Brainscape's Knowledge GenomeTM

Browse over 1 million classes created by top students, professors, publishers, and experts.


See full index

6 > Aerodynamics > Flashcards

Aerodynamics Flashcards

1
Q

Newton’s First Law

A

Inertia-A body at rest will remain at rest and a body in motion will remain in motion at the same speed and the same direction until acted upon by some external force.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

Newton’s Second Law

A

Acceleration- force required to produce a change in motion of body is directly proportional to its mass and rate of change in its velocity. Acceleration is directly proportional to force and inversely proportional to mass. (A=F/M, velocity=speed+direction) Greater force= greater acceleration Greater mass=less acceleration

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

Newton’s Third Law

A

action and reaction- For every action there is an equal and opposite reaction. (torque effect in single rotor helicopters)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

Increase in speed of airflow=

A

decrease in static pressure (therefore decrease in speed=increase in static pressure)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

when an airfoil is positioned at an angle to a flow of air…..

A

speedup of air and reduced pressure occurs above the airfoil and decrease of airflow causes increased pressure beneath the airfoil (lift)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

Airfoil

A

surfaced body or structure designed to produce lift or thrust force when subjected to airflow

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

Leading edge

A

rounded portion that projects into the relative flow of air (relative wind)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

Trailing edge

A

tapered portion that trails from the relative flow of air

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

Chord

A

length of the chord from leading edge to trailing edge; longitudinal dimension of the airfoil section

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

chord line

A

straight line intersecting leading and trailing edges of the airfoil (extends beyond edges)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

camber

A

shape or curvature; upper, lower and mean

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

mean camber line

A

line drawn halfway between the upper and lower surfaces (2 equal halves)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

span

A

length of the rotor blade from the point of rotation to the blade tip (hub to tip)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

center of pressure

A

point along the chord line through which all aerodynamic forces are considered to act ( lift, weight, thrust, drag)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

Aerodynamic center

A

point along the chord line where are changes to lift effectively take place (lift forces occur)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

Symmetrical airfoil

A

equal camber on each side of chord, constant center of pressure, ease of construction and low cost. Disadvantage- less lift at given angle of attack and undesirable stall

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
17
Q

Non-symmetrical airfoil

A

cambered upper surface, flattened lower surface, increased lift/drag ratios, better stall characteristics, more lift production at given AOA. Disadvantages- center of pressure movement causes twisting forces and stress, expensive. (more efficient and more aerodynamic)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
18
Q

Rotational relative wind

A

flow of air parallel to and opposite the flight path of an airfoil

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
19
Q

airspeed component of relative wind

A

component of the total relative wind velocity created by directional flight velocity/airspeed (factor in airspeed to advancing and retreating blade-add to advancing, subtract from retreating)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
20
Q

Induced flow (downwash)

A

a downward component of air (vertically through rotor system, reduced by forward flight). At max during stationary hover and no wind

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
21
Q

Resultant relative wind

A

airflow from rotation that is modified by induced flow (strikes rotor blade). Rotational relative wind modified with vertical induced flow

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
22
Q

Angle of incidence

A

(pitch angle, mechanical angle) this is the acute angle between the chord of an airfoil and the plane of rotation (tip path plane). Changed on all blades simultaneously by collective pitch control. (change of individual blades is done by cyclic)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
23
Q

Angle of attack

A

(aerodynamic angle) the acute angle between the chord of an airfoil and the resultant relative wind (can change with no change in angle of incidence). Larger= more lift (less induced flow) Smaller= less lift (more induced flow)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
24
Q

Critical angle

A

exceeding the maximum angle of attack and producing stall. Max AOA is 15 to 20 degress on most airfoils

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
25
Q

Dissymmetry of Lift

A

unequal lift between the advancing and retreating halves of the rotor disc caused by the different wind flow velocity across each half. Overcome by flapping

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
26
Q

Flapping

A

advancing blade produces more lift- flaps up increasing angle of attack and loses lift. retreating blade loses lift- flaps down increasing angle of attack and gains lift.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
27
Q

Blowback

A

when blade flapping has compensated for dissymmetry of lift, the rotor disk is tilted to the rear (blowback)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
28
Q

Total aerodynamic force

A

pressure differentials between the upper and lower surfaces of the airfoil combined with the air resistance on the airfoil (constantly shifting). Acts as center of pressure and is normally inclined up and to the rear.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
29
Q

Two components of TAF

A

Lift-useful component, PERPENDICULAR to resultant relative wind, increases with AOA, decreases rapidly at stalling angle. Drag- non useful component, parallel and same direction of resultant relative wind, increases with AOA, increases sharply at stall angle.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
30
Q

Induced Drag

A

results from producing lift; retards forward motion caused by wing tip vortices (larger=more induced drag) and induced flow. Major source of drag at a hover, but decreases with forward airspeed

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
31
Q

profile drag

A

frictional resistance of the rotor blades passing through the air. relatively constant at low airspeed but increases slightly at higher airspeed ranges

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
32
Q

parasite drag

A

drag created by fuselage; strut, skin friction, interference (any nonlifting components). lowest at hover, increases with airspeed. Major source of drag at higher airspeeds

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
33
Q

total drag

A

sum of induced, profile and parasite. Decreases with forward airspeed until best rate of climb speed is reached. speeds greater than best r/c will cause decrease in overall efficiency due to increasing parasite drag

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
34
Q

Unaccelerated flight

A

no change in speed or direction; all opposing forces are equal and opposite. lift=weight thrust=drag ( law of inertia)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
35
Q

Accelerated Flight

A

any time opposing forces become unequal, acceleration will result in direction of the greater force (law of acceleration)

36
Q

L= Cl P/2 S V2 pilot can control….

