11. Theory Of Flight PDF - UniKL Malaysian Institute of Aviation Technology

11. THEORY OF FLIGHT 8 December 2021  LEARNING OUTCOMES On completion of this topic you should be able to: Describe about theory of flight. 1. Relationship between lift, weight, thrust and drag. 2. Glide ratio. 3. Steady state flights, performance. Prepa...

11. THEORY OF FLIGHT 8 December 2021  LEARNING OUTCOMES On completion of this topic you should be able to: Describe about theory of flight. 1. Relationship between lift, weight, thrust and drag. 2. Glide ratio. 3. Steady state flights, performance. Prepared By: Wan Nur Shaqella Bte Wan 2 Abdul Razak  11.1 RELATIONSHIP BETWEEN LIFT, WEIGHT, THRUST AND DRAG Prepared By: Wan Nur Shaqella Bte Wan 3 Abdul Razak FORCES ACTING ON AIRCARFT Prepared By: Wan Nur Shaqella Bte Wan 4 Abdul Razak  FORCES ACTING ON AIRCARFT THRUST The aircraft’s propelling force LIFT Arranged symmetrically to the Acts at right angle to the line of centre line flight & through the Centre of Act parallel to the line of flight Pressure of the wings DRAG WEIGHT@ GRAVITY Opposes the forward motion Acts vertically downwards Regarded as a rearward through acting force the Centre of Gravity Prepared By: Wan Nur Shaqella Bte Wan 5 Abdul Razak  FORCES ACTING ON AIRCARFT An aircraft flying at constant height and speed LIFT = WEIGHT THRUST = DRAG Under these condition i. Angle of attack altered to adjust the production of lift exactly equals the weight which it must support ii. Engine thrust set to exactly equal the aircraft drag generated at that particular speed Prepared By: Wan Nur Shaqella Bte Wan 6 Abdul Razak  ARRANGEMENT OF FORCES Lift = Weight and Thrust = Drag § Aircraft tend to rotate nose up or nose down if the forces line of action not correctly arranged § Proper arrangement of the forces (depends on aircraft design) i. Centre of pressure aft of centre of gravity à nose down ii. Thrust line below drag line à nose up Prepared By: Wan Nur Shaqella Bte Wan 7 Abdul Razak  ARRANGEMENT OF FORCES The ideal arrangement of the four forces 1. The ideal arrangement is where the centre of gravity is forward of the centre of pressure (centre of lift) – which produces a nose down couple. 2. The thrust line is lower than the centre of drag, which produces a nose up couple. 3. Each couple opposing the other and cancelling each other out. Prepared By: Wan Nur Shaqella Bte Wan 8 Abdul Razak  ARRANGEMENT OF FORCES LIFT WEIGHT LIFT and WEIGHT = nose down couple Prepared By: Wan Nur Shaqella Bte Wan 9 Abdul Razak  ARRANGEMENT OF FORCES THRUST and DRAG = nose up couple DRAG THRUST Prepared By: Wan Nur Shaqella Bte Wan 10 Abdul Razak  ARRANGEMENT OF FORCES THRUST and DRAG = nose up couple LIFT DRAG THRUST WEIGHT LIFT and WEIGHT = nose down couple Prepared By: Wan Nur Shaqella Bte Wan 11 Abdul Razak  FOUR FORCES OF FLIGHT For aircraft to be flying in a Straight, Level and at Constant Speed. Weight Forces = Lift Drag = Thrust Lift act through the centre of pressure (CP) while weight through the centre of gravity (CG). Thrust and drag act in opposite directions parallel to the direction of flight. Prepared By: Wan Nur Shaqella Bte Wan 12 Abdul Razak 11.2 GLIDE RATIO Prepared By: Wan Nur Shaqella Bte Wan 13 Abdul Razak  GLIDE RATIO Condition aircraft with no thrust from engine. Glide ratio distance covered to high lost. Highest Lift/Drag ratio give maximun distance by flying with minimum drag. Prepared By: Wan Nur Shaqella Bte Wan 14 Abdul Razak Prepared By: Wan Nur Shaqella Bte Wan 15 Abdul Razak  Glide Ratios (Example)  AIRCRAFT GLIDE It is rare for powered aircraft need to glide, but it is possible to happens. During a glide, only 3 forces involved instead of 4. The forces are: 1. Weight 2. Lift 3. Drag One important thing for an aircraft to glide is aircraft C of G must be in front of C of P. Prepared By: Wan Nur Shaqella Bte Wan 17 Abdul Razak  THEORY OF TURN When the pilot wants to turn the aircraft, the first thing he needs to do is to roll the aircraft (banking). The lifting forces are now can be divided into 2 components. 