Dear Frans, Remi, Brian and all who were
interested
Thank you for your Very interesting messages (they
are below).
During last three days my engine (912S) has got
his 250 hrs service (in fact 50 hrs service only)
+ max and full care inspection because of the
topic: Heavy In-flight Vibration Riddle.
Before that (after my hazard and when changing
sparks only) I had flown flawlessly 2 hrs 25
minutes w/o any problems and The Engine has
performed great.
The inspection and service was completed w the
best pros in Finland available (I was there also,
just looking behind their shoulders, do not
worry).
1) Engine is like a new one and between The
Factory Limits and Measurements excluding
following
2) Right carburrettor, 2nd float, "some" material
has "obviously" separated, gone and disappearred
somewhere.
- pls notice: these floats have checked last
spring when completed 200 hrs engine service. They
looked like ok then but did not checked very
carefully, of course.
- that little "separated" part could be also a
malfunction of production, maybe it has never been
there
3) That blue colored spark plug was really totally
dead (it was NGK R DCPR8E)
What ideas we got?
A) if some part of the float separated during the
flight it could have blocked partially fuel flow.
After case it could have gone through the system
and no problems anymore. If that is so, changeing
sparks meaned nothing - a new start up the engine
meaned.
If that is so, please check your floats. For your
information, there was a Service Bulletin about 15
years ago about those floats. I have not checked
it so far (and that should be nothing in my case
[engine 2006] but who ever knows).
B) this case is a bit embarrassing but I am brave
enough to report it to you (could be worth of it
for some of you).
We tried the engine with that broken spark. As
Remi writed A single misfiring spark plug on one
cylinder cannot cause the high level of vibration
I have experienced.
Confirmed. It cannot. I tried. But, what if (after
checking the mags) I took off with one magneto
only! And loosed one spark just after take-off.
Then I had only three sparks!
I have to say - I tried it today - and the The
Vibras were very known. I have been there. If that
is really so, I flied about one hour with three
sparks only (there was a heavy head wind but I
still was wondering where all the power has gone).
That is also the well known CS prop syndrom: The
RPMs are fixed: it is not so obvious to see engine
limitations.
***
What can I say:
* check out your floats in the carburrettor
chambers (well, Rotax owners at least)
** double check before take-off you have selected
dual magnetos: if you loose one spark w two
magnetos you will not notice but if you loose one
spark with one magneto you will surely notice. And
that will vibra you!
I have a Cessna type key operated magneto. It is
not so easy to see what magneto(s) is (are) valid:
A, B or Both. If you are building a plane, have
two separate switches. They are easy to confirm;
both upp (and a secure latch down)!
I took off after sunset and was a bit hurry and
maybe also more all less nervous. That is a
typical start upp for a chain which will easily
lead up to the accident.
In my case, what about loosing 1/4 spark during
take-off - that was a very short grass strip.
*** if you have engine problems during a flight
try always magnetos. That is what you have learnt
when flying your PPL. I did not by purposely but
I was (maybe) wrong.
_____________________
Trying to be a better pilot. A flight today was a
last one I think until a year or even more has
gone and the new season 2012 will begin...
_____________________
The Competition has got The Winners - there are
three of them.
I will publish The Names of The Winners ( I assume
I am free to do that ) very soon.
Cheers, Raimo Toivio
Europa XS Mono OH-XRT #417
Updated flight hours /landings: 258,15 /466
37500 Lempaala
FINLAND
p +358-3-3753 777
f +358-3-3753 100
toivio@fly.to
www.rwm.fi
-----Alkuperinen viesti-----
From: Brian Davies
Sent: Wednesday, October 19, 2011 2:20 PM
Subject: RE: Europa-List: Re: Heavy In-flight
Vibration Riddle /The Solution /The Winner(
<brian.davies@clara.co.uk>
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
-----Original Message-----
From: owner-europa-list-server@matronics.com
[mailto:owner-europa-list-server@matronics.com] On
Behalf Of Remi Guerner
Sent: 19 October 2011 10:02
Subject: Europa-List: Re: Heavy In-flight
Vibration Riddle /The Solution
/The Winner(
--> <air.guerner@orange.fr>
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
<frans@privatepilots.nl>
On 10/18/2011 03:58 PM, Raimo Toivio wrote:
> 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!
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.
> The spark plug head was blue, you remember?
Precisely.
> I think it has been very hot. Maybe because it
> was totally short
> circuited.
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.
> 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.
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.
> Anyway - this is quite an unusual think to
> happen.
Sure it is. Therefore, dig to the root of it
before flying it again.
Frans
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