AMT 100 Physics. Chapter 5

Transcription

1 AMT 100 Physics Chapter 5

2 Physics Physics - the natural science that deals with matter and energy and the relationships between the two. Matter is anything that takes up space and has mass Mass - the quantity of matter in a body regardless of its volume or of any forces acting on it

3 Physics Weight - measure of the force of gravity on a body! Weight is proportional to mass Weight = Mass X Gravity! The moon has 1/6 th the gravity of earth On the moon, you would weigh 1/6 th your earth weight Your mass is the same on the earth as the moon

4 Atom The basic unit of a chemical element. Basic particles - protons, neutrons, and electrons Center of an atom is made up of protons and neutrons! Electrons orbit around the center of the atom Proton and neutrons around the same mass! Electron mass = about 1/1836 proton mass

5 Atom

6 Atom

7 Electric charge:! Neutron none Atom! Proton Positive +! Electron Negative - Compound - combination of elements that contains a specific number of atoms of each element! Molecule - the smallest particle of matter that can still remain the same substance (compound)! e.g. Water 2 hydrogen & 1 oxygen H 2 O

8 Molecule

9 States of Matter Gas - perfect molecular mobility and the property of indefinite expansion! Fills any confined space! Compressible Solid - structural rigidity and resists changes of shape or volume Liquid flows and resists compression! Conforms to container shape! Maintains volume

10 States of Matter Plasma - collection of charged particles that respond strongly and collectively to electromagnetic fields, taking the form of gaslike clouds or ion beams! Described as an "ionized gas"

11 States of Matter

12 States of Matter

13 Plasma

14 Density Density - measure of the amount of matter in a certain volume of material Specific gravity - the ratio of the density of a material to the density of pure water Specific Gravity = Weight of the subs tance Weight of an equal volume of water Specific Gravity = Density of the subs tance Density of water

15 Density

16 Specific Gravity

17 Specific Gravity

18 Specific Gravity

19 Specific Gravity

20 Force Force - causes a object to undergo a change in speed, a change in direction, or a change in shape! Cause an object to move up, down, back and forth, & sideways! Causes an object to speed up or slow down! Maintains a speed or position against an opposing force

21 Work Work - the amount of energy transferred by a force acting through a distance in the direction of the force! Work = Force X Distance A 500 pound box lifted 6 feet Work = 500 pound X 6 feet Work = 3000 foot-pounds

22 Energy The ability to do work! Something that changes, or tries to change, matter Types of energy:! Potential Energy in an object caused by its position, configuration, or chemical composition.! Kinetic Energy in an object caused by its motion.

23 Potential Energy

24 Conversion of Energy

25 Conversion of Energy Aircraft Engine! Energy source: Avgas Chemical potential energy (no conversion of mass)! Converted to: Rotation motion Light (inside cylinder) Heat transferred to engine! Thermal and friction! Air, oil and fuel cooled Heat in exhaust Increased exhaust velocity! Energy in = Energy out What goes in must come out

26 Work How much work is accomplished when a tow tractor is hooked up to a tow bar and a Boeing airplane weighing 130,000 lb is pushed 80 ft into the hangar? The force on the tow bar is 5,000 lb.! Distance = 80 ft! Force = 5,000 lb! Work = Force X Distance Work = 5,000 lb X 80 ft Work = 400,000 ft-lb

27 Static friction! The break loose force! The greatest friction Friction! This is why you have anti-lock brakes Sliding friction! The resistance to motion offered by an object sliding over a surface! Much less than static friction Rolling friction! Resistance to motion from the wheels or rollers

28 Power Power - the rate at which work is performed! Power = Work / Time! Power = (Force X Distance) / Time! 1 Horsepower = 33,000 foot-pounds per minute Created by James Watt to sell steam engines 1 Horsepower = 1 HP 1 HP = 33,000 foot-pounds/minute 1 HP = 550 foot-pounds/second! 1 HP = 746 watts

