Introduction to Aerospace Engineering

Unit-1

Aircraft Configurations: Brief History- airplanes and Helicopters – Components of an airplane

and their functions. Different types of flight vehicles, classifications, and Basic instruments
for flying.

Introduction to Principles of Flight: Physical properties and structure of the atmosphere,

Temperature, pressure and altitude relationships, Evolution of lift, drag and moment, different
types of drag.
1. Brief history of airplanes, highlighting the key milestones in their development:

1. Early Concepts and Dreams (Before 1900)

• Ancient myths and sketches: Human fascination with flight dates back to ancient
times (e.g., Greek myth of Icarus).

• Leonardo da Vinci (15th century): Designed flying machines and studied bird flight,
 though none were built successfully.

• 19th century: Balloon flights (e.g., hot air balloons by the Montgolfier brothers) and
early glider experiments by pioneers like Otto Lilienthal.

2. First Powered Flight (1903)

• Wright Brothers (Orville and Wilbur Wright):

o On December 17, 1903, made the first controlled, powered, and sustained
flight in Kitty Hawk, North Carolina.

o Aircraft: Wright Flyer

o Flight lasted 12 seconds and covered 120 feet.

3. Early Aviation Developments (1904–1914)

• Rapid improvements in aircraft design.

• Introduction of propellers, stronger engines, and better control surfaces. •

Airplanes began to resemble modern aircraft.

4. World War I (1914–1918)

• Massive leap in aircraft use and development.

• Airplanes used for reconnaissance, dogfights, and bombing missions. • Fighters

and bombers were developed with improved speed and maneuverability. 5. Between the

Wars (1919–1939)

• Civil aviation and commercial flights began.

• Development of metal airframes and more powerful piston engines.

• Charles Lindbergh's solo nonstop flight across the Atlantic (1927) in the Spirit of St.

Louis.

6. World War II (1939–1945)

• Aircraft technology advanced dramatically:

o Introduction of radar, pressurized cabins, long-range bombers, and jet engines.

• First operational jet aircraft: German Messerschmitt Me 262.

• Aircraft played a decisive role in combat.

7. Jet Age and Commercial Aviation (1950s–1970s)

• First commercial jet airliner: de Havilland Comet (1952).

• Boeing 707 revolutionized global air travel (1958).

• Supersonic flight: Concorde (1976) flew passengers faster than the speed of sound.

8. Modern Era (1980s–Present)

• Use of composite materials, fly-by-wire systems, and advanced avionics. •

Introduction of fuel-efficient wide-body jets like Boeing 787 and Airbus A350. •

Increasing use of automation and AI in flight systems.

2. Civil Aircraft Types & Classifications

The FAA classifies airplanes for various purposes, including their design and flight
operations. For design, different rules and regulations apply specifically to the type, size, and
weight of the airplane, i.e.,

• Airplanes that can carry nine or fewer passengers, with a gross takeoff weight of up to
12,500 lb (5,670 kg).

• Normal or non-acrobatic flight operations.

• Utility or limited acrobatic flight operations.

• Acrobatic use, i.e., unlimited flight maneuvers.

• Propeller-driven airplanes with more than 19 seats or a maximum takeoff weight
greater than 19,000 lb (8,618 kg).

• Multi-engine airplanes with 19 or fewer passengers, with a gross takeoff weight of

less than 19,000 lb (8,618 kg).

• Jet (turbine) propelled airplanes with ten or more seats or a maximum takeoff weight
greater than 12,500 lb (5,670 kg).

For flight operations and piloting, the FAA classifies aircraft according to categories, classes,
and types. The primary categories and classes of civil aircraft are:

• Airplanes:

o Single-engine land (SEL)

 o Multi-engine land (MEL)

o Single-engine sea (SES)

o Multi-engine sea (MES)

• Rotorcraft:

o Helicopter

o Gyroplane

o Tiltrotor

• Lighter-than-air or aerostats:

o Airship (e.g., a blimp or dirigible)

o Balloon (e.g., a hot-air balloon)

• Glider (or sailplane).

Other aircraft categories include:

• Powered-lift (which may consist of uncrewed aerial vehicles or UAVs). •

Powered parachutes:

o Land operation.
o Sea operation.

• Weight-shift aircraft (e.g., hang-gliders):

o Land operation.

o Sea operation.

