1
Q
Density
A
weight taken up for a given volume.
2
Q
unit volume
A
The unit volume selected for use in the English system of
measurement is 1 cubic foot (ft3). In the metric system, it
is 1 cubic centimeter (cm3). Therefore, density is expressed
in pounds per cubic foot (lb⁄ft3) or in grams per cubic
centimeter (g⁄cm3).
3
Q
density of gases
A
Pressure is more critical when measuring the density of gases than it is for other substances. The density of a gas increases in direct proportion to the pressure exerted on it
4
Q
Specific Gravity
A
Also known as relative density
hydrometer is used for measuring specific gravity of liquids
Weight of a substance divided by weight of an equal volume of water
Density of a substance divided by Density of water
Water is the standard/constant
5
Q
Gasoline
A
Potential to release heat energy measured in BTU -> each BTU is capable of 778 ft-lb of work
6
Q
Work
A
in the mechanical sense of the term, is done when a
resistance is overcome by force acting through a measurable
Distance.
In calculating work done, the actual resistance overcome is
measured. This is not necessarily the weight of the object
being moved.
7
Q
Power
A
Includes TIME (ft-lb/s - ft-lb/min - mi-lb/hr - 1 hp = 746 watts (electricity conversion)
8
Q
Torque
A
Whereas work is described as force acting through a distance, torque is described as force acting along a distance.
9
Q
Force
A
Thrust: intensity of an input
The unit for force in the English system of measurement
is pounds, and in the metric system it is newtons
In the English system, the force will be identified in pounds
and the distance either in feet or inches, so the units will be
foot-pounds or inch-pounds. Notice these are the same units
that were used for potential and kinetic energy.
In the metric system, the force is identified in newtons (N)
and the distance in meters, with the resultant units being
joules. One pound of force is equal to 4.448 N and one meter
is equal to 3.28 feet. One joule is equal to 0.74 ft-lb
10
Q
Distance Mechanical Advantage
A
(Diameter) Drive over Driven
Driven = Effort
11
Q
Force Mechanical Advantage
A
(Diameter?) Driven over Drive
Driven = Effort
*
12
Q
Sun gear
A
Ring Teeth over Sun Teeth
13
Q
Centrigrade
A
0 Freezing 100 Boiling
14
Q
Fahrenheit
A
32 Freezing 212 Boiling
15
Q
Kelvin
A
Absolute 0 = -273C
*
16
Q
Rankine
A
Converts F to Absolute using 460
*
17
Q
Units for measuring Atmospheric Pressure
A
PSI, HG- refers to inches of mercury (inHg) or millimeters of mercury (mmHg), milibars/mbar (1 is equivalent to 100 pascals) (barometer- used in determining altitude)
18
Q
Absolute Pressure
A
PSIa = Gauge Pressure + Atmospheric Pressure
19
Q
Gauge Pressure
A
gPSI = Pressure reading above ambient: Oil…
20
Q
Differential Pressure
A
dPSI = Pressure on one side then pressure on the other; difference between pressure at 2 locations. (Overall pressure goes up during blockage)
21
Q
Hydrostatic pressure
A
pressure exerted increases as you go deeper. : Earth’s atmosphere is hydrostatic. Air gets thinner as you go higher.
22
Q
Volume and Pressure
A
Inversely Related
23
Q
Volume and Temp
A
Proportionate
24
Q
Pressure and Temp
A
Proportionate
25
Boyle + General Gas Law
Charles
26
General Gas Law
27
Dalton’s Law
Mix of non-reactive gases exert pressure equal to sum of the pressures the gasses would exert separately if alone.
28
Fluid Pressure
Height solely determines pressure exerted, even if liquids were different volumes.
29
Metered pressure
measures contained fluid; fully controlled.
30
Mach number
the ratio of the speed of an aircraft to the speed of sound
-Sound
Speed of sound is 761 mph or MACH 1.
Subsonic is less than MACH 1.
Supersonic is greater than MACH1.
31
Speed of sound is affected by
medium and temperature.
32
Shear
cutting force
33
Tension
pulling force
34
Compression
crushing force
35
Torsion
twisting force
36
Bending
Peak Tension + Compressed Compression
37
Strain
Matter tends to be elastic. Forced out of shape. When object is distorted by force object is strained.