29 Power Lift 500 pounds 3 feet in 5 seconds! Power = Work / Time! Power = (Force X Distance) / Time! Power = 500 pound X 3 feet / 5 seconds! Power = 300 foot-pounds/second! Power = 300 ft-lb/sec X 1 HP/550 (ft-lb/sec) 1 HP = 550 ft-lb/sec (ratio) Cancel units! Power = HP! Power = HP X (746 watts/hp) 1 HP = 746 watts (ratio)! Power = watts

30 Power Calculations An engine is 27% efficient. It burns 10 gallons of avgas per hour. How much power does the engine produce? Establish what you are starting with! 10 gallons of avgas/hour! Converting energy to power at a rate of 27% Determine what your need to end up with! Engine power output! Engine output is expressed in HP

31 Power Calculations Use ratios to make the conversion Carefully use one ratio at a time Write down your work Use unit canceling to determine how to use the ratios

32 Power Calculations Starting 10 gal avgas/hour HP is expressed in ft-lb/min! Start with hour to minute conversion 1 hour = 60 min 1 hour 60 min or 60 min 1 hour 10 gal/hour X X 1 hour X 60 min = gal/min

33 Power Calculations gal/min 1 gal = 113,280 BTU 1 gal 113,280 BTU or 113,280 BTU 1 gal gal/min X X 113,280 BTU 1 gal X = 18,880 BTU/min

34 Power Calculations 18,880 BTU/min 1 BTU= 778 ft-lb 1 BTU 778 ft-lb or 778 ft-lb 1 BTU 18,880 BTU/min X X 778 ft-lb 1 BTU X = 14,688,640 ft-lb/min

35 Power Calculations 14,688,640 ft-lb/min 1 HP = 33,000 ft-lb/min 1 HP 33,000 ft-lb/min or 33,000 ft-lb/min 1 HP 14,688,640 ft-lb/min X XXXX 1 HP 33,000 ft-lb/min XXXX = HP

36 Power Calculations HP is power provided by gas 27% efficient HP X 27% = HP

37 Torque Torque - the measure of a force's tendency to produce torsion and rotation about an axis Torque = Force Distance! Work is measured in ft-lb! Torque is measured lb-ft Torque = Horsepower 5,252 RPM! RPM Revolutions Per Minute

38 Mechanical Advantage An automobile jack is a form of lever we use to get a mechanical advantage. A small force acting down-ward produces a much larger force acting upward.

39 Lever Pulley Wheel and axle Inclined plane Screw Gear Simple Machines

40 Mechanical Advantage Mechanical Advantage - a measure of the force ratio achieved by using a tool, mechanical device or machine system! 10 lbs of force on a jack lifts a 350 lb object! Advantage = 350/10 or 35/1 Force out Force in = 350 lb 10 lb

41 Lever Lever simple machine! A rigid bar, free to pivot, or rotate about a point called the fulcrum. An input force is applied at one point, and an output force is taken from the lever at another point.! Used to increase applied force! Used to increase distance! Used to increase speed

42 Lever When the lever is balanced, the sum of the moments about the fulcrum is zero.

43 Lever Formula - Force Force in X Arm Length in = Moment in Force out X Arm Length out = Moment out If well balanced, Moment in = Moment out Force out = Force in X Force in = Force out X Arm Length in Arm Length out Arm Length out Arm Length in

44 Lever Formula Arm Movement Movement out = Movement in X Arm Lengthout Arm Length in Movement in = Movement out X Arm Length in Arm Length out

45 Lever Formula Arm Speed Speed out = Speed in X Arm Lengthout Arm Length in Speed in = Speed out X Arm Length in Arm Length out

46 First Class Lever When the lever is balanced, the sum of the moments about the fulcrum is zero.

47 Second Class Lever Second-class lever.

48 Third Class Lever Third-class lever.

49 Inclined Plane An inclined plane is used to gain a mechanical advantage.

50 Pulley A. With one section of supporting rope, no mechanical advantage is gained. B. Two sections of supporting rope give a mechanical advantage of 2. C. Four sections of supporting rope give a mechanical advantage of 4.

