RC Airplane Series

RC Airplane Series – Part 6

In this article, we will learn how to perform ESC Calculations. Also, we are going to study the control systems connections (basically, how the electronics are connected)!

1. What is an Electronic Speed Controller (ESC)?

ESC stands for Electronic Speed Controller. Its job is to provide a set appropriate voltage across the BLDC motor according to the throttle given on the transmitter. 

• For example, suppose I give 25% throttle, so to get the speed corresponding to 25% throttle, what should be the voltage applied across the motor -> this is the job of the ESC! (speed is controlled by controlling current)
• The main thing to understand is that we will be controlling the voltage across the motor with the help of the ESC. We are already aware of the motor kV relation:

$\text{motor } kV = \frac{\text{RPM of motor}}{\text{Voltage across the motor}}$

• So, according to the relation, varying the voltage will vary the RPM of the motor, which will result in speed variation as well.

From the example itself, we can understand that choosing a proper ESC is very crucial so that everything is under control and also safe at the same time. 

Wiring connections for ESC:

2. How to choose an appropriate ESC?

Let’s understand the procedure using an example!

Suppose we finally choose the motor for our model: 

A2212 10T 1400kV BLDC motor

Step-1: Find out the maximum current that the current draws. If this value is not directly given, it can be calculated from the relation.

 $P = V \times I$

(‘P’ is max. power of motor, ‘V’ is the nominal voltage of our battery used, and ‘I’ is the max current from the motor.

From the datasheet:

In our case, the maximum power of the motor is 180W, and we consider that we are using a 3S LiPo battery, which gives us 11.1 V voltage

$P = V \times I$

$180\,W = (11.1\,V)\times I$

$I = 16.2\,A$

Step-2: But we should choose an ESC such that this maximum current value should just be 75% of the actual ESC current, which we will be buying. (Read it again !). We call this current ‘Actual ESC Current.’

Calculating 80% of ‘Actual ESC Current’ (this value needs to be on the ESC we would be finally buying) would give us the ‘Maximum motor current.’

$80\% \text{ of Actual ESC Current} = \text{Max motor Current}$

$\frac{75}{100} \times \text{Actual ESC current} = 16.2\,A$

$\text{Actual ESC current} = 20.25\,A$

This implies that we need an ESC that has a rating of 20.25 A. But in reality, there is no such ESC with this current rating being manufactured. So we need to go with an ESC that has a bigger value than 20.25

We can go with a 30A ESC or a 40A ESC, which would also be perfect in our case.

3. Connections of all of the RC Electronics involved

Now, by this article 6 of the RC Airplane Series, we already know about all the basic electronic requirements for an RC Airplane. Let’s list it down :

• Motor and Propeller
• LiPo Battery
• ESC (Electronic Speed Controller)
• Receiver (On board)
• Transmitter (Not on board)
• 4 Servos (1 for each aileron, 1 for elevator, 1 for rudder) 

In this example, let’s say we are using a 6-channel transmitter and receiver.

• Usually, in most of the cases, we have to attach the connectors to the 2 wires assigned for the battery in the ESC. For this, we can use the XT60 connector, which is very commonly used as well. They come in a set of female and male connectors. The female one is to be attached to the ESC, while the male one is to be attached to the battery

For more clarity on the above figure, you can also refer to the diagram below.

4. Why use Y-junction wire for ailerons?

• If you look into the connection diagram carefully, we can see that the servos attached to the 2 ailerons are connected to a Y-junction wire. This then goes on to connect to the receiver, and it uses just one channel on the receiver for 2 servos!

The reason behind us doing this thing can be learnt from the article – RC Airplane Series-2: ‘Understanding Control Surfaces.’

In the above article, the focus is on the aileron part to understand the reasoning behind the Y-junction cable. In short, we can summarize it as follows: 

To get a roll, having the ailerons deflect in the opposite sense helps even more. For example, if we need to take the right roll, then on giving just one stimulus through the transmitter, the right aileron will deflect upwards while at the same time, the left aileron also deflects downwards.

