Two Aileron Servos

TWO IS BETTER THAN ONE (Does that count for servos?) - by Ron Lockhart - (Does that count for servos?) - by Ron Lockhart - via internet- published in "The Radiator", Atlantic City Skyblazers, Atlantic City, N.J.

Take the case of the lonely aileron servo. Normally one servo is mounted in the center of a wing to drive two ailerons. To get the servo output wheel motion to each aileron, we often use a set of aileron torque rods. Sometimes linkage from the servo goes to a bellcrank for each aileron, and then to the aileron. Yet another method is to run nyrod casings from the servo into the wing and bend them 90 degrees to get them to the ailerons. All of these linkage methods have their problems. The main one is the slop or play that can be felt at the aileron.

Bad stuff - slop/play/looseness in ailerons (or any control surface). It contributes to possible control surface flutter, linkage and servo wear, and maybe servo failure. It makes the airplane harder to fly well, because the airplane wanders in heading and altitude. Each linkage point, the torque rod bearing, the bellcrank pivot, each pushrod that flexes, etc, add to the un- desirable play at the aileron. Curved nyrod casings add drag and make it hard for the servo to find neutral.

How about using two aileron servos, one for each aileron.? Mount them partly outboard in the wing ahead of the ailerons. Both servos can be plugged into the receiver aileron channel using a "Y" cord. It's that simple. If your radio has a provision for a left and right aileron channel, use it. That has benefits that could be the subject of another article. The super simple linkage is the beauty of this system. One short push rod goes from the servo wheel to the aileron horn in a straight line.

Minimal/no slop! Great! The two servo system is not perfect either though. You have to find another servo, (yes, same kind!) and build servo mounts into the wing. That isn't tougher than torque rods, bellcranks, and such, just different. Depending on how far out on the wing the servos are mounted, you may need to lengthen the servo cords (using an aileron extension is the easy way) to reach the receiver. Extra weight? -Two servos may not be much heavier than one with the extra linkage. Since each servo is doing half the work (actually less than half since linkage drag is reduced) you could use smaller servos to save weight.

Will two aileron servos be better than one for your model? As all things it seems, it depends. The bigger and faster a model is, and the more precisely you want the aircraft to fly, the more benefit you will find in using two servos. There is also some benefit in having the redundancy of two servos in case of a servo or linkage failure. In some installations, not having the one center mounted aileron servo protrude into the fuselage area is helpful.

Two is better than one, probably more often than we think!