• Rockets

3. Classification of aircraft structures based on Airworthiness

For airworthiness assessment, aircraft structures are broadly classified as follows:

Primary structure—structure that carries flight, ground, or pressurisation loads, and whose
failure would compromise the aircraft’s structural integrity.

• Effect of Failure: Failure of primary structure can cause a loss of load-carrying capacity,
leading to a potential structural collapse, loss of control, or catastrophic failure of the
 aircraft. Examples include the wings, fuselage, and critical control surfaces.

• Examples: Wings, fuselage, tail structure, control surfaces (ailerons, elevators, rudder).

Secondary structure—structure that, if it were to fail, would affect the operation of the
aircraft but not lead to its loss.

• Effect of Failure: While secondary structure failure can affect the aircraft's
performance, it is not expected to cause immediate catastrophic failure.

• Examples: Engine nacelles, fairings, some access panels, and certain interior
components.

Tertiary structure—structure where failure would not significantly affect operation of the
aircraft.

• Effect of Failure: Failure of tertiary structure is not expected to significantly affect the
aircraft's safety or operation.

• Examples: Some fairings, minor access panels, and decorative elements.

4. Important components of an airplane and their functions
Component Function

Fuselage The central body of the airplane that holds the cockpit, passengers,
cargo, and connects all other components.

Wings Generate lift due to their airfoil shape; they are critical for flight.

Empennage (Tail Provides stability and control. It includes the horizontal and
section) vertical stabilizers.

Landing Gear Supports the airplane while on the ground and during
takeoff/landing. Can be fixed or retractable.

5. Important Flight Control Surfaces of an airplane and their functions

Component Location Function

Ailerons Outboard wings Control roll (banking left or right).

Elevators Horizontal stabiliser (tail) Control pitch (nose up/down).

Rudder Vertical stabilizer (tail) Controls yaw (nose left/right).

Flaps Inboard wings Increase lift and drag for slow-speed

flight (used during takeoff and landing).
Slats Leading edge of wings Help increase lift at low speeds.

Spoilers Upper wing surface Reduce lift and increase drag (used
for descent and braking).

6. Components of Powerplant (Propulsion System)

Component Function

Engine Provides thrust to move the airplane forward. Types: piston,

turboprop, jet, turbofan.

Propeller (if Converts engine power into thrust (common in small aircraft).
present)

Jet Nozzle Expels high-speed gases to produce thrust (jet engines).

Nacelle Housing that encases the engine.

Fig: Parts of an Airplane

Fig Parts of an Aircraft Wing
Classification of aircraft structures

Understanding the classification of aircraft structures based on failure consequences helps in

prioritizing inspection, maintenance, and design safety. Major aircraft structures are
intricately designed to support aerodynamic performance, maintain structural integrity, and
ensure safe and stable flight under various operational conditions.

Class of Description Effect of Failure Examples

Structure

Primary These are essential Catastrophic failure: Wing spar,

Structures load bearing structures Loss of control or fuselage frame,
that directly affect structural integrity, empennage,
flight safety. potentially leading to landing gear
crash. supports.
 Seconda Non-primary load Serious impact but may Wing ribs,
ry bearing parts that not immediately cause a fairings, control
Structur contribute to crash. Can lead to surface skins.
es aerodynamic shape or mission failure or forced
support systems. landing.

Tertiary Non-load bearing Minimal impact; failure Interior panels,

Structures components, often may affect comfort or seat brackets,
associated with appearance but not flight decorative trim.
comfort safety.

7. Role of Major Structures on the Flight of an Aircraft

Each major aircraft structure plays a specific role in ensuring safe and efficient flight:
Major Structure Function Role in Flight

Fuselage Central body of the aircraft. Provides structural integrity,

Houses crew, passengers, center of gravity control, and
cargo, and connects other houses flight systems.
parts.

Wing Provides lift. Includes Generates the aerodynamic

components like spars, ribs, lift required for flight;
and fuel tanks. houses control surfaces (e.g.,
ailerons).

Empennage (Tail Comprises the horizontal and Maintains stability and

Section) vertical stabilizers and control in pitch and yaw
control surfaces (elevators, axes.
rudders).

Landing Gear Supports the aircraft during Enables safe ground

ground operations (takeoff, movement, absorbs landing
taxi, landing). loads.

Powerplant Houses engines and Provides thrust; mount must

Nacelle/Engine associated systems. withstand dynamic loads and
Mounts vibration.
 Control Surfaces Movable parts used to Enable the pilot to steer the
(e.g., ailerons, control the aircraft’s aircraft—roll, pitch, and yaw
elevators, rudder) attitude. control.

