Difference between Helicopter & Gyrocopter

[Billdo]

In the Another Couple Helicopter Questions (http://boards.straightdope.com/sdmb/showthread.php?threadid=45137) thread, one of our resident pilots, Johnny L.A., said:

I don't think he's looking for an autogyro. I seem to recall seeing the described helicopter, and it wasn't a gyrocopter. (BTW, gyrocopter and helicopter licenses are two different ratings.)

What is the difference between a helicopter and a gyrocopter and/or autogyro? What are gyrocopters or autogyros used for?

In fact, the only time I've heard of an autogyro is in the classic 1934 Frank Capra film It Happened One Night (http://us.imdb.com/Title?0025316) when the society groom arrived at a wedding in an autogyro.

[Danielinthewolvesden]

A helicopter propels itself, and gets its lift, thru means of its rotors. An Autogyro propels itself by means of its propeller, in front, but gets its lift thru its rotors (on top), which usually are not powered. Other than for fun, with a home-built ultralite- Autogyros have no use anymore.

[Robot Arm]

In a helicopter, the engine drives the main rotor and makes it turn. In an autogyro, the rotor isn't connected to the engine, the air flowing through the blades makes it turn, like those little twirling seed pods that fall off a tree and spin around while they're floating to the ground. An autogyro doesn't need a tail rotor like a helicopter does, but it needs a propellor on the front or back to push it through the air. An autogyro can't take off vertically. In fact, I don't think the rotor turns at all until you start rolling and the air starts flowing through it.

The classic autogyro scene in a movie is the Little Nellie sequence in You Only Live Twice.