Theory of Flight Part 1 Writing in regular script down here is to be taught Writing in italics is for extra information References: FTGU 29th Pages 3-23, Pilot’s Handbook of Aeronautical Knowledge Chapters 1- 3

Review from last class What is the VFR weather minima for fixed wing aircraft <1000’ AGL in uncontrolled airspace? You are on final approach and you receive a flashing red light from the tower. What does it mean and what do you do? Day - 2 SM day, clear of cloud Night - 3 SM day, clear of cloud It means airport unsafe, do not land. You would overshoot.

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

The Airplane

What is an airplane? The Canadian Air Regulations defines an aeroplane 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 Number of engines Configuration of the undercarriage

Parts of an Airplane

Parts of an Airplane Vertical Stabilizer Rudder Aileron Horizontal Stabilizer Flaps Elevators Wing Strut Aileron Propeller Landing Gear Engine Cowl

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 type Monocoque Semi-monocoque

Truss Type (SGS 2-33A) Longerons: 3-4 steel or aluminum tubes that make up the frame (wood in antique aircraft) Strength is achieved by welding tubes into triangles called “trusses” Frame covered in fabric, metal or composite Generally used in the construction of ultra-light and amateur-built aircraft Truss, N-Girder and Warren Truss Warren Truss: alternatively inverted equilateral triangles N-Girder: isosceles triangles

Monocoque (Katana) Uses a stressed metal skin to handle all loads Example: pop can Main construction consists of round formers to give shape and bulkheads to seal off and connect sections Stringers run lengthwise to hold everything together 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 Semi-monocoque: When stiffeners are provided to form the structure and resist part of the loads

Review What is an aeroplane according to the CARs? What are the main parts of an airplane? What are the three types of fuselage construction? 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 Power plant Landing gear Fuselage Wings Empennage Truss Monocoque Semi-monocoque

Wings Create lift to carry aircraft in the air 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

Construction of the Wing Leading edge: the forward part of the wing which meets the relative airflow Trailing edge: rear edge of the wing from which the air flows off the wing Wing root: inner edge of the wing, where it attaches to the fuselage Wing tip: outer edge of the wing, furthest from the fuselage 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 Cantilever: wings without external bracing 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 Flap – Movable section next to the wing root Wingspan – Distance from wingtip to wingtip

Compression Struts Drag & Anti-Drag Wires

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

Construction of Empennage Empennage: provides longitudinal and directional control and stability Fin or Vertical stabilizer: vertical surface placed ahead of the stern-post to provide directional stability Rudder: hinged vertical control surface attached to the vertical stabilizer, providing directional control (yaw) Stabilizer: horizontal airfoil placed at the rear of the fuselage to provide longitudinal stability Elevator: mobile surface attached to stabilizer, providing longitudinal control (pitch) Trim tab: adjustable surface, fixed or mobile, attached to the elevator and/or rudder. Helps the pilot by eliminating the need to exert excessive pressure on the flight controls during the various phases of flight

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 Servo tabs: Devices found on larger airplanes. Connected directly to the control column and are used to ease the strain on the controls. The pilot moves the control surface by controlling only the servo tab; the control surface is free floating in the air. Anti-servo tabs: Exactly the same as a servo tab except that they are meant to make the controls feel harder. Mainly used with stabiliators

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 Some aircraft have a regular tail but add a canard for more manoeuvrability Canard

Review What surfaces make up the empennage? What are the main components of the wing? What is the chord? Vertical stabilizer, fin, rudder Horizontal stabilizer, elevator Spars, ribs, compression struts, ailerons, flaps Imaginary line running from leading edge of the wing to the trailing edge

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

Equipment, Radios, Instruments All instruments, radios, and other various equipment are located inside the cockpit. A radio which enables contact with the ground, ATC, and other aircraft. Instruments panel (airspeed indicator, altimeter, compass, etc.). ELT (Emergency Locator Transmitter).

