Basic knowledge of model aircraft

I believe that most men, or men who are not men yet, are deeply shocked when they first enter this forum or other model forums. It turns out that they have always harbored a dream of flying. It is not difficult to achieve. That was me two months ago. I accidentally came to this forum when I was at work. I was so excited that I can't express it in words. I was so anxious that I wanted to fly into the sky right away. Alas, my childhood dream. But I had to buy equipment, so I browsed the forum and asked, what equipment do I need? How to build a plane and fly into the sky as quickly as possible? But the more I looked, the more dizzy I became. What is KV, what is 2S, 3S, and why are chargers more expensive than batteries?

The following text is only for newbies like me, friends who have just become possessed. Don't ask on the forum what equipment you need to buy. Is the bigger the KV better, or the smaller the better? Because there are many posts about these issues in the forum, you have to learn to dive. I believe that before buying equipment or making a machine, novices will have many questions answered after reading this article, and will save themselves the trouble of looking around. After reading this article, they will forget about that article.

Since I am also a novice, many questions may not be expressed clearly, or there may even be errors. Please correct me if you are experienced.

Equipment

For an airplane to fly into the sky, it definitely requires a lot of equipment. What equipment is needed? Basic electronic equipment includes: transmitter, receiver (including crystal), engine (electric or oil-driven), steering gear, ESC, and battery. All the above equipment are indispensable. In addition to electronic equipment, you also need paddles, rudder angles, etc. Let’s focus on electronic equipment here.

1. Remote control equipment

Remote control equipment includes transmitters, receivers and crystals. The function of transmitting is to send signals so that we can control the flight of the aircraft; while receiving is self-evident, it receives the signal from the transmitter; the crystal allows transmitting and receiving to work at the same frequency, so as not to conflict with other transmitting and receiving. When you are ready to buy a remote control device, these three pieces are usually matched with each other. Of course, you must also ask the merchant clearly, because some merchants only sell transmitters.

The price of TAOBAO Shangtiandifei 06A is around 250 yuan. Contains a 6-channel transmitter, 6-channel receiver, and a pair of crystals with a frequency of 72mhz.

The most important parameter is the channel for both transmitting and receiving.

The channel represents several signal modes. One channel corresponds to one signal, which is relatively abstract.

For example, our Piaopiao is often a three-way. Then the first channel uses a servo to control the ailerons (or the first channel controls the direction), the second channel controls the elevation and descent, and the third channel controls the motor speed through the throttle. Therefore, novices who are starting to build airplanes should at least have three links.

The TDF06A mentioned above and the remote control generally discussed in the forum are proportional remote control, and another type of control is switch remote control. There is a very big difference between these two types of controls, and there is also a considerable price gap, and there is an essential difference: an aircraft based on the former can be called a remote control model; while an aircraft based on the latter can only be called a remote control toy. So what is a proportional remote control? To put it figuratively speaking, a proportional remote control controls a certain channel and can simulate real mechanical operations. For example, taking the control of the throttle as an example, it is bigger, bigger, bigger... the maximum; Smaller, smaller, smaller... smallest. Controlling other channels is similar. The switch remote control does not work. One channel of the switch remote control can only be on-off. Like a light switch, the channel cannot be controlled proportionally. On TAOBAO, there are many remote control aircraft (gliders) under 200 that have this kind of switch control.

Let’s talk about the crystal used for remote control. The frequency of the transmitting and receiving crystals must be the same in order to operate at the same frequency. For example, if the crystal on the transmitter is 72.310MHZ, then a 72.310MHZ crystal must be inserted on the receiver. If the reception above is 72.180, then obviously the transmitter cannot control this reception. When buying remote control equipment, the crystals on the transmitter and receiver are already configured, so there is no need to worry about this.

2. Motor

I don’t understand oil-driven ones, and I believe most people don’t intend to buy it. Since it is an electric version, I will only talk about the motor.

