A friend has given us an old conversion project from a lidl glider to a radio-controlled plane. The plane did not fly fine, so we have modified the original glider to turn it into a STOL. STOL's are airplanes capable of rising from and descending to the ground with only a short length of runway. A competition of this type of aircraft is held every year in Valdez, Alaska. To make the short landing we need high drag aerodynamic devices that we do not have. To perform the short takeoff, we need a little wing loading, a large thrust-to-weight ratio, and a high lift-to-drag ratio.
In the first modifications, we have cut the nose of the glider and have mounted a puller motor. A Racerstar BR2212 brushless motor with 1000 speed constant is used, along with a 10-inch diameter and 4.7-inch pitch propeller. This set provides a thrust of 885 grams with a three-cell battery. This provides the high thrust-to-weight ratio necessary for short takeoffs.
The bay is 10 centimeters long from the leading edge of the wing to the base of the motor, and is built using six wooden sticks 4 millimeters in diameter. The bay is filled with a piece of low-density extruded polystyrene. This elongated bay let us to set the center of gravity in the right position using a little battery weight. The center of gravity is 5.5 centimeters from the leading edge of the wing, which corresponds to 29% of the wing chord.
For the tests, we have used a graphene battery of three cells and 500 milliamps per hour, with a weight of 66 grams. We have verified that a battery of two cells and 500 milliamps per hour, with a weight of 36 grams, placed next to the base of the motor, would also leave the center of gravity in the right position. This would reduce the total weight of the aircraft by 30 grams.
The mass of the landing gear lowers the height of the center of gravity of this model, leaving it half a centimeter below the lower side of the wing. Therefore, the thrust line is placed at this height to prevent the thrust line from creating undesirable moments on the plane.
The way to verify that the thrust line passes through the center of gravity is to lay the plane on its side, pivoting on the motor axis line, and check if it balances in this position.
The area of the ailerons has been increased by extending its surface using strips of foam core board one centimeter wide. These ailerons do not have horns. The servo arm sticks to the side of the ailerons, and the servo is inserted into the body of the wing, lying parallel to it. This system leaves the wing lower surface cleaner than the typical horn system.
The original rudder was cut directly from the horizontal stabilizer. It was too small, so it has been extended by a sheet of foam core board. It is controlled by a servo with the typical horn system.
A landing gear made with wire and wooden sticks has been added so as not to break the propeller in the landings. The wire easily bends after impacts, so it is necessary to reinforce it with wooden sticks of 5 millimeters in diameter. Two V-shaped sticks act as struts, placed parallel to the direction of the impact force during landing. The tail of the landing gear is made using a wire inserted in a piece of high density extruded polystyrene.
The plane includes wooden sticks for reinforcement, both on the wings and in the fuselage.
This first version weighs 420 grams with all the electronics included, which includes the graphene battery. The ESC is 30 amps. The servos are 9 grams. The thrust to weight ratio is greater than two. The wing area is zero point twelve square meters. The wing loading is 3.5 kilograms per square meter. Flight tests are shown, which includes the takeoff and landing of the plane.
In the last minutes of the video, you can watch the crashes of a previous version of the plane, that was quite unstable. Although most of the crashes are due to the inability of our inexperienced test pilots.
And this is all, thanks.
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