Prop/Governor check question

[P&H]

In the Seminole during ME training, I remember doing the governor check at 1500RPM, bringing the prop lever all the way back momentarily until the engine RPM dropped (about 4 to 500 RPM) , and then brought it back full. That was the feather test.

Then, the governor check involved bringing the engine to 2000RPM, bringing the prop back to see an RPM drop (100RPM) to make sure it's working, then forward againmaking sure it holds the setting.

Is this how you guys typically do the checks? And anything you'd add to it?

 

[tgrayson]

Is this how you guys typically do the checks? And anything you'd add to it?

The Seneca's procedure is the same, as you would expect. However, the Duchess AFM doesn't call for two separate checks.

It's not clear to me that the feather check is truly different from a governor check. I asked our Chief Mechanic about it years ago and he seemed to think you were testing the same mechanism. But then, I don't have a great deal of faith in most A&P's theoretical understanding of the systems they work on.

 

[Crockrocket94]

We would excercise the oil in the prop governer prior to doing the feather check.

Its just a simple three times to bring it back to about 1800 i thought, maybe I am wrong?

I have no idea where my Seminole checklist went, but we brought it back to the specified RPM 3 times, then seperatly we would set it 1500, and do the feather check.

 

[Dugie8]

Keep in mind the feather check, on most pistons, isn't checking the governor it is check that the "anti feathering" pins will actually disengage and allow the prop to feather, the governor check is checking that the governor can actually control the prop (and the changes in RPM you have been seeing while taxiing are not just inertial forces changing the blade angle).

I suppose you could accomplish the two checks at the same time by pulling the prop lever back slowly to get a 500 RPM or so drop then pulling the lever into feather.

 

[tgrayson]

Keep in mind the feather check, on most pistons, isn't checking the governor it is check that the "anti feathering" pins will actually disengage and allow the prop to feather,

Do you believe this is being checked even if the props don't move into the feather position?

 

[Dugie8]

Do you believe this is being checked even if the props don't move into the feather position?

If you do the check properly (this coming from flying seminoles, barons and King Airs) you will get a LARGE change in RPM very quickly and, in the case of the King Air, a momentary spike in torque.

I should have expanded further, the feather check checks the anti feathering pins (underspeed governor on TPs) and full travel of the shuttle valve to allow all the oil out of the hub.

 

[tgrayson]

If you do the check properly (this coming from flying seminoles, barons and King Airs) you will get a LARGE change in RPM very quickly and, in the case of the King Air, a momentary spike in torque.

So you're saying that the quick, LARGE drop in RPM is indicative that a different mechanism is involved?

I've never noticed any difference on the Seneca; my view on that aircraft is that the feathering mechanism could be inop, but I couldn't tell because the RPM drop with both checks is pretty much the same.

 

[Dugie8]

So you're saying that the quick, LARGE drop in RPM is indicative that a different mechanism is involved?

I've never noticed any difference on the Seneca; my view on that aircraft is that the feathering mechanism could be inop, but I couldn't tell because the RPM drop with both checks is pretty much the same.

Remember, I said do the check properly. To check the governor you should be moving the prop lever slowly along its full range, at 2000 RPM (and 20" inches or so) that should be about 500 RPM drop from full forward to full "aft". When you go into the feather position the rpm drop should continue to about 900 to 1000 RPM. There should also be a noticeable change in the sound as the props go into feather, a very distinctive "wump wump". I realize that isn't the most scientific way to check but it is an indication.

Another good check is when you bring the prop out of feather it should almost overspeed or at the very least go over the 2000 RPM as all the oil is pumped back in and the governor simply doesn't have the authority to stop the inertia the blades have from going to a fine pitch (low pitch).

 

[tgrayson]

To check the governor you should be moving the prop lever slowly along its full range, at 2000 RPM (and 20" inches or so) that should be about 500 RPM drop from full forward to full "aft".

The Seneca POH says to do it differently: advance the throttle until you get 2000 RPM, then bring the prop back until you just get a 100-200 RPM drop. Leave it there and advance the throttle, making sure the RPM says the same.
I'm not convinced that this method is superior to just pulling the prop back and watching the RPM drop.

 

[Dugie8]

The Seneca POH says to do it differently: advance the throttle until you get 2000 RPM, then bring the prop back until you just get a 100-200 RPM drop. Leave it there and advance the throttle, making sure the RPM says the same.
I'm not convinced that this method is superior to just pulling the prop back and watching the RPM drop.

Well that is accomplishing what you want to check, at 2000 RPM (im guessing that is about 20 inches or so) the governor is just able to control the prop, bring it back a few hundred and push the power up the governor should maintain the RPM (as you described). The excercising way gets more oil in and out of the hub (good for cold weather ops and if the airplane has been sitting a while) but I think it gives a better indication of the "health" of the governor.

Next time you fly, pull the prop lever fully aft and let the RPMs stabilze, then pull it all the way into feather and see what you get. Keep in mind the amount of load you are putting on the prop hub(s) when you do this though and doen't let it sit in feather very long.

I like to do it/did it this way since it accomplishes three things in one movement, check the governor, check that the prop will feather and it fully cycles the oil in and out of the hub.