38
Kinematics
Relationship between velocity, acceleration, and distance
39
Acceleration
Rate change of Velocity
40
Boyle’s Law
Volume and Pressure inversely related. PV=k. Constant Temperature (fixed mass)
41
Charles’ Law
Volume and Absolute Temperature (Kelvin) Proportional. Constant Pressure (fixed amt gas)
42
Pascal’s Law
Pressure change, in confined incompressible fluid, is transmitted equally and undiminished. (Hydraulic Systems)
43
Bernoulli’s
Increase in Speed of Fluid, is Accompanied by Decrease in Pressure.
44
AoA
Angle between Chord and Relative Wind. As AoA increases, Lift on Wing Increases. If AoA becomes too great the airflow can separate which destroys lift - Stall
45
Angle of Incidence
Angle formed by insection of the wing chord line and horizontal plane passing through the longitudinal axis. Many planes are designed with greater Angle of Incidence at the root of the wing than at the tip, and this is referred to as washout. This feature causes the inboard part of the wing to stall before the outboard part, which helps maintain aileron control during the initial stages of a wing stall.
46
High Aspect Ratio
Less drag (glider)
Low stall speed
47
Angle of Attack and Lift are:
Proportional
48
As the friction between the air and the surface of the wing increases:
the boundary layer thickens and becomes more turbulent and eventually a wing stall occurs. With a smooth and clean wing surface, the onset of a stall is delayed and the wing can operate at a higher angle of attack.
49
Methods of Controlling Boundary Layer
Wing Leading Edge Slots: duct that allows air to flow from the bottom of the wing, through the duct, to the top of the wing
Air Suction through small holes on Wing’s Upper Surface: suction on the top of the wing draws away the slow-moving turbulent air, and helps keep the remainder of the airflow in contact with the wing
Vortex Generators: Low pressure air mixes with turbulent airs: used on airplanes that fly at high subsonic speed, where the velocity of the air on the top of the wing can reach Mach 1. As the air reaches Mach 1 velocity, a shock wave forms on the top of the wing, and the subsequent shock wave causes the air to separate from the wing’s upper surface. Vortex generators are short airfoils, arranged in pairs, located on the wing’s upper surface. They are positioned such that they pull high-energy air down into the boundary layer region and prevent airflow separation
50
3 Principles of Lift
Bernoulli’s Principle
Newton’s 3rd Law
Coanda Effect: tendency of fluid to stick to curved surfaces.
51
Inverse of Thrust
Drag
52
Wingtips
Weaker Vortex
Reduce Drag - Improve fuel efficiency
53
Inverse of Lift
Weight (Gravity)
54
Chord
leading edge to trailing edge
55
Dihedral
upward angle: when banking or rolling, dihedral wing on one side gives stability or lateral control.
56
Anhedral
downward angle
57
Wingtips
weaker vortex. Reduce drag - improve fuel efficiency.
58
(Plane) Vertical Axis
Yaw: Rudder (Left Right): Rudder Pedals
59
(Plane)Lateral Axis
Pitch: Elevator (Up Down): Yoke
60
(Plane) Longitudinal Axis
Roll: Aileron (Barrel Roll): Yoke
61
(Rotorcraft) Vertical Axis
Yaw: Anti-Torque rotor or Tail Rotor (Left Right): Anti-Torque Pedals / Rudder Pedals
62
(Rotorcraft) Lateral Axis
collective and cyclic pitch controls
63
(Rotorcraft) Longitudinal Axis
collective and cyclic pitch controls
64
Collective Pitch Lever
Side of pilot’s seat: When lever is raised blade angle of all rotor blades increases uniformly and they create LIFT for vertical take-off. Grip on the end of collective pitch control is the throttle, which is rotated to increase engine power as the lever is raised.
65
Cyclic Pitch Lever
Front of pilot’s seat in the middle.: Pitch of Rotor Blades: Bank Left Right: Comparable to YOKE, pushed forward or pulled backward, moved left and right. : Pitch Change Rods: When the cyclic pitch lever is pushed forward, the rotor blades create more lift as they pass through the back half of their rotation and less lift as they pass through the front half. The difference in lift is caused by changing the blade angle, or pitch, of the rotor blades. The pitch change rods that
the pilot will also push on the right anti-torque pedal to counteract the main rotor torque. By using the anti-torque pedals, the pilot can intentionally make the helicopter rotate in either direction around the vertical axis. Some helicopters have a vertical stabilizer, such as those shown in Figures 5-90 and 5-92. In forward flight, the vertical stabilizer creates a force that helps counteract the torque of the main rotor, thereby reducing the power needed to drive the anti-torque system located at the end of the tail boom.
