We have bought a glider in Lidl for a price of 10 euros. This glider has a wingspan of 86 centimeters.
In order to reinforce the foam body, we have purchased a carbon fiber rod in Decathlon. The rod is 4 millimeters in diameter and 160 centimeters long. A piece of rod has been placed along the wings, another piece along the belly of the plane, and a last piece has been inserted in the nose through the tip. This last piece will be placed just under the battery. The battery, being the most massive object on the plane, usually breaks the nose of the foam body when any hit occurs, so a specific reinforcement is necessary for it.
The horizontal stabilizer of this glider model has a certain dihedral angle. This is a hindrance when adding the elevator, so we made two cuts and flattened the stabilizer. The elevator has been made from a sheet of polystyrene foam. It has been sewn to the stabilizer in four points, and the hinge line has been covered with packing tape.
The motor is tilted 20 degrees downward, so that the thrust line passes through the first quarter of the wing chord, where the center of gravity is supposed to be. So we prevent the motor from generating a pitching moment down. The inclination of 20 degrees implies that, for every 100 grams of motor thrust, there is a downward vertical force of 34 grams. This vertical force opposes the lift force, and reduces the lift-to-drag ratio of the aircraft. So the angle should always be the as small as possible. However, a low inclination has the disadvantage of leaving little room for the propeller. We have placed a small propeller with two blades and 4 inches in diameter.
The ailerons have been cut from the wings. In the upper part, wooden sticks have been arranged to define the hinge line. In addition, strips of thick packing tape have been arranged to fix the hinge.
The nose has been hollowed out to build a bay for the battery. The bay is long, so that we can move the battery inside it for convenience. This will allow to later adjust the center of gravity by moving the battery along the bay.
Since a landing gear has not been added, extruded polystyrene supports are added that absorb the impact on the landing of the aircraft.
The foam body, without the cabin, but with the reinforcement rods already included, weighs 138 grams. The final weight, with all the electronics included, is 432 grams. The wing area is 0.115 square meters. The wing load is 3.76 kilograms per square meter.
We are using a battery of three cells and 1500 milliamps hour. A 40 amp ESC. Three servos of 9 grams. A Fly-Sky FS-ia6 receiver. A propeller with two blades and 4 inches in diameter. An alarm for lost airplanes.
The motor we are using is a Racerstar BR2212 with a constant velocity of 2200. We have check that, with the 4-inch propeller and a three-cell battery, the thrust is up to 400 grams. This means that the thrust to weight ratio of the aircraft is equal to or greater than one.
Now, we see the first flight tests to find the right position of the center of gravity.
Once the right position of the center of gravity is found, which is located 6.5 centimeters from the leading edge of the wing, we fix the battery in the bay and arrange the cables so that the cabin can be closed. In addition, the angle of the ailerons has been increased. With this setup, we test the plane again.
In a new version of the plane, we have added a rudder with its corresponding servo. The rudder is used in combination with the ailerons to get smoother turns. The two-blade propeller has been changed to a four-blade propeller, also 4 inches in diameter, made of glass reinforced polycarbonate. This new propeller gives more thrust, but decreases the energy efficiency of the motor set. The center of gravity has been moved forward. Now, it is 5 centimeters from the leading edge of the wing. So we avoid the tendency of the plane to climb too high. Since we had no choice but to add weight on the nose of the plane to move forward the center of gravity, the battery of 1500 milliamps hour has been changed to an 1800 milliamps hour one. This new version weighs 485 grams, and is capable of aerobatic maneuvers. Some members of the Nerja Aeromodelling Club, has tested the aerobatic capabilities of the plane.
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