Mike McConville explained how to perform a "proper" snap roll in the March 2006 issue of Model Airplane News, page 126. In the article, he describes how the common pilot snap rolls by inputting full stick deflections, and how this makes the snap too "deep", causing the model to lose too much energy. He then goes on to describe an "unloaded" snap, that is still a full snap that is legal in competition and retains much of the plane's energy.
Here is part of the article, where he explains the procedure:
"The snap is initiated with elevator only. For a positive snap, first pull hard up elevator. For a negative snap, push hard down. As soon as there a visible pitch up of the nose, move the aileron and rudder simultaneously to full deflection. The same applies to a negative snap, except there will be a visible pitch down of the nose before moving the ailerons and rudder to full deflection.
At the same instant as you start to move the ailerons and rudder, also start removing the elevator. The object is for the elevator to return to the neutral position at the same moment as the aileron and rudder reach full deflection. A very easy way to look at this is for the right stick (mode 2 pilots) to draw an imaginary checkmark (he then refers to a figure). When done correctly, you will see a fast pitch in the direction of the snap, meaning up for positive and down for negative. Immediately, the model will begin to autorotate around the roll, yaw, and pitch axes. Because the elevator is unloaded, however, the model wont go as deep into the snap and it will stop faster, lose less energy, and remain on the original heading it was on before the snap. .....
The ailerons control the snaps speed. As you do a snap with this technique, if the speed of the snap is too slow, increase the amount of aileron travel. If its too fast, reduce the aileron travel. Rudder input controls how deep the model stays through the snap. If the snap is too axial (that is, if it looks like a fast roll and the nose doesn't move far -if at all- off the model's line of direction as it snaps), increase the rudder input. If, however, the snap still looks too deep, there is probably too much rudder throw even though you are unloading the elevator correctly. Using a computer radio makes these adjustments very easy.
Do everything as described above, and you will be 95% there. But there's one last thing: when you exit the snap, release rudder and aileron when the model is where you want it to be. With the unloading technique, the model wont really over-rotate much. At time, though, the model will wiggle a little as it stops rotating.
Here is one last tip and you will know just as much about snaps as I do: When the model is a 1/4 turn from where the snap is supposed to stop, release the rudder. When it gets to where you want it to stop, release the aileron. This will get rid of the wiggle, and it will look great."
(Copied verbatim from the March 2006 issue of MAN. Author: Mike McConville)