51 Pulley Can change direction Mechanical advantage! Mechanical advantage = # of support ropes! Example: Picture C has 4 support ropes Mechanical advantage = 4 For 100 lb load! 100 lb/4 = 25 lb needed to lift 100 weight

52 Spiral Inclined Plane

53 Spiral Inclined Plane - Screw

54 Inclined Plane - Wedge

55 Change direction Change speed Gears Speed out = Speed in X Teeth in Teeth out Mechanical advantage Torque out = Torque in X * Torque at center of shaft Teeth out Teeth in

56 Gears Gears are used to change the direction of rotation between shafts and to gain a mechanical advantage.

57 Stress Stress - a force set up within an object that tries to prevent an outside force changing its shape! Tension! Compression! Shear! Bearing! Torsion! Bending

58 Strain Strain - a deformation or physical change caused by stress in a material! Deformation - proportional to the stress as long as the elastic limit is not exceeded Returns to original shape while still in elastic limit! Yield point - the stress at which a material begins to deformation will be permanent and non-reversible! Ultimate strength point - where the material breaks

59 Strain Below Elastic Limit If the elastic limit of the spring in the scale is not exceeded, it will stretch an amount proportional to the weight and will return to zero when the weight is removed.

60 Strain Past Yield Point If too much weight is put on a spring scale, the spring will be deformed, and the scale will not return to zero when the weight is removed.

61 Tension Tension is the stress that tries to pull an object apart! Object is under tension or tensile stress! Tensile strength

62 Compression Compression - the stress that tries to squeeze the ends of an object together When a rivet is driven with a compressive force on its ends, it expands to tightly fill the hole.

63 Compression & Tension

64 Compression & Tension

65 Tube Fuselage

66 Tube Fuselage

67 Wing Spar

68 Compression & Tension Torsion is a combination of tension and compression. These two stresses act at right angles to each other and at 45 to the axis of the shaft.

69 Bending The wing of an airplane is subjected to a bending stress. On the ground the top of the wing is under tension and the bottom is under compression. In flight, the opposite is true; the bottom is under a tensile stress and the top is under a compressive stress.

70 Shear Stress Shear stress - the external force acting on an object or surface parallel to the slope or plane in which it lies! The stress tending to produce shear (cutting).

71 Shear Stress A shear stress tries to slide the clevis bolt apart.

72 Stress

73 Vector Speed - the rate of motion! 100 Knots! If you are going 100 knots, where are you going? You don t know Vector a quantity which has both direction and magnitude Velocity - the rate and direction of motion! Southwest at 100 knots

74 Vector 45 Vector A shown here has a length, or magnitude, of 10 units, and its direction is 45 clockwise from north.

75 Sum of Two Vectors - Resultant The resultant, vector R, is the hypotenuse of a right triangle with vectors A and B as the two sides. The length of R is the square root of the sum of the squares of the lengths of A and B.

76 Navigation is about Vectors Vector addition is used to find the heading required to fly a given track, and to find the ground speed when the airspeed, track and wind direction and velocity are known.

77 Newton s First Law of Motion Objects at rest tend to remain at rest; objects in motion tend to remain in motion at the same speed and in the same direction.! Objects don t like to change

78 Newton s Second Law of Motion When a force acts upon a body, the momentum of that body is changed. The rate of change of momentum is proportional to the applied force.! The harder you push, the faster you go! Acceleration and Deceleration

79 Newton s Third Law of Motion For every action there is an equal and opposite reaction.! The law behind thrust propulsion! Push enough air backwards and the aircraft moves forward

80 Circular Motion The bucket of water is trying to obey Newton s first law and travel in a straight line from A to B. But the rope holds it along the curved path A to C. The resultant, C-B, is the centrifugal force, and this is the force that holds water in the bucket and makes the bucket heavier.

81 Circular Motion Video Video 2 Video 3 When a helicopter rotor is not turning, gravity causes the blades to droop. But when the rotor is turning, centrifugal force holds the blades straight out.

