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M17 > M17.1 Fundementals > Flashcards

M17.1 Fundementals Flashcards

1
Q

Do page 22

A
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2
Q

What principle does a propeller work on?

A

A reaction principle

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3
Q

What does a reaction principle mean in regards to how propellers work??

A

The air mass flowing through the propeller plane is accelerated by differential velocity. This is due to the differing pressures in front and behind the prop plane. Which occurs as a result of air flowing around the prop blade aerofoil.

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4
Q

How does a propeller get thrust?

A

A propeller converts engine torque into thrust

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5
Q

Does a propeller acceleration a small or large amount of airflow?

A

A propeller accelerates a large mass of air slowly rearwards

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6
Q

What Mach are props most efficient at?

A

0.5 - 0.6 Mach

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7
Q

What is another name for blade angle?

A

Beta

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8
Q

What are the two ways to describe blade angle?

A

. Coarse - a greater horizontal blade angle
. Fine - a more vertical blade angle

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9
Q

How can you work out the blade angle/ angle of incidence?

A

The angle between the propeller chord and the rotational plane of the propeller

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10
Q

Explain what the reference blade station is??

A

As the blade angle is not constant over the whole length of the blade, a part of the blamed is termed reference blade station and this is between 0.5-0.75 of the radius of the propeller

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11
Q

Can can the angle of attack also be called?

A

Alpha

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12
Q

What is the angle of attack??

A

The angle between the profile chord line and the relative airflow towards it

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13
Q

What is the angle of advantage or helix angle?

A

The angle between the rotational plane of the propeller and the relative airflow (RAF).

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14
Q

What happens to the angle of advance when airspeed increases?

A

The angle increases

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15
Q

Blade angle = ?

A

Helix angle + angle of attack = blade angle

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16
Q

If RPM increases what happens to vertical speed and angle of attack?

A

If RPM increases vertical speed will increase and so will angle of attack

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17
Q

What happens to angle of attack if airspeed increases when on a decent?

A

Angle of attack will decrease, could result in a negative torque (windmilling)

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18
Q

Explain what wind milling is?

A

The airflow now drives the propeller which will then drive the engine and produce a negative torque

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19
Q

What are main disadvantages of fixed pitch propellers?

A

. They can only operate efficiently within a certain speed range

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20
Q

What are the 3 types of flight regimes fixed pitch propellers are designed for?

A

. Climb
. Hugh cruise speeds
. Towing

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21
Q

What is propeller brake?

A

The effort which is required to be able to spin the propeller

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22
Q

At a constant rotational speed the sun of prop brake moment and engine torque is what?

A

Zero

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23
Q

What does a change in airspeed or rotational velocity affect??

A

It effects the relative airflow direction and velocity

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24
Q

If airspeed if increased what does this alter for the propeller?

A

AoA would be decreased which would reduce the braking moment, therefore increasing RPM.
(Have to be careful not go exceed maximum permissible rotational speed)

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25
Q

During windmilling, the thrust is relatively large but is directed against the direction of flight. So what does this cause?

A

Increased aircraft drag due too windmilling propeller

26
Q

How can drag by windmilling be greatly reduced?

A

If the propeller is driven into a feathered position, so the leading edge is presented into the oncoming airflow

27
Q

What does FD stand for?

A

Drag

28
Q

What does FT stand for?

A

Brake moment

29
Q

What does FS stand for?

A

Thrust

30
Q

What does FL stand for?

A

Lift

31
Q

What does FR stand for?

A

Resultant force

32
Q

What does U stand for?

A

Rotational speed

33
Q

What does V stand for?

A

Airspeed

34
Q

What does W stand for?

A

Relative airflow (RAF)

35
Q

What is pitch the same as?

A

Blade angle

36
Q

What is the reverse pitch function used for?

A

An additional braking action

37
Q

How does a reverse pitch work?

A

The prop turns in the same direction, but the blade angle is positioned to the other side of fine pitch - negative pitch.
Therefore, tye air is pushed away from the aircraft, producing a braking force.

38
Q

What happens to brake moments when the blade angle is moved into the reverse pitch?

A

The brake moments occur very quickly and become very large

39
Q

What is the blade angle in degrees when reverse pitch occurs?

A

-2 to -8 degrees

40
Q

By having a thickened root area of the blade what does this cause?

A

The root area can withstand high stresses, but loses of aerodynamic efficieny

41
Q

What are the tip losses on a blade?

A

Tip vortices and induced drag at the tip at high rotational speeds

42
Q

How can you maintain a constant angle of attack at differing rotational speeds?

A

The leading edge of the propeller blade is twisted downwards from the root to the tip

43
Q

What does slip mean?

A

The difference between geometric pitch and effective pitch

44
Q

How can you define propeller pitch?

A

The distance that a propeller will move forward in one revolution

45
Q

Explain what geometric pitch is??

A

The design point and only occurs if the propeller was 100€% efficient (ideal)

46
Q

What is effective pitch?

A

It is the actual path on which the propeller moves through the air - taking into account the efficiency loses

47
Q

What is propeller efficiency?

A

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

48
Q

What is motive performance?

A

The same as output power of the engine

49
Q

What is motive power for a piston engine compared to a turboprop?

A

. Piston engine = brake power
. Turboprop = shaft power

50
Q

What are the normal propeller efficiency ranges?

A

0.8 - 0.9 (80 - 90%)

51
Q

What are the 5 static loads that propeller take??

A

. Centrifugal force
. Thrust bending force
. Torque bending force
. Aerodynamic twisting moment
. Centrifugal twisting moment

52
Q

How much more can the load of centrifugal force be on the prop blade?

A

More than 7500 times the weight of the blade

53
Q

What does the thrust bending force do to the blade?

A

Try’s to bend the prop blade top forwards

54
Q

What does the torque bending force do to a blade?

A

Try’s to bend the blade against the direction of propeller rotation, creating a resistance to the torque being produced

55
Q

What does aerodynamic twisting moment do to the blade?

A

The centre of pressure being forward of the blades centre of rotation means it will try toturn the blade to the higher (coarser) blade angle

56
Q

What does the centrifugal twisting moment do to the blade?

A

The mass of the blade is thrown out from the blades centre of rotation trying to turn the blade to the lower (finer) blade angle

57
Q

Where are all the static loads felt at??

A

On the blade root

58
Q

Can you have damage or repair work in the blade root area?a.

A

No

59
Q

Which load is greater, CTM or ATM.

A

Centrifugal twisting moment is always greater, and it always opposes aerodynamic twisting moment

60
Q

What are the efficient airspeed machs that props work at?

A

0.5-0.6 Mach- low to medium airspeeds

61
Q

What is angle of advance or helix angle?

A

The angle between the rotational plane of the prop and the relative air lode (RAF) - increases with increasing airspeed

62
Q

Blade angle =

A

Helix angle + angle of attack

M17 (12 decks)

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