I realize this isn't an aircraft maintenance forum, nor is it really a real world aviation forum, per se. But I'm hoping some of my knowledgable friends here can give their own thoughts.

 

A C182R was subjected to a brief moment of mild .5-0 Gs today. The aircraft immediately developed a bad (severe) "surge", couldn't maintain RPM, a strong smell of avgas entered the cockpit, and having the throttle anymore than halfway would compound the "miss" or "surge". It seemed as if the engine was flooded. After several options to make an off field landing were passed up, the runway was finally made (thank goodness). When on the ground and shut down, I immediately got in and started aircraft back up. I could barely get the RPM above 1,000 and a strong smell of fuel was noticeable.

 

The question is: What would cause this? Is it a stuck float, etc? I'm no wrench but I was not happy with the mechanic's "must be trash at the fuel jet" hypothesis.

This is out of my league but maybe a stuck float? Strong smell of fuel though I would be scared to start up.

This is out of my league but maybe a stuck float? Strong smell of fuel though I would be scared to start up.

 

I'm glad we're on the same wavelength. I had our DPE and mechanic standing by with a fire extinguisher.

Did you have fuel running out of the bottom of the cowling after you landed? If the float was stuck down and therefore the needle valve was stuck open the fuel bowl in the carb would continue to fill until it was overflowing. I would think with neg Gs though that the float would be forced up and the needle valve closed. If I was to make a guess as to what happend I'd say the fuel in the bowl of the carb was forced from the bowl into the engine and flooded it. If thats the case the fuel would eventually evaporate and/or drain out of the cylinders and the engine would be back to normal.

Did you have fuel running out of the bottom of the cowling after you landed? If the float was stuck down and therefore the needle valve was stuck open the fuel bowl in the carb would continue to fill until it was overflowing. I would think with neg Gs though that the float would be forced up and the needle valve closed. If I was to make a guess as to what happend I'd say the fuel in the bowl of the carb was forced from the bowl into the engine and flooded it. If thats the case the fuel would eventually evaporate and/or drain out of the cylinders and the engine would be back to normal.

 

I'd be inclined to believe that but given yesterday's and then today's failed run-up, I think the carburetor is completely shot.

I'm no wrench but I was not happy with the mechanic's "must be trash at the fuel jet" hypothesis.

 

Trash in a metering jet would make the engine lean if anything and the fuel odor isn't consistent with that condition. Trash in the (float) needle & seat however could prevent it from stopping the flow when the bowl was full however. A negative G condition could concievably dislodge a chunk of crap somewhere that might eventually make it's way into the needle & seat but with all the filters in place it would likely have to originate from inside the float bowl itself. I've also seen an engine primer start leaking internally and cause a similar condition, but I can't see where a negative G condition would ever trigger the primer to start leaking. Nothing surprises me at this point though. It's impossible to diagnose without pulling the cowling off, but the clogged metering jet theory doesn't wash.

 

The mechanic would probably realize that if he spent a few minutes thinking about it, people tend to expect an immediate sight-unseen diagnosis whenever they bring something to a mechanic but the fact of the matter is he won't know what's wrong until he get's into it and starts tearing sh*t apart. He probably just blurted out the first thing that came to mind knowing full well that he'd be reserving any official diagnosis until he'd had a chance to get into it. I wouldn't loose confidence in him just yet if it were me, he was probably still fully engrossed with the spar repair he was working on when you walked into the shop.

 

Jim

Trash in a metering jet would make the engine lean if anything and the fuel odor isn't consistent with that condition. Trash in the (float) needle & seat however could prevent it from stopping the flow when the bowl was full however. A negative G condition could concievably dislodge a chunk of crap somewhere that might eventually make it's way into the needle & seat but with all the filters in place it would likely have to originate from inside the float bowl itself. I've also seen an engine primer start leaking internally and cause a similar condition, but I can't see where a negative G condition would ever trigger the primer to start leaking. Nothing surprises me at this point though. It's impossible to diagnose without pulling the cowling off, but the clogged metering jet theory doesn't wash.

 

The mechanic would probably realize that if he spent a few minutes thinking about it, people tend to expect an immediate sight-unseen diagnosis whenever they bring something to a mechanic but the fact of the matter is he won't know what's wrong until he get's into it and starts tearing sh*t apart. He probably just blurted out the first thing that came to mind knowing full well that he'd be reserving any official diagnosis until he'd had a chance to get into it. I wouldn't loose confidence in him just yet if it were me, he was probably still fully engrossed with the spar repair he was working on when you walked into the shop.

 

Jim

 

I haven't lost confidence in our mechanic (he does work exclusively for our school). I just wanted to discuss more possible theories between that time and tomorrow when the carb. is torn down. I suppose your theory has merit. I'm at a loss and can't wait to see.

I suppose your theory has merit.

 

Hopefully some merit as I've been an A&P for more than 30 yrs now :) .

 

Chances are you'll never know what the problem was. The carb will be removed and tipped and turned 13 different directions by the time he gets it onto the bench so any debris may likely be flushed back into the bowl by the time he gets it apart. A good cleaning and reassembly is in order though it sounds like.

but I can't see where a negative G condition would ever trigger the primer to start leaking.

 

Unless someone's knee inadvertently unlocked it? Or wasn't locked to begin with and bumped?

 

Chances are you'll never know what the problem was.

 

This is why I didn't respond (besides the fact I worked only a "short time" as an A&P) it could be "anything"... like my wife asking me when the dryer stopped working, "what is wrong with it?" (ok, let me put on my Carnac the Magnificent hat...) many times until you get in there how to know.

 

-Rob

The aircraft immediately developed a bad (severe) "surge", couldn't maintain RPM, a strong smell of avgas entered the cockpit

 

So Zach... what was it? Any word?

So Zach... what was it? Any word?

 

Thanks for asking, Rob. Turns out it was indeed some trash that had been upset in the bowl. 70% of the jet was blocked by a whitish substance. Now the mission is to find out where all of this junk came from since the 2001 engine overhaul.

70% of the jet was blocked by a whitish substance.

 

Oh my... wow... yeah wonder what that could be. Thanks

The airplane most not get flown very much.

 

Were you able to send the sludge out to be analyzed?

The airplane most not get flown very much.

 

Were you able to send the sludge out to be analyzed?

 

It did sit before it's pre-buy two years ago. Since then, it's gotten a bit of time on it as everyone wants to get their mits on that plane at the flight school. I'm glad it happened to me and not someone with 1-2 hours in that plane --or with kids/family on board.

 

Sure did. And the carb. off to be overhauled.

 

 

Oh my... wow... yeah wonder what that could be. Thanks

It reminds me of a deposit found in most shower heads that aren't cleaned too often. Bummer!

White Trash:

 

1.) old gas.. separated Tetraethyl lead deposits.

2.) any tank liner or repair substance.

 

Only a guess, but am very interested in what you find out.