82 Heat Heat is a form of energy! Energy can be stored in the form of heat! Energy can be removed in the form of heat It is called cooling Air conditioners are heat pumps Heat - speeds up the movement of the material's molecules! Heat increases a molecules kinetic energy! Usually causes material to expand (molecules moves faster)! Can cause material to change state Ice (solid) to water (liquid), Water to steam (gas)

83 Forms of heat! Mechanical Heat Friction! Chemical Burning! Electrical! Radiation! Nuclear! Sun form of nuclear

84 Units Heat! calorie c 1 gram of water raised 1 C! Calorie C 1 kilogram (1000 grams) of water raised 1 C! British Thermal Unit BTU 1 lb of water raised 1 F

85 Heat Sensible heat - heat that raises the temperature of a substance without changing its state. Latent heat - heat that changes the state of a substance without raising its temperature! Heat water to 212 F and it will change to steam! Heat ice to 32 F and it will melt

86 Heat When sensible heat is added to water, its temperature increases, but the water does not change its physical state. When latent heat is added to water, its temperature remains constant, but the water changes its state from liquid water into steam.

87 Heat Transfer - three methods of heat transfer! Conduction! Convection! Radiation Heat Conduction - heat transferred from one molecule to another because the molecules are touching. The molecules never physically move.! Heat moving within an object or two objects touching

88 Heat Conduction When the end of the bar is heated with the flame, heat is transferred through the bar by conduction.

89 Heat Conduction

90 Heat Transfer Convection Heat Transfer - a mechanism of heat transfer occurring because of bulk motion (observable movement) of fluids (gas or liquid)! Water radiator! Oil radiator/cooler! Cooling fins

91 Convection Heat Transfer When water in a container is heated by conduction, it becomes less dense and rises, forcing the cold water down to where it can be heated. This is heat transfer by convection.

92 Heat Transfer Radiation - method of heat transfer by electromagnetic wave action! No touching

93 Radiation Heat energy from the sun reaches the earth through the vacuum of empty space by radiation. Invisible heat energy passes through empty space in the same way as visible light energy.

94 Heat Transfer

95 Temperature Absolute zero - the temperature at which all molecular movement inside a material stops. It is zero degrees on both the Kelvin and Rankine scales and -273 C and -460 F. Absolute temperature temperature measured from absolute zero. Absolute temperature is measured in degrees Kelvin or degrees Rankine! Some calculations need to be referenced to absolute zero

96 Temperature

97 Temperature Conversion F = 1.8 ( C) + 32 C = ( F - 32 ) / 1.8 K = C C = K 273 R = F F = R - 460

98 Specific Heat Specific heat - the ratio of the amount of heat energy needed to raise the temperature of a certain mass of a material 1 C to the amount of heat energy needed to raise the temperature of the same mass of pure water 1 C The higher the specific heat number, the more heat needed to change the temperature of a material

99 Specific Heat Specific heat of various materials.

100 Dimensional Changes Caused by Heat Heat causes molecules to move faster and an object to expand! Metals expand when they get warmer! Metals contracts when they get colder! Water expands when it freezes Interference fit can be made by using different temperatures! Heat the cylinder head to expand it! Ice the cylinder to contact/shrink it! When the temperature stabilizes interference fit

101 Coefficient of Expansion

102 Pressure Pressure is the amount of force acting on a specific amount of surface area! Usually measured in Pounds per Square Inch or psi

103 Atmospheric Pressure Atmospheric pressure is the force per unit area exerted on to a surface by the weight of air above that surface in the atmosphere of Earth! Also called barometric pressure

104 Simple Barometer

105 Atmospheric Pressure

106 Standard Day Atmospheric Pressure 14.7 psi (pounds per square inch) Hg (inches of mercury) millibars! Millibar = bar/1000! Bar = 1,000,000 dynes per square centimeter! Dyne = 1 gram accelerated at one centimeter per second

