THEORY OF FLIGHT - TOPICS • The Sections of an Airplane • • • • • • • • Control Surfaces Aerofoils Definitions The Four Forces of Flight The Three Axes of Flight Stability Stalls, Spins, Spiral Dives, Load Factor Pitot/Static System THE AIRPLANE Aeroplane: 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. Aircraft: Any machine capable of deriving support in the atmosphere from reactions with the air. An aeroplane is an aircraft, but an aircraft is not always an aeroplane. Other Aircraft: Airship, Helicopter, Balloon, Glider, Ultralight. PARTS OF AN AIRPLANE The essential components of an airplane are: •The fuselage or body •The wings or lifting surfaces •The Empennage (tail) or canard •The propulsion system, ie. Engines •The undercarriage or landing gear PARTS OF AN AIRPLANE PARTS OF AN AIRPLANE The Fuselage •Central body •Accommodates crew, passengers and cargo •Part which the other components attach to Construction Types •Truss Type • • Longerons, N girders, warren trusses for a frame Fabric, metal or composite materials for the covering. •Monocoque • • Stringers, formers, bulkheads for carrying the loads. Stressed skin to carry some of the loads too. •Semi-monocoque • When stiffeners are provided to carry some of the load. PARTS OF AN AIRPLANE The Empennage •Horizontal stabilizer •Elevator •Fin •Rudder Unconventional Parts • Canard • Stabilator PARTS OF AN AIRPLANE Wings Configurations: •Monoplane •Biplane Positioning •High Wing •Mid Wing •Low Wing Internal Construction •Spars •Ribs •Compression Struts •Drag / Anti-drag Wires External Construction •Ailerons •Flaps •Struts •Engine Cowl Definitions Wing Span: Maximum distance from wing tip to wing tip. Leading Edge: Front edge of the wing. Trailing Edge: Rear edge of the wing. Chord: An imaginary straight line joining the leading edge and trailing edge PARTS OF AN AIRPLANE Aerofoil Designs There are many different types of designs, each for a specific purpose. Basically an aircraft designed for slow speeds will have a thick wing. A thin wing is best for high speeds. A wide but narrow wing is best for gliders. PARTS OF AN AIRPLANE Types of Aerofoils Conventional: thick for better structure and lower weight for better stall characteristics. The thickest part is at 25% chord. Laminar flow: usually thin. Originally designed to fly faster. The leading edge is more pointed and its lower and upper surfaces are nearly symmetrical. The thickest part is at 50% chord. PARTS OF AN AIRPLANE Aspect Ratio = Wing Span Average Chord PARTS OF AN AIRPLANE Landing Gear Function: •Absorb shock of landing •Support the weight of the aircraft •Enable aircraft to move around on the ground Types •Fixed •Retractable Configuration •Tricycle •Tail dragger PARTS OF AN AIRPLANE Propulsion system General aviation aircraft today use a gasoline powered, air cooled, internal combustion engine which drives a 2 or 3 bladed propeller. QUESTIONS? The Airplane Parts of the Airplane Fuselage Empennage Wings Propulsion system Landing gear How do we classify a 2 wing aircraft? What do we call the configuration of landing gear which has three wheels, 2 under the wings and one under the nose? What is the chord line? What is the wing span? THE FOUR FORCES The four forces: 1.Lift 2.Weight 3.Thrust 4.Drag THE FOUR FORCES Chord Line: Straight line running from the leading edge to the trailing edge of the wing. Angle of Attack: The angle formed between the chord line and the relative airflow. Camber: The curvature of the upper or lower surface of the wing. THE FOUR FORCES Relative Airflow: the direction in which the air is moving relative to the chord of the wing. The flight path and relative airflow are always parallel but opposite. Center of Pressure: the point on the wing where all lift acts through. THE FOUR FORCES Laminar Airflow: The smooth streamlined airflow over the wing. Turbulent Airflow: Airflow over the wing which is no longer smooth, but has become chaotic. Transition Point: The point where the laminar airflow changes to turbulent airflow. Boundary Layer: the very thin layer of air that stick to the wings due to skin friction. This layer of air consists of the laminar and turbulent airflow. Separation Point: the point at which the boundary layer pulls away from the wing. Mean Chord: the average chord of the wing. THE FOUR FORCES Angle