Flat pitch or feather???

[apcooper]

In a piston twin if you lose all oil pressure will the prop seize in the feather position even if you leave the prop control full forward? I've heard this is the case but am puzzled by this since every time you shut down the engines on the ramp therefore depriving them of oil P the prop is in the flat pitch. Someone enlighten me!!

 

[Workin'Stiff]

Most "featherable" props have anti-feathering pins which fall into place for that very reason. You shut the engine down, the oil pressure drops, but these pins engage and prevent the prop from feathering on the ground. I know on the Duchess you can override this by placing the prop handle in feather. I just don't know why you'd want to do that. Not only that, it's hard on the starter to get it going again with the prop in feather.

 

[MTpilot]

The pins are hooked to squat switches on the gear.

 

[Flechas]

The pins are hooked to squat switches on the gear.

It depends on the plane, in most light twins the pins are spring loaded and driven by centrifugal force, that's why you have to make sure to feather the prop above 800 rpm.

 

[paulsalem]

In our Barron 55 the pins are held disengaged until about 300 RPM by centrfigal force (actually inertia, but thats another rant). So as long as the blades are feathered either by the prop control or the sudden loss of oil pressure in the govs you'll be fine.

There is no relation to the squat switch in the baron


That is how I understand it atleast.

 

[minitour]

I know on the Duchess you can override this by placing the prop handle in feather.

Wow...Didn't know that...I guess they didn't teach it to us because it is tough on the starter...

-mini

 

[Flechas]

Is not that you can override that. That's what the prop handle is for, to feather the prop.

 

[minitour]

Is not that you can override that. That's what the prop handle is for, to feather the prop.

wow...when you say it like that, I guess I did know that...

-mini

 

[ackattacker]

This thread needs clarification... the feather position does not "override" anything...

In your typical piston twin the oil pressure provided by the prop governor acts to bring the propeller to a flatter pitch (higher rpm). Moving the propeller control to feather directs the prop governor to drop oil pressure to the prob hub, the same as if would happen if you ran out of oil or the oil pump failed (or the engine seized).

Aerodynamic forces normally would act to bring a spinning propeller to flat pitch, however in a piston twin this is counteracted by some combination of springs/air pressure/counterweights, so that the loss of oil pressure brings the propeller to feather.

However, the "feather locks" will lock the propeller in a non-feather position if the prop is stopped or at a very low RPM at the time that the oil pressure loss occurs (be it from actual loss of oil pressure or moving the prop control to feather). These feather locks are actual physical hooks on the blade hubs which drop into place when the prop RPM is very low.

So, when you stop the engine on the ground, the engine stops turning before the oil pressure has a chance to drop significantly, so the feather locks drop into place and prevent the prop from going into feather. This makes the engine easier to start. If you accidentally stop the engine while it is feather ed (or land with the engine feathered), you will have to start the engine to bring it out of feather unless you have an unfeathering accumulator.

If the engine seizes suddenly in the flight the propeller will not feather, nor will it be possible to feather it due to the feather locks. It cannot be "overriden". This doesn't matter, since a stopped prop creates very little drag whether feathered or not.

If oil pressure drops suddenly in flight the propeller will feather, and there's nothing you can do to stop it.

If the engine fails in flight, without losing oil pressure, and you get slow enough that the engine is just "barely" windmilling, then it may not be possible to feather it because of the feather locks. You may have to increase airspeed to bring propeller RPM above the point where the feather locks engage, then feather the propeller.

got it?

 

[Lead Sled]

Changing the subject just a little...

The next time you guys are out on the ramp, notice the different ways the Garrett vs. the Pratt & Whitney turboprops are started up and shut down. The PT-6s are either put into feather before they are shut down or they go into feather as they are spooling down and the oil pressure bleeds off if the pilot forgot. They are started in the feather position.

During shutdown, Garrett-powered airplanes keep the propeller in flat-pitch using "start locks" or pins in the propellor hub. This is done by moving the power levers into beta (reverse) as the engine is spooling down allowing the pins to move into position. If the pilot fails to do this the blades will move into feather as the engine spools down and the oil pressure bleeds off. If the pilot screws up, he must use the electric unfeathering pump to put the blades in flat pitch and pop the start locks into position proir to start. After the engines are started the pins must be moved out of the way, centrifically, by momentarily going into beta after the engines are started.

