Sukhoi SU 31M
Building instructions - Sukhoi SU 31M
3
Small servos weighing around 13 g are required for this model; they should fit in the servo wells in the
fuselage from the underside
(Fig 5)
. Fix the pushrod connectors (38) to the servo output arms using
the self-locking nuts provided.
The tunnels in the fuselage for the snake outer sleeves (36) can be pierced using a length of stout
wire. The exit slot for the rudder snake should be located about 50 mm forward of the tail end of the
fuselage on one side
(Fig. 20)
. The elevator snake outer (36) should be central at the tail end, lining
up with the elevator horn (32)
(Figs. 5 + 6)
. Please ensure that the snakes are as straight as possible
to avoid stiffness in the linkage; any curves must be of large radius. Glue the snake outers (36)
securely to the fuselage at several points. The pushrods (snake inners) are the steel rods (37). Form a
Z-bend in one end of the elevator pushrod and connect it to the middle hole of the elevator horn. Slip
the pushrod through the snake outer and
thread it through the pushrod connector
mounted on the elevator servo. Elevator
travel should be 20 mm up and 20 mm
down. Glue the tailplane to the fuselage.
Secure the pushrod (37) in the pushrod
connector (38) with a grubscrew, then snip
off excess rod length using side-cutters.
Fin and rudder
Apply the film strips (58) in the V-channels between the fin (7) and the rudder on both sides to
strengthen the hinge line. Separate the fixed rudder from the fin at the top by cutting forward
(Fig. 7)
using a sharp balsa knife.
Form a Z-bend in one end of the rudder pushrod (37), slip it into the snake outer (36) and connect it to
the pushrod connector (38) mounted on the rudder servo. Temporarily tape the fin (7) to the tailplane
(5) and establish the correct position for the horn (33) on the rudder. Screw the horn (33) to the rudder
using the spreader and M2 screws (48), and cut off excess
screw length.
Cut a slot for the hinge (55) in the centre of the fuselage tail post
using a balsa knife, and glue the hinge in it. Cut a matching slot
in the rudder. Form a Z-bend in the pushrod (37) as for the
elevator and connect it to the inner hole in the rudder horn. Slip
the steel pushrod into the snake outer (36) and through the
pushrod connector (38) mounted on the servo. The fin can now
be glued to the tailplane, gluing the bottom hinge in the rudder at
the same time. Secure the pushrod (37) to the pushrod
connector (38) using a grubscrew, and cut off excess rod length
using side-cutters. The rudder should be capable of 50 mm
travel to each side of centre.
Final assembly - fuselage
The servos can be glued to the fuselage once you have checked the control surface (servo) travels.
Glue the fuselage turtle deck (4) to the fuselage (3).
The piece removed from the centre of the elevators can now be glued to the fuselage between the
elevators. Take care not to glue it to the elevators, as that would prevent them deflecting. Attach the
wheel axles (machine screws, part 45) to the GRP undercarriage unit (40) using the nuts (46) and
shakeproof washers. Fit the wheels (44) followed by the self-locking nuts (47). Fix the undercarriage
(40) to the fuselage using the nylon screws (41).
The next step is to cut three to five holes of around 10 mm Ø in the front face of the fuselage to
provide a cooling airflow; the motor cables also pass through them. Screw the motor to the motor
mount and run the cables back into the fuselage.
Attach the lower part of the cowl (23) to the fuselage with tape, followed by the top section (24). Drill
four 1 mm Ø holes through the cowl sections into the balsa screw supports (14) on either side of the
fuselage, and fix the cowl sections in place using the self-tapping screws (54). Remove the cowl, fill
the holes in parts (14) with a drop of epoxy, then fit a self-tapping screw in each and remove it again
immediately; the epoxy hardens the threaded holes. Tape the cowl sections together at the front using
adhesive film (scrap decal sheet material).
