Fouling a spark plug at altitude

meritflyer

Well-Known Member
Heard recently that this is a real possibility and could ultimately account for an in-flight, partial power loss if the mixture is mis-managed.

Has anyone else heard details on such?

Would a carb engine or EFI carry a greater risk?
 

norcalpilot25

Well-Known Member
I haven't personally experienced it but I have a few friends who have. It seems to mostly happen due to excessive rich mixture at altitude (ie full rich at 5,000 and above). Doesn't seem to matter if its Carb engine or Fuel Injected engine. Although I would assume it would be easier to get it to happen on a Carb engine due to the fact that they typically have a rich running cylinder or two no matter what.
 

Yank&BankmyRJ145

New Member
Heard recently that this is a real possibility and could ultimately account for an in-flight, partial power loss if the mixture is mis-managed.

Has anyone else heard details on such?

Would a carb engine or EFI carry a greater risk?
OK, maybe this is along the same lines. I guy told me last week he puts a lot of prime into the engine when its cold. It his airplane does not start on the first time or second the plugs glaze over and it will not start for hours. :confused:
 

mikecweb

Well-Known Member
Heard recently that this is a real possibility and could ultimately account for an in-flight, partial power loss if the mixture is mis-managed.

Has anyone else heard details on such?

Would a carb engine or EFI carry a greater risk?
I had it once in the Baron.
We'd run them full rich in the climb for better cooling and at least one plug got effed at about 6000ft. I leaned it to peak and left it for about 5 mins and it worked itself out.
 

Barty

Well-Known Member
OK, maybe this is along the same lines. I guy told me last week he puts a lot of prime into the engine when its cold. It his airplane does not start on the first time or second the plugs glaze over and it will not start for hours. :confused:
It is natural for an engine to take an extra pump from the primer when it is cold outside. After all, colder air = denser air which requires more fuel for the proper mixture. However I would not use more than one additional shot over what is required for a normal cold (engine, not OAT) start.

It sounds like he might just be getting carried away with the primer and is flooding the engine.

Unfortunately leaded fuel is very unforgiving when it comes to proper mixture. Too rich of a mixture leads to cool cylinders, which leads to lead fouling the plugs. I would avoid going full rich in a climb at higher altitudes unless the POH specifically calls for it.
 
R

Roger, Roger

Guest
It's certainly possible to foul up a plug in cruise by running too rich. I've never had it happen, but it could. As a previous poster said, I would guess that a carbed engine would be more susceptible, as they are a little more likely to have one or more rich cylinders. Some aircraft (such as the 172R) actually recommend leaning even in the climb, above 3000' to get peak RPM.

As far as the cold starting, I have found that the best way to start a 172R engine cold is to prime the crap out of it. I suspect there are 2 things at work. First, the cold air is denser. Second, in the colder air the fuel will not vaporize and ignite as easily. I did have one occurrence in a carbed 172 where after trying a cold start we couldn't get the thing to light off for the life of us. My CFI siad something about frosting the spark plugs. That's all I've ever heard this phenomenom, and I'm kind of curious about whether or not its an OWT.

Also, point of order to the OP-EFI stands for electronic fuel injection. All mainstream aviation fuel injection systems are hydro-mechanical.
 

USMCmech

Well-Known Member
Also, point of order to the OP-EFI stands for electronic fuel injection. All mainstream aviation fuel injection systems are hydro-mechanical.
I've never seen an "Electronic" fuel injected airplane engine, and I doubt that one has ever been certified.

All FI airplane engines are hydro-mechanical, as Rodger said. They have more in common with a 57 Chevy, than a modern Honda.
 

Barty

Well-Known Member
There are some EFI systems available for experimentals and I would assume for LSAs.

I think you're more likely to see electronic (probably distributorless) ignition available in certified aircraft than EFI since it isn't difficult to maintain redundancy with such a system. Ultimately it will probably have to happen to make higher HP engines compatible with something aside from 100LL avgas. A typical magneto does not possess the ability to adjust timing on the fly to compensate for engine load, which is amongst the reasons why some aircraft require the higher octane fuel.

