frans(at)privatepilots.nl
Guest
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 Posted: Tue Oct 18, 2011 7:18 am Post subject: Heavy In-flight Vibration Riddle /The Solution /The Winner( |
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On 10/18/2011 03:58 PM, Raimo Toivio wrote:
| Quote: | I have earlier forgot to mention one thing: when I tried to increase
power by moving a power lever forward, I got significantly less power!
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This is a weird thing. Maybe the carb slide was stuck after all, so
opening the throttle further would result in a leaner mixture. A leaner
mixture burns hotter and slower. Maybe that caused the spark plug to fail.
Another option is that you had a hidden problem: One spark plug lead
cross coupled from another cylinder (so it was firing when the piston
was at one of its lower positions), maybe due to a short circuit between
two spark plug cables. The interesting thing is that nothing bad happens
as long as the correct spark plug fires, because for the one with the
wrong timing there is nothing left to ignite and it sparks into a
non-combustible void. But then as soon as the correct plug fails, the
mixture will be ignited by the remaining spark plug which fires at the
wrong time, and the burning mixture works against the up-moving piston.
This will also heat the spark plugs and cause a hell of a vibration.
| Quote: | The spark plug head was blue, you remember?
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Precisely.
| Quote: | I think it has been very hot. Maybe because it was totally short
circuited.
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No, you can't get it hot by short circuiting it. Ignition has a very
high voltage but low amperage. Total energy is very low, way to low to
even warm the plug.
| Quote: | Also, I assume the coils are somehow connected together. I mean, a
missfiring in one spark and in one cylinder, could it also disturb
another one (spark /cylinder) ??? If so, that means more vibra.
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I think you really have to carefully check the whole ignition and carbs.
I wouldn't fly it anymore until this is done. I know it runs ok now, but
maybe there was a reason why the spark plug failed, and if this reason
still exists it will happen again.
As far as I can tell, the whole situation is not what you would get with
just a faulty spark plug.
| Quote: | Anyway - this is quite an unusual think to happen.
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Sure it is. Therefore, dig to the root of it before flying it again.
Frans
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