Brainscape's Knowledge GenomeTM

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


See full index

Backup Transonic > High Altitude Operations > Flashcards

High Altitude Operations Flashcards

1
Q

Why can modern aircraft fly higher than previous high speed aircraft?

A

Lighter weight materials that are also high strength and higher engine thrust from high bypass turbofan engines. (Less fuel burn , better range )

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

Indicated airspeed is derived how?

A

Difference between total and static pressure = dynamic pressure or airspeed.

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

What is calibrated airspeed?

A

IAS corrected for instrument /installation errors and positional error (static source position)

ICET, it’s a pretty cool drink 😎

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

What is equivalent airspeed ?

A

Calibrated airspeed corrected for compressibility error. (At high speeds, stagnation pressure recovered in the pitot tube is not representative of the free stream dynamic pressure due to compressibility magnification).

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

What is True airspeed?

A

Equivalent airspeed corrected for Density altitude.

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

Define Mach number ?

A

Ratio of TAS to the LSS. Measured in decimals of 1.00

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

Define Mcrit?

A

The free stream Mach number at which local sonic flow commences due to the air speeding up over the surface.

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

Operating at / above Mcrit does what ?

A
  • increase drag (wave drag )
  • decrease lift
  • change pitching moment
  • cause buffet
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

Explain changeover altitude and what is it when flying the PC24?

A

When the limiting speed of the aircraft changes from Vmo (concerned with airframe structural limits and flutter) to Mmo (compressibility and flutter limits).
PC24 = 28000ft

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

What are the 3 types of shockwave ?

A
  1. Normal shock (perpendicular to wing) with compressibility
  2. Oblique shock (at an angle) with compressibility
  3. Expansion wave (no shock )
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

Describe a normal shockwave ?

A

Perpendicular to the wing on upper and lower surface of the wing
Increase in pressure and density behind the shockwave
Large increase in wave drag as the boundary layer separates and the air becomes turbulent.

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

Describe an oblique shockwave ?

A

Associated with supersonic flight, supersonic airflow in front of and behind the shockwave
Pressure and density behind the shockwave still increases, airflow changes direction to follow the wing surface.

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

Describe an expansion wave?

A

Supersonic flow throughout

Increased velocity behind the wave hence decreased pressure and density behind the wave Follows the surface of the wing.

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

What is centre of pressure ?

A

The point along the wing chord that lift acts the most. Occurs usually between 23-27% chord

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

What is wave drag?

A

As a normal shockwave forms, airflow behind the wave separates and becomes turbulent.

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

What is Mach tuck?

A

Is a nose down pitching moment caused by the centre of pressure moving aft as the shockwave forms . Beyond Mmo the wave moves further aft compounding the effect.

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

How do we counter Mach tuck ?

A
  • operate below Mmo
  • have a movable horizontal stabiliser
  • incorporate a Mach trimmer
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
18
Q

What is high speed buffet?

A

• an all you can eat feast at high speed above Mmo

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

What actually is high speed buffet ?

A

As the shockwave forms and speed is further increased , boundary airflow hits the shockwave and it separates. Can be induced in a high alt/ speed bank where lift /boundary flow is sped up with with loading.

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

What is the load factor if flying twice Vs and pitching for max lift ?

A

4g
Load factor is proportional to the square of speed.
So if flying 3 times Vs, load factor is 9.

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

What is the most critical gust load ?

A

Vertical gust loads , due to the fact they change angle of attack , hence lift , hence load factor.

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

What gust loads must an aircraft be certified to?

A

+/- 30ft/sec (18kts ) at Maximum level flight speed

23
Q

What is better for gust loads, high aspect or low aspect ratio?

A

A swept low aspect ratio wing (due to the lower lift curve)

24
Q

What is roll reversal / aileron reversal?

A

At high speeds, aileron input causes high torsional forces on the wing causing a reduced AoA on the downward going aileron side. This causes the aircraft to roll opposite to that intended. Can be defined as a speed. Above that speed structural damage can occur.

25
Q

What is put in place to alleviate aileron reversal?

A

Mid span control device , either a flaperon or roll spoiler.

Ailerons are commonly locked out at high speed

26
Q

What is divergence ?

A

When aerodynamic force over powers torsional stiffness. Can lead to structural failure. Short span, sweep back and taper all increase divergence speed.