One Advantage and One Disadvantage:

Advantage :

• We can get a better roll due to 2 ailerons moving in opposite sense and everything is completed by using just 1 channel

Disadvantage :

• We can’t make the ailerons to be used as flaps since they will always move in the opposite sense. (i.e., flaperons are not possible)

Conclusion:

• So in this RC Airplane-6, we have learnt to do the ESC Calculations. Similar stuff is used while drone designing as well, since it also includes BLDC motors whose speed needs to be controlled. 
• Here, we have completed the basic design of the RC Airplane. Hope you enjoyed the Series and got to learn something new through this. But again, reminding you, this was just the Basics. 

RC Airplane Series (All previous Articles)

• Part-1: What’s in the Wings!
• Part-2: Understanding the control surfaces!
• Part-3: Designing your Airplane !!
• Part-4: Motor and Propeller Selection
• Part-5: How to choose a LiPo Battery?

Any suggestions from your side are welcome!

Keep Learning

All the Best

RC Airplane Series – Part 5

In this article, we are going to learn about the correct battery selection for our RC Airplane Project. This step is very crucial as the battery is going to be serving as the powerhouse for the entire set of electronic components on the plane. 

I will be covering some examples as well for your clarity. So, without any further delay, let’s straightaway start with the topic

---

Why choose LiPo Battery?

Among so many batteries, when it comes to the electronic projects (especially RC aircrafts), we directly choose LiPo over others. 

LiPo stands for Lithium Polymer batteries. These are known for their ‘High Energy Density‘. 

By comparing the definitions, we can see that, if more mass is accumulated in lesser volume, we term that substance as highly dense substance. Similarly, if given energy can be stored in a lesser volume, we term the substance as the one having ‘high energy density’ !

---

Battery Specifications:

When it comes to LiPo batteries, we have 3 main parameters which we need to check in order to select the right LiPo for our project. Those are :

• Number of cells (Voltage of the battery (in volts))
• Capacity (in mAh)
• ‘C’ rating/discharge rate

Voltage of LiPo battery:

A battery is a combination of cells. So basically, to calculate the total voltage of the battery, we need to know the voltage of a single cell. 

Thumb rule:

• The voltage of the cell in a LiPo battery should not go below 3.3V, and also should not cross 4V, as in both cases it might damage the cell and hence the battery
• So, we decide a term called ‘Nominal Voltage‘. This is basically an approx. The average value of the max and min voltages. In the case of LiPo, we take it as 3.7 V. For batteries, we always consider the nominal voltage

‘S’ represents the number of cells

Based on the S number, we calculate the total voltage of battery.

For example, the above battery is ‘3S’ which implies that it has 3 cells in it. Therefore,

$\text{Battery Voltage} = (\text{S number}) \times (\text{Nom. Voltage of a cell})$

$\text{Battery Voltage} = 3 \times 3.7 = 11.1\,V$

Suppose, we select a model for our BLDC motor : DYS D2826-10 1400KV Outrunner Brushless Motor

Now, we need to correctly choose our motor based on the motor suggested specifications or check datasheet

Now, selecting 2s LiPo or 3s LiPo depends on your model and requirements. The more voltage you apply, the more RPM you will get for the same given motor by the relation :

$kV = \frac{\text{RPM of motor}}{\text{Nominal Voltage of Battery}}$

Capacity of Battery:

The Capacity of Battery gives you an idea of the time in which the battery will get drained off. The unit of Capacity for LiPo is ‘mAh’. It stands for milli-Amp hours.

We try to understand the same with an example. Suppose I have a battery of 4200 mAh. 

• It implies that my battery will get drained off completely if I keep drawing 4.2 A from the battery continuously for 1hr.
• Now, from the same battery, if I draw only 2.1 A (less than 4.2 A), then the battery will drain off after 2 hrs ; giving me more usage time. 
• It’s Pretty Obvious that if you draw less current, the battery will allow more usage time.

For RC Airplanes, Capacity plays an important role for determining the flight time (time for which the plane will fly).

We will discuss about Flight time in coming section below

‘C’ Rating / Discharge Rate:

This thing is nothing but a simple multiplier. It is used to know the actual strength of our battery. This value helps us to calculate the maximum current (continuous and burst) which the battery can provide safely. 

