Here’s a common, very popular way to install aileron servos. To make field maintenance more convenient, install your servos with hatches built into the wing so they are flush with the wing’s underside..
The first thing I do to get the aileron servo hatch properly aligned is to install the aileron control horn and then attach the linkage. I then use the linkage as a guide for the placement of the servo arm slot I cut into the hatch. The linkage should be straight and 90 degrees to the aileron hinge line.
Once I have the slot location figured out, I draw a rough sketch on the inside of the hatch cover centered on the servo spline. Here I am using ProTek RC T330 digital, metal spline servos from A-Main Hobbies.
To support the hatch cover, I use lite-ply to line the servo compartment opening. Here you see some balsa strip material glued to the lite-ply cross piece to form the opening. It is about 3/8 inch wide to give plenty of support to the fabric covering. Once this is all done, I place the hatch cover (also made of Lite-ply), in position and I trace the clearance around the opening. This is to determine the placement of the servo and its supports.
I use hardwood blocks for the servo mounts and I support them with 1/16-inch plywood gussets. All is glued with Thick Zap CA Glue.
Here I am making sure the servo arm is centered on the slot guideline which lines up with the aileron control linkage. A Heavy Duty Du-Bro servo arm is being used. A slot about 1/4 inch wide is best for most servo installations. I use a Moto-Tool and a round bit to cut two holes at either end of the slot. I then use a hobby knife to cut the slot between the two holes. A little sandpaper makes the slot neat and clean.
Here the hatch and servo have been installed and screwed into place. You will need to determine the length of the slot by using your transmitter to move the servo arm back and forth. You can see I had to make a little clearance in the lite-ply support cross piece to clear the servo arm.
To complete the control linkage, I use a scrap of wood and a couple cloth pins to center the aileron.
The servo hatch is now screwed into place with cap head sheet metal screws. You can also used flush fitting counter sunk wood screws if you like. it’s your choice. Since this is my 1/3-scale Triplane with a 94 inch span and a 80cc engine, I secured the hatch with six screws. For smaller airplanes, four screws (one in each corner) will be enough.
Also here you see the clevis at the servo has been soldered to the 4-40 control linkage wire. I use Stay-Brite high silver content solder for all my control linkage soldering.
That’s it. Give it a try, it looks much neater than just having the servos sticking out of the wing.