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Theory of Flight > Ai > Flashcards

Ai Flashcards

1
Q

What is interference drag?

A

Interference drag occurs when airflow over one aircraft component mixes with airflow over another component, causing increased drag.

This is commonly observed at the intersections of wings and fuselages.

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2
Q

What causes eddy currents in aircraft?

A

Eddy currents are caused by the mixing of airflow over different aircraft components, such as wings and fuselage.

These currents lead to turbulent flow, which is not ideal for aerodynamic efficiency.

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3
Q

Where is a prominent example of interference drag found?

A

At the intersection of the wing and fuselage at the wing root.

This location is where airflow from the fuselage collides with airflow over the wing.

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4
Q

What is the impact of eddy currents on airflow?

A

Eddy currents restrict the smooth passage of airflow over the aircraft, increasing drag.

This disruption affects overall aerodynamic performance.

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5
Q

What role do fairings play in aircraft design?

A

Fairings are fitted at intersections to help reduce the amount of interference drag by allowing smoother airflow transitions.

They are particularly useful at the wing root and fuselage junction.

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6
Q

Fill in the blank: Fairings help the airflow transition smoothly between areas like the wing root and _______.

A

fuselage.

This design consideration is crucial for enhancing aerodynamic efficiency.

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7
Q

True or False: Interference drag only occurs at the wing tips of an aircraft.

A

False.

Interference drag can occur at various intersections, including the wing root.

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8
Q

What is skin friction?

A

Drag due to surface roughness and viscosity of the air

Skin friction slows the layers of air above the surface producing a Boundary Layer.

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9
Q

What are the two types of boundary layers that can occur over a surface?

A

Streamline (laminar) and turbulent

The boundary layer can be either streamline or turbulent depending on the airflow characteristics.

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10
Q

What is the thickness range of a laminar boundary layer?

A

0.1 to 0.2 mm

A laminar boundary layer is thin and experiences small skin friction.

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11
Q

What is the thickness of a turbulent boundary layer?

A

5 mm or more

A turbulent boundary layer is thicker and results in larger skin friction.

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12
Q

What is the Transition Point in relation to the boundary layer?

A

The point where the boundary layer tends to break away from the surface and become turbulent

The transition point moves forward as aircraft speed increases.

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13
Q

What effect does increasing aircraft speed have on the boundary layer?

A

Moves the transition point forward, increasing the turbulent area

More of the boundary layer becomes turbulent, leading to greater skin friction.

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14
Q

What causes induced drag in aircraft?

A

Vortices leaving the wing tips

A vortex is a particular form of turbulence that contributes to drag.

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15
Q

True or False: Induced drag is caused by smooth airflow over the wings.

A

False

Induced drag is associated with turbulence created by vortices.

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16
Q

What does the pressure distribution over an aircraft wing look like?

A

Negative pressure below atmospheric and positive pressure above atmospheric

This pressure distribution is crucial for understanding lift and drag characteristics.

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17
Q

What must occur around the wing tips due to pressure differences?

A

A flow of air from the high-pressure region below the wing to the low-pressure region above the wing

This flow is essential for understanding lift and drag in aerodynamics.

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18
Q

What two types of velocity combine at the wing tips?

A

Rotational and linear velocity

This combination forms wing tip vortices, which are important in understanding induced drag.

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19
Q

What direction does the starboard wing rotate when viewed from behind the aircraft?

A

Anticlockwise

The port wing will have a clockwise motion.

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20
Q

How can induced drag be minimized?

A

By having wings that are long and thin, i.e., with a high Aspect Ratio

This design reduces the wing tip area and consequently the adverse wing tip effect.

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21
Q

What is the relationship between aircraft speed and Form Drag?

A

As aircraft speed increases, Form Drag increases

The increase follows the formula: Drag Force = ½ x p x v² x S x CD.

22
Q

What happens to Skin Friction as aircraft speed increases?

A

Skin Friction increases

This is part of the overall drag experienced by the aircraft.

23
Q

What surprising effect does an increase in aircraft speed have on Induced Drag?

A

Induced Drag reduces

The Coefficient of Induced Drag (CDi) decreases much more rapidly than the velocity increases.

24
Q

Fill in the blank: The formula for Drag Force is _______.

A

½ x p x v² x S x CD

This formula applies to both Form Drag and Skin Friction with different values of CD.

25
Q

What is the effect of aircraft speed on Total Drag?

