Army Aviation Information Test Flashcards
(145 cards)
1
Q
Describe the components of the helicopter structure.
A
- Fuselage
- Mast
- Engine
- Main rotor
- Second rotor
2
Q
What is the fuselage?
A
Body of the craft
3
Q
What is a mast?
A
Cylindrical metal shaft that protrudes upward out of the fuselage.
4
Q
What does the engine of the craft do?
A
Drives power upward through the mast to the rotor blades, which are controlled by the pilot.
5
Q
What is the main rotor used for?
A
To generate lift and thrust
6
Q
How is thrust from the main rotor balanced?
A
By a second rotor. (Usually a tail rotor)
7
Q
What is a tail rotor intended for?
A
To account for the effects of torque.
8
Q
What direction is it conventional for rotors in the USA, UK, and Germany to turn?
A
Main rotor rotates counter clockwise.
9
Q
What are some advantages of rotorcraft?
A
- Takeoff vertically
- Hover
- TOL in places planes can’t
- Perform tasks such as drop cargo/troops in challenging conditions.
10
Q
What are the helicopter types?
A
- Single main rotor helicopters
- Tandem rotor helicopters
- Coaxial rotor helicopters
11
Q
What is the most common design for a helicopter?
A
Single main rotor helicopters
12
Q
Describe the single main rotor helicopter.
A
- Single main rotor generating power with a secondary rotor such as a tail rotor
- Tail rotor is used to offset the effects of torque
13
Q
What’s one disadvantage of the single main rotor helicopter design?
A
Some power is used for countering torque, rather than being used solely for lift.
14
Q
Describe the tandem rotor helicopter.
A
- Has a front and rear main rotating blade
- Each set of blades rotates counter to the other, meaning torque is automatically offset
- No need for a tail rotor to deal with torque
- Because of this, all of the power from the engine can be used for lift.
- These are some of the fastest and most powerful in existence
15
Q
Describe the coaxial rotor helicopter.
A
- Two sets of blades above and beneath each other
- Mounted to the same mast
- Rotates in opposite directions to each other
- This has the advantage of reducing payload and allowing for greater cargo/passenger capacity.
16
Q
What is thrust created by?
A
The engine(s)
17
Q
How is thrust transferred into motion?
A
Via the mast and rotors
18
Q
Define drag.
A
A force which acts against thrust.
19
Q
What causes drag?
A
The shape and size of the aircraft disrupting the flow of air as it travels.
20
Q
What are the types of drag that impact helicopters?
A
- Profile drag
- Form drag
- Skin friction drag - Induced drag
- Parasite drag
- Total drag
21
Q
How is profile drag created?
A
Caused by the frictional resistance of helicopter blades passing through the air.
22
Q
Describe the two components of profile drag.
A
Form: Increases as the speed of the helicopter increases.
Skin: Caused by microscopic roughness of the helicopter blades.
Any roughness on the surface causes air to become trapped and drag to increase.
23
Q
How is induced drag created?
A
- Caused by airflow circulation around the blades creating vortices
- This type of drag increases when the helicopter is flying at lower speeds and decreases when it is flying at higher speeds.
- During low speed flight, induced drag is the main cause of drag.
24
Q
How is parasite drag created?
A
- By the helicopter components that are external to the fuselage
- EX: Landing gear, cowlings, and doors can all create parasite drag.
- This drag slows down the speed of a helicopter by opposing thrust.
25
Define total drag.
The sum total of the profile, induced and parasite drag acting upon the helicopter at any given time.
26
What are some benefits of total drag being at its lowest?
- Maximum endurance
- Best rate of climb
- Minimum rate of descent in autorotation.
27
Define weight.
- Force which results from the combines mass of a helicopter being acted upon by gravity.
- It is a downward force which acts through the center of gravity of the helicopter.
28
Define lift.
The upward force created by the spinning of the helicopter blades allowing air to pass over them.
29
Define AOA (angle of attack).
A description of the angle at which the helicopter blade's direction of movement is relative to the air.
30
What can impact the AOA?
- Sometimes manipulated by the pilot, by moving the cyclic and collective
- Also impacted by factors outside the control of the pilot, such as blade flapping and flexing and turbulent conditions.
31
Describe the angle of incidence.
- Is the intersection of the chord line with the plane of rotation.
- Also known as the blade pitch angle.
