QUOTE(Yanni BA632 @ Nov 19 2006, 11:11 AM)
Yes, Turbo props have some kind of reverse thrust the propeler blades feather meaning that they switch direction that is what you see ont-props when they land that the propeler looks like it is going backwards but it is just feathered
Well, not quite. The propeller blades change pitch. They do not change direction. The props on all planes always turn in the same direction.
When a propeller is feathered that means that it is turned parallel to the direction of flight. I.e. the leading edge of the prop is turned forward. This presents the lowest possible drag when the engine is not providing power and reduces asymetrical drag as much as possible.
The reason a propeller looks like it's turning backwards is because your brain can only process images at about 50 times per second. As you process one image you see the blades at a certain position. The next image your brain processes, about 1/50th of a second later, you see the blade at a position that is just prior to it's position in the previous image in your brain. The blades are turning at a frequency that doesn't coincide with the frequency you are processing their movement. So it appears to be turning backwards.
The degree to which a propeller appears to be turning backwards or forwards depends on it's speed of rotation. Spinning at lower that 50 Hz (50 times/minute) it looks like it's going backwards. Turning faster than 50 Hz and it will appear to be turning forwards (as it actually is).