Landing Gear Absorbs shock of landing Supports weight of aircraft 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)

Landing Gear Advantages Conventional Tricycle Less parasite drag Cheaper to build and maintain Less damage if broken Easier to handle on ground Less propeller damage on rough strips due to distance from ground Less airframe damage due to landing shock absorption Easier to switch to skis Reduced nose-over tendencies Reduced ground looping tendencies Better ground visibility Better ground manoeuvrability in high wind conditions Better crosswind control Easier to learn to land

Review What are the two types of landing gear? What are some advantages/disadvantages of those landing gear? What are the main components of the propulsion system? Conventional (tail dragger) Tricycle Conventional Advantages: less parasite drag, cheaper, better ground handling and rough strip handling Disadvantages: difficult to land, nose-over, poor gnd vis, poor xwind Tricycle Advantages: easy to land, good gnd vis, good xwind, less gnd looping Disadvantages: parasite drag, poor gnd clearance for prop, poor rough surface handling Engine Propeller Cowling

The control systems

Aircraft controls Aircraft can move around or in three axes In order to move, some type of control mechanism must be in place Three main control surfaces: Ailerons (roll) Elevator (pitch) Rudder (yaw) All aircraft movements are done around the center of gravity

Ailerons Control surfaces attached to the outboard trailing edge of the wing Move in opposite directions When the control column is moved to the right, the left aileron goes down (increasing lift) and the right aileron goes up (decreasing lift), this causes the plane to roll to the right The angle of bank increases until the stick is returned to the neutral (centered position) Generally necessary to apply counter-pressure (small amounts of stick in the opposition direction of the roll) to maintain a constant bank angle while in a turn Source: Pilot’s Handbook of Aeronautical Knowledge

Elevators and Stabilators Hinged to the trailing edge of the horizontal stabilizer Move up or down when the pilot pulls the column back or pushes forward Controls the pitching motion of the airplane When stick is moved forward, the elevator descends, creating lift at the tail The empennage rises and the nose of the aircraft descends Source: Pilot’s Handbook of Aeronautical Knowledge

Rudder Attached to the vertical stabilizer and moves the aircraft left and right through a motion called yaw Controlled by the rudder pedals at the pilots feet Causes the rudder to deflect and a force is created at the tail Pressure on the left rudder pedal moves the rudder to the left, creating lift on the right side of the fin and moving the tail to the right and nose to the left Source: Pilot’s Handbook of Aeronautical Knowledge

Secondary Effects of Controls Rudder Ailerons 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 Secondary Effect of the Ailerons When an aircraft rolls, it tends to slip towards the inside of the turn. The relative airflow therefore impacts the side of the fuselage. Because the surface in front of the C-of-G is smaller than the surface behind the C-of-G, a yawing moment in the same direction as the turn is generated. This yaw is the secondary effect of the ailerons. Secondary Effect of the Rudder When rudder is applied, the aircraft yaws in the direction of the rudder pedal depressed. The wing outside the turn moves through the air more rapidly than the inside wing, thereby creating more lift and producing a rolling moment in the direction of the turn. This roll is the secondary effect of the rudder.

Trim Tab Helps eliminate excess force on the controls by the pilot Acts as an small elevator on the control surface which creates a force to keep it in a constant position Moves in the opposite direction of the surface Hinged, adjustable tab on the trailing edge of a control surface Designed to move above or below the chord line of the control surface to which it is attached, thereby creating an aerodynamic force on the surface which helps the pilot keep the control surface in the desired position. For example, to keep the elevator in a high position the trim tab would be moved down, exerting an upward force on the surface and relieving the pilot of the need to pull back on the stick. Source: Pilot’s Handbook of Aeronautical Knowledge

