Take a look back through modeling history - pattern planes flying with piped .61's flew on one aileron servo. Those servos had about 1/2 the speed and 1/2 the power of today's standard sport servo, and many of those 7 lb - 9 lb planes flew well over 100 mph. For a primary or secondary trainer (since the question was posted in the Beginners Forum) a single aileron servo is all that is needed.

Hogflyer