0 Buy engines and equipment. (70% of the funds are spent)
1 Prepare tools.
2 Understand the internal structure of the model (similar to the real plane, but much simpler).
Prepare and understand information (cost 10-20%).
Drawing, I use Autocad to design the output.
5 production debugging.
Find a remote control model to take you on a test flight, because you may be excited that day.
How to make a remote-controlled plane
It is divided into several parts:
1: remote control part. 2. Radio transmitting and receiving part. 3. Control circuit part. 4. Aircraft mechanical parts.
I'm not familiar with the last part, but I think I'll take it. You can buy a model of that plane and bring it back for modification.
As for the remote control, if you don't have many functions, you can use 2262-2272 codec chips. As for radios, some sell well-made transmitting and receiving modules. It's troublesome to do it yourself, and sometimes it's not enough. It's better to buy a ready-made one.
Connect the above things and you can output the signal of 2272. Using this signal to control the stepping motor and so on, of course, you need to connect a circuit yourself. It's not difficult to design it yourself.
In fact, the mechanical technology is very simple. The first is the selection of materials, which must be light and have a certain strength. At present, nano-materials are the most widely used in small models, which look a bit like foam, but have greater strength.
The second is machinery. For a simple model, you need two motors, which are installed on the wing of the plane. The motor only needs to control the speed. When both motors rotate at high speed, the propeller is driven to take off the plane. When the speed is low or stopped, the plane descends. When the speed of the motors on both sides is unbalanced, the plane tilts to the direction of the low-speed motor, as long as the control circuit of the motor is completed.
I can only tell you briefly that an airplane model can be divided into rubber band power, internal combustion engine power, micro turbojet power and electric power. The airplane model consists of fuselage, wing, tail, receiver, steering gear and wheels. This is the most basic. For example, an aircraft driven by an internal combustion engine costs $ 5.0CC, 500. The steering gear is used to control the lifting of the nose, and the tail is the direction. There is also a fuel tank and wheels. Oil pipe, receiver (the more advanced, the more complicated), fuselage and wing, remember that fuselage is 70%-80% of the length of wing. If you are a beginner, I recommend you to use the electric one. It's not bad, cheap and simple. Because time is limited, I won't say too much. I am also a beginner in model airplane! There are two planes, and we plan to build an aircraft carrier this year, haha!
Aircraft model making
How envious!
It's not about money. It won't cost much.
1. Large flow workbench and woodworking workbench.
2. Professional production platforms (including drilling machines and small lathes, etc.). ).
3. Two toolboxes, if elegant, make a working wall.
4. If possible, leave a small paint booth.
If possible, build a small swimming pool.
6. Electrician production table and supporting tools.
7. Design a writing desk.
8. Omni-directional lighting.
9. Complete set of test equipment (multimeter, speedometer, etc.). ).
10. All kinds of small parts (this depends on your usual collection).
One by one, not all. You accumulated it yourself.
General knowledge of aviation model
1. What is an aviation model?
In the competition rules formulated by the International Air Transport Federation, it is clearly stipulated that "an aviation model refers to an aircraft that is heavier than air, has a limited volume, has an engine or not, and cannot carry people, so it is called an aviation model.
Its technical requirements are:
The maximum flying weight, including fuel, is five kilograms;
The maximum lifting area is 150 square decimeter;
Maximum wing loading100g/dm2;
The maximum working volume of piston engine is 10 ml.
1, what is an airplane model?
Generally speaking, a model made in a certain proportion according to the actual size of an airplane is called an airplane model.
2. What is a model plane?
Generally speaking, models that can fly in the air are called model planes and aviation models.
Second, the composition of the aircraft model
Like a manned aircraft, an airplane model is mainly composed of five parts: wing, tail, fuselage, landing gear and engine.
1, wing-is a device that generates lift when the model airplane flies, and can maintain the lateral stability when the model airplane flies.
2. Tail-including horizontal tail and vertical tail. The horizontal tail can maintain the pitching stability of the model aircraft, while the vertical tail can maintain the directional stability of the model aircraft. The elevator on the horizontal tail can control the lift of the model plane, and the rudder on the vertical tail can control the flight direction of the model plane.
