How to Aliexpress foam glider conversion to 3 channel radio-controlled plane.
We have purchased a launch glider made with foam in AliExpress. These gliders have a wingspan of 48 centimeters, and a fuselage length of 46 centimeters. They can be found for a price of 3 euros.
The weight of the plane is 52 grams. If we remove the cabin, the weight is 35 grams.
We prepared a first version of the plane with a brushed motor of 85 by 20 millimeters and a propeller of 55 millimeters. This motor have a thrust of 23 grams using a 3.7-volt battery. We use a Fly-Sky receiver and an ESC for DC motors with a maximum amperage of 10 amps.
We place the motor in pusher configuration, that is, placed behind the wing and pushing forward. We tilt the motor shaft so that the thrust line passes through the center of gravity of the aircraft, which is usually located in the first quarter of the wing. Thus, we avoid that the airplane has an accused tendency to pitch down. We prepare a support for the motor using a piece of extruded polystyrene.
The plane, as it is, has a natural tendency to yaw to the right. To correct this effect, we placed a small rudder made with extruded polystyrene taken from a food tray. We apply to the rudder a fixed angle of a few degrees to the left. This corrects the adverse yaw of the plane.
Finally, we apply a dihedral angle by tensing the wings with a thread. The dihedral angle improves the lateral stability of the aircraft, and correct the tendency of the plane to go into a spin.
The final weight of the aircraft is 71.5 grams, then the thrust to weight ratio is 0.32. The wing load is 1.8 kilograms per square meter. The cubic wing load is 9.0.
Next, we see some images of the flight of the plane.
In the next step, we add a 3.7-gram weight servo to control the yaw of the plane. So we changed the 3.7-volt battery for a 7.4-volt, 500-milliamp-hour battery, which weighs 30 grams. We prepare a twin-engine plane that supports the weight provided by the new battery. We use a pair of identical motors of type N-30, with propellers of 75 millimeters. These motors, connected in parallel to the 7.4-volt battery, provides a maximum thrust of about 40 grams.
The rudder has been placed in a lower height, so that the barycenter of its surface is located almost at the same height as the aircraft`s center of gravity. This will cause the plane to rotate in a horizontal plane when the rudder is apply. If the barycenter were very high, the plane would turn in an inclined plane, affecting its stability.
To improve the aerodynamics of the airplane, we cover the battery with the cabin. The cabin has been previously hollowed out to reduce its weight. In addition, we place the receiver plus the ESC in a hollow of the fuselage. All cables are carefully attached to the fuselage so that they do not disturb the airflow.
The final weight of the aircraft is 114.5 grams, then thrust to weight ratio is 0.35. The wing load is now 2.9 kilograms per square meter. The cubic wing load is now 14.6.
Now, we see some images of the flight of the plane.
We have bought a different model of glider. It is a more optimized model in terms of weight and dimensions. This model, without the cabin, weighs 29 grams, compared to 35 grams that weighs the previous model without the cabin. The wings of this model are polyhedral, which is very good to give the necessary dihedral angle. This is done by tensing the wings with a thread.
We have modified the design to mount a three-channel airplane, adding a channel to handle the elevator. Therefore, we will have a better control over the altitude of the plane. Since the new servo and rudder add extra weight to the plane, we have changed the battery to a lighter one of 350 milliamp hour and 21 grams of weight.
Taking advantage of the oversized vertical stabilizer, we have included the rudder inside it. We have detected that the adverse yaw of the previous models was due to the lateral de-centering of the tail. In addition, the tail buckles exaggeratedly when the rudders are applied. Therefore, we have added threads to anchor and center the tail in order to avoid these problems. We have also reduced the thickness of the vertical stabilizer with a cutter so that the transition with the rudder is smooth. Built the plane with all the necessary elements, we have a final weight of 105 grams, and a thrust-to-weight ratio of 0.38. Flight autonomy is about three minutes. As we see in the video, there is an improvement in lateral stability thanks to the polyhedral wings.
The propeller is centered as best as possible to also avoid such vibrations. The rudder surface has also been decreased so that the yaw is softer when turning. Again, we have changed the 500-milliamp-hour battery to a lighter one of 350 milliamp hour and 21 grams of weight. The weight of the plane is now 105 grams, leaving the thrust-to-weight ratio at 0.62. The final images of the plane are shown.
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