Formulation : 

$\text{Maximum continuous discharge current} = \text{Capacity} \times \text{C rating}$

$\text{Maximum burst discharge current} = \text{Capacity} \times \text{burst C rating}$

Some times, we need some more current than the maximum continuous current value as well. So in that case, the burst continuous current comes into picture. It shows that the battery can provide some extra amount of current as well if required though only for a short interval of time.  

Usually, on batteries, only continuous discharge rate is given. For burst rate, we need to check the battery specifications on websites

For example, 

My battery has specifications 2200 mAh, 11.1V and  I want to decide the appropriate C rating to be chosen. I also know that the maximum current requirement for all my electronic components (majorly motor) is 20 A.

Solution :

So, I need a battery which must have the strength/ability to continuously providing 20A (though its not always needed). By the above formula,

We get,   

$20 = 2.2 \times (\text{C rating})$     

$\text{C rating} = 9.1\,C$

So now, anything more than 9.1 C (like 10C, 15C, etc) is absolutely fine BUT less than 9.1 C is NOT OK !!

---

Flight Time Calculations :

A very important concept and is crucial especially for competitions were time constraints are there. As discussed in Capacity sub-section above, this concept is a lot dependent on the Capacity of battery. 

Note the step-by-step procedure :

Flight Time Calculations Flow (Text)

1. Calculate/Find the maximum current drawn by the motor. This is called the Motor Amps.
2. Add current contributions of other electronic components (receiver, ESC electronics, etc.). These are usually not significant, so this step is optional.
3. Find the Battery Amps from the capacity value.
   Example:
   If the battery capacity is 5200 mAh, then Battery Amps = 5.2 A.
4. Formula for flight time is given below:

$\text{Flight Time (in minutes)} = \frac{\text{Battery Amps}}{\text{Motor Amps}} \times 60$

After completing all the steps, we get a flight time value. But once this flight time is completed for an RC plane, the battery will be completely drained, and WE DON’T WANT THIS !!

• It is always advisable for LiPo batteries to keep atleast 25 % remaining (i.e. use only 75 % of the battery). So if only 75 % of the battery is to be used, then we will obviously get only 75 % of our calculated flight time. This will be our min. actual flight time. It can be more than this but not less, since we calculated this value based on the ‘Max.’ current from motor.

---

Detailed Example for Battery Selection

The document below is a short example designed to get you more clarity on the theory part. Do go through the document once you have gone through the article completely. Keep both, this article and the example, side-by-side, and then learn and analyze how it’s done.

RC-Airplane-Series-5-Example

RC Airplane Series – All Articles  (You are at Part – 5 !)

• Part-6 (Next) : ESC Calculations and Electronics Connection
• Part-4 (Previous): Motor and Propeller Selection
• Part-3 : Designing your Airplane !!
• Part-2 : Understanding the control surfaces !
• Part-1 : What’s in the Wings ?

---

Conclusion

From this article, we got to learn about the procedure to select the correct LiPo battery for our project. In the next upcoming articles, we will cover the ESC calculations and also learn about the thrust test. Till then, Enjoy Learning !!

All the Best !!

RC Airplane Series – Part 4

Now, we enter into the electronics side of the RC Airplane. In this article, we discuss ‘How shall we exactly choose a motor for our RC Airplane ?’. This is one of the very crucial steps because your electric motor and propeller combination in RC Airplane does the work similar to the fan engines in real RC aircraft. This motor + propeller combination is responsible for providing the necessary ‘thrust’ required.

Just to clarify!

I am sure you will have a question that, if, in the last article, I asked you to refer to a plan from online sources, then why not copy their electronic components as well? 

There’s a problem with that!

Many students/hobbyists aim to participate in various aeromodelling competitions. And when there’s a competition, there are some rules/constraints that we need to follow. Basically, this is where it’s important to know exactly how to model the aircraft (design part + electronics part). Otherwise, if there were no rules, there would be so many resources about ‘How to make an RC airplane?’ So, everyone would copy them.

And apart from this, the joy and the interest which u generate in the field of aeromodelling once you try to understand these concepts is unmatchable.

---

1. Electronic Components for RC Airplane

• Motor + Propeller combination
• ESC (Electronic Speed Controller)
• Battery
• Servo motors
• Receiver
• Connectors

Here, we are just naming the electronics needed to drive an RC plane. We cover the motor and propeller selection in this post. In the upcoming articles, we start discussing each one in detail. We are going to keep everything to the point, but discuss the important and necessary things in detail.

