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Seminole question

DLconnection

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I know that if u lose your governor that the prop will go to the feathered position, due to lack of oil, the counter wgts, and the nitrogen in the propleller hub.

Now, if I was was to lose all of my oil pressure in the engine. Would the prop automatically feather or do I have to do it myself? If I lose all of my oil, the oil pressure would be nil and the oil temp. would steadly rise. Then the engine would die. I understand that, but I am not sure if the prop would feather.

I want to say no. Even though the engine is dead, the prop is still windmilling and there is some oil still in the governor. However the eng. driven oil pump won't be operating. Someone who has flown a seminole or a seneca...please clarify this one for me.
 

upndsky

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The prop on the Seminole has a nitrogen charged piston assisted by a spring. There are no counterweights (too heavy). If you loose all the oil, the blades would move to the feather position. However, there are locking pins that come out when the RPMs reach 800 or 950 RPMs, depending on the age of the airplane. These pins prevent the props from going to full feather, ie. when you shut the engines down at the end of the flight. The only way you can keep the locking pins from engaging is to move the prop handles to the feather detent. If your engine failure is due to a loss of oil, you don't want to hesitate feathering the prop. If you don't pull that blue handle all the way back, the engine will eventually grind to a halt but the prop won't be completely feathered.
 

treetop flyer

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upndsky,

Everything you posted about the PA-44 is correct, HOWEVER the Seminole DOES have counterweights (albeit small ones). I'd be interested to hear about a Seminole that has been modified to operate without them.

Regards, TF
 

Cattlepanel

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I'll confirm that counterweight deal. Same engine as the ol' Beech Duchess.......WOW, that was a great question that blew some dust off the brain.....Love the Seminole!!!!!
Ya'll fly safe
 

Data

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To answer the question, it would be automatic as the prop handle regulates oil pressure. If oil pressure is completly lost, the nitrogen charged spring is going to do its job. For the prop to not feather, well, it would have to be a catastrophic engine failue or something that would cause the props (and therefore the engine because it is connected directly to the prop) to drop below 950rpm in the time it would take for the spring to feather the prop (around 6 seconds).

And another thing, it's not really a centrifigal stop pin, it's more like a flyweight with a spring wrapped around it that prevents the prop from feathering below 950.

Hope it helps.
 

Hovernut

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See the pic over there to the left? That's what it's going to do! That has been a Comair interview question of late, at least to us CAA instructors. When the engine loses quantity/pressure, the governor pump has nothing to draw from and all the hub oil will leak back out. I had a Lycoming engine guy at Sun-N-Fun explain the interface between the governor oil supply/return and the crankshaft. He said there were no seals there, but a tight clearance. So, the governor is always "feeding and bleeding" the hub. Without positive pressure, the spring/N2/counterweights would squeeze all the oil out of the hub and feather the prop.

But, the hanging question is: with a catastrophic loss of quantity/pressure, will the engine weld the bearings and sieze faster than the prop will "autofeather!?" Hmmmm! I dunno!
 

jetdriven

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IF you have oil and the engine is windmilling, as hovernut says, the prop will not feather. If you lose oil quantity and therefore oil pressure (as in you left off the oil cap or an oil cooler hose is stripped) then the prop will feather but it will take six seconds. This is about the time it takes for the oil pressure to bleed from the hub, and since the governor is not replacing it, the prop will feather. I dont think an engine will catastrophically fail in that time due to lack of oil, but if it throws a rod and windows the case then it couold come to an instantaneous stop, with a non-feathered prop.
I knew some guys that had a C-421B that the engine suddenly siezed and the prop COULD NOT feather. It didnt bother them too much as they flew it another 250 miles before landing.
I have also seen a PA-31-350 Chieftain that had an oil cooler hose pop off on final and it lost oil pressure on 1/2 mile final. The prop feathered but the engine was still running! It sure couldnt develop much RPM or usable trust though. The pilot taxies into the freight ramp at DEN with one good engine and one feathered. Those of you who have tried to taxi a Chieftain on one engine know it is almost impossible. If you keep it moving and you use a LOT of brake on the "good engine side" you can make a go of it. Long story short is he taxies up with one feathered and opposite main brake on fire! Ha, that rotor was red hot and brake fluid whizzing out and catching fire. sheesh!
A duchess that crashed in tulsa 2 yrs ago because of the same thing. The RH engine caught fire due to an oil cooler hose leak and by the time they got on final the fire had damaged the gear system, and the had no green on RH side. Too bad the instructor thought he could take it around from 200 feet with one on fire and feathering, gear down, and full flaps.
 
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