M17.1 Fundementals

Question 1

Do page 22

Question 2

What principle does a propeller work on?

Answer 2

A reaction principle

Question 3

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

Answer 3

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.

Question 4

How does a propeller get thrust?

Answer 4

A propeller converts engine torque into thrust

Question 5

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

Answer 5

A propeller accelerates a large mass of air slowly rearwards

Question 6

What Mach are props most efficient at?

Answer 6

0.5 - 0.6 Mach

Question 7

What is another name for blade angle?

Answer 7

Beta

Question 8

What are the two ways to describe blade angle?

Answer 8

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

Question 9

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

Answer 9

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

Question 10

Explain what the reference blade station is??

Answer 10

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

Question 11

Can can the angle of attack also be called?

Answer 11

Alpha

Question 12

What is the angle of attack??

Answer 12

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

Question 13

What is the angle of advantage or helix angle?

Answer 13

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

Question 14

What happens to the angle of advance when airspeed increases?

Answer 14

The angle increases

Question 15

Blade angle = ?

Answer 15

Helix angle + angle of attack = blade angle

Question 16

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

Answer 16

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

Question 17

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

Answer 17

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

Question 18

Explain what wind milling is?

Answer 18

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

Question 19

What are main disadvantages of fixed pitch propellers?

Answer 19

. They can only operate efficiently within a certain speed range

Question 20

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

Answer 20

. Climb
. Hugh cruise speeds
. Towing

Question 21

What is propeller brake?

Answer 21

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

Question 22

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

Answer 22

Zero

Question 23

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

Answer 23

It effects the relative airflow direction and velocity

Question 24

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

Answer 24

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

Question 25

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

Answer 25

Increased aircraft drag due too windmilling propeller

Question 26

How can drag by windmilling be greatly reduced?

Answer 26

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

Question 27

What does FD stand for?

Answer 27

Drag

Question 28

What does FT stand for?

Answer 28

Brake moment

Question 29

What does FS stand for?

Answer 29

Thrust

Question 30

What does FL stand for?

Answer 30

Lift

Question 31

What does FR stand for?

Answer 31

Resultant force

Question 32

What does U stand for?

Answer 32

Rotational speed

Question 33

What does V stand for?

Answer 33

Airspeed

Question 34

What does W stand for?

Answer 34

Relative airflow (RAF)

Question 35

What is pitch the same as?

Answer 35

Blade angle

Question 36

What is the reverse pitch function used for?

Answer 36

An additional braking action

Question 37

How does a reverse pitch work?

Answer 37

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.

Question 38

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

Answer 38

The brake moments occur very quickly and become very large

Question 39

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

Answer 39

-2 to -8 degrees

Question 40

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

Answer 40

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

Question 41

What are the tip losses on a blade?

Answer 41

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

Question 42

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

Answer 42

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

Question 43

What does slip mean?

Answer 43

The difference between geometric pitch and effective pitch

Question 44

How can you define propeller pitch?

Answer 44

The distance that a propeller will move forward in one revolution

Question 45

Explain what geometric pitch is??

Answer 45

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

Question 46

What is effective pitch?

Answer 46

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

Question 47

What is propeller efficiency?

Answer 47

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

Question 48

What is motive performance?

Answer 48

The same as output power of the engine

Question 49

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

Answer 49

. Piston engine = brake power . Turboprop = shaft power

Question 50

What are the normal propeller efficiency ranges?

Answer 50

0.8 - 0.9 (80 - 90%)

Question 51

What are the 5 static loads that propeller take??

Answer 51

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

Question 52

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

Answer 52

More than 7500 times the weight of the blade

Question 53

What does the thrust bending force do to the blade?

Answer 53

Try’s to bend the prop blade top forwards

Question 54

What does the torque bending force do to a blade?

Answer 54

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

Question 55

What does aerodynamic twisting moment do to the blade?

Answer 55

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

Question 56

What does the centrifugal twisting moment do to the blade?

Answer 56

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

Question 57

Where are all the static loads felt at??

Answer 57

On the blade root

Question 58

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

Answer 58

No

Question 59

Which load is greater, CTM or ATM.

Answer 59

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

Question 60

What are the efficient airspeed machs that props work at?

Answer 60

0.5-0.6 Mach- low to medium airspeeds

Question 61

What is angle of advance or helix angle?

Answer 61

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

Question 62

Blade angle =

Answer 62

Helix angle + angle of attack