AMT 100 Physics Chapter 3 Physics •  Physics -­‐ the natural science that deals with ma;er and energy and the rela=onships between the two. •  Ma;er is anything that takes up space and has mass •  Mass -­‐ the quan=ty of ma;er in a body regardless of its volume or of any forces ac=ng on it Physics •  Weight -­‐ measure of the force of gravity on a body !
Weight is propor=onal to mass •  Weight = Mass X Gravity !
The moon has 1/6th the gravity of earth •  On the moon, you would weigh 1/6th your earth weight •  Your mass is the same on the earth as the moon Atom •  The basic unit of a chemical element. •  Basic par=cles -­‐ 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 Atom Atom •  Electric charge: Atom Neutron – none !  Proton – Posi=ve – “+” !  Electron – Nega=ve – “-­‐” !
•  Compound -­‐ combina=on of elements that contains a specific number of atoms of each element Molecule -­‐ the smallest par=cle of ma;er that can s=ll remain the same substance (compound) !  e.g. Water – 2 hydrogen & 1 oxygen – H2O !
Molecule States of Ma;er •  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 !
States of Ma;er •  Plasma -­‐ collec=on of charged par=cles that respond strongly and collec=vely to electromagne=c fields, taking the form of gas-­‐
like clouds or ion beams !
Described as an "ionized gas" States of Ma;er States of Ma;er Plasma Density •  Density -­‐ measure of the amount of ma;er in a certain volume of material •  Specific gravity -­‐ the ra=o of the density of a material to the density of pure water Weight of the substance
Specific Gravity =
Weight of an equal volume of water
Density of the substance
Specific Gravity =
Density of water
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Density Specific Gravity Specific Gravity Specific Gravity Specific Gravity Force •  Force -­‐ causes a object to undergo a change in speed, a change in direc=on, 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 posi=on against an opposing force !
Work •  Work -­‐ the amount of energy transferred by a force ac=ng through a distance in the direc=on of the force !
Work = Force X Distance •  A 500 pound box liged 6 feet •  Work = 500 pound X 6 feet •  Work = 3000 foot-­‐pounds Energy •  The ability to do work !
Something that changes, or tries to change, ma;er •  Types of energy: !
Poten=al •  Energy in an object caused by its posi=on, configura=on, or chemical composi=on. !
Kine=c •  Energy in an object caused by its mo=on. Poten=al Energy Conversion of Energy Conversion of Energy •  Aircrag Engine !
Energy source: Avgas •  Chemical poten=al energy (no conversion of mass) !
Converted to: •  Rota=on mo=on •  Light (inside cylinder) •  Heat transferred to engine !
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Thermal and fric=on Air, oil and fuel cooled •  Heat in exhaust •  Increased exhaust velocity !
Energy in = Energy out •  What goes in must come out Work •  How much work is accomplished when a tow tractor is hooked up to a tow bar and a Boeing 737-­‐800 airplane weighing 130,000 lb is pushed 80 g into the hangar? The force on the tow bar is 5,000 lb. Distance = 80 g !  Force = 5,000 lb !  Work = Force X Distance !
•  Work = 5,000 lb X 80 g •  Work = 400,000 g-­‐lb •  Sta=c fric=on Fric=on The “break” loose force !  The greatest fric=on !  This is why you have an=-­‐lock brakes !
•  Sliding fric=on The resistance to mo=on offered by an object sliding over a surface !  Much less than sta=c fric=on !
•  Rolling fric=on !
Resistance to mo=on from the wheels or rollers 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 Wa; to sell steam engines •  1 Horsepower = 1 HP •  1 HP = 33,000 foot-­‐pounds/minute •  1 HP = 550 foot-­‐pounds/second !
1 HP = 746 wa;s Power •  Lig 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 g-­‐lb/sec X 1 HP/550 (g-­‐lb/sec) !
•  1 HP = 550 g-­‐lb/sec (ra=o) •  Cancel units Power = 0.545 HP !  Power = 0.545 HP X (746 wa;s/HP) !
•  1 HP = 746 wa;s (ra=o) !
Power = 406.57 wa;s Power Calcula=ons •  An engine is 27% efficient. It burns 10 gallons of avgas per hour. How much power does the engine produce? •  Establish what you are star=ng with 10 gallons of avgas/hour !  Conver=ng 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 !
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Power Calcula=ons Use ra=os to make the conversion Carefully use one ra=o at a =me Write down your work Use unit canceling to determine how to use the ra=os Power Calcula=ons •  Star=ng 10 gal avgas/hour •  HP is expressed in g-­‐lb/min !