3, fuselage-the main part that connects all parts of the model into a whole is called the fuselage. At the same time, the fuselage can be loaded with necessary control components, equipment and fuel.
4. Landing gear-the device for taking off, landing and parking of model aircraft. The first landing gear and the last three landing gears are called the first three points; There are three landing gears on both sides of the front, and the rear landing gear is called the rear three-point landing gear.
5. Engine-It is the device for generating flight power for model aircraft. The power devices commonly used in airplane models are rubber bands, piston engines, jet engines and motors.
Three, aviation model technology commonly used terms
1, Span- the linear distance between the left and right wing tips of the wing (tail). (The part that passes through the fuselage is also included).
2. The total length of the fuselage-the linear distance from the front end to the rear end of the model aircraft.
3. Center of gravity-The point where the gravity of all parts of the model airplane acts together is called the center of gravity.
4. Tail center arm-the distance from the center of gravity to the quarter chord length of the leading edge of the horizontal tail.
5. Airfoil-The cross-sectional shape of the wing or tail.
6. Leading edge-the front end of the airfoil.
7. Trailing edge-the last end of the airfoil.
8. chord-connecting line between leading edge and trailing edge.
9. Aspect ratio-the ratio of wingspan to average chord length. A high aspect ratio means that the wings are long and narrow.
Flight principle of flying wing model glider
The flying wing ejection glider consists of wings, folding hinges, reset hooks, ejection hooks and reset rubber bands. There is a tab at the trailing edge of the wingtip (Figure 1). Fold the two wings into a whole, use a rubber band to play hard, and it will go straight into the blue sky. Soon, the wings will spread out and fly like a big bird, which is very interesting. It is easy to fly, easy to adjust and very safe.
A flying wing is an airplane without a horizontal tail. How can a flying wing fly without a tail? We know that the glider generates lift from the wing, and the forward component of gravity provides the forward speed of the glider (Figure 2). The horizontal tail grasps the balance (Figure 3), which makes it have good pitching stability. Flying wings have wings and gravity, and like ordinary gliders, they have a certain speed of progress, can generate lift, but have no tail; How to maintain balance and stability? It turns out that the center of gravity of the flying wing is in front. On the one hand, the lift generated by the wing is used to overcome the gravity, on the other hand, it generates the bow moment, while the pull ring of the flying wing near the wing tip generally inclines upward to generate the downward force, which is the head-up moment to the center of gravity and keeps the balance of the whole model (Figure 4). At the same time, the pull ring also plays a role in maintaining the pitching stability of the flying wing, which makes the flying wing the same as the conventional aircraft: it has forward flight speed, the lift generated by the wing overcomes gravity, and the pull ring maintains balance and safety.
The flying method of the flying wing catapult glider is as follows: Hold the catapult lever with the right hand, hold the folded wing tip with the left hand, and hang the catapult rubber band on the right catapult hook (that is, the right reset hook), with the catapult direction vertically upward (Figure 5). When the left hand is released, the folded flying wing model will shoot into the sky like a rocket. It must be noted here that when holding the ejection stick in your right hand, you must use the ejection hook on the right. If you use the ejection hook on the left, the flying wing will bounce on the ejection lever (Figure 6) or even the right hand.
The gliding attitude of the flying wing depends on the angle of the adjustment tab, and the adjustment method is similar to that of the ordinary model: if the model falls downward, that is, the head is heavy, then the adjustment tab can be pulled upward to increase the upward angle; If the model appears wavy flight or stall, that is, the head is light, then pull down the adjusting piece, that is, reduce the upward angle of the adjusting piece, so that students can adjust it in repeated flights and get an optimal angle.
When adjusting, we should also pay attention to the fact that the dihedral angle of the flying wing should not be too large, because the dihedral angle is used to maintain the lateral stability of the model, and the swept angle of the flying wing can also play the role of dihedral angle, so the dihedral angle should not be too large. If the glider swings from side to side during the test flight, the dihedral angle is too large and can be reduced.
When the flying wing catapult glider rises at high speed, it relies on the oncoming powerful aerodynamic force to make the two wings close together. When the speed decreases, the aerodynamic force also decreases. When the air pressure on the wings is less than the tension of the reset rubber band, the wings of the flying wing naturally open and enter the gliding state. If the force to reset the rubber band is great, the flying wing will not play high. Properly adjusting the strength of the reset rubber band can make your model bounce higher, but ensure that the wings can be deployed smoothly.
