Brainscape's Knowledge GenomeTM

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


See full index

xxxFOF > Chap C: Aerofoil & other aerodynamic shapes > Flashcards

Chap C: Aerofoil & other aerodynamic shapes Flashcards

1
Q

why is curved surface better than flat surface?

A

1) air flow smoother
2) more lift (compared to drag)
3) greater depth/thickness (more space for fuel & structural strength)

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

which flow speed is faster, above or below the aerofoil?

A

above the aerofoil

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

how does static pressure change when air flows on aerofoil and how does it affect the total pressure?

A

upper surface: static pressure decreases

lower surface: static pressure increases

Ptotal is constant, so when Pstatic decreases, Pdyn increases

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

what is total reaction force resolved into?

A

lift (perpendicular to direction of airflow)
drag (parallel to direction of airflow)

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

when aircraft is in straight and level flight, lift is?

A

vertical

(lift is horizontal during vertical climb)

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

pressure coefficient formula & signs of Cp when pointing in and out

A

(Plocal - Pfree stream) / Pdynamic of free stream

Cp -ve when pointing out
Cp +ve when pointing in

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

how does streamlines change when above the aerofoil?

A

bunched together indicating increased in flow velocity

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

force of wing formula using pressure differential

A

F = pressure differential x area

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

define pitching moment

A

a turning effect tending to raise or lower its nose results when the centres of gravity and pressure do no coincide

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

how does change in centre of pressure (CP) affect the nose wrt CG

A

if CP is forward of CG: nose pitch up

if CP is aft of CG: nose pitch down

if CP & CG same point: net forces cancel each other

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

define angle of attack

A

α, angle between chord line and relative wind

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

what is chord line?

A

line joining leading edge to trailing edge

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

what is stalling angle?

A

stalling angle is the AOA for maximum lift

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

important factors in stalling

A

1) suddenness & magnitude of lift loss
2) increase in pitching moment

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

what is the difference between stall speed and stall angle?

A

stall speed: minimum speed to maintain weight level flight

stall angle: max angle of wing to reach max lift

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

list the 3 types of drag

A

1) form/pressure drag
2) skin friction
3) induced drag

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

how is drag relative to AOA?

A

drag increases rapidly as AOA increases

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

how does lift change when AOA changes?

A

as AOA increases, lift also increases

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

best lift drag ratio is called

A

rigger’s angle / angle of incidence

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

what is best lift drag ratio?

A

when lift is the max and drag is min

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

what happens when we pitch moment about Leading Edge (LE) and Trailing Edge (TE)?

A

about LE: nose down, AOA decreases

about TE: nose up, AOA increases

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

effects of AOA on airflow

A

separation bubbles forms at trailing edge at no AOA

separation point moves forward as AOA increases

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

how does CP change when AOA changes?

A

Cp moves forward of aerofoil when AOA increases up till stalling

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

define aerodynamic centre

A

point on chord about which pitching moment is nearly constant at all AOAs

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

where is aerodynamic centre usually at?

A

25% chord length measured from leading edge

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

which is fixed, aerodynamic centre or CP?

A

AC is fixed,

CP moves forward as AOA increases up till stalling

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

NACA naming aerofoil

A

ABC
A - thickness of max camber as %tage of chord
B - location of max camber in 10th of chord
C - max thickness of aerofoil in %tage of chord

NACA 4412
max camber of 4% (A), located 40% (B) of leading-edge, max thickness of 12% (C).

28
Q

wing span formula

A

b = 2s

b - wing span
s - semi span

29
Q

fineness and thickness ratio formula

A

fineness ratio = c / tmax

thickness ratio = tmax / c

c - chord
tmax - max thickness

FR no dimensions
TR in %tage

30
Q

fineness ratio wrt to frontal profile

A

increase in FR, decrease in frontal profile

31
Q

what does thickness ratio affect?

