Question for King Air Pilots

[Crism]

This may sound stupid but here it goes. I know when on the ground you're supposed to keep the "Mixture Levers" at Low Idle. However, if you pull them far enough back, not enough to stop the engines, is it possible to stop the props (but keep the turbine running) no matter what location the prop lever is at? If you power up from there, would the props just start spinning again? Thanks!

 

[81Horse]

Doesn't sound stupid, Crism. You just need to understand a little more about the PT6 engines, and how they're controlled. Here's an interesting link: http://www.avweb.com/news/avtraining/182740-1.html

Because the engine power section and gas generator section are not directly connected in the PT6, it is possible to feather the prop while the engine is running normally.

Perhaps you've seen this -- some operators prefer to start up and shut down the engines with the prop in feather; the prop can also be feathered in flight while the engine continues to run. When the prop is feathered, it generally will turn at a slow to moderate speed; however, it can be stopped (some aircraft had braking systems installed to allow safe passenger boarding with an operating engine).

In fact, certain boneheaded pilots of my acquaintance have been known to sneak up under a wing to hold a prop blade still while the pilot starting the engine wonders why in the HELL the prop is seized up. (Funny, I mean stoopid, trick -- don't try this at home!)

On the King Air, and most PT6-equipped airplanes, there are three sets of levers: power or torque levers, prop levers (to set prop RPM), and condition levers (to set the engine idle speed for flight or ground operations, or for fuel cutoff shutdowns).

Your original question asks about mixture control; that function (more or less) is accomplished by the condition levers. Prop control, including feathering, is mostly done with the prop levers. Power control (torque) is done with the power levers.

Some functions of the levers overlap, because of several types of fuel control and governing systems. For instance, use of the power levers below the normal range controls prop blade angle and engine power in the beta and reverse ranges (for speed control in taxi and landing).

Anyway -- it all seems complicated, but it's extremely easy to operate and very rugged. Just to reiterate, the simple answer to your question is: yes, you can fully feather a King Air prop with the engine running normally. It's commonly done, for a variety of reasons.

 

[Crism]

Ahh ok. Thanks for the info!

One more question: Why is it that on all of the PT6 engined aircraft, the props are feathered for shutdown? Does it really make a difference?

 

[Diesel]

Inside the props is a reallly huge spring. I mean it's HUGE.

Anyways this spring is allways pushing the props to feather. While the oil in the hub is pushing the props to pitch. So when you shut down you can either pull the props to feather which dumps the oil. Or leave them in pitch and as the oil pressure is reduced with the engines shutting down the spring will push them to feather.

In the king air I fly with Avia 5 blade props there is no spring. Oil is used to both go from fine pitch to feather. If you shut the engines off the props will stay in whatever position you last left them. If you have an engine failure and for some reason you can't get the prop levers featherd in time there is a big red button you can push. It dumps and pumps the oil both at the same time with a motor and pushes the prop to feather.

 

[tej823]

Generally speaking PT6's are feathered prior to shutdown to reduce the gearbox/prop to the minimum speed and push the oil from the prop to the gearbox. Part of the arguement goes that once the fuel is shutoff and the engine shuts down the oil pressure pump stops, and it is better to have the rest of the engine slowed or nearly stopped to reduce the time when active oil pressure is not available to all of the rotating componenets.