Dumb question, but need to know what is the autofeather switch for in props? Thanks. I did a search for "autofeather" but no luck-Mike Patel

Here's the definition of feather (from http://www.pakaviation.com/PVA/Library/Dictionary/)"to set the angle of Constant Speed or Variable Pitch propeller edge-on to the airflow to minimise drag and rotation following engine failure on multi-engined aircraft. Also applies to motor gliders which have feathering propellers to enhance engine-off soaring performance. "When you set it to auto-feather, the autopilot will do that for you.

It feathers the props. Automatically.;)Scroll to the bottom of the page:http://www.avweb.com/news/avtraining/182740-1.htmlAllcott

Autofeather is usually found on higher performance twins. When an engine failure occurs in a twin, the pilot must reduce the drag as quickly as possible to prevent the adverse affects of the dead engine sending him into an unrecoverable flight attitude, know as a Vmc roll. The autofeather system assist in that task by doing exactly what the name says, automatically feathering the props. Feather means that you turn the props perpendicular to the flight path of the aircraft, thus reducing the drag factor. When the prop is windmilling, it has been associated with the flight characteristics of a large metal disc; all drag, no thrust.The prop hub and governor is what controls the pitch of the blades, or the bite of air that it takes as it spins. When the governor detects that the RPM is too high for what the pilot has set on his prop control lever (an "overspeed situation"), the governor, along with a spring and compressed air in the front of the prop hub force oil out of the hub, thus allowing the propeller to go to a higher angle of attack, taking a bigger bite of air, and slowing the RPMs. The opposite holds true for an "underspeed" situation. The pilot has set a specific RPM with his prop control lever, the props are turning slower than that RPM, so the governor allows more oil into the hub, thus reducing the angle of attack of the blades, taking a smaller bite of air, and increasing the RPM.When an engine fails, the oil pressure decreases. Remember that when the oil pressure decreases in the prop hub, the propeller increases its angle of attack, taking a bigger bite, and the RPMs reduce. When the reduction of oil pressure is drastic, such as an engine failure, all of the oil in the hub is drained and the prop goes to a full feathered position, reducing the drag as quickly as possible.This system (in piston twins) is operated by a switch in the cockpit. It is normally only on during takeoff and landing. There is no need to rush into feathering the prop (or having it done automatically) when you're in cruise. There may be a chance that you can restart it if its a problem such as lack of fuel to the engine. Restarting is made that much harder when the propeller is stopped completely.Check this photo out to see what a feathered prop looks like in flight. Believe me, its kinda weird to look out there and know that its supposed to be spinning, but its not. http://www.ossipeeaviation.50megs.com/pict...ztec/feath.htmlAnd Steven, this function has nothing to do with the autopilot.

There is a little-known law of physics which says that a rotating propeller generates as much resistance as a solid disk of the same size. What that means is, if you take one of those toy windmills that kids sometimes get for Easter and hold it out of a car window, you will feel as much force from the wind pushing on it as you would feel if you had a solid disk of the same diameter. In other words, a lot of resistance, a lot of force.This is also the principle that lets a helicopter autorotate and land safely if it loses an engine. It might be a hard landing, but the crew can probably survive. Think about it, a helicopter weighing more than a ton can be slowed by its own propeller blades just like if it had a parachute. That's a tremendous amount of force.Now consider what happens to a twin engine aircraft if it loses an engine. It will have a huge source of drag out there on one of its wings. It's going to yaw like an SOB! A good pilot can recover of course, but if that happens during short final, you'll be in big trouble.What autofeather does is, it detects that an engine has stopped and automatically turns the propeller blades into the wind. With the blades pointing into the wind, you no longer have a windmill, you have three (or how many blades there were) airfoils. It's not much drag at all.That's what autofeather is for.

Wow thanks for the info guys! So I only need to worry about it if I experience an engine failure during flight. Well I hope my new PMDG B1900 Prop is built solid!

Thanks for the explanation. I misspoke about the autopilot. On the King Air, it won't autofeather unless I arm the autofeather.