8. “Six-pack”—essential for safely flying under both VFR and IFR conditions

VFR stands for Visual Flight Rules, and IFR stands for Instrument Flight Rules. They are
two distinct regulatory frameworks that govern how pilots fly an aircraft depending on
weather, visibility, equipment, and airspace. VFR (Visual Flight Rules) means flying
primarily by looking outside—using the horizon, landmarks, and other visual cues—so it's
only allowed in good weather (clear skies, sufficient visibility, and staying away from
clouds).
IFR (Instrument Flight Rules) means flying exclusively by reference to cockpit
instruments—like attitude indicator, altimeter, and navigation systems—used when visual
references aren’t sufficient (e.g. in clouds, fog, or at night). IFR flights require an instrument
rated pilot, a properly-equipped aircraft, a filed flight plan, and ATC clearance and guidance.

Pitot-Static Instruments

1. Airspeed Indicator (ASI)

Measures speed relative to the air using pitot and static ports. Critical for takeoff,
climb, cruise, and approach, it displays color-coded ranges like stall speed, normal,
caution, and never-exceed speed

2. Altimeter
Shows altitude above mean sea level using static pressure. It resembles a clock with
multiple pointers and requires periodic pressure setting

3. Vertical Speed Indicator (VSI)

Indicates rate of climb or descent in feet per minute (or meters/sec), based on changes
in static pressure

Gyroscopic Instruments

4. Attitude Indicator (AI)

The artificial horizon, showing aircraft pitch and bank using a gyro. It's crucial when
you can’t rely on outside visual cues

5. Heading Indicator (HI)

A directional gyro showing magnetic heading. More stable than a magnetic compass
 but must be manually aligned with it every ~15 min
6. Turn Coordinator
Displays rate and direction of turn (standard rate = 3°/sec) and includes a ball to
indicate slip or skid—helping maintain coordinated, safe turns

Fig: 8. “Six pack”—essential for safely flying

9. Pitch, yaw, and roll

In flight dynamics, pitch, yaw, and roll describe the three fundamental rotations an aircraft can
perform around its centre of gravity. Pitch is the rotation around the lateral axis (nose
up/down), yaw is the rotation around the vertical axis (left/right), and roll is the rotation
around the longitudinal axis (tilting the wings). These rotations are controlled by the aircraft's
control surfaces: elevators for pitch, rudder for yaw, and ailerons for roll.
Elaboration:
1. Pitch:

• Definition: Rotation around the lateral axis (wing to wing).

• Control: Elevators, located on the horizontal stabilizer (tail). Moving the elevators up or
down creates a force that rotates the aircraft's nose up or down.

• Sketch: Imagine a line going through the wings, and the nose of the plane rotating up or
down around that line.

2. Yaw:

• Definition:

Rotation around the vertical axis (going through the top and bottom of the plane).

• Control:

The rudder, located on the vertical stabilizer (tail fin). Moving the rudder left or right creates a
force that rotates the aircraft's nose left or right.

• Sketch:

Imagine a line going straight up and down through the middle of the plane, and the nose
rotating around that line.

3. Roll:
• Definition: Rotation around the longitudinal axis (nose to tail).

• Control: Ailerons, located on the trailing edge of each wing. Moving the ailerons up on
one wing and down on the other creates a force that rolls the aircraft.
 • Sketch: Imagine a line going from the nose to the tail of the plane, and the plane
rotating around that line, tilting the wings.

Control Surfaces and their Functions:

• Elevators: Control pitch.

• Rudder: Controls yaw.

• Ailerons: Control roll.

How Control Surfaces Work:

• When a control surface is deflected, it changes the airflow over that part of the aircraft.

• This change in airflow creates a force that pushes or pulls on the aircraft, causing it to
rotate.

• By manipulating the control surfaces, a pilot can control the aircraft's pitch, yaw, and
roll to manoeuvre in the desired direction.
10. The principles of flight

The principles of flight are governed by four fundamental forces: thrust, lift, drag, and weight.
Thrust is the force that propels the aircraft forward, while lift counteracts the force of gravity.
Drag acts in opposition to the aircraft's motion, and weight represents the gravitational force
acting on the aircraft. To achieve stable flight, these forces must be meticulously balanced.