'Sled

 

[SIG600]

Just to elaborate on what 'sled said.. this is done because

Pt-6's are a free air turbine, not directly connected to the engine. Thus starting in a feathered pitch does not affect the engine.

You can not start a Garret (or something similar) in a feathered pitch, because it's a direct drive set up, it will increase the load on the starter and everything else as the engine tries to spool up.


And most piston twins I've flown are held in a flat pitch by oil pressure, and while they may not self feather, they will go to a higher pitch with a loss of oil and towards a feathered position.

 

[bafanguy]

This all just proves that those whirling metal things in front of the engine are just too much trouble and should be avoided...unless driven by an R2800, in which case, the sound is worth the complication.

 

[Lead Sled]

This all just proves that those whirling metal things in front of the engine are just too much trouble and should be avoided...unless driven by an R2800, in which case, the sound is worth the complication.

Man you've got that right. Propellors are for boats.

'Sled

 

[BD King]

Now then, If ya really want to look cool, here is what you do, at least in my case. After flying the King Air for the past 3 or 4 weeks, and jump into the C-340, you pull up on the ramp and at shut down feather both props. Cool.

www.bdkingpress.com

 

[jaywc7]

Coooooooooool! I gotta try that!

I don't have much to back up what I know about this topic, other then to say that I've done quite a bit of reading, and know a little about Duchess props.

Anyways - with each post I read, something popped into my head that I wanted to say. Then as I read on, I found that the next consecutive post included exactly what I was thinking! This went on and on and on, and I finally figured by the end that there was nothing much else to say! It encompassed everything I've come to know, or claim to know anyways.

As far as the feathring of the 340 props though! That's just hilarious!!!

 

[Lead Sled]

Now then, If ya really want to look cool, here is what you do, at least in my case. After flying the King Air for the past 3 or 4 weeks, and jump into the C-340, you pull up on the ramp and at shut down feather both props. Cool.

Funny stuff, but it's actually not a bad idea. The C-340 isn't your typical MEL trainer and other than during runups, its props are seldom feathered. Even then, you're just checking for a drop in RPM and you really don't know if the props are actually going into feather. I've flown a couple of cabin-class twins that were misrigged and during the annual were found to have a propellor that wouldn't feather - not a good thing given the pathetic single-engine performance capabilities of piston twins.

Yup, it's problably a good idea not to take something that your life's going to depend on for granted. Check it all the way to feather once in a while. Your mechanic can walk you through the procedure.

'Sled

 

[jaywc7]

Funny stuff, but it's actually not a bad idea. The C-340 isn't your typical MEL trainer and other than during runups, its props are seldom feathered.

So - I'm curious now... You are saying that the C-340 is different, in that it can be fully feathered at shutdown if desired? Or am I confused about what was wrote? That would still be hard on the engine to start up with them feathered wouldn't it???

Check it all the way to feather once in a while.

YEAH!!! I always feather each of my props individually, and then both together on my runup... Isn't that common practice???

 

[bigD]

So - I'm curious now... You are saying that the C-340 is different, in that it can be fully feathered at shutdown if desired? Or am I confused about what was wrote?

I think what Lead Slead is saying is that since the 340 isn't typically used as a trainer, the props are rarely fully feathered - unlike a plane such as a Seminole where the props are feathered for practice quite often.

 

[BD King]

So - I'm curious now... You are saying that the C-340 is different, in that it can be fully feathered at shutdown if desired? Or am I confused about what was wrote? That would still be hard on the engine to start up with them feathered wouldn't it???



YEAH!!! I always feather each of my props individually, and then both together on my runup... Isn't that common practice???

It is sop to pull the props into feather at shutdown on a KingAir, unless its a B100. Out of habit, I grabbed the wrong set of levers. The engines will jump and shake a little on the start.

 

[jaywc7]

I think what Lead Slead is saying is that since the 340 isn't typically used as a trainer, the props are rarely fully feathered - unlike a plane such as a Seminole where the props are feathered for practice quite often.

Ok. I understand. You are refering to feathering in flight for simulated engine failures and such. I see i see...

Out of habit, I grabbed the wrong set of levers. The engines will jump and shake a little on the start.

Funny!