- This is a mechanical angle, rather than an aerodynamic angle.
32
What are the 3 scientific principles that apply to helicopters.
1. Bernoulli's principle
2. Venturi flow
3. Newton's third law of motion
33
Define Bernoulli's principle.
-When lower pressure occurs over a wing blade than under it, lift is achieved.
- This happens because the airflow is traveling faster above the blade than underneath it.
34
Describe what venturi flow means.
- States that the amount of energy within a closed system, a tube, does not change, but can change form.
- This applies to the top of the blades.
- The flow of air accelerates over the curved area of the blade.
- This creates a needed pressure differential. caused by an imbalance of static and dynamic pressure.
35
Describe Newton's third law of motion.
- "For every action, there is an equal and opposite reaction."
- The downward deflection of air causing an equal opposing reaction, pushing the blade upward.
36
What are the 4 main flight controls?
1. Cyclic
2. Pedals
3. Collective
4. Throttle
37
What does a cyclic resemble?
A joystick.
38
What does moving the cyclic do?
Allows the pilot to alter the pitch angle of the main rotor blades, which causes thrust in a particular direction.
39
Where is the collective located and what does it do?
- Located to the left side of the pilot's feet and serves the purpose of simultaneously moving the pitch angle of the main blades.
- This impacts upon the total level of lift or thrust.
- As a result, the collective is used to increase or decrease altitude or airspeed.
40
Where are anti-torque pedals located?
At the pilots feet.
41
What do the anti-torque pedals do?
- Adjust the pitch of the tail rotor, altering the amount of thrust produced.
- Changes the direction of the nose of the helicopter.
42
What does the throttle control usually resemble?
Motorcycle-style rotating grip.
43
What's the difference in throttles for dual engine aircraft?
There is a separate throttle for each engine, usually taking form of a lever.
44
What are the 4 basic flight maneuvers?
1. Straight and level
2. Turns
3. Climbs and descents
4. Hovering
45
What is straight and level flight?
- When a helicopter moves at a steady altitude and heading.
46
How is straight and level flight achieved?
- Tilting the nose forward, increasing the speed at which the helicopter moves.
- The lower the nose, the more power required.
47
How are turns achieved?
- By pushing the cyclic in the desired turning direction.
- This causes the rotor to tilt.
- The anti-torque and throttle controls are used in conjunction to ensure the altitude is maintained during the turn and the process is smooth.
48
What is hovering?
When helicopter moves as minimally as possible at a constant heading and altitude over a reference point.
48
How are climbs and descents achieved?
- Through manipulation of the collective.
- Moving the collective manipulates the amount of lift, causing the helicopter to rise or fall as the pilot desires.
49
How is hovering achieved?
By the pilot subtly correcting variations in motion
50
What is the key to hovering?
Make very small corrective motions which are ceased before the helicopter begins to move.
51
What are the 3 types of helicopter taxi?
1. Hover taxi
2. Air taxi
3. Ground taxi
52
How high does hover taxiing occur?
25 ft or less above ground level.
53
How high does air taxiing occur?
100 ft or less and requires the pilot to avoid flying over people, vehicles, and other aircraft.
54
What are the types of army aircraft?
- Sikorsky UH-60 Blackhawk
- Boeing CH-47 Chinook
- Boeing AH-64 Apache
- Eurocopter UH-72 Lakota
- Bell OH-58 Kiowa
55
Describe the Sikorsky UH-60 Blackhawk and its purpose.
- Four-bladed, single main rotor helicopter.
- Introduced in 1979.
- 4 crew (2 pilots 2 crew chiefs)
- Max load 2640 lbs (or 11 combat equipped troops)
- 150 knots/320 nm range
- Primary medium-lift utility transport and air assault aircraft
- Built for long range, high threat missions
- Used as a troop carrier in combat assault missions, MEDEVAC, cargo delivery, special ops support, & humanitarian assistance
- Has the capacity to carry combinations of guns and other weaponry, including M240 machine guns, M134 Minions, Hydra-70 rockets, and the VOLCANO mine field dispersal system.
56
Describe the Boeing CH-47 Chinook and its purpose.
- Twin engine, tandem rotor helicopter.
- Introduced in 1962.
- Speeds up to 170 knots ish
- Primarily used for heavy lifting purposes, such as transporting cargo or troops.
57
Describe the Boeing AH-64 Apache and its purpose.
