Loss of Oil Pressure on PA-44

[buxflyr]

Loss of Oil on PA-44

I was asked a question in the Private-Multi oral and wanted to get everyone's opinion on how they thought the Seminole reacted to this situation. The question was...

"Say I am flying along and run out of oil in the left engine. How would this affect the prop?"


How does it affect the prop?? Feather? No change immediately? What about the anti-feathering pins?


Comments??

 

[minitour]

Assuming it's like the other piston twins I've flown (duchess and twinkie), if you are losing oil pressure the prop will want to head towards feather...

BUT

If you're losing RPM at the same time (perhaps the engine is seizing(sp) up?), the pins may not let the prop feather.

Bad stuff..

if oil pressure is dropping, try to remedy, then shut it down (feathered) and land...asap!

JMHO

-mini

 

[Amish RakeFight]

Remeber that there is an important difference between constant speed props on complex singles and twins. In most cases (that I'm aware of) when you lose oil pressure in a single engine airplane, the prop tends to move to a low pitch - high RPM setting. This is due to the aerodynamic effects of centrifugal force. In other words, oil pressure holds the prop in a high pitch, low RPM setting.

In a twin, the REVERSE is true. Oil pressure will hold the prop in a low pitch - high RPM setting. Due to counterweights and a spring in the hub, a loss of pressure will casue the prop to move to a high pitch - low RPM setting, or if you will a feathered position which is more streamlined with the relative wind, providing a reduction in drag. As Minitour mentioned, centrifugal pins in the hub may prevent feathering, but only when RPM is down to a certain value. If the RPM drops too low, the pins will prevent feathering to occur.

 

[Learsforsale]

Remeber that there is an important difference between constant speed props on complex singles and twins. In most cases (that I'm aware of) when you lose oil pressure in a single engine airplane, the prop tends to move to a low pitch - high RPM setting. This is due to the aerodynamic effects of centrifugal force. In other words, oil pressure holds the prop in a high pitch, low RPM setting.

In a twin, the REVERSE is true. Oil pressure will hold the prop in a low pitch - high RPM setting. Due to counterweights and a spring in the hub, a loss of pressure will casue the prop to move to a high pitch - low RPM setting, or if you will a feathered position which is more streamlined with the relative wind, providing a reduction in drag. As Minitour mentioned, centrifugal pins in the hub may prevent feathering, but only when RPM is down to a certain value. If the RPM drops too low, the pins will prevent feathering to occur.

950 RPMs, I believe

 

[Amish RakeFight]

Here's a portion of the PA44-180 oral questions I put together for my MEL ride at ATP flight school.


4. Describe the propeller system.
A. Who makes the propellers?
Hartzell
Two-bladed
Controllable pitch
Constant speed
Full feathering
Metal propellers

B. What does oil pressure do to the propeller? Low Pitch / High RPM

C. Which lever manipulates oil pressure to the propeller? The blue prop control.
Think of the prop control lever as an oil valve:
All the way up – ADDS oil.
All the way back – REMOVES oil.


D. Which unit regulates oil pressure to the propeller? The governor

E. What is the function of the nitrogen cylinder?
The nitrogen-charged cylinder is a cylinder charged with nitrogen that will assist in moving the prop into the feathered position. When oil pressure is lost or decreased, it moves the prop to a high pitch / low RPM setting.

F. What is the purpose of the spring in the prop dome?
Together with the nitrogen-charged cylinder and blade counterweights, the spring drives the prop to a High Pitch / Low RPM setting.
The prop hub fills with oil, which compresses the spring at full RPM, when the prop needs to come back to low RPM, oil pressure is reduced and the spring/nitro cylinder/ C.W. help bring the prop back.

G. Define constant speed.
A Constant engine RPM is maintained by the propeller governor which adjusts the propeller pitch.

H. What unit adjusts the propeller to maintain a constant RPM and how does it do it?
A flywheel in the propeller governor regulates the pilot valve by adjusting engine oil pressure in and out of the propeller hub. The oil pressure works against a piston in the hub to adjust propeller pitch to maintain engine RPM.

I. Define full feathering.
When the propeller blades are in alignment with the relative wind, they are feathered.
Feathered propeller blades reduce the drag caused by the blade area exposed to the relative wind.
The propeller is “Feathered” when the blue control handle is moved fully aft past the low RPM detent, into the “FEATHER” position.
The Propeller takes approx. 6 seconds to feather.
The mixture should be placed in the “CUTOFF” position to stop engine combustion.

J. Will the propeller always feather?
NO. Centrifugal stop pins prevent feathering below 950 RPM.
Regardless of the prop lever position, if oil pressure is lost, the propeller will feather when the RPM is above 950 RPM.

K. What are centrifugal stop pins?
A mechanism designed to prevent feathering below 950 RPM.



L. What is the true purpose of the centrifugal stop pins?
The purpose is to allow the propeller blades to remain in a low pitch upon engine shutdown. This will prevent excessive loads on the engine starter during the next engine start.

 

[buxflyr]

Thanks alot guys... much appreciated!

 

[User546]

I agree with all the above.

Two things of importance here. The propeller will fail (unaided) to a feathered-like position.

The bigger problem here is not what the prop is going to do, but the fact that your engine is out of oil. Time to get proactive and shut that baby down, and feather it manually. The longer you wait the more damage your possibly going to do, and there's no chance your probably getting that engine back at that point anyways.

I'd personally secure the engine then land at the nearest PRACTICAL airport.

 

[MauleSkinner]

...The propeller will fail (unaided) to a feathered-like position.

...In the Seminole, not ALL multi-engine airplanes (just to be anal )

I used to fly a Baron that required oil pressure to feather the props...not sure why they did it that way on that model year, but for some reason they did, and I'm sure there are other examples.

Fly safe!

David

 

[minitour]

...In the Seminole, not ALL multi-engine airplanes (just to be anal )

I used to fly a Baron that required oil pressure to feather the props...not sure why they did it that way on that model year, but for some reason they did, and I'm sure there are other examples.

Fly safe!

David

Ouch! That had to be a ..... BEECH ..... if you lost oil pressure!

Har har har!

-mini

 

[FL420]

Time to get proactive and shut that baby down, and feather it manually.

Wouldn't it be wiser to feather the engine first, while the RPM's are >950, then shut the engine down?