UNIVERSITY INSTITUTE OF

ENGINEERING
BE-AEROSPACE ENGINEERING
Course Name: Physics of Flight
Course Code: 22AST-215
Faculty: Er. Sukumar Dhanapalan

INTRODUCTION TO MANAGEMENT DISCOVER . LEARN . EMPOWER

Principles of Flight

Lift and Drag

Er. Sukumar Dhanapalan-AP/Aerospace- CU

 LIFT
Lift is the force created by the interaction between the wings and the
airflow. It always act upwards. It is considered to be the 'most important
force' as without it, an aircraft cannot ascend from ground and maintain
altitude.
 Lift is an aerodynamic force
 Lift must exceed weight for flight
 Generated by motion of aircraft through air
 Created by the effects of airflow past wing
 Aircraft lift acts through a single point called the center of pressure.

POF by Mr. SUKUMAR DHANAPALAN, AP-SOA.

 Newton's First Law of Motion
According to Newton's first law of motion (inertia), an object at rest will remain at
rest, or an object in motion will continue in motion at the same speed and in
the same direction, until an outside force acts on it.
For an aircraft to taxi or fly, a force must be applied to it. It would remain
at rest without an outside force. Once the aircraft is moving, another force
must act on it to bring it to a stop. It would continue in motion without an
outside force. This willingness of an object to remain at rest or to continue
in motion is referred to as inertia.

POF by Mr. SUKUMAR DHANAPALAN, AP-SOA.

 Newton’s Second Law of Motion
The second law of motion (force) states that if a object moving with uniform
speed is acted upon by an external force, the change of motion
(acceleration) will be directly proportional to the amount of force and inversely
proportional to the mass of the object being moved.
The motion will take place in the direction in which the force acts. Simply
stated, this means that an object being pushed by 10 pounds of force will travel
faster than it would if it were pushed by 5 pounds of force. A heavier object will
accelerate more slowly than a lighter object when an equal force is applied.
F=m×a
POF by Mr. SUKUMAR DHANAPALAN, AP-SOA.
 Newton’s Third Law of Motion
The third law of motion (action and reaction) states that for every action
(force) there is an equal and opposite reaction (force). This law can be
demonstrated with a balloon. If you inflate a balloon with air and release it
without securing the neck, as the air is expelled the balloon moves in the
opposite direction of the air rushing out of it. Figure shows this law of motion.
Balloon

Reaction Air Action

POF by Mr. SUKUMAR DHANAPALAN, AP-SOA.

 BERNOULLI'S PRINCIPLE
Bernoulli's principle states that when a fluid flowing through a tube reaches a
constriction or narrowing of the tube, the speed of the fluid passing through
the constriction is increased and its pressure is decreased.
Pressure Drop in Venturi Tube

POF by Mr. SUKUMAR DHANAPALAN, AP-SOA.

 BERNOULLI'S PRINCIPLE
Bernoulli asserted in “Hydrodynamica” that as a fluid moves faster, it
produces less pressure, and conversely, slower moving fluids produce
greater pressure.
The total mechanical energy of the moving fluid comprising the gravitational
potential energy of elevation, the energy associated with the fluid pressure
and the kinetic energy of the fluid motion, remains constant.

POF by Mr. SUKUMAR DHANAPALAN, AP-SOA.

 Bernoulli Every Day

 Garden Hose (Thumb or Nozzle)

 Perfume atomizer

 Chimney on a windy day

 Tornados often blow windows out

 Pumps

 Carburetors

POF by Mr. SUKUMAR DHANAPALAN, AP-SOA.

Bernoulli’s Strip
Activity

POF by Mr. SUKUMAR DHANAPALAN, AP-SOA.

Bernoulli Demonstration

POF by Mr. SUKUMAR DHANAPALAN, AP-SOA.

 Airfoil as a Venturi Tube

kinetic energy velocity

(velocity) increases
potential energy pressure
(pressure) decreases

Lift force appear

POF by Mr. SUKUMAR DHANAPALAN, AP-SOA.
 How Lift is Created (Bernoulli)

• The Longer Path Explanation: holds that the top surface of a wing is
more curved than the bottom surface. Air particles that approach the
leading edge of the wing must travel either over or under the wing.
POF by Mr. SUKUMAR DHANAPALAN, AP-SOA.
 How Lift is Created (Bernoulli)

• Let's assume that two nearby particles split up at the leading edge, and
then come back together at the trailing edge of the wing.
• Since the particle traveling over the top goes a longer distance in the
same amount of time, it must be traveling faster.

POF by Mr. SUKUMAR DHANAPALAN, AP-SOA.

 How Lift is Created (Bernoulli)

• Bernoulli's equation, a fundamental of fluid dynamics, states that as the

speed of a fluid flow increases, its pressure decreases.
• The Longer Path explanation deduces that this faster moving air
develops a lower pressure on the top surface, while the slower moving
air maintains a higher pressure on the bottom surface.
POF by Mr. SUKUMAR DHANAPALAN, AP-SOA.
 Why is it not entirely correct?
(HAND-OUT) (Bernoulli)
• There are several flaws in this theory, although this is a very common
explanation found in high school textbooks and even encyclopedias:
• The assumption that the two air particles described above rejoin each
other at the trailing edge of the wing is groundless. In fact, these two air
particles have no "knowledge" of each other's presence at all, and there is
no logical reason why these particles should end up at the rear of the wing
at the same moment in time.
• For many types of wings, the top surface is longer than the bottom.
However, many wings are symmetric (shaped identically on the top and
bottom surfaces). This explanation also predicts that planes should not be
able to fly upside down, although we know that many planes have this
ability.
POF by Mr. SUKUMAR DHANAPALAN, AP-SOA.
 How Lift is Created (Newtonian)
Wing

Air Particles

• Newton’s 3rd Law: For every action there is an equal, and opposite,
reaction.

