Hot air balloon;

1783, Montgomery brothers made an airbag with a diameter of about 30.5 meters with paper lining and linen, and performed a floating performance in the Anon market. The balloon rose to the height of1830m and floated for 2300m. This success has brought great inspiration and imagination to the world, and people who fly into the sky with great enthusiasm have devoted themselves to it, and a hot air balloon fever has risen all over Europe.

Second, the father of aviation science: George Kelly?

However, the hot air balloon basically has no power. It can fly mainly by heating under the balloon. Apply the principle of air heating to increase volume, reduce density and reduce weight to make balloons fly ~

So George Kelly? focused his research on the development of powered aircraft.

First of all, Kelly put forward the design concept of fixed-wing aircraft. In his book About Air Flight, he expounded the flight principle of aircraft heavier than air and systematically discussed the concept of modern aircraft. Influenced by this book, many people began to develop aircraft heavier than air, so Kelly was called "the father of aviation science".

Third, the father of hang gliding: Otto Lilienthal

Otto's power flight basically imitates the wings of birds, which is quite strange. Its basic idea is to use compressed carbon dioxide to drive an engine with about two horsepower, so that the wing swings up and down, but the flight test is not as smooth as expected, because compressed carbon dioxide can only last for a short time, the engine stops running for a while, and the wing only takes a few shots. Moreover, the weight doubles, the landing speed is faster, and the degree of danger increases accordingly. So in 1896, Otto launched the No.2 aircraft with a wing area of 20 square meters, and the accident occurred before the test flight. Because it was an accident, relatives and friends specially engraved "sacrifice is inevitable" on Otto's tombstone, which was Otto's mantra before his death.

Fourthly, the first plane (Voyager 1) was made by the Wright brothers.

1903 12 17 In Hawke Beach, North Carolina, Voyager 1 stands tall like a huge white bird and looks very light. Its fuselage skeleton and wings are made of light and strong Chinese fir, and its propeller is also made of Chinese fir. The curved wings are covered with thin and strong cotton cloth. The length of this plane is

On this day, Voyager 1 flew four times. The first test flight was piloted by my brother Orville Wright. The plane staggered in the air for 12 seconds and landed at a distance of 36 meters from the ground. Later, the first free flight recognized by the world was the fourth flight by my brother wilbur wright. The plane flew 260 meters in 59 seconds. This flight is empty. But this is a great achievement: this is the first successful power-driven, manned, sustained, stable and maneuverable heavier-than-air aircraft in human history. This successful flight is of great historical significance, which opens a new page for mankind to conquer the sky and marks the arrival of the era of aviation aircraft.

The Wright brothers completed the first human plane flight. Since then, countries all over the world have invested in aircraft development and research. 1952 saw the British comet jet, 1970 saw the introduction of the American jumbo jet, and 1976 saw the cooperation between Britain and France to complete the supersonic Concorde.

Take Concorde as an example, its flying speed is about 40 times that of Voyager I, and the weight of jumbo jet is more than 1000 times that of Voyager I!

It is precisely because of the rapid progress of airplanes that we can travel around the world by plane today!

Model Voyager 1

According to the design drawing, a same plane with the scale of 1/2 was copied.

Flight principle:

Flying in the air, what we need to consider is nothing more than the air force. To build an aircraft with air superiority, four basic elements must be considered: weight, lift, resistance and thrust.

Speaking of weight, in addition to the weight of the car body, fuel also includes the load of the goods.

Lift is the force that an airplane exceeds its weight.

Drag is the force that all kinds of airflow interweave to lead the plane to the rear.

Thrust is the force that overcomes the resistance and pushes the plane forward in the air.

The lift of birds and aircraft is mainly caused by the airflow flowing over the wing surface.

There used to be a saying in the aviation industry: "As long as there is a powerful engine, even the door panels can fly." Although this sentence is a bit exaggerated, it is not unrealistic, because as long as the propeller is given strong horsepower, any clumsy wings can be pulled up. But a more efficient way to fly in the air is to adjust the shape of the body. In other words, it is to maximize the lift and minimize the drag.

