Liberate Yourself Chapter 21

1

Everyone who sees birds flying in the sky will dream that they can grow a pair of wings and can fly in the blue sky without restraint. Free flight is a longing of my life and a common expectation of all people living under the oppression of feudal autocracy. When I was young, my brother not only taught me to skate and step on stilts, but also taught me how to make an aero model. This is a special hobby of "Big Brother" and a teaching to me. Brother said to me, do you want to fly to the sky? If you want to be free, then you must learn to liberate yourself. You should learn to build airplanes. The plane flies to the sky, your happiness will fly to where you want to go.

Big brother likes to make aviation models. My aunt is an air force officer, my mother's brother-in-law is the deputy chief of staff of the Jinan Military Region Air Force, and their son also served in the Air Force. After my father's brother was transferred from the army, he was responsible for civil aviation in Shanghai, Beijing, Taiyuan and other places. He was the general manager of China Civil Aviation Freight Company. That was in the early 1980s. Perhaps for these reasons, our family has more connections with the aviation industry. Big Brother has always dreamed of flying to the blue sky.

In order to realize his dream of flying, "Big Brother" is obsessed with making aviation models.

Aviation model sports is a scientific and technological sport that can control and release self-made or assembled model aircraft for outdoor activities, training competitions or recording flights.

Modern aviation model sports are divided into five categories: free flight, line control, radio remote control, simulation and electric. According to the power mode, it is divided into: piston engine, jet engine, rubber power model aircraft and unpowered model glider. The maximum lift area of ​​the aero model is 500 square decimetres; the maximum weight is 25 kilograms; the maximum working volume of the piston engine is 250 milliliters.

The competition themes of aviation models include: flight time, flight speed, flight distance, stunts, "air combat" and so on. The World Championship currently holds 30 events every two years. The aviation model also has a record item that specifically records all absolute results. At present, the International Air Transport Association has established 90 world records of world aviation models.

The vitality of aviation model sports lies in its interest and knowledge. My brother likes to make his own airplane model and imagines that he can become a majestic eagle and soar in the blue sky. When producing airplane models, his brother had many wonderful reveries, which inspired his dream of continuous pursuit, so he could enter the ideal of devoting himself to the aviation industry of his country.

2

Flying is the biggest dream of mankind. Since ancient times, people have been eager to fly freely in the sky like a bird, which has prompted many people to study hard and imitate the flight dynamics of birds. In the process of failed attempts, mankind finally realized the mystery, but what really made flying is no longer out of reach is the father of flying "Wright Brothers". And my elder brother thinks that Luban was the first person to invent the flying machine. Big Brother is a carpenter, he admires Luban in particular.

In my childhood, Big Brother would make a "bamboo dragonfly" for me, or fold an old newspaper into a "paper plane." This was the first aero model made by Big Brother.

Don’t think that the simple aviation model is nothing special. In fact, the knowledge inside is great. Not only the choice of materials, but also the power and angle used when throwing the aircraft need to be learned. If you understand and master the skills After that, you can really enjoy the fun brought by the flight model.

Big Brother often tells me about making model airplanes. He said: "The key is to make the propeller of the airplane."

A propeller is a device that turns the power of an engine into tension. The efficiency of the propeller will directly affect the flight performance of the model aircraft.

Propeller blades work very similarly to wings. If you remove the blade and observe it, you will find that it is a twisted wing. The blade profile is similar to the wing profile. The difference between the blade and the wing is that the movement of the wing in the air is basically translational, and the blade rotates around the axis of the propeller and advances as the aircraft is raised. The propeller's pulling force is generated by the blade moving in the air. Because the blade has both rotary and forward motion, the airflow blowing through the blade includes two parts: one is the airflow from the side perpendicular to the blade axis, and the other is the airflow from the front parallel to the blade axis.

3

Big Brother also likes to paint. He drew a view of an airplane model.

He told me to put a model plane in a horizontal state in the middle of three planes perpendicular to each other and make the longitudinal axis of the fuselage perpendicular to one of the planes and parallel to the other two planes. If we look at the model airplane far enough away from three directions, and draw the shape we see on each plane, that is, project the model airplane on three planes that are perpendicular to each other, and then put these three Three planes can be obtained by expanding the planes perpendicular to each other: top view, side view and front view. In general, these three views can more accurately represent the shape and main dimensions of a model aircraft.

