How to conversion Aliexpress FX-703 glider to twin engine RC plane 4 channels 69 cm wingspan

We have bought a glider in Aliexpress for a price of about 12 euros. The wingspan is 69 centimeters and the wing area is 0.0654 square meters. The center of gravity for the glide is 3.5 centimeters from the leading edge of the wing, which corresponds to the first third of the wing chord. The weight of the original glider is 99 grams. The weight of the glider without the canopy is 72 grams.

The plane has a hard plastic canopy plus a soft plastic tip. It also has an EVA rubber protector on the belly to cushion landings. In addition, the glider mount some led lights on the belly that are light on by a switch.

We have bought a 3 mm diameter carbon fiber rod in the decathlon store. Using the rod, we have reinforced the wings and tail. The stabilizers have been reinforced with wooden sticks.
The ailerons have been cut from the wings. On top, wooden sticks have been placed to define the hinge line. In addition, strips of thick packing tape have been arranged to fix the hinge. On the trailing edge, sticks have been placed to prevent the deformation of the ailerons.

The tail arrived with a little deviation, so we have placed a small piece of 2.5 mm diameter carbon fiber rod on the trailing edge of the wing and we have anchored the tail to the rod with a thread. This way we corrected the deviation of the tail. Anyway, we have added a rudder without servo in case we had to make any corrections in the yaw of the plane.

The elevator has been cut from an extruded polystyrene sheet taken from a food tray. It has a width of two centimeters and is sewn in four points to the horizontal stabilizer. The elevator has been linked to the servo with a wooden stick of 3 millimeters in diameter.

The motorization has been carried out with a pair of N-60 motors with 3-inch diameter 3-blade propellers. Both motors are wired in parallel and controlled by an ESC for brushed motors. The set provides a maximum thrust of 100 grams with a two-cell battery. We can achieve up to 140 grams using a three-cell battery, but in this case, the motors overheat, so we have decided to better use the two-cell battery.

The motors have been mounted on nacelles made of wooden sticks. It is convenient to separate horizontally the propellers from the leading edge of the wing, to minimize the propeller-wing aerodynamic interference.
We use servos of 3.7 grams of weight. Since the angle of these servos is little, we have lengthened the arms by mounting on top of the original arm the typical ones of the 9-gram servos, which are longer.

The weight of the first version is 225 grams. The thrust-to-weight ratio is 0.44 and the wing loading is 3.44 kilograms per square meter.

In the tests, we noticed that the center of gravity of the motorized aircraft is in the same position as in the glider, that is, 3.5 centimeters from the leading edge of the wing. This means that the thrust of the motor does not create unbalanced moments on the plane. Anyway, we have lowered the position of the battery a little to make sure that the thrust line of the motors passes through the center of gravity.

We also noticed that the plane flies well at half power. That is, it flies with a thrust equivalent to approximately half of the maximum thrust. This indicates that the aerodynamics of the aircraft let us to operate with a thrust-to-weight ratio below 0.3, which implies that, we can add more weight without compromising its ability to fly. In addition, when operating with low power, we extend the life of the N60 motors. Master Rafa, member of the Aeromodelism Club of Nerja, tests the plane.

In the final version of the plane, a servo has been added to control the rudder. The linking to the rudder is made by threads, so we add the minimum weight to the glider. The rudder and the ailerons have been mixed in the transmitter to do coordinated turns. Coordinated turns are used in commercial aviation to prevent the plane from slipping in the opposite direction to the turn, that is, to prevent the nose of the plane from sliding out of the turning path. The opposite effect, when too much rudder is applied during a coordinated turn, is the skidding of the tail. In the transmitter, we have to find the right mixing percentage for the rudder channel and the aileron channel so that the turning is as smooth as possible. The weight of the final version is 230 grams. The thrust-to-weight ratio is 0.43 and the wing loading is 3.5 kilograms per square meter. We see the final images of the plane. And this is all, thanks.