As the abbreviation suggests, elevons are a combination of elevator and aileron. This mixing is most commonly used on delta wing airplanes where you do not have a separate elevator and ailerons. Therefore when you move the elevator stick, both ailerons move up or down acting like an elevator. When you move the aileron stick, they act like normal ailerons. By moving the stick in combinations, they act like both. For example, if you move the stick to the bottom right corner, the ailerons will move up together like an elevator and also turn right. Naturally, you need separate servos on each control surface. Back in the olden days, you had to make a sliding tray with the aileron servo in it and the elevator servo moved the tray back and forth, thus creating the elevator motion. Aren't computer radios wonderful! Hope this answers your question.