of Incidence: the angle at which the wing is permanently inclined to the longitudinal axis. Wash in/Wash out: Wings that are slightly twisted, causing the wing root to have a higher angle of attack. The wing root will stall first. Spoilers/Dive brakes: devices fitted into the wing to increase drag and decrease lift. Spoilers are on top, dive brakes are on the bottom. THE FOUR FORCES Wing Fences: fin like surfaces on the upper part of the wing to control airflow, providing better slow speed handling and stall characteristics. Slats: auxiliary aerofoils fitted to the leading edge of the wing to improve lateral control. Slats pull out from wing at high angles off attack. Pushes the turbulent airflow further back. Slots: are air passage ways built into the wing on the leading edge. At high angles of attack the air flows through the holes and smoothing out the turbulent airflow. PARTS OF AN AIRPLANE Slots Slats THE FOUR FORCES Lift The upward force which sustains the aircraft in flight. Lift acts through the center of pressure, perpendicular to the relative wind or flight path, regardless of the angle of attack. THE FOUR FORCES Newton’s Three Laws of Motion: 1.An object when in motion tends to remain in motion. 2.An external force must be applied to alter the state of motion. 3.For every action there is an equal but opposite reaction. THE FOUR FORCES Bernoulli’s Principle: The total energy in any system remains constant. If one element increases, the other element must decrease to counterbalance it. Air flowing over the upper surface of a wing will accelerate to catch up to the air flowing under the wing. As the air speeds up, the pressure will decrease. On the bottom of the wing the pressure will increase. The differential in pressure between the upper and lower surfaces of the wing is what causes the upward force, known as lift. THE FOUR FORCES Downwash: the flow of air downward towards the trailing edge of the wing. The airflow passing under the wing is deflected downward by the bottom surface of the wing. The wing receives an upward force, therefore downwash contributes to lift. THE FOUR FORCES Bernoulli’s Principle THE FOUR FORCES Bernoulli vs. Newton Bernoulli: The total energy in a system remains constant. As air velocity increases, pressure decreases. Newton: For every action there is an equal and opposite reaction. THE FOUR FORCES Weight The downward force due to gravity, directly opposed to lift. Weight acts through the center of gravity. THE FOUR FORCES Thrust The force produced by the propeller. Air is pushed backwards, causing thrust in the opposite direction. Thrust can be moving a large mass of air backwards at a slow speed, such as a propeller, or a small mass of air backward at a high speed, such as with a turbine engine. THE FOUR FORCES Drag The resistance of forward motion. For an aircraft to maintain steady flight there needs to be enough lift to overcome weight and enough thrust to overcome drag. THE FOUR FORCES Drag Total aircraft drag Parasite drag Induced drag Interference drag Profile drag Form drag Skin friction THE FOUR FORCES Total Drag: the resistance the aircraft experiences when moving through the air. There are 2 major types of drag. Induced Drag: Drag caused by the parts of the aircraft which contribute to lift. Parasite Drag: Drag caused by the parts of the aircraft which do not contribute to lift. Parasite Drag can be broken down into 2 types of drag. THE FOUR FORCES Induced Drag: The higher pressure on the lower surface of the wing will cause the air to flow outwards (high pressure wants to push away) The lower pressure on the upper surface will cause the air to flow inwards (lower pressure wants to gather together) Nature needs balance: higher pressure air will flow to areas of low pressure to equalize. Airflow moving outwards from the bottom of the wing will curl up over the wingtip. This drag is commonly called wing tip vortices. THE FOUR FORCES THE FOUR FORCES Interference Drag: A parasite drag. Drag caused by the joining of two or more parts. Solution: Streamline parts. Profile Drag: A parasite drag which is further broken down into 2 types. Form Drag: A profile drag which is drag caused by the shape of the aircraft. Skin Friction: A profile drag caused by the tendency of air flowing over a surface to stick to it. THE