High Speed Effects Flashcards
When is air considered compressible?
At abouve or equal to 0.4 Mach
When air compressibility effects felt?
As aircraft approaches initial Mach no. Dues to build up of pressure concentration
Define compressibility effects?
Undesirable effects felt in the transonic range
How can pressure concentration form?
As a shockwaves
What are some issues with pressure concentration.
-sudden rise in drag
-reduction in lift
-uncommanded changes in trim and stability
What is a shockwave?
Sound or pressure wave resulting from air being disturbed as the aircraft moves through it
Where do sound or pressure waves radiate from?
Source of disturbance
What happens to shockwaves if the aircraft is slower than the speed of sound?
The shockwave travels ahead at the speed of sound
What happens to pressure wave when the aircraft is at the speed of sound?
They can’t get away from the aircraft and begin to compress & accumulate forming a bow shockwave
What happens to the shockwave when the aircraft is abouve the speed of sound?
Shockwaves get overtaken and radiate behind the aircraft
When do normal shockwaves form?
In transonic range at MCrit
What angle does a normal shockwave form at relative to the path of the airflow?
90 degree angle
What does a supersonic aero foil typically include?
Sharp/pointed leading edge
What does a pointed air of oil allow for?
Allows bow wave to attach and slope backwards to form an oblique shockwave
Is airflow forward of an oblique shockwave above or below Mach 1?
Above
Is airflow slower or faster after passing thru a shockwave?
Slower
Going thru an oblique shockwave airflow will…?
Have a slight increase in temp and pressure
Are expansion waves considered shockwaves?
No
How are expansion waves formed?
When airflow changes direction around a curve/corner away from preceding airflow direction
In an expansion wave is there a change in useful energy or total pressure?
No change
What decreases from expansion waves?
Static pressure,density & temperature all decrease
What are the two types of supersonic profile?
-double wedge profile
-circular arc profile
In a double wedge profile what is the net lift at 0 degrees angle of attach?
No net lift
What is the advantage of a double wedge profile?
Produces lift with only a slight angle of attach
