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# PRINCIPLES OF FLIGHT

PRINCIPLES OF FLIGHT. DEFINITIONS. Mass :- Mass is the quantity of matter in a body Density :- Density is the mass per unit volume. Pressure :- Pressure is the force per unit area. (Units:- lbs / sq inch).

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## PRINCIPLES OF FLIGHT

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1. PRINCIPLES OF FLIGHT

2. DEFINITIONS

3. Mass:- Mass is the quantity of matter in a body Density :- Density is the mass per unit volume. Pressure :- Pressure is the force per unit area. (Units:- lbs / sq inch)

4. Momentum :- The quantity of motion in a body is known as momentum of the body and is equal to the product of mass and velocity (M = m x v) Motion :- When a body changes its position in relation to its surroundings. Speed :- Speed is the rate of change of position.

5. Velocity :- Velocity is the speed in a particular direction. Velocity is a vector quantity having both magnitude and direction. Acceleration :- Acceleration is the rate of change of velocity.

6. Work :- Work is said to be done on a body when a force acting on it physically moves the point of application in the direction of the force. Work done = Force x Distance moved in the direction of force (Units : Foot Pounds) • Power :- Power is the rate of doing work. (One horse power is equals to 550 lbs/sec)

7. Energy :- Energy is the capacity to do the work. Energy can exist in many forms i.e heat, light, electrical, sound, chemical, atomic, pressure, mechanical etc... • Potential Energy :- Due to the position of a body above ground level. Potential Energy (PE) = Mgh • Kinetic Energy :- Due to the motion in the body. Kinetic Energy (KE) = ½ mv²

8. Couple :- A couple consists of two equal, opposite and parallel forces not acting through the same point. • Equilibrium :- A body is said to be in equilibrium when (a) Algebraic sum of all the forces acting on the body is zero. (b) Clockwise moment is equal to the anticlockwise moment about any point.

9. Boyles’ Law :- The volume of a given mass of a perfect gas is inversely proportional to the pressure, provided the temperature remains constant. p x v = constant (temp unchanged) • Charles’ Law :- The volume of a perfect gas increases by 1/273 of its value at 0°C for every degree C rise in temperature, provided the pressure remains constant.

10. Laws Of Motion

11. Newton’s First Law Of Motion :- A body which is in a state of rest or of its uniform motion will continue to be in the same state unless an external force is applied upon it. This property of all bodies is called inertia and a body in such a state is said to be in equilibrium.

12. Newton’s Second Law Of Motion :- The rate of change of momentum of a body is directly proportional to the applied force and takes place in the direction of the application of the said force. • Newton’s Third Law Of Motion :- To every action, there is an equal and opposite reaction.

13. GLOSSARY OF TERMS

14. Aerofoil :- A body is designed to produce more lift than drag. A typical aerofoil section which is cambered on top surface and is more or less straight at bottom surface.

15. Chord Line :- It is a line joining the centre of curvature of leading and trailing edges of an aerofoil section. Chord Length :- It is the length of chord line intercepted between the leading and trailing edges.

16. Angle Of Attack :- It is the angle between the chord line and the relative airflow undisturbed by the presence of aerofoil. Angle Of Incidence :- The angle between the chord line and the longitudinal axis of the aircraft.

17. Angle of Incidence :- The angle between the chord line and the longitudinal axis of the aircraft. Total Reaction :- It is a single force representing all the pressures ( force per unit area ) over the surface of the aerofoil. It acts through the centre of pressure which is situated on the chord line.

18. Lift :- The vertical component of total reaction resolved at right angles to the relative air flow. Drag :- The horizontal component of the total reaction acting parallel and in the same direction as the relative airflow.

19. ATMOSPHERE

20. Introduction:- • The word Atmosphere is derived from the Greek ‘Atoms’ means ‘vapour’ and ‘phere’ means ‘sphere’. • Atmosphere means the gaseous sphere surrounding the earth.

21. Composition:- • Air is a mixture of number of gases consisting of :- Nitrogen - 78.03 % Oxygen - 20.99 % Argon - 00.94 % CO2 and other gases - 00.04 %

22. Apart from the above gases air also contains some impurities like dust and salt particles. Water vapour and traces of other gases are also present.

23. Divisions Of Atmosphere :- • The atmosphere is divided in four main regions :- • Tropo Sphere • Strato Sphere • Iono Sphere • Exo Sphere

24. Tropo Sphere :- It extends from the surface to a height of about 9 km near the poles and 17 km near the equator. Tropo pause:- Tropo pause is the dividing line between Tropo Sphere and Strato Sphere.

25. Strato Sphere :- It extends from the Tropopause upto a height of about 3 km. Iono Sphere :- Above Stratosphere, it extends upto a height of 24 km. Exo Sphere :- It extends from Ionosphere upto a height of 1126.5 km.