66
Trim Tab
Acrodynamic: Secondary flight control - Set to parameter to counterbalance roll - can only be on wing but not always.
67
Flaps
Aerodynamic: Surface that changes the chord line of the wing to produce more lift. (Inboard flap, Outboard aileron)
68
Airplane Movement
1. When an airplane is accelerating, it has more thrust than drag.
2. When an airplane is decelerating, it has less thrust than drag.
3. When an airplane is at a constant velocity, thrust and drag are equal.
4. When an airplane is climbing, it has more lift than weight.
5. When an airplane is descending, it has more weight than lift.
6. When an airplane is at a constant altitude, lift and weight are equal
69
Humid air is not as efficient in engines
Less air less combustion.
70
Pressure altitude is converted to density altitude by
calibrated altimeter settings.
71
For a Particular gas, density is determined by
pressure and temperature
72
Density decreases with:
increased altitude
73
Atmospheric Density
Since both temperature and pressure decrease with altitude, it might appear that the density of the atmosphere would remain fairly constant with increased altitude. This is not true, however, because pressure drops more rapidly with increased altitude than does the temperature. The result is that density decreases with increased altitude. By use of the general gas law, studied earlier, it can be shown that for a particular gas, pressure and temperature determine the density. Since standard pressure and temperatures have been associated with each altitude, the density of the air at these standard temperatures and pressures must also be considered standard. Thus, a particular atmospheric density is associated with each altitude. This gives rise to the expression “density altitude,” symbolized “Hd.” A density altitude of 15,000 ft is the altitude at which the density is the same as that considered standard for 15,000 ft. Remember, however, that density altitude is not necessarily true altitude. For example, on a day when the atmospheric pressure is higher than standard and the temperature is lower than standard, the density which is standard at 10,000 ft might occur at 12,000 ft. In this case, at an actual altitude of 12,000 ft, we have air that has the same density as standard air at 10,000 ft. Density altitude is a calculated altitude obtained by correcting pressure altitude for temperature.
74
Dew Point
The dew point is the temperature to which humid air must be cooled at constant pressure to become saturated. If the temperature drops below the dew point, condensation occurs. People who wear eyeglasses have experience going from cold outside air into a warm room and having moisture collect quickly on their glasses. This happens because the glasses were below the dew point temperature of the air in the room. The air immediately in contact with the glasses was cooled below its dew point temperature, and some of the water vapor was condensed out. This principle is applied in determining the dew point. A vessel is cooled until water vapor begins to condense on its surface. The temperature at which this occurs is the dew point.
75
Vapor Pressure
Vapor pressure is the portion of atmospheric pressure that is exerted by the moisture in the air, which is expressed in tenths of an inch of mercury. The dew point for a given condition depends on the amount of water pressure present; thus, a direct relationship exists between the vapor pressure and the dew point.
76
Simple Machines A machine is any device with which work may be accomplished. For example, machines can be used for any of the following purposes, or combinations of these 5 purposes:
1. Machines are used to transform energy, as in the case of a generator transforming mechanical energy into electrical energy.
2. Machines are used to transfer energy from one place to another, as in the examples of the connecting rods, crankshaft, and reduction gears transferring energy from an aircraft’s engine to its propeller.
3. Machines are used to multiply force; for example, a system of pulleys may be used to lift a heavy load. The pulley system enables the load to be raised by exerting a force that is smaller than the weight of the load.
4. Machines can be used to multiply speed. A good example is the bicycle, by which speed can be gained by exerting a greater force.
