Hello
Quick introduction, my name is Christian Laursen and i'm from Denmark, more specific from a little flying club in the northern part of Denmark. (Called NULF)
I'm a certified B1, working both in GA (as mechanic) and Airline (as part-M).
I have a Eurostar ev-97
msn 2005-2605
Reg OY-9301
TTSN 497
TCSN 1447
Propel: woodcomp klassic 170 3/R
Motor: rotax 912 ULS
Sn: 5645166
I have during the last ~100 hours experienced an increasing vibration in my aircraft during flight, more specific between 3700-4800 rpm.
Below 3700 rpm I assume i start to enter the idle range and the vibrations I'm experiencing is normal, and the rumble changes to a more recognizable idle vibration.
The fault is unable to be recreated on ground, and only with a minor carburator balancing issue around 3000 rpm. (Where the two balancing needles is just a hairline apart)
~10 flight hours ago the propel was pitched for 5100 WOT then the vibrations predominately was between 3700-4100 rpm
As part of troubleshooting, I pitched the prop a little finer (5400 WOT) now the vibrations predominately is between 4100-4800 rpm.
The aircraft have just undergone a 100 hour inspection on engine and airframe, and as part of troubleshooting, an inspection of floats, needle and membrane in the carburators.
Plus a mechanical and pneumatical balance of the carbs.
Engine leak check:
Cyl 1 ~3.5%
Cyl 2 ~4.2 %
Cyl 3 ~10 %
Cyl 4 ~3.8 %
Cyl 3 increased leak is only at the intake valves, and iaw the LMM the tolerance is 25%
The vibrations is best described as a deep rumble far lower frequency then the engine rpm, and they appear out of nowhere from one second to the next.
If the vibrations starts, and the rpm is increased above 4700-4800 rpm the vibrations stop, until the rpm drops down in the above mentioned range again. The specifik point where the vibrations starts is random.
I would really appreciate your qualified take on this problem, or at least point me in the right direction, because with my current technical background, I would deem the aircraft not airworthy with this condition.
