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M17 > 17.1 > Flashcards

17.1 Flashcards

1
Q

In simple terms a propellor converts what into what?

A

Converts torque into thrust
Accelerates a large mass of air rearwards

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2
Q

Propellor engines are efficient where?

A

Low to medium speeds

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3
Q

What is the blade angle?

A

The angle between chord line and propellor plane of rotation

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4
Q

Plane of rotation is where?

A

90 degrees/ perpendicular to engine

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5
Q

If angle of advance increases then what decreases?

A

The angle of attack

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6
Q

Blade angle is made up of what?

A

Angle of attack
Helix angle

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7
Q

Blade reference station for blade angle is usually between where on the prop radius?

A

50%-70%

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8
Q

Blade angles change with what?

A

With the twist in the blade

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9
Q

On a fixed pitch propellor what is the blade angle known as?

A

Angle of incidence

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10
Q

Relative airflow is made up of what?
What does this determine?

A

Made up from a vector of airspeed velocity and propellor rotational velocity.
Determines RAF (Relative airflow) direction and magnitude

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11
Q

What angle increases with airspeed?

A

Helix angle

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12
Q

What angle reduces with airflow?

A

Angle of attack

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13
Q

What is windmilling?

A

Airspeed is now turning the propellor, which turns the engine and gives negative torque value

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14
Q

Fixed propellor are limited to their role, they either give good…… performance or good…… performance?

A

Either good take off/climb performance
Or good cruise performance

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15
Q

At a constant rotational speed the sum of what is zero?

A

Propellor brake moment and engine torque

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16
Q

How does an increase in forward speed effect angle of attack, helix angle and torque moment?

A

Angle of attack reduces
Helix angle increases
Torque moment reduces

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17
Q

What is FT?

A

Brake moment

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18
Q

What is FR?

A

Resultant force

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19
Q

With constant pitch, if airspeed increases rapidly or rotational speed is greatly reduced, what happens to angle of attack?

A

Angle of attack on will reduce and can become negative

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20
Q

What is increased by a windmilling propellor?

A

Aircraft drag

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21
Q

Increased drag can be greatly reduced if propellor is driven into what position?

A

Feathering position

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22
Q

If the blade angle is reduced to an extent that the angle of attack is less than zero angle of attack, where will thrust be acting?

A

Thrust acting against the direction of flight results (reverse thrust)

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23
Q

In an event of a stall or emergency what position should engine go into?

A

Feathered position

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24
Q

What is root losses?

A

A thickened root area can withstand high stresses but loses aerodynamic efficiency. Airflow at the root is affected by the engine

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25
Q

What are tip losses?

A

Tip vortices and induced drag cause tip losses at high rotational speeds. Further losses are caused by compressibility effects

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26
Q

What is blade washout?

A

To maintain a constant angle of attack at differing rotational speeds along the blade, the leading edge of the propellor blade is twisted downwards from root to tip

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27
Q

What is pitch distribution?

A

The blade angle becomes smaller the further it is from the centre axis in order to keep a nearly constant angle of attack.

28
Q

Because a propellor blade is a rotating aerofoils what is the term to describe how it produces lift?

A

Produces lift by aerodynamic action

29
Q

The further the profile section of the propeller blade is from its rotational axis, the greater the what?

A

The greater the peripheral velocity will be at a constant rotational speed

30
Q

What is the bottom of the blade called?

A

Blade butt

31
Q

What is the difference known as between geometric and effective pitch?

A

Slip

32
Q

What is propellor pitch?

A

Defined as the distance that a propellor will move forward in one revolution

33
Q

What is geometric pitch?

A

The theoretical distance one revolution should move the body forwards

34
Q

What is effective pitch?

A

The actual helical path on which the propeller moves through the air has an angle of pitch which corresponds to the angle of advance

35
Q

In simple terms what is propeller efficiency?

A

the performance produced by the propeller in relationship to its motive performance.

36
Q

Normal propeller efficiency ranges are in region of what?

A

80%-90%

37
Q

Aerodynamic twisting moment will try and move blade to what angle?

A

Higher angle
(Coarser)

38
Q

Centrifugal twisting moment tries to move blade angle where?

A

Lower blade angle
(Finer)

39
Q

What is the greatest load felt on a propeller?

A

Centrifugal force

40
Q

What is thrust bending force?

A

attempts to bend the propeller blade tips forwards

41
Q

What is torque bending load?

A

tends to try and bend the blade against the direction of propeller rotation

42
Q

Where are highest vibrations felt on a blade?

A

Felt at 80% of blade length

43
Q

How is vibration decreased on propeller?

A

Decreased by correct aerofoils and tip design

44
Q

What is the high vibration point on propeller profile known as?

A

Outer nodal point
(At 80% of chord length)

45
Q

What is the best option for converting horse power to thrust (Adding more thrust)?

A

Increase the number of propeller blades

46
Q

Why would increasing propeller rpm be impractical to make more thrust?

A

The tips will get to the point where they are supersonic, causing shockwaves and drag is caused

47
Q

A torque reaction links to which one of newtons laws?

A

3rd law
Each reaction has an equal and opposite reaction

48
Q

To compensate for the effects on engine torque what do propeller aircraft have?

A

Some aircraft will be offset with more lift on down-going wing

49
Q

How do you compensate for twist effect on prop aircraft?

A

The vertical stabiliser is mounted obliquely 1 or 2 degrees to the aircraft’s longitudinal axis
Only ideal for cruise

50
Q

When a tail wheel aircraft with propeller raises the tail on take off, the resultant force acts 90 degrees ahead, what does this cause?

A

Causes a yawing moment to the left around the vertical axis

51
Q

How does the pilot compensate for a yawing moment?

A

With rudder and elevator offset on take-off

52
Q

If two engines are turning in the same direction to one another, what occurs?

A

Asymmetric loading

53
Q

If Engines turning opposite to each other, where is thrust felt?

A

Towards the Outboard

54
Q

What is the engine called that creates the smallest yaw moment should the other engine fail?

A

The critical engine

55
Q

How is rotation noise produced?

A

Produced from the pressure field of a rotating propeller

56
Q

How is vortex house caused?

A

Caused by vortices leaving the blade tip and blade trailing edge

57
Q

What is displacement noise?

A

Displacement of the air by the propeller blades

58
Q

When does blade vibration noise occur?

A

Occurs with periodic blade stalls

59
Q

What is inconsistent airflow?

A

Vortices if preceding blades hit the leading edge of the following blade

60
Q

How do power settings influence noise?

A

Mainly when RPM drops to create low frequency noise

61
Q

How does propeller diameter influence noise?

A

Larger=more noise
Smaller= less noise

62
Q

How does the number of blades influence noise?

A

More blades=less noise
Less blades= more noise

63
Q

How does blade tip Mach speed influence noise?

A

Increase in tip speed= increase in noise

64
Q

Does the shape and material of a blade effect noise?

A

Yes

65
Q

What is the minimum clearance required between propeller tip and ground on aircraft fitted with a nose wheel?

A

7 inches

M17 (10 decks)

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