11.1.2 Flashcards
high speed flight
how may times is the speed of sound in water than air
4.3
4 speed ranges
subsonic , transonic , supersonic, hypersonic
subsonic speed range
up to 0.8
supersonic speed range
1.2-5
transonic speed range
0.8-1.2
hypersonic speed range
above mach 5
what property of air changes with the onset of transonic flight
air becomes compressible
what is mach number
aircraft speed / speed of sound
what is crit mach number
fastest speed aircraft can go without becoming subject to supersonic airflow
what wing design delays onset of crit mach
Swept wing
where does supersonic airflow first occur on an aerofoil
upper surface
what forms on upper surface when crit mach is reached
shockwave
what happens to airflow behind a shockwave
large increase in static pressure & flow separation
what do u oblique shockwaves do
slow supersonic airflow before shockwave occurs
where are oblique shockwaves employed
in the intakes
what happens to air velocity in an expansion wave
It increases
why does flow separation occur behind a shockwave
boundary layer does not have enough kinetic energy to withstand the large increase in static pressure
when does a bow wave form
flight speed exceeds speed of sound
which wing profile is known as wing loaded
Transonic
advantages of rear loaded profile
lighter, greater fuel capacity, less drag, less sweepback, smaller wing, better low speed charactericts
how is tuck under avoided
mach trim system
what drag increases due to vortex generators
Parasitic Drag
method of reducing wave drag
area rule
where does shockwave first form on wing
wing root
two types of shockwaves
normal and oblique
what shockwave causes an increase in velocity in airflow
none, only expansion wave causes increase in velocity
how does vortex generator re-energise the boundary layer
transfers energy from free airflow to the boundary layer
when does the boundary layer separate from aerofoil section
when the normal shockwave forms
what effect does aerodynamic heating have on metal
they lose strength
what point is airflow over a wing at its maximum but below speed of sound
Critical mach number
normal swept wing angle
30 degrees
transonic wing profile
flatter upper surface
curved leading edge
thinner trailing edge
than normal
how is shock stall corrected
with horizontal stabiliser
where is c.o.g located on balance control surface
on hinge line
how is high speed turn controlled by flying control surfaces
aileron and roll spoilers
what automatic system of the horizontal stabiliser corrects tuck under
Mach trim
how many ailerons fitted to large aircraft
4 , 2 outbound, 2 inbound
when do inbound ailerons operate
low speed and high speed
when do outbound ailerons operate
low speed only
aluminium strength lose how much strength at temperatures over 250 degrees
80%
On a swept wing where does it stall first
Tip
Dutch roll is movement is in which direction
Yaw and roll
What are Kruger flaps
Leading edge flap hinges
How are peto tubes heated
Electrically
What is the artificial feel system used for
Required for power operated systems
Where does shockwaves form
Highest point of camber
when does a bow wave form
Above speed of sound
What does vortex generator do
Re-energises boundary layer
Purpose of swept wing
Aerodynamic purposes creating a longer thinner wing with an angle of 30 degrees
Why do transonic profiles perform well in transonic reigons
There’s no flow separation behind the shockwave as this flow would generate lift
If velocity increases what happens to the centre of pressure
Moves rearwards
How is centre of pressure moving rearward offset
By horizontal stabiliser
What are the waves formed by supersonic flow
Shock waves and expansion waves
How can we increase critical Mach
Decreasing camber and increasing chord
What happens during stall shock
Lift increases and drag decrees
What happens to crit mach with a thicker camber
Crit Mach lowers
How much faster is speed of sound in water than air
4.3 times out of
How much faster is speed of sound in air than water
4.3 times slower
What’s another name for flight tabs
Servo tab
Where is the balance panel effective
High speeds