Review What are the three main control surfaces and where are they located? How do ailerons roll the aircraft? If we wanted to hold a nose high attitude, which direction would we want to the trim tab to move? Elevator(s) on horizontal stabilizer Rudder on vertical stabilizer Ailerons on trailing edge of wing The down-going aileron causes more lift than up-going aileron allowing it to move up Trim tab down

Forces acting on an airplane in flight

The Four Forces Thrust – force exerted by engine and propeller(s) which pushes air backward causing reaction, or thrust, forward Drag – resistance to forward motion directly opposed to thrust Lift – force upward which sustains airplane in flight Weight – downward force due to gravity, directly opposed to lift

The Four Forces

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 In equilibrium the aircraft is not under any acceleration

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

Airfoils An airfoil is any surface designed to create lift Most suitable surface for creating lift is a curved or cambered surface Wing profile: Thickness and curvature of the upper and lower surfaces of the wing. The purpose for which the aircraft is intended has a strong influence on the shape of the wing of that aircraft. An aircraft intended for low-speed, high lift flight will have a thick wing which generates high lift but also high drag. An aircraft intended for high-speed, high-altitude flight will have a thin wing profile which generates less drag (as well as less lift).

Camber Camber is the curvature of the upper and lower surfaces of the wing Usually the upper surface is more curved than the lower surface

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 1st law: If thrust equals drag there is no change in the horizontal motion. If lift equals weight is no change in the vertical motion. If any of these is increased or decreased so the formula is unbalanced, a change will occur. 2nd law: (F=ma) The law defines the amount of force, produced by lift, needed to overcome the effects of gravity. This lift is achieved in part by use of the Bernoulli principle, and also Newton’s Third Law of motion. 3rd law: As the air is deflected downward, it pushes on the wing in an equal and opposite direction.

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) In a closed system, total energy remains constant. In other words, in a closed energy system, when one factor increases, another diminishes in equal measure.

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 L Assume an imaginary line above the wing to simulate a venturi-type system H

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 wing DOWNWASH Force acting on air

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

Angle of Attack Angle of attack – angle airfoil meets the relative airflow As angle of attack increases, pressure (lift) increases until the critical angle of attack Beyond this angle, they decrease

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 If the total distribution of pressure is considered a single force, it can be represented by a single vector. The junction between this line and the chord of the wing is called the centre of pressure. The centre of pressure is the resultant of all lift forces.

Center of Pressure As lift increases, the center of pressure moves forward until the wing stalls Will always occur at the critical angle of attack The C of P then moves backwards; this can cause the aircraft to become unstable

Review What is Bernoulli’s Principle? What are Newton’s three laws of motion? How does a wing create lift? Energy in a system must remain constant 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 As the air flows over the wing, it accelerates as it moves over the cambered surface. This causes the pressure above the wing to decrease, creating a force that sucks the wing upwards.

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 Limits Limits are normally expressed in inches from the datum line. For some aircraft, the C-of-G limits are expressed as a percentage of Mean Aerodynamic Chord (the average chord of the wing). The position of the Centre of Gravity affects the stability of the aircraft. The engineers who design aircraft specify the forward and aft C-of-G limits which must not be exceeded. They exist to guarantee that the pilot will have sufficient deflection of the elevator during all phases of the flight. C-of-G too far forward: The aircraft will be nose-heavy; significant control pressure will need to be applied on the elevator and the aircraft will be harder to trim. If the aircraft stalls or falls into a spiral dive, it will be difficult and possibly very slow to recover from the dive. This is critical at low altitudes. The aircraft, being nose-heavy, requires aft control pressure to create downwards « lift » from the tailplane in order to keep the nose up. This downward force effectively adds itself to the aircraft’s weight and extends the vector acting downwards. This increase in downward force means that more upward force (Lift) must be generated for a given flight profile, which results in an increase in stall speed. C-of-G too far aft: The aircraft will be tail-heavy; this is the more dangerous of the extremes. An aircraft with a C-of-G too far aft can be dangerously unstable, and the stall and spin characteristics will be abnormal. Recovery from unusual attitudes will be difficult if not impossible because the pilot will potentially need more control movement on the elevator than there is available. The responsibility to ensure proper weight distribution rests on the shoulders of the pilot; correct loading will respect C-of-G limitations. The stall speed will decrease with an aft loading because, in order to maintain a normal flying attitude, the pilot will have to apply forward pressure, creating positive lift from the tail surface which will help support the aircraft in flight. Loading aircraft aft WHITIN LIMITS is used on large aircraft to reduce induced drag, gain a few knots and save fuel. For this, they transfer fuel in the horizontal stabilizer. What happen is that a forward loaded aircraft get nose heavy and back pressure is needed to keep normal flight. The horixontal stabilizer is therefore creating a downward lift adding to the weight which will require more lift from the wing to balance the normal weight and the fake added weight of the downward lift. This creates in turn more drag that would have to be compensated by burning more fuel. This is eliminated by loading the aircraft aft but within limit. This principle is valid for large aircraft as no appreciable gain will be made on a slow-light aircraft.

