Accessing a child of a movieClip composed of other movieclips


I made a ship in flash, composed of different movieclips exported for actionscipt, then I converted the whole ship in a movieclip. I wanna access a wing to make it rotate but I don’t know how. I tried this:

    import flash.display.MovieClip;
    public class Prueba extends MovieClip{
        public function Prueba(){
            var nave:Ship = new Ship();
            nave.x = 50;
            nave.y = 50;
            nave.getChildByName("LeftSpacer").rotation = 20;

but it doesn’t work like that
what is the correct form of doing that?

thanks for reading