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raimo.toivio(at)rwm.fi
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 Posted: Tue Oct 18, 2011 6:01 am Post subject: Heavy In-flight Vibration Riddle /The Solution /The Winner( |
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Marcel, Frans and rest of you fine people
My plan is to open and check the engine by
professional during a winter delay.
So far I think the piston # 3 is essential to
check.
Before that I will happily fly about 10 hrs. It
runs so smoothly after replacing the spark plugs
that I will not worry about possible damaged
engine.
Pls notice - the heavy (infact very frightening
and scary) vibration and shaking was only quite
momentous. I found quite soon a MAP & RPM
combination which made sense. During the flight I
tried couple of times if it will go better outside
that combination but immediately came back.
I was not worried my engine so much - that is only
an engine and w/o it a plane is still very well
flyable. Instantly I worried about the engine
fixing, structural things, engine separation and
such things. I was happy I completed that Mod "an
engine mounting frame strenghtening". I knew I
have to make a soon decision to quit the engine
and made a forced landing. When I managed to find
a good power /rpm -selection, I was happy, relaxad
a bit and went on flying. I was so satisfied that
I did not try to find a solution and try magnetos
A ja B separately. Maybe I thought -"the situation
is good enough now - do not try to irritate it and
dig any blood from my nose!".
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!
That combination was somekind a sweet pot.
The spark plug head was blue, you remember?
I think it has been very hot. Maybe because it was
totally short circuited. Then it was red glowing
all time long - that is why I was talking about
detonation. The mixture was maybe full time and
totally exploded before the correct time. That is
known to happen when for example one valve is red
hot. If there has been detonation - there should
also be some marks in the piston: after a hard
load detonation the piston will be burned, a low
load detonation can even split the piston.
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.
Anyway - this is quite an unusual think to happen.
A Rotax Service Agent in Finland told me that
there has only once before reported him about an
inflight broken spark plug. That means about 1
plug failures let us say in every 25.000 flight
hours or less (under his thumb there are about 100
Rotaxes, 10 years and +50 hrs /year / engine).
So, obviously there are no reasons to worry about
loosing a spark plug during a flight. We all are
changing them every 100 hrs flight time, are not
we?
Raimo OH-XRT Finland, will be in Sicily in few
hours
Viestit: 121
Liittynyt: 13:35 Tiistai 10 02 2004
Paikkakunta: Toijala
-----Alkuperäinen viesti-----
From: zwakie
Sent: Monday, October 10, 2011 3:01 PM
To: europa-list(at)matronics.com
Subject: Re: Heavy In-flight
Vibration Riddle /The Solution /The Winner(
<mz(at)cariama.nl>
I have another thought on top: what will this have
done to the crankshaft and/or piston rod and
bearings?
Should one be worried about increased tolerances,
excessive wear a.s.o., especially having continued
flight for an hour?
I have made the same mental note that Frans has
made, I too would not have expected vibrations to
become so imminent by one failing spark plug.
Thanks Raimo!
--------
Marcel
(Europa Classic Tri-Gear PH-MZW)
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Remi Guerner
Joined: 14 Dec 2010
Posts: 284
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| Posted: Wed Oct 19, 2011 1:01 am Post subject: Re: Heavy In-flight Vibration Riddle /The Solution /The Winn |
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Hi Raimo,
As an engineer who has been working two decades for a spark plug company, I want to add a few thoughts about your engine problem:
A misfiring spark plug, cannot cause detonation.
A single misfiring spark plug on one cylinder cannot cause the high level of vibration you have experienced.
There are only two cases where a spark plug can cause detonation: the first one is if you are using a spark plug with a too hot heat rating. In this case, the nose core and the center electrode of the spark plug becomes red hot and ignite the fuel mixture even without a spark. The second case is when the spark plug is not torqued enough, becomes loose so that the heat transfer from the shell to the cylinder head is limited, causing the spark plug to become very hot. Both cases will cause preignition and possible detonation.
I assume you were using the right spark plug type and that your blue spark plug was found to be tighten correctly. So in my opinion, the very hot blue spark plug you got was not the cause but the consequence of another phenomenon, probably preignition and/or detonation, caused by something else.
The two main causes of detonation are: a too lean mixture and a too low octane fuel. This is were I would direct my investigation.
Preignition and detonation may seriously damage all combustion chamber parts such as piston, rings, and valves.
After such a problem I would ground the aircraft until the root cause is found, and I would carefully check the above parts for damage. Before removing the cylinder, I would perform a compression check and a boroscope inspection of the combustion chamber.
Hope that helps.
Remi Guerner
F-PGKL
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brian.davies(at)clara.co.
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| Posted: Wed Oct 19, 2011 3:24 am Post subject: Heavy In-flight Vibration Riddle /The Solution /The Winner( |
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Following on from Remi's post, it might be worth following the recent blog
on the Rotax Owners website. A Rotax 912 owner suffered a partial fuel
blockage to one carb that only showed itself under high power conditions-
and then only intermittently. In your case, if you have a partial fuel flow
problem to one carb, reducing fuel flow by changing power settings could
make the symptoms disappear.
Worth checking?
Regards
Brian Davies
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