Prop Governor Question

scott_l

Well-Known Member
This happened in a Twinstar and this is what I wrote to maintenance. What do you guys think happened?

I flew XXXX this afternoon and found the right engine was having random drops of RPM by about 30 RPM at full power almost every minute. When I reduced the throttle(we reduced to cruise climb power 25”/2400 RPM) per the oscillating RPM memory item the frequency decreased but it was still happening every few minutes. When we reduced to cruise power(21”/2200 RPM) it seemed to stop, but on approach I found the right governor was maintaining the RPM plus or minus 10 RPM while the left maintained RPM right on. Through this time nothing was out of the ordinary for any engine indications other than RPM.

Not a huge problem but I was just wondering what the cause might be.
 

z987k

Well-Known Member
How in the hell can you tell it was plus or minus 10 rpm? Turbulence causes more than a 10 or even 30 rpm change.

Ops check normal.
 

scott_l

Well-Known Member
G1000...the other engine was not wavering at all. This airplane has been breaking down nonstop and this is probably just another thing to add to the list. Props were just overhauled because the sheath on the leading edge was separating from the wooden blade.
 

KSCessnaDriver

Well-Known Member
How in the hell can you tell it was plus or minus 10 rpm? Turbulence causes more than a 10 or even 30 rpm change.
Digital tach? What are you flying that turbulence causes a 30RPM change? I see all kinds of crazy, long period turbulence and never get any movement of RPM during it.
 

scott_l

Well-Known Member
The other thing was there was a noticeable yawing motion whenever the right engine dropped back in RPM....slightly disconcerting on initial climb out.
 

Capt. Chaos

Well-Known Member
Let's see, on the list of things I have seen cause those symptoms..
Gunk in the screen at the prop governer
Internal leak in the prop hub itself
Found a paper towel left in the prop hub
Oil pressure regulator on the way out
Intermittent spark plug or mag
Bad mag timing
Had the harness fall off the back of a mag
The engine was just a pos
Wrong governor installed
And once the govorner was actually bad.
 

Hammertime

Well-Known Member
If, as you say, the change is noticeable without looking at the engine instruments, then it's a valid write up. If not, then you fallen victim to digital instrumentation information overload...

I'm not familiar with the Twinstar or FADEC, but it could as be as simple as the prop governor control being a little loose (there's some slop in the control cable).
 

z987k

Well-Known Member
Digital tach? What are you flying that turbulence causes a 30RPM change? I see all kinds of crazy, long period turbulence and never get any movement of RPM during it.
Are you kidding me? Every airplane with a prop. You must not know what turbulence actually is.

I concur with the yaw. If it's yawing due to un-commanded prop change, then ya, write it up. Otherwise. LOL!
I had a prop go into beta un-commanded once. That is worth a write up.
 

tiredcfi

Not a child of magenta
It's a known problem. I had to shut one down once because the oscillations got out of hand. Does the FADEC have the lastest firmware? (lol)
 

scott_l

Well-Known Member
If, as you say, the change is noticeable without looking at the engine instruments, then it's a valid write up. If not, then you fallen victim to digital instrumentation information overload...

I'm not familiar with the Twinstar or FADEC, but it could as be as simple as the prop governor control being a little loose (there's some slop in the control cable).
Guess I should have been a little more clear. This is the L360 Twinstar with the good ol' 6 levers and there was noticeable yaw.
 

ppragman

FLIPY FLAPS!
Let's see, on the list of things I have seen cause those symptoms..
Gunk in the screen at the prop governer
Internal leak in the prop hub itself
Found a paper towel left in the prop hub
Oil pressure regulator on the way out
Intermittent spark plug or mag
Bad mag timing
Had the harness fall off the back of a mag
The engine was just a pos
Wrong governor installed
And once the govorner was actually bad.
How you likin' Klawock Cable?
 

Hammertime

Well-Known Member
Nice! I hear that thing is a rocketship. If the linkage between the governor and the control is loose, your fluctuations could be vibration related... You would know by how it responded to inputs. (e.g. if the rpm doesn't change immediately with a control input.) I'm sure your mechanic will figure it out...

edit: JC doesn't like my cell phone keyboard...
 

Roger Roger

Paid to sleep, fly for fun
I doubt you have a problem with the governor itself. Probably there is something else going on in the engine causing a power fluctuation (intermittent magneto, fuel injection system issue, etc) and what you are seeing is just the governor overshooting as it tries to keep up with the power fluctuations. In my limited experience governors are pretty bulletproof and the only time we've had to pull them is when you max out the adjustment and they still won't give you max takeoff RPM. Either way, as a CFI troubleshooting is sort of out of your hands and it's obviously a legit problem. If no one has already, someone needs to take a mech up with them and demo the problem.
 

KSCessnaDriver

Well-Known Member
Are you kidding me? Every airplane with a prop. You must not know what turbulence actually is.

I concur with the yaw. If it's yawing due to un-commanded prop change, then ya, write it up. Otherwise. LOL!
I had a prop go into beta un-commanded once. That is worth a write up.
For real? I've flown multiple piston multi engine aircraft, and have never seen turbulence change the RPM's on an airplane.
 

z987k

Well-Known Member
For real? I've flown multiple piston multi engine aircraft, and have never seen turbulence change the RPM's on an airplane.
Ya, and not just multi's and certainly not just constant speed either. I don't understand how you haven't seen this.
 
Top