Model airplanes are sized down models of an aircraft

The calculations are easy and the importance is given to building of the plane

Forces acting on a plane

Lift It’s the upward force acting on the plane

due to the air flow over the wings It is determined by the design of the

wing and the wind nature as

L=1/2ρV2ACL

CL is the lift coefficient

V is flight speed , A is wing area

ρ is density of air

Thrust

It’s the force provided by the engine of the plane

Mainly two type of thrust generators are used1. IC Engines

2. Electric Motors

We will be seeing about electric motors here

Weight

This is the weight of the plane along with its payload and motors

This should be minimized as much as possible by proper design

Drag This is the force that

opposes the motion of the plane and is basically the air friction

This too can be reduced by having proper construction of the surfaces of the plane

Wings and Aerofoil

The lift generation is decided by the shape of the wings and the aerofoil

The lifting force is provided by the difference in the pressure of air flowing below and above the wing and is governed by Bernoulli’s principle

How do you design a good wing? By proper calculation of the wingspan ,

wing loading and aspect ratios By making a good aerofoil By optimizing the angle of attack to have

good lift to drag ratios

Types of aerofoil

Angle of Attack(aoa)

Relation between aoa & lift Angle of attack is

directly proportional to the lift coefficient till a maximum limit which is generally about 17o

After which the plane stalls

These are the surfaces which divert the direction of wind to provide change in direction of flight

There are basically three types of rotation of plane which provide the change in direction

Rotation of a plane

Turning the plane

The plane can be turned in right or left direction by using the ailerons to roll onto the side of movement and using the elevators to move up.

This can also be done by using the rudders

Channels

Generally a channel used to control a servo which decides a control surface and two servos are used for the ailerons leading to a 4-channel model

But amateurs can use a 3-channel which has only 1 servo for the ailerons

Wing Loading

It is the ratio of the weight of the plane to the wing area

Gives a measure of the load given per unit area of the wing

Wing loading is an important factor which decides the balance between the forces

Aspect Ratio(AR)

Aspect Ratio is the ratio of square of wingspan to the area of the wing

AR = l2 / A

Where ‘l’ is the wingspan and A is the area of wing

Typical aspect ratios for gliders are 6-8

Powering the plane

Motor specifications

After the thrust required is calculated the configuration of the motor is decided

The motor is selected by its KV rating which is basically the RPM per volt it can deliver

The KV rating is calculated by max current so while selecting a battery and ECS see to it that continuous current rating is greater than motor rating.

Typical motors

One of the usually motors used is the 2204 motor which provides about 350 gms of thrust

The thrust provided also depends upon the propellers used which is again specified by its pitch and diameter length.

Electronic control system(ECS) Brushless DC motors do not have

carbon brushes to have a constant direction of motion of the motor

So an ECS is used to provide switching action so that the polarity is changed and unidirectional rotatory motion is obtained.

Batteries

Usually Lithium Polymer batteries are used in aeromodels.

They come with voltage and current rating which must comply with our motor and ECS.

Another suggestion

A 1000mAh battery will provide power for approx. 10 minutes in a 2204 motor.

But since the motor is going to be powered for only 30 secs a battery wit lesser power can be used which will reduce weight.

Electronic Components

Servo

They are motors with high torque and are used to control the control surfaces

They are decided by the required weight,torque, speed, dimensions

Receiver It consists of receiver

module and a antennae wire of about 2-3 feet long.

The receiver gets signal from the transmitter and then acts upon the servos

Nowadays there are ECSs which have separate power for the receiver so there is no need for separate power.

Transmitter

This consists of a hand console which sends signals according to the movement of a stick or switch

The frequency of the transmitter receiver is determined by a transducer crystal