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  1. 1. 8.4 FLIGHT STABILITY AND DYNAMICS www.part66.blogspot.com
  2. 2. AXES OF AN AIRCRAFTAircraft is completely free to move in any directionManoeuvre  dive, climb, turn and roll, or perform combinations of these.Whenever an aircraft changes its attitude in flight, it must turn about one or all of these axes.Axes – imaginary lines passing through the centre of the aircraft. AXES ON AIRCRAFT
  4. 4. Longitudinal Axiso Lengthwise from nose to tail through center of gravityo Rotation about this axis is called rollo Rolling is produced by movement of ailerons AXES OF AN AIRCRAFT
  5. 5. Lateral Axiso Spanwise from wingtip to wingtip through center of gravityo Rotation about this axis is called pitch (nose up or nose down)o Pitching is produced by movement of the elevators AXES OF AN AIRCRAFT
  6. 6. Normal or Vertical Axiso Passes from top to bottom of the aircraft through center of gravityo Right angle to longitudinal and lateral axiso Rotation about this axis is called yawo Yawing is produced by movement of the rudder AXES OF AN AIRCRAFT
  7. 7. STABILITYo Aircraft characteristic to fly (hands off) in a straight and level flight patho To maintain a uniform flight path and recover from the various upsetting forces, such as, local air gusts or air density changes that cause deflections from the intended flight patho Aircraft ability to return to original position after being disturbed from its flight patho Changes are corrected automatically relieving the pilot from the task of correcting these deviations STABILITY
  8. 8. Longitudinal Stability Stability about lateral axis  motion in pitch Longitudinally stable aircraft does not tend to put its nose down and dive or lift its nose and stall The aircraft has a tendency to keep a constant angle of attack Longitudinal Stability maintained by the horizontal stabilizer By correcting nose up or down moment will return the aircraft to level flight. STABILITY
  9. 9. Lateral Stability Stability about longitudinal axis  rolling motion Laterally stable aircraft tend to return to the original attitude from rolling motion Lateral stability is maintained by the wing (design) a. Dihedral – the upward inclination of the wings from their point of attachment b. Sweepback – wing leading edges are inclined backwards from their points of attachment STABILITY
  10. 10. Lateral StabilityDihedral Sweepback STABILITY
  11. 11. Directional Stability Stability about the vertical axis Directionally stable aircraft tends to remain on its course in straight and level flight Directional stability is maintained by keel surface of the vertical stabilizer Sweptback wings also aid in directional stability (frontal area) STABILITY
  12. 12. Directional Stability STABILITY
  13. 13. Types of stability and motionStability Axes Motion about the AxisLongitudinal Lateral PitchLateral Longitudinal RollDirectional Normal Yaw
  14. 14. CONTROL IN FLIGHTDifferent control surfaces used to provide aircraft control about each of the three axesMovement of the control surface will change the airflow over the aircraft’s surface  disturbed the balanced forcesAircraft controls are designed to be instinctive CONTROL IN FLIGHT
  15. 15. Control surfaces movement
  16. 16. Lateral Control Controlling the aircraft about its longitudinal axis (rolling motion) Provided by the ailerons Rolling motion – produce by increasing lift on one wing and reduce lift on the opposite wing Ailerons – Hinged to the trailing edge towards the wingtips and form part of a wing – Operated from the cockpit by mean of a control wheel or control stick or joystick CONTROL IN FLIGHT
  17. 17. Lateral Control Sideways movement of the pilot’s control stick will cause the aileron on one wing to move upwards and, simultaneously, the aileron on the other wing to move downwards The unequal wing lift on each side of the aircraft produces a roll CONTROL IN FLIGHT
  18. 18. Lateral Control For aircraft to roll  one aileron deflected upward and one downward Lowered aileron – lift increase + drag also increase (aileron drag or adverse yaw) The increased drag tries to turn the aircraft in the direction opposite to that desired Frise aileron or differential ailerons travel system used to overcome the problem of aileron drag CONTROL IN FLIGHT
  19. 19. Aileron Drag/Adverse YawDifferential ailerons travel Frise aileron CONTROL IN FLIGHT
  20. 20. Longitudinal Control Controlling the aircraft about the lateral axis (pitching motion) Provided by elevators Elevators are hinged to the trailing edge of the horizontal stabilizer Pitching motion – Forward control column  elevators moves down giving the tailplane a positive camber thereby increasing its lift on the tail  nose pitch down (dive) – Backward control column  elevators moves up giving the tailplane a reverse camber, producing negative lift on the tail  nose pitch up (climb) CONTROL IN FLIGHT
  21. 21. Longitudinal Control CONTROL IN FLIGHT