- Twin turboshaft attack helicopter.
- Introduced in 1986.
- Equipped with a 1200 round M230 chain gun.
- Carries a combination of Hydra-70 air to ground rockets and AGM-114 hellfire missiles.
58
What all governs the speed of the air flowing across the blades?
1. Shape of the revolving blade
2. Air velocity of the helicopter
3. Position of the airfoil in the plane
59
What is unique about the shape of a helicopter blade?
- It is made in such a way that for every revolution, the longitudinal velocity vector is sometimes with the helicopter's forward velocity and sometimes opposite to it.
- EX: A regular helicopter blade that revolves counterclockwise generates a maximum airflow velocity at its 3 o'clock position and a minimum at its 9 o'clock position.
60
What is autorotation?
- A situation during flight of an airborne helicopter, when air lift in generated only by the air flowing across its blades.
- In case of a failure, this feature allows pilots to land the helicopter without crashing it.
- On failure, the freewheeling unit comes in effect to disconnect power to the mains rotor.
- As a result, the blades spin freely, causing autorotation of the helicopter by the air present around them.
61
What is freewheeling?
Mandatory feature for autorotation in helicopters according to aviation standards, and all helicopter pilots are trained to use this feature in case of emergencies to avoid crashes.
62
How is autorotation during. helicopters forward motion minimized?
- By reducing the driven region on the retreating blade.
- During forward motion, the rotor disc experiences lift by upward flowing air on the driven, driving and stall region along the length of the blade, and on the retreating side of the blades (in counter clockwise motion, the blades move from the nose to the tail).
- The driven region expands on the advancing side due to the lower AOA, while the stall region expands on the retreating side.
- The driven region on the retreating side is also reduced by reversed airflow.
63
True or False:
The relative wind is slower near the root of the blade than on the tip.
True. This results in different aerodynamic forces across the surface of the blade in the driven, driving, and stall regions.
64
What effect does blade twist have one the AOA in the driven region?
- Makes the AOA in the driven region smaller than the AOA in the driving region.
- This causes deceleration of the rotor, as the lift produced by hovering ins neutralized by air drag, due to total aerodynamic force (TAF).
65
What 3 things influence the size of the driving region?
1. Number of RPM
2. Blade pitch
3. Rate of descent
*Therefore, the driving region can be altered by changing any of these features.*
- This generates an acceleration force responsible for thrust.
66
Describe the stall region of a hovering helicopter.
- Is the circular area formed by the revolving of the first quarter of the blade from the root of the rotor.
- The AOA during hovering is maximized, creating drag and subsequently, reducing blade rotation.
67
What causes blade flapping?
Greater airlift during hovering.
68
In regards to blade flapping, describe the blade angles design.
- It is designed in such a way that during hovering, air lift is balanced by the centrifugal forces of the spinning wheel.
- The blades move faster to balance the lift that is increased by airflow, or spins of the blades, during autorotation while hovering.
69
What is a blade span?
The distance between the tip of the blade and the drive shaft on the rotor it is attached to.
70
What is blade twist?
A design feature of a helicopter blade to distribute air lift evenly throughout the surface of the airfoil.
71
How is blade twist attained?
By generating greater pitch angles toward the blade root. one low rotational velocities, and vice versa.
72
When does dissymmetry of lift occur?
During take off.
73
What causes dissymmetry of lift?
- Caused by the difference in amounts of force experienced by advancing and retreating blades of the helicopter on either side of the rotor disc.
* Due to forward motion, the wind speed on the advancing is more prone to create unbalance, which eventually causes the helicopter to crash*
74
How is dissymmetry countered ?
By blade flapping, which. its when the retreating blade flaps down and the advancing blades flaps up, and vice versa.
75
When is maximum ground effect noticeable?
When a helicopter hovers above a smooth, hard surface at a height equal to the diameter of the circular path of the revolving blades.
76
How does lift act in ground effect?
Vertically, reducing induced rage and creating optimized conditions for maximum efficiency of the rotor system.
77
What is setting with power?
- That state of a helicopter's flight when it descends vertically downward, at about a rate of 5 ft per second and low forward speeds.
- It is a state of stall when, even though the main rotor system is using 20% up to 100% of the power generated by the engine, the down flow produced by the spinning blades is uses to overcome the up flow caused by drastic descent, leading to turbulence.
