Fei Bao MiG-21 Fishbed Instruction Manual (Draft Rev 0)
Page 6 of 24
Rudder Servo Installation and Rudder
Plywood mounts for the rudder servo have been pre-installed in the fin. A mid-mount style servo
such as the JR DS3301 can be screwed directly to the plywood. A couple of strips of ply or
hardwood should be glued to the back side of the ply mounts to increase the thickness and give
the servo screws bit more grip.
A JR DS3421sa servo which has a bit more torque can also be used. This servo only has
traditional mounts molded into the servo case and will require that the plywood mounts in the fin
be cut/ground back and hardwood blocks glued in place (contacting the fin skin, ply mounts, and
then reinforced with balsa angles). The servo is mounted to aluminum or carbon fiber
reinforced plastic angles which are, in turn, screwed to the hardwood blocks in the fin.
The servo lead routes out to the fin root without the need for a short extension.
Control Horn - A slot has been precut in the rudder to receive the control horn. The horn itself
needs to be trimmed slightly at the front so that the clevis hole aligns with the hinge line. The
photo below shows the trimmed rudder horn and a "stock" horn. The horn is roughened up with
a Perma-Grit file and Hysol'd in place. An alcohol swab is used to clean any residual Hysol from
the area.
Hinges - Three "point" style hinges are pre-glued into the rudder with the matching holes pre-
drilled in the fin. Apply a drop of light oil should be applied to the hinge pin to prevent glue from
jamming the hinge. Apply Hysol to the barbed portion of the hinge and install the rudder into the
fin. Do not push the rudder too far into the fin but ensure that the rudder can freely move to the
recommended travel limits.
Linkage - The kit includes linkages (rods with 4-40 threads, jam nuts, a threaded clevis at one
end, and a blue anodized aluminum rod end at the other) but the builder may choose to use
other linkage components based on their own preferences. Final adjustment of the pushrod,
centering the rudder, and installation of the servo cover will be done when setting up the control
throws.