5. Machines can be used to change the direction of a force. An example of this use is the flag hoist. A downward force on one side of the rope exerts an upward force on the other side, raising the flag toward the top of the pole. There are only six simple machines. They are the lever, the pulley, the wheel and axle, the inclined plane, the screw, and the gear. Physicists, however, recognize only two basic principles in machines: the lever and the inclined plane. The pulley (block and tackle), the wheel and axle, and gears operate on the machine principle of the lever. The wedge and the screw use the principle of the inclined plane. An understanding of the principles of simple machines provides a necessary foundation for the study of compound machines, which are combinations of two or more simple machines
77
Mechanical Advantage of Machines
a machine can be used to multiply force or to multiply speed. It cannot, however, multiply force and speed at the same time. In order to gain one force, it must lose the other force. To do otherwise would mean the machine has more power going out than coming in, and that is not possible. In reference to machines, mechanical advantage is a comparison of the output force to the input force, or the output distance to the input distance. If there is a mechanical advantage in terms of force, there will be a fractional disadvantage in terms of distance. The following formulas can be used to calculate mechanical advantage. Mechanical Advantage = Force Out ÷ Force In or Mechanical Advantage = Distance Out ÷ Distance In
78
Levers
Both first and second class levers are commonly used to help in overcoming big resistances with a relatively small effort. The first class lever, however, is more versatile. Depending on how close or how far away the weight is placed from the fulcrum, the first class lever can be made to gain force or gain distance, but not both at the same time. The second class lever can only be made to gain force.
There are occasions when it is desirable to speed up the movement of the resistance even though a large amount of effort must be used. Levers that help accomplish this are third Resistance “R Effort “E “L” “l” Fulcrum “F class levers
The retractable main landing gear on an airplane is a good example of a third class lever. The top of the landing gear, where it attaches to the airplane, is the pivot point. The wheel and brake assembly at the bottom of the landing gear is the resistance. The hydraulic actuator that makes the gear retract is attached somewhere in the middle, and that is the applied effort
A single fixed pulley is really a first class lever with equal arms. The only advantage of a single fixed pulley is to change the direction of the force, or pull on the rope.
This single, movable pulley will act like a second class lever. This type of pulley would have a mechanical advantage of two because the diameter of the pulley is double the radius of the pulley. In use, if someone pulled in 4 ft of the effort rope, the weight would only rise off the floor 2 ft. If the weight was 100 lb, the effort applied would only need to be 50 lb. With this type of pulley, the effort will always be one-half of the weight being lifted.
A block and tackle is made up of multiple pulleys, some of them fixed and some movable. The number of weight supporting ropes determines the mechanical advantage of a block and tackle,
Two gears with teeth on their outer edges, as shown in Figure 5-13, act like a first class lever when one gear drives the other. The gear with the input force is called the drive gear, and the other is called the driven gear. The effort arm is the diameter of the driven gear, and the resistance arm is the diameter of the drive gear. Imagine that the blue gear is driving the yellow one, which makes the blue the drive and the yellow the driven. The mechanical advantage in terms of force would be the effort arm divided by the resistance arm, or 9 ÷ 12, which is 0.75. This would actually be called a fractional disadvantage, because there would be less force out than force in. The mechanical advantage in terms of distance, in rpm in this case, would be 12 ÷ 9, or 1.33. This analysis tells us that when a large gear drives a small one, the small one turns faster and has less available force. In order to be a force gaining machine, the small gear needs to turn the large one.
Whenever a machine is in operation, be it a simple machine like a lever or a screw, or a more complex machine like an aircraft piston engine or a hydraulically operated landing gear, the parts and pieces of that machine will experience something called stress. Whenever an external force is applied to an object, like a weight pushing on the end of a lever, a reaction will occur inside the object which is known as stress. Stress is typically measured in pounds per square foot or pounds per square inch (psi)
79
Input Piston Area (Distance Moved)=
Output Piston Area (Distance Moved) This formula shows that the volume in is equal to the volume out. This concept is shown in Figure 5-45, where a small input piston moves a distance of 20 inches, and the larger output piston only moves a distance of 1 inch. Example: A two-piston hydraulic system, like that shown in Figure 5-45, has an input piston with an area of 1⁄4 in2 and an output piston with an area of 15 in2. An input force of 50 lb is applied, and the input piston moves 30 inches. What is the pressure in the system, how much force is generated by the output piston, how far would the output piston move, and what is the mechanical advantage? Pressure = Force ÷ Area = 50 ÷ 1⁄4 = 200 psi Force = Pressure × Area = 200 × 15 = 3,000 lb Mechanical Advantage = Force Out ÷ Force In = 3,000 ÷ 50
80
Mechanical Advantage
Force Out over Force In
81
Absolute Humidity
Is the actual amount of water vapor in an air/water mixture
Warmer air has a higher level of absolute humidity
Hotter air can absorb more water
82
Relative Humidity
Water actually in the atmosphere compared to if it was fully saturated at that given temp and pressure
83
Speed of Sound is affected by
Medium and temparture
(Doubled under water)
General 1
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