107 Pressure Absolute pressure - pressure that is measured from zero pressure, or from a vacuum! No atmospheric pressure! Used for manifold pressure The manifold pressure on a non-running engine should read the current atmospheric pressure Gage pressure - pressure measured from the existing atmospheric pressure! Atmospheric pressure is the zero reference! Used for oil, fuel, hydraulic pressures

108 Pressure Differential pressure - pressure which is the difference between two opposing pressures! Is used to measure the flow of a fluid (gas or liquid)

109 Pressure Differential pressure! Used to measure oil flow, welding gas flow rate, fuel flow and turbine engine output (turbine pressure ratio)! Example: A fluid is forced through a fixed opening (orifice). The differential pressure is measured by comparing the input side to the output side. The higher the differential pressure, the higher the flow.

110 Gas A gas will change both its shape and its volume and will expand to fill its entire container Gas calculations are done in absolute temperature

111 Boyle's Law If the temperature and amount of gas is held constant:! If the volume decreases, the pressure increases This is how a compressor works! If the volume increases, the pressure decreases

112 Charles's Law If the pressure and amount of gas is held constant:! If the temperature decreases, the volume decreases! If the temperature increases, the volume increases If the volume and amount of gas is held constant:! If the temperature decreases, the pressure decreases! If the temperature increases, the pressure increases Pressure tanks can blowup if they get too hot

113 Fluids Liquids are non-compressible Pressure = fluid density X height Density and specific gravity of various liquids.

114 Fluids The pressure at the bottom of a column of liquid is caused by the height of the liquid, and it is not affected by the quantity of the fluid or the shape of the container.

115 Pascal's Law Pascal's law when pressure is applied to a fluid in an enclosed container, the pressure is transmitted equally throughout all of the fluid, and it acts at right angles to the walls that enclose the fluid! In a hydraulic system or pressurized fluid system where the fluid is free to move about, the pressure is equal throughout the system

116 Not Contained Pressure Based on Height The pressure produced by a liquid in a container is caused by the height of the liquid above the point at which the pressure is measured. The higher the liquid above the gage, the greater the pressure.

117 Pascal's Law Pressure is Equal For our calculation, the weight of the fluid will be almost nothing compare to the pressure applied to the fluid. For our calculations, P1, P2 and P3 will be the same. When we apply pressure on the liquid in a closed container, the pressure rises the same amount in all parts of the container.

118 Fluid Pressure Formulas Force = Pressure X Area! Pressure = Force / Area! Area = Force / Pressure

119 Force = Pressure X Area The amount of force produced by the piston in a hydraulic cylinder may be found by multiplying the area of the piston by the amount of pressure inside the cylinder.

120 Area = Force / Pressure The area of a piston needed to produce a given amount of force with a certain amount of pressure may be found by dividing the amount of force by the pressure.

121 Pressure = Force / Area The amount of pressure produced in a hydraulic cylinder may be found by dividing the amount of force on the piston by the area of the piston.

122 Hydraulic System Hydraulic cylinders produce a mechanical advantage. A 1-pound force (F 1 ) can lift a 10-pound weight (W 2 ), but no work is gained. The work done by the small piston is the same as that done by the large piston.

123 Hydraulic System Hydraulic systems are used to create mechanical advantage like a lever or gear system! Turn a small force into a larger force Brakes and hydraulic jacks! Turn a small distance into a larger distance Trade distance for force! Example: Car jack Lots of strokes of the jack at very little pressure Heavy car raises a short distance

124 Simple Hydraulic System

125 Hydraulic Jack

126 Hydraulic System Formulas Force out = Force in X Area out / Area in Distance out = Distance in X Area in / Area out Mechanical Advantage = Area out / Area in! Force and Distance formulas are based on the Mechanical Advantage ratio! For a round piston (circle): Mechanical Advantage = Π X Π X Dout 2 2 Din 2 2 Mechanical Advantage = D out D in 2

127 Hydraulic System Formulas For a round piston (circle)! Force out = Force in X (D out / D in ) 2! Distance out = Distance in X (D in / D out ) 2! Mechanical Advantage = (D out / D in ) 2

128 Hydraulic System Practices IN OUT

129 Fluid System Questions An open cylinder, 5 tall, is filled with avgas (density = pci or pound per cubic inch). What is the pressure at the bottom of the cylinder?! Pressure = fluid density X height! height = 5 X 12 in/foot = 60 in! Pressure = lb/in 3 X 60 in! Pressure = 1.56 lb/in 2 or psi

130 Fluid System Questions An 100 lb weight is rested on a piston inside a cylinder. The piston has an area of ¼ in 2. How much pressure does the weight create in the cylinder? How much work is produced?