1. Vertical Component 2. Horizontal Component The horizontal component will cause the aircraft to turn. Prepared By: Wan Nur Shaqella Bte Wan 18 Abdul Razak FORCES DURING NORMAL COORDINATED TURN Prepared By: Wan Nur Shaqella Bte Wan 19 Abdul Razak  When aircraft is banking, there are few effects that need to be consider: 1. Adverse Yaw 2. The lift produce by the wing has been divided into 2 therefore the lift to counteract the weight must be increase to prevent the aircraft from falling. 3. Load Factor Prepared By: Wan Nur Shaqella Bte Wan 20 Abdul Razak  ADVERSE YAW Adverse yaw is the natural and undesirable tendency for an aircraft to yaw in the opposite direction of a roll. It is caused by the difference in profile drag between the upward and downward deflected ailerons, the difference in lift and thus induced drag between left and right wings, as well as an opposite rotation of each wing's lift vector about the pitch axis due to the rolling trajectory of the aircraft. Prepared By: Wan Nur Shaqella Bte Wan 21 Abdul Razak  ADVERSE YAW To roll the aircraft 1 aileron must comes down (increased lift) and the other must comes up (decrease lift). This will create an adverse yaw, and must be corrected by applying rudder. Prepared By: Wan Nur Shaqella Bte Wan 22 Abdul Razak  MINIMIZING THE ADVERSE YAW THERE ARE A NUMBER OF DESIGN CHARACTERISTICS WHICH CAN BE USED TO REDUCED ADVERSE YAW: vAILERON TO RUDDER MIXING vLIFT COEFFICIENT vYAW STABILITY vDIFFERENTIAL AILERON DEFLECTION vFRISE AILERONS vROLL SPOILERS Prepared By: Wan Nur Shaqella Bte Wan 23 Abdul Razak  LOAD FACTOR The amount of stress (load factor) that an aircraft can withstand before structural damage or failure occurs is expressed as the aircraft’s limiting load factor. Primarily a function of aircraft design, an individual aircraft’s limiting load factor is published in the aircraft flight manual (or: pilot operating handbook) in terms of maximum positive or negative g. Limiting load factors of +3.5g to +3.8g and -1.5g to - 1.8g are quite common for various general aviation and transport category aircraft.  LOAD FACTOR 1. Load factor is the ratio of the maximum load an aircraft can sustain to the gross weight of the aircraft. With the a/c flying straight and level the Load Factor is one. With the aircraft in a banked turn the load factor is increased. Angle of Bank G Loading Load Factor 60o X2 X2 70o X3 X3 2. For an average 200 ton ( = 200 metric tonnes) airliner these figures are respectively 400 tons/tonnes and 600 tons/tonnes. Prepared By: Wan Nur Shaqella Bte Wan 25 Abdul Razak  LOAD FACTOR qWith the structural design of aircraft planned to withstand only a certain amount of overload, a knowledge of load factors has become essential for all pilots. Load factors are important for two reasons: Ø It is possible for a pilot to impose a dangerous overload on the aircraft structures. Ø An increased load factor increases the stalling speed and makes stalls possible at seemingly safe flight speeds. Prepared By: Wan Nur Shaqella Bte Wan 26 Abdul Razak  LOAD FACTOR IN AIRCARFT DESIGN q Aircraft designed under the category system are readily identified by a placard in the flight deck, which states the operational category (or categories) in which the aircraft is certificated. q The maximum safe load factors (limit load factors) specified for aircraft in the various categories are: 1 For aircraft with gross weight of more than 4,000 pounds, the limit load factor is reduced. To the limit loads given above, a safety factor of 50 percent is added. Prepared By: Wan Nur Shaqella Bte Wan 27 Abdul Razak  Category Limit Load Factor Normal1 3.8 to – 1.52 Utility (mild 4.4 to – 1.76 acrobatics, including spins) Acrobatic 6.0 to – 3.00 Note: 1For aircraft with gross weight of more than 4,000 pounds, the limit load factor is reduced. To the limit loads given above, a safety factor of 50 percent is added. Prepared By: Wan Nur Shaqella Bte Wan 28 Abdul Razak Source : http://en.wikipedia.org/wiki/Load_factor_(aeronautics) Prepared By: Wan Nur Shaqella Bte Wan 29 Abdul Razak  LOAD FACTOR  STALL SPEED Stall is a condition where the lift generated by the aircraft’s wings no longer supports its weight. The higher load factor in constant-altitude turns caused by the centrifugal force will also increase the stall speed. An increased stall speed means that the aircraft stalls earlier, i.e. at a higher speed. Stalls that occur with g-forces on an aircraft are called ’accelerated stalls’.  