There are two types of motors, brushed and brushless. Brushless is popular nowadays, firstly because of its sufficient power, secondly because of its long life, thirdly because of its high efficiency, and fourthly because it is not expensive. So here we only talk about brushless motors

A brushless motor has three wires. There is no pair of brushes like brushes, so it is called brushless. When the brushes of a brushed motor are used a certain number of times, the brushes are worn out and must be replaced. Brushless motors have no brushes, which is the main reason why their lifespan is much longer than that of brushed motors.

Brushless efficiency is higher than that of brushes. Note that this does not mean that brushless will necessarily provide stronger power than brushes. High efficiency means that brushless can provide greater power than brushed ones using the same amount of electricity.

You don’t need ESC equipment when brushed to rotate, but for a brushless motor to work, it must be equipped with an ESC. About ESC, we will talk about it below.

What are the brushless motors 2208, 2408, 2822, 1806? This parameter is different for different manufacturers. For brushless, the most important parameter is the KV value. What is KV? You can refer to this article. /thread-6058-1-1.html KV is the speed of the motor (no load) = KV value * voltage

And the larger the KV value, the smaller the torque. A low KV value will increase the torque. So the KV value determines what kind of paddle you get, because larger paddles require more torque.

For example, AX 1806N, KV 2100. Then under the voltage of 11.1 volts, its rotation speed (without propeller) is 2100*11.1=23310 rpm. KV2100 is suitable for use with 5030 paddles at 11.1 volts. You may want to ask, can I bring an 8060 paddle? Can you turn it? The answer is no, it can be turned. But your motor and ESC may be OVER soon! Why? Because in this case, driving the 8060 propeller requires more torque, and the faster the speed, the smaller the torque provided. Don't ask why, it can be solved by the law of conservation of energy. For details, you can read the post on this aspect. (If you have objections to this question, please refer to the reply on the 22nd floor)

So is KV2100 suitable for carrying 5030 propellers under any circumstances? no! If the voltage is higher, such as 16.4 volts, the speed will be higher, the torque will be reduced, and the propeller needs to be smaller. On the contrary, if the voltage is low, 7.4V, you can use a larger paddle.

Is there a motor with high KV and high torque? For model motors, no! The reason is simple. High KV and high torque require larger diameter and longer copper wires and stronger magnets, and rotation requires greater current and voltage. As a result, the motor will be heavier. For things flying in the sky, weight is a very important factor.

Whether they have the same KV, different motors, and the same propeller, the pulling (push) force is the same, and the theory is the same. But due to workmanship and technical reasons. It's probably different. Maybe the KV2100 motor from one manufacturer is lighter and has slightly greater torque than the KV2100 motor from another manufacturer. But it is impossible that the motor of KV2100 has greater torque than the motor of KV1000!

So, when choosing a motor, choose KV. Because KV decides what kind of aircraft you make and what kind of propeller you choose.

In addition, weight is also an important consideration when choosing a motor. Of course the lighter the better!

What kind of motor should a novice choose? It is recommended to choose Aoxiang (AX) 1806N (also known as 1818). The KV of this motor is 2100, 2600, 2900. For construction, choose 2100 because it is said that the 1806N of KV2100 is equipped with a 5030 propeller, and the operating current at full throttle does not exceed 7A, which is very energy-saving. The pull (push) force exceeds 300g, suitable for back push or waist push Piao Piao, paper airplane, SU-27, F22, etc. In addition, when you buy this motor, it usually comes with a propeller protector and a 5030 propeller. The price is about 65 yuan.

3. Electric adjustment

Electric adjustment corresponds to different motors, which are divided into brushless ESC and brush ESC.

A brushed motor can work without an ESC, but without an ESC, it is impossible to control the speed of the motor.

There may be many friends who are just starting out like me and want to find ready-made equipment around them to make airplanes. Firstly, it saves money; secondly, generally speaking, equipment is not available in small cities and can only be purchased online. So there are many posts asking if it is possible to use the motor in a toy car as power. The answer is: Yes, but there is insufficient motivation. Even if the power is good, you still need a brush ESC, so don't try to use a brush motor without an ESC to make a model aircraft.

