Radial Format

This type of engine is called a Radial Engine.  It is known by this name because the pistons within this engine are arranged in a circular alignment.  It is a very different style of engine and not used as much in these modern times.  This format is unique because the connecting rods attatched to the head of the pistons are all connected in the center of the crankshaft.  Within this engine there is a master cylinder and a master piston rod attatchment.  As you can see in the illustaration below the top cylinder has a piston with a piston rod larger than the others.  This is because that particular piston holds all of the others together and keeps the timing right for the rest of them.

These engines are mainly used in aviation.  They are used for this purpose because they take up less room at the nose of the plane.  It then creates room for other vital equipment.