When the plane is moving forward, the airflow above the wing is lower than that below the wing, that is to say, the flying plane is a foreign body inserted by the airflow in the air, which urges the airflow to push the plane upward.

Lift is determined by various factors.

One of them is the area of the wing. The larger the area blown by the airflow, the greater the lift. The second factor is speed. The faster the airflow passes through the wing, the greater the pressure difference between the upper and lower parts. The third factor is the angle of attack, that is, the inclination of the wing relative to the airflow is within a certain boundary, which makes the airflow path above the wing longer, the speed increases, the difference between the speed and the lower part of the wing increases, and the lift also increases, so the angle of attack.

With the action of lift and the advance of the plane, the so-called resistance is produced. There are three main types of resistance, namely, friction resistance, shape resistance and induced resistance. The first two are because the plane passes through the air, which can be reduced by the progress of aviation science and the adjustment of fuselage streamline. We can imagine the difference between the resistance of a square box and that of a ball in the air. Induced drag is a by-product of the lift generated by the wing. It can be said that this is the inevitable price of the elevator. Because the lift force is caused by the pressure difference, but at the same time it also blows off or accompanies the flow. This is mainly caused at the wing tip. When the plane moves forward, the wing tip will produce a spiral tail to pull the plane back. This is called induced resistance.

A wing can't be infinite, it must have a destination. Now we know that the wing tip is the root of many problems. Due to the geometric shape, the airflow at the leading edge of the wing not only flows backward, but also flows outward, which makes the airflow at the wing end more complicated.

So there are many ways to reduce induced resistance, and the common ones are:

1: Make the wing end arc, and do your best.

2. Shape the lower wing surface upwards, and hope that the vortex is as far away from the wing end as possible.

3. Install the wing end with oil tank or electronic warfare equipment, and isolate the airflow by the way to prevent it from turning up.

Winglets: At present, most winglets extend upward, but some extend downward. The winglet of the real plane is obvious and can be seen clearly during the flight. I believe many people who have sat on the Boeing 747-400 winglet have noticed that the winglet can not only isolate the air above and below the wingtip and reduce the induced resistance, but also provide some forward components to save some horsepower caused by the installation angle.

In addition to these three kinds of resistance, there is actually another kind of resistance, but this will only happen when the plane flies at supersonic speed.

After the plane can fly in the sky, the flight time of the plane is an important factor we need to consider next, and the aspect ratio is an important factor for the plane to fly for a long time, because if the glider has a very high aspect ratio, it can still glide for a long time even if it does not take the updraft.

The so-called aspect ratio is the ratio of wing length to wing chord length. Generally speaking, the greater the aspect ratio, the slimmer the wing will be. Through the aspect ratio of the wing, we can know how far the plane can fly with a certain amount of fuel.

Of course, the most important part of an airplane is the wing. Aircraft can fly in the air completely by the buoyancy of wings, and the cross section of wings is called airfoil. In order to meet various needs, aviation predecessors have developed various airfoils, from those suitable for supersonic aircraft to those suitable for hand-thrown gliders. For example, the names of various parts of the wing, such as 100, have been systematically studied by quite a few units and individuals. However, there are so many types of wings that they are usually called wings in the aircraft industry.

1, fully symmetric wing: the upper and lower arcs are convexly symmetric.

2. Semi-symmetrical wings: the upper and lower arcs are convex but asymmetrical.

3. Clark y wing: the lower arc is a straight line, but it should actually be called a plano-convex wing. There are many other plano-convex airfoils, but Clark Y-wing is the most famous, so this airfoil is called Clark Y-wing, but it should be noted that there are several kinds of Clark Y-wing.

4.S-shaped wing: an S-shaped wing with a flat arc in the middle. When the angle of attack changes, the pressure center of this type of wing is relatively constant, which is often used in tailless aircraft.

5. Concave wing: The downward arc is on the chord line, and the lift coefficient is large, which is common in early airplanes and towed gliders. All birds are of this type except hummingbirds.