131 Fluid Pressure Formulas Force = Pressure X Area! Pressure = Force / Area! Area = Force / Pressure

132 Fluid System Questions An 100 lb weight is rested on a piston inside a cylinder. The piston has an area of ¼ in 2. How much pressure does the weight create in the cylinder?! Pressure = Force/ Area! Pressure = 100 lb / ¼ in 2 = 400 lb/in 2 or psi How much work is produced?! None nothing moved, the weight is at rest. Like you, no work gets done when you are resting

133 Fluid System Questions A cylinder must be pressurized. What weight must be placed on a 2 in 2 piston to create 100 psi?

134 Fluid Pressure Formulas Force = Pressure X Area! Pressure = Force / Area! Area = Force / Pressure

135 Fluid System Questions A cylinder must be pressurized. What weight must be placed on a 2 in 2 piston to create 100 psi?! Force = Area X Pressure! Force = 2 in 2 X 100 lb/in 2! Force = 200 lb

136 Hydraulic System Practices IN OUT

137 Hydraulic System Practices Input piston area = 5 in 2 Output piston area = 100 in 2 What is the Mechanical Advantage?! Mechanical Advantage = Output area / Input area! Mechanical Advantage = 100 in 2 / 5 in 2 = 20

138 Hydraulic System Practices Input piston area = 5 in 2 Output piston area = 100 in 2 Input force = 100 lb What is the equalizing force on the output side?! Output force = Input force X Output area / Input area! Output force = 100 lb X 100 in 2 / 5 in 2 = 2000 lb The system has how much hydraulic pressure?! Pressure = Force / Area! Pressure = 100 lb / 5 in 2 = 20 lb/in 2 or psi! Pressure = 2000 lb / 100 in 2 = 20 lb/in 2 or psi

139 Hydraulic System Practices Input piston area = 5 in 2 Output piston area = 100 in 2 Input force = 100 lb Output force = 2000 lb Input distance = 10 What is the output distance?! Output Distance = Input distance X Input area / Output area! Output Distance = 10 in X 5 in 2 / 100 in 2 = ½ in

140 Hydraulic System Practices Input piston area = 5 in 2 Output piston area = 100 in 2 Input force = 100 lb Output force = 2000 lb Input distance = 10 Output distance = ½ How much work is generated?! Work = Force X Distance! Work = 100 lb X 10 in = 1000 in-pounds! Work = 2000 lb X ½ in = 1000 in-pounds What goes in, must come out

141 Hydraulic System Practices Work = 1000 in-pounds How much power (in HP) is need to lift the output weight in 5 seconds! 1 HP = 550 foot-pounds/second! Power = Work / Time! Power = 1000 in-pounds / 5 seconds! Power = 200 in-pounds/sec X (1 ft / 12 in)! Power = 16.7 foot-pounds/sec X (1 HP/550 footpounds/sec)! Power = 0.03 HP

142 Hydraulic System Practices Power = 0.03 HP How much power is needed in Watts?! 1 HP = 746 Watts! Power = 0.03 HP X 746 Watts / HP = 22.4 Watts

143 Bernoulli s Principle Where in aviation?! Lift generated by a wing! Propulsion provided by a propeller! Propulsion provided by a turbine engine! Fuel flow to a carburetor

144 Bernoulli s Principle Conservation of energy! Total amount of energy in an isolated system remains constant over time! What goes in, must come out Forms of energy! Kinetic energy Speed! Potential Height Pressure