A

Cl and V2- coefficient of lift (angle of attack) and velocity (square of velocity of relative wind is most dominant factor)

37
Q

Air density increases….

A

high pressure, low temp., low humidity (conditions good for flight)

38
Q

Semirigid rotor system

A

simple, two blade construction, tilting disc relative to mast, opposite unit works simultaneously (flapping)

39
Q

Articulated rotor system

A

multibladed, blades are hinged independently at hub and offset from the center of the mast (stationary hub), blades can flap up or down and lead or lag (each blade can flap at different angles), tilting of the disc is relative to the hub

40
Q

Centrifugal Force

A

outward force produced whenever a body moves in a curved path (most dominant force). Proportional to rotational velocity; provides rigidity to rotor system.

41
Q

Centripetal force

A

inward force directed toward the center of rotation

42
Q

Blade coning

A

upward flexing of rotor blades (lift and centrifugal force determine. lift stronger= cone up centrifugal force stronger= reduces coning). Greatest coning angle is at the tip of the blade.

43
Q

Causes of excessive coning

A

Low RPM, High gross weight, High “G” manuevers, turbulent air

44
Q

adverse effects of excessive coning

A

loss of disc area, loss of total lift available, stress on blades (most critical), could lead to blade cracking or blade separation from the rotor system

45
Q

gyroscopic precession

A

occurs in rotating bodies that manifest an applied force 90 degrees after an application in the direction of rotation (phase leg). Overcome by offsetting the linkage in the cyclic pitch control system to create an input of 90 degrees ahead of desired action (cyclic rigging).

46
Q

gyroscopic stability

A

rigidity is space which is proportional to mass and speed of rotation

47
Q

Blade twisting

A

necessary to better equalize lift along the span of the rotor blade. twisted- positive angle at hub (more lift) which decreases to negative angle at tip (less lift). Used on most production line helicopters

48
Q

Blade tracking in the rotor system

A

refers to the track or path of each blade in the plane of rotation; each tip should pass through the exact same point in space as the preceding blade

49
Q

Effects when blade area out of track

A

low frequency VERTICAL vibration 1:1 or 2:1 (depends on number of blades out of track), increased instability in the rotor system

50
Q

Pendular action

A

CG below supporting elements, tilting rotor in one direction results in fuselage swinging in opposite direction, over control results in exaggerated pendular action, move cyclic at rate that main rotor and fuselage move as a unit

51
Q

Effects of torque

A

newton’s 3rd law, combination of forces that tend to cause rotation, amount of yaw experienced is proportionate to engine power being delivered to rotor (greater power=yaw right decrease power=left yaw)

52
Q

Control of torque (single rotor)

A

tail rotor powered from main rotor transmission system, provides right thrust (opposite of torque), amount of thrust controlled by pitch of tail rotor blade (right pedal=pitch decrease and less thrust left pedal=pitch increased more thrust)

53
Q

Pedal turns at a hover

A

right pedal turn- turns with torque reaction and less power used (AOA decrease). left pedal turn-turn against torque reaction and more power is used (AOA increase)

54
Q

Translating tendency (counterclockwise main rotor)

A

helicopter tends to drift laterally to the right and is caused by the thrust exerted to the right by the tail rotor to compensate for main rotor torque

55
Q

overcome translating tendency

A

corrected by tilting main rotor to the left- rigging of the flight control systems, tilting mast slightly (built in left tilt), left cyclic (pilot induced)

56
Q

contribution of rotor blade- rotation

A

creates rotational relative wind

57
Q

contribution of rotor blade-flapping

A

overcomes dissymmetry of lift (semi rigid-relative to mast articulate-relative to hub; blades flap independently)

58
Q

contribution of rotor blade- feathering with cyclic

A

increases angle on one half rotor and decrease angle in other half, pilot uses to tilt rotor disc for directional control and control dissymmetry of lift

59
Q

contribution of rotor blade- collective feathering

A

equally and simultaneously changes pitch of all blades, adjust overall AOA, pilot controls total lift and vertical control

60
Q

contribution of rotor blade- hunting

A

ARTICULATED rotor system- relieves stress forces on rotor blades created by flapping action Coriolis effect- blade flaps up, CG moves inboard, blade speeds up, drag hinge allows blade to lead, drag damper regulates amount/rate of lead (opposite sequence when blade flaps down)

61
Q

Total Force to tip path plane

A

(plane of rotation) TF acts perpendicular to the tip path plane. If tip path plane is tilted by cyclic, the TF will incline in same direction of rotor tilt. *tilt does not change amount of TF- changes direction

62
Q

Total force

A

multitude of total aerodynamic force act along the span of each blade can be summed together into a single force emitting from the center of the rotor disc.