Start with hour to minute conversion •  1 hour = 60 min 1 hour 60 min 10 gal/hour X
X or 1 hX
our 60 min 60 min 1 hour = 0.166… gal/min Power Calcula=ons •  0.166… gal/min •  1 gal = 113,280 BTU 1 gal 113,280 BTU 0.166… gXal/min X or 113,280 BTU 1 gal 113,280 BTU 1 gX
al = 18,880 BTU/min Power Calcula=ons •  18,880 BTU/min •  1 BTU= 778 g-­‐lb 1 BTU 778 g-­‐lb 18,880 BTU/min X X
778 g-­‐lb 1 BTU or 778 g-­‐lb 1 BTU X
= 14,688,640 g-­‐lb/min Power Calcula=ons •  14,688,640 g-­‐lb/min •  1 HP = 33,000 g-­‐lb/min 1 HP 33,000 g-­‐lb/min or 33,000 g-­‐lb/min 1 HP 1 HP 14,688,640 gXXXX
-­‐lb/min X = 445.1 HP 33,000 g
-­‐lb/min XXXX
Power Calcula=ons •  445.1 HP is power provided by gas •  27% efficient •  445.1 HP X 27% = 120.2 HP Torque •  Torque -­‐ the measure of a force's tendency to produce torsion and rota=on about an axis •  Torque = Force × Distance Work is measured in g-­‐lb !  Torque is measured lb-­‐g !
•  Torque = Horsepower × 5,252 ÷ RPM !
RPM – Revolu=ons Per Minute Mechanical Advantage An automobile jack is a form of lever we use to get a mechanical advantage. A small force ac=ng down-­‐ward produces a much larger force ac=ng upward.
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Simple Machines Lever Pulley Wheel and axle Inclined plane Screw Gear Mechanical Advantage •  Mechanical Advantage -­‐ a measure of the force ra=o achieved by using a tool, mechanical device or machine system 10 lbs of force on a jack ligs a 350 lb object !  Advantage = 350/10 or 35/1 !
Forceout Forcein = 350 lb 10 lb 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 !
Lever When the lever is balanced, the sum of the moments about the fulcrum is zero.
Lever Formula -­‐ Force •  Forcein X Arm Lengthin = Momentin •  Forceout X Arm Lengthout = Momentout •  If well balanced, Momentin= Momentout Forceout Forcein = Forcein = Forceout X Arm Lengthin Arm Lengthout X Arm Lengthout Arm Lengthin Lever Formula – Arm Movement out Arm L
ength
Movementout = Movementin X Arm Lengthin in Arm L
ength
Movementin = Movementout X Arm Lengthout Lever Formula – Arm Speed Speedout Speedin = = Speedin Arm Lengthout X Arm Lengthin Speedout Arm Lengthin X Arm Lengthout First Class Lever When the lever is balanced, the sum of the moments about the fulcrum is zero.
Second Class Lever Second-­‐class lever.
Third Class Lever Third-­‐class lever.
Inclined Plane An inclined plane is used to gain a mechanical advantage.
Pulley A. With one sec=on of suppor=ng rope, no mechanical advantage is gained. B. Two sec=ons of suppor=ng rope give a mechanical advantage of 2. C. Four sec=ons of suppor=ng rope give a mechanical advantage of 4.
Pulley •  Can change direc=on •  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 lig 100 weight Spiral Inclined Plane Spiral Inclined Plane -­‐ Screw Inclined Plane -­‐ Wedge •  Change direc=on •  Change speed Speedout Gears X Teethin Teethout = Torquein X Teethout Teethin = Speedin •  Mechanical advantage Torqueout * Torque at center of shaft
Gears Gears are used to change the direc=on of rota=on between shags and to gain a mechanical advantage.
Stress •  Stress -­‐ a force set up within an object that tries to prevent an outside force changing its shape Strain !  Tension !  Compression !  Torsion !  Bending !  Shear !
Strain •  Strain -­‐ a deforma=on or physical change caused by stress in a material !
Deforma=on -­‐ propor=onal to the stress as long as the elas=c limit is not exceeded •  Returns to original shape while s=ll in elas=c limit Yield point -­‐ the stress at which a material begins to deforma=on will be permanent and non-­‐reversible !  Ul=mate strength point -­‐ where the material breaks !
Strain – Below Elas=c Limit If the elas=c limit of the spring in the scale is not exceeded, it will stretch an amount propor=onal to the weight and will return to zero when the weight is removed.
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.
Tension •  Tension is the stress that tries to pull an object apart Object is under tension or tensile stress !  Tensile strength !
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 =ghtly fill the hole.