6. Other special airfoils.

The above classification is only a rough classification. Observing an airfoil, the most important thing is to find its centerline, and then look at the thickness distribution on both sides of the centerline. The bending mode of the centerline determines the characteristics of the airfoil. The more curved the arc, the greater the lift coefficient, but generally speaking, it is very unreliable to look at it with the eyes. The midline of Clark's Y wing is more curved than many concave wings.

When evaluating aircraft performance, wing loading is an important index to evaluate aircraft performance. Wing loading is the weight shared by the main wing per unit area. How many grams per square inch [g/dm2] are used for model airplanes, and how many newtons per square meter [n/m2] are used for real airplanes. The greater the wing load, the greater the weight of the wing with the same area. If you buy an airplane kit, most of the wing loading are marked on the design drawings. Calculating wing loads is very simple. Weigh the aircraft in grams (without refueling), and then calculate the wing area in square inches (generally to simplify the calculation, it still includes the part combined with the fuselage). The wing load is obtained by separating the two parts. For example, a 30-level training machine weighs1.700g, and its main wing area is 30m2.

The lift of the wing increases with the increase of the angle of attack, which is the included angle between the chord and the airflow (as shown in Figure 3- 10). When the angle of attack is zero, the symmetrical wing does not generate lift, but the Clark Y wing and concave wing still have lift, and the latter two airfoils do not generate lift until the angle of attack is negative. The angle of attack that does not produce lift is called zero-lift angle of attack (as shown in Figure 3- 1 1), so we all know that there is an upper limit for the increase of angle of attack, beyond which it will stall. When does the wing stall? (Figure 3- 12a) is the airflow passing through the wing when the aircraft is in normal flight, and (Figure 3- 12b) is the airflow when the aircraft is stalling. At this time, the upper wing surface produces strong turbulence, and the direct result is that the resistance increases greatly, and the airflow impacts the upper wing surface, and the lift decreases greatly.

Then we want to know when the wing will stall in advance, so it is necessary to know Reynolds number. The original formula of Reynolds number is:

Re=ρ V b/μ

Re=ρ V b/μ ρ is the air density, V is the air velocity, B is the chord length, and μ is the viscosity coefficient.

The larger Reynolds number is, the sooner the boundary layer passing through the airfoil transitions from laminar boundary layer to turbulent boundary layer, and the turbulent boundary layer is not easy to separate from the airfoil, so it is not easy to stall. Before the laminar boundary layer transitions to the turbulent boundary layer, the wing boundary layer with small Reynolds number will separate. General airfoil data will indicate at what Reynolds number the data was obtained, unless otherwise specified, the aspect ratio is infinite. According to the airfoil data, the metropolis tells you when Reynolds number is at several degrees of attack angle. The larger the Reynolds number, the less likely it is to stall (as shown in Figure 3- 13). The stall angle of aircraft is not a definite value. The slower the speed (the smaller the Reynolds number), the easier it is to stall. The greater the wing load, the easier it is to stall because of the greater the angle of attack during flight. The chord length of delta wing aircraft is very long, so it is not easy to stall because of the high Reynolds number.

When designing a real airplane, we will try to shake the wing or joystick before stalling, or install an airflow separation warning device on the wing to warn the pilot that the airplane is about to stall.

Aircraft design process;

The so-called aircraft design is a series of actions and work from the generation of ideas to the actual specific aircraft, through conception, investigation and analysis, preliminary proofing, drawing detailed blueprints, parts manufacturing, equipment procurement, flight test and so on …

General aircraft design can be divided into three stages:

Molding design stage

At this stage, the overall size, shape and internal layout of the aircraft should be properly studied and decided. The research method is to analyze and compare wing loading, wing sweep angle, chord length ratio, thickness ratio, and the positions of general wings and tails by parameter comparison, and select the most suitable data and layout.

At the same time, a variety of engines are analyzed and compared, and the engine that is most suitable for the aircraft shape structure and can meet the mission requirements is selected. The size of the control surface depends on the requirements of static stability and control.

