What is a snap roll and how do you do it.

A snap roll is a high speed spin. The key is the plane must be stalled (a stall can occur at any speed and is related to angle of attack) which will pitch the plane toward the canopy or the landing gear dependant on positive or negative "g" force and can be performed on any line from upright or inverted.

First the plane must be set up and be a capable design.

Start with a good amount of altitude as the exit might not stop where you think it might. Lower the throttle to about half on a horizontal line. Input at the same time full up elevator and aileron and rudder (either left or right for right or left rotation).

For a negative snap input full down elevator with full aileron and rudder in opposite directions.

EXCAP232

Anticipate releasing the controls when you reach inverted. Most planes will "over rotate" after you let go.
RickP