Module 6 - Drag Measurements

Question 1

What are the four forces of flight?

Answer 1

• lift
• drag
• thrust
• weight

Question 2

as an aircraft moves/travel through air, every part of it that is exposed to the airflow produces a different type of resistance to the forward motion

Answer 2

drag

Question 3

forms of drag

Answer 3

• total drag
• parasite drag
• induced drag
• skin friction drag
• form drag
• interference drag
• profile drag

Question 4

is comprised of all the forces that work to slow an aircraft’s movement which includes resistance of air moving over aircraft’s surface

Answer 4

parasite drag

Question 5

is an inevitable consequence of lift and is produced by the passage of an airfoil through the air

Answer 5

induced drag

Question 6

is the aerodynamic resistance due to the contact of moving air with the surface of an object

Answer 6

skin friction drag

Question 7

factors that affect the type of flow in the boundary layer

Answer 7

• flow quality
• shape
• texture
• pressure gradient
• Reynold’s number
• heating of the fluid

Question 8

a pressure gradient where the static pressure increases in the direction of the flow

Answer 8

adverse pressure gradient

Question 9

A laminar layer cannot exist when pressure is rising in the _______________.

Answer 9

direction of the flow

Question 10

On a curved surface, such as an airfoil, the transition point is usually ___________ the point of maximum thickness.

Answer 10

at, or near

Question 11

Because of the adverse pressure gradient existing on a curved surface, such as an airfoil, the transition point will be ___________ than if the surface was flat.

Answer 11

further forward

Question 12

is generated due to the aircraft’s shape and the airflow around it

Answer 12

form drag

Question 13

When the air has to separate to move around a moving aircraft and its components, it eventually ______ after passing the body. How quickly and smoothly it does is representative of the _________ it creates, which creates additional force to overcome.

Answer 13

rejoins, resistance

Question 14

How to reduce form drag?

Answer 14

delay the separation as close to the trailing edge as possible

Question 15

increases the ratio between the length and depth of the body, reducing the curvature of the surfaces and thus the adverse pressure gradient

Answer 15

streamlining

Question 16

measure of streamlining

Answer 16

fitness ratio

Question 17

formula for fitness ratio

Answer 17

fitness ratio = length/depth

Question 18

an example of this would be the intersection created by the connection of the wing and the fuselage at the wing root

Answer 18

interference drag

Question 19

The most interference drag is observed when two surfaces meet at _________________.

Answer 19

perpendicular angles

Question 20

What is used to reduce interference drag?

Answer 20

fairings

Question 21

factors affecting parasite drag

Answer 21

• indicated airspeed
• configuration
• airframe contamination

Question 22

parasite drag varies with the square of the _________

Answer 22

indicated airspeed

Question 23

parasite drag varies directly in proportion to the frontal area presented to the airflow, also known as the _________________

Answer 23

Parasite Area

Question 24

contamination by ice, frost, snow, mud or slush will increase the ________________

Answer 24

parasite drag coefficient

Question 25

is an inherent component, a rather undesirable by-product of lift

Answer 25

induced drag

Question 26

Wing tip vortices modify upwash and downwash in the vicinity of the wing which produces a rearward component to the lift vector known as the ___________

Answer 26

induced drag

Question 27

factors affecting induced drag

Answer 27

- size of the lift force - speed of the aircraft - aspect ratio of the wing

Question 28

lift must be equal to _______ in flight so induced drag will depend on the _______ of the aircraft

Answer 28

weight, weight

Question 29

induced drag will be _______ at higher aircraft weights

Answer 29

greater

Question 30

certain maneuvers require the lift force to be ________ than the aircraft weight

Answer 30

greater

Question 31

the relationship of lift to weight ratio is also known as the _________

Answer 31

load factor

Question 32

relationship of load factor and induced drag

Answer 32

directly proportional

Question 33

relationship of induced drag and speed of the aircraft

Answer 33

inversely proportional

Question 34

as speed increases, the downwash caused by the tip vortices become ________________, the rearward inclination of the lift is _____, and therefore induced drag is less

Answer 34

less significant, less

Question 35

relationship of induced drag and aspect ratio of the wing

Answer 35

inversely proportional

Question 36

factors to consider if one decides to continue the increase of the aspect ratio

Answer 36

- excessive wing bending moments - reduced rate of roll - reduced ground clearance in roll during take-off and landing

Question 37

methods of reducing induced drag

Answer 37

- wing-end plates - tip tanks - winglets - wing tip shape

Question 38

a flat plate placed at the wing tip will restrict the tip vortices and have a similar effect to an increased aspect ratio, but without the extra bending loads

Answer 38

wing-end plates

Question 39

What type of drag do wing-end plates cause?

Answer 39

parasite drag

Question 40

fuel tanks placed at the wing tips will have a similar beneficial effect to an endplate, will reduce the induced drag

Answer 40

tip tanks

Question 41

Small vertical aerofoils which form part of the wing tip. Shaped and angled to the induced flow, they generate a small forward force.

Answer 41

winglets

Question 42

________ partly block the air flowing from the bottom to the top surface of the wing, reducing the strength of the tip vortex

Answer 42

winglets

Question 43

the _____________ can affect the strength of the tip vortices, and designs such as turned down or turned up wing tips have been used to reduce induced drag

Answer 43

shape of the wingtip

Question 44

is the sum of an aircraft's induced drag and parasite drag

Answer 44

total drag

Question 45

a number that aerodynamicists use to model all of the complex dependencies of shape, inclination, and flow conditions on aircraft drag

Answer 45

drag coefficient