STALL SPEED In fact, the stall speed increases in proportion to the square root of the load factor. To counteract the increase in aircraft load you need to increase the lift produce by wing. To increase lift you can do 2 things: 1. Increase Angle of Attack 2. Increase Aircraft Speed Example: If an aircraft has a stalling speed of 55 knots at 1g, then it will stall at twice that speed (i.e. at 110 knots) when the load factor becomes 4g, which corresponds to a bank angle of 77°. Prepared By: Wan Nur Shaqella Bte Wan 32 Abdul Razak  There is a limit to increase Angle of Attack normally around 15 degrees. To increase the lift further is by increasing aircraft speed. The minimum speed needed to create enough lift to counteract the aircraft load at maximum angle of attack is called STALL SPEED. Therefore an increase in aircraft load will increase its Stall Speed. Prepared By: Wan Nur Shaqella Bte Wan 33 Abdul Razak  Source : http://en.wikipedia.org/wiki/Load_factor_(aeronautics) Prepared By: Wan Nur Shaqella Bte Wan 34 Abdul Razak  FLIGHT ENVELOPE Flight envelope describe aerodynamic and structural limitation of aircraft. Pilot fly the aircraft based on the envelope. Prepared By: Wan Nur Shaqella Bte Wan 35 Abdul Razak FLIGHT ENVOLOPE AND STRUCTURAL LIMITATION It will describe the boundaries of altitude and airspeed within which normal flight manoeuvring can be safely conducted. Normally aircraft Flight Envelope can be found in the Aircraft Flight Manual. Prepared By: Wan Nur Shaqella Bte Wan 36 Abdul Razak PIEL EMERAUDE FLIGHT ENVELOPE Prepared By: Wan Nur Shaqella Bte Wan 37 Abdul Razak Prepared By: Wan Nur Shaqella Bte Wan 38 Abdul Razak  FLIGHT ENVELOPE The aircraft’s flight is limited to a regime of airspeeds and load factor which do not exceed the limit (redline) speed (225 mph), do not exceed the limit load factor (4.4 G), and cannot exceed the maximum lift capability. The aircraft must be operated within this “envelope” to prevent structural damage and ensure the anticipated service lift of the aircraft is obtained. Any maneuver and/or gust outside the structural envelope can cause structural damage and effectively shorten the service life of the aircraft. Prepared By: Wan Nur Shaqella Bte Wan 39 Abdul Razak  11.3 STEADY STATE FLIGHTS, PERFORMANCE Prepared By: Wan Nur Shaqella Bte Wan 40 Abdul Razak  Airplane controls, movement, axes of rotation, and type of stability Prepared By: Wan Nur Shaqella Bte Wan 41 Abdul Razak 737 CONTROL SURFACES Prepared By: Wan Nur Shaqella Bte Wan 42 Abdul Razak  THE BANKED TURN 1. For the a/c to carry out a turn it must produce a force towards the centre of the turn (centripetal force). 2. When the a/c banks the lift force is placed at an angle (when viewed from the front or rear) by the pilot moving the control column to one side moving the ailerons. 3. The force of a banking turn manoeuvre can be divided into its component: a) Lift Component – Must be equal and opposite to weight if the aircraft is to not lose or gain height. b) Centripetal Component – to be equal and opposite to the centrifugal force created by the aircraft, and to provide the force required to “pull” the aircraft around the corner. 4. If the centripetal force is larger than the aircraft will go into a tighter turn, if is smaller the radius of turn will get greater. Prepared By: Wan Nur Shaqella Bte Wan 43 Abdul Razak  THE BANKED TURN What are the control surfaces involved in a banking turn maneuver? Prepared By: Wan Nur Shaqella Bte Wan 44 Abdul Razak  THE CLIMB When the a/c climbs all the force vectors move with the a/c. Prepared By: Wan Nur Shaqella Bte Wan 45 Abdul Razak  CHANGE IN LIFT DURING CLIMB ENTRY During the transition from straight-and-level flight to a climb, a change in lift occurs when back elevator pressure is first applied. Raising the