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 Thrust: Force generated by the engine and propeller, which pushes air backwards in order to cause a reaction towards the front. Thrust can be generated in various ways, moving the aircraft forward in different manners. The effect is the same whether generated by a propeller moving a large amount of air backwards slowly, or a jet engine moving a small amount of air backwards rapidly. “Thrust” in gliding flight: A glider must always keep a slight nose-down attitude to maintain forward motion and keep enough air over the wings to maintain lift. This forward motion is generated by the forward component of the weight, which comes from the aircraft assuming a nose-down attitude. If the nose of the glider is raised above the horizon, airspeed will drop off and the wing will not generate sufficient lift to counteract weight. Pay attention, can never provide trust as it is perpendicular to direction of flight!

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 Parasite drag increases as speed increases Interference drag: Drag created by two parts of the aircraft that create eddies where they intersect (such as the struts and wings) Streamlining: technique of designing an object to minimize air resistance and therefore the drag it generates Eliminate parts of airplane that cause drag – wing struts replaced by cantilever, retractable landing gear Skin friction reduced by removal of dust, dirt, mud or ice collected on airplane Interference drag reduced in aircraft design

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 Induced drag can only be reduced during design process High aspect ratio produces less induced drag (long span, narrow chord) Wingtip vortices and turbulent layer over the wings are manifestations of induced drag

Review What do we call the point at which all weight acts through? How is thrust generally produced? What are the two types of drag? Centre of gravity Moving the air backwards to produce an opposite reaction forward Parasite drag Induced drag

Wing Tip Vortices Decreased pressure on top of wing causes air to flow inward Higher pressure on lower surface of wing causes air to flow outward and curl upward over wing tip Two airflows meet and causes eddies that create resistance on the wing

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 S Drag equation: D = ½ CD v2 ρ S The relation between lift and drag is obtained by dividing the coefficient of lift by the coefficient of drag CL/CD. The optimum ratio is obtained at 0degree angle of attack. At this angle the wing is generating maximum lift for minimum drag. Effect of temperature and density on performance The density of the air decreases as altitude and temperature increase. The density of the air is an important factor in the production of lift. The denser the air, the more lift is generated. This is why an aircraft departing a high-elevation airfield on a hot day requires more runway length to take off. The aircraft will experience a reduced rate of climb, a more rapid approach speed and longer landing roll-out as well. To take into account the effect of altitude, pressure and temperature, one calculates the density altitude to find an equivalent ICAO standard atmosphere altitude. That computed value is then compared with performance data provided by the aircraft manufacturer.