If the sweepback angle of the wing is properly increased (Figure 7), your small plane can fly more stably. Because the sweep angle is slightly increased, the wing tip can extend backward, which is beneficial to the stability of the flying wing.
Classification of aviation models
I. Classification and classification of popular aviation models (competition events)
I. Free flight (P 1)
P1a-towing model glider (divided into P 1A- 1 and P 1A-2).
P1b-rubber band model glider (divided into P 1B- 1 and P 1B-2).
P1c-piston engine model glider (divided into P 1C- 1 and P 1C-2).
P 1D- indoor model aircraft (divided into P 1D- 1 and P 1D-2).
P 1e- electric model plane
P1f-rubber model helicopter
P1s-hand-thrown model glider (divided into blank time and straight line distance)
P 1t- ejection model glider.
Second, the line manipulation class (P2)
P2B—— aerobatic model controlled by wire (divided into P2B- 1 and P2B-2 levels)
P2C Line Control Team Competition Model Aircraft
P2D air combat model aircraft by wire control
P2E- electric aerobatic model aircraft by wire (divided into P2E- 1 and P2E-2 levels)
P2X—— Model airplane with rubber band by wire
Three, radio remote control class (P3)
P3A—— Radio remote control stunt model aircraft (P3A- 1, P3A-2)
P3B—— Radio-controlled model glider (divided into P3B- 1 and P3B-2 levels).
P3e- Radio Remote Control Electric Model Aircraft.
The second is the aviation model project widely carried out among teenagers.
First, the paper model plane.
Second, the hand-throwing model glider (short for hand-throwing, number P 1S)
Third, the rubber model helicopter
4. Ejection model glider (referred to as ejection, number P 1T)
Verb (abbreviation of verb) tows a model glider (traction for short, general grade number is P 1A- 1 and P 1A-2, and international grade number is F 1A).
Six, rubber band model aircraft (referred to as rubber band, the popularization level number is P 1B- 1 and P 1B-2, and the international level is F1B.
Aircraft model wing
Commonly used aeromodelling airfoils are symmetrical, biconvex, plano-convex, concave-convex and S-shaped. , as shown.
The middle arc of the symmetrical airfoil coincides with the chord, and the upper and lower arcs are symmetrical. The drag coefficient of this airfoil is relatively small, but the lift-drag ratio is also small. Generally used for on-line control or remote control of aerobatic models.
Both the upper arc and the lower arc of the biconvex airfoil are outward convex, but the camber of the upper arc is greater than that of the lower arc. The lift-drag ratio of this airfoil is greater than that of symmetrical airfoil. Generally used for online control of racing cars or remote control of aerobatic models.
The lower arc of a plano-convex airfoil is a straight line. The maximum lift-drag ratio of this airfoil is greater than that of the biconvex airfoil. Generally used for primary by-wire or remote control model aircraft, low-speed friction.
The lower arc of the concave-convex airfoil is concave inward. This airfoil can produce great lift and great lift-drag ratio. Widely used in space-time flight models.
The middle arc of the S-shaped airfoil is like a transverse S-shape. The airfoil has stable torque characteristics and can be used for model aircraft without flat tail.
Wing lift principle
If you hold a piece of tissue paper in each hand, make the distance between them about 4~6 cm. Then blow air between these two sheets of paper with your mouth, as shown in the figure. You will see that the two pieces of paper are not separated, but close, and the greater the speed of the most blown gas, the closer the two pieces of paper are. It can be seen from this phenomenon that when there is air flowing between two sheets of paper, the pressure becomes smaller, and the pressure outside the paper is greater than the pressure inside the paper, so the pressure difference between inside and outside pushes the two sheets of paper to the middle. The faster the intermediate air flow, the greater the pressure difference between the inside and outside of the paper.