  22. 22. Directional Control Involves rotation about the normal axis (yawing motion) Controlled by rudder which is hinged to the trailing edge of the vertical stabilizer (Fin) Movement of rudder is by a pair of rudder pedals located in the cockpit Yawing motion – Yaw to the left move the left pedal forward, rudder is moved to the left and the nose will turn to the left about normal axis. – The opposite effect is obtained from the forward movement of the pilot’s right foot. CONTROL IN FLIGHT
  23. 23. Directional Control
  24. 24. FLIGHT CONTROL SURFACESMovable airfoils designed to change the attitude of the aircraft about its three axes during flightDivided into three groups:- i. primary group ii. secondary group iii. auxiliary group FLIGHT CONTROL SURFACES
  25. 25. Primary Groupi. Ailerons hinged horizontally at the outboard trailing edge of each wingii. Elevators hinged horizontally at the rear of each horizontal stabiliseriii. Rudder hinged vertically at the rear of the vertical stabiliser The ailerons and elevators are operated from the cockpit by a control stick or by a control wheel or by a joy stick. The rudder is operated by foot pedals. FLIGHT CONTROL SURFACES
  26. 26. Secondary GroupTabs – small auxiliary control surfaces hinged at the trailing edge of a main flying control surfacesVarious types of tab and fitted for various reasons i. Trim tab ii. Balance tab iii. Servo tab iv. Spring tab FLIGHT CONTROL SURFACES
  27. 27. Trim Tabs System To trim out any unbalanced condition exist during flight, without applying any pressure on the primary controls Each trim tab is hinged to its parent primary control surface, but is operated by an independent control Trim Tab can be sub divided into two types: i. Fixed trim tabs – Only adjustable on ground before flight ii. Controllable trim tabs – Can be controlled in flight by pilots (control by mechanical linkage or electric motor) FLIGHT CONTROL SURFACES
  28. 28. Trim Tabs SystemFixed trim tab Controllable trim tab FLIGHT CONTROL SURFACES
  29. 29. Trim Control Trim tab(aileron, rudder, elevator) can be controlled manually or electrically Manual – control knob or wheel located on the centre console Electrical – by a thumb switch located on the control column for aileron and elevator  rudder trim switch located on the centre console adjacent to the rudder trim wheel During operation, the tabs will always moved in the opposite direction from the primary control surfaces FLIGHT CONTROL SURFACES
  30. 30. Elevator TrimRudder TrimAileron Trim FLIGHT CONTROL SURFACES
  31. 31. Manual Control• To lower the right wing of the airplane and raise the left, the aileron tab control wheel is moved to the right and the reverse direction is used to lower the left wing.• To trim the nose up, the elevator tab control wheel is moved rearward, and to lower the nose, the wheel is moved forward.• To yaw to the left, the rudder tab control wheel is moved to the left and to yaw to the right, the control wheel is moved to the right. FLIGHT CONTROL SURFACES
  32. 32. Electrical Trim Controls• Electrically operated systems are controlled by switches located at the top of the control column.• These switches are moved forward or aft, to move the elevator tab and moving the switch to the left or right will move the aileron tab.. FLIGHT CONTROL SURFACES
  33. 33. Aileron Trim Controls FLIGHT CONTROL SURFACES
  34. 34. Elevator Trim Controls FLIGHT CONTROL SURFACES
  35. 35. Rudder Trim Controls FLIGHT CONTROL SURFACES
  36. 36. Balance Tabs System• Assist pilot in moving the control surface (reduce pilot’s effort  large control surface)• Control rod cause the tab to move in the opposite direction to the movement of the primary control surface  aerodynamic forces acting on the tab, assist in moving the main control surface FLIGHT CONTROL SURFACES
  37. 37. Servo Tabs System• Help in moving large primary control surfaces (similar to balance tab but differs in operation)• Pilot input from the cockpit moves the tab, and the tab in turn develops forces which move the primary control surface• A movement of the tab down will cause theFLIGHT CONTROL SURFACES control surface to move
  38. 38. Spring Tabs System At high speed , the control surfaces become increasingly difficult to move due to aerodynamic loads The spring tab helps to overcome this problem At low speed the spring tab remains in a neutral position, inline with the control surface. Only at high speed, where the aerodynamic load is great, the tab functions as an aid in moving the primary control surface. FLIGHT CONTROL SURFACES
  39. 39. Auxiliary Group This group of flight control surfaces include:- i. wing flaps ii. spoilers iii. speed brakes iv. leading edge flaps v. slots and slats May be divided into two sub-groups; Those whose primary purpose is lift augmenting e.g. flaps, slots and slats those whose primary purpose is lift decreasing e.g. speed brakes and spoilers FLIGHT CONTROL SURFACES
  40. 40. FlapsHigh lift device hinged on the inboard trailing edge of the wingControlled from the cockpit, and when not in use fits smoothly into the lower surface of each wingFlaps increases the camber of a wing and therefore the lift of the wing, making it possible for the speed of the aircraft to be decreased without stallingFlaps are primarily used during take-off and landing FLIGHT CONTROL SURFACES