78
What is the vortex ring state?
Another name for settling with power. Since maximum power is used by the rotor, minimal or no power is available for the pilot to stop the descent.
79
What can be classified into scalar and vectors?
All physical quantities, such as length, time, mass, speed, velocity, and force.
80
What is a scalar?
- Physical quantities that have only a magnitude or size.
- EX: distances between two points and mass of a body.
81
Describe force.
- A vector quantity, having both magnitude and direction. It is defined as a push or pull.
- The international system of units (SI) unit of force is Newton (N).
- It can also be measured in pounds force (1bF)
82
What’s another name for Newtons 1st law of motion?
Law of inertia
83
What is Newton’s 1st law of motion?
- The law that states that “Until acted on by an external force, an object’s velocity will remain constant.”
84
What is intertidal of a body?
The force inside the body that resists the change in state of rest or motion of a body.
85
What is Newton’s 2nd law of motion?
States that the acceleration of an object depends upon two variables - the net force acting on the object and the mass of the object.
86
Mathematically, Newton’s 2nd law of motion is…
Force = Mass of the body x acceleration on the body
87
What is Newton’s 3rd law of motion?
For every action there is an equal and opposite reaction.
88
What is Newton’s law of gravitation and weight?
- States that every body in the universe is attracted to every other body by a force directly proportional to their masses, and inversely proportional to the square of the distance between them.
- Mathematically, the force between two bodies is given by:
Force = G x mass of body 1 x mass of body 2 / Distances between the bodies ^2
Where G is the constant of proportionality and is equal to 6.674 x 10 ^-11 Nm^2/kg^2
89
What is the mathematical formulas for force and weight?
- Force = mass x acceleration
- Weigh = mass x acceleration due to gravity
90
What is the difference between mass & weight?
- The mass of the body is fixed. It is the amount of substance in a body.
- Weight depends on acceleration due to gravity. If the gravitational field is changed, weight changes, while mass remains the same.
91
What is center of gravity?
That point of a body through which the weight of the body acts.
92
Define torque.
- The product of force and moment arm.
- It is a vector quantity with the SI unit of Nm
- Also called a moment of a force
- It causes a rotation of a body about a point called the pivot or the fulcrum
93
What is the formula for torque?
Torque = Force x perpendicular distance from the pivot
94
What are the two types of friction?
Static & kinetic
95
Define static friction.
Defined as the friction applied by a body at rest in reaction to a force attempting to move it.
96
What two forces does a body at rest experience?
It’s weight acting downwards and the reaction of the weight acting normal or perpendicular to the weight.
97
How does kinetic friction occur?
- When a force is applied to move the body, the force preventing it to move is the force of static friction.
- It is in the opposite direction of applied force.
- the magnitude of frictional force os limited, and once a force greater than frictional force is applied, the body begins to move.
- Once the body is set in motion, it no longer experiences static friction, but now kinetic friction.
- The direction of al types of friction is opposite to the direction of applied force
98
What does the law of conservation of energy state?
Energy can neither be created, nor be destroyed, but it can only. Change from one form to another. (Measure in foot-pound force ft-1bF)
99
How is potential energy of a body due?
Due to the position of a body at rest
100
What is the formula for potential energy?
Potential energy = mass x acceleration due to to gravity x height = mgh
101
What is the formula for kinetic energy?
- Kinetic energy of a body is due to its motion
-Kinetic energy = 1/2 x mass x (velocity of the body)^2 = mv^2
102
Define work.
- The product of force and displacement.
- When a body is moved a distance, the work done by the body is proportional to the force applied and the distance through which it is placed.
103
What is the formula for work done?
- Work done = Force x displacement
- Measured in foot-pound force (ft-lbf)
104
Define power
Rate of work done.
105
What is the formula for power?
Power = Work done/time taken
106
What is the formula for mechanical advantage?
Mechanical = Output force/Input force
107
What do levers consist of?
Three mechanical bodies
1. Input arm
2. Fulcrum/pivot
3. Output arm
108
What are the 3 types of levers?
1. First class levers
2. Second class levers
3. Third class levers
109
Describe first class levers.
- They have the pivot in the center and the input and output arms on either side.
- The input force, applied perpendicular on the input arm, creates a torque about the pivot.
- The pivot transfers the torque to the other side.
