Installing a rudder servo

[Michael]

I recently bought a GH-Air L39 EDF jet from Great Hobbies. This is a relatively small model that is intended for 3 channel control: throttle, ailerons an elevator. It's a nice model and it flies nicely when properly balanced and set up.

I had a problem with the model on its first flight. The problem was with my flying technique. I instinctively use rudder to turn my flying models, and use opposite ailerons to keep the role/bank flat or shallow. So, when I was trying to turn left, without thinking, I used left rudder and a bit of right aileron to keep the wings flat. The problem is, the plane has no functioning rudder, so the plane rolled right instead of the intended left.

Anyway, I then flew the model as intended (no rudder; ailerons only for turning), and everything was fine; I landed safely.

After a few more flights, I decided that I would enjoy flying the model more if I had rudder control, so I decided to install a servo for rudder operation.

This thread shows how I did it, although the process will differ from model to model.

[Michael]

I cut the rudder from the fin. There were lines molded in the model, so cutting it out was easy. I made sure I trimmed a bit on the top and bottom so there would be no friction when moving, and I beveled the leading edge of the rudder. I installed 2 pin hinges (not glued yet) and cut a spot for a control horn (an extra came with the model kit).

[Michael]

I cut a servo shaped hole in the fin for a 5-gram servo, and a shallow channel down the fin to the fuselage for the servo wire, as well as a a hole in the fuselage.

(Nothing glued yet.)

[Michael]

I cut a channel inside the fuselage so the wire wouldn't interfere with the airflow from the EDF (fan unit), I taped it down firmly, and I trimmed the hatch to allow the wire to pass on the side of the EDF unit to the front of the fuselage. The EDF unit was originally glued in place, so I had to pry it out in order to run the servo wire. It was easy to glue it back in. I reconnected the wires to the motor and tested that it was running in the correct direction. I then closed everything up.

[Michael]

I painted the white Styrofoam where I cut it.

(more tomorrow)

[Michael]

The cutting out of material from the fin has left it more vulnerable to damage or failure in flight, so I cut a groove in the leading edge of the fin, and glued in a length of carbon fiber rod. This should keep it strong.

[Michael]

rudder-hinges glued onto the fin, control horn glued on, servo glued in, pushrod cut to shape and installed. It works great.

If you do anything like this, make sure everything works in the right direction, and add some weight to the nose to keep the plane balanced.

The work I did here is specific to this model, but does give a basic idea on how to install a functioning rudder on small model airplanes.