Rpm fluctuations
Hello, I have an '05 T182T with the G1000. 1800 tach hrs, engine IRANed by previous owner 500 hrs ago. On a recent CC flight immediately after an oil change I noticed rpm fluctuations at cruise. I typically fly 22 squared and watch my engine numbers like a hawk (yes Im anal). For as long as I can remember my digital rpm gauge would read +/- 10 rpm. Now Im seeing +/- 40 rpm and notice a slight +/- in corresponding airspeed. I fly ROP, usually at 60% power and manage TIT in the 1560-75 range which gives approx 11.9gph. the prop gov. was overhauled 500 hrs ago and I have noticed no oil leaks. Engine uses 1 quart/25 hrs and oil analyses always good. Fuel injectors cleaned at every annual etc. MAP is rock steady as are CHTS and EGTs (which are all within 30 degr. of one another). I cannot hear or feel any perceived engine changes and plane functions great. Am I being overly concerned? I realize this legacy G1000 system is approaching 20 yrs old, could the tach just be showing its age?
Thanks in advance.
Comments
When was the prop IRAN'd last? If the pitch change mechanism in the propeller is getting sticky that can cause the behavior you are seeing. The governor makes a small change in pressure to correct a change in RPM due to an updraft or whatever. If the prop does not change pitch smoothly the governor keeps changing pressure until something happens, which in this case is an overshoot.
The prop was replaced with a new one during the previous IRAN. I have flown since the aforementioned flight and rpms now occasionally +/- 30, and seemingly more steady. I wonder if some dirt from oil change led to partially clogging oil feed to governor? Otherwise plane makes full power and runs fine.
Before you get carried away on the expensive stuff, Look over the connnections at the gov and make sure there is NO play in the control lever or the control cable/rod end. Make sure prop control cable is NOT the culprit . carl
IA 47yr A&P DAL A/C Inspector 172n