Aircraft, what is the first thing that comes to your mind?....
How does it manage to fly at such high altitude? What is the aerodynamic centre, well, u guys are at the right place, yes, we will answer to all your question let's see what makes an aircraft fly.
let's start with what kind of forces acts on an aircraft. Four types of forces act on an aircraft
1. Lift
2. Drag
3. Thrust
4. Weight
and as we can see in the equation no.1 that dynamic pressure is directly propositional to the square of velocity i.e. if we want to increase lift, velocity will be increased by its square.
How does it manage to fly at such high altitude? What is the aerodynamic centre, well, u guys are at the right place, yes, we will answer to all your question let's see what makes an aircraft fly.
let's start with what kind of forces acts on an aircraft. Four types of forces act on an aircraft
1. Lift
2. Drag
3. Thrust
4. Weight
1. LIFT (L)
The component of Aerodynamic force perpendicular to the relative wind
Or
It is an upward force which acts opposite to the weight of an aircraft
Lift is denoted by L
2. DRAG (D)
2. DRAG (D)
Component of aerodynamics forces
parallel to the relative wind is called a drag
Or
Drag is an aerodynamics force
which acts opposite to the thrust and restricts the aircraft’s the motion
through the air
Drag is produced through
1 Wing
2 Vertical and Horizontal Tail
3 Fuselage
4 Thrust
5 landing Gear
TYPES OF DRAG
1 Induce Drag: Is the drag
created by the vortices at the tip of an aircraft's wing. It is the drag due
to lift. Induce Drag is direct proportion to the angle of attack i.e. Angle of
Attack increase Induce Drag increase, Angle of Attack decrease Induce Drag
decrease.
2 Skin friction Drag: It is caused by the actual contact of
the air particles against the surface of the aircraft. Skin friction drag is an
interaction between a solid (the aeroplane surface) and a gas (the air), the magnitude of skin friction drag depends on the properties of both the solid and
the gas. For the solid aeroplane, skin friction drag can be reduced, and airspeed
can be increased somewhat, by keeping an aircraft's surface highly polished and
clean
3 Form or Pressure Drag: A
drag which is caused by the air that is flowing over the aircraft or airfoil.
The separation of air creates turbulence and results in pockets of low and high
pressure that leave a wake behind the aeroplane or airfoil (thus the name
pressure drag). This opposes forward motion and is a component of the total
drag. Since this drag is due to the shape or form of the aircraft, it is also
called form drag. Streamlining the aircraft will reduce form drag
4 Parasite Drag: it is the sum of Skin Friction, Form, and
Interference Drag
5 Interference Drag: It comes from the intersection of air
streams that create turbulence, For
example, the intersection of the wing and the fuselage at the wing root has
significant interference drag. It is also very high when two surfaces meet at
perpendicular angles.
6 Wave Drag: Wave Drag is a
drag that retards the forward movement of an aeroplane in both supersonic
and transonic flight, as a consequence of the formation of shock
waves.
HOW IS LIFT PRODUCE
When the aerodynamic flow is passed over an airfoil it follows the law of nature, namely continuity equation and newton's second law of motion (Bernoulli's and Euler's equation)
As we can see in the figure the upper portion of an airfoil has an obstruction, because of this stream tube is squashed to a smaller cross-sectional area, according to continuity equation ( ρAV =constant ), velocity must be increased in the stream tube.where the tube is been squeezed on the lower portion, there is no obstruction, so the cross-section area increases and according to the continuity equation velocity tends to decrease
We can say that
Flow velocity increase over the top surface of an airfoil is more than the bottom surface.
For incompressible flow, from Bernoulli's equation, we can say if velocity increase so, static pressure decrease this tend is valid for compressible flow from Euler's equation we can say dv is positive so dp has to be negative
so we can say this if velocity increases pressure tends to decrease
from this, we can state that,
On the top surface of the airfoil, there is low pressure and on the bottom surface we have high pressure
This pressure difference creates in a force in an upwards direction called a lift
WHY MOST OF THE LIFT IS PRODUCED BY THE FIRST 20 TO 30%?
The most to the lift are produced by the first 20 to 30% because the largest difference in pressure on the top and bottom surface is on the front part of the airfoil. as shown in figure
The main function of the back part is for streamline shape to avoid flow separation.
Factories affecting lift
1. Free stream velocity
2. Free stream density. (altitude)
3. Wing area
4. Angle of attack
5. Shape of airfoil
6. Viscosity coefficient
7. Compressibility of airflow
QUESTION AND ANSWER
Q1. Explain different types of aerodynamic forces?
Ans. there are 4 different types of aerodynamic forces
1. Lift(L): The component of Aerodynamic force perpendicular to the relative wind .we can also say It is an upward force which acts opposite to the weight of an aircraft.
