M17

Question 1

What principle does the propeller work on?

Answer 1

Reaction.

Question 2

What does an engine propeller convert torque to?

Answer 2

Thrust.

Question 3

Where do all the measurements of the blade come from?

Answer 3

The centre of rotation.

Question 4

What Mach speeds are efficient?

Answer 4

0.5-0.6

High propulsive efficiencies.

Question 5

What happens to the cross section behind the propeller?

Answer 5

Reduces.

Question 6

Are the pressure differences on the blades and acceleration of air mass small or large?

Answer 6

Small.

Accelerates large mass of air slowly rearward.

Question 7

What is the blade angle (beta)?

Answer 7

Angle between the propeller chord and the rotational plane of the propeller.

(Also angle of incidence)

Question 8

What is the angle of attack (alpha)?

Answer 8

Angle between the profile chord line and the relative air flow towards it.

(Achieving desired lift)

Question 9

What is RAF?

Answer 9

Resultant Relative airflow.

Determines direction and magnitude of the velocity

Question 10

What speeds does the angle of advance increase?

Answer 10

As speeds increase.

Question 11

How is blade angle worked out?

Answer 11

Helix angle + angle of attack

Question 12

What happens to the angle of attack when there is a change in airspeed of rotational velocity?

Answer 12

Negative angle of attack.

Question 13

What are fixed pitch propellers good for?

Answer 13

Good climb performance
High speeds cruising
Towing

Question 14

What is the sum of propeller brake moment and engine torque at constant rotational speeds?

Answer 14

Zero.

Question 15

What happens to the brake moment with a reduction in blade angle?

Answer 15

Reduces.

Question 16

What forces act on the propeller as it rotates?

Answer 16

Torsion, tension, bending and compression.

Question 17

What is the greatest load felt on the propeller?

Answer 17

Centrifugal force.

Can be 7500 times the weight of the blade

Question 18

Where are most of the stresses felt on the blade?

Answer 18

Root and the hub.

Question 19

How does the thrust bending force affect the blade?

Answer 19

Bends the blade in the opposite direction of travel.

Question 20

Where is the vibration effect highest?

Answer 20

Tip of the blade.

Around 80% of blade length

Question 21

What will the natural frequency of the blade depend on?

Answer 21

Length, shape and blade root.

20 Hz (metal)
60 Hz (wood)

Question 22

What is the maximum number of blades on a propeller?

Answer 22

8.

Question 23

What is the minimum clearance between the propeller and the fuselage?

Answer 23

1 inch.

Question 24

What does the amount of lift on propellers depend on?

Answer 24

Aero foil shape, RPM and angle of attack

Question 25

Why must the blade be twisted?

Answer 25

Ensure a nearly constant angle of pitch.

Blade angle smaller as it moves away from centre of axis