PA44 Hydraulic Q....

GreenDayPilot

GreenDayPilot

Well-Known Member
Can anyone tell me about the accumulators in the Seminole's PROP System? Anything and everything about'em...

Thanks! :D

EDIT: PROP... ooops...
 
They store oil pressure to bring the props out of feather. So if you fully shut down and feather an engine the accumulator has oil pressure stored. This means to get the props out of feather all you need to do is push the prop lever forward, the accumulator releases the oil pressure and the props start to unfeather, then the prop will start spinning from the wind (and the engine will start assuming it has fuel and spark). In seminoles without unfeathering accumulators you have to use the starter to get the prop spinning and out of feather.

That's the simple version. I'm sure there are much better/more accurate explanations out on the interweb somewhere about accumulators in general.

Also, I've never heard of them referred to as part of a "hydraulic system" when talking about the seminole. Although in many applications accumulators are often a piece of a hydraulic system.

Here is a similar thread from this forum:

http://forums.jetcareers.com/airlin...nals-atp/26691-unfeathering-accumulators.html
 
Now here's a question I remember being asked, that I have since forgotten: Is the oil in the accumulator engine oil, or hydraulic oil? The point of the question is to understand whats putting the oil in them.



Another tidbit I remember is that the oil is countered by compressed nitrogen(?) so that when you unfeather, the oil doesn't just stay in there.
 
"Is the oil in the accumulator engine oil, or hydraulic oil?"

It's prop oil. Don't you ever check your prop oil?






Just kidding....

It's engine oil.

In my Apache, flaps and gear run off of a hydraulic pump in the left engine, or the emergency hand pump. The props work off of engine oil.
 
Swen said:
Now here's a question I remember being asked, that I have since forgotten: Is the oil in the accumulator engine oil, or hydraulic oil? The point of the question is to understand whats putting the oil in them.



Another tidbit I remember is that the oil is countered by compressed nitrogen(?) so that when you unfeather, the oil doesn't just stay in there.
Click to expand...

Well, okay, first of all, the props are always controlled by engine oil pressure. On multi-engine planes, oil pressure holds the blades in the flattest pitch position, and counterweights, compressed nitrogen, or sometimes other methods try to feather the props. The reason for this is if the engine should loose oil pressure or fail that the prop will feather to reduce drag since you still have another engine to keep you going.

Single engine planes are the opposite with the oil pressure used to force the blades into the higher pitch position.

Now, since oil pressure is required to unfeather a prop in a multiengine plane, it can be rather difficult to get them unfeathered since the engine must be spinning to produce enough oil pressure to unfeather the props. This is where the accumulators come in. They help unfeather the props enough to get the engine spinning (windmilling), producing oil pressure, and hopefully running again.

There's a basic explanation.
 
True story...

When I was instructing in PHX we had almost all 2000 models out there. The 79 versions didn't do as well in the heat so we lucked out with the newer ones. Our newest instructor at the time lived in PHX and had done the 90 day program out of PHX. He went off to JAX, did his standardization and came back out to PHX to instruct. Somehow, in all the Seminole flying he had never been in a 79 model. Anyhow, his very first day on the job he took up an MEI candidate to do some airwork. I was up doing pattern work with another student when they called up tower about 20 minutes later and declared an emergency. Apparently they had shut down the left engine in flight for a training maneuver but could not get it started. So the trucks rolled and I cut my lesson short and landed to be on the ground when they got back. The approach and landing were pretty good and the biggest issue was the CFI trying to taxi the plane single engine. The trucks followed him to the ramp where he shut down no problem, gave the ARFF guys some info and called it a day. He was all set to call JAX and get some MX for the airplane when I had him walk through what happened. He described shutting down the engine, doing the maneuver and then bringing the the prop out of feather to get the engine spinning again, but of course nothing happened.

It took me about 10 minutes to stop laughing and explain to him that there were no accumulators on the 79 model and he had to bump the prop with the starter.
 
BobDDuck said:
True story...

When I was instructing in PHX we had almost all 2000 models out there. The 79 versions didn't do as well in the heat so we lucked out with the newer ones. Our newest instructor at the time lived in PHX and had done the 90 day program out of PHX. He went off to JAX, did his standardization and came back out to PHX to instruct. Somehow, in all the Seminole flying he had never been in a 79 model. Anyhow, his very first day on the job he took up an MEI candidate to do some airwork. I was up doing pattern work with another student when they called up tower about 20 minutes later and declared an emergency. Apparently they had shut down the left engine in flight for a training maneuver but could not get it started. So the trucks rolled and I cut my lesson short and landed to be on the ground when they got back. The approach and landing were pretty good and the biggest issue was the CFI trying to taxi the plane single engine. The trucks followed him to the ramp where he shut down no problem, gave the ARFF guys some info and called it a day. He was all set to call JAX and get some MX for the airplane when I had him walk through what happened. He described shutting down the engine, doing the maneuver and then bringing the the prop out of feather to get the engine spinning again, but of course nothing happened.

It took me about 10 minutes to stop laughing and explain to him that there were no accumulators on the 79 model and he had to bump the prop with the starter.
Click to expand...

Wasn't there an attempt to restart in the checklist? I think I remember something about that in those long, horrible checklists ATP had...
 
Can't remember. I do remember something about having to pitch over a bit for airspeed, but I don't recall anything about the starter for the 2000 models.
 
Stone Cold said:
Wasn't there an attempt to restart in the checklist? I think I remember something about that in those long, horrible checklists ATP had...
Click to expand...

If he had the right checklist with him it's in there. My guess is he either had the 2000 checklist stuck in his bag from his training days, or he thought he had it memorized and didn't read it.
 
Oh... I see what you are saying. Yeah, on the 79 model it says to hit the starter. If I recall he had a 2000 checklist with him. Apparently he didn't know there was a difference.
 
I've feathered both props on the Apache (not at the same time). They start back up okay, but there is some shaking and rumbling going on, at first. No need to dive for airspeed, though.

I was wondering if you could get them to start by diving without using the starter? Not brave enough to try it.
 
the ATP checklist for the 00 models notes to engage the starter if the prop fails to windmill.
 
BobDDuck said:
It took me about 10 minutes to stop laughing and explain to him that there were no accumulators on the 79 model and he had to bump the prop with the starter.
Click to expand...

No wonder I never heard of accumulators...I only flew in some raggedy old 'Nole.
 
Swen said:
No wonder I never heard of accumulators...I only flew in some raggedy old 'Nole.
Click to expand...

ME TOO!!

accumulators? You mean they help start the dead engine? It takes me about ten minutes to get that damn thing started:)

Its fun when the starter breaks on you during an engine shutdown! ;)
 
DE727UPS said:
I was wondering if you could get them to start by diving without using the starter? Not brave enough to try it.
Click to expand...

the 2000 and newer pa44s have unfeathering accumulators so that the props will unfeather without the engine running (they store oil under pressure to unfeather the prop) When the props unfeather, they windmill so all you have to do is turn on the mags. If this is not installed, the prop will not unfeather without the engine runing to produce oil pressure so you will have to start the engine with the props feathered first
 
Whether its a new or old seminole if that engine doesnt start spinning after going through the restart checklist the first thing I do is turn on the starter. Seems logical. I know it puts some stress on the starter but is it bad enough to where it would break something on a newer one or say a duchess.
 
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