2. Drag(D): Component of aerodynamics forces parallel to the relative wind is called a drag or we can say, Drag is an aerodynamics force which acts opposite to the thrust and restricts the aircraft’s the motion through the air.
3. Weight(W): Weight is a gravitational force which acts opposite to lift force. In steady-state flight W=L
4. Thrust(T): Thrust is a propulsion force it makes the aircraft moves in a forward direction.
Q2. What is the aerodynamic centre? Which is the most preferred location for an aerodynamic centre
Ans. Aerodynamic centre is a point where submission of all the aerodynamic forces is equal to zero.
The aerodynamic centre should lie before the centre of gravity because these types of configuration give a stable effect to the aircraft.
Q3. What is the difference between the conventional tail configuration and canard configuration?
Ans. When the horizontal stabilizer is behind the wing it is called conventional tail configuration. In the conventional tail configuration, the lift on the tail is generally in the downward direction. This can be avoided if a control surface is located ahead of the wing. Such a configuration is called canard (see Wright flyer)It may be added that a canard, being ahead of c.g., has a destabilizing contribution to.
Q4. What is the lift coefficient?
HOW IS LIFT PRODUCE
When the aerodynamic flow is passed over an airfoil it follows the law of nature, namely continuity equation and newton's second law of motion (Bernoulli's and Euler's equation)
As we can see in the figure the upper portion of an airfoil has an obstruction, because of this stream tube is squashed to a smaller cross-sectional area, according to continuity equation ( ρAV =constant ), velocity must be increased in the stream tube.where the tube is been squeezed on the lower portion, there is no obstruction, so the cross-section area increases and according to the continuity equation velocity tends to decrease
We can say that
Flow velocity increase over the top surface of an airfoil is more than the bottom surface.
For incompressible flow, from Bernoulli's equation, we can say if velocity increase so, static pressure decrease this tend is valid for compressible flow from Euler's equation we can say dv is positive so dp has to be negative
so we can say this if velocity increases pressure tends to decrease
from this, we can state that,
On the top surface of the airfoil, there is low pressure and on the bottom surface we have high pressure
This pressure difference creates in a force in an upwards direction called a lift
WHY MOST OF THE LIFT IS PRODUCED BY THE FIRST 20 TO 30%?
The most to the lift are produced by the first 20 to 30% because the largest difference in pressure on the top and bottom surface is on the front part of the airfoil. as shown in figure
The main function of the back part is for streamline shape to avoid flow separation.
2. Free stream density. (altitude)
3. Wing area
4. Angle of attack
5. Shape of airfoil
6. Viscosity coefficient
7. Compressibility of airflow
Factories affecting lift
1. Free stream velocity2. Free stream density. (altitude)
3. Wing area
4. Angle of attack
5. Shape of airfoil
6. Viscosity coefficient
7. Compressibility of airflow
QUESTION AND ANSWER
Q1. Explain different types of aerodynamic forces?
Ans. there are 4 different types of aerodynamic forces
1. Lift(L): The component of Aerodynamic force perpendicular to the relative wind .we can also say It is an upward force which acts opposite to the weight of an aircraft.
2. Drag(D): Component of aerodynamics forces parallel to the relative wind is called a drag or we can say, Drag is an aerodynamics force which acts opposite to the thrust and restricts the aircraft’s the motion through the air.
3. Weight(W): Weight is a gravitational force which acts opposite to lift force. In steady-state flight W=L
4. Thrust(T): Thrust is a propulsion force it makes the aircraft moves in a forward direction.
Q2. What is the aerodynamic centre? Which is the most preferred location for an aerodynamic centre
Ans. Aerodynamic centre is a point where submission of all the aerodynamic forces is equal to zero.
The aerodynamic centre should lie before the centre of gravity because these types of configuration give a stable effect to the aircraft.
Q3. What is the difference between the conventional tail configuration and canard configuration?
Ans. When the horizontal stabilizer is behind the wing it is called conventional tail configuration. In the conventional tail configuration, the lift on the tail is generally in the downward direction. This can be avoided if a control surface is located ahead of the wing. Such a configuration is called canard (see Wright flyer)It may be added that a canard, being ahead of c.g., has a destabilizing contribution to.
Q4. What is the lift coefficient?
As u can see in the picture lift is directly propositional to lift coefficient, dynamic pressure, wing area, that means if we want to increase lift or lift coefficient we have to increase wing area and dynamic pressure (square of velocity)
the lift coefficient is derived using dimensional analysis
the lift coefficient is derived using dimensional analysis
Q5. Why aircraft fly at such a high speed?
Ans. As u can see in the above formula lift is directly propositional to dynamic pressureand as we can see in the equation no.1 that dynamic pressure is directly propositional to the square of velocity i.e. if we want to increase lift, velocity will be increased by its square.
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