081.01 SUBSONIC AERODYNAMICS .02 - .12 (airflow, drag, flaps)

Question 1

The centre of pressure of a symmetrical aerofoil is located at approximately (…)% of the section chord behind the leading edge.

Answer 1

The centre of pressure of a symmetrical aerofoil is located at approximately (25)% of the section chord behind the leading edge. Irrespective of AoA

Question 2

The aerodynamic centre of a wing is the point relative to which (the pitching moment coefficient does not change with varying AoA / the aeroplane becomes longitudinally unstablle when the CG is moved beyond it in an aft direction).

Answer 2

The aerodynamic centre of a wing is the point relative to which (the pitching moment coefficient does not change with varying AoA).

source: https://aviation.stackexchange.com/questions/19388/what-is-the-difference-between-centre-of-pressure-aerodynamic-centre-and-neutra

Question 3

The total drag of an aerofoil in two-dimensional flow comprises (…) drag and (…) drag.

Answer 3

The total drag of an aerofoil in two-dimensional flow comprises (form, profile or pressure) drag and (skin friction) drag.

Question 4

The maximum C_L/C_D ratio is typically at an AoA of (…)°.

Answer 4

The maximum C_L/C_D ratio is typically at an AoA of (4)°.

Question 5

Minimum drag of an aeroplane in straight and level flight occurs at (…).

Answer 5

Minimum drag of an aeroplane in straight and level flight occurs at (maximum C_L/C_D).

Question 6

A polar curve of an aerofoil is a graphic relation between (…) and (…).

Answer 6

A polar curve of an aerofoil is a graphic relation between (C_L) and (C_D).

Question 7

Curve 1 in the attachment is a (positively cambered/negatively cambered/symmetrical) aerofoil.

Answer 7

Curve 1 in the attachment is a (positively cambered) aerofoil.

Question 8

Curve 2 in the attachment is a (positively cambered/negatively cambered/symmetrical) aerofoil.

Answer 8

Curve 2 in the attachment is a (symmetrical) aerofoil.

Question 9

Curve 3 in the attachment is a (positively cambered/negatively cambered/symmetrical) aerofoil.

Answer 9

Curve3 in the attachment is a (negatively cambered) aerofoil.

Question 10

List of which of the following lift coefficient (C_L) is a function:

• density
• pressure
• temperature
• camber of the aerofoil section
• AoA of aerofoil section

Answer 10

List of which of the following lift coefficient (C_L) is a function:

• density
• pressure
• temperature
• camber of the aerofoil section
• AoA of aerofoil section

Question 11

Excluding constants, the induced drag coefficient is the ratio of (…) and (…).

Answer 11

Excluding constants, the induced drag coefficient is the ratio of (C_L²) and (aspect ratio).

- So induced drag is proportional to C_L² and inversely proportional to AR. -

Question 12

Induced drag is the result of (…).

Answer 12

Induced drag is the result of (downwash generated by tip vortices).

Question 13

With flaps deployed, at constant IAS in straight and level flight, the magnitude of tip vorices (remains the same/increases/decreases).

Answer 13

With flaps deployed, at constant IAS in straight and level flight, the magnitude of tip vorices (decreases).

- Flaps increase C_L, so for a constant IAS a lower AoA is needed to maintain straight and level flight. Lower AoA means lower induced drag. -

Question 14

State if the induced drag increases or decreases in the following cases:

• lower AoA
• increased aspect ratio
• deployment of flaps while load factor = 1 and speed constant
• fitting of winglets
• replacing a rectangular wing by an elliptical
• flying slower while maintaining straight and level flight
• increasing aeroplane mass at constant load factor

Answer 14

State if the induced drag increases or decreases in the following cases:

• lower AoA = decrease
• increased aspect ratio = decrease
• deployment of flaps while load factor = 1 and speed constant = decrease
• fitting of winglets = decrease
• replacing a rectangular wing by an elliptical = decrease
• flying slower while maintaining straight and level flight = increase
• increasing aeroplane mass at constant load factor = increase

Question 15

Total drag is the sum of (…) drag and (…) drag.

Answer 15

Total drag is the sum of (induced) drag and (parasite) drag.

Question 16

If the runway is warm, ground effect will (remain the same/increase/decrease).

Answer 16

If the runway is warm, ground effect will (decrease).

- lower air density, so less ‘cushion’ effect -

Question 17

Ground effect will occur at a height (…).

Answer 17

Ground effect will occur at a height (half the wingspan of the aircraft).

Question 18

Trailing-edge flap type number 1 shown in the attachment is a (…) flap.

source: https://www.cfinotebook.net/graphics/operation-of-aircraft-systems/high-lift-devices/four-basic-flap-types-labeled.webp

Answer 18

Trailing-edge flap type number 1 shown in the attachment is a (plain) flap.

source: https://www.cfinotebook.net/graphics/operation-of-aircraft-systems/high-lift-devices/four-basic-flap-types-labeled.webp

Question 19

Trailing-edge flap type number 2 shown in the attachment is a (…) flap.

source: https://www.cfinotebook.net/graphics/operation-of-aircraft-systems/high-lift-devices/four-basic-flap-types-labeled.webp

Answer 19

Trailing-edge flap type number 2 shown in the attachment is a (split) flap.

source: https://www.cfinotebook.net/graphics/operation-of-aircraft-systems/high-lift-devices/four-basic-flap-types-labeled.webp

Question 20

Trailing-edge flap type number 3 shown in the attachment is a (…) flap.

