Twin Feather Check/Governing range

rwillis1

Well-Known Member
Hello,
Our run-up checklist for the PA-44 has the pilot set 1500RPM using the throttles and then bring the props in and out of feather to ensure that the feathering mechanism works. Can someone explain why this is done at 1500RPM? I know it's because it's out of the "governing range" but I'm not sure I really grasp why that is.

Thanks in advance
 

z987k

Well-Known Member
You could do it a max rpm to, doesn't matter. My guess the reason is because someone wanted to add items needlessly to a checklist. People in flight departments that don't fly much are pretty awesome at coming up with all kinds of fun things like that.
 

Houston

Well-Known Member
I'm just taking an uneducated stab at the answer, but I suspect it has to do with how much abuse the engine could stand. Worst case scenario is if the prop would not come back out of feather or the pilot let it run too long with the prop feathered.
 

Roger Roger

Paid to sleep, fly for fun
I'm just taking an uneducated stab at the answer, but I suspect it has to do with how much abuse the engine could stand. Worst case scenario is if the prop would not come back out of feather or the pilot let it run too long with the prop feathered.
Picture it this way... Would you rev your engine with the clutch in, while stopped, then shift into 5th and drop the clutch? Because that would be exactly what you'd be doing if you feather checked at higher RPM.
 

Houston

Well-Known Member
Picture it this way... Would you rev your engine with the clutch in, while stopped, then shift into 5th and drop the clutch? Because that would be exactly what you'd be doing if you feather checked at higher RPM.
Well, I did once have a 55 Chevy that would do something like that. The poor thing was so beat up that if you floored it in third gear (three on the column) it would pop out of gear. Sort of like it was saying "I'm old and tired, don't treat me that way". The best one was one night with a friend and when I floored it, the thing popped out of third so hard that it went into second. I think I just about had my friend believing that it was an automatic downshift feature.
 

Autothrust Blue

"...I know bait when I see it..."
Hello,
Our run-up checklist for the PA-44 has the pilot set 1500RPM using the throttles and then bring the props in and out of feather to ensure that the feathering mechanism works. Can someone explain why this is done at 1500RPM? I know it's because it's out of the "governing range" but I'm not sure I really grasp why that is.

Thanks in advance
Being nothing but a stupid pilot, I'd imagine it's a combination of:
(1) Enough RPM that it's off the feather locks, if the specific propeller has that feature
(2) Enough power to keep the engine running as it takes the large change in load
(3) Not enough power to cause damage due to that load

You could probably do it at any arbitrary RPM, but that's a nice, round, consistent number.
 

matthew

Well-Known Member
I think the reason it has to be out of governing range is because taking the prop from full forward to feather back to full forward relatively quickly is going to induce an unnecessary load on the prop system (for just a feather check).
 

Houston

Well-Known Member
Just taking another uneducated stab at it, I think the reason to keep it out of the governing range is to ensure a there is no confusion between a change to feather and a change to control the RPM by pitch change. As an example, if the prop would not feather, but would change pitch, and we were running at a high RPM when the prop lever were pulled aft, there would be a slowing of the engine RPM. How would we know that was from feathering rather than just a normal pitch change of the governor. That along with it would impose a stress the engine isn't designed to take would seem to be the primary reasons. But again, I'm just guessing.
 
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