---

2. Deciding the Type of Flight

In order to select a motor, we need to first decide the type of flying we need from our plane. 

And based on that, we have a term called ‘Thrust-to-weight’ ratio, also known as ‘TWR’ or ‘T/W’. Based on the type of flying we choose, we need to fix our TWR accordingly. To elaborate,

$TWR = \frac{\text{Thrust}}{\text{Weight of RC Airplane}}$

Based on the TWR value, we can categorize flying into 2 types:

• Controlled and Slow flying (T/W<1)
• Fast and Aerobatic Flying (T/W>1)

• So, the first step for motor selection will be to fix the TWR for your plane.

---

3. Choosing the motor

We need to follow a specific procedure in order to get therequired motor. Refer to the following flowchart for that :

Step-1:

In the previous article, we learnt to calculate the ‘model weight’ (i.e., only the design part). Now, we need to first assume the electronic components and calculate the ready-to-fly weight. It means that the plane is fully ready (design + electronics) to fly, and the weight of the plane is then called here as ‘ready-to-fly‘ weight. 

Assuming electronic components:

• Most of the components (motors, ESC, battery, etc) have their weight within a fixed range. And note that, you DON’T have to be very specific and exact for this. We need an approximate weight of the aircraft. 
• Refer to the product’s website and check the specification section to get the weight
• This part will become clearer once you have the knowledge of all the components used in an RC plane. I have attached a file below as an example to demonstrate the whole process.

Note: If you are using landing gears for your plane instead of a hand takeoff, you need to include that weight as well.

Step-2:

From the previous section, we have fixed our TWR. Use this value to calculate the thrust. This will be the thrust required to achieve the required TWR for the aircraft.

Step-3:

Q. What is meant by the RPM of the motor?

The number of revolutions (one complete circle) that the motor rotates in one minute of time is known as the RRM of the motor. RPM stands for Revolutions per minute. For e.g. 2500 RPM implies the motor rotates 2500 times in one minute. So basically, RPM is the unit of ‘angular velocity.‘ 

Q. What is the kV of the motor?

kV rating of a motor gives the idea of: At what RPM will the motor run when a certain voltage is applied. For e.g. If we have a motor of 1000kV and let’s say the safe operating voltage range is 5V-12V. So if I am operating the motor at 5V, the motor will run at 5000 RPM, while if I operate it at 12V, it will run at 12000 RPM. 

Based on this, we can formulate the kV rating as:

$motor\ kV = \frac{\text{Motor RPM}}{\text{Nominal Voltage}}$

How to choose the kV of the motor?

Recall the type of flying that you chose earlier. Generally, for controlled and slow flying, we choose a low kV BLDC motor, which has a range up to 1500 kV, while on the other hand, for Fast and Aerobatic Flying, we choose a high kV BLDC motor that has a range greater than 1700 kV

Now, once the motor kV is fixed, go to the online electronic stores’ website and search for the motors of the calculated kV that are able to provide the required thrust. A thrust value greater than required is OK!

(Look through the specifications/description section of the product’s page for thrust value)

Step-4:

The propeller is another very important factor to consider since this fan-like thing is the most responsible for generating the thrust required for our airplane. Check the datasheet or the recommended propeller size for the selected motor.

---

4. Choosing Appropriate Propeller:

Working Principle of a Propeller:

The propeller basically ‘pushes’ the air backwards so that the reaction force acts on the propeller, making it move in the forward direction. The working of a propeller is a simple application of Newton’s third law.

Dimensions of Propeller

Diameter: The end-to-end length of the propeller. Mainly responsible for the rotary motion

Pitch: It is the distance covered by the propeller in the forward direction when one revolution is completed. Pitch is mostly responsible for the translatory motion of aircraft. Pitch is connected to the speed of the aircraft.

Notation : Example : 10×4.5 propeller implies diameter = 10 inches and pitch = 4.5 inches

How to select a Propeller?

Again, recall the type of flying chosen for your aircraft. Based on that, we need to fix the size of the propeller. 

