Module 7 - Wing and High Lift Devices Testing

Question 1

What is compressibility effect?

Answer 1

Changes in airflow behavior near speed of sound.

Question 2

What three speed regimes are studied?

Answer 2

Subsonic, Transonic, Supersonic.

Question 3

What happens to streamline pattern at low subsonic speeds?

Answer 3

Disturbances propagate far ahead.

Question 4

What happens to streamlines at high subsonic speeds?

Answer 4

They crowd near the airfoil, increasing suction.

Question 5

What is dynamic pressure?

Answer 5

Kinetic energy per unit volume: (1/2) * density * velocity^2.

Question 6

Why does lift coefficient increase with Mach number?

Answer 6

Due to streamline steepness and increased dynamic pressure.

Question 7

What does the Prandtl-Glauert factor predict?

Answer 7

Increased lift and pressure coefficient with Mach number.

Question 8

What is the Glauert factor formula?

Answer 8

sqrt(1 - M∞^2).

Question 9

Is Prandtl-Glauert valid near Mach 1?

Answer 9

No, only for subsonic flows.

Question 10

Define critical Mach number.

Answer 10

Mach number where local flow first reaches Mach 1.

Question 11

What forms at Mcrit?

Answer 11

Shock wave on the upper surface.

Question 12

How does incidence affect Mcrit?

Answer 12

Higher incidence lowers Mcrit.

Question 13

What is a shock wave?

Answer 13

Sudden pressure, temperature, and velocity change.

Question 14

What is transonic drag rise?

Answer 14

Sharp increase in drag during transonic flow.

Question 15

What causes a shock stall?

Answer 15

Shock waves separating boundary layer.

Question 16

What happens to lift during shock stall?

Answer 16

Lift decreases rapidly.

Question 17

What happens to drag during shock stall?

Answer 17

Drag increases sharply.

Question 18

What is buffeting?

Answer 18

Vibrations from separated airflow hitting tail surfaces.

Question 19

How can designers delay transonic effects?

Answer 19

Use thinner wings, sweepback, and area rule.

Question 20

What is the area rule?

Answer 20

Fuselage shape must change smoothly to minimize drag.

Question 21

Why is sweepback useful?

Answer 21

Reduces normal velocity component, delaying shocks.

Question 22

What happens if sweep is too much?

Answer 22

Tip stall and poor lateral control.

Question 23

What is wing loading?

Answer 23

Weight carried per unit area of wing.

Question 24

Why are high-speed wings thinner?

Answer 24

To reduce local acceleration and shock formation.

Question 25

Where is maximum thickness placed on high-speed wings?

Answer 25

Further back (around half-chord).

Question 26

What happens if leading edge is too round?

Answer 26

Causes early flow separation.

Question 27

What is a separation bubble?

Answer 27

Pocket of separated flow near leading edge.

Question 28

Why are symmetrical wings preferred at supersonic speeds?

Answer 28

Reduces drag and avoids negative lift effects.

Question 29

What shape is a delta wing?

Answer 29

Triangular planform.

Question 30

What is the main advantage of delta wings?

Answer 30

Strong structure, good storage space.

Question 31

What are M and W wings designed for?

Answer 31

Reducing pitch-up from tip-stall.

Question 32

What is a crescent wing?

Answer 32

Wing with changing sweep angles across the span.

Question 33

What happens to airflow over a sharp leading edge?

Answer 33

Oblique shock is formed.

Question 34

What happens with a blunt nose at supersonic speeds?

Answer 34

Detached bow shock forms.

Question 35

What is the preferred shape for supersonic airfoils?

Answer 35

Flat plate or double wedge.

Question 36

Why must supersonic wings be thin?

Answer 36

To minimize shock losses.

Question 37

What happens to lift at high supersonic Mach numbers?

Answer 37

Lift decreases slowly.

Question 38

What happens to the shock as Mach increases?

Answer 38

Shock moves backward along the wing.

Question 39

What is a detached shock?

Answer 39

Shock not attached to the nose of the wing.

Question 40

What is an attached shock?

Answer 40

Shock stuck to the leading edge.

Question 41

What is shock attachment Mach number (MSA)?

Answer 41

Mach number where shock reattaches to nose.

Question 42

What is porpoising?

Answer 42

Oscillation from center of pressure movement.

Question 43

How does shock affect stability?

Answer 43

Rapid changes in center of pressure affect stability.

Question 44

What is trim drag?

Answer 44

Extra drag from tail balancing forces.

Question 45

How can fuselage help reduce wing load?

Answer 45

By generating lift itself.

Question 46

What is interference drag?

Answer 46

Drag from airflow interaction between aircraft parts.

Question 47

What happens with poor area distribution?

Answer 47

Higher transonic drag rise.

Question 48

How does sweep affect aspect ratio?

Answer 48

Generally reduces it.

Question 49

Why use canard configuration?

Answer 49

Provides positive lift from front surfaces.

Question 50

Why avoid heavy tip-stall?

Answer 50

To maintain longitudinal stability.