Aerodynamic Principals Flashcards
(110 cards)
1
Q
What does aerodynamics deal with?
A
The motion of air and the forces acting on bodies moving relative to the air.
2
Q
What are the four forces of flight?
A
Lift
Weight
Thrust
Drag
3
Q
What is lift?
A
The force created by the effect of airflow as it passes over and under a wing. The ariplain is typically supported in flight by lift.
4
Q
What is weight?
A
The downward pull of gravity.
5
Q
What is thrust?
A
The forward force which propells the airplane through the air. It varies with the amount of engine power being used.
6
Q
What is drag?
A
It’s a backward or retarding force which limits the speed of the airplane.
7
Q
What is unaccelerated flight?
A
The plane is maintaining a constant speed–neither accelerating or decelerating.
8
Q
What are vectors?
A
The arrows that show the forces acting on an airplane. Magnitude is indicated by the arrow’s length and direction is indicated by the arrow’s orientation.
9
Q
What is a resultant?
A
When two or more forces act on an object at the same time.
10
Q
In straight and level flight, describe the state of the four forces?
A
They are in equalibrium. Lift is equal to Weight and Thrust is equal to Drag.
11
Q
What is the resultant of two oposite forces that are equal in magnitude?
A
The resultant is zero.
12
Q
What is the direction of the resultant when Horizontal and Vertical forces are applied?
A
The resultant is diagonal.
13
Q
What is Newton’s first law of motion?
A
A body at rest tends to remain at rest, and a body in motion tends to remain moving at the same speed in the same direction.
14
Q
What is Newton’s second law of motion?
A
When a body is acted upon by a constant force, its resulting acceleration is inversely proportional to the mas of the body and is directly porportional to the applied force. (Force= mass X acceleration)
15
Q
What is Newton’s third law of motion?
A
For every action there is an equal but opposite reaction.
16
Q
What is Bernoulli’s principle?
A
As the velocity of a fluid (such as air) increases, it’s pressure decreases.
17
Q
What is an airfoil?
A
Any surface (such as a wing) that provides aerodynamic force when it interacts with a moving stream of air.
18
Q
How does the shape of a wing cause air to circulate over it?
A
Air accelerates as it passes over the wing and decellerates as it passes under the wing.
19
Q
What is upwash?
A
The deflection of the oncoming airstream upward and over the wing.
20
Q
What is the leading edge?
A
The part of the airfoil which meets the airflow first.
21
Q
What is the trailing edge?
A
The portion of the airfoil where the airflow over the upper surface rejoins the lower surface airflow.
22
Q
What is downwash?
A
The downward deflection of the airstream as it passes over and under the wing and past the trailing edge.
23
Q
What is the angle of attack?
A
The angle formed by the wing chord line and relative wind.
24
Q
What is a chord line?
A
An imaginary straight line drawn through the airfoil from the leading edge to the trailing edge.
25
What is relative wind?
The airflow which is parallel to and opposite the flight path of the airplane.
26
What is a wing's camber?
The characteristic curve of the airfoil's upper and lower surfaces. It impacts the difference in velocity between the airflow on the top and on the bottom of the wing.
27
Is flight path and attitude always the same thing?
No. A plane can be flying straight and level but still be descending due to less power. In this case the flight path would be forward and down and the relative wind would be upward and back.
28
How does Bernoulli's theorem relate to wing lift?
The increase in speed on the top of an airfoil produces a pressure drop on the top of the wing and the decreased in airspeed below the wing causes an increase in pressure below the wing. Together these pressures result in lift.
29
How does Newton's third law relate to downwash?
The opposite reaction to downwash results in an upward force on the wing.
30
What is coefficient of Lift?
A way to measure lift as it relates to angle of attack. Maximum lift occurs at a different angle of attack for every airfoil depending on design.
31
When does a stall occurr?
When the critical angle of attack is exceeded. This is regardless of airspeed, flight attitude, or weight.
32
How does coefficient of Lift relate to maximum lift and the angle of attack?
As the angle of attack increases, so does the coefficient of lift until you reach maximum lift. Once maximum lift is exceeded, lift rapidly decreases and there is a stall and the moment of the stall is the critical angle of attack.
33
What is the critical angle of attack?
The angle of pitch that causes and airplane to stall.
34
What is the definition of a stall?
A separation of airflow from the wing's upper surface.
