THEORY OF FLIGHT 1

PO 402

CI Norwood

References: FTGU Pages 9-50, Pilot’s Handbook of Aeronautical Knowledge Chapters 1-3

Review from last class

1. What is the VFR weather minima for fixed wing aircraft <1000’ AGL in uncontrolled airspace?

2. You are on final approach and you receive a flashing red light from the tower. What does it mean and what do you do?

Topics to be covered today

The fuselage and empennage Parts of the airplane Four forces acting on an aircraft How lift is created Boundary layer

What is an airplane?

The Canadian Air Regulations defines an airplane as:

“A power driven, heavier-than-air aircraft, deriving its lift in flight from aerodynamic reactions on surfaces that remain fixed under given conditions of flight”

Definitions Aircraft: any machine capable of deriving

support in the atmosphere from the reactions of the air

Glider: heavier-than-air aircraft not equipped with a motor, which derives its lift from aerodynamic reactions on surfaces which remain fixed under given conditions of flight

Airframe: Total structure of the aircraft including fuel systems and fuel tanks but excluding instrumentation and engines

Classification

Aircraft can be classified according to:

Position and number of wings

The number of engines

configuration of the undercarriage

Parts of the Airplane

Fuselage

The fuselage is the main body of the aircraft

Holds all passengers and cargo Almost all parts of the aircraft are

attached to the fuselage Three types of fuselage construction:

Truss typeMonocoqueSemi-monocoque

Truss Type (SGS 2-33A)

Steel or aluminum tubing (wood in antique aircraft)

Strength is achieved by welding tubes into triangles called “trusses”

Longerons make up the frame which are supported by diagonal and vertical members

Monocoque (Katana)

Uses a stressed skin to handle all loads

Main construction consists of formers to give shape and bulkheads to seal off and connect sections

Very strong but heavy due to the strength requirement of the skin

Semi-Monocoque (Airbus 320)

Structure of formers, bulkheads and stringers to create a frame

Frame is covered by a stressed skin to take some of the bending stresses

Most common type of fuselage construction

Review

1. What is an aeroplane according to the CARs?

2. What are the main parts of an airplane?

3. What are the three types of fuselage construction?

Empennage

Horizontal stabilizer – Non movable horizontal surface

Elevator – Movable surface attached to the horizontal surface

Fin or Vertical stabilizer – Non movable vertical surface

Rudder – Movable surface attached to vertical stabilizer

Canard

In some aircraft, the horizontal tail is moved forward

Seen in early aircraft such as the Wright Flyer and modern aircraft such as the Beech Starship and fighter aircraft

Canard

Stabilator

One piece movable surface that replaces the elevator and horizontal stabilizer

Stabilators have a movable surface called an anti-servo tab which act as trim tab to relieve control surfaces

The Wings and Lifting Surfaces

Two main types of wing configuration

Monoplane – One wing

Biplane – Two wing

Wing Positioning

Three positions for the wing relative to the fuselage:

High-wing – Attached on top

Mid-wing – Attached in the middle

Low-wing – Attached on the bottom

Review

1. What surfaces make up the empennage?

2. What is a stabilator?

3. What are the three types of wing positioning?

Construction of the Wing

Spar – Run from wing root to tip, stiffens the wing

Ribs – Run from leading edge to trailing edge and give wing its shape

Compression struts – Tubes placed between spars to handle compression loads

Construction of the Wing

Drag and anti-drag wires – Resists bending forces from the wing going through the air

Ailerons – Movable surface on the outboard sections that control roll. Move in opposite directions on each wing

Construction of the Wing

Flap – Movable section next to the wing root

Wingspan – Distance from wingtip to wingtip

Construction of the Wing

Chord – Imaginary straight line from the leading edge to the trailing edge

Struts – External bracing that support the wings, mainly seen in high wing aircraft Struts

Review

1. What are the main components of the wing?

2. What do ailerons do?

3. What is the chord?

Landing Gear

Absorbs shock of landing

Allows the movement of the aircraft on the ground

Can be either fixed or retractable

Type of Landing Gear

Conventional (Tail dragger)

Tricycle (Nose wheel)

Mono-wheel

Conventional Gear

Less parasite drag

Cheaper Better ground

handling Better handling

on rough strips

More difficult to land

Has tendency to nose-over

Poor ground visibility

Poor crosswind handling

Advantages Disadvantages

Tricycle Gear

Easy to land Good ground

visibility Good crosswind

handling Very small chance

of ground looping

More parasite drag

Poor ground clearance for propeller

Poor performance on rough surfaces

Advantages Disadvantages

Propulsion System

For smaller GA aircraft the main parts of the propulsion system are:

Engine: Provides rotation for the propeller

Propeller: Creates thrust through rotation

Cowling: Covers the engine and provides cooling through air ducts

Review

1. What are the two types of landing gear?

2. What are some advantages/disadvantages of those landing gear?

3. What are the main components of the propulsion system?

The Four Forces

Lift

Lift opposes weight through aerodynamic reactions

Creation of lift can be explained through two separate principles:

Newton’s Three Laws of Motion Bernoulli’s Principle

Newton’s Three Laws of Motion 1st law: An object in motion will stay in

motion and an object at rest will stay at rest unless acted on by another force

2nd law: Acceleration of an object is inversely proportional to the mass of the object and proportional to the force applied (ex. You trying to push a school bus as opposed to a soccer ball)

3rd law: Every action has an equal and opposite reaction

Bernoulli’s Principle

Energy in a system must remain constant If we look at a venturi tube, the amount

of air entering in the tube must equal the air exiting the tube (flow rate)

Bernoulli’s Principle

As the tube decreases in size the velocity of the air must increase to maintain the same flow rate, therefore kinetic energy increases

This causes the pressure to drop and the energy remains constant

How lift is actually created

As the air flows over the wing, it accelerates as it moves over the cambered surface (just like in a venturi tube)

This causes the pressure above the wing to decrease, creating a force that sucks the wing into the air

H

L

How lift is actually created

On the underside of the wing, the air is deflected downwards which pushes up on the wing

Also, air flowing off the top of the wing is deflected downwards, this contributes to lift

This phenomenon is called downwash and is a result of Newton’s 3rd law

Force acting on air

Force acting on wing

DOWNWASH

Review

1. What is Bernoulli’s Principle?

2. What are Newton’s three laws of motion?

3. How does a wing create lift?

Weight

Weight is the downward force created on the aircraft due to gravity

All of the weight acts through a single point called the centre of gravity

Thrust

Thrust is force that moves the aircraft forward through the air

While there are many ways of producing thrust, all rely on the principle of moving air backwards to create a reaction to push the aircraft forward

Drag

Resistance to the motion of the aircraft through the air

There are two main types of drag: Parasite drag – Created by parts of the

aircraft that do not contribute to lift Induced drag – Created by parts of the

aircraft that contribute to lift

Parasite drag

Form Drag: Drag created by the shape of the aircraft. Can be reduced through streamlining

Skin friction: Drag created by the roughness of the skin, can be made worse through dirt and ice accumulation

Interference drag: Drag created by two parts of the aircraft that create eddies where they intersect (such as the struts and wings)

Parasite drag increases as speed increases

Induced drag

Created by parts of the plane that create lift

Cannot be completely eliminated

Greater the lift, greater the induced drag

Reduces as speed increases

Review

1. What do we call the point at which all weight acts through?

2. How is thrust generally produced?

3. What are the two types of drag?

Airfoils

An airfoil is any surface designed to create lift

Most suitable surface for creating lift is a curved or cambered surface

Camber

Camber is the curvature of the upper and lower surfaces of the wing

Usually the upper surface is more curved that the lower surface

Equilibrium

When two forces are equal and opposite, they are said to be in equilibrium

When the forces are equal, the aircraft will continue to move at a constant rate of speed

Couples

When two forces are opposite and parallel, but not acting through the same point, a couple is created

This couple will cause rotation about a given axis

An example of this would be drag acting opposite and parallel above thrust, this would cause the nose of the aircraft to rise

Relative Airflow (Relative Wind) Direction of the airflow

with respect to the wing Created by the motion of

the aircraft through the air

Can also be created by air moving around a stationary object

When an aircraft is on the take-off roll, the aircraft will be subjected to the relative wind by it’s own motion through the air and by the wind

Review

1. What is camber?

2. What is equilibrium and when would an aircraft be in equilibrium?

3. What is a couple and what can it do to an aircraft?

4. What is relative airflow?

Aileron Drag

When an aircraft banks to turn, one ailerons moves up, the other one goes down

The down going aileron compresses the air underneath the wing and creates more lift, rolling the aircraft