Lift and Drag Curves When the angle of attack increases, lift and drag increase as well Lift: As angle of attack increase, lift increases. Lift continues to increase until the critical angle of attack is reached. Once past the critical angle, lift decreases and the wing stalls. Two ways of increasing the lift. -increasing the angle of attack (to or below the stalling angle), which increase the CL term in the formulae by deepening the low pressure above the wing and the downward air deflection -increase speed which as a squared effect on lift production. By doubling the speed, lift gets four time stronger Drag: drag increases rapidly as angle of attack increases towards the critical angle of attack. Drag is at its highest at low speed (just before stalling) and at high speed passing through its minimum between those two extremes. Low speed drag is composed of mainly induced drag and pressure drag due to separation of the boundary layer which creates a vacuum behind the wing High speed drag is mainly composed of skin friction drag

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 is influenced in speed and direction by the airfoil shape Laminar layer: smooth and regular-flowing part of the boundary layer. It produces little friction drag but is very fragile to separation

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 Turbulent layer: thicker, more turbulent part of the boundary layer. Situated aft of the transition point. It produces way more friction drag but it is way more resistant to separation. This is why a golf ball uses holes provoking transition to keep its boundary layer attached as long as possible, preventing the growth of disastrous pressure drag Separation point: where the turbulent layer is no longer in contact with the wing surface. It stops following the wing camber, leaving behind it a huge vacuum which turns into pressure drag. This happens at high angles of attack As angle of attack increases, the transition point moves forward As speed increases, transition point moves forward Transition point

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 A couple generates a rotating force around a given axis (couples act around the centre of gravity.) · If weight is forward of lift, the couple created will rotate the aircraft’s nose downwards. · If lift is forward of weight, the couple will rotate the aircraft’s nose upwards. · If drag is above thrust, the couple will rotate the aircraft’s nose upwards. · If thrust is below drag, the couple will rotate the aircraft’s nose downwards.

Couples Weight ahead of Lift – Nose down

Couples Lift ahead of Weight – Nose up

Couples Thrust below Drag – Nose up

Couples Drag below Thrust – Nose down

Review What factors affect lift and drag? Explain the concept of couples. Angle of attack and airfoil shape Wing area Velocity Air density When two forces are opposite and parallel but acting through two different points Causes rotation around a particular axis

Design of the Wing

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 Wing is thick, allowing for a more robust structure and lower weight. Thickets part of the wing is at 25% of the chord. This profile creates more lift and drag. Suits slower aircraft Low camber, low drag, high speed, thin wing section. Suitable for race planes, fighters, interceptors, etc. Deep camber, high lift, low speed, thick wing section. Suitable for transports, freighters, bombers, etc. Deep camber, high lift, low speed, thin wing section. Suitable as above. Low lift, high drag, reflex trailing edge wing section. Very little movement of centre of pressure. Good stability. Symmetrical (cambered top and bottom) wing sections. Similar to above. GA(W)-1 airfoil, thicker for better structure and lower weight, good stall characteristics, camber is maintained farther rearward which increases lifting capability over more of the airfoil and decreases drag.

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 Thickest point is farther back to maintain laminar flow and control transition point, reducing drag Generate way less drag than a conventional airfoil but also less lift Suitable for high speed and high performance aircraft such as an F-18. Stall characteristics are usually more violent than with a conventional airfoil.

Planform Shape of wing from above Wing shapes: Rectangular Tapered (from wing root to wing tip) Elliptical Delta

Aspect Ratio Wing span divided by chord A high aspect ratio wing will generate more lift and less induced drag. For example, a wing with a span of 24 ft and a chord of 6 ft has an aspect ratio of 4, while a wing with a span of 36 ft and a chord of 4 ft will have an aspect ratio of 9, for an identical area of 144 square feet. High aspect ration wings are preferred for glider construction, where high lift and low drag are critical

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 Angle between the chord line of the wing and the longitudinal axis of the aircraft. Well situated wing improves in-flight visibility, take-off and landing characteristics and reduces drag in cruising flight Angle of Incidence Longitudinal Axis Longitudinal Axis