Consider the example below (PDF file) for better understanding. I have discussed a real problem statement, which is generally given in RC Airplane competitions. You can take a similar approach while selecting the motor and propeller for your application

---

5. Example:

A problem statement has been given (Like a competition), and based on the constraints, the procedure to select a motor has been given. Go through it thoroughly to get a complete understanding. (We are assuming that we chose some plan, and on calculating the model weight of the airplane, it came out to be 250 g.

example-for-motor-1-1

Enjoy Learning!

RC Airplane Series – All Articles  (You are at Part – 4 !)

• Part-5 (Next): How to choose a LiPo Battery?
• Part-6: ESC Calculations and Electronics Connection
• Part-3 (Previous): Designing your Airplane !!
• Part-2: Understanding the control surfaces!
• Part-1: What’s in the Wings?

For Best Experience, View on Desktop/Laptop

RC Airplane Series – Part 3

In this article, we are going to discuss about designing the plane and after which in the next article (RC Airplane Series – 4), we discuss how shall we exactly select a motor for our RC Airplane. There is proper procedure for motor selection and is one of the important step in RC airplane designing. 

Designing the plane

This RC Airplane Series is going to be for ‘Beginners’ or for the ones who are not much experienced in this field but just want to know the basics of RC Airplane. Due to this reason, we avoid getting into the details of the analysis. The actual Analysis includes a lot more like: Aerofoil selection through XFLR software, ‘Ansys Fluent’ software for model analysis, etc. 

But for now, we keep it very simple

For beginners, a suggestion would be to use online available plans in order to develop your aircrafts. By readymade plans, I mean that , you can get information with figures about the dimensions of fuselage, rudder, elevator, horizontal stabilizer, vertical stabilizer and all…..

How to Apply the Theory?

Let’s take an example for now: 

I have considered this below shown plan as an example. You will get a lot of such similar plans online on various youtube channels and website. 

The one which I am using below is from the website :  https://www.rcpano.net/2020/01/28/fpv-airplane-making-rc-airplane/ . I have modified the plan a bit for simplicity ! And also this website does have a lot of more plans. Do check it out !!

• A good resource to consider for setting the dimensions of your airplane: https://rcplanes.online/design.htm

DOWNLOAD

Design Plan example final

• As shown in the above flowchart, after selecting a plan, we need to choose the material which we are going to use.

In this case, I decided to go with styrofoam and after which I searched for the density of styrofoam on the internet or you can also get it in the ‘specifications’ section from the website page using which you are going to buy it.

The density came out to be 60 g/L.

• Then, We calculate the mass of the seperate component using the density formula.
•  For this, first calculate the Area first. Area can be calculated by breaking the figure into simple geometric figures (rectangles, triangles, trapezium, etc) . Then, calculate volume and then calculate mass using density formula.

Conclusion

This was a very short article on the designing of RC Airplane. We will for sure discuss this topic again at an Advanced Level. But for now, for the Beginners stage, lets keep it simple and easy to understand !! After all that’s our main goal.

Enjoy Learning !

RC Airplane Series – All Articles  (You are at Part – 3 !)

• Part-4 (Next) : Motor and Propeller Selection
• Part-5 : How to choose LiPo Battery ?
• Part-6 : ESC Calculations and Electronics Connection
• Part-2 (Previous) : Understanding the control surfaces !
• Part-1 : What’s in the Wings ?

---

RC Airplane Series – Part 2

In the previous part (RC Airplane Series -1), we learnt about the wings of the aircraft and the reason behind the generation of Lift for the airplane. Now that we have learnt to take the airplane into the air, it’s time to control the aircraft. So, in this part, we are going to learn how the control surfaces are used in order to control the aircraft properly.

---

1. Classification of Control Surfaces

For the controls part, we have them divided into two parts: Primary and Secondary Control Surfaces

• Primary: Ailerons, Rudder, Elevator

           (These are the necessary ones! Like Air, Water, and Food for us)

• Secondary: Flaps 

           (These are the extra ones that help in controlling the aircraft more precisely.) In the Secondary part, we do have some more surfaces, but for basic RC planes, Flaps are enough 

---

2. Dimensions of Movements:

There are basically 3 axes about which the movement of the aircraft happens :

• Longitudinal: It goes from the nose to the tail of the aircraft
• Lateral: It goes from wingtip to wingtip and is perpendicular to the longitudinal axis
• Vertical: It is mutually perpendicular to both the longitudinal and lateral axes

                                                                               Fig. Movements exhibited by an aircraft

• Pitch: It is the rotational motion of the aircraft about the Lateral Axis (Nose – Up and Down)
• Roll: Rotation about the longitudinal axis is Roll. During this, the aircraft tilts its wing up and down
• Yaw: Rotation about the vertical axis is Yaw. Basically, moving right and left in the plane itself

3. Ailerons:

Ailerons are the control surfaces situated on the wings and are responsible for the ‘Roll’ motion of aircraft.

