Lift 2008

Slide 1: 

FORCES ACTING ON AN AIRCRAFT IN FLIGHT

OBJECTIVES : 

OBJECTIVES STATE THE FORCES OF AN AIRCRAFT IN FLIGHT IDENTIFY THE METHODS USED TO GENERATE LIFT UNDERSTAND THE TERMINOLOGY USED TO DESCRIBE AN AEROFOIL

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FORCES ACTING ON AN AIRCRAFT IN FLIGHT FOUR FORCES: 1. LIFT 2. WEIGHT 3. THRUST 4. DRAG

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GENERATION OF LIFT

Slide 9: 

GENERATION OF LIFT LIFT IS THE KEY AERODYNAMIC FORCE LIFT OPPOSES THE AIRCRAFT WEIGHT (MASS) AND GRAVITY IN STRAIGHT AND LEVEL FLIGHT, WHEN THE LIFT IS EQUAL TO THE AIRCRAFT MASS, THE AIRCRAFT IS SAID TO BE IN A STATE OF EQUILIBRIUM.

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FACTORS AFFECTING LIFT LIFT IS ACHIEVED IN 3 BASIC WAYS 1. BERNOULLIS PRINCIPLE 2. NEWTONS THIRD LAW 3. COANDA EFFECT

BERNOULLIS PRINCIPLE : 

BERNOULLIS PRINCIPLE

Daniel Bernoulli1700-1782 : 

Daniel Bernoulli1700-1782

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THE TOTAL PRESSURE (ENERGY) OF THE AIR IN THE AIRFLOW REMAINS CONSTANT. TOTAL PRESSURE CONSISTS OF STATIC PRESSURE AND DYNAMIC BERNOULLIS THEOREM Ptotal = Pdyn + Pstatic A RIVER FLOWING THROUGH A NARROW BRIDGE AIRFLOW OVER AN AEROFOIL THIS CAN BE SHOWN WHEN A FLUID FLOWING THROUGH A NARROWING TUBE (VENTURI) SPEEDS UP AND CAUSES A DROP IN PRESSURE.

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PRESSURE AND VELOCITY CHANGES IN A VENTURI + - + - VELOCITY INDICATOR PRESSURE GAUGE

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THIS IS AFFECTED BY SEVERAL FACTORS THE AEROFOIL SHAPE IS THE PRINCIPLE FACTOR THE AEROFOIL IS DESIGNED TO SPLIT THE AIRFLOW INTO AREAS OF HIGHER PRESSURE BELOW THE AEROFOIL AND LOWER PRESSURE ABOVE THE AEROFOIL THE DIFFERENCE IN THESE TWO PRESSURES IS THE MAIN SOURCE OF LIFT GENERATION OF LIFT DURING FLIGHT THE PRESSURES ON THE UPPER AND LOWER AEROFOIL SURFACES ARE UNEQUAL

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AIRFLOW OVER AN AEROFOIL WHEN THE AIRFLOW SPLITS AT THE LEADING EDGE AND TRAVELS OVER THE TOP AND BOTTOM SURFACES IT MEETS AGAIN AT THE TRAILING EDGE IN THE SAME AMOUNT OF TIME. AS THE AEROFOILS UPPER SURFACE IS MORE CURVED, THE AIR FLOWING OVER IT HAS TO TRAVEL FURTHER THAN THE AIR FLOWING OVER THE LOWER SURFACE. THIS MEANS THAT THE UPPER SURFACE AIRFLOW TRAVELS QUICKER THAN THE LOWER SURFACE AIRFLOW. THIS INCREASE IN VELOCITY CAUSES A DECREASE IN PRESSURE

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INCREASED VELOCITY LOWER PRESSURE HIGHER PRESSURE

ANY QUESTIONS ? : 

ANY QUESTIONS ?

Slide 19: 

NEWTONS THIRD LAW OF MOTION

Sir Isaac Newton 1642 - 1727 : 

Sir Isaac Newton 1642 - 1727

Slide 21: 

NEWTONS THIRD LAW OF MOTION THE AEROFOIL LOWER SURFACE ALSO PRODUCES LIFT FOR EVERY ACTION THERE IS AN EQUAL AND OPPOSITE REACTION AIRFLOW THAT IS DIRECTED DOWNWARDS WILL PRODUCE AN UPWARDS OR LIFTING REACTION IF YOU PUT A HAND OUTSIDE OF A MOVING VEHILCE WINDOW PALM DOWN AND THEN TILT THE LEADING PART OF THE PALM UPWARDS INTO THE AIRFLOW, THE AIR WILL BE DEFLECTED DOWNWARDS AND THE REACTION WOULD BE TO MOVE THE HAND UPWARDS.

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THE COANDA EFFECT

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Henri Coanda 1886-1972

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THE COANDA EFFECT A FLUID JET TENDS TO ATTACH ITSELF TO A DOWNSTREAM SURFACE ROUGHLY PARALLEL TO THE JET AXIS IF THE DOWNSTREAM SURFACE CURVES DOWN, THIS JET WILL FOLLOW IT. THE REACTION TO THIS JET WILL BE AN UPWARD FORCE IN THE OPPOSITE DIRECTION SIMILAR TO NEWTONS THIRD LAW

Slide 26: 

LIFT LIFT IS ACHIEVED IN 3 BASIC WAYS 1. BERNOULLIS PRINCIPLE 2. NEWTONS THIRD LAW 3. COANDA EFFECT

ANY QUESTIONS ? : 

ANY QUESTIONS ?

