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Is it possible to blame power loss on faulty glow plug?

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Is it possible to blame power loss on faulty glow plug?

Old 08-21-2008, 09:23 AM
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Default Is it possible to blame power loss on faulty glow plug?

I heard this hypothesis at my field but it didn't make much sense to me. Apparently some members of my club do think that an engine can loose power due to a faulty plug specially when the engine unloads. I don't see how can this make any sense but I figured I'd ask.
Old 08-21-2008, 09:32 AM
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Default RE: Is it possible to blame power loss on faulty glow plug?

It's quite true. The heat of the glowplug (amongst other things) determines the ignition timing and plugs can go bad (act hotter or colder). Kind of like messing with the distributor timing in a car. To be more precise, it's not so much the actual temperature of the plug but how easily it can ignite the mixture. A "hot" plug ignites it more easily than a "cold" plug.
Old 08-21-2008, 10:11 AM
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Default RE: Is it possible to blame power loss on faulty glow plug?

Ok, this is a very good point, but why would it sort of accentuate when the plane starts moving and the engine load diminishes?
Old 08-21-2008, 12:42 PM
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Default RE: Is it possible to blame power loss on faulty glow plug?

Downunder can better speak to this, but...

As an engine unloads, the mixture is effectively leaner.

Usually if the engine gets too lean the plug may burn out... or if it continues to function the engine runs too lean and hot, causing it to develop less power... much like when you turn the needle too far to lean while tuning...

If you use the wrong or defective plug, you may tune the engine for it on the ground, which can exacerbate the problem in the air.

Let's say that the plug is not "hot" enough on the ground because of a manufacturing error. So you end up tuning the engine to what you think is optimum on the ground, but once in the air the engine leans out way too much resulting in reduced power.

If the plug is in the right range however, holding idle well in a slightly rich condition and you tune it accordingly, when the engine leans out in the air, it may be "in the zone" so to speak because of the extra margin, producing optimum power.

Old 08-21-2008, 01:15 PM
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Default RE: Is it possible to blame power loss on faulty glow plug?

In a simple answer – yes. I’ve had glow plugs go bad in flight to the point that I couldn’t throttle up beyond ¼ throttle. I’ve seen other guys run their engine lean and get them too hot for one flight, and after resetting the mixture the engine just wouldn’t come up to speed or run right until the plug was changed.

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Old 08-21-2008, 03:25 PM
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Default RE: Is it possible to blame power loss on faulty glow plug?

Hi!
It could happen! But...99% of the time it's a lean setting that is the culprit!
Old 08-21-2008, 08:37 PM
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Default RE: Is it possible to blame power loss on faulty glow plug?

I think Jaka is correct in your case but for racing A lot of the pilots put in new glow plugs before each race just because of the reasons DU stated. Better safe then sorry. I see A lot of IMAC pilots do the same thing. For sport or weekend pilots???? When the engine quits when the heat is removed could give you A clue it's time to replace.
Old 08-21-2008, 10:08 PM
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Default RE: Is it possible to blame power loss on faulty glow plug?

You can be right in the middle of a real hard run and hear the plug go away. There will be a slight loss of rpm because the engine is now running like a pure deisel and the plug element could be already laying in the grass somewhere. In a less extreme example, as the plug element sacrifices itself to catylize combustion it will finally reach a point where it can't do the job completely, only partially. A lot of plugs never make it to this stage depending on how they have been used or abused, the elements just break from fatigue.
Old 08-22-2008, 12:20 AM
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Default RE: Is it possible to blame power loss on faulty glow plug?

In my book, flying plane == good plug. It's good to know about this. I'll check with another plug.

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