• There are mainly 2 types of Ailerons (in Trainer Aircraft mostly): Strip Aileron and Normal Ailerons

Strip Ailerons are the ones that span over the entire half wing and have a width = 1/8 of the chord length

In normal ones, the length = 1/4 of wingspan and are situated towards the wingtip, and have a width = 1/4 of the chord length

Working of Ailerons:

For example, we need our airplane to roll to the right. For this to happen, the Right Wing should be lowered while the Left wing should be lifted (when viewed from the tail)

I will try to explain this in a very simple manner. Just remember that,

“Obstruction causes velocity to decrease.“

(This applies to all control surfaces.)

• Now, we want to roll our aircraft towards right. So we control the Aileron with the help of a transmitter (in case of RC Airplane), a steering wheel in case of a real aircraft. 

On giving the signal, the right Aileron is raised while the left Aileron is lowered. For the moment, let’s focus on the Right Aileron. The control surface here has been moved up & now, and this causes Obstruction for the Air.

• Because of this obstruction, the velocity of air in the upper part decreases, and hence Pressure in the upper part increases. (refer to RC Airplane Series- Part 1) And this causes the Right wing to go down and the left wing goes up, and as an overall effect, we get the Roll towards the right.

4. Elevator:

The elevator is connected to the horizontal stabilizer. The elevator is responsible for controlling the pitch of the Aircraft.

Working of Elevator:

Consider an example where we need to pitch up the plane (make the nose up !). In this case, when the signal is given, the elevator is deflected upwards. Now, again, the air flow in the upper region feels an obstruction, which lowers the velocity of air in the upper region. This causes the Pressure in the upper region to get bigger. 

This results in the ‘pressing‘ of the horizontal stabilizer downwards. Due to this, the nose of the aircraft (front part) rises up.

(Just consider a pencil and hold it somewhere.

• The process is the same for all, whether it’s the aileron, elevator, or the rudder

Consider an example of a pencil. Its CG (center of gravity) is marked. So when we apply pressure on the back side (Fig P(a)), the front part (the part which is ahead of CG) rises (which we say here as ‘pitch up’) as it rotates about the lateral axis passing through CG (Fig P(b))

5. Rudder:

The rudder is attached to the Vertical stabilizer. It is responsible mainly for the Yaw motion of the aircraft. Basically, Yaw is like moving right and left in your plane itself!

Working of Rudder:

Consider that we need to shift to the left while being in the plane of the aircraft (i.e., just try to give the nose a different direction)

• When the signal is given such that you want the nose of the airplane to move towards the left, then the rudder also deflects towards the left. Now the rudder acts as an obstruction to the airflow on that side. Hence, velocity decreased. Therefore, pressure increased. The higher pressure causes the front part to move to the left (in the geometric plane)

6. Flaps:

Flaps are the Secondary Control Surfaces, which help the pilot to have stronger control and stability over the airplane. Flaps are situated beside the Ailerons. Sometimes, the Ailerons themselves work as Flaps as well (in case of a single servo for each Aileron **). In this case, we call those control surfaces ‘Flaperons’ (Flaps + Ailerons)

You must have heard pilots saying “FLAPS ON!” or “FLAPS DOWN”. This tells that the Flaps are to be deflected downwards. 

We are very well aware of the Lift generated because of the Flaps getting deflected downwards. (Same as Ailerons getting deflected downwards) But there is an important factor to consider, which is ‘DRAG.’

DRAG:

There is lift, but there is also DRAG developed due to the downward deflection of flaps. Since, due to this, the contact between the airflow and the surface gets broken.

