BCP:

First, generalities.

When at speed flying on the wing, the outer portion of the ailerons do 90% of the roll control. At lower speeds using engine thrust to hold the plane up, or doing 3D, the inner part of the ailerons exposed to the prop blast, does the job.

With a four channel radio you have no flap option, and a single aileron servo operating through torque rods works fine.

With a five channel radio the 5th channel is usually just a switch, normally for retracts. If this is what you are using, a single flap servo is fine, the flaps will be either zero or full travel. No 3D since you wont have inboard ailerons.

A six channel radio, non computer, can have either proportional control of channel six, or a switch, often 3 position. If your tx has just the switch, or no mixing capability, again, one servo. But this time you will have either one or two extended flap positions, or with propo, flaps at whatever extension you want. But still no 3D.

With six or more channels and mix capability, your options are greatly expanded, The first, and most commonly used, is flaperons. Now you are back to having full span ailerons, and 3D is again a possibility if you use a separate servo for each 1/2 flap, four wing servos total. And the inner parts will still work as flaps. Another popular set up is "Quad" flaps, the normal flap portion is deflected full down, and both ailerons are deflected full up. This is also referred to as "Crow," and vertical dives can be spectacular. Very few six and seven channel radios are capable of doing crow, but flaps and flaperons are available. Most eight channel radios will do it.

The simplest is a single servo for the ailerons, next is still just two servos, one operating the flaps through torque rods and the other operating the ailerons through linkage. And on up to the use of four servos, one for each moving surface. You have to decide how complex or simple you want it.

But it would be foolish to do a four servo install if your radio can't handle it.

Hope this helps.

Bill.