Propellers

Question 1

Which part of a propeller is most thrust generated

Answer 1

3/4 measured from root
75%

Question 2

Role of a spinner

Answer 2

Covers the propeller hub and reduces drag

Question 3

Propeller disc

Answer 3

Circular area which the blade rotates

Question 4

Blade Angle (Blade Pitch)

Answer 4

Angle between plane of rotation and the chord line

Question 5

Blade Twist

Answer 5

Reduction in blade angle from hub to tip to provide a uniform AOA across the blade with increasing angular velocity at the tip

Question 6

Helix Angle

Answer 6

Angle between plane of rotation and the relative airflow

Blade angle - AOA

Question 7

Blade Angle Of Attack

Answer 7

Angle between relative airflow and the chord line

Question 8

Geometric Pitch

Answer 8

Distance propeller moves forward in one rotation with no aoa

Question 9

Effective Pitch is

Answer 9

Distance propeller actually moves in 1 revolution

Geometric pitch = effective pitch + slip

Question 10

Fine Pitch has a what pitch angle

Answer 10

Small pitch angle

Question 11

Coarse pitch angle has a what pitch angle

Answer 11

Large pitch angle

Question 12

Fixed Pitch Propeller

Answer 12

Blade angle is fixed
One set RPM/Speed for maximum efficiency

Question 13

Two Pitch Propellers

Answer 13

Fine pitch or coarse pitch setting

Question 14

Adjustable pitch propeller

Answer 14

Blade angle adjusted on ground then acts as a fixed pitch propeller at that setting

Question 15

Constant speed propeller

Answer 15

Adjust blade angle at different flight speeds to maintain AOA

Question 16

Forces acting in plain of rotation

Answer 16

Torque drag
Shaft torque

Question 17

Forms perpendicular to axis of rotation

Answer 17

Thrust and total reaction

Question 18

TAS on blade angle

Answer 18

Higher TAS gives a lower AOA

Think about air getting closer to propeller

Lower TAS gives a greater AOA

Question 19

RPM on Blade Angle

Answer 19

RPM increases blade AOA increases

RPM decreases blade AOA decreases

Question 20

Negative Blade alpha

Answer 20

Beyond fine pitch
Can occurs at very low RPM
Negative AOA
Total reaction inclined backwards
High drag (torque drag)

Question 21

Types of variable pitch propellers

Answer 21

Adjustable - Manually adjusted with pitch control lever

Constant speed propeller - blade pitch angle mechanically controlled by speed governor to keep blade angles at optimum AOA across wide range of airspeeds

Question 22

Adjusting pitch in variable pitch propeller

Answer 22

T/o with low TAS propeller is set to fine pitch

High speed propeller is set to coarse

Question 23

What is windmilling

Answer 23

Torque drag exceeds shaft drag
CSU fines off blade angle
Drag produces small driving torque which rotates propeller in usual direction

+ assists engine restart in flight
- reduces glide performance

Question 24

Feathering

Answer 24

Blade angle is set at zero lift AOA no driving force so propeller is stationery

Little drag

Question 25

Reverse Thrust is

Answer 25

Produced when blade angle moved beyond fully fine pitch Requires lots of power Set past fine pitch not coarse pitch Drag/reverse thrust

Question 26

Propeller Noise is related to

Answer 26

Propeller tip speed If tip speed increases transonic region shockwaves If blade numbers reduced longer blades are needed which will have higher tip speed = more noise

Question 27

How can power absorption be increase on a propeller

Answer 27

Propeller length Increase propeller solidity (frontal area of blade) Increase chord of blades Contra rotating propellers

Question 28

Contra Rotating Propellers

Answer 28

Mounted on the same shaft driven in opposite direction

Question 29

Propeller solidity

Answer 29

Ratio of the total frontal area of the blades to the area to the propeller disc

Question 30

counter rotating propeller

Answer 30

Eliminate problems with critical engine association

Question 31

Propeller efficiency

Answer 31

Thrust power to engine torque