26. Temperature:- • The temperature of earth’s surface depends almost entirely upon the heat received from the sun. As a rule, temperature decreases with height. The hotter the earth’s surface becomes, more readily it radiates its heat back again to space. • Heat is transferred by three methods i.e. (i) Conduction (ii) Convection and (iii) Radiation • The instrument used for measuring temperature is called thermometer and the units of measure is either “Fahrenheit” or “Centigrade” in degrees.

27. Variation of Temp with Height:- • In the atmosphere the temperature as a rule decreases with height. • Lapse rate :- The decrease of temperature with height is known as “Lapse” and the rate of decrease is known as “Lapse Rate”.

28. Air Density :- • The density of air is defined as the mass of the air contained in unit volume and is measured in “grams per cubic meter”. • Presence of water vapour in the atmosphere decreases the air density. Also the air density decreases if pressure decreases or its temperature increases.

29. Variation of Density :- • Variation of air density at the surface :- At the surface, variations of air density are due to temperature variations. When temperature is maximum, air density is minimum and vice-versa. • Variation of density with height :- Air density decreases with height mainly due to the effect of the pressure. The decrease in air density with height due to fall in pressure is much more than the increase in air density due to fall in temperature with height.

30. BERNAULI’s THEOREM & VENTURI EFFECT

31. Bernauli’s Theorem :- In the early days of the Industrial revolution, Daniel Bernauli, an Italian physicist, discovered certain properties relating to fluids in motion, which he summarized as follows:- The total energy in a moving fluid is the total sum of three forms of energy i.e. Potential, Kinetic and Pressure Energy. In a stream line flow of an ideal fluid, the sum of all these three energies remains constant.

32. Venturi Tube :- • A tube which has inlet portion gradually narrowing then a throat or neck followed by an out let which widens gradually is called a venturi tube or convergent / divergent duct.

33. Venturi Tube :-

34. Venturi effect and Bernauli’s Theorem :- • In the previous chapter, we have seen that for a flow of air to remain streamlined, the volume passing at a given point in unit time’ must remain constant. • If a venturi tube is placed in such an air stream, then the mass flow in the venturi tube must also remain constant and streamlined. • In order to achieve this and still pass through the restricted section of the venturi, and accompanying pressure drop is a natural consequence according to Bernauli’s theorem.

35. Therefore when a wing moves through the air, the pressure on the upper surface is less than atmospheric and more than atmospheric on the bottom surface. This pressure difference existing between the top and bottom surface, is the main lifting force of a flying aircraft.

36. Venturi Effect :- • When a stream line air flow is passing through a venturi tube the mass flow remains constant at all points in the tube. • Since the cross sectional area at throat is less, to maintain the constant air flow either the air should get compressed or it should speed up.

37. It almost behaves like an incompressible fluid and therefore speeds up. Its kinetic energy is increased and therefore according to Bernauli’s theorem the pressure energy drops. This phenomenon is called Venturi Effect.

38. FORCES ACTING ON AIRCRAFT

39. Introduction :- An aircraft is considered to be in straight and level flight when it is flying at a constant altitude and speed, maintaining lateral level and direction.

40. Forces Acting on Aircraft :- • Weight • Lift • Thrust • Drag

41. Direction of Flight • Lift • Thrust • CP • Drag • CG • Weight

42. Weight :- Weight of the aircraft acting vertically downwards through C.G Lift :- Lift acting vertically upwards through C.P Thrust :- Thrust acting horizontally forward along the propeller shaft. Drag :- Drag acting horizontally backwards along the line of total drag of the aircraft.

43. Forces acting on straight and level flight :- • Weight :- Weight of the aircraft acting vertically downwards through C.G • Lift :- Lift acting vertically upwards through C.P • Thrust :- Thrust acting horizontally forward along the propeller shaft. • Drag :- Drag acting horizontally backwards along the line of total drag of the aircraft.

44. Equilibrium :- • In a straight and level flight, the following conditions must be satisfied for equilibrium. • (a) Algebraic sum of forces acting horizontally = 0 • (b) Algebraic sum of forces acting vertically = 0 • It follows that L = W and T = D.

45. At any instant, the weight of an aircraft is a certain quantity and the aircraft is flown at such an angle of attack and air speed that it produces lift equal to weight. Under these conditions, the aircraft has certain amount of drag which is counteracted by the pilot adjusting his engine controls so that T = D • The position of CG is always kept ahead of the CP so that if the engine cuts, the aircraft assumes a gliding attitude without difficulty.

46. GLIDE

47. Glide :- Glide is that condition of flight in which the aircraft is losing height without power at a constant speed maintaining lateral level and direction. Gliding Angle :- Gliding angle is the angle between earth’s horizon and the path of the aircraft.

48. Forces Acting On Glide :- • The forces acting on an aircraft in a glide are • Weight • Lift • Drag

49. Weight :- Weight acting vertically down wards. Lift :- Lift acting at right angles to the glide path. Drag :- Drag acting backwards along the glide path.

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