Unfeathering Accumulators

[BrettInLJ]

My school just got one of the newer model Seminoles and so far I have only instructed in the older models. I was looking at the unfeathering accumlator for one of the engines when the cowling was off and notice that it is a nitrogen cylinder attached to the firewall that has a hose routed to the prop governer.

I was wondering how the nitrogen charge is maintained in the cylinder and whether it has limited uses before recharging. I have heard of other accumulators that work using oil pressure, so any info on the mechanics of what is going on with the nitrogen in the governer I would appreciate. I have talked to a mechanic and looked in the POH but there is not enough information there for me. I figured since there are plenty of the newer models at ATP an instructor or student here could help me out.

 

[Maximilian_Jenius]

Any chance of your school getting a brand new twin engine Diamond Twinstar I think there called (DA-46) before I arrive?

 

[Dugie8]

My school just got one of the newer model Seminoles and so far I have only instructed in the older models. I was looking at the unfeathering accumlator for one of the engines when the cowling was off and notice that it is a nitrogen cylinder attached to the firewall that has a hose routed to the prop governer.

I was wondering how the nitrogen charge is maintained in the cylinder and whether it has limited uses before recharging. I have heard of other accumulators that work using oil pressure, so any info on the mechanics of what is going on with the nitrogen in the governer I would appreciate. I have talked to a mechanic and looked in the POH but there is not enough information there for me. I figured since there are plenty of the newer models at ATP an instructor or student here could help me out.

The nitrogen in the cylinder is used to "store" energy. A liquid (engine oil) cannot be compressed, so when the engine is running the engine driven oil pump system has a tap off line that goes to the prop hub, that pressurizes the nitrogen in that cylinder. The cylinder is divided by a flexible diapraghm (sp?), when oil is pumped in, the nitrogen is compressed to roughly the equivilent of the engine oil system (45 psi or so). When you feather the engine a valve is closed trapping that pressurize oil in the cylinder. When you move the prop lever out of feather that valve is opened and that oil is pushed out by the 45 psi Nitrogen into the prop hub causing the blades to twist just enough to start "catching" the air and start to windmill. When the prop starts to windmill, that turns the engine driven oil pump, which starts pressurizing the oil system, including the prop governor, which in turn puts more oil into the prop hub, causing the blades to flatten even more.

You can see how it becomes a self sustaining process.

 

[BrettInLJ]

Thanks for your help. I couldn't find that info anywhere.

And Matt, I think that would be a big no.