Compression & Tension Compression & Tension Tube Fuselage Tube Fuselage Wing Spar Compression & Tension Torsion is a combina=on of tension and compression. These two stresses act at right angles to each other and at 45° to the axis of the shag.
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 bo;om is under compression. In flight, the opposite is true; the bo;om is under a tensile stress and the top is under a compressive stress.
Shear Stress •  Shear stress -­‐ the external force ac=ng on an object or surface parallel to the slope or plane in which it lies !
The stress tending to produce shear (cuzng). Shear Stress A shear stress tries to slide the clevis bolt apart.
Stress Vector •  Speed -­‐ the rate of mo=on 100 Knots !  If you are going 100 knots, where are you going? !
•  You don’t know •  Vector – a quan=ty which has both direc=on and magnitude •  Velocity -­‐ the rate and direc=on of mo=on !
Southwest at 100 knots Vector 45°
Vector “A” shown here has a length, or magnitude, of 10 units, and its direc=on is 45° clockwise from north.
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.
Naviga=on is about Vectors Vector addi=on is used to find the heading required to fly a given track, and to find the ground speed when the airspeed, track and wind direc=on and velocity are known.
Newton’s First Law of Mo=on •  Objects at rest tend to remain at rest; objects in mo=on tend to remain in mo=on at the same speed and in the same direc=on. !
Objects don’t like to change Newton’s Second Law of Mo=on •  When a force acts upon a body, the momentum of that body is changed. The rate of change of momentum is propor=onal to the applied force. The harder you push, the faster you go !  Accelera=on and Decelera=on !
Newton’s Third Law of Mo=on •  For every ac=on there is an equal and opposite reac=on. The law behind thrust propulsion !  Push enough air backwards and the aircrag moves forward !
Circular Mo=on 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. Circular Mo=on Video
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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. 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 condi=oners are “heat pumps” •  Heat -­‐ speeds up the movement of the material's molecules Heat increases a molecules kine=c energy !  Usually causes material to expand (molecules moves faster) !  Can cause material to change state !
•  Ice (solid) to water (liquid), Water to steam (gas) •  Forms of heat !
Heat Mechanical •  Fric=on !
Chemical •  Burning Electrical !  Radia=on !  Nuclear !  Sun – form of nuclear !
•  Units Heat calorie – c – 1 gram of water raised 1°C !  Calorie – C – 1 kilogram (1000 grams) of water raised 1°C !  Bri=sh Thermal Unit – BTU – 1 lb of water raised 1°F !
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 !
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.
Heat •  Transfer -­‐ three methods of heat transfer Conduc=on !  Convec=on !  Radia=on !
•  Heat Conduc=on -­‐ 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 Heat Conduc=on When the end of the bar is heated with the flame, heat is transferred through the bar by conduc=on.
Heat Conduc=on Heat Transfer •  Convec=on Heat Transfer -­‐ a mechanism of heat transfer occurring because of bulk mo=on (observable movement) of fluids (gas or liquid) Water radiator !  Oil radiator/cooler !  Cooling fins !
Convec=on Heat Transfer When water in a container is heated by conduc=on, it becomes less dense and rises, forcing the cold water down to where it can be heated. This is heat transfer by convec=on.
Heat Transfer •  Radia=on -­‐ method of heat transfer by electromagne=c wave ac=on !
No touching Radia=on Heat energy from the sun reaches the earth through the vacuum of empty space by radia=on. Invisible heat energy passes through empty space in the same way as visible light energy.
Heat Transfer 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 calcula=ons need to be referenced to absolute zero Temperature Figure 3-­‐50. The four temperature scales have values for absolute zero and for the points at which pure water freezes and boils.
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Temperature Conversion °F = 1.8 (°C) + 32° °C = (°F -­‐ 32°) / 1.8 °K = °C + 273° °C = °K – 273° °R = °F + 460° °F = °R -­‐ 460° Specific Heat •  Specific heat -­‐ the ra=o 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 need to change the temperature of a materal Specific Heat Specific heat of various materials.
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 !
Coefficient of Expansion Pressure •  Pressure is the amount of force ac=ng on a specific amount of surface area !
Usually measured in Pounds per Square Inch or psi 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 Simple Barometer Atmospheric Pressure Standard Day Atmospheric Pressure •  14.7 psi (pounds per square inch) •  29.92” Hg (inches of mercury) •  1013.2 millibars Millibar = bar/1000 !  Bar = 1,000,000 dynes per square cen=meter !  Dyne = 1 gram accelerated at one cen=meter per second !
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 exis=ng atmospheric pressure Atmospheric pressure is the “zero” reference !  Used for oil, fuel, hydraulic pressures !
