The Rock-O-Plane is an amusement park ride designed by Lee Eyerly in 1948 and manufactured by the Eyerly Aircraft Company of Salem, Oregon. It is sometimes nicknamed "the cages" or "the eggs". Its shape is similar to that of a Ferris wheel, but with seats that are enclosed and rock and roll as the ride turns. If the rocking builds sufficient momentum the seats will flip upside-down and end-over-end. There is usually a wheel inside that participants can use to lock the seat and prevent it from rocking. This can be used to make the ride less scary by ensuring that the seats don't rock too much; or to make it more intense by locking the seats at crucial points in the ride's revolution, causing the seats to flip upside down and spin erratically. The minimum rider height requirement is 36 inche