (e.g. a firm grip with salty and sweaty hands). I've gotten hit hard enough to hurt trying to pick up a 12 car battery by pulling on the terminals. That said, normally 30v or less is barely perceptible when touching with a hand.

As to the notion that ignition might be coupling to the engine controls I've gotta say that seems virtually impossible if the engine passes a mag check and it would require a direct connection between the inner wire of an ignition cable and the control cable. Strobe supplies do put out around 300v but I can't think of any plausible scenario where the HV could show up on an engine control unless the supply was mounted behind the panel.

I wouldn't eliminate the possibility that this isn't electrical. It's possible that the OP is experiencing something that feels like an electric shock but is actually some kind of nerve issue. One way to confirm this as electrical would be to use a digital voltmeter with the airframe as a reference.

I was also wondering if the OP's airplane has sheepskin or plastic seat covers.
 
Most of the strange electrical sensations I've experienced have been caused by reversed polarity of some kind. That's about all I know about it other than when the polarity was reversed the problem stopped. Can something of that nature be the cause of his problem?

gismo said:
28v or even 14v can deliver a fatal shock if your skin resistance is low enough (e.g. a firm grip with salty and sweaty hands). I've gotten hit hard enough to hurt trying to pick up a 12 car battery by pulling on the terminals. That said, normally 30v or less is barely perceptible when touching with a hand.

As to the notion that ignition might be coupling to the engine controls I've gotta say that seems virtually impossible if the engine passes a mag check and it would require a direct connection between the inner wire of an ignition cable and the control cable. Strobe supplies do put out around 300v but I can't think of any plausible scenario where the HV could show up on an engine control unless the supply was mounted behind the panel.

I wouldn't eliminate the possibility that this isn't electrical. It's possible that the OP is experiencing something that feels like an electric shock but is actually some kind of nerve issue. One way to confirm this as electrical would be to use a digital voltmeter with the airframe as a reference.

I was also wondering if the OP's airplane has sheepskin or plastic seat covers.
Click to expand...
 
gismo said:
Strobe supplies do put out around 300v but I can't think of any plausible scenario where the HV could show up on an engine control unless the supply was mounted behind the panel.

I wouldn't eliminate the possibility that this isn't electrical. It's possible that the OP is experiencing something that feels like an electric shock but is actually some kind of nerve issue. One way to confirm this as electrical would be to use a digital voltmeter with the airframe as a reference.

I was also wondering if the OP's airplane has sheepskin or plastic seat covers.
Click to expand...

The strobes on this airplane are run through a combination circuit breaker/ rocker switch on the panel. There is no relay involved, so that bolsters the possibility that the strobe system might be responsible.

As I mentioned it was a warm and humid night, the air was saturated and forecast to become LIFR fog no more than 2-3 hours after my flight. Since we never left the pattern it was very humid in the airplane and I probably had a pretty good connection with the throttle and yoke (the yoke is not plastic).

I've never had any sort of nerve issue and I am 100% sure this is not a nerve issue or a figment of my imagination. I've never been shocked through the controls of an airplane or car before. If I had some sort of super sensitivity to electricity, I would have discovered it by now.
 
Transponders have a mighty high transmit power...
 
dell30rb said:
The strobes on this airplane are run through a combination circuit breaker/ rocker switch on the panel. There is no relay involved, so that bolsters the possibility that the strobe system might be responsible.
Click to expand...
Only the 14v or 28v supply goes through that CB/ switch. The HV only exists in the supply itself and the wiring that goes from the supply to the flashtubes.

As I mentioned it was a warm and humid night, the air was saturated and forecast to become LIFR fog no more than 2-3 hours after my flight. Since we never left the pattern it was very humid in the airplane and I probably had a pretty good connection with the throttle and yoke (the yoke is not plastic).

I've never had any sort of nerve issue and I am 100% sure this is not a nerve issue or a figment of my imagination. I've never been shocked through the controls of an airplane or car before. If I had some sort of super sensitivity to electricity, I would have discovered it by now.
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With that much humidity your skin resistance was likely very low, especially if your hands were the least bit sweaty. In that case I think you were experiencing a connection to ship's power somehow, probably the result of a wire shorting into an engine control cable. It wouldn't require a dead short either because you can easily feel a few hundred microamps of current and with 14v the total resistance including your skin could be as high as 30,000 ohms. I wouldn't be too concerned about the shock hazard itself but there's a significant chance the leaking connection might get worse and cause the control cable to weld stuck or break.

Again, I'd take a good DVM, attach one lead to a good airframe ground and probe everything you were touching with the other lead to see if I could find more than a few hundred mv on something. You might need the airplane to be in the same condition as when you experience the shock and if that was in the air, I'd have a helper to fly the plane or probe the controls.

It's also plausible that your shocks were the result of a static charge buildup on something that somehow transferred to something you were touching but unless you were hanging onto a windshield mounted compass that seems pretty far fetched and static buildup on an airplane normally only occurs when the air is very dry and hazy or in dry snow unless there's convective activity about.

BTW, given your forum ID I have to ask: Was there any lighting in the vicinity?
 
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SCCutler said:
Transponders have a mighty high transmit power...
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But virtually no transmit energy because the transmissions are very brief and infrequent. I'm pretty sure that if you had one hand on the antenna when it replied to an interrogation you wouldn't feel a thing. I haven't actually tried this though, YRMV:D.
 
gismo said:
BTW, given your forum ID I have to ask: Was there any lighting in the vicinity?
Click to expand...