The outline of an airplane wing is also called an airfoil. Generally, the front end of airfoil is blunt, the rear end is sharp, the upper surface is arched, and the lower surface is flat and fish-shaped. The front end point is called the leading edge, the rear end point is called the trailing edge, and the connecting line between the two points is called the chord. When the airflow flows head-on over the wing, the streamline distribution is shown in Figure 2. It turned out to be an airflow, which was divided into two streams due to the insertion of the wing. After crossing the wing, it rejoined at the trailing edge. Because the upper surface of the wing is arched, the channel of upper air flow becomes narrow. According to the principle of airflow continuity and Bernoulli theorem, the pressure above the wing is lower than that below the wing, that is to say, the upward pressure on the lower surface of the wing is greater than the downward pressure on the upper surface of the wing, and this pressure difference is the lift generated by the wing.
Main points of use and related common sense
(a) the use of small engines: the use of small engines should pay attention to the following aspects:
1. Run-in operation-All new engines must run at a low speed for a period of time ranging from half an hour to an hour or more, which is called run-in operation. Running in is very important. If the running-in operation is not good, the engine will not only have short life, low horsepower and difficult start-up, but also bring many faults. It is one-sided to say that grinding the car is useless and it is a waste of the engine. Correct running-in operation will never shorten the life of the engine, on the contrary, it will prolong the life and improve the performance. That is, taking new cars and motorcycles as an example, when leaving the factory, the carburetor is equipped with a plug to limit the speed, or it is stipulated that the speed cannot exceed a certain limit. After driving for hundreds of kilometers, the speed can be gradually increased, that is, all parts must run.
Why grinding the car?
Because each small engine is assembled by several parts, the mutual cooperation of these parts has not been fully coordinated, and there will inevitably be bumps or burrs on each friction surface. If you work at high speed at this time, the piston, cylinder and other parts will overheat or even get stuck, causing damage such as surface galling. Running-in operation means running at a slow speed, slowly and bit by bit "grinding" the surfaces of parts in contact with each other very smoothly, which can adapt to each other and coordinate with each other. It's like feeling a little uncomfortable when we just put on a new pair of shoes. If you keep running at this time, your feet will not adapt. If you wear it for a few days before running, your feet will feel much smoother.
Grinding must be carried out on a solid test bench or workbench, and never on the model plane or other wooden boards that are not strong enough to avoid vibration and damage to parts during operation.
Grinding requires a large propeller to limit the engine speed, which is generally maintained at about 5000~6000 rpm, and then gradually increase the speed. Too low rotation speed will produce large vibration, which is not good for parts. It is best to have a stable and even medium speed. During grinding, don't use oil with additives, turn up the throttle a little, and don't press the pressure adjusting lever too tightly.
General grinding steps are as follows:
When grinding the car just now, the engine was running 1~2 minutes later, and the oil circuit was quickly closed, and then the car was started after the engine cooled down slightly. Don't run continuously for a long time. Doing so is also conducive to getting familiar with the start and adjustment of this engine. Then, run at a low speed for 20 to 30 minutes. If the cylinder head is not too hot (finger pressing 1~2 seconds is tolerable) and the rotating speed is even, you can lightly press the pressure regulating rod, turn down the oil needle and increase the rotating speed. Continue grinding for about 20 minutes. Then install a smaller propeller and gradually increase the speed. Finally, use the propeller of the flying model to grind the car at high speed 10~20 minutes.
When the new engine was just ground, black oil spots were sprayed from the exhaust port. If you put your finger near the exhaust port, a layer of oil will be sprayed, and shiny metal powder can be seen from the oil layer in the sun. Generally, after grinding for about half an hour, the black oil ejected is greatly reduced or eliminated. At this point, the speed should be gradually increased. If the rotating speed is always stable and there is no "thermal death" phenomenon, the grinding is over and the engine can be installed on the model plane for use. The grinding time of each engine is different, which should be decided according to the specific situation. It usually takes about an hour.
A small engine with proper grinding has good air tightness, easy starting and easy and flexible rotation. Even if it runs continuously at high speed, the rotational speed will not change (judging from the sound).
2. Installation-compression ignition small engines can be used as power devices for aviation, navigation and land models. When used on model airplane, it can be installed in front of the nose (pull-in type), which is the most common style; is very good also
When installed at the tail and other parts (propulsion type), the distance between the rear paddle pad and the front end face of the casing must be smaller than the distance between the crank pin and the rear cover of the casing, so that the thrust of the propeller can be transmitted to the end face of the casing through the rear paddle pad, and the crank pin and the rear cover will not rub.