35
How do you recover from a stall?
Decrease the angle of attack.
36
What are signs that a stall is beginning?
Mushy flight controls
A Stall Warning Horn
Slight buffetting of the airplane
37
What are the four things to be considered with wing design?
Wing planform
Camber
Aspect Ratio
Total Wing Area
38
What does Cl stand for?
Coefficient of Lift
39
What does Clmax stand for?
Maximum Lift
40
What is the boundary layer?
A thin layer of air next to the surface of an airfoil which shows a reduction in speed due to the air's viscocity or stickiness.
41
What are the two ways to describe a boundary layer?
Laminar
| Turbulent
42
What is a laminar airflow?
It begins near the leading edge and consists of smooth layers of air sliding over eachother. It eventually transitions to a thicker turbulent flow with higher velocities.
43
Which has higher velocity, laminar or turbulent airflow?
Turbulent
44
Is pressure higher or lower closest to the leading edge?
Pressure is highest closest to the leading edge and decreases with distance.
45
What is aspect ratio?
The relationship between the length and width of a wing. It's one of the primary characterisitics in determining lift and drag. The higher the aspect ratio, the more efficient the lift.
46
What is planform?
The shape of an airplane's wing when viewed from above or below.
47
What are four types of planform wings?
Eliptical
Rectangular
Tapering
Sweptback
48
What are the pros and cons of an eliptical planform wing?
Great for slow speeds
Hard to construct
Stall characterisitics are not as good as a rectangular wing
49
What are the pros and cons of a rectangular planform wing?
Not as efficient as eliptical
Good stall warning
Good aileron effectiveness
50
What are the pros and cons of a tapering planform wing?
Good for high speeds
| Best when combined with rectangular (so Tapering rectangular wing)
51
What are the pros and cons of a sweptback planform wing?
Efficient at high speeds but poor low speed performance
| Higher stall speeds
52
What is another name for sweptback wings?
Delta wings
53
What is the critical Mach number?
The speed at which the wing experiences supersonic airflow
54
What are the pros and cons of sweep forward wings versus sweep back wings?
Sweep back wings stall first at the wingtips
Sweep forward wings don't stall first at the wing tips and are much more efficient at slow speeds but do have a tendency to have their wings twist when high flight loads are applied and this can cause structural failure.
55
What is the angle of incidence?
The slight upward incline of the chord where the wings are attached to the fuselage. That angle is the angle of incidence.
56
What is Wing Twist as it relates to wing design?
The wing tip has a lower angle of incidence than the wing root.
57
What is another name for wing twist?
Washout
58
Why is it undesirable to have the wing stall at the tip first?
Because it can make your aileron's so ineffective that you can't control the airplane.
59
What are stall strips?
Metal strips attached to the leading edge of a wing near the fuselage. They disrupt air at high angles of attack causing the wing area directly behind them to stall before the wingtips stall.
60
What is the usual difference in angle of incidence on a wing twist?
2 or 3 degrees.
61
What is the byproduct of Lift?
Drag
62
How does a pilot increase lift?
Change the angle of attack
Lower flaps
Increase airspeed
63
How does lift and parasite drag relate to speed?
Lift and parasite drag are both proportional to the square of the airplain's speed.
64
How is the airspeed necessary to sustain a craft in flight determined?
Flap position
Angle of Attack
Weight
65
What are the two factors that determine lift?
Airspeed
| Angle of Attack
66
If speed decreases and you want to maintain lift, what must you do?
Increase the angle of attack
67
What do high lift devices do?
Increase the efficiency of the airfoil at low speeds.
68
What is the most common high lift device?
The trailing edge flap--it decreases the stall speed and increases lift.
69
What is the benefit of flaps in landing?
Allow you to steepen the angle of descent on an approach without increasing airspeed.
70
What is configuration?
The position of the landing gear and flaps
71
What is a clean configuration?
Landing gear and flaps are up (Landing gear can be down if it's not retractable)
72
What are vortex generators?
Small airfoil like surfaces on the wing which project vertically into the airstream and add energy to the boundary layer to prevent airflow separation. They reduce stall speed and increase takeoff and landing performance and are generally seen only on high speed aircraft.
73
What are the four types of flaps?
