11.1 High Speed Flight Flashcards
What are the two types of shock waves that are formed at supersonic flight?
Normal and oblique
What happens to air temperature behind a shock wave?
The temperature rises
How does the area rule effect an aircraft’s transonic flight performance?
It reduces wave drag
In dry air at 20 degrees C what is the speed of sound?
343.2 metres per second
Speed of sound varies depending on its substance, what does it travel the fastest an£ slowest through?
Fastest through a solid object
Slowest through a gas
What are the three region of aircraft speeds?
. Subsonic
. Transonic
. Supersonic
Define transonic
Some speeds around the aircraft are below the speed of sound and some are above the speed of sound
As an aircraft approaches the speed of sound, what is formed after the leading edge?
A shock wave
What is the Mach number for subsonic flight?
<0.8 Mach
What is the Mach number for transonic flight?
0.8-1.2 Mach
What is the Mach number for supersonic flight?
1.2-5.0
How do you calculate the Mach number?
It’s aircraft’s speed divided by speed of sound
What is the critical Mach number?
The highest possible Mach number that you can reach without turning to supersonic flight
When does a normal shock wave take place?
At 1.2 Mach
What is wave drag?
It is the portion of total drag that is caused by shock waves
What are the two ways to reduce wave drag?
. Area rule
. Vortex generators
What is the disadvantage of a vortex generator?
It increases parasite drag
How does area rule effect the aircraft transonic flight performance?
Decreases the amount of wave drag
When speed is increased to 0.8 Mach, we get shock waves. Therefore for fast aircraft you must have a what profile?
Thin profile
Most modern aircraft have a sweep back wing of what?
30 degrees
What is the main advatange of having a movable swept wing?
High performance at both low and high speed flight
What are the three characteristics for an aircraft that flies at transonic flights?
. Flatter upper surface
. More curved leading edge
. Thinner trailing edge
What can a wing with a transonic profile also be called?
Rear loaded wing
What is the main advatange of a transonic wing profile?
It uses the skin as the torque box, therefore lighter and has greater fuel capacity. Therefore reducing drag.
What is a flow separation on a wing also called?
Shock stall
When the aircraft passes critical Mach was is its reaction?
Nose down - tuck under effect
How can the tuck under effect be corrected?
By the horizontal stabiliser as it has the Mach trim system
When a supersonic airflow passes through a shock wave, what happens to temperature?
Temperature increases
When a supersonic airflow passes through a shock wave, what happens to pressure and density?
They increase
When a supersonic airflow passes through a shock wave, what happens to velocity?
Decrease
What are the two main types of WAVES formed in supersonic flow?
. Shock waves
. Expansion waves
What are the two types of shock waves?
. Normal
. Oblique
Where is a normal wave formed in conjunction to the object?
In front of the object
Where is a oblique wave formed in conjunction to the object?
Formed above and below the object
When a supersonic airstream passes through a normal shockwave what happens?
The velocity of airflow is decreased to subsonic (but not direction change)
When a supersonic airstream passes through a oblique shockwave what happens?
Change in airflow direction and speed decreases but Stays at supersonic.
When is an expansion wave formed?
Where the supersonic air stream turns away from preceding flow direction
When a supersonic airstream passes through an expansion shockwave what happens?
The velocity increases
Direction stays same as long as no flow separation
What are the two typical supersonic profiles?
. Double wedge profile
. Circular arc profile
When flying a supersonic flight, the air entering the engine inlets must be slowed to what?
Subsonic range without wasting energy
What is the correlation between Mach number and temperature?
At Mach number increases so does temperature
