Seneca Prop Operation

[Frank Natoli]

Learning to fly a Seneca II with three bladed props.
A copy of the Seneca II POH that I obtained online has two separate sections for prop operation, one for two bladed props, one for three. The section for two bladed props says prop control is a function of oil pressure, springs and nitrogen. The section for three bladed props omits mention of nitrogen.
A hardcopy of the Seneca II POH that I purchased from my FBO does not separate two from three bladed prop operation, and does mention nitrogen.
Do three bladed props use nitrogen to move into feather?

 

[FlySlater]

Hi Frank, Nitrogen is common but not always used in feathering propellers. A spring in the prop hub and/or counterweights at the blade roots can accomplish the same function. As for your specific aircraft, it'll depend on the propellers installed. It's possible that the propellers are one of the original certificated options could even be installed by STC and wouldn't be listed in the original POH at all. If you look at the POH from the aircraft itself (tail-number specific) it should have the information for those props in there. Or, if you just need a quick answer on whether it uses nitrogen, one of the FBO mechanics should be able to tell you.

 

[Radar Contact]

Do three bladed props use nitrogen to move into feather?

I don't know the answer. I would be concerned if my props required nitrogen to go into feather. My unfeathering accumulators use nitrogen to drive the props out of feather which isn't a big deal to me because if the nitrogen doesn't work (has happened), I can still unfeather them with the starter. In a twin, I want there to be zero chance that the prop won't feather when commanded.

 

[MauleSkinner]

I don't know the answer. I would be concerned if my props required nitrogen to go into feather. My unfeathering accumulators use nitrogen to drive the props out of feather which isn't a big deal to me because if the nitrogen doesn't work (has happened), I can still unfeather them with the starter. In a twin, I want there to be zero chance that the prop won't feather when commanded.

Isn't that why you do a feather check on the run up?

 

[dell30rb]

Learning to fly a Seneca II with three bladed props.
A copy of the Seneca II POH that I obtained online has two separate sections for prop operation, one for two bladed props, one for three. The section for two bladed props says prop control is a function of oil pressure, springs and nitrogen. The section for three bladed props omits mention of nitrogen.
A hardcopy of the Seneca II POH that I purchased from my FBO does not separate two from three bladed prop operation, and does mention nitrogen.
Do three bladed props use nitrogen to move into feather?

If you are going to take a checkride in the airplane you should find out.

If you are just renting it for occasional flights I wouldn't be too concerned about how the feathering system works (though more knowledge is always good) just that it does, in fact work. If the prop didn't have anything visibly wrong with it (like a leak or something) and passes the feather check then you're good to go.

 

[dell30rb]

I don't know the answer. I would be concerned if my props required nitrogen to go into feather. My unfeathering accumulators use nitrogen to drive the props out of feather.

Its not uncommon for propellers to use compressed nitrogen in lieu of a spring to go into feather. The pressure from the compressed nitrogen or spring is constantly trying to drive the propeller into the feather position. Engine oil pressure, regulated through the propeller governor, drives the blades to fine pitch as needed to develop RPM. As long as you don't have a leak, the nitrogen pressure should remain and not need any regular servicing (save for at annual, etc...). If it passes the feather check, you know the nitrogen charge is sufficient.

Your accumulators may use nitrogen in a bladder or on the other side of a piston as a way of "storing" oil pressure. The engine might be developing ~ 50psi of oil pressure running at speed, and when you put the propeller control into the feather position a valve shuts on the accumulator, closing it off from the falling engine oil pressure as the engine shuts down. The accumulator retains some oil at 50psi pressure. When you unfeather the engine, this stored oil pressure is used to give the propeller a quick push to get it instantly out of the feather position, instead of having to spin the engine with the starter and wait a few seconds for the oil pressure to come back up naturally.

 

[denverpilot]

The three bladers on the Turbo Seminole have the nitrogen charge. Can’t say on the Seneca but Piper did use them.