Fig: Diagram: A basic schematic illustrating the forces acting on an aircraft during
flight would resemble the following design

Explanation of the Forces:

• Thrust: This is the forward force generated by the aircraft's engine (propeller or jet
engine). It acts in the direction of the aircraft's motion.

The equation for thrust in an airplane can be expressed as:

F = (ṁ * Ve) - (ṁ₀ * V₀) + (Pe - P₀) * Ae.

Where:

F: represents the thrust force.

ṁ: is the mass flow rate of the exhaust (or air in some cases).
Ve: is the exhaust velocity.
ṁ₀: is the free stream mass flow rate (usually air entering the engine).
V₀: is the free stream velocity (velocity of the air entering the engine).
Pe: is the exhaust pressure.
P₀: is the free stream pressure.
Ae: is the exit area of the engine nozzle.

• Lift: This upward force generated by the wings (and other lift surfaces) counteracts the
force of gravity, allowing the aircraft to stay airborne. The shape of the wings
(cambered surface) and the airflow over them create this lift, based on Bernoulli's
principle.

he equation for lift in aerodynamics is L = 1/2 * ρ * v² * S * Cl, where: L is the lift force, ρ is
the air density, v is the velocity of the object through the air, S is the surface area of the wing,
and Cl is the lift coefficient.

The lift coefficient (Cl) is a dimensionless value that depends on the shape of the object, its
angle of attack (the angle between the wing and the oncoming airflow), and other factors like
the air's viscosity and compressibility.

Equation: L=12ρV2SCLL = \tfrac12 \rho V^2 S C_LL=21ρV2SCL

• Drag: This is the force that resists the aircraft's movement through the air. It is caused
by friction and turbulence as the aircraft moves through the atmosphere. Drag acts in
the opposite direction of thrust.

The drag equation is: D = 1/2 * ρ * V² * A * Cd

Where: D is the drag force, measured in Newtons (N).

•Ρ (rho) is the density of the fluid, measured in kilograms per cubic meter (kg/m³). • V is
the velocity of the object relative to the fluid, measured in meters per second (m/s). • A is
the reference area, the area of the object that is perpendicular to the flow direction,
measured in square meters (m²).
• Cd is the drag coefficient, a dimensionless value that depends on the object's shape and
 surface conditions.
The drag coefficient (Cd) is a crucial factor, and is often determined experimentally or
estimated using computational fluid dynamics. It encapsulates how streamlined or blunt an
object is, impacting how much resistance it encounters in a fluid.

• Weight: This is the force of gravity acting on the aircraft, pulling it downwards.

Balance and Control:

• Stable Flight: For an aircraft to maintain stable, straight-and-level flight, the forces of
lift and thrust must be equal to the forces of weight and drag, respectively.

• Control Surfaces: Control surfaces (ailerons, elevators, rudder) are used to adjust the
forces and maintain control of the aircraft in flight.

• Manoeuvring: By adjusting the angles and forces, pilots can change the direction and
altitude of the aircraft.

Bernoulli's Principle:

Bernoulli's Principle states that in a flowing fluid, an increase in the fluid's speed occurs
simultaneously with a decrease in pressure or potential energy. The mathematical expression
for Bernoulli's Principle is:

where P is the pressure, ρ is the fluid density, g is the acceleration due to gravity, h is the
height, and V is the fluid velocity.

The difference in pressure creates an upward force on the wing known as lift. The lift force
can be expressed as: Lift = (PA−PB) × Area of the wing. This upward force allows the
aeroplane to fly.
The airplane flies due to the pressure difference created by the varying speeds of air above and
below the wings, as explained by Bernoulli's Principle. The faster-moving air over the curved
top surface of the wing results in lower pressure compared to the slower-moving air below the
wing, generating lift.

Newton's Third Law

Newton's Third Law, which states that for every action, there is an equal and opposite
reaction, is fundamental to how aircraft fly.

Fig: Newton's Third Law demonstrated for aerodynamics

The principle of action and reaction plays a crucial role in the functioning of aircraft,
particularly in explaining how lift is generated by an airfoil. In this context, the airfoil deflects
air downward, resulting in an upward force on the wing in reaction. Similarly, when it comes
to a spinning ball, the air is directed to one side, causing the ball to move in the opposite
direction. Additionally, jet engines produce thrust through this action-reaction principle. As
the engine expels hot exhaust gases out the back, it generates a thrusting force in the opposite
direction.

