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Principles Of Flight > 81 02 Introduction To High Speed Flight > Flashcards

81 02 Introduction To High Speed Flight Flashcards

1
Q

What is the equation for the Local Speed of Sound?

A

LSS (a) = 39 x Sq Root (k)

k is temp in kelvin

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2
Q

What is the equation of the Mach Number?

A

Mach Number = TAS / a (LSS)

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3
Q

What is LSS effected by and how?

A

Temperature. As temp increases, LSS increases.

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4
Q

What is the Free Stream Mach Number?

A

The speed of the air flow around the AC or of the AC itself

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5
Q

What is the Local Mach Number?

A

Speed of the air flow around the aerofoil etc.

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6
Q

Describe the four air flow speed transition areas

A

Subsonic: High and Low
- All Local Mach Numbers are below 1.0

Transonic:

  • Some points ML < 1.0
  • Some points ML = 1.0
  • Some points ML > 1.0

Supersonic:
- All Local Mach Speeds are > 1.0

Hypersonic:
- All Local Mach Speeds are >= 5.0

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7
Q

What is Mcrit?

A

Mcrit is the fastest speed an AC can travel with out having any supersonic air flow

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8
Q

Describe the following regarding a Normal Shockwave:

  • Flow velocity and local Mach Number
  • Total Pressure and Temperature
  • Pressure and Density
  • Orientation
  • Strength and Length
  • Occurrence and Location
A
  • Flow velocity and Local Mach Numbers reduce
  • Going from supersonic to subsonic
  • Total Pressure decreases and Temperature increases
  • Total Pressure energy is lost to Temperature increase
  • Static Pressure and Density increase
  • Form normal to the air flow
  • Stronger changes than oblique shockwaves
  • Short, extending only a short distance
  • Strength and length increase with increasing Mfs
  • Limited to the Transonic region
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9
Q

Describe the following regarding an Oblique Shockwave:

  • Flow velocity and local Mach Number
  • Total Pressure and Temperature
  • Pressure and Density
  • Orientation
  • Strength and Length
  • Occurrence and Location
A
  • Flow velocity and local Mach Number decrease
  • From supersonic flow to slower supersonic flow
  • Total Pressure decreases and Temperature increases
  • Total Pressure energy is lost to Temperature
  • Static Pressure and Density increase
  • Flow direction always changes
  • Weaker than Normal Shockwaves but longer, reaching to the ground
  • Occur during Transonic and Supersonic regions
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10
Q

Describe a Bow Wave

A
  • A shock wave with develops on the leading edge of an aerofoil
  • Centre section consists of a Normal Shockwave
  • Turns into a Oblique Shockwave further out
  • Occurs during the Transonic region
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11
Q

What is the equation for the Mach Angle?

A

Sin (Mue) = 1 / Mach Number

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12
Q

Describe Expansion Waves and the effect on:

  • Flow Velocity and Mach Number
  • Static Pressure and Density
  • Temperature and LSS
  • Energy and Total Pressure
A
  • Form on sharp corners where the supersonic air remains connected to the surface
  • This forms an expansion region
  • Flow velocity and Mach number increase
  • Static pressure and density decrease
  • Temperature and LSS decrease
  • Energy and Total pressure stay the same
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13
Q

In straight and level flight, what effect does rising temperature have on TAS, CAS, Mach Number and LSS?

A
  • LSS increases
  • TAS increases
  • Mach Number remains constant
  • CAS remains constant
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14
Q

Describe the phrase ‘Chicken Tikka Masala’ when:

  • Climbing or descending
  • Above the Tropopause
  • In an Inversion
A
  • CAS (Chicken), TAS (Tikka), Mach No (Masala)
  • Chicken, TikkaMasala (TAS and Mach No do the same)
  • Chicken, Masala, Tikka
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15
Q

Why do airliners transition from climbing at constant CAS to constant Mach Number?

A
  • As altitude increases, at constant CAS, TAS and Mach Number increase
  • Eventually the AC will reach Mmo (Max Mach Operating)
  • So to prevent this they switch to climbing at constant Mach
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16
Q

During a climb describe what is happening as:

  • Climb on constant CAS
  • Switch to climb on constant Mach Number
A

Constant CAS:

  • CAS, AOA and CL all remain constant
  • CAS^2 is prop to 1/2 rho V^2 S CL
  • Flight path angle and Pitch angle must decrease
  • Sin (gamma) = (T-D)/W
  • Thrust decreases with altitude

Constant Mach Number

  • CAS and TAS decrease
  • AOA and CL increase
  • Pitch angle and Flight Path angle both decrease
17
Q

During a descent describe what is happening as:

  • Descend on constant Mach Number
  • Switch to Descending on constant CAS
A

Constant Mach Number:

  • CAS and TAS increasing
  • AOA and CL decrease
  • Flight path angle (angle of descent) increases
  • Pitch Angle decreases

Constant CAS:

  • CAS, AOA and CL remain constant
  • Flight and Pitch angles remain constant
18
Q

At what speed (approximately) will a Bow Wave form?

A

A free stream Mach Number just above M=1

19
Q

The increase in stall speed (IAS) with increasing altitude is caused by?

A

Compressibility Effects

Principles Of Flight (23 decks)

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