Plain--attached to the back of the wing by a hinge and extends downward to increase lift. Increases camber and chord line
Split--attached to the lower portion of the wing. Increases lift but has greater drag than the plain flap due to its turbulent wake
Slotted--similar to the plain flap but has an extra slot on the wing which adds lift, accelerates airflow, and delays aiflow separation
Fowler--attached to the back of the wing by a track and roller system. Increases total wing area, camber, and chord line
74
Why do many manufacturerers limit takeoff settings to half flaps or less?
Up to half flap extention, lift produced is much greater than drag. After half flap extention, the equation is reversed and more drag is produced for small increases in lift.
75
What do spoilers do?
Reduce lift for rapid descents on high speed aircrafts.
76
What things might change the weight of a plane?
Fuel consumption
Sky Divers
Equipment installed
Presence of passengers
77
How does thrust related to Newton's second law of motion?
An unballanced force acting on a mass will accelerate the mass in the direction of the force.
78
What are the two types of drag?
Parasite
| Induced
79
What is parasite drag?
It's caused by any aircraft surface that interferes with the smooth flow of air around the plane.
80
What are the three types of parasite drag?
Form Drag
Interference Drag
Skin Friction Drag
81
What causes skin friction drag?
The roughness of an airplain's surface
82
What causes interference drag?
When the airflow from one part of the plane meets the airflow from another part (ex. Where the wings and the fuselage meet)
83
What causes form drag?
The turbulent wake caused by the separation of airflow from the surface of a structure. It's related to both the size and shape of the structure protruding into the relative wind (ex. Antenae)
84
How is induced drag related to an airplain's speed?
Induced Drag is inversely proportional to the square of the plain's speed.
85
What are wingtip vortices?
Spiral currents of air that come from high pressure joining low pressure at the wingtip. They deflect the airstream downward and increase downwash and produce induced drag.
86
What is the angle between total lift and Average Relative Wind?
90 degrees.
87
What is induced drag?
The difference in angle between vertical lift and total lift given the downward angle of average relative wind produced by wingtip vortices.
88
What does L/Dmax stand for?
Lift to Drag ratio. It's the airspeed where you get the greatest amount lift with the least amount of drag.
89
What is total drag?
Parasite Drag + Induced Drag
90
What is ground effect?
It happens when an airplain is flying close to the ground and decreases upwash and backwash by restricting the downward deflection of the airstream. It can cause a plane to take flight before reaching its recommended takeoff speed. It reduces induced drag.
91
Why is ground effect undesirable?
It does allow for less thrust to be required to get off the ground, but as you ascend and ground effect lessens, the thrust necessary to stay in the air increases. If you haven't reached that level of thrust, you'll come back down.
92
What kind of wing configuration experiences more ground effect?
Low wing because the wings are closer to the ground
93
When do you experience ground effect during landing?
When you're one wingspan above the ground. Ground effect here can cause you to float.
94
Why is stability important in an airplane?
It makes the plane easier to control and impacts your ability to recover from stalls and spins.
95
What are three interrelated design characteristics?
Stability
Manueverability
Controllability
96
What does stability mean?
It's a characteristic of a plane that causes it to return to a condition of equlibrium after it is disturbed.
97
What are the two types of stability?
Positive static stability
| Positive dynamic stability
98
What is positive static stability?
The tendency of a craft to return to the position from which it was displaced.
99
What is positive dynamic stability?
When an aircraft returns to the position from which it was displaced via a series of small oscilations.
100
What is manueverability?
The characteristic of a plane that allows you to manuever easily and allows the plane to withstand the pressures of maneuvers.
101
What are the five things that determine manueverability?
```
Size
Weight
Flight Control System
Structural Strength
Thrust
```
102
What is controlability?
The ability of an aircraft to respond to your control imputs, particularly with regard to attitude and flight path.
103
What are the three axes of flight?
Longitudinal--nose to tail
Lateral--Wing tip to wingtip
Vertical
104
What does CG stand for?
Center of Gravity which is where the entire weight of the plane is concentrated. All three axes pass through this point.
105
Which control allows movement around the logitudinal axis?
Aileron
106
Which control relates to pitch around the lateral axis?
Elevator
107
Which control relates to Yaw around the vertical axis?
Rudder
108
What are the three controls that govern motion around the center of gravity?
Aileron
Elevator
Rudder
109
What does nuetralizing the controls mean?
Return them to their original position
110
What is yawing?
Rotation around the vertical axis
