RC Airplane Series

ESC Calculation & Electronics Connections

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#RC Airplane Series-6

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

Topics Covered :
  • What is ESC ?
  • How to choose a ESC ?
  • How to connect all the electronic components?
  • Use of Y-junction (optional)

1. What is ESC ?

ESC stands for Electronic Speed Controller. It’s job is to provide 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 voltage applied across the motor –> this is the job of 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 ESC. We are already aware of the motor kV relation :

  • 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 much crucial so that everything is under control and also safe at the same time 

Wiring connections for ESC :

                                                                                              Fig. Wiring Connections of ESC

2. How to choose ESC ?

Let’s undertand the procedure using an example !

Suppose, we finally choose the motor for our model: 

A2212 10T 1400kV motor

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

                                                                                                          P = V x I 

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

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 as ‘Actual ESC Current’

This implies that we need an ESC which 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 which has a bigger value than 20.25

We can go with 30A ESC or an 40A ESC would also be perfect !!

3. Connections of all Electronics

Now, by this article 6 of RC Airplane Series, we already got to 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 ailerons, 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 battery in ESC. For this, we can use XT60 connector which is very commonly used as well. They come in a set of a female and male connector. 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 above figure, you can also refer to the diagram below

4. Why Y-junction wire for ailerons ? (optional)

  • 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 onto 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, mainly focus on the ailerons part in order to understand the reasoning behind Y-junction cable. In short, we can summarize it as : 

           In order to get a roll, making the ailerons deflect in opposite sense helps even more. For example, if we need to take right roll, then             on giving just one stimulus through 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 opposite sense. (i.e. flaperons is 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 designing of 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)

Any suggestions from your side are welcomed !!

Keep Learning !!

All the Best !!

How to choose LiPo battery ?

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Author – Saurabh Salvi

#RC Airplane Series – 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. Let’s directly dive into 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. 

Thumbrule :

  • The volatge of the cell in 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. average value of the max and min voltages. In 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,

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

from Robu.in

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 :

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. 
  • Pretty Obvious that if you draw lesser 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 : 

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 * (C rating)     

                                                                                         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 :

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 off !! 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

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

DOWNLOAD EXAMPLE FILE RC Airplane Series-5 Example

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

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 !!

Motor & Propeller Selection

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#RC Airplane Series – 4

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

Topics Covered :
  • Electronic Components in RC Airplane
  • Deciding the type of flight
  • Choosing the motor – Motor Terminologies & Procedure 
  • Choosing the appropriate Propeller
  • Example for Better Understanding

Just to clarify !

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

There’s a problem in that !!

Many students/hobbyists aim to participate in various aeromodelling competitions. And when there’s a competition, there are some rules/constraints which we need to follow. Basically, this is where, it’s important to know how to exactly model the aircraft (design part + electronics part) OR else if there were no rules, there are so many resources about ‘How to make an rc airplane ?’. So , everyone would just 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 motor, We need to first decide the type of flying which 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,


  • So, the first step for motor selection will be to be 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 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 at that point of time is 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 aircraft. 
  • Refer the product’s website and check the specification section to get the weight
  • This part will become more clear once you have the knowledge of all the components used in 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 hand takeoff, you need to include that weight as well.

Step – 2 :

From 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 aircraft.

Step-3 :

It is advised to use BLDC (Brushless DC motors) due to : 

  •  High Efficiency

 

  • Longer Life span

 

  • Better speed control

 

  • Prevents over-heating

 

Q. What is RPM of motor ?

The number of revolutions (one complete circle) that the motor rotates in one minute of time is known as RRM of 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 kV of 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 lets 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 kV rating as :

How to choose kV of motor ?

Recall the type of flying which you chose. 

Now, once the motor kV is fixed, then go to the online electronic stores’ website and search for the motors of the calculated kV which 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 to generate the thrust required for our airplane. Check the datasheet or the recommended propeller size for the selected motor

4. Choosing Appropriate Propeller :

Working :

The propeller basically ‘pushes’ the air backwards so that the reaction force is acted on the propeller makes it move in forward direction. The working of 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 propeller in 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 in & pitch = 4.5 in

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 below example (pdf file) for better understanding

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 airplane, it came out to be 250 g.

DOWNLOAD

example for motor (1) (1)

Enjoy Learning !!