A

maximum lift, critical Mach number

32
Q

define angle of incidence

A

angle which an aircraft wing is mounted relative to its fuselage (also same as rigger’s angle)

33
Q

possible lift & drag variables

A

1) shape
2) flow velocity
3) fluid density
4) AOA
5) viscosity (Re)

for lift: plan area
for drag: frontal area

34
Q

life coefficient relative to AOA

A

same as lift vs AOA graph

CL increases linearly with AOA

35
Q

why use plan area to calculate drag?

A

as frontal area change is much larger & harder to estimate

36
Q

Pitching moment coefficient formula

A

use lift coefficient formula and change L to M and times 1/c, where c is chord length

37
Q

pressure coefficient formula simplified

A

Cp = 1 - (Vlocal / V)2

38
Q

what causes skin friction?

A

1) drag due to boundary layer (shear stress on the surface)

2) total effect taken over entire surface

3) higher in turbulent boundary layer

39
Q

what cause induced drag?

A

aka trailing vortex, due to pressure differential between upper & lower surface of wing

exists in inviscid fluids as is not viscosity related

40
Q

what does induced drag affect?

A

loss of lift at wing tips
greatest at high AOAs

direct proportional to lift2
inverse proper. to speed or b2

41
Q

2 important factors during level flight/cruise

A

1) Lift = Weight
2) Thrust = Drag

42
Q

induced drag relative to dynamic pressure and velocity

A

Di is inversely proportional to Pdyn & velocity

43
Q

what do vortices create?

A

upwash away from the plane
downwash within the wing span

44
Q

why do birds/aircraft fly in delta formation?

A

as the following bird/aircraft will have easier flight due to upwash from the leading bird/ac

higher lift, less drag

45
Q

what is parasite drag?

A

drag due to non-lifting surfaces combined

46
Q

what consists of profile drag and what does it depend on?

A

skin friction and parasite drag,

it depends on frontal area, density@alt and velocity

47
Q

how to minimise induced drag?

A

1) increase aspect ratio (longer span/ shorted chord)
2) lower AOA
3) higher speed (requires less CL for the same lift

48
Q

best theoretical planform for least induced drag

A

elliptical wings

49
Q

what is winglet used for?

A

increase aspect ratio without substantially increasing wing span

50
Q

what do winglets do?

A

reduce mixing of airflow between upper and lower surfaces of wing, therefore reducing induced drag

51
Q

what are high-lift devices used for?

A

reduce take-off/landing speeds and distances

52
Q

how does suction increase lift?

A

suction sucks in the sluggish flow thereby delaying flow separation

(not practical as it may be clogged)

53
Q

how does blowing increase lift?

A

high-pressure air blown out energises sluggish air flow and delays separation

(more practical than suction but complicated piping)

54
Q

how does slots/slats increase lift?

A

as it opens up, high pressure air is forced from lower to upper surface energies sluggish boundary layer near trailing edge,

increases stall angle and CLmax

55
Q

how does flaps increase lift?

A

increases camber, which increases lift, which improves take-off performance and generate more lift at lower airspeed

56
Q

list high lift devices

A

1) boundary layer control (suction & blowing)
2) camber change
3) increase in area

57
Q

what do spoilers do?

A

mess up airflow to increase drag

58
Q

what do speed brakes do?

A

enable optimum descent without decreasing thrust or slowing down the aircraft quickly when landing

59
Q

what do lift dumpers do?

A

destroy lift to create more drag

flaps at 90 degrees and spoilers double up as lift dumpers

60
Q

what do wing fences do?

A

control airflow, provide better slow speed handling and stall characteristics

61
Q

why is it better to compare lift & drag coefficient rather than lift and drag?

A

as the coefficients do not have dimensions, it does not depend of wing area and Pdyn

62
Q

how can flow separation be delayed?

A

by reducing AOA

63
Q

what will increase lift but lower stalling angle?

A

increasing aerofoil camber

64
Q

induced drag is resistance caused by?

A

trailing vortices at wing tips

65
Q

MAC formula

A

b / AR

66
Q

difference between symmetric and non-symmetric airfoil graphs

A

L or CL: Symmetric starts from origin
non-symmetric starts above

Drag: both starts above origin

CL/CD: symmetric starts from origin
non-symmetric starts above origin

xxxFOF (6 decks)

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