8.4 high speed flight

what is low speed aerodynamics assumption of the air

its incompressible

how is the speed of sound calculated

Local speed of sound (LSS) = 39 x root of Absolute Temperature

how does speed of sound relate to temperature

the higher the temperature the higher the speed of sound

sounds waves cause a continuous series of what

pulses or pressure waves radiating outwards equally in all directions from the point of origin

speeds of sound depends on

density of the material

at sea level (15 degrees) what is the speed of sound

761mph (661.7 knots)

why is the speed of sound constant above 11,000 meters

temperature of -56 degrees stays constant

what is the doppler affect

due to the nature of sound waves as you move in the direction of travel the sound waves are getting compressed and thats why it changes tone when the objects moves past you

what is compressblitly effect

the changes of air pressure and density when traveling in a venturi air needs to slow down to compress this pressure and density needs to increase

why is the transonic flight range the most troublesome

part of the air flowing over the wing some of the air is subsonic and some supersonic and upset the aerodynamic balance of the wing

what is considered supersonic flight

all of the aircraft is traveling above the speed of sound

a air craft traveling exactly the speed of sound is said to be travelling

mach 1

what is the subsonic mach number range

below 0.75

what is the transonic mac number range

mach 0.75 to 1.2

what is the supersonic mach number range

mach 1.2 to 5.0

what is the hypersonic flight range

above mach 5.0

at constant speed what does the speed of the airflow depend on

the curve and camber of the airlfow

what is the critical mach number

the speed that the air starts to flow supersonic over the wings

non supersonic aircraft flying in the transonic range will normally be limited to a maximum speed below the?

critical mach number

what is free stream mach number

mach number that the flow at a point is unaffected by the presence of an aircraft

what is the local mach number

a specified region of flow that could be below or above the speed of sound

what is the critical mach number

the lowest MFS which for a given aerofoil and angle of attack give a rise to the local mach number to 1.0

what type of wing can fly faster in the transonic range before the unwanted effects

a thin wing

what is the characteristics super critical wing

a thin wing delays the onset of shockwaves however a thin wing produces less lift due to less camber so a super critical wing has a longer chord to over come this

what is the pros and cons of a super critical wing

perfect for transonic poor lift at low airspeeds and needs high lift devices

what are the adverse effects of the transonic range

buffeting shockwaves increase in drag decrease in lift movement of CP

if the air of the air is traveling at mach 1 before the aircraft what is affected

the smoothness of the airflow over the wing

what is compressibility buffeting and what could happen

when flying controls experience violent vibration if allowed to continue control loss or structural damage can happen

what is the compresablitly mach number

The Mach number at which, because of compressibility effects, control of an aircraft becomes difficult, and beyond which loss of control is probable

what is the two types of shock waves

• Normal: at 90° (perpendicular) to the shock medium's flow direction.

• Oblique: at an angle to the direction of flow.

what is shockwave termed

propagating disturbance.

how is a normal shock wave created

blunt body in supersonic flow.

what happens to the sound waves in a normal shock

sound waves cannot outrun the object, and they pile up a short distance in front of the object.

what is a shock wave known as

a bow shock wave

as air passes through a shock wave what happens to temperature pressure density and velocity

temperature, pressure, and density dramatically rise as its velocity falls.

the airflow downstream of a normal shock is?

subsonic

what is a oblique shock

sharp edged shock wave that is formed when supersonic flow is turned on itself.

whats stronger normal or oblique shock

normal

what is the type of airstream in a oblique shock

the air stream behind the shock is not necessarily subsonic

what happens to the temprature pressure density WRT oblique shock

temperature, pressure, density, and air stream velocity are reduced

what happens in a expansion fan shock

essentially an infinite number of Mach Waves, and has the opposite effects of an oblique shock. When the airfoil is turned around a corner, the temperature, pressure, and density fall as the Mach numbers rises.

what happens with separation point during a shock wave

As speed begins to increase, the point of separation moves forward, extending the turbulent wake.

how is a shockwave formed

flight speed reaches and exceeds the critical Mach number, the airflow over the top of the wing speeds up to supersonic velocity and a shock wave starts to form.

