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xxxFOF > Chap B: Basic Aerodynamics > Flashcards

Chap B: Basic Aerodynamics Flashcards

1
Q

mass flow rate equation

A

ρAV (kg/s)

ρ - density
A - cross-section area
V - Flow velocity

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2
Q

what is the maximum velocity for compressibility to be neglected?

A

100m/s (M = 0.3)

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3
Q

what happens when compressibility is accounted for?

A

density, ρ, changes

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4
Q

types of flow and its explanation

A

steady flow - no change in parameters at any given time

unsteady flow - parameters at point of consideration are constantly changing

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5
Q

streamline definition

A

imaginary line joining all particles moving along the same path, there is no flow across streamlines (no exchange)

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6
Q

what is a stream tube?

A

a bundle of streamlines for a stream tube (no exchange of particles)

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7
Q

how is velocity related to area in continuity equation?

A

as cross-section area decreases, flow velocity increases

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8
Q

Total energy equation

A

ET = P∀ + 1/2 mairV2 + mairgz

P - static pressure
∀ - volume of air
V - speed of air
z - height above reference datum

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9
Q

which factor is the same between reality view and wind tunnel view?

A

airspeed & Vrelative

magnitudes are the same just that airspeed for real. view is against drag whereas Vrelative in WT view is same direction as drag

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10
Q

what does Bernoulli’s equation neglect?

A

it assumes that there is no fluid friction (energy lost due to friction is ignored)

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11
Q

What is static pressure?

A

static pressure is pressure exerted by still air at a point (not moving)

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12
Q

what is dynamic pressure?

A

pressure exerted by moving air (1/2 ρV2

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13
Q

what is stagnation pressure?

A

flow is brought to rest (Pdyn = 0)

so Pstagnation = Ptotal = Pstatic

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14
Q

how to measure stagnation pressure?

A

stagnation tube or pitot tube

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15
Q

dynamic pressure formula using difference of pressure

A

1/2 ρV2 = Pstagnation - Pstatic

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16
Q

why would using difference of pressure to calculate velocity be inaccurate?

A

1) as it requires density, and it cannot be measured during flight. And using ISA table is not accurate it assumes SL density is 1.225kg/m3

2) compressibility effect

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17
Q

what does pitot tube and static tube measure?

and what does pitot-static tube measure?

A

pitot tube - total pressure
static tube - static pressure

pitot-static tube measures the differential pressure (ΔP) to calculate airspeed

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18
Q

what is indicated airspeed?

A

IAS -measured by pressure difference and flight altitude density

19
Q

what is equivalent airspeed?

A

EAS - airspeed using SL density, using Pdyn at altitude and bring it down to SL to get speed at SL.

20
Q

what is true airspeed?

A

TAS - obtained with accurate density at flight altitude, when flow is incompressible, TAS = IAS

21
Q

what is calibrated airspeed?

A

CAS - airspeed obtained by SL pressure and temp. (P0 & T0)

approx speed only, as speed increases, it is less accurate

22
Q

types of error in airspeed measurements

A

1) density error - EAS is using SL density to calculate airspeed (EAS always < TAS when flying at altitude other than SL)

2) compressibility error - density changes for speed > M0.3

3) instrument error - not calibrated properly

4) position error

23
Q

types of position error in airspeed measurements

A

1) location & orientation of the pitot-static tube

2) pitot tube may not sense full stagnation pressure at high angle incline

3) static port will not sense correct pressure when landing gears/flaps are extended / covered in ice

24
Q

what is VIAS equal to in pressure formula?

A

VIAS = V

V in 1/2 ρV2

25
Q

what does subscript s in Ps and P stands for in airspeed calculations?

A

Ps: Stagnation pressure
P: static pressure

s means stagnation

26
Q

what is calibrated airspeed corrected for?

A

instrument & position errors

compressibility error at high speeds & altitudes

27
Q

what is ground speed?

A

speed of aircraft relative to ground (sum of TAS & wind speed)

28
Q

what affects ground speed?

A

headwinds (lowers ground speed)
tailwinds (increases ground speed)

29
Q

what is boundary layer?

A

molecules adjacent to surface tend to stick to it when viscous fluid flow past objects (V = 0)

molecules further away from surface has more velocity

30
Q

what is laminar flow?

A

aka streamline flow,

flow parameters may vary from point to point but remains constant wrt time at their respective points

no exchange of particles between streamlines

assumed to be frictionless & steady

31
Q

what is turbulent flow?

A

breakdown of flow, randomness of motion of each particle. For high speed flow & friction

32
Q

difference between laminar & turbulent flow

A

laminar:
- low thickness
- uniform flow
- low velocity next to surface
- gradual velocity change
- low skin friction

turbulent:
- greater thickness
- random flow
- higher velocity next to surface
- sharp velocity change
- high skin friction

33
Q

what is transition point?

A

a point where flow changes from laminar to turbulent

34
Q

range of Reynolds number for air

A

laminar flow: <= half a million
transition flow: 500000 to 10 million
turbulent flow: >= 10 million

35
Q

what causes flow separation?

A

adverse pressure gradient leads to separation and lost of lift as fluid is flowing to a region of higher pressure

36
Q

difference between laminar and turbulent flow separation

A

laminar flow separation:
less energy in boundary layer, early separation

turbulent flow separation:
greater energy in boundary layer, separation further aft

37
Q

what is magnus effect?

A

generation of lift due to imbalanced pressure on both sides of a spinning object

38
Q

flow separation may occur when?

A

flow slows down and static pressure increases

39
Q

why do golf balls with dimples that act as turbulators travel further?

A

dimples induced turbulent boundary layer

turbulent boundary layer has more kinetic energy than laminar to go against adverse pressure gradient

lesser chance of flow separation which increases total drag

40
Q

how to calculate CAS when TAS, a0, Palt is given?

A

use TAS formula to find Pstag, sub Pstag into CAS equation

41
Q

lift, drag, and L/D graphs against AOA

A

lift against AOA: increasing until stalling angle, then decreases a bit

drag against AOA: exponential graph, starts above origin

L/D against AOA: increases sharply until max point, before going down to stalling angle near the end

42
Q

define reynolds’ number

A

ratio of forces of inertia which is force of motion to force of resistance.

43
Q

reynolds’ number equation variables

A

ρ - fluid density
V - flow speed
d - distance from LE to location
µ - viscosity

xxxFOF (6 decks)

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