aircraft’s nose increases the AOA and momentarily increases the lift. Lift at this moment is now greater than weight and starts the aircraft climbing. After the flight path is stabilized on the upward incline, the AOA and lift again revert to about the level flight values. Prepared By: Wan Nur Shaqella Bte Wan 46 Abdul Razak FORCE ACTING DURING THE CLIMB CHANGE IN LIFT DURING CLIMB ENTRY Prepared By: Wan Nur Shaqella Bte Wan 48 Abdul Razak  CHANGE IN SPEED DURING CLIMB ENTRY If the climb is entered with no change in power setting, the airspeed gradually diminishes because the thrust required to maintain a given airspeed in level flight is insufficient to maintain the same airspeed in a climb. When the flight path is inclined upward, a component of the aircraft’s weight acts in the same direction as, and parallel to, the total drag of the aircraft, thereby increasing the total effective drag. Consequently, the total drag is greater than the power, and the airspeed decreases. The reduction in airspeed gradually results in a corresponding decrease in drag until the total drag (including the component of weight acting in the same direction) equals the thrust. Due to momentum, the change in airspeed is gradual, varying considerably with differences in aircraft size, weight, total drag, and other factors. Consequently, the total drag is greater than the thrust, and the airspeed decreases. Prepared By: Wan Nur Shaqella Bte Wan 49 Abdul Razak CHANGE IN SPEED DURING CLIMB ENTRY Prepared By: Wan Nur Shaqella Bte Wan 50 Abdul Razak LIFT AND DRAG AUGMENTATION DEVICES Prepared By: Wan Nur Shaqella Bte Wan Abdul Razak 51  LIFT AUGMENTATION ØDuring aircraft take off and landing, the lift produce by the wing is less, due to the aircraft low speed. ØNormally lift is increased for landing and take- off by the use of: Leading edge devices Trailing edge devices. Prepared By: Wan Nur Shaqella Bte Wan Abdul Razak 52  LEADING EDGE DEVICES The basis for leading edge devices is to cause an increase in velocity of the airflow over the top surface of the aerofoil. This increase in velocity results in the transition to turbulence being delayed and the transition point is caused to move back towards the trailing edge. The result is that an increase in angle of attack and hence an increase of lift coefficient. Prepared By: Wan Nur Shaqella Bte Wan Abdul Razak 53  SLOTS A leading edge slot is a fixed (non-closing) gap behind the wing’s leading edge. Prepared By: Wan Nur Shaqella Bte Wan Abdul Razak 54  Air from below the wing can accelerate through the slot towards the low pressure region above the wing, and exit from the slot moving parallel to the upper wing surface. Prepared By: Wan Nur Shaqella Bte Wan Abdul Razak 55  This high-speed flow then mixes with the boundary layer attached to the upper surface and delays boundary layer turbulance from the upper surface. Prepared By: Wan Nur Shaqella Bte Wan Abdul Razak 56  SLATS Slats are aerodynamics surfaces on the leading edge of the wings of fixed wing aircraft which, when deployed, allow the wing to operate at a higher angle of attack. Two types of slats 1. Fixed Slats 2. Movable Slats Prepared By: Wan Nur Shaqella Bte Wan Abdul Razak 57 Prepared By: Wan Nur Shaqella Bte Wan Abdul Razak 58  FIXED SLATS Prepared By: Wan Nur Shaqella Bte Wan Abdul Razak 59 Prepared By: Wan Nur Shaqella Bte Wan Abdul Razak 60  MOVEABLE SLATS They are usually used while landing or performing manoeuvres which take the aircraft close to the stall, but are usually retracted in normal flight to minimize drag. Prepared By: Wan Nur Shaqella Bte Wan Abdul Razak 61  LEADING EDGE FLAPS Another methods to increase the lift of a wing at low speeds is by using leading edge flaps. When the leading edge flaps are lowered, it increases the camber. 