Small engines can be installed vertically (with the cylinder head facing upwards), upside down (with the cylinder head facing downwards) and horizontally (with the cylinder head facing sideways). The most common are formal dress and horizontal dress. It is difficult to start backwards, and it is easy to cause too much oil. In order to protect the engine, the online control model, especially the online control stunt model, is often installed horizontally. The horizontally mounted engine can still start well.
Figure 13 shows the starting method when the small engine is installed horizontally on the model plane. The assistant crouches slightly behind the right side of the model, grasps the fuselage part close to the engine with his left hand (mainly grasping, and don't press the model to the ground hard to avoid the landing gear bending or the propeller touching the ground), and gently holds the right wing tip with his right hand; The starter paddles with the right hand and holds the pressure adjusting lever with the left hand, so that the compression ratio can be adjusted at any time according to the force felt by the right hand. Skillfulness can also be started by one person, grasping the model with his left hand and paddling with his right hand.
The small engine must be firmly and reliably installed on the engine frame of the model; After each flight, if there is looseness, it must be checked and tightened immediately. An unreliable engine will produce severe vibration after starting, which will make the model fly badly.
When adjusting the engine installed on the model, we should not only pay attention to the ground operation, but also consider the flight conditions and requirements. For example, the aerobatic model plane controlled by wire has vertical ascent, dive and inverted flight. After the engine is started, it is necessary to adjust the engine by putting the model airplane in the state of level flight, bow down, level flight and inverted flight, so as to achieve the maximum horsepower when looking up and a little fuel when looking down. In other states, it can work normally without stopping.
In the practical application of small engines, there will still be such problems. We should be good at analyzing and finding out the reasons, and pay attention to summing up experience through practice.
3. Peacetime maintenance:
(1) Always keep the engine clean inside and outside, and do not let dust, lime sand, paper scraps or other dirt enter the engine. When the engine is not in use, wrap it with clean cloth or paper. After each use or release, clean the dirt outside the engine with clean waste paper or rag and wrap it; At the same time, wipe off the oil on the model plane with a cloth stained with some gasoline or kerosene, and then wipe it with a dry cloth. Don't drive or take off in dusty or sand; When you have to take off on the sand, you should splash some water or pad some thick paper and boards to prevent sand from entering the engine. When making a model plane, it is often necessary to measure the position and size with an engine, and the air inlet and air outlet of the engine should be wrapped to prevent paper, sawdust and other dirt from entering.
(2) Maintain the engine. Do not drive continuously at high speed or use too short propellers and flywheels unless necessary. Don't press the pressure adjusting lever too tightly.
(3) Do not disassemble or disassemble the engine as little as possible.
(4) Choose the right tool, the right propeller and the right clean oil.
(5) The refueling appliances, tools and airplane models that are in frequent contact with the engine should be kept clean. A clean small box should be prepared, which is specially used to hold refueling tools. Don't put the refueling tools around, so as to avoid dust entering the engine with refueling. Dust, like abrasive, will soon wear out the engine. It is best to put the refueling toolbox, oil bottle and wrench in specially prepared cloth bags or small wooden cases. It is not only convenient to use, but also clean, and it can also avoid forgetting to bring some necessary tools when flying out.
4. Pay attention to safety-although the model airplane engine is small, its speed is very high. So pay attention to safety and prevent accidents.
After starting, do not stand on the rotating surface of the propeller. Never use a broken or unbalanced propeller, and never use a propeller that breaks after gluing. Never use a propeller made of metal.
When storing oil, don't be near high temperature or fire. Do not smoke when preparing mixed oil and cleaning the engine with gasoline, and prevent smokers from approaching. Don't develop power indoors and try to avoid inhaling ether and waste gas. The outside of the mixed oil bottle should be marked toxic to avoid misuse.
