Whether you will need an extension or not depends on the installation on each plane. Many planes will tell you if you need extensions in the "Additional items needed" list. If not, you can look at the plans (if you are building a kit) and measure if you are going to need an extension. Most servos will have approximately 3"-6" of cable on them already. You will need to work from there.

Additionally, if you are building a plane with 2 aileron servos may need a Y-harness if you plan on running both servos from a single channel on your radio. If your radio can support 2 aileron servos (most do these days) you won't need a Y-harness. Most people simply run both servos from a single channel at this level. Later on down the road as you advance you may want to run 2 servos from 2 different channels. The biggest reason for doing this is so that you can program aileron differential into your ailerons.

Hope this helps

Ken
<br type="_moz" />