63
Q

Total Force when tip path plane is tilted

A

thrust is produced by tilting tip path plane- vertical component of TF opposes weight (acts as lift) and horizontal component opposes drag (acts as thrust) vertical lift+horizontal thrust= total force

64
Q

Ground effect

A

improved performance encountered when hovering near a surface, one rotor diameter from rotor to ground, more pronounced over smooth, open surfaces with no wind. Reduction of downwash. Decreased induced drag-reduced tip vortices

65
Q

Loss of ground effect

A

altitude greater than one rotor diameter, trees and brush, tall grass, uneven terrain (slopes), tilt tip path plane, wind

66
Q

Effective translational lift

A

additional lift obtained because of increased efficiency of the rotor system with airspeed obtained either by horizontal flight or hovering into wind. Relative wind entering rotor become more horizontal. Occurs approx. 16-24kts. Flapping increases with forward airspeed and nose pitches up with left yaw.

67
Q

efficient operating airspeed range during translational flight

A

ETL (outrun old vortices), induced drag/total drag reduced, increased efficiency continues UNTIL best rate of climb speed is reached. *airspeeds greater than best r/c will result in lower efficiency due to increased parasite drag

68
Q

Transverse flow effect

A

drag differential between front and rear of rotor (greater in aft), 10-20kts., more induced drag aft/less forward, causes shudder or vibration

69
Q

Settling with power

A

air upward flow through center of rotor. Conditions: vertical descent of 300 fpm, use of 20-100%, slow airspeed (less than ETL). Can develop vortex ring state and increase with increase of collective.

70
Q

conducive to settling with power

A

hover out of ground effect, formation flights, mask/remask ops, downwind approaches, steep approach with high rate of descent

71
Q

corrective action for settling with power

A

increase speeds with cyclic, reduced collective pitch as altitude permits, adjust rotor RPM to normal operating range

72
Q

angular unbalance in articulated rotor system

A

unequal number of degrees between each blade, caused by unequal hunting, CG of rotor system is thrown off center and aggravated by centrifugal force, LATERAL vibration, leads to ground resonance

73
Q

Ground resonance

A

articulated system only- can cause complete destruction of aircraft within seconds. 1) drag dampers allow excessive lead and lag, 2)defective landing gear/struts, 3)hard landings on one skid or wheel, 4)ground taxi over rough terrain, 5) hesitant or bouncing landings (80-90% airborne-light on the skids)

74
Q

Recover from ground resonance

A

if operating RPM exists become airborne then land first suitable spot and check damage; if operating RPM does not exist, place firmly on ground by reducing power and normal shutdown procedures

75
Q

Regions of main rotor during autorotation

A

stall- inboard, operates at max AOA, very little lift/considerable drag. Driving-middle portion, operates high AOA, TAF slightly forward of axis of rotation (creates lift), provides thrust. Driven- tip/end, less AOA, TAF is slightly aft of axis (creates drag)

76
Q

Autorotative turns

A

rotor RPM will increase, disc tilted causes a loss of vertical lift, rate of descent increases, driving region increases due to change in increased upflow or relative wind, pilot must prevent rotor RPM overspeed with collective control (increase drag to slow rotor RPM- collective increase)

77
Q

3 conditions for dynamic rollover

A

Pivot point, rolling motion, exceed critical angle (static rollover angle/critical angle)

78
Q

3 types of dynamic rollover

A

level ground, down slope, upslope during takeoff

79
Q

factors for dynamic rollover

A

physical factors (TIMSGCC) and human factors (FLIII)

80
Q

dynamic rollover recovery

A

smooth, slow collective reduction

81
Q

characteristics of stalls

A

caused by an excessive angle of attack–15 to 20 degrees

82
Q

correcting stalls

A

reduce the angle of attack to something less than the critical angle

83
Q

retreating blade stall

A

critical advanced stage of dissymmetry of lift;(contributing factors)- excessive airspeed (primary factor), high blade loading, low rotor RPM, high DA, high G manuevers, turbulence

84
Q

symptoms of retreating blade stall

A

abnormal vibrations 2:1 (two bladed rotor), pitch-up of nose, roll toward stall side (left), loss of control (number of vibrations per one rotation of main rotor will be number of blades in main rotor-all blades)

85
Q

corrective actions of retreating blade stall

A

reduce collective pitch (lower AOA), regain control of aircraft (cyclic as necessary-not forward, makes stall worse), reduce airspeed, increase rotor RPM to normal op range, minimize maneuvering, descend to lower altitude (high air density)

6 (6 decks)

Brainscape helps you reach your goals faster, through stronger study habits.
© 2024 Bold Learning Solutions. Terms and Conditions