Furthermore, at this stage, we should also make a preliminary analysis of the future cost and manufacturing. Although the design completed at this stage can generally meet the needs of the task, it is still allowed to make appropriate corrections in the further process of design. All the work at this stage is an armchair strategist!

preliminary design phase

In the molding design stage, the best size, shape and arrangement are selected according to the cost or performance. After the wind tunnel test, the model is further adjusted and modified, and the shape is gradually fixed without modification.

At this time, the engine used in the aircraft is selected, and the structure of the inlet and nacelle of the engine is studied in detail. If the inlet structure is very complicated, wind tunnel test is necessary. Determine the flight performance of aircraft or other aircraft, such as speed, altitude, etc. In addition to factors such as aircraft weight and engine thrust, the most important factor is the aerodynamic force acting on the aircraft. Aerodynamics mainly depend on the appearance of the aircraft. When designing and developing an aircraft, the first thing is to design its shape, so that the aerodynamic forces acting on the aircraft can be laid and the flight performance can be calculated. However, this work can only be done at the forefront, not after the aircraft is built. Therefore, the experimental design to determine the aerodynamic force of aircraft is mainly wind tunnel.

At this time, the load, stress and deflection analysis of the main structure should be carried out together with the structural design. Aeroelasticity, fatigue and flutter analysis should also be carried out, and static tests of some structural components should be planned and implemented.

At this stage, more accurate weight estimation and more thorough performance analysis are needed. At the same time, it is necessary to make detailed plans and arrangements for manufacturing methods, tools, models and fixtures, and the influence of dynamic stability and control on the control surface should also be decided at this time.

Detailed design stage

At this point, all the external shapes have been decided and no changes will be made. A final decision should be made whether to produce or not. Detailed structural design should be completed at this stage. All tool designs, manufacturing blueprints, fixture designs, fixture joints, etc. It should also be completed at this stage. Internal details, such as the fixing of the fixing seat for equipment installation, the fixing of hydraulic pipeline, ventilation pipeline, control wire rope and wire conduit, etc., shall be determined.

For practical convenience, the solid model can be used to assist the internal arrangement. According to the actual work progress, further estimate the cost reliably. All the assembly and other parts have been decided.

Question:

What is a wind tunnel?

In short, the wind tunnel is used to test the wind resistance, aerodynamics and other coefficients of an object, which can be a car model, an airplane model and a wing model.

The basic principles of wind tunnel experiment are relativity principle and similarity principle. According to the principle of relativity, the aerodynamic force of an aircraft flying in still air is the same as that of an aircraft at rest, and the air blows in the opposite direction at the same speed. However, the windward area of the aircraft is relatively large. For example, the wingspan of its wings is several meters, ten meters and tens of meters (Boeing 747 is 60 meters), so the windward area airflow is equal to the flight speed. The power consumption will be amazing. According to the similarity principle, the plane can be made into a small-scale model with geometric similarity, and the airflow speed can also be lower than the flight speed in a certain range. The experimental results can be used to calculate the aerodynamic forces acting on the aircraft in actual flight.

Moreover, wind tunnel experiments play an important role in the development of space science and technology. The Wright brothers successfully tested the power plane in 1903, and the wing airfoil design was based on wind tunnel experiments. Up to now, the development of aircraft still depends on wind tunnel test to a great extent, and the data obtained are needed for design and performance verification. The application of wind tunnel test has also expanded from aerospace to other fields, such as pollution diffusion and prevention, wind engineering, architectural design, environmental planning and so on. Therefore, wind tunnel test technology has a wide range of engineering applications.

Must the plane take off against the wind?

Of course not. No matter whether it is downwind or headwind, it can take off. Otherwise, when there is a headwind at the airport, all airlines will stop.

Just taking off against the wind has many advantages:

Increase the indicated airspeed of the aircraft, so that the aircraft can reach the normal takeoff speed ahead of schedule.

Shorten the runway length required for the aircraft to take off and let the aircraft fly off the ground in advance.

In case the plane gives up taking off on the runway for some reason, the headwind will help the plane slow down and stop.