Specifically for aircraft, the engines create thrust by pushing air backward, and according to
the law of action and reaction, the air exerts an equal and opposite force on the engine,
propelling the aircraft forward. This principle is also vital for generating lift, where the wings
push air downward, and in response, the air pushes upward on the wings.

11. Types of drag

Aircraft encounter several types of drag during flight: parasite drag (including form, skin
friction, and interference drag), induced drag, and wave drag. Parasite drag arises from the
aircraft's shape, surface smoothness, and interaction between different parts. Induced drag is a
consequence of producing lift, while wave drag is present at transonic and supersonic speeds
due to shock waves.

Types of Drag and Their Sources:

• Parasite Drag:

• Form Drag (or Pressure Drag): This type of drag is caused by the shape of the
aircraft and its interaction with the air. A blunt shape creates a higher form
drag compared to a streamlined shape.

• Skin Friction Drag: This drag is generated by the roughness of the aircraft's
 surface. As air flows over the surface, it experiences friction, creating drag.

• Interference Drag: This drag occurs where different parts of the aircraft, like
the wings and fuselage, meet. The interaction of these parts creates turbulence
and additional drag.
• Induced Drag:

• This drag is a direct result of the production of lift. As an aircraft generates lift, it
creates vortices at the wing tips, which induce a downstream force that
contributes to drag.

• Wave Drag:

• This type of drag is prevalent at transonic and supersonic speeds. At these

speeds, shock waves form on the aircraft, causing a significant increase in drag.

12. Dimensionless values to quantify the aerodynamic characteristics

Trendsfor variation of Lift Coefficient (CL), Drag Coefficient (CD), and Lift-to-Drag
Ratio (L/D) with Angle of Attack (α), followed by the recommended cruise point:

Graphical Representation

Let’s consider the three curves:

1. CL vs Angle of Attack (α):

• CL increases with α up to a maximum point (CLmax).

• Beyond this point, lift drops sharply due to stall.

2. CD vs Angle of Attack (α):

• CD increases gradually at low α.

• As α increases beyond a critical point, drag rises steeply due to flow separation and
stall.

3. L/D Ratio vs Angle of Attack (α):

• L/D increases with α up to a peak (best efficiency point).

• After this peak, L/D falls due to increasing drag and stalled lift.
Recommended Point for Cruise Flight

• Cruise flight aims for maximum efficiency, not maximum lift.

• Hence, operate at or near the angle of attack where L/D ratio is maximum. •

This gives optimal fuel efficiency and longer range.

Recommended Operating Point:

• Angle of Attack (α): ~4° to 6°

• Why: Maximum L/D ratio → Best aerodynamic efficiency

• Avoid: High α near stall → High drag and risk of instability

Model Questions for Unit 1

1. Analyse and explain, with the help of sketches, the role of control surfaces in
manoeuvring aircraft along different axes, using appropriate figures. 2. Elucidate in detail
the historical evolution of aeroplanes and helicopters. 3. Summarise, as bullet points, the
technological evolution of aircraft and space vehicles post Second World War in terms of
structures, engines/propulsion, navigation and control capabilities, as well as materials of
construction.
4. Assess the role of flight instruments in the control of flight and manoeuvres of an
aircraft, providing a list of such essential instruments and their utility. 5. Differentiate
between classes of structures from the point of view of the effect of their failure
(airworthiness).
6. Examine the role of the major structures in the flight of an aircraft. 7. Classify aircraft,
clearly mentioning the basis for each categorisation. 8. Depict the various arrangements of
wings and state the reason for such arrangements with sketches.
9. Draw a diagram and locate various parts of an aeroplane.
10. Explain pitch, yaw, and roll in flight dynamics with required sketches. How can they
be controlled?
11. Elucidate in detail the principles of flight with a neat schematic diagram. 12. Illustrate
two primary theories that explain lift generation in aircraft. 13. Inspect the role of
aerodynamic forces in the flight of an aircraft and give the equations for each of these
forces.
14. Distinguish and identify the different types of drag encountered in the flight of an
aircraft along with their sources.
15. With the help of a graph, explain the trends in variation of CL, CD and L/D ratio with
angle of attack and recommend the point of operation for cruise flight conditions. 16.
Explain in detail the temperature, pressure and altitude relationship with suitable
empirical relations.
17. Calculate the standard atmosphere values of T, ρ and P at a geopotential altitude of 14
km, given the lapse rate from 0 km to 11 km as α = -6.5 K/km, followed by an
isothermal region from 11 km to 14 km.