FOUR FORCES Parasite drag INCREASES with velocity. Induced drag DECREASES with velocity. THE FOUR FORCES Reducing Parasite Drag: Form: •Streamlining •Reduce frontal area of a/c (ie. Radial engines) •Retractable landing gear Skin Friction: •Clean aircraft •Wax •Flush rivets Interference Drag •Landing gear fairings •Streamlined design (rounded fuselage) THE FOUR FORCES Reducing Induced Drag •High aspect ratio wings (ratio of the span to the mean chord) Aspect ratio = induced drag •Winglets •Ground effect THE FOUR FORCES Equilibrium When two forces are equal but opposite. A Steady state of motion. Couples When two forces are equal and opposite, but parallel. A couple will cause a turning motion about an axis. THE FOUR FORCES Lift and Weight When lift and weight are equal, but opposite, the aircraft will be in a state of equilibrium. Lift > Weight will cause the aircraft to climb. Lift<Weight will cause the aircraft to descend. Thrust and Drag When equal but opposite, they will be in a state of equilibrium. Thrust>Drag will cause the aircraft to accelerate. Thrust<Drag will cause the aircraft to decelerate. THE FOUR FORCES Weight and Lift If weight is ahead of lift, the couple will cause the nose to turn down. If lift is ahead of weight, the couple will cause the nose to turn up. Thrust and Drag If drag is above thrust, the nose will turn up. If thrust is above drag, the nose will turn down. THE THREE AXES THE THREE AXES Axis (About) Movement Control Surface Control Input Longitudinal Roll Ailerons Stick/Control Column (left/right) Lateral Pitch Elevator Stick/Control Column (aft/forward) Normal (Vertical) Yaw Rudder Rudder Pedals THE THREE AXES Longitudinal Axis: The imaginary line which runs from the nose to the tail. Movement ABOUT this axis is known as ROLL and is produced and controlled by the AILERONS. Movement OF this axis is known as PITCH and is produced and controlled by the ELEVATOR. THE THREE AXES Lateral Axis: An imaginary line running from wing tip to wing tip. Movement ABOUT this axis is known as PITCH and is produced and controlled by the ELEVATOR. Movement OF this axis is known as ROLL and is produced and controlled by the AILERONS. THE THREE AXES Vertical or Normal Axis: An imaginary line running vertically through the center of gravity. Movement ABOUT this axis is known as YAW and is CONTROLLED by the RUDDER. MOVEMENTS AND ATTITUDES Movements are related to the aircraft. Attitudes are related to the horizon. Movements are produced and controlled to achieve an attitude. MOVEMENTS Roll: movement about the longitudinal axis. Achieved through the lateral movement of the control column. When the column is moved left the left aileron will move up, while the right aileron will move down. The up-going aileron will cause a lower angle of attack, and therefore less lift. The down-going aileron will create a larger angle of attack, and therefor more lift. The aircraft will roll to the upgoing aileron. Aileron Drag: in rolling the wings, the down-going aileron increases the lift on the outside wing, increasing induced drag. The result is a slight turn in the opposite direction. MOVEMENTS Roll MOVEMENTS Pitch: movement about the lateral axis. Achieved through the aft/forward movement of the control column. When the column is moved aft the elevator will move up, causing the tail to be pushed down and the nose pushed up. The opposite holds true if the column is moved forward. MOVEMENTS Pitch MOVEMENTS Yaw: movement about the normal/vertical axis. Controlled through the movement of the rudder. We do NOT produce yaw, we just control yaw! MOVEMENTS Yaw LEFT TURNING TENDENCIES Adverse Yaw/Aileron Drag: In a roll the aircraft has a tendency to initially roll in the opposite direction of the turn. The downgoing aileron has an increased camber, causing more induced drag. The airplane skids outward on the turn. Controlled by applying rudder in the direction of the turn. LEFT TURNING TENDENCIES Asymmetric Thrust: At high angles of attack, the down-going propeller blade meets the relative airflow at a higher angle of attack, creating more lift on the right side, therefore the aircraft will yaw to the left. Corrected by the application of right rudder. Propellers turn clockwise from the view of the pilot. LEFT TURNING TENDENCIES Asymmetric Thrust LEFT TURNING