:rofl:

Grounding out a multi-meter and testing is probably the way to go. Although since the airplane is a club plane and the A&P is pretty busy these days, I doubt it will get looked at unless someone complains of a similar problem. We flew it on a maintenance flight immediately after consulting with the A&P with no problems. My instructor and I took turns flying and neither of us got zapped. Probably only a matter of time.
 
dell30rb said:
:rofl:

Grounding out a multi-meter and testing is probably the way to go. Although since the airplane is a club plane and the A&P is pretty busy these days, I doubt it will get looked at unless someone complains of a similar problem. We flew it on a maintenance flight immediately after consulting with the A&P with no problems. My instructor and I took turns flying and neither of us got zapped. Probably only a matter of time.
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Wear gloves...:yes::D
 
dell30rb said:
:rofl:

Grounding out a multi-meter and testing is probably the way to go. Although since the airplane is a club plane and the A&P is pretty busy these days, I doubt it will get looked at unless someone complains of a similar problem. We flew it on a maintenance flight immediately after consulting with the A&P with no problems. My instructor and I took turns flying and neither of us got zapped. Probably only a matter of time.
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Like I said, it's not the shocking potential (NPI) that worries me, it's the possibility that the unintended connection between ships power and a control cable that I think you ought to be concerned about. If this were my airplane I'd dig until I either found the problem or convinced myself that there was no chance of a control cable failure from this.
 
gismo said:
Like I said, it's not the shocking potential (NPI) that worries me, it's the possibility that the unintended connection between ships power and a control cable that I think you ought to be concerned about. If this were my airplane I'd dig until I either found the problem or convinced myself that there was no chance of a control cable failure from this.
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Agreed.........

My bet is on a spark plug lead shorting somewhere...
 
Or maybe a intermittently collapsing field on the alternator rotor? Not obvious just how though.....
 
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guardrail said:
And you need a really long tongue...
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Nah, just two wires and a little bit of tape. Used to test batteries that way when I was a kid, much easier than looking for a multitester.
 
dell30rb said:
This is really strange.

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?
Click to expand...

Renjamin,


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.

Thanks,
 
Also, next time it occurs, determine if the shock is coming from the yoke or the throttle. One is the source, one is the ground.
If I had to guess, I would bet the throttle/cable assembly is getting energized (it runs through and around a lot of energized areas).

So, next time it occurs, hold the throttle, release the yoke and control the plane with the rudder, and ground yourself on something else (other yoke, seat frame, something metal). If nothing, grab the yoke and release the throttle, then ground yourself to something else.

I would bet a loose wire making intermittent contact with the throttle cable.
 
Unlikely to be static as the static charge builds around the entire moving system, so the skin, the engine, the flight controls, and the pilot would all have a raised potential if it were static. The voltage differential between the static charged plane and the pilot sitting in the seat would not typically cause a discharge. However, if it were static, once discharged ti doesn't seem that it would continue doing it over and over again. As the charge rebuilds, it should all charge up together. Also, static can have a rather high potential voltage, but it takes a lot of ionization to produce much current(lightning is actually static charge, but it takes a lot of movement of charged particles to generate a bolt).

Discounting static, the next most likely is a pinched high tension wire from the strobe box, out to the wing tip. It doesn't take much, and the pinch doesn't even need to break the insulation completely for there to be a condition which would jump the arc under humid conditions. This can be tested with another flight on a humid day, or with a meter between the engine ground, and the flight control, which is somewhat insulated enough to cause the different potential needed to feel a shock.

Last would be the ignition. voltage buildup from the ignition is typically due to a breakdown of both the insulating wrap, and the conductance of the core. When this happens, often together the voltage can 'stand' on the outside wire of the ignition lead and still fire the plug, although at reduced intensity. We mask this somewhat with our dual ignition systems, so that the mixture keeps firing even in the event of a poor spark on one lead. Test for this is both easy and yet a bit dangerous. First, remove all the plugs and look for one that is not like the others. The color may be different, or it may have a deposit on it, or it may be much too clean. Further, the cap on the mags can be removed, and you can test the conductance of the leads with a meter, while wiggling them in the harness to verify good connection. Lastly, put it all back together, remove the cowl or prop it open securely, then find the darkest place on the field in the darkest time of night, and have someone CAREFULLY inspect the ignition wires with the engine running. They are looking for breakdown voltage that may be dancing on the wire insulation, it may be light blue or yellow. Keep the surrounding area very dark, and let your eyes adjust to the darkness for about 20 minutes before starting. Look behind the tin to the mags as well, and as always, stay clear of the prop.
 
MooneyMan said:
Renjamin,


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.

Thanks,
Click to expand...


That sounds exactly like what I experienced. Sometimes it was zapping me through the throttle, sometimes through the yoke, and sometimes both. It was a humid warm night and I was sweating in the cockpit.

I've flown 5 hours in the same airplane over the past two weeks and didn't get zapped. All daytime however and I was not sweating.

The instrument lights might be the culprit. I usually flip on ALL the lights for landing even during the daytime. They are LED's so why not? However I never have the panel lights on except at night (duh)
 
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