As mentioned earlier, brushless operation requires an ESC, otherwise it cannot rotate. The brushless ESC has several functions: first, it provides low-voltage alternating current for the brushless motor to work (is this true? Experts please correct me!) so that the motor can rotate; second, it converts the battery voltage for the receiver to work.

The brushless ESC has a maximum current when working. In other words, this current cannot be exceeded during operation. So you should pay attention to this issue when choosing an ESC. Is that a one-and-done solution to choosing the maximum current? No! Because the ESC with the larger current is heavier, you need to choose a suitable ESC (is this true? Experts can correct me!).

The price of brushless ESCs ranges from high to low. Beginners can choose a 30A ESC that costs about 100 yuan; if you plan to buy a brushed ESC, the cheapest one from TAOBAO is as low as 15 yuan, and I have one in my hand.

4. Steering gear

The steering gear is also essential. Because to fly an airplane, in addition to controlling the motor rotation. You also have to operate ailerons, lift, and rudder. Otherwise, I won’t be able to fly freely! These tasks require steering gear to complete. There seems to be nothing to say about choosing a servo. However, the servo has a torque parameter, and of course the bigger the better. However, under the same circumstances, the greater the torque, the heavier the steering gear will be. For novices, for an aircraft weighing about 500g, choose 9g for about 25 yuan, or even a 5g servo is enough! The five servos I bought are all 9g. 22 yuan each.

A three-way aircraft requires two servos, and a four-way aircraft requires at least three.

5. Battery

The model mainly uses lithium batteries and nickel metal hydride. Lithium batteries are divided into lithium ion and lithium polymer. Currently, lithium polymer is mainly used. Under the same circumstances, nickel metal hydride is heavier than lithium battery. So it’s better to choose lithium battery!

When it comes to batteries, it is often 2s or 3s. To put it simply, 2s refers to two batteries connected in series, and 3s refers to three batteries connected in series. What are the benefits of connecting in series? That is to increase the voltage. As mentioned before when talking about KV, voltage and speed are related.

For lithium batteries, 2s has a voltage of 7.4V, and 3s has a voltage of 11.1V. Because the voltage of a lithium battery is 3.7V. Look at the battery of your mobile phone. Is it like this? The nickel metal hydride battery has only 1.2 volts per cell, so 2s is 2.4 volts, and 10s is only 12 volts.

Please note that whether it is lithium battery 3.7V or nickel metal hydride 1.2V, it does not refer to the voltage when the battery is fully charged. For lithium batteries, the voltage generally reaches 4.2V after being fully charged. I believe most people have mobile phone batteries with universal charging capabilities. You can take a look. Generally, the output voltage marked on it is 4.2V. NiMH can reach about 1.5V when fully charged.

In addition to voltage, then there is capacity and discharge rate. The capacity of the battery is measured in mah (milliamp hours) and the discharge rate is measured in C. For C numbers, simply put. 1C is different for batteries with different capacities. 1C means that the battery can continue to work for 1 hour with 1C discharge.

Example: If a battery with a capacity of 1500mah continues to work for 1 hour, then the average current is 1500ma, which is 1.5A. 1.5A is the 1C of this battery. If the above nominal value is 10C, what is the maximum discharge current of this battery? It is 1.5A*10=15A. This means that this battery is safe when used at 15A.

For another example, 1C in 1000mah is 1000ma, which is 1A. If the above nominal value is 15C, then the maximum discharge current is 1A*15=15A, and the maximum discharge current of this battery is also 15A. However, the battery above works at 15A and discharges at 10C. Theoretically, the maximum current working time is 60/10=6 minutes. . When 1000mah works at 15A, it discharges at 15C. In theory, it can be used for 60/15=4 minutes when working at this current.

So relatively speaking, a 1500mah, 10C battery will last longer. So it’s not enough to just look at the C number when buying a battery. The discharge of a battery with a small C number may be greater than that of a battery with a large C number. This is related to capacity.

Under the same circumstances, the larger the battery capacity, the heavier the weight. In order to control the weight of the machine. So don’t be greedy for large capacity when buying batteries, but be moderate.