If the aerofoil is symmetrical and set at zero degrees angle of attack the shockwave would form

equally between the upper and lower surfaces

wing is usually set to an angle of incidence of about 3 degrees were would the shockwave form

on the top surface

what is the shockwave boundary between

subsonic and supersonic

how many times higher is the drag of a shockwave

10x higher

what is the drag called created by sockwaves

shock drag

what are the two components of shock drag

Wave Drag, resistance caused by the wave itself and Boundary Layer Drag, due to the increased turbulent region over the surface of the wing.

as the aircraft speed increase after the onset of a shock wave what happens to the wave

wave will extend outwards and begin to move aft towards the trailing edge of the wing. A second wave begins to form on the lower surface, as the airflow here also speeds up to supersonic velocity

as static pressure and density increases some of the energy is dissipated as

heat

what % of the speed of sound of do aircraft typically flight

87%

low speed flight is based that air is

incompressible

what is the flow mixture in the transonic region

some supersonic some transonic

what is the formula for local speed of sound

(LSS)=39x (square root of absolute temperature)

sound waves/pressure waves radiate in what directionn

outwards equally in all directions

the speed pressure/sound waves depend on temperature but what else

density of the material

at sea level (15 degrees0 what is the aprox speed of sound in mph

761 mph

what altitudes will speed of sound stay constant

11,000 meters to 27,000 meters

at subsonic speed how far a head can the air “feel” the aircraft coming and what is this called

100 meters in front - called the doppler effect

give a example of the doppler effect

emergency vehicle driving past and the change in the pitch

high speed flight is based that the air is

compressible

what happens to velocity pressure and density in subsonic flow through a duct

in subsonic when flow os converging

pressure degreases

velocity increases

constant density

when flow is diverging

pressure increases

velocity decreases

constant density

what happens to velocity pressure and density in supersonic flow through a duct

in supersonic flow when converging

pressure increases

velocity decreases

density increases

when flow is diverging

pressure decreases

velocity increases

density decreases

what part of the aircraft are effected the most by the transonic region

the wings

as the aircraft is travelling at the speed of sound what happens to the pressure waves

they form a shockwave

shock waves upset the aerodynamic balance of?

the wing

what causes a mach cone

the aircraft travelling faster than its pressure wave

a aircraft traveling exactly at the speed of sound is travelling how fast

mach 1

what its the critical mach number

the minimum speed were air reaching the the maximum thickest part of the wing is travelling supersonic

what is free stream air (MFS)

the mach number of a point unaffected by the presence of a aircraft

what is the local mach number (ML)

when a aerofoil is travelling in subsonic airflow and some air is accelerated and some slowed down to speed to a specified region

what is critical mach number

the lowest MFS which for a given angle of attack will give a rise to mach 1

what type of wing can fly faster in the transonic region

a thin wing (supercritical wing)

how does a supercritical wing overcome the less lift produced by the shallow camber

it has a longer chord

at slow speeds a supercritical wings aircraft needs…

high lift devices

what is the few unwanted effects as the critical mach number is approched

buffeting, shockwaves, drag, movement of the centre of pressure

what is compressibility mach number

the mach number that because of compressibility effects control of the aircraft becomes difficult and beyond loss of control is probable

what shape is a normal shock wave

90 degrees or perpendicular to the flow

what angle is a oblique shock wave

at a angle to the direction of flow

in a normal shock the air flow down stream is

subsonic

what creates a normal shock

a blunt body in a supersonic flow and the pressure wave building up

when normal shock wave builds up and is forced to change the air around the body this is called ?

bow shock

how is a oblique shock formed

when supersonic flow is turned going through the shock wave

how fast is the air downstream of a oblique shock

the air could be subsonic or supersonic

the mach number calculated behind the oblique shock is calculated from

the upstream shock and the angle the flow has turned

what is a expansion fan opposite to

oblique shocks

what happens to temperature pressure and density in a explanation fan

temperature pressure and density falls, velocity increases

how many mach waves in a expansion fan

infinite

the first indication of a change in the nature of the flow

breakaway from the airflow resulting in turbulence

as speed increases what happens to the point of separation

it moves forward

when a shockwave is produced what happens to the pressure distribution

its alters the values of lift, drag and affects control operations

a normal shock wave is a boundary between

between subsonic and supersonic airflow

drag increases how much more when there is a shockwave

10 times

if the centre of pressure is altered what will it affect

the pitching moment

the extra drag caused by a shockwave is known as

shock drag

what two components is shock drag made up from

wave drag and boundary layer drag

the air leaving the shockwave remains

supersonic

in shock wave energy is also dissipated as what

heat

once a bow wave attaches to the wing the airflow over the wing will be

supersonic