• You can see a good example of this by watching two skaters at an ice
rink. If one pushes on the other, both move -- one due to the action force
and the other due to the reaction force.
POF by Mr. SUKUMAR DHANAPALAN, AP-SOA.
 How Lift is Created (Newtonian)
Wing

Air Particles

• Each individual air particle bounces off the bottom surface of the wing
and is deflected downward.

• As the air particles strike the bottom surface of the wing, they impart
some of their momentum to the wing, thus incrementally nudging the
wing upward with every molecular impact.
POF by Mr. SUKUMAR DHANAPALAN, AP-SOA.
 Why is it not entirely correct?
(HAND-OUT) (Newtonian)
• The Newtonian explanation provides a pretty intuitive picture of how the
wing turns the air flowing past it, with a couple of exceptions:
• The top surface of the wing is left completely out of the picture. The top
surface of a wing contributes greatly to turning the fluid flow. When only
the bottom surface of the wing is considered, the resulting lift calculations
are very inaccurate.
• Almost a hundred years after Newton's theory of ship hulls, a man named
Leonhard Euler noticed that fluid moving toward an object will actually
deflect before it even hits the surface, so it doesn't get a chance to
bounce off the surface at all. It seemed that air did not behave like
individual shotgun pellets after all. Instead, air molecules interact and
influence each other in a way that is difficult to predict using simplified
methods. This influence also extends far beyond the air immediately
surrounding the wing.
POF by Mr. SUKUMAR DHANAPALAN, AP-SOA.
Newton’s Third Law and Lift

POF by Mr. SUKUMAR DHANAPALAN, AP-SOA.

Newton’s Second Law and Lift

POF by Mr. SUKUMAR DHANAPALAN, AP-SOA.

Lift: Wing Section

Lift Equation: L=CL × ½ ρ × A × V2

POF by Mr. SUKUMAR DHANAPALAN, AP-SOA.
 Angle of Attack
• The angle of attack is the angle between the chord line and the average
relative wind.
• Greater angle of attack creates more lift (up to a point).

POF by Mr. SUKUMAR DHANAPALAN, AP-SOA.

Angle of Attack and Lift Force
High velocity
Low pressure

Low velocity
High pressure

POF by Mr. SUKUMAR DHANAPALAN, AP-SOA.

 References
Text Book
Sr No Title of the Book Author Name Volume/Edition Publish Hours Years Link
Charles E Dole, James chrome-
Flight Theory and
1 E Lewis, Joseph R Third edition Wiley 2017 extension://efaidnbmnnnibpcajpcglclefindmkaj/https://soaneemrana.org/
Aerodynamics
Badick and onewebmedia/THEORY%20OF%20FLIGHT.pdf
2 Introduction to Flight John D Anderson Jr Eighth edition McGraw Hill 2016 https://toaz.info/doc-view-2

3 Basics of Space Flight Dave Doody Fourth edition NASA/JPL-Caltech 2011 https://www.amazon.in/Basics-Space-Flight-Dave-
Doody/dp/0615476015
https://www.google.com/search?q=flight+without+formulae+by+a.c.+ker
mode+pdf+free+download&ei=z5ynZInZL6rfseMP6fSy8AI&start=10&sa
4 Flight without Formulae Kermode, A.C Fifth edition Pearson Education 2004
=N&ved=2ahUKEwjJ_IWE6fv_AhWqb2wGHWm6DC4Q8tMDegQIAxAE
&biw=1366&bih=600&dpr=1

Reference Book
Sr No Title of the Book Author Name Volume/Edition Publish Hours Years Link

Manuel Soler [Ed.]. https://e-

Fundamentals of Printed by Create archivo.uc3m.es/bitstream/handle/10016/21184/fundamentals_aerospac
1 Aerospace Engineering Manuel Soler Arnedo 2nd Edition Space. Madri 2017 e_engineering_soler_2014.pdf
Introduction to
Aerospace Engineering https://www.amazon.in/Introduction-Aerospace-Engineering-Flight-
with a Flight Test Perspective/dp/1118953363
2 Perspective Stephen Corda First edition Wiley 2017

chrome-
Principles of Flight for extension://efaidnbmnnnibpcajpcglclefindmkaj/https://www.abul.org.br/bi
3 Pilots P J Swatton First edition Wiley 2011 blioteca/82.pdf
Introduction to Space https://www.amazon.in/Introduction-Space-Flight-Francis-
4 Flight Francis J. Hale First Edition Pearson 1994 Hale/dp/0134819128
 THANK YOU

For queries
Email: sukumar.e13312@cumail.in
Er. Sukumar Dhanapalan-AP/Aerospace- CU