The lithium battery costs about 80 yuan for 2s, and the 3s battery for about 100 yuan should be enough.

6. Charger.

Although the aircraft does not use it, it must be used to charge the battery. It is best to use balance charging for lithium batteries. Why? There is a post about batteries in the forum, which is very clear. I can’t find it. You can look it up.

I believe that novices are like me when buying equipment. Buying this is the most heartbreaking thing. Because the balanced charge is at least about 150 yuan. More expensive than batteries! If you have the conditions, you can directly buy B6, the price is about 350 yuan. If you want to be cheap, you can choose a nickel-metal hydride plus power charger for about 15 yuan. But it is difficult to control the weight of the aircraft very light. In fact, a large part of the weight of the aircraft is due to the battery.

If you choose nickel metal hydride, I suggest you don’t even need to buy a charger, just find a current adapter and change it. Pay attention to the output voltage type and size, such as 10s NiMH, the voltage is 12V. But after full charging, it is about 1.4V to 1.5V. Then the input voltage is between 14V and 15V. The output current is around 500ma, and the principle is not too small. If you don't understand electronics like me, pay attention to the output voltage type. If it is marked output DC 15V 500ma, it means that the output DC voltage is 15V and the current is 500ma. If it is marked AC, it means the output AC voltage is 15V, so it must not be used. The day before yesterday, I happily got back a 15V power adapter for a scanner from my workplace. It turned out that it was marked as AC output. I was so happy for nothing.

7. Paddles

Paddles are not expensive, as cheap as about 3 yuan. Good ones are generally around 5 yuan to 13 yuan. The propeller has two important parameters, the propeller diameter and the propeller pitch, both in inches

For example, the 8060 propeller means that the diameter of the propeller is 8 inches. That is 8*2.54=20.32 centimeters. The pitch is 6 inches. The pitch represents the distance the propeller travels in one revolution. The intuitive understanding is that you take a 20.32 cm thin piece of wood, hold both ends with both hands, and twist it in opposite directions. Twist it once and it becomes 8010, twist it again and it will become 8020, and twist it harder and it will become 8060, haha! I don’t know if this is right.

The larger the propeller diameter and pitch, the greater the pulling (push) force the propeller can provide. Note that the paddle diameter refers to the diameter of the circle formed by the rotation of the paddle, not the total length of the paddle. For a two-blade propeller (two blades, which is the most commonly used propeller), it is exactly the sum of the lengths of the two blades; for a single-blade propeller, the diameter is the length of the blade * 2; and for a three-blade propeller, the diameter is not The sum of the paddles.

If there is no small paddle in hand, many masters will cut off the big paddle and use it. After the propeller is cut off, the diameter of the propeller will become smaller, but the pitch will not change. For example, if the 7035 propeller is cut to 5 inches, it becomes the 5035 propeller. (I don’t know if I’m right, experts can correct me!))

When choosing a propeller, you should also pay attention to the appropriate KV value of your motor. This article /thread-6058-1-1.html makes it very clear.

In addition, when choosing a propeller, there are slow-speed propellers and direct-drive propellers. In fact, slow-speed propellers do not mean slow. It mainly means that slow-speed propellers are generally used on reduction groups. Of course, they can also be used. Direct drive. There is not much difference in terms of tension and so on (I don’t know if this is correct or not, experts can correct me!).

Furthermore, we often talk about pulling forward and pushing back. So is there a difference between a paddle that pulls forward and a paddle that pushes backward? No! Just turn the paddle upside down when pushing back. Of course, there are also special push-back propellers. For this type of propeller, the motor shaft can be directly inserted into the propeller hole without the need for a propeller protector or screw cap. Because it is pushed backward, there is a forward force when turning, and the paddle will not shoot out. And if you change it to forward pulling, it will be easy for the paddle to shoot!

Generally speaking, if you want the plane to fly slowly, use large propellers; if you want the plane to fly fast, use small propellers.