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

Designing your Airplane !!

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#RC Airplane Series-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…..

Example (for application purpose)

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 !!

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 !)

Understanding the Control Surfaces !

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# RC Airplane Series-2

In the previous part (RC Airplane Series -1) , We learnt about the wings of the aircraft and what is 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 are the control surfaces used in order to control the aircraft properly.

TOPICS TO BE COVERED :
  • What are different control surfaces in aircraft ?
  • Different dimensions of movement 
  • Aileron
  • Elevator
  • Rudder
  • Flaps

1. Different 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 which 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 

                                                                          Fig. Positions of Ailerons, Rudder & Elevator


2. Dimensions of Movements :

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

  • Longitudinal : It goes from nose to 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, longitudinal and lateral axis

                                                                               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 longitudinal axis is Roll. During this, the aircraft tilts its wing up and down
  • Yaw : Rotation about vertical axis is Yaw. Basically, moving right and left in the plane itself



                                                                                              Fig. How it exactly happens?

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 which span over the entire half wing and have a width = 1/8 of chord length

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

Working of Aileron :

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

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

                                                                         “Obstruction causes velocity to decrease“

(This is applicable for all control surfaces)

                                                        Fig. Right Aileron is raised up while Left Aileron is lowered down

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

          On giving the signal, the right Aileron is raised while the left Aileron is lowered down. For the moment, let’s focus on the Right                      Aileron. The control surface here as been moved up & now, 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 RC Airplane Series-1) and this causes the Right wing to go down and left wing goes up and as an overall effect, we get the Roll towards right.

4. Elevator :

Elevator is connected to the horizontal stabilizer. The elevator is responsible to control 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 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

                                                                                       Fig. Elevator is deflected upwards

  • The process is the same for all, whether its the aileron, elevator or the rudder

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


FigP(a). Pressure is applied at the back end of pencil                                    FigP(b). Result of the application of pressure (Nose Rises) 

5. Rudder :

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 move shift to left while being in the plane of the aircraft (i.e. just try to give nose a different direction)

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

                                                                                                           Fig. Rudder 

6. Flaps :

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

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

                                                                                                        Fig. Positioning of Flaps

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 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 an fast one. So the drag component takes care of reducing the speed of aircraft while on the other hand we also have the Lift generated which combinedly gives a slow and controlled descent.

 

  • From 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 control stick !!

Conclusion :

Through this article, We discussed about the Controlling of the Aircraft. Go through it slowly and try to visualize 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 hopw you enjoy this Series !!

Keep Learning !!

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

What’s in the Wings!

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# RC Airplane Series – 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.  

What’s the principle behind this ?

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:

” The sum of the pressure, kinetic energy density & the gravitational potential energy density at a point in streamline remains constant “

The mathematical equation for this looks like :

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”

Conducting a small activity

What 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 !!

The step-by-step procedure & it’s result is shown in the figure below  (  !! Not that good at drawing, but pls manage !! :))  )

Fig. A-4 sheets experiment procedure

Why did this exactly 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)

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

        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

About Aerofoil Shape

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

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

Fig. Aerofoil shape explanation

       1. Consider points A and B. At point A, the streamlines diverge to pass over the aerofoil and then meet up again at point B. Now, we                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.

      2. We already know that the upper surface has greater length as compared to lower one. Hence to meet at B at 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, 

But, by Bernoulli’s principle we know that, 


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

Some frequently used terms in Aerodynamics


  • Leading Edge & Trailing Edge :

               – Leading edge is the foremost edge of the wing. This is the first part of the wing which comes in contact with the air flow. It is                          mostly rounded in order to have a smooth airflow over the wing.

               – Trailing edge is the rearmost edge of 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


  • 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.

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


  • 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 atleast                               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.

                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


  • Aspect Ratio (AR):

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

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

                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)

         1. The fuselage length = 75% of wingspan

                                                 = 75 % of 100cm

                                                 = 75 cm

          2. Now for Trainer Aircraft, Aspect Ratio is 5:1

              hence, chord = wingspan/5

                                      = 100/5

                                      = 20cm

          3. Aileron length has to be 1/4th of wingspan

              Aileron length = (1/4) x wingspan

                                        = (1/4) x 100cm

                                        = 25cm

We can clearly see that in all calculations, somehow or the 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 !)