TENDENCIES Gyroscopic Procession: A propeller acts like a gyro. Any force applied to a spinning gyro will act 90 degrees to the direction of the rotation. Raising the aircraft tail will apply a force to the top of the propeller arc, resulting in the force applied to the right of the arc, causing a yaw to the left. LEFT TURNING TENDENCIES Gyroscopic Procession LEFT TURNING TENDENCIES Torque: As the propeller spins clockwise the result is the aircraft rotating counter-clockwise. LEFT TURNING TENDENCIES Slip stream: Airflow from the rotating propeller cork-screws around the aircraft hitting the fin on the left side pushing the tail right and nose left. ATTITUDES The rolling movement produced and controlled by the ailerons will achieve a BANKED ATTITUDE. The pitching movement produced and controlled by the elevator will achieve a PITCH ATTITUDE. STABILITY The tendency of an aircraft in flight to remain in its trimmed attitude and return to this attitude if disturbed without help from the pilot. Static Stability: The INITIAL tendency of the aircraft to return. Dynamic Stability: The OVERALL tendency of the aircraft to return. STABILITY Types of Stability Positive: Tendency of aircraft to return to equilibrium. Neutral: New equilibrium reached at any point of displacement. (Doesn’t return to original position) Negative: Tendency to continue in direction of displacement. STABILITY Longitudinal Stability: Stability AROUND the lateral axis – PITCH stability Longitudinal Stable: Tend to return to its trimmed Angle of Attack Longitudinal Unstable: Tendency to climb or dive STABILITY Factors Influencing Longitudinal Stability: •Horizontal Stabilizer • • The larger the size the more stable the aircraft. Being positioned at the far end of the lever arm cause a more stable aircraft. •Center of Gravity • • • Loading within the Center of Gravity will be stable Too far forward will cause more of a tail down force and therefore a greater apparent weight, and a higher stalling speed. Could lead to the inability to pull out of a dive. The nose would be too heavy and the take-off distance would be longer. Too far aft will be more dangerous than too far forward. Very unstable in pitch regardless of speed. Elevators may be ineffective in stall and spin recoveries. STABILITY Lateral Stability: Stability AROUND the longitudinal axis – ROLL Stability Lateral Stability is achieved through •Dihedral •Keel Effect •Sweepback STABILITY Dihedral The angle that each wing makes with the horizontal. A displaced wing will drop, and the resulting unbalanced force will cause a sideslip, which will put the lower wing at a higher angle of attack. The lower wing will then produce more lift and the wings will return back level. STABILITY Keel Effect Most high wing aircraft are laterally stable because of their position of the wings to the body. The weight is therefore low. When the airplane is disturbed and one wing is low, the low weight will act like a pendulum and the aircraft will return to its original position. STABILITY Sweepback A sweptback wing is one which has a rearward sloping leading edge. When a disturbance causes a slip or a dropped wing, the lower wing will have more of its leading edge presented to the relative airflow, resulting in that wing being pushed back to its original position. STABILITY Directional Stability: Stability AROUND the normal or vertical axis. Stability is achieved through the fin and rudder. An airplane has the tendency to fly head on into wind, like a weather vein. If the airplane yaws away from its course, the airflow will strike the side of the fin or rudder from the side and for it back to its original position. CLIMBING The ability to climb is dependant upon the ability to produce thrust. Lift always acts perpendicular to the relative airflow. Therefore the vertical component of lift must increase to balance the vertical component of thrust. CLIMBING Best Rate of Climb The rate of climb which will gain the most altitude in the least time. This climb is normally used on take-off. Best Angle of Climb The angle that will gain the most altitude in the least distance. Climb used when climbing over obstacles. Normal Climb The rate of climb which should be used for any prolonged cruise climb. GLIDING In gliding there is NO power from the engine and the aircraft is