Here’s a common, very popular way to install aileron servos. To make field maintenance easy, install your servos with hatches built into the wing so they are flush with the wing’s underside and are held in place with screws.
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 hingeline.
Once I have the slot location figured out, I draw a rough sktech 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) and I trace the clearance around the opening. This is to determine the placement of the servo and its supports.
I use hardwood blocks as servo mounts and I support the blocks with 1/16-inch plywood gussets. All is glued with Thick Zap 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 FMA servo arm is being used. I have found that 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 clearence 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.
Here the servo side clevis has been soldered to the 4-40 control linkage wire. I use Stay-Brite liquid solder flux and high siver content solder for all my control linkage soldering.
A unique feature for my current project, a Balsa USA 1/3-scale Fokker Triplane, is that I am using a secondary RC receiver, battery pack and charge jack/switch installed in the top wing. I am doing this to eliminate the long servo wire leads that usually run up the cabane strut to connect the aileron servos the main receiver in the fuselage. The NoBS Batteries available from Hangtimes Hobbies are A123 LiFE type and they have a capacity of 2300mah. The NoBS heavy duty switch harness also has a charging jack in it so all I need to do is attach my single charging lead to balance charge the pack at a high rate. This can be done easily with the FMA 4S A123 charger and it is basically plug it in and forget it operation. No settings to set or get wrong.\
As with the main receiver located in the fuselage, the secondary Spektrum DSMX 7-channel receiver in the wing also has a auxilary receiver installed in the wing. The radio compartment is in the center section of the top wing and there is a removable hatch cover for access to the radio and battery pack similar to the servo hatches.
Here the radio compartment hatch has been installed but the charging jack/switch still has to be installed.
This technique can be used on any open bay, cloth covered wing structutre, to provide quick access to your servos and radio equipment.