Prop Unfeathering Accumulators - Question
 

I've enjoyed my twins in the past that had unfeathering accumulators.

With accumulators, its much smoother to restart an engine after practicing single engine work. Just push the prop lever forward, give the motor some throttle and mixture, and its immediately running smoothly again. Without accumulators, the engine shakes badly when you start it using the starter, which is the only option you have if the prop is feathered. Hard on the starter, hard on the prop, hard on the Lord mounts, and hard on the crew.

This is one reason most training these days is "zero thrust" where the ME instructor "simulates" an engine out by reducing MP to 12". The motor never actually gets shut down. That's fine and dandy for flight school safety, but that training method cannot, and does not, demonstrate the actual immediate loss of performance with a windmilling prop and a dead engine. I want to train under real-world conditions with the dead engine windmilling, so if it does happen in real life, I've seen it before, and know what to do. So...

I'd like to install accumulators. I can buy a set for well under $1k, and they don't weigh very much. The service manual doesn't show exactly where the accumulators are mounted.

Would one you guys with accumulators installed post a few pics of them, both front and rear, so I can get an idea of where the factory mounted them?

Here is the page from my parts manual 1967 337b

Thanks Frank. My manual is similar to yours.

I can see that the rear is mounted on the engine mount frame somewhere (with what appear to be hose clamps), but the front doesn't give much reference to where its installed.

Actual photos is what Id really love to see!

Actually, it looks it would require special governors as well as the accumulators, so I guess I'll just deal with the "shaky start up" upon unfeathering. Not willing to spend $3k on this little "improvement".

They were standard on O2s. If I were getting shot at, I'd want them for sure. The seconds they save on restart could save your life!

If I was gonna do ME flight training on a regular basis in it, I'd still consider them though.

Most of the accumulators on these planes were removed back in the day. No one wanted the maintain them and they just weren't needed. The start up isn't so bad without them and just go easy on the starter when you do this. Make sure you follow the procedure in the book for in flight restart, works like a charm

Here is one with accumulators trying to restart front engine.
@ 7:30

https://youtu.be/tAB486BKI10

You could see how hard it was on the starter, and they never even got it running again, at least in the video. Based on the narration, I assume they eventually did.

If the accum. was working, as soon as the prop lever was moved up out of the feather position, the oil pressure in the accum. would move the blades to their normal operating position, which would force the prop to start windmilling. Engine is spinning at this point, ready to start, without ever touching the starter. Just get the throttle/mixture setting correct, and it will fire right up!

I read you have to service the nitrogen in the accumulators every 90 days. Seems as if theirs had not been serviced recently. So glad I have my own nitrogen tank for servicing struts, would work for the accum. as well.

The rear accumulator was mounted on the RT side of the engine mount. the front was mounted in the nose wheel well forward of where the nose gear would be when retracted. The plane also had Woodard governors on it
Kim

Did you use them?

Along these same lines, have not been able to get my props to feather on the ground. What has been others experience? Trying to figure out where to go from here. Props just serviced and out of prop shop. We've played with control cable rigging without change. Governor problem?

I must admit - the "feathering gates" are a BAD idea!

Every other twin I've trained in and flown, you pull the prop levers all the way back, the props feather. Not so with the 337 - Cessna felt an additional memory item was required in this most critical time - "lift the prop control into the feathering gate".

When I first flew the plane, I didn't realize these "gates" existed, and had I tried to feather a prop in a true emergency, I would have failed because WHY DID CESSNA PUT THESE RETARDED GATES ON THE PROP LEVERS??? I guess they thought Skymaster drivers were so dumb, they may accidentally feather a prop. What other possible reason?

Rant over!

I love the Skymaster, but I won't pretend its perfect.

That said wslade2, how are you going about testing feathering? Prop has to be spinning to release the feathering locks. You can't just feather it with the engine shut off. I'm sure you know that, but a lot of pilots, especially those coming out of singles, don't truly understand how fully-feathering props work.

I sure they were used during check rides if an engine was pulled. We did remove them during an engine change. The rear mount was repaired in the area where the accumulator was mounted and was going to take some engineering to remount it. so we decided to just remove them.

On the feathering issue: am aware of gates. In attempt to feather on ground, run up engine/warm up, then smartly pull back throttle and prop control being sure to lift up and over gate. No joy on seeing prop in feather position after engine stops. It's been a while but pretty sure manual says prop feather supposed to happen like that. Watching video earlier in this thread, looks like would be assured steady decent on one engine if am unable to feather a prop, but hope of maintaining altitude if prop would feather.

wslade,
At what RPM are you at when you try to feather on the ground? If your RPM is not high enough(>1700 approx.), the feather latches will not have moved out of the way.

I may be the only one that likes the feather gates...they seem logical to me, much like aircraft I have flown (turboprop) that has a reverse gate. It is a helpful small step that makes you really "think" about the action you are taking - ensuring you intend on feathering.

Jeff

The gates totally make sense to me and in fact when flying other piston twins and singes I can't believe they don't have gates. I too have lots of time in TurboProps so it was easy for me to use the gates when going into Beta with those

wslade, when you do your run up before takeoff based on the book, there is no feather? I pull the levers up in high pitch then bring them back to feather. Try leaving the props in high RPM and lift up the lever then pull all the way back (down)