under influence of gravity. Of the four forces thrust is now absent and a state of equilibrium must be maintained by lift, drag and weight only. GLIDING Best Glide Speed for Range The speed at which the aircraft will glide the furthest distance for altitude lost. Best Glide Speed for Endurance The speed at which an aircraft will glide the greatest amount of time for altitude lost. TURNS TURNS The force of lift acts 90º to the wing span. In a turn this force of lift is inclined away from the vertical. Therefore the vertical forces are no longer in a state of equilibrium. The airplane will descend unless the angle of attack is increased to produce more lift. TURNS In a turn the lift force has two components. •Vertical: opposes weight (lift) •Horizontal: makes the airplane turn. This horizontal force is known as Centripetal force (toward the turn) TURNS Steeper the angle of bank: •The greater the rate of turn •The less the radius of turn •The higher the stalling speed; and •The greater the loading Higher airspeed in a turn: •Slower rate of turn; and •Larger radius of turn STALLS A stall is the result of the inability of a wing to produce lift to counteract the weight of the aircraft. A smooth laminar airflow is needed to produce lift. The stall occurs where the angle of attack is increased up to the point where the laminar flow is unable to follow the curvature of the upper surface. STALLS The airflow separates from the wing, becoming turbulent, resulting in a loss of lift. As the angle of attack increases, the center of pressure moves forward on the wing until the CRITICAL ANGLE OF ATTACK is reached. At this point the C of P moves abruptly backwards on the wing, which is now stalled. STALLS Factors Affecting the Stall Weight: greater weight = higher angle of attack = higher stalling speed. C of G: forward C of G = higher angle of attack = higher stalling speed Turbulence: higher stalling speed because an upward vertical gust could cause the aircraft to exceed its critical angle Turns: an increase in bank = increased load factor = higher stalling speed Flaps: increases lifting potential = lower stalling speed Aircraft Condition: contaminated wings will increase drag = higher stalling speed STALLS An aircraft will stall if the critical angle of attack is exceeded. It will stall at any airspeed if the critical angle of attack is exceeded. It will stall at any attitude if the critical angle of attack is exceeded. It will stall at the same indicated airspeed regardless of altitude. SPINNING The auto-rotation developed after an aggravated stall. If a stalled plane drops a wing, or if rudder is applied to produce yaw, the down-going wing will have a greater angle of attack to the relative airflow, will receive less lift and drop more rapidly. Drag on the down-going wing increases sharply, increasing the AoA on this wing, stalling it further and further. The nose drops and auto-rotation sets in. SPINNING SPIRAL DIVE A spiral dive is a very steep descending turn where the aircraft is in an excessively nose down attitude and at an excessively increasing rate of descent. Characterized by •Excessive angle of bank •Rapidly increasing airspeed •Rapidly increasing rate of descent SPIRAL DIVES VS. SPINS A spiral dive resembles a spin, but it is extremely important the recognize the difference between them. In a spin the airspeed is constant and low (at or near the stall speed) In a spiral dive the airspeed is increasing rapidly. LOAD FACTOR Dead Load: the weight of the aircraft standing on the ground. Live Load: the change in dead load due to acceleration or turns. Load Factor: the ratio of the actual load acting on the wings to the gross weight of the aircraft. Live load divided by the dead load. LOAD FACTOR Why are load factors important? •A Dangerous overload is possible •An increase in load factor will result in an increase in the stalling speed LOAD FACTORS We express load factors in ‘G’s. •When on the ground or in straight and level unaccelerated flight, you are said to be under the force of 1G or one time the force of gravity. •As the angle of bank increases, so does the load factor. •In a banked attitude of 60 = 2G's. PITOT/STATIC SYSTEM Pitot Tube: Measures dynamic and static pressures and is positioned to be clear of the slipstream and facing the line of flight. Airspeed