EASA PART-66 MODULE 8.2 : AERODYNAMICS
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EASA PART-66 MODULE 8.2 : AERODYNAMICS

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EASA PART-66 MODULE 8.2 : AERODYNAMICS EASA PART-66 MODULE 8.2 : AERODYNAMICS Presentation Transcript

  • 8.2 AERODYNAMICS www.part66.blogspot.com
  • Effect of Shapes on Streamlined Flow (a) Flat Plate 100% Resistance (b) Sphere 50% Resistance (c) Ovoid 15% Resistance (d) Streamlined 5% Resistance STREAMLINED
  • Boundary Layer Unaffected airflow Each layer experience retardation until some distance away from surface Next layer slowed down but not stop Airflow nearest the surface come to rest STREAMLINED
  • Boundary Layer STREAMLINED
  • Separation and turbulence at various AOA STALLING
  • AERODYNAMIC TERMStagnation pointVelocity = 0m/s Wing tip vortices
  • Airfoil Shape Symmetrical – no lift at zero angle of attack Asymmetrical – lift created even at small angle of attack AIRFOIL
  • Airfoil Shape• Medium and high speed aircraft – much less curvature  lift comes from their additional speed through the air.• Low speed aircraft – cambered  not for high speed (excess lift as well as drag) AIRFOIL
  • CAMBER (CURVE)• Camber  curvature of an aerofoil (wing) above and below the chord line Camber (curvature) of an aerofoil PRODUCTION OF LIFT
  • AIRFOIL @ AEROFOIL• Any surface which produces a reaction (lift) as air passes over it• The airfoil should provide this reaction (lift), whilst having a shape which presents the least possible resistance, or drag, to its passage through air AIRFOIL
  • T/C AND FINENESS RATIO Thicness/Chord ratio = CD AB
  • MEAN AERODYNAMIC CHORD• Average distance between leading and trailing edge of wing• Mean chord = Wing Area Wing Span
  • ANGLE OF ATTACK• The acute angle formed between the relative wind striking an airfoil and the chord line.• Increasing the angle from zero degree to a maximum (between 15 degrees and 18 degrees) will increase lift, but will also increases drag. CENTER OF PRESSURE
  • ANGLE OF INCIDENCEo Angle formed by the intersection of the wing chord line and the horizontal plane or longitudinal axis of aircrafto Positive Angle of Incidence (AOI) – leading edge higher than trailing edgeo Correct AOI  low drag + longitudinal stabilityo ‘Wash out’ – higher AOI at wing root than at wing tipo ‘Wash in’ – higher AOI at wing tip than at wing root ANGLE OF INCIDENCE
  • WASH IN AND OUT• Wash in : – Angle of incident increase from root to tip – Tip will stall 1st• Wash out : – Angle of incident decrease from root tip – Root will stall 1st
  • CENTER OF PRESSURE (c.p) The position whereby the resultant force (lift) cuts through chord line and considered to act Total Lift Shape of airfoil and angle of attack influence the c.p Position of lines denotes location and direction direction of lift Length of line denote magnitude of lift Direction of airflow Center of Pressure CENTER OF PRESSURE
  • CENTER OF PRESSURE (c.p)o Position of c.p varies during flight as the angle of attack (AOA) altered a. Increase AOA – c.p moves forward b. Decrease AOA – c.p moves backwardo In normal flight the AOA usually between 2˚ and 4˚ (seldom below 0˚ or above 16˚) Small AOA Medium AOA Large AOA Nose Heavy Balance OF PRESSURE CENTER Flight Tail Heavy
  • WING SHAPE
  • ASPECT RATIO• Ratio of aircraft wingspan to its mean chord length
  • PRODUCTION OF LIFT To keep flying  aircraft must produce a force equal to its own weight Greater force – to lift the aircraft from the ground Force (lift) is provided by the wing The production of lift is based on Bernoulli’s theory PRODUCTION OF LIFT
  • LiftWeight
  • Bernoulli’s theorem• Air velocity increase – the pressure decreases (and vice versa)• The total energy of a moving fluid is made up of three forms of energy:  Potential Energy – due to height or position  Kinetic Energy – due to motion  Pressure Energy – due to pressure• In a streamline flow of an ideal fluid, the sum of all those energy is constant Potential + Kinetic + Pressure = Constant PRODUCTION OF LIFT