- EX: seesaw
- The limitation of this lever is that it cannot move loads over a great distance.
110
Describe a 2nd class lever.
- Have the output force, or load, between the fulcrum and the input force.
- EX: Wheel barrow
111
Describe third class levers.
- They have the input force acting between the fulcrum and the output load.
- EX: When a batsman hits a ball using a bat, his front arm behaves like a fulcrum, his back arm provides the input force, and the output load is experienced by the ball he strikes
112
Define an inclined plane.
- Defined as planes making a certain angle with level ground.
- The slope of incline planes depend on this angle.
- The greater the angle, the greater the slope of the plane, and vice versa.
113
What is the formula for mechanical advantage and what is it used for?
Used to determine mechanical advantage of an inclined plane
Mechanical advantage = Length of the inclined plane/height of the plane
114
Do you have a greater mechanical advantage with a longer or shorter ramp?
- Longer, however, it is not feasible to make ramps with very long lengths because the weight of a body on the ramps act vertically downward.
115
What does a screw consist of?
Consists of an inclined plane tied around its circumference.
116
What is the small distance between two successive threads called? What does it represent?
The pitch of the screw and it represents the distance traveled by the screw on one complete rotation.
117
Describe a wedge.
Two inclined planes are used to work.
118
What is the formula for the mechanical advantage of a wedge?
Length of wedge / Thickness across the wedge
119
What is the formula for mechanical advantage of pulley?
Input force / output force
120
How can you increase the mechanical advantage of a pulley?
- Multiple wheels are ensembles together in a block and tackle arrangement.
- For a block and tackle arrangement, mechanical advantage is equal to the number of cord segments in the assembly.
121
How does the block and tackle arrangement increase the mechanical advantage of the pulley system?
- At the cost of distance moved by the output load.
- The dit=stance moved by the output load decreases by the reciprocal of the mechanical advantage, for the same amount of force required.
122
What is the formula for mechanical advantage of a simple machine formed by a wheel and axle that is attached coaxially?
Radius of input wheel / Radius of output wheel
123
What is the mechanical advantage for a single axle that can be used to rotate two wheels of different sizes?
Radius of input wheel / Radius of output wheel.
124
What do gears form?
A simple machine used to transmit torque and rotation over greater distances.
125
What is the formula for the mechanical advantage of gear?
1 / Mechanical advantage of wheel and axle
126
What does it mean when the mechanical advantage of a gear arrangement is 2?
It means the output gear has a radius double the input wheel, and it rotates once every two rotations of the input wheel.
127
What do wheels and gears work off of?
The basis of torque equilibrium.
128
Why are gear trains applied?
To increase or decrease torque and speed.
129
How is the the increased or decreased torque and speed obtained?
By using gears of different sizes at input and output.
130
What does a smaller input gear driving a bigger output gear do?
Multiplies torque, but reduces speed.
131
What does a bigger input gear driving a smaller gear do?
Reduces torque, but increases speed.
132
What is a fluid?
Anything that flows and is incompressible, such as liquid and pressurized gases.
133
What are fluids used for?
To transmit force over great distances where it is not feasible to install mechanical systems.
134
Define pressure.
Defined as force per unit area.
135
What are the different units of pressure?
- Pascals (Pa)
- Pounds per square inch (psi)
- Newton per square meter (N/m^2)
- Inches of mercury (inHg)
136
What happens to pressure applied to a liquid column?
Like tension in a rope, it is evenly distributed throughout the bulk of fluid present. This is why it is important for the fluid to be incompressible.
137
How is pressure applied in a basic hydraulic system?
Pressure applied on the input piston is transmitted to the output piston by the fluid present between them
138
What does input pressure equal mathematically?
Output pressure
139
What does the mechanical advantage of 2 mean in a hydraulic pressure system?
The area of the output piston is double the area of the input piston, but moves 1/2 the distance moved by the input system.
140
What is the formula for mechanical advantage of a hydraulic pressure transmission?
Area of the output piston / Area of the input system
141
What does the aw of conservation of mass state?
That the volumetric flow rates of a fluid at input and output are equal.
142
What does volumetric flow rate eat input equal mathematically?
Volumetric flow rate at output.
143
What is volumetric flow rate a product do?
Cross-sectional area of pipe and velocity of fluid particles.
144
What does Bernoulli’s principle state?
Energy must be conserved in the flow of a fluid.