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AEROFOIL TERMINOLOGY

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AEROFOIL TERMINOLOGY AN AEROFOIL IS ANY SURFACE SUCH AS A WING, ROTOR BLADE OR PROPELLER WHICH PRODUCES AN AERODYNAMIC FORCE WHEN IT IS PASSED THROUGH A STREAM OF AIR THE FOLLOWING TERMS ARE USED TO DESCRIBE PARTS OF THE AEROFOIL AND THE INTERACTION OF THE AIRFLOW ABOUT IT

Slide 30: 

LEADING EDGE THIS IS THE LEADING PART OF THE AEROFOIL WHICH FIRST MEEETS THE AIRFLOW - ITS SECTION IS NORMALLY CURVED TRAILING EDGE THIS IS THE TRAILING PART OF THE AEROFOIL WHERE THE UPPER AND LOWER AIRFLOWS MEET - ITS SECTION IS NORMALLY KNIFE-EDGED

Slide 31: 

CAMBER THIS IS THE CHARACTERISTIC CURVE OF THE AEROFOILS UPPER AND LOWER SURFACES. A POSITIVE CAMBER DESCRIBES A CONVEX SURFACE A NEGATIVE CAMBER DESCRIBES A CONCAVE SURFACE. LOW SPEED WINGS GENERALLY HAVE A LARGE POSITIVE CAMBER HIGH SPEED WINGS GENERALLY HAVE A SMALL POSITIVE CAMBER GIVING A MUCH SLIMMER AEROFOIL SHAPE

Slide 32: 

CHORD THIS IS AN IMAGINARY STRAIGHT LINE DRAWN FROM THE LEADING EDGE TO THE TRAILING EDGE. THE WING ROOT CHORD IS NORMALLY THE LARGEST THE WING TIP CHORD IS NORMALLY THE SMALLEST THE MEAN CHORD IS THE AVERAGE OF THESE MEASUREMENTS ON A SWEPT BACK WING THE MEAN AERODYNAMIC CHORD IS USED. THIS IS BASED ON PRODUCING AN IMAGINARY AVERAGE WING WHICH WILL BEHAVE LIKE THE ACTUAL WING

Slide 33: 

RELATIVE WIND / RELATIVE AIRFLOW THIS IS THE DIRECTION OF THE AIRFLOW WITH RESPECT TO THE WING THE RELATIVE WIND IS PARALLEL TO THE FLIGHTPATH BUT IN THE OPPOSITE DIRECTION IF A WING MOVES FORWARDS HORIZONTALLY THE RELATIVE WIND MOVES BACKWARDS HORIZONTALLY

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ANGLE OF ATTACK THIS IS DEFINED AS THE ANGLE OF THE AEROFOIL (THE CHORD LINE) IN RELATION TO THE RELATIVE WIND IN STRAIGHT AND LEVEL FLIGHT THE AEROFOIL PRODUCES ENOUGH LIFT TO BALANCE THE WEIGHT OF THE AIRCRAFT THE WIND DIRECTION IS MEASURED IN THE FREE AIR STREAM AWAY FROM ANY DISTURBANCES

Slide 35: 

ANGLE OF INCIDENCE THIS IS DEFINED AS THE ANGLE OF THE AEROFOIL (THE CHORD LINE) IN RELATION TO THE AIRCRAFTS LONGITUDINAL AXIS

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CENTRE OF PRESSURE THE POINT AT WHICH THE TOTAL LIFT FORCE ON AN AEROFOIL IS SAID TO ACT

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ANGLE OF ATTACK -4 0 4 8 12 16 20 AEROFOIL CROSS SECTION 0 0.2 0.4 0.6 0.8 1.0 LEADING EDGE AEROFOIL CENTRE OF PRESSURE CURVES

Slide 38: 

AEROFOIL TERMINOLOGY

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LIFT LIFT ACTS PERPENDICULAR TO THE RELATIVE WIND LIFT GENERALLY ACTS PERPENDICULAR TO THE AEROFOILS CHORD LINE LIFT IS GENERATED BY THE REDUCED PRESSURE CAUSED BY THE SMOOTH AIRFLOW ACCELERATING OVER THE UPPER AEROFOIL SURFACE LIFT CAN BE INCREASED BY: INCREASING THE AIRSPEED INCREASING THE ANGLE OF ATTACK (WITHIN LIMITS)

ANY QUESTIONS ? : 

ANY QUESTIONS ?

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COEFFICIENT OF LIFT

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COEFFICIENT OF LIFT THE COEFFICIENT OF LIFT CAN BE THOUGHT OF AS BEING A MEASURE OF THE LIFTING EFFECTIVNESS OF THE AEROFOIL IT DEPENDS ON THE AEROFOIL GEOMETRY AND ITS ANGLE OF ATTACK AS FLIGHT SPEED INCREASES THE COEFFICIENT OF LIFT DECREASES AS THE ANGLE OF ATTACK IS REDUCED IT VARIES WITH THE FLIGHT CONDITIONS BUT ITS VALUE CHANGES PRIMARILY WITH THE ANGLE OF ATTACK

ANY QUESTIONS ? : 

ANY QUESTIONS ?

OBJECTIVES : 

OBJECTIVES STATE THE FORCES OF AN AIRCRAFT IN FLIGHT IDENTIFY THE METHODS USED TO GENERATE LIFT UNDERSTAND THE TERMINOLOGY TO DESCRIBE AN AEROFOIL

Slide 45: 

WEIGHT