Aeromodelling event

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Aeromodelling event
The Wright Design
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• Model airplanes are sized down models of an
  aircraft
• The calculations are easy and the importance is
  given to building of the plane

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Basic Aerodynamics
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Forces acting on a plane
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Lift

• Its 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
• L1/2?V2ACL
• CL is the lift coefficient
• V is flight speed , A is wing area
• ? is density of air

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Thrust

• Its the force provided by the engine of the
  plane
• Mainly two type of thrust generators are used
• IC Engines
• Electric Motors
• We will be seeing about electric motors here

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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

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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

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Wing Aspects
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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 Bernoullis principle

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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

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Types of aerofoil
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Angle of Attack(aoa)
This is the relative angle made by the wind with
the wings
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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

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Control Surfaces
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• 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

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Rotation of a plane
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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

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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

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Design Principles
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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

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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

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Powering the plane
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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.

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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.

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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.

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Batteries

• Usually Lithium Polymer batteries are used in
  aeromodels.
• They come with voltage and current rating which
  must comply with our motor and ECS.

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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.

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Electronic Components
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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

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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.

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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