This Drag causes the wing speed to decrease

• For Landing, we need the plane to be slow-moving since ofcourse it’s easier to handle a slow-moving car than a fast one. So the drag component takes care of reducing the speed of the aircraft, while on the other hand, we also have the Lift generated, which combinedly gives a slow and controlled descent.
• From the takeoff point of view, we need Lift to be generated at lower speeds itself, and hence Flaps are essential in this case as well.

Note that: “FLAPS UP” implies the retracting of flaps to the original position (no deflection)

The amount of deflection can be controlled based on the need with the help of the control stick !!

Conclusion:

Through this article, we discussed the control of the Aircraft. Go through it slowly and try to visualize it by yourself. You will definitely get it. In this Series, we will keep going step by step and gradually make the whole basic RC Airplane model. I hope you enjoy this Series.

Keep Learning!

RC Airplane Series – All Articles  (You are at Part – 2 !)

• Part-3: Designing your Airplane !!
• Part-4: Motor and Propeller Selection
• Part-5: How to choose a LiPo Battery?
• Part-6: ESC Calculations and Electronics Connection
• Part-1 (Previous): What’s in the Wings?

---

RC Airplane Series- Part 1

RC Airplanes are fun to make and really a nice beginning step to understand Aeromodelling. This series aims to cover the aspects necessary for the modelling of RC aircraft, and this will teach you can you design your own RC airplane based on your constraints/requirements.

In this article, we are going to discuss about one of the most important aspect of the airplane, i.e. Wings.  

---

1. What’s the principle behind Wings?

So, in order to understand about how the wings help to generate the lift, we need to know about the Bernoulli’s Principle. It states that:

Bernoulli’s Theorem:
“The sum of the pressure, kinetic energy density & the gravitational potential energy density at a point in streamline remains constant“

The mathematical equation for Bernoulli’s Theorem looks as follows:

$P + \frac{1}{2}\rho v^{2} + \rho g h = \text{constant}$

All this looks a bit complicated, isn’t it !?

But the only thing which we require from this equation, to understand the reasoning is that :

“As pressure increases, velocity in that region decreases & vice versa is also true”

$P \uparrow \quad v \downarrow \quad and \quad P \downarrow \quad v \uparrow$

2. Conducting a small activity

What all do we need?

• A-4 sheets x2
• A quiet room (FANS OFF please !)

Procedure:

1. Hold the 2 papers vertically with each paper in each hand.
2. Observe that nothing happens here
3. Now, blow air with your mouth into the region B (region between the 2 papers)
4. Observe what happens !!

Why did this happen?

Note : The region between the 2 sheets is named as ‘B’ while the region except B is called ‘region A’ (i.e. the surroundings to region B)

1.  Initially, the pressure in region B and A is the same since the velocity of air is same everywhere
2. Now, we blow air into the region B (between the sheets). This causes the velocity of air in the region B to increase in comparison to its surroundings (region A)

$v_{B} > v_{A}$

       3. Now, by Bernoulli’s principle, we can derive the conclusion that, 

$P_{B} < P_{A}$

        4. Because of this, the sheets are pushed towards each other by the surroundings due to the relative higher pressure of the                              surroundings than that of the region B

3. About Airfoil/Aerofoil Shape

Now, to use the above results in an application, we have a shape known as ‘Airfoil’. We can describe this shape by its upper and lower surfaces. The upper surface has a curvature known as ‘Camber,’ and the upper surface has a larger length as compared to the lower surface, which is done purposely.

To understand the shape, have a look at the figure below. (I will try improving my drawing skills !!)

Consider points A and B. At point A, the streamlines diverge to pass over the airfoil and then meet up again at point B. Now, we know that the flow is streamlined and laminar, the air particles flowing over the upper surface have to keep up with the air particles passing under the lower surface.

We already know that the upper surface has a greater length than the lower one. Hence, to meet at B at the same instant, the velocity of air passing over the upper surface has to be greater since it has to cover more distance in the same time.  

Hence, 

$v_{\text{upper}} > v_{\text{lower}}$

But, by Bernoulli’s principle we know that, 

$P_{\text{upper}} < P_{\text{lower}}$

This is how lift is generated !! & we can see that the airfoil shape has a lot of role to play in this.