Indicator is the only instrument connected to the pitot. Static port: Measures static pressure and is vented to allow air pressure inside the instrument case to equalize with the outside air pressure. ASI, ALT and VSI use static pressure. ALTIMETER Measures the pressure in the atmosphere, which is the weight of the air above you at any given altitude. This weight will change as the aircraft climbs or descends causing the altimeter to register a change in pressure. The altimeter is made of a stack of aneroid capsules each set at standard sea level. As the altitude changes these capsules expand and contract, moving gears and thus the hands on the altimeter face. ALTIMETER ERRORS Pressure: the atmospheric pressure changes when flying from place to place. If not corrected, the altimeter would be inaccurate. Temperature: the altimeter is constructed to work on the values of the ICAO standard atmosphere. The temperature is not always this value. Mountain Effect: when flying near mountains, winds can be gusty and cause a drop in local pressure. Consequently, the altimeter will not give an accurate altitude indication. AIRSPEED INDICATOR Tells the pilot how fast they are travelling through the air and not over the ground. Measures the difference between pressures in the pitot and static ports. The reading on the ASI is referred to as the IAS. TAS is the CAS corrected for ASI error due to density and pressure. AIRSPEED INDICATOR The instrument is made up of an aneroid capsule which measures the pitot pressure. The interior of the case is sealed and the static pressure is measured there. The changes in dynamic pressure (pitot) cause the aneroid capsule to expand and contract. This movement is transmitted to a connected linkage that moves the hand on the ASI. AIRSPEED INDICATOR ERRORS Density: Atmospheric density varies and as a result this will change the accuracy of the ASI. Position: Eddies that form as air passes over the wing are responsible for the error. Lag: The slowness of the working parts. Icing: Ice formation blocking either the pitot or static tube could give inaccurate readings. Water: Water could block the tubes causing inaccurate readings. VERTICAL SPEED INDICATOR Indicates the rate of climb and descent and is measured in feet per minute. Measures the change in pressure between the capsule and the case of the instrument. The capsule will expand and contract which is transmitted by a linkage to the hands on the VSI. The instrument tends to lag 6 – 9 seconds. MAGNETIC COMPASS Consists of two north-seeking magnets, which are attached to a float, which is also attached to a compass card. This complete magnet system is mounted on a pivot and is free to rotate. The whole assembly is mounted within the compass bowl, which is filled with alcohol to reduce the weight of the compass card and the magnets. The lubber line indicates the direction the aircraft is heading and is in line with or parallel to the longitudinal axis of the aircraft. GYROSCOPES A gyroscope is a rotor or a spinning wheel, rotating at a high speed in a universal mounting, called a gimbal, so its axis can be pointed in any direction. Gyroscopic Inertia: the tendency of a rotating body to maintain its plane of motion. Precession: the tendency of a rotating body, when a force is applied perpendicular to its plane of rotation, to turn in the direction of its rotation 90 degrees to its axis and take up a new plane of rotation parallel to the force applied. GYRO INSTRUMENTS Heading Indicator: An instrument designed to indicate the heading of the airplane, and because it is steady and accurate, to enable the pilot to steer that heading with the least effort. GYRO INSTRUMENTS Attitude Indicator: Provides the pilot with an artificial horizon as a means of reference when the natural horizon cannot be seen because of cloud, fog, rain or other obstructions to visibility. It shows the pilot the relationship between the wings and nose of the plane and the horizon of the earth. GYRO INSTRUMENTS Turn and Bank Indicator: Aircraft indicates the direction of the turn. Ball indicates slipping or skidding. If the ball is opposite to the direction of turn you are in a skidding turn. With the ball and aircraft to the same side, the turn is slipping. A ball centered in a turn indicates a coordinated turn.