2) Common knowledge about small engines:
We have learned about the working principle of some internal combustion engines, and initially mastered the start-up and use of internal combustion engines in model aircraft. Everyone must want to know more about internal combustion engines. So what are the factors that affect the performance of internal combustion engines? How can we make better use of this model airplane engine in our hands? Here are some common sense about this:
1. Air separation timing diagram-The start and end times of intake, exhaust and exhaust of small engines are called air separation timing. The timing of air separation has a very important influence on engine power, speed, fuel consumption and starting performance. It is necessary to reasonably choose the timing of gas distribution, make full use of the inertia generated by gas flow, drive out the exhaust gas as cleanly as possible, and inhale more fresh mixed gas to improve the power of the engine. The gas separation timing chart is used to show the time and sequence of gas inlet, gas transmission and exhaust. From the chart, we can see the start and end time of a process and the length of the opening duration. On the timing chart, the opening and closing time of each valve is expressed by the angle of crankshaft rotation.
On the right side of Figure 14 is the valve timing diagram of crankshaft type small intake engine (such as Yin Yan 1.5). According to the rotary motion of the left crank pin (a circular pin with a connecting rod at the rear end of the crankshaft) in Figure 14, when the piston descends to the exhaust port, the exhaust starts, and the position of the crank pin is equivalent to "1"on the time sequence diagram; When the crank pin is turned to "2", the gas transmission port is opened and gas transmission begins; The piston begins to rise after passing the bottom dead center, and when the crank pin turns to the position equivalent to "3", the gas transmission stops; When it reaches "4", the exhaust is terminated; When the piston continues to rise and the crank pin rotates to the position equivalent to "5", the air intake hole on the crankshaft is communicated with the air intake pipe and air intake begins; After the piston passes the top dead center, the steering descends. When it reaches "6", the air intake hole on the crankshaft is no longer connected with the air intake pipe, and the air intake is terminated.
2. Load characteristic curve —— When the engine is working, the power used to rotate the propeller is called engine effective power, which is referred to as engine power for short. Engine power is an important criterion to measure the performance of small engines. When the engine works at a constant maximum allowable intake pressure on the ground (blocking the intake with anything will not increase the intake resistance), the speed can be changed by changing the crankshaft load (such as using propellers of different sizes). With the change of speed, the effective power of the engine also changes. The relationship between the effective power and the rotational speed is called the load characteristic of the engine. The curve used to express the change of engine effective power (horsepower) with crankshaft speed (revolutions per minute) is called engine load characteristic curve, or external characteristic curve and power speed curve. According to this curve, the power of the engine at a certain speed can be calculated. For example, on the curve of figure 15, when the speed of this engine is 7000 rpm, its power is about 0. 135 horsepower; 10000 rpm, maximum power, and the speed at this time is called maximum power speed; If the speed increases again, the power will decrease. Different types of engines have different power and speed curves.
From this point of view, in order to give full play to the maximum power of the engine, it is necessary to choose a propeller with appropriate size, so that the speed of the engine in flight is just around the maximum power speed. In flight, the engine speed is generally about 10% higher than the ground. The specifications of some small engines are attached with power and speed curves for reference.
3. Determine the speed-As mentioned above, if you can know the speed of the engine, you can calculate the power according to the power speed curve of the engine. Even if there is no power speed curve, the power can be roughly estimated from the speed. Because the maximum power speed of the commonly used compression ignition small engine is about 10000~ 14000 rpm, knowing the speed can roughly estimate whether the maximum power of the engine is exerted.
The rotational speed can be measured by centrifugal or flash tachometer, and its measuring range is about 20000 rpm. You can also make a simple and practical vibration tachometer, which is made according to the vibration principle in physics and will not consume the power of the engine when measuring the speed.
The vibration tachometer consists of more than a dozen steel wires with different lengths (Figure 16). The natural frequency of each steel wire is different. The longer the steel wire, the lower the natural frequency. The shorter the length, the higher the natural frequency. When the small engine is working, the piston moves up and down once every revolution, resulting in vibration. When the vibration frequency generated by the engine is the same as or an integer multiple of the natural vibration frequency of the steel wire, the steel wire will start to vibrate due to the vibration. When in use, fix the vibration tachometer near the engine or directly lean against the cylinder head of the engine with the base; As long as we observe which steel wire has the largest vibration amplitude, we can measure the engine speed according to the scale of the steel wire. Its accuracy is slightly different according to the quality and diameter of the steel wire and the clamping degree between the steel wire and the base, generally 200 rpm. It is best to calibrate the scale with a standard tachometer first.