145 Bernoulli s Principle Converting energy forms! Potential to Kinetic Height to speed! Kinetic to Potential Speed to height! The amount of energy must always stay the same Bernoulli s insight was to apply these principles to fluids

146 Bernoulli s Principle Bernoulli s converting energy forms! Potential to Kinetic Increase the speed of a fluid and the pressure will decrease! Kinetic to Potential Decrease the speed of a fluid and the pressure will increase! The amount of energy must always stay the same

147 Bernoulli s Principle

148 Bernoulli s Principle Bernoulli s catch! Works only for non-compressible fluids! But air is a gas and gas is compressible? Under the speed of sound, air acts like a non-compressible fluid

149 Bernoulli s Principle

150 Bernoulli s Principle

151 Bernoulli s Principle

152 Sound Sound is a vibration in the audio range (20 Hz to 20,000 Hz)! Pitch is the sound frequency Sound levels are measured in decibels (db)! Decibel is a logarithmic unit. An increase of 3 db is a factor of 2 Speed of sound the rate at which sound travels through a medium! Speed varies from one medium to another The reason things sound funny underwater! Mach Number the ratio of speed to the speed of sound Mach 1 = speed of sound

153 Sound Speed of sound Air! At the speed of sound, air starts to compress! The speed of sound will change with temperature At 32 F, the speed of sound is 1,087 fps (feet per second)! Will increase 1.1 fps for each degree of Fahrenheit

154 Sound Doppler Effect - A change in the observed frequency of a wave, as of sound or light, occurring when the source and observer are in motion relative to each other! The frequency increasing when the source and observer approach each other! The frequency decreasing when they move apart Doppler Effect Video

155 Vibration Vibration is the up-and-down or back-and-forth movement of an object Vibrations use up energy and cause wear Frequency - the number of complete cycles of a recurring event that takes place in one unit of time! Usually measured in Hertz (Hz). One cycle per second

156 Vibration Natural frequency - the frequency at which a system naturally vibrates once it has been set into motion Resonance - the buildup of large vibration amplitude that occurs when a structure or an object is excited at its natural frequency.! Resonance video

157 Resonance Vibration! Some aircraft have a RPM range that is off limits Prevents the propeller from hitting resonance! Control surfaces can flutter (resonance) One of the reasons aircraft have a maximum top speed Control surfaces must be balanced after a repair! Resonance video! Resonance video Beat Frequency! Video beat frequency

158 Atmosphere Atmospheric temperature decreases as the altitude increases! Levels off around 7 miles to 20 miles! More lift and engine power with colder temperature Atmospheric pressure decreases as the altitude increases! Less lift and engine power with lower pressure

159 Atmosphere The atmosphere contains water vapor! Water vapor is lighter than dry air! Less lift and engine power with more water vapor Absolute humidity the amount of water vapor in a mixture of air and water Relative humidity - the amount of water vapor present in air expressed as a percentage of the amount needed for saturation at the same temperature! The higher the temperature, the more water vapor the air can hold

160 Atmosphere Dew Point the temperature below which water droplets begin to condense and dew can form.! Relative humidity is 100% at the dew point Vapor pressure - The pressure exerted by water vapor in the atmosphere! The higher the atmospheric pressure, the harder it is get water in it The higher the atmospheric pressure, the higher the boiling point of water

161 Four Forces of Flight

162 Wing

163 Wing Lift Bernoulli s Principle! The wing camber cause the air to travel faster over the wing top The faster airflow causes a lower pressure on wing top The imbalance between the higher pressure on the wing bottom and lower pressure on the wing top creates lift Newton s Third Law! The wings Angle of Attack (AOA) creates a force that increases lift! The air leaving the trailing edge pushes down which creates lift

164 Wing Geometry

165 Wing Wing Aspect Ratio the ratio of the wing area to the mean cord! In a rectangular wing, the ratio of the span to the cord! The greater the ratio (like a glider), the less drag created and lower the stall speed Wing Dihedral - upward inclination of an aircraft wing in relation to the lateral axis! Adds to lateral stability helps level the aircraft