The Cuban 8 is a figure 8 laying on its side with rolls at the cross over point. It is a good looking maneuver that can be done low for an impressive effect on the spectators.
A lot of people can do a Cuban 8, but can't make it look good. The thing that they probably are doing wrong is doing it in the wrong direction. Nearly every looping type maneuver is started into the wind. Not the Cuban 8. It should be started with the wind or down wind. If you start into the wind, it is hard to get the second half back where you want it. When you try to stretch a maneuver and you are inverted going into the wind, there ain't no way (as they say) to make it look good. Always start it down wind.
Start the maneuver at full power and parallel to the runway. Pull up like you are going to do a loop. Now if you remember the Immelmann, you stop the loop at the top and roll out. With the Cuban 8, you go a little bit farther and do the same thing. For the first one, wait until the plane is slightly nose down, or just past the Immelmann position. Release all the elevator, and this is important, then roll right side up. If you hold any up elevator in during the roll, it will pull the nose of the plane off to one side or give you a barrel looking roll. Let the plane continue downward until you are at the same altitude as when you started and then pull up into the partial loop again, doing as before. This will complete the "8".
For your first Cuban 8's, don't try for steep downward angles before rolling. Complete the maneuver and get your confidence up that you can do it, then go for the steeper angles. You'll also notice that with just about any plane except a pattern plane, that downward angle will naturally increase as you roll out, making it steeper than when you started. If you start with a 45 degree down angle before you roll, you might end up with a very steep dive after the roll is completed.
Let's look back at some of the keys in the maneuver.
First, always do it down wind. Next, use a shallow angle to start with.
Increase as you gain proficiency. Finally, release all the up elevator
before you roll right side up. If you don't you'll pull the plane off
to the side during the roll.