Pressure •  Differen=al pressure -­‐ pressure which is the difference between two opposing pressures !
Is used to measure the flood of a fluid (gas or liquid) Pressure •  Differen=al pressure Used to measure oil flow, welding gas flow rate, fuel flow and turbine engine output (turbine pressure ra=o) !  Example: A fluid is forced through a fixed opening (orifice). The differen=al pressure is measured by comparing the input side to the output side. The higher the differen=al pressure, the higher the flow. !
Gas •  A gas will change both its shape and its volume and will expand to fill its en=re container •  Gas calcula=ons are done in absolute temperature 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 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 Fluids •  Liquids are non-­‐compressible •  Pressure = fluid density X height Density and specific gravity of various liquids.
Fluids The pressure at the bo;om of a column of liquid is caused by the height of the liquid, and it is not affected by the quan=ty of the fluid or the shape of the container.
Pascal's Law •  Pascal's law – when pressure is applied to a fluid in an enclosed container, the pressure is transmi;ed 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 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.
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.
Fluid Pressure Formulas •  Force = Pressure X Area Pressure = Force / Area !  Area = Force / Pressure !
Force = Pressure X Area The amount of force produced by the piston in a hydraulic cylinder may be found by mul=plying the area of the piston by the amount of pressure inside the cylinder.
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.
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.
Hydraulic System Hydraulic cylinders produce a mechanical advantage. A 1-­‐pound force (F1) can lig a 10-­‐pound weight (W2), but no work is gained. The work done by the small piston is the same as that done by the large piston.
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 li;le pressure •  Heavy car raises a short distance Simple Hydraulic System Hydraulic Jack Hydraulic System Formulas •  Forceout = Forcein X Areaout / Areain •  Distanceout = Distancein X Areain / Areaout •  Mechanical Advantage = Areaout / Areain Force and Distance formulas are based on the Mechanical Advantage ra=o !  For a round piston (circle): !
Mechanical Advantage =
⎛ Dout ⎞ 2
Π X ⎜
⎟
⎝ 2 ⎠
⎛ Din ⎞ 2
Π X ⎜
⎟
⎝ 2 ⎠
Mechanical Advantage =
€
Dout
Din
Hydraulic System Formulas •  For a round piston (circle) Forceout = Forcein X Dout / Din !  Distanceout = Distancein X Din / Dout !  Mechanical Advantage = Dout / Din !
Hydraulic System Prac=ces IN
OUT
Fluid System Ques=ons •  An open cylinder, 5’ tall, is filled with avgas (density = 0.026 pci or pound per cubic inch). What is the pressure at the bo;om of the cylinder? Pressure = fluid density X height !  height = 5’ X 12 in/foot = 60 in 3
!  Pressure = 0.026 lb/in X 60 in 2
!  Pressure = 1.56 lb/in or psi !
Fluid System Ques=ons •  An 100 lb weight is rested on a piston inside a cylinder. The piston has an area of ¼ in2. •  How much pressure does the weight create in the cylinder? •  How much work is produced? Fluid Pressure Formulas •  Force = Pressure X Area Pressure = Force / Area !  Area = Force / Pressure !
Fluid System Ques=ons •  An 100 lb weight is rested on a piston inside a cylinder. The piston has an area of ¼ in2. •  How much pressure does the weight create in the cylinder? Pressure = Force/ Area 2
2
!  Pressure = 100 lb / ¼ in = 400 lb/in or psi !
•  How much work is produced? !
None – nothing moved, the weight is at rest. •  Like you, no work gets done when you are res=ng Fluid System Ques=ons •  A cylinder must be pressurized. What weight must be placed on a 2 in2 piston to create 100 psi? Fluid Pressure Formulas •  Force = Pressure X Area Pressure = Force / Area !  Area = Force / Pressure !
Fluid System Ques=ons •  A cylinder must be pressurized. What weight must be placed on a 2 in2 piston to create 100 psi? Force = Area X Pressure 2
2 !  Force = 2 in X 100 lb/in
!  Force = 200 lb !
Hydraulic System Prac=ces IN
OUT
Hydraulic System Prac=ces •  Input piston area = 5 in2 •  Output piston area = 100 in2 •  What is the Mechanical Advantage? Mechanical Advantage = Output area / Input area 2
2
!  Mechanical Advantage = 100 in / 5 in = 20 !
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Hydraulic System Prac=ces Input piston area = 5 in2 Output piston area = 100 in2 Input force = 100 lb What is the equalizing force on the output side? Output force = Input force X Output area / Input area 2
2
!  Output force = 100 lb X 100 in / 5 in = 2000 lb !