Oh yeah...you also tend to get less plug fouling when you have proper timing advance across the operating range of the engine. :D
 

USMCmech

Well-Known Member
There are some EFI systems available for experimentals and I would assume for LSAs.

I think you're more likely to see electronic (probably distributorless) ignition available in certified aircraft than EFI since it isn't difficult to maintain redundancy with such a system. Ultimately it will probably have to happen to make higher HP engines compatible with something aside from 100LL avgas. A typical magneto does not possess the ability to adjust timing on the fly to compensate for engine load, which is amongst the reasons why some aircraft require the higher octane fuel.
My understanding is that Contentials "FADEC" system is exactly that, a distributerless variable ignition timeing system.

There are 2 or 3 similar systems for experimantal aircraft engines. Most planes I've seen have one magneto, and one computer ignition system.
 
R

Roger, Roger

Guest
Yeah, that Continental FADEC system is pretty neato. I saw it on the Liberty XL2. I would imagine it makes quite an improvement in fuel efficiency and performance.
 

Barty

Well-Known Member
My understanding is that Contentials "FADEC" system is exactly that, a distributerless variable ignition timeing system.

There are 2 or 3 similar systems for experimantal aircraft engines. Most planes I've seen have one magneto, and one computer ignition system.
Cool...I figured someone would have come out with something by now, I just wasn't aware of it.

I've almost made up my mind that when I do decide to own an airplane of my own, it will probably be an experimental. There area couple of engine control units that were initially developed for automotive purposes that have been successfully adapted to aircraft that I will probably install and forgo magnetos altogether. IMHO, they're relics of a bygone age that should have gone the way of the dodo in airplanes 10-15 years ago at least. With a redundant electrical system, a distributorless electronic ignition system should be much more reliable than magnetos, not to mention offer easier starting, more fuel options, and better engine performance.
 

norcalpilot25

Well-Known Member
A few years ago Moony put a Porsche engine in a production aircraft. It had advanced fuel injection and ignition systems and preformed really well. In the end it never caught on, it was too expensive and too heavy. It seems most people are just too afraid to try new technology when we have been using the same tech for the past 50 years with few problems.

Heres an interesting read: http://www.seqair.com/Other/PFM/PorschePFM.html
 
R

Roger, Roger

Guest
Yeah, I think Continental may have the right idea. An air-cooled, horizontally opposed engine (just like we've always done it) is pretty light for the power output, and fairly bulletproof. They just need a serious update to the fuel injection and ignition systems.
 

Barty

Well-Known Member
It seems most people are just too afraid to try new technology when we have been using the same tech for the past 50 years with few problems.
That's the biggest problem right there.

Over on the AOPA boards, someone made the comment about how there were so few 20 and 30-somethings at fly-ins and the like. Basically the biggest obstacle is convincing the older crowd that the stuff works as well as their beloved magnetos, carbs and mechanical fuel injection. How many times have you heard someone (usually someone in the 50-60 age range) grumble about how you can't work under the hood of a car anymore? Its the same issue.

Personally, I'd much rather work on and drive on a daily basis a vehicle that uses EFI and electronic ignition opposed to one with a carburetor and breaker point ignition. It is more reliable, requires less regular maintenance and runs a hell of a lot better! I'd much rather fly an airplane using those as well, for the same reasons. Most of the mis-conceptions are based on 20+ year old experiments, like the Porche-Mooney, and totally ignores the progress that has been made in the meantime.
 

USMCmech

Well-Known Member
My solution is to have the FAA completely do away with regulating the design and manufacture of piston aircraft below say 8000 MGTOW.

If you want advanced technology in a piston airplane you have to look over to homebuilts. That sector of GA is booming, with new advanced stuff coming out every year. From self contained AHRS/PFI displays that fit in the plam of your hand, to EFI and ignition advances for aircraft engines.

The main reason that the tradional manufacturers can't or won't follow is the enormus cost of certifying anything through the FAA.
 
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