High Speed Flight Flashcards
When the local velocity on the upper surface of the wing is increased so that the area exceeding M1 is enlarged, the centre of pressure of the wing will move ___
aft
With increased transonic speed, the CP moves ___ and the longitudinal stability ___. If the aircraft trim is not adjusted, the aircraft may begin to enter a dive, known as ___ ___.
aft, increase, mach tuck
Mach buffet forms as a result of ___
The separation of the boundary layer behind the shockwave hammering on the wing skin.
Mach buffet, with continued acceleration, may lead to ___
shock stall
Additional zero lift drag at transonic speed is called ___ ___
wave drag
With ___ volume, wave drag increases
increasing
Max operating speeds are generally limited by two requirements ___
- Ability to withstand gusts without permanent deformation
- Not show any irregularities in control forces, effectiveness, or stability
Critical Mach number can be increased by ___
swept wing/vortex generators
Shockwave development can be delayed by positioning the maximum camber of the airfoil further ___, at around ___ the chord
aft, half
Describe a supercritical wing section
- Thicc
- Flat upper surface
- Rounded leading edge
- Cambered lower surface
- Downwards-pointing trailing edge
Supercritical wings have a ___ max angle of attack
limited
Sweepback gives the wing a ___ thickness chord ratio in the direction of the airflow
lower
In supersonic flow, the centre of pressure is moved to ___ the chord of the surface
half
Higher weight gives a ___ low-buffet speed
higher
Higher weight gives a ___ high-buffet speed
lower
The purpose of Mach Trim is to ___
compensate for the elevator stick force in order to make it easier to maintain a range of Mach numbers over the critical mach range from an initially trimmed condition
Considering supersonic flow, in a convergent duct, flow speed ___ and pressure ___
decreases, increases
Considering supersonic flow, in a divergent duct, flow speed ___ and pressure ___
increases, decreases
The greater the Mach number, the ___ the Mach angle
lower
Mach angle formula =
Sin( Mach Angle ) = 1 / M
A normal Mach wave is created at Mach _ and is ___ to the flight path
1, normal
Advantages of the delta wing are ___
- High angle of sweep at the leading edge
- Low thickness/chord ratio at the root
- Low aspect ratio means higher Mcrit
- Stable vortices develop at high AoA to prevent tip stall
Disadvantages of the delta wing are ___
- high drag at low speeds
- Superstall tendency
Behind a shock wave, the temperature ___
increases
Behind a shock wave, the static pressure ___
increases
Behind a shock wave, the total pressure ___
decreases
Behind a shock wave, the velocity ___
decreases to subsonic
Behind a shock wave, the density ___
increases
Behind a shock wave, the Mach number ___
decreases
Behind a shock wave, the speed of sound ___
increases
Behind an expansion wave, the temperature ___
decreases
Behind an expansion wave, the static pressure ___
decreases
Behind an expansion wave, the total pressure ___
increases
Behind an expansion wave, the velocity ___
increases
Behind an expansion wave, the density ___
decreases
Behind an expansion wave, the Mach number ___
increases
Behind an expansion wave, the Speed of Sound ___
decreases
Behind an oblique shock wave, the temperature___
increases
Behind an oblique shock wave, the static pressure ___
increases
Behind an oblique shock wave, the total pressure ___
decreases
Behind an oblique shock wave, the velocity ___
decreases, but remains supersonic
Behind an oblique shock wave, the density ___
increases
Behind an oblique shock wave, the Mach number ___
decreases
Behind an oblique shock wave, the speed of sound ___
increases
Outline the effect of exceeding Mcrit on the stick force stability of an aeroplane with swept back wings without any form of stability augmentation
Decrease; loss of lift in the wing root area
Optimum altitude will ___ with decreasing mass and ___ Mach number
increase, decreasing
Compressibility effects depend on ___
Mach number
Speed of sound can be calculated approximately by ____
644 + 1.2 TATc
With increasing Mach number in straight and level flight, the shock wave on the upper surface will move towards the ___ edge
trailing
At the drag divergence mach number, the aerodynamic drag begins to ___ rapidly
increase
The drag divergence Mach number is often found ___ Mcrit
above
The drag divergence Mach number is determined by ___ and ___
aerofoil profile and AoA (to which it’s inversely proportional)
Aerofoil pressure distribution in supersonic flight is ___
rectangular
