Propellers and Governors

Question 1

What is the point of the propeller?

Answer 1

-To turn the movement by the heat engine into forward thrust for the aircraft. It absorbs the power output of the engine

Question 2

What does the anatomy of a propeller look like?

Answer 2

Consists of central hub connecting 2 or more propellers

Question 3

A propeller is made up of rotating_______

Answer 3

Wings

Question 4

What does the propeller create?

Answer 4

Thrust. Technically, the blades of the propellers are wings which create “lift” in the horizontal axis therefor we call it thrust

Question 5

What power does the engine supply?

Answer 5

Brake horsepower(BHP)

Question 6

What does the propeller convert BHP into?

Answer 6

Thrust horsepower(THP)

Question 7

When do we lose power while converting BHP to THP?

Answer 7

We will ALWAYS lose power because it is never 100% efficiency

Question 8

How efficient are the most efficient propellers?

Answer 8

~50%

Question 9

What is slip?

Answer 9

The difference between how much the prop should push the a/c vs. the actual distance that the a/c advances. In other words: Geometric pitch(theoretical pitch) vs. effective pitch(actual pitch)

Question 10

What is the shape of the propeller like?

Answer 10

The propeller is a twisted airfoil of irregular planform

Question 11

Where do we lose power to when converting BHP to THP?

Answer 11

The physical rotation of the propeller and friction are the main causes of power lost

Question 12

Why are propellers shaped irregularly?

Answer 12

To make sure the base and tip of the prop create the same amount of “lift” while rotating at the same speed, therefor moving at different speeds due to rotational physics

Question 13

What does the blade back side of the prop refer to?

Answer 13

The cambered side of the prop

Question 14

What does the front side of the prop refer to?

Answer 14

The side the pilot sees while sitting at the flight deck

Question 15

What verbiage do we use to describe the prop?

Answer 15

The same that we use to describe the wings

Question 16

What does fine pitch tell you about a prop’s pitch?

Answer 16

It tells us the pitch is at a relatively low angle to oncoming airflow

Question 17

What does coarse tell you about a prop’s pitch?

Answer 17

It tells us the pitch is steeper and bites more air

Question 18

What forces act on a propeller?

Answer 18

Centrifugal, torque, aerodynamic twisting force, thrust and bending forces. The hub provides the centripetal force

Question 19

What does the aerodynamic twisting force do?

Answer 19

It tries to twist the airfoil shape because it is exerting pressure on a focused point of the propeller blade

Question 20

What is the torque bending force?

Answer 20

The force acted upon by the oncoming air that the prop encounters, pushing back against the motion of the propeller

Question 21

How does the propeller create thrust?

Answer 21

1. Deflects air backwards and the equal and opposite force is a forward movement of the propeller and everything attached to it
2. It creates a low pressure zone on the top of the wing (front of the propeller) and a high pressure zone on the other

Question 21

What pitch would a general all purpose prop have?

Answer 21

20-25%

Question 22

Can you adjust pitch on a constant speed propeller?

Answer 22

Yes

Question 23

How do we use a constant speed propeller?

Answer 23

During t/o-Set pitch low so it spins faster and more easily. We then pitch the propeller up more once we speed up. It is similar to setting gears on a car

Question 24

What are constant speed propellers usually controlled by?

Answer 24

A pressurized oil governor. When the prop starts turning at a higher RPM than set by the pilot, the governor adjust to prop to a steeper AoA to the rotation of the propeller, slowing it down. It decreases the pitch when when the prop is not fast enough

Question 25

On a single engine, what would an engine oil loss (aka engine failure) do to the propeller?

Answer 25

Oil pressure usually increases blade pitch. In the event of an engine failure, the prop will continue to spin from the oncoming airflow. Thus increasing the likelihood of an airflow assisted restart

Question 26

On a multi engine, what would an engine oil loss (aka engine failure) do to the propeller?

Answer 26

On a multi engine, the oil loss will cause the prop to feather, decreasing drag on the failed engine.

Question 27

What is the effect of oil loss on aerodynamics?

Answer 27

The oil loss and counter weights turn the angle of the prop

Question 28

What if we feather the prop and we want to un-feather it to try and re-start the engine?

Answer 28

Some aircraft are equipped with un-feathering accumulators, that store high pressure oil to help create the force to get the propeller out of feather

Question 29

What do we need to check when inspecting the propeller?

Answer 29

-Nicks, chips, cracks -Oil leaks -Spinner security

Question 30

What position should you have your prop at while parked?

Answer 30

It depends but usually 10:00 and 4:00 because you can still see and birds don't land on it

Question 31

What does high humidity and temperatures do to power availability?

Answer 31

It decreases the performance of our engine and decreases our power

Question 32

What are some rules to follow while operating a naturally aspirated engine?

Answer 32

1. All adjustments should be slow and smooth 2. In a constant speed propeller, add power from right to left and reduce from left to right(throttle-->prop pitch-->mixture) 3. Watch out for shock cooling and shock heating 4. Don't forget to clear the engine after prolonged power off times 5. Full power should imply full mixture, unless the POH says otherwise 6. Watch for carb ice, especially at low RPMs 7. Always prep a cold engine before starting