source: https://www.cfinotebook.net/graphics/operation-of-aircraft-systems/high-lift-devices/four-basic-flap-types-labeled.webp

Answer 20

Trailing-edge flap type number 3 shown in the attachment is a (slotted) flap.

source: https://www.cfinotebook.net/graphics/operation-of-aircraft-systems/high-lift-devices/four-basic-flap-types-labeled.webp

Question 21

Trailing-edge flap type number 4 shown in the attachment is a (…) flap.

source: https://www.cfinotebook.net/graphics/operation-of-aircraft-systems/high-lift-devices/four-basic-flap-types-labeled.webp

Answer 21

Trailing-edge flap type number 4 shown in the attachment is a (Fowler) flap.

source: https://www.cfinotebook.net/graphics/operation-of-aircraft-systems/high-lift-devices/four-basic-flap-types-labeled.webp

Question 22

On a C_L/α graph, flaps extention moves the curve (up/down) and (left/right).

Answer 22

On a C_L/α graph, flaps extention moves the curve (up) and (left).

Question 23

The effect of trailing flaps extention in level flight will be a nose (up/down) pitching moment.

Answer 23

The effect of trailing flaps extention in level flight will be a nose (down) pitching moment.

- Because CP moves aft and furter away from CG -

Question 24

Vortex generators are fitted in front of control surfaces to (prevent flutter/re-energise the boundary layer/increase effective AoA).

Answer 24

Vortex generators are fitted in front of control surfaces to (re-energise the boundary layer).

Question 25

Flap asymmetry causes a large (rolling moment/yawing moment/difference in C_Lmax) whereas slat asymmatry causes a large (rolling moment/yawing moment/difference in C_Lmax).

Answer 25

Flap asymmetry causes a large (rolling moment) whereas slat asymmatry causes a large (difference in C_Lmax)​.

Question 26

When extending the trailing edge flaps, the effective angle of attack (remains the same/increases/decreases).

Answer 26

When extending the trailing edge flaps, the effective angle of attack (increases).

Question 27

Referring to wing downwash; when flaps are extended, the negative AoA of the tailplane (increases/decreases) and the effectiveness of the tailplane (increases/decreases).

Answer 27

Referring to wing downwash; when flaps are extended, the negative AoA of the tailplane (increases) and the effectiveness of the tailplane (increases).

Question 28

The main function of a leading edge slat is to (increase C_Lmax/increase α_crit).

Answer 28

The main function of a leading edge slat is to (increase α_crit).

Question 29

The main function of a trailing edge flap is to (increase C_Lmax/increase α_crit).

Answer 29

The main function of a trailing edge flap is to (increase C_Lmax).

Question 30

An aeroplane has the following flap setting: 0°, 15°, 30°, 45°. Slats can also be selected. State which of the following selections will provide the highest contribution to C_Lmax.

• Flaps from 0° to 15°
• Flaps from 15° to 30°
• Flaps from 30° to 45°
• Slats from retracted to T/O position

Answer 30

An aeroplane has the following flap setting: 0°, 15°, 30°, 45°. Slats can also be selected. State which of the following selections will provide the highest contribution to C_Lmax.

• Flaps from 0° to 15°
• Flaps from 15° to 30°
• Flaps from 30° to 45°
• Slats from retracted to T/O position

Question 31

An aeroplane has the following flap setting: 0°, 15°, 30°, 45°. Slats can also be selected. State which of the following selections will most adversely affect the C_L/C_D ratio.

• Flaps from 0° to 15°
• Flaps from 15° to 30°
• Flaps from 30° to 45°
• Slats from retracted to T/O position

Answer 31

An aeroplane has the following flap setting: 0°, 15°, 30°, 45°. Slats can also be selected. State which of the following selections will most adversely affect the C_L/C_D ratio.

• Flaps from 0° to 15°
• Flaps from 15° to 30°
• Flaps from 30° to 45°
• Slats from retracted to T/O position

Question 32

State which of the following configurations gives the highest C_L/C_D ratio.

• Clean configuration
• Only trailing edge flaps fully extended
• Only sleading edge slats fully extended
• Both leading and trailing edge flaps fully extended

Answer 32

State which of the following configurations gives the highest C_L/C_D ratio.

• Clean configuration
• Only trailing edge flaps fully extended
• Only sleading edge slats fully extended
• Both leading and trailing edge flaps fully extended

Question 33

Upon wing spoiler extension, if the AoA remains constant C_D (increases/decreases/remains unaffected) and C_L (increases/decreases/remains unaffected).

Answer 33

Upon wing spoiler extension, if the AoA remains constant C_D (increases) and C_L (decreases)​.

Question 34

Upon wing spoiler extension, if speed and load factor remain constant C_D (increases/decreases/remains unaffected) and C_L (increases/decreases/remains unaffected).

Answer 34

Upon wing spoiler extension, if speed and load factor remain constant C_D (decreases) and C_L (remains unaffected)​.

Question 35

With reference to the skin of aircraft; (form/skin friction/interference/induced) drag will increase with increasing aircraft age.

Answer 35

With reference to the skin of aircraft; (skin friction) drag will increase with increasing aircraft age.

- So parasite drag. Due to dents in skin etc. -

Question 36

If ice is present on the leading edge of the wings, it may increase landing distance due to a higher V_AT bu as much as (5-10% / 10-20% / 30-40% / 40-50%).

Answer 36

If ice is present on the leading edge of the wings, it may increase landing distance due to a higher V_AT bu as much as (40-50%).