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EK24 > Aeroplanlære - Kap 4 (Drag) > Flashcards

Aeroplanlære - Kap 4 (Drag) Flashcards

1
Q

When moving through a fluid (Air) we encounter a resistance. What is this called?

A

Drag

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2
Q

In two dimensional flow which 2 forms of drag do we have?

A

Skin friction drag
Form drag

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3
Q

What causes form drag?

A

Caused by the difference in pressure in front and behind the aerofoil

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4
Q

What causes skin friction drag?

A

Caused by shear forces in the boundary layer due to the air’s viscosity

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5
Q

What are form drag and skin friction drag together known as?

A

Profile drag

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6
Q

Does profile drag produce lift?

A

No

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7
Q

What is the equation for form drag?

A
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8
Q

What happens to the air molecules when they hit the aerofoil?

A
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9
Q

What is the boundary layer?

A

The layer from the aerofoil extending out to 99% of the free stream flow

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10
Q

Where does skin friction drag take place?

A

Within the boundary layer

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11
Q

When is the most energy produced in this airflow?

A

When the airflow becomes turbulent

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12
Q

Is the laminar boundary layer higher or lower than the turbulent boundary layer?

A

The laminar is lower than the turbulent boundary layer

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13
Q

Does laminar flow produce more or less skin fraction than turbulent air?

A

The laminar flow produce less and possesses less kinetic energy than turbulent

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14
Q

Does airflow speed increase or decrease when getting further from the surface in a laminar boundary layer?

A

It increases the further from the surface

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15
Q

Does airflow speed increase or decrease when getting further from the surface in a turbulent boundary layer?

A

It increases the further from the surface but less than a laminar boundary layer

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16
Q

In which way does turbulent airflow move?

A

It has flows in many directions

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17
Q

Why do turbulent airflow in the turbulent boundary layer create more skin friction drag?

A
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18
Q

What is the point where the laminar boundary layer switches too a turbulent boundary layer?

A

Transition point

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19
Q

What is the equation for reynolds number?

A
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20
Q

What does Reynolds number tell us?

A
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21
Q

Where is the lowest surface pressure located on an aerofoil?

A

Approximately at the point of maximum thickness

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22
Q

From the leading edge too the lowest surface pressure, which way is the pressure gradient?

A

The same way as the direction of the flow

23
Q

What is the adverse pressure gradient?

A

When the high pressure from under the wing seeks towards the top of the wing from trailing edge towards leading edge

24
Q

What is the point where turbulent airflow separates from the aerofoil?

A

Separation point
* Caused by low speed and the adverse pressure gradient

25
Q

Will profile drag occur if there is no lift being generated

A

Yes

26
Q

What causes induced drag to be produced?

A

It is caused by the vortices produced whenever lift is produced

27
Q

When is interference drag produced?

A
28
Q

Which categories of aircraft drag is there and how are they connected?

A
29
Q

Which factors affect form drag?

A
30
Q

Which factors affect skin friction drag?

A
31
Q

Which factors affect interference drag?

A

When the airflow across one component of an aircraft is forced to mix with the airflow across an adjacent or proximal component

32
Q

Which form of drag increases when airspeed increase?

A

Parasite drag

33
Q

When using flaps and gears which form of drag increase?

A

Parasite drag (Greater frontal area)

34
Q

What is the equation for parasite drag?

A
35
Q

What causes changes in the coefficient of parasite drag?

A
36
Q

Which form of drag decreases when airspeed increase?

A

Induced drag

37
Q

Does induced drag increase or decrease with higher weight?

A

Increase

38
Q

Does a glider have a higher induced drag than short winged aircraft?

A

No since induced drag is inversely proportional with aspect ratio and a glider has a high wing aspect ratio, therefore less vortices

39
Q

What is the equation for induced drag?

A
40
Q

What is downwash and the coefficient for induced drag proportional and inversely proportional too?

A
41
Q

An aircraft is flying straight and level and doubles it’s airspeed. What happens too lift and induced drag too keep flying straight and level?

A

Lift must be reduced to 1/4
Induced drag is equal to lift^2 so that must be 1/4 x 1/4 = 1/16

42
Q

What is total drag?

A

The sum of parasite drag and induced drag

43
Q

What is Vmd?

A

Velocity minimum drag

44
Q

When is speed stable and unstable?

A

Unstable behind velocity minimum drag and stable above

45
Q

What happens to the drag curve when increasing altitude?

A

It moves right and thereby Vmd is higher

46
Q

What happens to the drag curve when increasing weight?

A

It moves right and up and thereby Vmd is higher

47
Q

What happens to the drag curve when changing the configuration to a dirty configuration?

A

It moves left and up and thereby Vmd is lower

48
Q

What is the equation for total drag?

A
49
Q

How does the coefficient for parasite drag change with the coefficient for lift?

A

It has a constant stable drag until Clmax but with a slight increase at the end

50
Q

How does the coefficient for induced drag change with the coefficient for lift?

A

Lift and drag increase slightly until Clmax and then lift decrease after

51
Q

Explain where the different drag coefficients are seen on the drag polar

A

The coefficient for parasite drag is seen first thereafter it’s a combination

52
Q

How do you find the greatest ratio between the coefficient for drag and the coefficient for lift on the total drag curve?

A

By drawing a tangent line from zero to the graph

53
Q

What is not shown on the lift drag ratio graph?

A

Blue line = The coefficient for drag
Light blue line = The coefficient for lift
Orange line = The coefficient for lift / The coefficient for drag
X axis = Angle of attack

EK24 (29 decks)

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