27
Q

What is flutter ?

A

A combination of aerodynamic forces , inertia and elastic properties of a surface induced by subjecting a structure to a force frequency near its natural frequency which can lead to unstable oscillations. Occurs most commonly at wingtips.

28
Q

How is wing loading measured ?

A

Lb/ft2 or Kg/m2

29
Q

An aircraft with a high mass and small wings has what kind of wing loading ?

A

High

30
Q

What are the benefits of lower wing loading ?

A

More lift, slower takeoff and landing speeds , and hence shorter distances

31
Q

What is the wing loading of a B747 Vs a bird ? (Kg/m2)

A

730kg/m2 Vs 1-20kg/m2

32
Q

What is Dutch roll?

A

An out of phase yaw and roll oscillation induced by disturbances from equilibrium.
Presents when there is a stronger positive lateral stability and weaker positive directional stability

33
Q

Why does Dutch roll occur in transonic aircraft ?

A

It has strong lateral stability due to its large dihedral effect in comparison to static directional stability.

34
Q

When is Dutch roll dangerous ?

A

When oscillatory stability is negative and left uncorrected.

35
Q

What is used to correct /prevent Dutch roll?

A

Yaw Dampners. Or if correcting manually use brief aileron input only.

36
Q

Define an aircraft upset ?

A
  • Pitch attitude >25 up
  • Pitch attitude <10 down
  • Bank angle >45
  • inappropriate airspeeds
37
Q

What are the main 2 causes of fatalities?

A
  1. Loss of control in flight

2. CFIT

38
Q

What conditions could cause a high altitude wake turbulence event?

A
  • following too close
  • crossing paths or reciprocal tracks with 1000ft separating
  • generally high or super aircraft Vs medium wake cat
39
Q

What procedure can be used to mitigate high alt wake encounters?

A

SLOP - strategic lateral offset procedure up to 2nm to the right of cleared route

40
Q

The formula for thrust is?

A

Thrust = mass flow x (inlet velocity - exhaust velocity)
• thrust measured in lbs or newtons
• mass flow thorough the engine itself measured in slugs per second
• velocity measured in ft/sec or m/sec

41
Q

Do jet engines have higher or lower propulsive efficiency compared to turboprop or piston engines?

A

Lower. However they make up for it with size and weight of engine Vs thrust.

42
Q

What does the engine inlet do?

A

Reduces velocity and increases pressure

43
Q

What does the turbofan do?

A

First stage of compression and mainly to bypass a large of volume of air around the engine for thrust and cooling.

44
Q

What does the compressors do?

A

Compresses the air through stages (axial or centrifugal) and reduces volume

45
Q

What does the combustion chamber do?

A

Mixes fuel and the compressed air then ignites it to produce heat and pressure and an increase in volume.

46
Q

What does the turbine do?

A

Extracts the energy out of the gas flow with further expansion, increase volume and decrease in pressure.
Usually 3 stages to power the compressor, 1st high speed compressor, 2nd low speed compressor, 3rd the fan
PC24 - Single HP turbine powers single centrifugal HP compressor
2 LP turbines power the fan and 3 LP axial compressors

47
Q

What does the tailpipe/exhaust do?

A

Mixes all the mass flow and directs it rearwards. Convergent duct

48
Q

Where does maximum range occur?

A

Where the maximum proportion between the square root of the lift coefficient and drag coefficient occurs. i.e. tangent line on thrust required vs velocity graph

49
Q

How does altitude effect range (nil wind)?

A

Increased range at higher alts. Higher TAS, lower fuel flow for given thrust required

50
Q

How does aircraft weight effect range?

A

Higher weights mean higher thrust required to maintain the desired speed, so range is less. Speed must be reduced as fuel is burnt off to maintain best range.

51
Q

How can best range be achieved constantly?

A

Get a block level for climb and remain at optimum altitude for fuel burn off.

52
Q

How does temperature effect range?

A

Increased range as temperature decreases. Decreased temp reduces specific fuel consumption

53
Q

How does wind effect range?

A

Headwind will reduce range, vice versa.

Must fly faster in a headwind to counter wind and slower in a tailwind.

54
Q

When should a change in airspeed be made to counter wind for best range?

A

When wind velocity exceeds 25% of the zero wind cruise speed.

Backup Transonic (7 decks)

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