Big Brother also told me that the commonly used model aircraft wing types are symmetrical, biconvex, flat convex, concave and convex, s-shaped, etc., the center curve of the symmetric airfoil coincides with the chord, and the upper and lower arcs are symmetrical . This airfoil drag coefficient is relatively small, but the lift-to-drag ratio is also small. Generally, the upper and lower arc lines of the double-convex airfoil on the online control or remote control stunt model aircraft are outwardly convex, but the curvature of the upper arc line is greater than that of the lower arc line. This airfoil has a higher lift-drag ratio than a symmetric airfoil.

The lower arc of the flat convex airfoil is a straight line. The maximum lift-to-drag ratio of this airfoil is larger than that of the biconvex airfoil. Generally used in primary line control or remote control model aircraft where the speed is not too high

The lower arc of the concave-convex airfoil is concave inward. This type of airfoil can produce greater lift, and the lift-drag ratio is also larger. Widely used on model aircraft with empty time in competition

The center curve of the S-shaped airfoil is like a horizontal S-shaped. The torque characteristics of this airfoil are stable and can be used on model aircraft without a horizontal tail.

As long as the object moves relative to the air, there must be air resistance acting on the object. The resistance acting on the model aircraft mainly includes friction resistance, differential pressure resistance and induced resistance.

What is frictional resistance? My brother told me that when air flows over the surface of the wing, due to the viscosity of the air, frictional resistance will be generated between the air and the surface of the wing. If the boundary layer on the wing surface is a laminar boundary layer, the frictional resistance caused by air viscosity is relatively small. If the boundary layer on the wing surface is a turbulent boundary layer, the frictional resistance caused by air viscosity is relatively large. In order to reduce frictional resistance, the contact area of ​​the model aircraft with air can be reduced, or the surface of the model aircraft can be smoothed. However, the smoother the better, because the surface is too smooth, it is easy to maintain the laminar boundary layer, and the air flow in the laminar boundary layer is easy to separate, which will greatly increase the pressure resistance.

Big Brother asked me to take a piece of tissue paper in each hand so that the distance between them was about 4~6 cm. Then told me to blow between these two pieces of paper with my mouth. I saw a strange phenomenon. Not only did the two pieces of paper not separate, but they moved closer to each other. And the greater the speed of the gas blown out, the closer the two pieces of paper are.

The elder brother said: "From this phenomenon, we can see that when there is air flowing between the two papers, the pressure becomes smaller. The pressure outside the paper is greater than inside the paper. The pressure difference between the inside and outside presses the two papers toward the middle. The middle air The faster the flow, the greater the pressure difference between inside and outside the paper."

4

Big Brother started making airplanes. When he glued the wing to the fuselage, he put a few empty matchboxes under the wing to fix the position of the wing and the fuselage.

He explained to me that the wing profile of an aircraft wing is also called an airfoil. Generally, the front end of an airfoil is blunt and the rear end is sharp. The leading point is called the leading edge, the trailing end point is called the trailing edge, and the line between the two points is called the chord. When the airflow flows through the wing head-on, it is a stream of air. The airflow will be divided into two upper and lower streams due to the insertion of the wing. After passing the wing, it regroups at the trailing edge. As the upper surface of the wing is arched, the passage of the airflow above is narrowed. According to the principle of continuity of airflow and Bernoulli's theorem, the pressure above the wing is lower than the pressure below the wing, that is, the lower surface of the wing is subjected to upward pressure more than the upper surface of the wing. The pressure difference is the lift generated by the wing.

It was the big brother's guidance that taught me a lot of knowledge of aeromodelling and a lot of aerospace knowledge.

Big Brother can do all kinds of airplane models, but most of them are not decorated, but can fly. These flying airplane models, Big Brother himself seldom went to test flight, he always gave it to me, let me go to fly.

Before the flight, Big Brother will always sing: "Be careful of safety, and observe the crowd around when taking off and landing. When the takeoff and landing is not smooth, you would rather crash the plane than hit the person."

When I released the model airplane made by Big Brother, when I saw the plane sometimes rising, sometimes diving, sometimes gently, and sometimes tumbling, I felt that I was flying.

5

My big brother has been playing airplane model for many years. He is an out-and-out enthusiast. Every weekend, when he encounters big things, he will put it down and fly with me. He said: "The plane can give people a very mysterious feeling. The model is actually a scaled-down version of the plane. When you see that the plane you made can also fly smoothly, you will have a sense of accomplishment in your heart."

Big Brother also often said that the same sky has a different mood. Every time I fly, I will feel that the sky is so wide, so free, so relaxing and so comfortable. I was a model airplane, but it was my mood that let me fly. Whenever I think of these words from my big brother, I will pay special respect to my big brother.