1. Krueger Flaps 2. Variable Camber Leading Edge Flaps 3. Droop Leading Edge Flaps Prepared By: Wan Nur Shaqella Bte Wan Abdul Razak 62  KRUEGER FLAP It is hinged forward to increase the camber of the wing, and also increases the wing area Prepared By: Wan Nur Shaqella Bte Wan Abdul Razak 63 Prepared By: Wan Nur Shaqella Bte Wan Abdul Razak 64 Prepared By: Wan Nur Shaqella Bte Wan Abdul Razak 65  Variable Camber Leading Edge Flaps A modified Krueger Flap is called Variable Camber Leading Edge Flap. It is made from flexible composite material. When extended, the actuating linkage causes the flaps to change its curve ( contour ). A slot is also formed so that it also can functions as a slat. Prepared By: Wan Nur Shaqella Bte Wan Abdul Razak 66 Prepared By: Wan Nur Shaqella Bte Wan Abdul Razak 67 DROOP LEADING EDGE Prepared By: Wan Nur Shaqella Bte Wan Abdul Razak 68 Prepared By: Wan Nur Shaqella Bte Wan Abdul Razak 69 Prepared By: Wan Nur Shaqella Bte Wan Abdul Razak 70  TRAILING EDGE DEVICES Normally the trailing edge devices used are the flaps. Flaps are designed to increase the lift of the wing and decrease the stall speed, therefore the aircraft can fly at reduced speed. This is possible by changing the shape of the wing. Prepared By: Wan Nur Shaqella Bte Wan Abdul Razak 71  TYPE OF FLAPS Also known as Camber Flap Simplest flap design Normally used on small aircraft Can increase lift up to 50% Prepared By: Wan Nur Shaqella Bte Wan Abdul Razak 72 Only the bottom camber is changed, the upper camber does not change. Can increase lift up to 60% Even more drag than plain flap. Prepared By: Wan Nur Shaqella Bte Wan Abdul Razak 73 Prepared By: Wan Nur Shaqella Bte Wan Abdul Razak 74 When the flap is lowered, a slot is formed. Delayed Stall. Can increase lift up to 65% Prepared By: Wan Nur Shaqella Bte Wan Abdul Razak 75 Prepared By: Wan Nur Shaqella Bte Wan Abdul Razak 76 Prepared By: Wan Nur Shaqella Bte Wan Abdul Razak 77 Increases camber and wing area. Complicated mechanism. Can increase lift up to 90%. One disadvantages is that, when deployed it will cause large rearward movement of C of P Prepared By: Wan Nur Shaqella Bte Wan Abdul Razak 78  Double Slotted Fowler Flap Best flaps for lift. Complicated mechanism Can increase lift up to 100% Prepared By: Wan Nur Shaqella Bte Wan Abdul Razak 79 Prepared By: Wan Nur Shaqella Bte Wan Abdul Razak 80 Prepared By: Wan Nur Shaqella Bte Wan Abdul Razak 81  DRAG AUGMENTATION Sometimes there is a need for aircraft to slow down quickly and reduce lift. Few methods to do this are by using 1. Spoilers 2. Lift Dumpers 3. Speed Brake Prepared By: Wan Nur Shaqella Bte Wan Abdul Razak 82  SPOILERS They are normally situated on top of the wing forward of the flaps. It is a flat panels hinged at the forward edge. When the spoilers are deployed, they rise up, reduce lift and increase drag. Prepared By: Wan Nur Shaqella Bte Wan Abdul Razak 83 Prepared By: Wan Nur Shaqella Bte Wan Abdul Razak 84  They may carry out more than one function but are generally classified as: 1. Flight Spoilers/Differential Spoilers 2. Speed Brake 3. Ground Spoilers/Lift Dumpers 4. Gust Alleviation Spoilers * For correct terms please refer aircraft manufacturer Prepared By: Wan Nur Shaqella Bte Wan Abdul Razak 85  Flight Spoilers Also known as Roll Spoilers, Differential Spoilers. It used to help the up going aileron by reducing lift and increase drag. When the up going aileron raise to a certain degree, the roll spoiler will start to go up. Prepared By: Wan Nur Shaqella Bte Wan Abdul Razak 86  Speed Brakes When the spoiler is used as speed-brakes, the spoilers on both wing are raised together. It is controlled by the pilot using the speed- brake lever in the cockpit. Prepared By: Wan Nur Shaqella Bte Wan Abdul Razak 87  Ground Spoilers Also known as lift dumpers. During aircraft touchdown, both the flight spoilers and ground spoilers on both wing will rise up to its maximum angle to reduce the lift on the wing and to ensure the aircraft weight is on the landing gear. The drag created by the spoilers also helps to slow down the aircraft. Prepared By: Wan Nur Shaqella Bte Wan Abdul Razak 88  Tail Cone Brake Tail cone brake is also used to slow down the aircraft during landing. Speed brakes may be used during the final approach to touchdown as well as after landing. Prepared By: Wan Nur Shaqella Bte Wan Abdul Razak 89 END OF LESSON Prepared By: Wan Nur Shaqella Bte Wan Abdul Razak 90