I think that the answer to using four or two servos lays firstly in the size of the ailerons. On bipes such as the original CGM Ulitmate, servos on the bottom wing with GOOD linkages between the top and bottom ailerons work wonderfully. This is the way most full size bipes are confirgured and works very well. This does eliminate the wires coming out of the top wing running down the cabanes. With larger ailerons such as the DP Ultimate or the DV, four servos are a better choice. Tape the connectors to the inside of the cabanes and you will never really notice them at all.

For the advanced radios, you can use either Y harness methods or individual programmability and wire each in a separate channel. The Y harness keeps it simple using two channels and is my prefered method ofering differential throw, 3D trick set-ups and, or course, standard ailerons.

The individual programmability using four channels gives potential flight options (reflexive airbraking or differential throw between top wing and bottom wing ailerons) that MOST will never use or understand BUT it does provide easy fine adjustments to each aileron's subtrim position on the radio without changing the mechanics.

Either option still requires good and correct mechanical set-up to ensure no unwanted reflex or proflex that cause differential drag are present in the ailerons to keep the amount of needed subtrim to a minimum.

Mark