4. Some frequently used terms in Aerodynamics

4.1 Leading Edge and Trailing Edge

• The leading edge is the foremost edge of the wing. This is the first part of the wing that comes in contact with the air flow. It is mostly rounded in order to have a smooth airflow over the wing.
• The trailing edge is the rearmost edge of the wing. This is the portion where the airflow leaves the wing. This edge of the wing includes the control surfaces with Ailerons and the Flaps

4.2 Chord

The distance (straight line length) between the leading edge and the trailing edge of the wing is called ‘chord’.

It is not always that the wing will be rectangular, so, in that case, we consider the ‘mean’ chord length, which can be calculated based on the shape of the wing.

$\text{chord }(C) = \frac{\text{WingArea }(S)}{\text{Wingspan }(b)}$

For rectangular wing, the width of the rectangle becomes the chord.

4.3 Vortex Drag

Now, this is something which comes as a by-product with the ‘Lift’ which we don’t need, and hence we must try to at least minimize it as much as possible. 

                  Fig. explanation : When the air flows over the Wings, lift is generated & simultaneously, wing tip vortices are also formed                                                                which we need to minimize since it consumes fuel, hence dropping the fuel efficiency of plane.

When the air flows over the Wings, lift is generated & simultaneously, wing tip vortices are also formed, which we need to minimize since it consumes fuel, hence dropping the fuel efficiency of the plane.

Why does it happen?

The wing is an finite dimension part and hence it will come to an end at some point. This is the point which we call as ‘Wing tip. Just at the wing tips, there is still a high-pressure region below and a low-pressure region above. This pressure difference causes the air particles to execute a rotational type of motion, which we call ‘vortex.’

Now due to this,

1. The air particles exhibit rotational motion (as we see in the figure)
2. But from where do these particles get energy to exhibit this rotational motion
3. This energy is extracted from the wings (or indirectly, the part of the fuel is getting consumed to overcome this drag)
4. Therefore, we conclude that, the induced drag affects the fuel efficiency of airplane

4.4 Aspect Ratio

Aspect Ratio is defined as the ratio of the wingspan to the mean chord length

It is one of the most characteristic aspects of the object (here airplane), and AR for an aircraft is determined based on the work it is going to be used for. 

$\text{Aspect Ratio (AR)} = \frac{\text{Wingspan } (S)}{\text{mean chord length } (C)}$

For example,

High Aspect Ratio: Used to have more fuel efficiency for aircraft (due to lesser induced drag)

Moderate Aspect Ratio: Used to get the benefits of both: maneuverability & fuel efficiency

Low Aspect Ratio:  Used to get more maneuverability (ability to change direction)

Wingspan is everything!

While designing the RC airplane, the first most important thing which you need to fix, is the ‘Wingspan’ of your aircraft. Wingspan is nothing but the length of your wing (including fuselage width). 

Generally, while designing the RC Aircraft, we have a fixed set of ratios defined which tell us what all dimensions should different parts/components of airplane have.

For examples, we take some ratios like: (We fix Wingspan = 1m)

Example 1: The fuselage length = 75% of wingspan = 75 % of 100cm = 75 cm

Example 2: Now, for Trainer Aircraft, the aspect ratio is 5:1

Hence, chord = wingspan/5 = 100/5 = 20cm

Example 3: Aileron length has to be 1/4th of the wingspan

Aileron length = (1/4) x wingspan = (1/4) x 100cm = 25cm

We can clearly see that in all calculations, somehow or other, ‘Wingspan’ is getting involved. There are still many dimensions you can calculate directly/indirectly using wingspan.

Conclusion

To conclude this post, we learnt about the basic working principles of wings. Just making an RC Airplane is one thing while Understanding the RC Airplane is another thing. We are going to focus on the understanding part first which will surely make our further work much more easier + the additional satisfaction that we know the reasoning behind what we are doing !! 

Till then, Keep Learning & Enjoy the Process

RC Airplane Series – All Articles  (You are at Part-1 !)

• Part-2 (Next) : Understanding the control surfaces !
• Part-3 : Designing your Airplane !!
• Part-4 : Motor and Propeller Selection
• Part-5 : How to choose LiPo Battery ?
• Part-6 : ESC Calculations and Electronics Connection