This may be completely contrary to the thinking of friends who are just starting out. They think that if you want to fly fast, you should use a big paddle, and if you want to fly slowly, you should use a small paddle. Why? For example, assume that two propellers, 7035 and 5030, are used. In theory, the same electric power can be used to provide the same pulling (push) force. The 7030 only uses 10,000 rpm, regardless of resistance, and the distance traveled in one minute. It is 10000*3.5=35000 (inches); and if 5030 is used to provide the same pull (thrust force is required) 27440 rpm (how to calculate it, the pull force of the paddle is proportional to the cube of the diameter), there may be an error here, experts can correct me , but there is no objection that a higher speed is definitely needed). Regardless of resistance, the distance traveled in one minute is 27440*3=82320 (inches). Obviously the latter small paddle is much faster. Therefore, high-speed machines use small propellers with high KV motors, and slow-speed machines use large propellers with low KV motors.

In addition, when buying paddles, pay attention to buying more of different models. Because the paddle is most likely to break when the machine crashes.

8. Paddle protector

This is optional, but for your paddle, you must buy at least one. Not expensive, about 5 yuan. How it is protected will be known when you crash your phone. Before I had it, I would break the oar after dropping the plane twice on average. But with it, I haven't had any oars break now.

The necessary equipment is the above. Basically, both are indispensable.

Materials and Tools

In addition to equipment, making an airplane also requires materials and tools. There are many tools that are generally available as long as you have a home, such as knives. But things like KT boards are probably not available in most households.

1. KT board.

This is the main material for making airplanes, except of course for making airplanes like balsa wood.

KT board has two specifications: 240CM*120CM and 240CM*90CM. The color is usually white, but also black, red and other colors. The thickness is generally 5MM. The price is not expensive, usually 15 yuan a piece. Go to your local small advertising company or a place that wholesales advertising materials. If you have 3MM, you can also buy one. This is especially useful for making wings with wing shapes. The 3mm can effectively control the weight of the JJ. But everyone says that 3MM KT is not easy to buy nationwide.

Maybe you think the KT board is not very heavy, but the 5mm 90CM*15CM weighs 40g. Therefore, 3mm can effectively reduce the weight of the aircraft, but of course the strength of 3mm will definitely be reduced a lot.

2. Adhesives

Due to the material of KT boards, 502 and AB cannot be used to bond KT boards, and neither does universal glue. The best is foam glue. 10 yuan a bottle, yellow. Super cheap and relatively fast. It can be used in about 3 minutes. The initial viscosity is quite good. Once firmly adhered, it is stronger than the KT board. But this guy is not easy to buy. I searched all over our small county before I found it.

There is foam quick-drying glue available online for about 8 yuan, but it is only a small bottle. In terms of cost performance, it is a bit expensive.

Little Pudding said that 851 is easy to use, but I have never found it. Some people say that there is a kind of resin-type AB glue that can also be used, but it is slow and I have never found it. Also, remember to buy a hot melt glue gun and a glue stick. On TAOBAO, the price is as low as 12 yuan per gun, 20W. I bought the 60W model for 25 yuan. If you want to glue the KT board quickly, you must use this. However, hot melt glue is heavy. I weighed it and found that one stick weighs about 20g.

3. Cutting equipment

Cutting equipment is required to cut the KT board. The most commonly used one is a utility knife. The cheap one is 2 yuan, and the expensive one is only about 10 yuan. Of course, you can also use other knives, as long as they are easy to use. The principle is to be thin and fast.

You can make a thermal cut, which is especially useful when cutting foam. Search the forum for a method, and you will find that there are some electric irons, and some are made of computer power supplies and guitar strings. I made it with a power adapter and a 2-string guitar (the price of a 2-string guitar is usually 2 yuan).

4. Carbon rod.

This is mainly used to strengthen the machine. Go to a fishing gear store to buy it, but the price is relatively expensive. It is recommended to buy it from a wholesale fishing gear dealer or a professional model DIY store.

The thick ones can be used as tail rods, and the thin ones can be used as wing reinforcements and connecting rods. You don’t need bamboo sticks for this one because it is strong and light

Making machine parts

The equipment is back and you can make machines. When they first become addicted, most people initially think that making an airplane is not difficult, and flying an airplane is not difficult either. Two months ago, I thought the same thing. In fact, it is not as simple as you think, and it is certainly not as difficult as you think.