A

Total Drag is influenced by increases in Form Drag and Skin Friction, while Induced Drag decreases

This complex interaction is critical for aircraft performance analysis.

26
Q

What are the four main forces acting upon an aircraft in flight?

A

Lift, weight, thrust, drag

These forces are crucial for understanding aircraft dynamics.

27
Q

What condition must prevail for an aircraft in steady level flight?

A

Equilibrium must prevail

This means lift equals weight and thrust equals drag.

28
Q

Where does lift act on an aircraft?

A

Through the centre of pressure (CP)

The CP is the point where lift is considered to act.

29
Q

Where does weight act on an aircraft?

A

Through the centre of gravity (CG)

The CG is the point where the weight of the aircraft is balanced.

30
Q

In level flight, how do thrust and drag act?

A

In opposite directions parallel to the direction of flight

This is a simplification for the purposes of analysis.

31
Q

What is the lift/drag ratio?

A

May be as low as ten to one

This ratio can vary depending on speed and power used.

32
Q

What can cause a pitching moment in an aircraft?

A

The positions of CP and CG being variable

A change in angle of attack or fuel load can affect these positions.

33
Q

What happens when lift is in front of the CG?

A

It causes a nose-up pitching moment

This occurs because the lift and weight create a torque.

34
Q

What happens when lift is behind the CG?

A

It causes a nose-down pitching moment

The relationship between lift and CG is critical for stability.

35
Q

Fill in the blank: The unaccelerated condition of flight is achieved with the aircraft trimmed for lift to equal _______.

A

Weight

36
Q

Fill in the blank: The opposing forces of lift and weight set up a couple causing either a _______ or a nose-down pitching moment.

A

Nose-up

37
Q

What should ideally neutralize each other in level flight?

A

The pitching moments arising from thrust and drag

This ensures that there is no residual moment tending to rotate the aircraft.

38
Q

What arrangement is aimed for with thrust/drag and lift/weight couples?

A

Thrust/drag couple produces a nose-up moment, lift/weight couple produces a nose-down moment

The lines of action of each couple are positioned so that their strength is equal.

39
Q

What happens when the engine is throttled back in level flight?

A

The thrust/drag couple is weakened, and the lift/weight couple pitches the nose down

This causes the aircraft to assume a gliding attitude.

40
Q

What effect does re-applying power have on the aircraft’s attitude?

A

The growing strength of the thrust/drag couple raises the nose towards level flight attitude

41
Q

At low speed, what must the angle of attack be?

A

High

This is necessary to obtain the required amount of lift.

42
Q

At high speed, what is needed to obtain the necessary amount of lift?

A

A small angle of attack

43
Q

How does the aircraft’s attitude change with speed?

A

Markedly nose-up at very low speeds, less so as speed increases

44
Q

What is the difference in attitudes most marked on?

A

Aircraft having swept-back wings or unswept wings of low aspect ratio

45
Q

What do the curves of power or thrust required define?

A

The power or thrust required to achieve equilibrium

This is when lift equals weight or for constant altitude flight at various air speeds.

46
Q

What factors are specific curves of power or thrust required valid for?

A

A particular aerodynamic configuration, a given weight, and altitude

47
Q

What occurs at point C in relation to minimum flying speed?

A

Flight is in the vicinity of the minimum flying speed, with a major portion of thrust required due to induced drag.

Minimum flying speed is influenced by conditions of stall or stability and control problems.

48
Q

What determines the maximum level flight speed for an aircraft?

A

It is obtained when the power or thrust required equals the maximum power or thrust available from the engine.

This relationship highlights the balance between engine capability and aerodynamic requirements.

49
Q

What happens when an aircraft flying level at a given angle of attack reduces its weight?

A

The lift must also be reduced to balance the new weight, requiring a decrease in speed to maintain optimum conditions.

This situation often occurs when stores are dropped from the aircraft.

50
Q

What is the relationship between weight and Equivalent Air Speed (EAS) at a specific angle of attack?

A

The lower the weight, the lower the EAS corresponding to that angle of attack, with EAS proportional to the square root of the all-up weight.

This relationship is crucial for understanding flight dynamics and performance adjustments.

51
Q

At what angle of attack is the best Lift/Drag ratio typically found?

A

About 4º.

This angle is often used as a reference for optimizing lift and drag during flight.

Theory of Flight (3 decks)

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