•  The system has how much hydraulic pressure? Pressure = Force / Area 2
2
!  Pressure = 100 lb / 5 in = 20 lb/in or psi 2
2
!  Pressure = 2000 lb / 100 in = 20 lb/in or psi !
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Hydraulic System Prac=ces Input piston area = 5 in2 Output piston area = 100 in2 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 2
2 !  Output Distance = 10 in X 5 in / 100 in = ½ in !
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Hydraulic System Prac=ces Input piston area = 5 in2 Output piston area = 100 in2 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 Hydraulic System Prac=ces •  Work = 1000 in-­‐pounds •  How much power (in HP) is need to lig 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 g / 12 in) !  Power = 16.7 foot-­‐pounds/sec X (1 HP/550 foot-­‐
pounds/sec) !  Power = 0.03 HP !
Hydraulic System Prac=ces •  Power = 0.03 HP •  How much power is needed in Wa;s? 1 HP = 746 Wa;s !  Power = 0.03 HP X 746 Wa;s / HP = 22.4 Wa;s !
Bernoulli’s Principle •  Where in avia=on? Lig generated by a wing !  Propulsion provided by a propeller !  Propulsion provided by a turbine engine !  Fuel flow to a carburetor !
Bernoulli’s Principle •  Conserva=on of energy Total amount of energy in an isolated system remains constant over =me !  “What goes in, must come out” !
•  Forms of energy !
Kine=c energy •  Speed !
Poten=al •  Height •  Pressure Bernoulli’s Principle •  Conver=ng energy forms !
Poten=al to Kine=c •  Height to speed !
Kine=c to Poten=al •  Speed to height !
The amount of energy must always stay the same •  Bernoulli’s insight was to apply these principles to fluids Bernoulli’s Principle •  Bernoulli’s conver=ng energy forms !
Poten=al to Kine=c •  Increase the speed of a fluid and the pressure will decrease !
Kine=c to Poten=al •  Decrease the speed of a fluid and the pressure will increase !
The amount of energy must always stay the same Bernoulli’s Principle Animation
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 Bernoulli’s Principle Bernoulli’s Principle Bernoulli’s Principle Sound •  Sound is a vibra=on 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 ra=o of speed to the speed of sound – Mach 1 = speed of sound 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 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 mo=on rela=ve to each other The frequency increasing when the source and observer approach each other !  The frequency decreasing when they move apart !
•  Doppler Effect Video Vibra=on •  Vibra=on is the up-­‐and-­‐down or back-­‐and-­‐forth movement of an object •  Vibra=ons use up energy and cause wear •  Frequency -­‐ the number of complete cycles of a recurring event that takes place in one unit of =me !
Usually measured in Hertz (Hz). One cycle per second Vibra=on •  Natural frequency -­‐ the frequency at which a system naturally vibrates once it has been set into mo=on •  Resonance -­‐ the buildup of large vibra=on amplitude that occurs when a structure or an object is excited at its natural frequency. !
Resonance video •  Resonance !
Vibra=on Some aircrag have a RPM range that is off limits •  Prevents the propeller from hizng resonance !
Control surfaces can flu;er (resonance) •  One of the reasons aircrag have a maximum top speed •  Control surfaces must be balanced ager a repair Resonance video !  Resonance video !
•  Beat Frequency !
Video beat frequency Atmosphere •  Atmospheric temperature decreases as the al=tude increases Levels off around 7 miles to 20 miles !  More lig and engine power with colder temperature !
•  Atmospheric pressure decreases as the al=tude increases !
Less lig and engine power with lower pressure Atmosphere •  The atmosphere contains water vapor Water vapor is lighter than dry air !  Less lig and engine power with more water vapor !
•  Absolute humidity – the amount of water vapor in a mixture of air and water •  Rela=ve humidity -­‐ the amount of water vapor present in air expressed as a percentage of the amount needed for satura=on at the same temperature !
The higher the temperature, the more water vapor the air can hold Atmosphere •  Dew Point – the temperature below which water droplets begin to condense and dew can form. !
Rela=ve 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 Four Forces of Flight Wing Wing Lig •  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 bo;om and lower pressure on the wing top creates lig •  Newton’s Third Law The wings Angle of A;ack (AOA) creates a force that increases lig !  The air leaving the trailing edge pushes down which creates lig !
Wing Geometry Wing •  Wing Aspect Ra=o – the ra=o of the wing area to the mean cord In a rectangular wing, the ra=o of the span to the cord !  The greater the ra=o (like a glider), the less drag created and lower the stall speed !
•  Wing Dihedral -­‐ upward inclina=on of an aircrag wing in rela=on to the lateral axis !
Adds to lateral stability – helps level the aircrag