It is your first time to fly, what kind of aircraft is suitable? Generally speaking, novices can choose to use Piaopiao plus pushback and get started with paper airplanes. There are many drawings and how-to forums. Floater is a general term, which refers to a high-monoplane model aircraft with small wing load and slow flying speed. The high-monoplane has a lower center of gravity and is stable in flight. The wing load is small, so it can fly very slowly and has good gliding performance. After selection Pushing can protect the motor and propellers to the maximum extent when the machine crashes. Paper airplanes are easy to make and can usually be made in three hours.

So can we choose KT330 or SU-27? Many novices ask about these two models when they first come up. Although everyone has individual differences, you really shouldn’t think of making a plane or flying simply. Although the SU-27 has a beautiful appearance and is not complicated to make, as a novice, it is difficult to adjust the thrust lines and center of gravity. In addition, there is no wing shape, high flight speed requirements, and poor gliding performance. It is really not suitable for novices. The same goes for the 330. It has a large rudder surface, so most beginners will explode instantly on their first flight. I also had experience with several paper planes and Piao Piao before I made the SU-27. The first flight was successful and it was very beautiful, so don’t rush to make these two types of aircraft at the beginning.

How to ensure that the plane you make can fly into the sky? Flying in the sky seems not as simple as running in the water on the ground. What I emphasize from my own experience is to pay attention to the line of thrust and the center of gravity. If these two things are correct, the aircraft will generally make its first flight successfully. In addition, pay attention to controlling the weight of the aircraft from details, such as glue, reinforcement items, landing gear, tape, etc.

For an aircraft with a regular wing shape (what is a regular wing shape, I am talking about a pair of regular wings here, not the su-27 and the like) the center of gravity is in the front third of the wing. There are many ways to measure the center of gravity, here is a simple one. Just hold the aircraft with your hands, and after balancing the front and back, it will be the vertical line where the center of gravity is.

There are many posts about the thrust line (tension line), and I can’t explain it clearly. In fact, if you can figure it out clearly, it is not very accurate in application. The principle is that the motor shaft of an aircraft that is pushed backwards is tilted up a few degrees, and that of an aircraft pulled forward is tilted downwards by a few degrees.

If the aircraft does not have regular wings, such as a paper airplane, how to measure the center of gravity? It's very simple. Make a good airplane and don't install equipment. You can use AA batteries or other heavy objects to balance the center of gravity and throw it by hand to glide. If you can glide more than 5 meters smoothly like the paper airplanes you made when you were a child, you won't raise your head or cut down. , the center of gravity is OK, and then mark the position of the center of gravity with a pen to install the equipment.

Also, if you are building an aircraft with a tail such as Piao Piao, you must pay attention to the vertical tail not to be deflected, otherwise your aircraft will definitely miss the mark in the sky. It is difficult to fly in a straight line.

Equipment installation is very simple, and everyone can understand it. Note that some ESCs have 2s and 3s plugs similar to computer jumpers, and this guy happens to have a JST female plug that can be plugged directly into the battery. When I bought the device and tried it out, I connected the battery to this plug, but the motor didn't turn. Fortunately, the ESC was not damaged.

If you can solve the above problems, your plane will definitely be able to fly! For novices, most first flights are unlikely to last more than 2 minutes in the sky, and don't expect perfection in landing unless you have mastered previous simulations. In fact, I believe that most of my newbie friends are like me and do not have high requirements for the first flight. They just want to be able to make the plane they make actually fly.

Conclusion

Of course you also need small things like rudder angles and steel wires. These are not expensive, you can buy them or not, and you can find many materials around to replace them. Any phone card or the thin steel wire inside the tire can be used. Be careful to buy at least three servos and multiple paddles, otherwise you will spend more on postage.

None of the above is important. The important thing is not to be like me, who anxiously finished the airplane and went out in the middle of the night for test flights. It took two months before I could fly in a straight line or do somersaults. I only succeeded in landing twice.