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发布时间:2023-03-02 来源:http://www.quanyimoxing.com/

一节 活动方式和辅导要点
Section I Activity mode and main points of coaching
Aviation model activities generally include production, release and competition, which can also be divided into three stages:
The task of the production activity is to complete the model production and assembly. Through production activities, students will be educated about labor ideas, labor habits and labor skills. Make them learn to use tools, identify materials, master the processing process and get hands-on training.
Flying is a favorite activity for students. Successful flying can greatly improve their interest. The release activities should be carefully guided, follow the release procedures, introduce the knowledge of flight adjustment, and have demonstration and actual flight situation evaluation. The students are trained in applied knowledge and physical quality through flying.
The competition can bring the event to a climax, and the winners are encouraged and confident: the losers will either learn a lesson or not admit defeat, and will also hold their strength. It is a good way to guide students to sum up experience, stimulate creativity and keep forging ahead. Participating in large-scale competitions will give them great exercise and never forget it.
第二节 飞行调整的基础知识
Section II Basic knowledge of flight adjustment
Flight adjustment is the application of flight principle. Without basic knowledge of flight principles, it is difficult to adjust the flight model well. The instructor should guide students to learn aviation knowledge and introduce relevant basic knowledge according to their acceptance ability and the needs of production and release. At the same time, it is also necessary to prevent aircraft model activities from becoming specialized theoretical courses.
1、 Lift and drag
The reason why aircraft and model aircraft can fly is that the lift of wings overcomes gravity. The lift of the wing is formed by the pressure difference between the upper and lower air of the wing. When the model is flying in the air, the air velocity on the upper surface of the wing increases and the pressure decreases; The air velocity on the lower surface of the wing slows down and the pressure increases (Bernoulli's law). This is the cause of the pressure difference between the upper and lower wings.
There are two reasons for the change of the flow velocity of the wing: a. asymmetric airfoil; B. The wing and relative air flow have an angle of attack. An airfoil is the shape of an airfoil section. The wing profile is mostly asymmetrical, and the following arcs are straight and upward curved (flat and convex), and the upper and lower arcs are upward curved (concave and convex). Symmetrical airfoils must have a certain angle of attack to generate lift.
The lift is mainly determined by four factors: a. The lift is proportional to the wing area; B. The lift is proportional to the square of the aircraft speed. Under the same conditions, the faster the flight speed, the greater the lift; C. The lift is related to the airfoil. Generally, the lift of asymmetric airfoil wings is large; D. The lift is related to the angle of attack. At a small angle of attack, the lift (coefficient) increases linearly with the angle of attack. When the angle of attack increases, the lift decreases rapidly. This boundary is called the critical angle of attack.
The wing and horizontal tail generate drag in addition to lift, and other components generally only generate drag.
2、 Level flight
Horizontal uniform straight flight is called level flight. Level flight is the basic flight attitude. The conditions for maintaining level flight are that lift equals gravity and pull equals drag.
Since the lift and drag are related to the flight speed, if the horsepower of a model in the original level flight is increased, the pull will be greater than the drag to speed up the flight speed. As the flight speed increases, the lift will increase, and the model with lift greater than gravity will gradually climb. In order to maintain the level flight of the model at higher horsepower and flight speed, the angle of attack must be reduced accordingly. On the contrary, in order to maintain the level flight of the model under the condition of small horsepower and speed, the angle of attack must be correspondingly increased. So controlling (adjusting) the model to level flight is essentially the correct match between engine horsepower and flight angle of attack.
3、 Climb
As mentioned earlier, when the model is in level flight, if it increases the horsepower, it will change to climbing. The included angle between the climb path and the horizontal plane is called the climb angle. A certain horsepower may reach a new force balance under a certain climbing angle, and the model enters a stable climbing state (both speed and climbing angle remain unchanged). The specific condition for stable climbing is that the pulling force is equal to the backward component of resistance plus gravity (F=X X Gsin θ); Lift equals another component of gravity (Y=GCos θ)。 When climbing, part of the gravity is borne by the pull force, so it needs a larger pull force, and the lifting force burden is reduced. Similar to peace flight, in order to maintain a stable climb at a certain angle of climb, the proper matching of horsepower and angle of attack is also required. Breaking this match will not maintain stable climbing. For example, an increase in horsepower will cause an increase in speed, lift and climb angle. If the horsepower is too high, the climbing angle will increase continuously, and the model will climb along the arc path, which is a common phenomenon of pull-over.
4、 Glide
Gliding is flight without power. When gliding, the resistance of the model is balanced by the component of gravity, so gliding can only fly downward along the oblique line. The angle between the glide path and the horizontal plane is called the glide angle.
The condition for stable glide (glide angle and glide speed remain unchanged) is that the resistance is equal to the forward component of gravity (X=GSin θ); Lift equals another component of gravity (Y=GCos θ)。
Gliding angle is an important aspect of gliding performance. The smaller the gliding angle, the farther the gliding distance at the same height. The ratio of the glide distance (L) to the descent height (h) is called the glide ratio (k). The glide ratio is equal to the cotangent glide ratio of the glide angle, and is equal to the ratio of the lift to the drag of the model (lift-drag ratio). Ctg θ= 1/h=k。大型航空模型制作
Gliding speed is another important aspect of gliding performance. The higher the lift coefficient of the model, the smaller the glide speed; The greater the model wing load, the greater the glide speed.
When adjusting a certain model aircraft, the wing angle of attack is mainly changed by using the lifting adjustment piece and the center of gravity moving forward and backward to achieve the purpose of changing the glide state.
5、 Torque balance and adjustment means
Adjusting the model requires not only the balance of attention, but also the balance of torque. Moment is the rotational action of force. The rotation center of the model aircraft in the air is its own center of gravity, so gravity does not produce rotation torque on the model. As long as other forces do not reach the center of gravity, they will produce torque to the center of gravity. In order to facilitate the analysis of model rotation, the rotation around the center of gravity is decomposed into rotation around three imaginary axes, which are perpendicular to each other and intersect at the center of gravity. The longitudinal axis runs through the front and back of the model, and the rotation around the longitudinal axis is the rolling of the model; The vertical axis runs through the top and bottom of the model, and the rotation around the vertical axis is the direction deflection of the model; The horizontal axis runs through the left and right of the model, and the rotation around the horizontal axis is the pitch of the model.
For the adjustment model, it mainly involves four kinds of moments; This is the lift moment of the wing, the lift moment of the horizontal tail; Tensile torque of engine; Reaction torque of power system.
The wing lift moment is related to the pitch balance. The main factors that determine the wing lift moment are the longitudinal position of the center of gravity, the wing installation angle, and the wing area.
The lift moment of the horizontal tail is also the pitching moment, and its size depends on the installation angle and area of the tail arm and the horizontal tail.
If the tension line does not pass through the center of gravity, it will form pitching moment or directional moment. The magnitude of the tension moment depends on the magnitude of the distance between the tension line and the center of gravity. The reaction torque of the engine is the lateral (rolling) torque, its direction is opposite to the rotation direction of the propeller, and its magnitude is related to the power and the mass of the propeller.
The angle of attack of the wing is determined by the balance of the pitching moment: the angle of attack will be increased by increasing the heading moment or decreasing the bow moment; Otherwise, the angle of attack will be reduced. Therefore, the adjustment of pitch moment balance is very important. Generally, it is not achieved by adjusting the installation angle of the wing or horizontal tail, changing the pull up and down inclination, and moving the center of gravity forward and backward.