High Speed Flight

Question 1

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 ___

Answer 1

aft

Question 2

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 ___ ___.

Answer 2

aft, increase, mach tuck

Question 3

Mach buffet forms as a result of ___

Answer 3

The separation of the boundary layer behind the shockwave hammering on the wing skin.

Question 4

Mach buffet, with continued acceleration, may lead to ___

Answer 4

shock stall

Question 5

Additional zero lift drag at transonic speed is called ___ ___

Answer 5

wave drag

Question 6

With ___ volume, wave drag increases

Answer 6

increasing

Question 7

Max operating speeds are generally limited by two requirements ___

Answer 7

• Ability to withstand gusts without permanent deformation

- Not show any irregularities in control forces, effectiveness, or stability

Question 8

Critical Mach number can be increased by ___

Answer 8

swept wing/vortex generators

Question 9

Shockwave development can be delayed by positioning the maximum camber of the airfoil further ___, at around ___ the chord

Answer 9

aft, half

Question 10

Describe a supercritical wing section

Answer 10

• Thicc
• Flat upper surface
• Rounded leading edge
• Cambered lower surface
• Downwards-pointing trailing edge

Question 11

Supercritical wings have a ___ max angle of attack

Answer 11

limited

Question 12

Sweepback gives the wing a ___ thickness chord ratio in the direction of the airflow

Answer 12

lower

Question 13

In supersonic flow, the centre of pressure is moved to ___ the chord of the surface

Answer 13

half

Question 14

Higher weight gives a ___ low-buffet speed

Answer 14

higher

Question 15

Higher weight gives a ___ high-buffet speed

Answer 15

lower

Question 16

The purpose of Mach Trim is to ___

Answer 16

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

Question 17

Considering supersonic flow, in a convergent duct, flow speed ___ and pressure ___

Answer 17

decreases, increases

Question 18

Considering supersonic flow, in a divergent duct, flow speed ___ and pressure ___

Answer 18

increases, decreases

Question 19

The greater the Mach number, the ___ the Mach angle

Answer 19

lower

Question 20

Mach angle formula =

Answer 20

Sin( Mach Angle ) = 1 / M

Question 21

A normal Mach wave is created at Mach _ and is ___ to the flight path

Answer 21

1, normal

Question 22

Advantages of the delta wing are ___

Answer 22

• 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

Question 23

Disadvantages of the delta wing are ___

Answer 23

• high drag at low speeds

- Superstall tendency

Question 24

Behind a shock wave, the temperature ___

Answer 24

increases

Question 25

Behind a shock wave, the static pressure ___

Answer 25

increases

Question 26

Behind a shock wave, the total pressure ___

Answer 26

decreases

Question 27

Behind a shock wave, the velocity ___

Answer 27

decreases to subsonic

Question 28

Behind a shock wave, the density ___

Answer 28

increases

Question 29

Behind a shock wave, the Mach number ___

Answer 29

decreases

Question 30

Behind a shock wave, the speed of sound ___

Answer 30

increases

Question 31

Behind an expansion wave, the temperature ___

Answer 31

decreases

Question 32

Behind an expansion wave, the static pressure ___

Answer 32

decreases

Question 33

Behind an expansion wave, the total pressure ___

Answer 33

increases

Question 34

Behind an expansion wave, the velocity ___

Answer 34

increases

Question 35

Behind an expansion wave, the density ___

Answer 35

decreases

Question 36

Behind an expansion wave, the Mach number ___

Answer 36

increases

Question 37

Behind an expansion wave, the Speed of Sound ___

Answer 37

decreases

Question 38

Behind an oblique shock wave, the temperature___

Answer 38

increases

Question 39

Behind an oblique shock wave, the static pressure ___

Answer 39

increases

Question 40

Behind an oblique shock wave, the total pressure ___

Answer 40

decreases

Question 41

Behind an oblique shock wave, the velocity ___

Answer 41

decreases, but remains supersonic

Question 42

Behind an oblique shock wave, the density ___

Answer 42

increases

Question 43

Behind an oblique shock wave, the Mach number ___

Answer 43

decreases

Question 44

Behind an oblique shock wave, the speed of sound ___

Answer 44

increases

Question 45

Outline the effect of exceeding Mcrit on the stick force stability of an aeroplane with swept back wings without any form of stability augmentation

Answer 45

Decrease; loss of lift in the wing root area

Question 46

Optimum altitude will ___ with decreasing mass and ___ Mach number

Answer 46

increase, decreasing

Question 47

Compressibility effects depend on ___

Answer 47

Mach number

Question 48

Speed of sound can be calculated approximately by ____

Answer 48

644 + 1.2 TATc

Question 49

With increasing Mach number in straight and level flight, the shock wave on the upper surface will move towards the ___ edge

Answer 49

trailing

Question 50

At the drag divergence mach number, the aerodynamic drag begins to ___ rapidly

Answer 50

increase

Question 51

The drag divergence Mach number is often found ___ Mcrit

Answer 51

above

Question 52

The drag divergence Mach number is determined by ___ and ___

Answer 52

aerofoil profile and AoA (to which it’s inversely proportional)

Question 53

Aerofoil pressure distribution in supersonic flight is ___

Answer 53

rectangular