EASA PART-66 MODULE 8.2 : AERODYNAMICS

8.2 AERODYNAMICS

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Effect of Shapes on Streamlined Flow

STREAMLINED

(a) Flat Plate 100% Resistance (b) Sphere 50% Resistance

(c) Ovoid 15% Resistance (d) Streamlined 5% Resistance

Boundary Layer

STREAMLINED

Airflow nearest the surface come to rest

Next layer slowed down but not stop

Each layer experience retardation until some distance away from surface

Unaffected airflow

Boundary Layer

STREAMLINED

Separation and turbulence at various AOA

STALLING

AERODYNAMIC TERM

Stagnation point Velocity = 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

PRODUCTION OF LIFT

Camber (curvature) of an aerofoil

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 AreaWing 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 aircraft

o Positive Angle of Incidence (AOI) – leading edge higher than trailing edge

o Correct AOI low drag + longitudinal stability

o ‘Wash out’ – higher AOI at wing root than at wing tip

o ‘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

Shape of airfoil and angle of attack influence the c.p location and direction

CENTER OF PRESSURE

Center of Pressure

Total Lift

Direction of airflow

Position of lines denotes direction of liftLength of line denote magnitude of lift

CENTER OF PRESSURE (c.p)o Position of c.p varies during flight as the angle of attack (AOA)

altereda. Increase AOA – c.p moves forwardb. Decrease AOA – c.p moves backward

o In normal flight the AOA usually between 2˚ and 4˚ (seldom below 0˚ or above 16˚)

CENTER OF PRESSURE

Small AOA Medium AOA Large AOA

Nose Heavy Balance 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

Weight

Lift

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

PRODUCTION OF LIFT

Airspeed normalPressure normal

Airspeed maximumPressure minimum

Airspeed decreasePressure increase(equal to inlet area)

INLET CENTRE (THROAT) OUTLET

Camber (Curved)

PRODUCTION OF LIFT

• Airflow around the cambered wing behave exactly as airflow in a venturi tube

Airflow on wing (Lift distribution)

PRODUCTION OF LIFT

Provide 70% of the wing’s Total Lift

Providing 30% of the wing’s Total Lift

Decreased pressure

Increased pressure

Decreased SpeedIncreased Speed30% of Total Lift

Increased SpeedDecreased Speed70% of Total 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 dragii. Parasite dragiii. Induced drag

DRAG

DRAG

DRAG

RESISTANCE TO FORWARD MOTION

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 drag

Reducing parasite drag• reducing the number of exposed parts to as few as

practical and streamlining their shape.

DRAG

Streamlining

• Fixed landing gear

SKIN FRICTION DRAGA type of parasite drag most difficult to reduceAir particles in contact with surface of the aircraftReducing skin frictionglossy flat finisheseliminating 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.

DRAG

TOTAL 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 FLIGHT

FORCES ACTING ON AIRCRAFT IN FLIGHT

LIFTActs at right angle to the line of flight & through the Centre of Pressure of the wings

THRUST• The aircraft’s propelling force• Arranged symmetrically to the centre line• Act parallel to the line of flight

DRAG• Opposes the forward motion• Regarded as a rearward acting

forceWEIGHT@ GRAVITYActs vertically downwards throughthe Centre of Gravity

LIFT AND DRAG COEFFICIENT

• Theoritical value base onairfoil shapeLift = 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 lift

ii. Increase to higher AOA – excessive turbulence– Drag increase higher than lift created

Critical Angle of Attack – airflow separate + turbulenceCritical 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