By creating more lift, more drag is created and the aircraft yaws opposite turn

This is called adverse yaw

Aileron Designs

Differential Ailerons Frise Ailerons

Secondary Effects of Controls

Yawing moment in the direction of the turn created by the relative airflow hitting the side of the fuselage ahead of the c of g

Rolling moment in the direction of the turn due to the outside wing moving faster through the air creating more lift

Ailerons Rudder

Lift and Drag Curves

Lift and drag are dependant on several factors:

Angle of attack and the shape of the airfoil – CL and CD

Wing area – S The square of the velocity – v2 Density of the air – ρ Lift equation: L = ½ CL v2 ρ Drag equation: D = ½ CD v2 ρ

Lift and Drag Curves

Center of Pressure

If we consider the pressure distribution across the wing as a single force, it will act through a straight line

This is called the centre of pressure

Center of Pressure

As lift increases, the center of pressure moves forward until the wing stalls

The C of P then moves backwards, this can cause the aircraft to become unstable

Review

1. What is aileron drag and what does it create?

2. What factors affect lift and drag?

3. What is the center of pressure and how does it move when the angle of attack is increased?

Boundary Layer

The boundary layer is a thin sheet of air that sticks to the wing

This occurs because air is viscous (or has a resistance to flow)

The airflow slows down as it gets closer to the surface as a result of friction between the air and the surface

If we use a wing as an example, the airflow would be smooth at the front of the wing, this is called the laminar flow region

Boundary Layer

As the air continues to flow back, it slows down due to friction and eventually becomes turbulent, this is called the turbulent flow region

The point at which it changes from laminar to turbulent flow is called the transition point

Airfoil Design - Conventional Thick airfoil that allows

for better structure and lower weight

Camber is maintain further rearward which increases lift and reduces drag

Good stall characteristics

Thickest part of the wing is at 25% of the chord

Airfoil Design - Laminar

Designed for faster aircraft because of the reduced drag

Thinner than the conventional airfoil and the cambering is almost symmetrical

Thickest part of the airfoil is 50% of the chord

Review

1. What is the boundary layer?

2. What happens to the boundary layer as air flows back over a wing?

3. What is the main difference between a conventional and laminar airfoil

Angle of Incidence

Angle at which the wing is permanently inclined to the horizontal axis

Most airplanes have a small angle of incidence to ensure a small angle of attack and therefore a greater visibility during cruise

Wash-in/Wash-out

Reduces the tendency for the entire wing to stall at the same time

The wing is slightly twisted so that the wing root is has a higher angle of incidence (hence a higher angle of attack) than the wing tip, forcing it to stall first

This allows for the pilot to have more control during a stall

Flaps

High lift devices attached to the trailing edge of the wing at the root

They will provide the pilot with:- Better take off performance- Steeper approach angles- Slower approach and landing speeds

Spoilers and Divebrakes

Spoilers and divebrakes are devices attached to the upper and lower surfaces of the wing

When extended into the airflow, they will decrease lift and increase drag

This allows for a steeper approach angle without having to increase speed

Spoilers and Divebrakes

Review

1. What is wash-in/wash-out and why would we have it on an airplane?

2. What do flaps do?

3. What do spoilers and divebrakes allow the pilot to do?

Wing Fences

Fins attached to the upper surface of the wing

Control the movement of air over the wing to allow for better handling at low speed and improve stall characteristics

Winglets

Mounted vertically on the wingtips

Small airfoil surfaces

Break up the wingtip vortices which flow towards the upper surface of the wing

Slats and Slots

Extra airfoil on the leading edge of the wing

When a high angle of attack is encountered, the slat moves forward to allow for more airflow and increase lift

Passageway built into the leading edge of the wing

Increases airflow over the wing at high angles of attack

Remains stationary

Slat Slot

Slats and Slots

Vortex Generators

Small airfoils placed along the wing

When the air flows over them, small vortices will be created, re-energizing the flow which prevents the air from separating and becoming turbulent

This helps increase lift and decrease drag

Vortex Generators

Review

1. What are wing fences?

2. What’s the difference between a slat and a slot?

3. What do vortex generators do?

More review

1. What are the three types of fuselage

construction?

2. What are the four forces acting on an

aircraft?

3. How is lift created?

4. What is equilibrium?

5. What are flaps?

6. What do slats do?

Summary

Today we have covered: Parts of the aircraft Forces on the aircraft How lift is created Boundary layer

Next class we will continue theory of flight!