Wing Tip Design Designed to reduce wing tip vortices and induced drag Wing tip tanks Increase range, distribute weight across wing Wing tip plates Same shape as airfoil but larger Droop wing tips Winglets

Winglets Mounted vertically on the wingtips Small airfoil surfaces Break up the wingtip vortices which flow towards the upper surface of the wing

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 has a different angle of incidence than the wing tip, forcing one to stall first This allows for the pilot to have more control during a stall Wash-in: tip higher than root – tip stalls first Wash-out: tip lower than root – root stalls first – gives ailerons more control pre-stall

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 Resemble fences mounted vertically on the upper surface of the wing Control and direct the streams of air flowing off the upper surface of the wing: swept wings are located about two-thirds of the way out towards the wing tip and prevent the drifting of air toward the tip of the wing at high angles of attack straight wings control airflow in the flap area Normally located near the centre of the wing profile

Slats and Slots Slat Slot Extra airfoil on the leading edge of the wing, usually near wing tips At a high angle of attack, the low pressure on top of the wing pulls the slat forward At low angles of attack, the pressure pushes the slat back into the wing Allows for more airflow over the top of the wing to increase lift Passageway built into the leading edge of the wing Can be across entire length of wing or just in front of ailerons Increases airflow over the wing at high angles of attack Remains stationary Both increase lateral control

Slats and Slots

Review What is wash-in/wash-out and why would we have it on an airplane? What are wing fences? What’s the difference between a slat and a slot? Airfoil has a different angle of incidence at the tip than then root Used to cause one portion of the wing to stall first to ensure other portion of the wing has control before the whole wing stalls Fins attached to the top surface of the wing Slats move, slot is permanent

Spoilers and Divebrakes Spoilers and divebrakes are devices attached to the upper and lower surfaces of the wing respectively 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: -reduce lift -increase drag -consist of large movable metal plates on the upper surface of the wing of the 2-33A Glider which can be raised perpendicular to the airflow -destroy the lift generated by the wing, permitting the pilot to maintain a safe airspeed while increasing the rate of descent Dive brakes: (speed brakes) -large metal plates on the lower surface of the wing of the 2-33A, which can be lowered down into the airflow -increase drag, no effect on lift -generally on high performance aircraft -ensure optimal descent without requiring the engine to be throttled back to the point where this is a risk of shock cooling. Generate drag without changing the shape of the wing

Spoilers and Divebrakes

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 Increase the camber of the wing In some cases increase the lifting surface of the wing by moving back as well as down Increase performance on take-off and landing Permit a steeper angle of approach while limiting airspeed Reduce stall speed Increase lift but also increase drag

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 Small plates about an inch in height, placed standing on edge in a row, spanwise along the leading edge of the wing. Fixed at a certain angle of attack, and when the wing moves through the air they generate vortices. Prevent or delay the separation of the boundary layer by reenergizing it. Suction Method: Series of thin slots in the wing running out from the wing root towards the tip. A vacuum sucks the air down through the slots, preventing the airflow from breaking away from the wing and forcing it to follow the curvature of the wing surface. The air sucked in siphons out through the ducts inside the wing and is exhausted backwards to provide extra thrust.

Vortex Generators

Review What do flaps do? What do spoilers and divebrakes allow the pilot to do? What do vortex generators do? Flaps increase camber of the wing to increase lift and provide better performance Increase descent rate without increasing speed Re-energizes airflow to create more lift and ensure higher performance

More Review What is camber? What are the four forces acting on an aircraft? What is equilibrium and when would an aircraft be in equilibrium? What is the centre of pressure and how does it move when the angle of attack is increased? The curvature of the wing Lift, drag, weight, thrust When two forces are equal and opposite When not in acceleration in any direction; straight and level flight Imaginary point where all lift acts through Moves forward as angle of attack increases

Summary Today we have covered: Parts of the aircraft Forces of the aircraft How lift is created Boundary layer Next class we will continue Theory of Flight