The natural frequency of steel wire is related to its diameter, free length and steel elasticity. The natural frequency f of general steel wire can be calculated by the following formula:
Where: D steel wire diameter (unit cm)
L Free length of steel wire (unit cm)
Or where: n engine speed (rpm)
Using the above formula, we can find out the free length of steel wires with different diameters when they vibrate at a certain speed.
revolutions per minute
free length
millimetre
revolutions per minute
free length
millimetre
free length
millimetre
3000
3500
4000
4500
5000
5500
6000
1 17
1 10
103
98
94
90
86
6500
7000
7500
8000
8500
9000
9500
82.5
79
76.3
74
7 1.5
69.5
67.8
10000
10500
1 1000
1 1500
12000
12500
13000
66
64.5
63
6 1.5
60
59
58
If a steel wire with a diameter of 1 mm is used, the free length (the length of the steel wire exposed outside the base) representing various rotating speeds is shown in the above table.
The tachometer can also be made of metal plate as the base (Figures 17 and 18). The scale representing the rotating speed is written on the base near the root of the steel wire. In order to reduce the volume, a few steel wires can be used less. For the convenience of carrying, a movable pencil structure can also be adopted. There is a retractable steel wire at the position where the lead core is installed. When measuring the rotating speed, lean one end of the tachometer against the cylinder head to make the steel wire longer or shorter. Look at the place where the steel wire vibrates most violently, and then you can know the engine speed according to the corresponding scale.
4. Choose a propeller-you need a propeller when you practice starting a small engine of an airplane model. First of all, starting the propeller requires a propeller; In addition, the propeller also has the function of flywheel and cooling, which makes the small engine work continuously.
The propeller for starting and grinding the vehicle can be bigger and thicker than the flying propeller. The heavier propeller is beneficial to the stability of start-up and operation. If it is used in 1.5 ml engine, the diameter of the propeller is about 240 mm and the pitch is about1.20mm.: Used in 2.5ml engine, the diameter of propeller is about 260mm, and the pitch is about 130mm.
Propeller should be made of fine, clean, solid wood with good strength and easy processing. More suitable are pine and basswood. Birch is also suitable, but a little harder, time-consuming and laborious. Tung wood is too soft and weak to be selected.
Generally, the cross section of the blade should be a plano-convex airfoil with a circular leading edge and a thin trailing edge. The blade root should be thicker to ensure strength, and the root section is biconvex. When the exercise is started, it is often hurt or cracked by the trailing edge of the blade because of the repeated movements of the fingers. Therefore, it is necessary to make the trailing edge of the propeller for starting practice thicker and smoother.
When making propeller curved surface, it is better to use a wooden file than a knife, but the surface is rough after processing, so you can polish it with a rough steel file or sandpaper several times. The balance of the completed propeller should be carefully checked. It is required that the length, shape, weight and blade angle of the corresponding section of the blades on both sides should be consistent, especially the weight of the blades on both sides should be consistent. The unbalanced propeller will produce violent vibration after the engine is started, resulting in parking, loosening and grinding of bearings and other parts. The surface of the blade should be oiled three to five times (it can also be replaced by paint or spray painting) to prevent the engine fuel from infiltrating into the wood and affecting the balance.
Never use a metal propeller to prevent the handle from breaking. The new air-cooled engine cannot be driven by flywheel, and the flywheel will damage parts due to poor cooling.
Figure 19 shows the manufacturing steps of the propeller, and the bottom is the finished shape. Fig. 20 is a blade template (diameter 230mm) for reference.
Working principle of aircraft propeller
First, the working principle
A propeller can be thought of as a rotating wing. The airflow passing through each section of the blade consists of the forward speed along the rotating shaft and the tangential speed generated by the rotation. In this paper, we discuss the airflow on the propeller blade by taking two minimum cross sections at the propeller radius r 1 and R2 (r 1 < R2). V- axial velocity; N-propeller speed; φ —— airflow angle, that is, the included angle between airflow and propeller rotation plane; α —— Blade attack angle; β-blade angle, that is, the included angle between the chord length of blade section and the plane of rotation. Obviously β = α+φ. When the air flows through each small section of the blade, aerodynamic force, drag Δ D and lift Δ L are generated, which are always empty after synthesis.
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