Brainscape's Knowledge GenomeTM

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


See full index

MEC324 - Aerodynamic Design > Part III > Flashcards

Part III Flashcards

1
Q

What is the general rule of thumb about computer time and Re when simulating

A

PU time = Re^3

Storage requirement = Re^9/4

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

What is Breguet Range cruise distance equation

A

R = V/c * L/D * ln( Winitial / Wfinal)

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

What is payload fraction

A

payload/ total lift off weight

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

Was is useful payload fraction

A

payload + fuel / MTOW

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

What is fuel fraction estimation equation

A

Wf/Wo = 1.06(1-Wx/Wo)

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

Define stability

A

ability of aircraft to return to its original equilibrium position

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

Define control

A

ability of the pilot to produce moments about the various axis

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

Define static stability

A

Refers to the tendency of the aircraft to counter a disturbance

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

Dynamic stability

A

is concerned with how fast the aircraft returns to trim condition after a disturbance

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

For cambered aerofoils, if centre of pressure moves, what happens to the pitching moment at the aerodynamic centre

A

stays the same

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

What equation represents static stability

A

x / c

where:
x - distance between CG and AC
c - chord length

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

What is a canard

A

when the tail wing is in front of the main wing

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

List 2 benefits of canards

A
  1. Canard surface operates at high CL and almost makes aircraft ‘stall-proof’
  2. Can sometimes have larger range for CG
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

List 2 disadvantages of canards

A
  1. Wing operates in downwash from canard and therefore reducing its efficiency
  2. Difficult to apply flaps to wings
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

What is a flying wing design

A

an aircraft design with no tail (lowest possible drag)

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

Benefits of a flying wing design

A
  • Removes fuselage therefore improves aerodynamic efficiency
  • synergistic effect with relaxed static stability
  • low visibility on radar
  • distribute load easier
17
Q

What is drag crisis

A

In the transition period between laminar and turbulent flow, drag drops

18
Q

What is the reason for the drag crisis

A

When turbulence rapidly mixes rapidly-moving external air into the boundary layer, increasing the range over which it adheres to the surface. This makes the trailing low pressure wake smaller and thus reduces drag

19
Q

What can be done to a surface to ensure drag crisis happen more

A

roughening the surface i.e. golf ball

20
Q

What is the wall law

A

velocity of turbulent flow ∝ log(distance to the wall)

only works when distance < 20% of flow height

21
Q

What are streaks and what happens when they meander

A

Turbulent flows vortices form near a wall and are stretched by the mean flow - these are streaks

When they meander, this causes friction and drag to increase

22
Q

equation for streak size, spacing and length

A

size = a+ = ua/v (10y)

spacing = s+ = us/v (100y)

length = l+ = ul/v (1000y)

where:
u = friction velocity at wall
y = distance to wall
v = local kinematic viscocity

23
Q

What are riblets

A

a series of parallel grooves on a surface that can reduce drag and make a wall more streamlined

they are used to channel vortex streaks created near the wall

24
Q

List advantages of open circuit tunnels

A
  1. less expensive to build

2. pollutants are purged (smoke)

25
Q

List disadvantages of open circuit tunnels

A
  1. more expensive to run
  2. affects design of surrounding environment
  3. more noisy
26
Q

List advantages of closed circuit tunnels

A
  1. some energy is recovered
  2. shielded from weather
  3. quality of flow easily controlled
27
Q

List disadvantages of closed circuit tunnels

A
  1. more expensive to build
  2. air inside constantly heated
  3. full of dust and debris
  4. noisy
28
Q

Give equation for energy ratio of wind tunnel

A

Jet energy / sum of circuit losses

qUA / efficiency * motor power

29
Q

How to manage turbulence in wind tunnel

A

via honeycomb and screens

30
Q

What is hot wire anemometry used for

A

used to calculate pressure and velocity of airflow

how:

  • heated wire
  • gives off heat via convection to airflow
  • energy required to reheat is directly proportional to airflow
31
Q

Advantages of hot wire anemometry

A
  1. cheap

2. accurate

32
Q

Disadvantages of hot wire anemometry

A
  1. effects airflow
  2. can’t measure high intensity turbulence
  3. wind direction has no effect
  4. very fragile
  5. can ‘burn out’
33
Q

What can be used to measure velocity and pressure in multi-phase situations

A

hot film probe

more expensive and worse frequency response then hot wire anemometry however

34
Q

What is LDV

A

Laser Doppler Velocemetry

- use doppler effect to measure velocity/pressure

35
Q

What is PIV

A

Particle Image velocemetry

  • have particles in fluid that light up under a laser
  • post-process images to find velocity/pressure
  • can create 2D/3D velocity fields
36
Q

What equation shows that flight is stable

A

dCmp / dCl < 0

MEC324 - Aerodynamic Design (6 decks)

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