  • Venturi Effect• A short circular tube with large opening at both the front and rear end + restrictor between the opening• Venturi is a convergent/divergent duct• Bernoulli’s Theory is being proven by passing a streamline flow of air through a venturi duct PRODUCTION OF LIFT
  • Venturi Effect PRODUCTION OF LIFT
  • Venturi Effect INLET CENTRE (THROAT) OUTLETAirspeed normal Airspeed maximum Airspeed decreasePressure normal Pressure minimum Pressure increase (equal to inlet area) PRODUCTION OF LIFT
  • Camber (Curved)• Airflow around the cambered wing behave exactly as airflow in a venturi tube PRODUCTION OF LIFT
  • Airflow on wing (Lift distribution) Increased Speed Provide 70% of the wing’s Total Lift Decreased Speed Decreased pressure 70% of Total Lift Increased pressure Providing 30% of the wing’s Total Lift Decreased Speed Increased Speed 30% of Total Lift PRODUCTION OF LIFT
  • STREAMLINED Streamline – shape or contour that presents a minimum resistance to the air A perfect streamlined form is similar to the top view of a fish Air flows around non-streamlined object  air swirls into eddies + streamline distorted  disappear Airstream becomes turbulent Streamline air appears as smooth parallel lines• Smoke jets – introduce smoke into air  to observe and illustrate movement of air around object STREAMLINED
  • Effect of Shapes on Streamlined Flow STREAMLINED
  • DRAGAs an aircraft passes through the air, the air offers a resistance to the passage.This resistance, is known as ‘Drag’. (Resistance to forward motion)The total amount of drag on an aircraft is made up of many types of drag forces. • Common type of drag:- i. Form drag ii. Parasite drag iii. Induced drag DRAG
  • DRAGRESISTANCE TO FORWARD MOTION DRAG
  • FORM DRAGCaused by the shape or form of the aircraft• Reducing form drag• Streamlining – aircraft shaped to produce least resistance to the airflow• For least resistance  object length between 3-4 times greater than maximum thickness• Fineness ratio – ratio between length and maximum thickness DRAG
  • PARASITE DRAG A combination of many different drag forces Any exposed object on an aircraft offers some resistance to the airflow, and the more objects in the airstream, the more parasite dragReducing parasite drag• reducing the number of exposed parts to as few as practical and streamlining their shape. DRAG
  • Streamlining• Fixed landing gear
  • SKIN FRICTION DRAGA type of parasite drag most difficult to reduceAir particles in contact with surface of the aircraftReducing skin frictionglossy flat finisheseliminating protruding rivet heads, roughness, and other irregularities. DRAG
  • INDUCED AND TOTAL DRAG• Lift created by the airfoil also created drag  induced drag• Just as lift increases with an increase in angle of attack, induced drag also increases as the angle of attack becomes greater. TOTAL DRAG DRAG
  • THRUST AND WEIGHT• Thrust is forward force produce by engine• Determine by size and type use in propulsion system• Weight is a mass of aircraft act vertically downward• Determined by size and material used in aircraft
  • FORCES ACTING ON AIRCRAFT IN THRUST FLIGHT• The aircraft’s propelling force LIFT• Arranged symmetrically to the Acts at right angle to the line ofcentre line flight & through the Centre of• Act parallel to the line of flight Pressure of the wings DRAG • Opposes the forward motion WEIGHT@ GRAVITY • Regarded as a rearward acting Acts vertically downwards through force the Centre of Gravity FORCES ACTING ON AIRCRAFT IN FLIGHT
  • LIFT AND DRAG COEFFICIENT• Theoritical value base on airfoil shape Lift = CL x 1/2ρv2 x S Drag = CD x 1/2ρv2 x S IDEAL ANGLE
  • POLAR CURVE• Drag Polar is the relationship between the lift and its drag interm on coefficeient
  • STALL ‘Sudden lost of lift’i. Increase AOA – separation moves forward (turbulent) – Insufficient pressure drop on upper surface  no pressure differential to create liftii. Increase to higher AOA – excessive turbulence – Drag increase higher than lift created Critical Angle of Attack – airflow separate + turbulence Critical AOA = 15˚ and above STALLING
  • AIRFOIL CONTAMINATION• Any contamination on wing will affect its performance• Need to provide method to remove the contamination during flying• Type of contamination : – Ice – Snow – Frost