  42. 42. Plain flaps• Retracted to form a complete section of the wing trailing edge• When in use it is hinged downwards FLIGHT CONTROL SURFACES [Auxiliary Group]
  43. 43. Split flap • This flap is hinged at the lower part of the wing trailing edge. • When lowered, the wing top surface is unchanged, thus eliminating the airflow break-away like what occurring over the top of the plain flap when loweringFLIGHT CONTROL SURFACES [Auxiliary Group]
  44. 44. Zap Flap • Similar to the split flap except that the flap hinge travels rearward when lowered • Increases wing effective area as well as its camber without changing the shape of the top surface • Like the split flap there is little risk of flow separation on top of the wingFLIGHT CONTROL SURFACES [Auxiliary Group]
  45. 45. Fowler Flap • The fowler is similar to the split flap but, when in use, it is moved rearwards and downwards on tracks. • This action will increase the wing camber and also the wing area to give additional lift.FLIGHT CONTROL SURFACES [Auxiliary Group]
  46. 46. Slotted Flap • A gap or slot formed between the flap and the wing structure • Air will flow from the wing lower surface, through the gap and over the top of the flap • This airflow will maintain lift by speeding up as it passes through the slot and remaining in contact with the flat top surface, even at large flap angles • Without the slot the upper surface airflow would break awayFLIGHT CONTROL SURFACES [Auxiliary Group]
  47. 47. Slotted FlapFLIGHT CONTROL SURFACES [Auxiliary Group]
  48. 48. Slotted Fowler Flap • A Fowler flap with slot • Multi-slotted on improved design • Increase camber and area • The breakaway of the airflow from the flap upper surface can be delayed until even greater angles of flap depression by providing two or more slotsFLIGHT CONTROL SURFACES [Auxiliary Group]
  49. 49. Slotted Fowler FlapFLIGHT CONTROL SURFACES [Auxiliary Group]
  50. 50. Leading edge flap • Referred as Krueger’s Flap • To increase lift at low speed • Increase camber  increase lift • Leading and trailing edge flaps are normally coupled to operate together • May be lowered automatically when the aircraft’s speed falls to near the stalling speedFLIGHT CONTROL SURFACES [Auxiliary Group]
  51. 51. Slats • For low speed operation other than take-off or landing • A small, highly-cambered airfoils fitted to the wing leading edges • May be fixed open, or controlled to operate alone or jointly with the flaps • Some aircraft have slats which open automatically when the wing angle of attack exceeds a predetermined valueFLIGHT CONTROL SURFACES [Auxiliary Group]
  52. 52. SlatsFLIGHT CONTROL SURFACES [Auxiliary Group]
  53. 53. Slot • Is a series of suitably shaped apertures built into the wing structure near the wing tips • It increase the stalling angle by guiding and accelerating air from below the wing and discharging it over the upper surface in the normal wayFLIGHT CONTROL SURFACES [Auxiliary Group]
  54. 54. Airbrakes/Speed brakes • Movable panels forming part of the contour of the wings or fuselage • Deflected into the airflow by hydraulic actuators to give a rapid reduction in speed when is required. • Used to control speed during descent and landing approach • Installed on the strongest airframe structure able to accept the braking loads and also where the braking drag does not effect the aircraft stabilityFLIGHT CONTROL SURFACES [Auxiliary Group]
  55. 55. Spoilers • Are plates fitted to the upper surface of the wing and usually deflected upward by hydraulic actuators • The purpose is to disturb the smooth airflow across the top of the wing, thereby increasing drag and decreased lift on that aircraftFLIGHT CONTROL SURFACES [Auxiliary Group]
  56. 56. DUAL PURPOSE CONTROLS The design of some aircraft makes it impossible to mount the conventional aileron, elevator and rudder control surfaces in their normal positions. An example of this is a delta wing type aircraft. This has no separate tailplane, and the elevators have to be mounted on the wing trailing edges. This presents a space problem because the wings already house the ailerons and flaps. The solution in this case is to use one set of control surfaces to perform the function of both. DUAL PURPOSE CONTROLS
  58. 58. Elevonso Use to perform the function of both elevators and aileronso The surfaces are moved in the same direction to serve as elevators and in opposite directions to DUAL PURPOSE CONTROLS
  59. 59. Ruddervatorso Prevent hot exhaust gases from the turbo-jet engine playing on the tail unit surfaces, and for other design considerations, some light aircraft have tailplanes with very pronounced dihedral angleso ‘V’ tailplane with its hinged aft control surfaces provides DUAL PURPOSE CONTROLS
  60. 60. Taileronso On some high speed aircraft it is often necessary to have flaps which occupy the entire trailing edges of the wings, leaving no space for the ailerons.o Controllable tailplane move separately.o Pitch  angling both sides either up, or down, togethero Roll  angling one side up and, simultaneously, th e other side down DUAL PURPOSE CONTROLS