Chapter 25: Propellers

Question 1

Definitions

4 Elements of prop. Where is face? Where is prop cut taken at?

Answer 1

Tip
Root
Spinner
Disk
Face: face the face
Cut at 75%

Question 2

Blade Angles (3)
Around what does it rotate?

Answer 2

Blade AoA: blade chord to RAF
+ Helix Angle: plane of rotation to RAF
= Blade pitch
Around axis of rotation

Question 3

Blade Pitch Range (2)

Answer 3

Alpha: fine - coarse, normal operations
Beta: feathered, reverse

Question 4

Propeller Slip Equation

Answer 4

Effective Pitch + Slip = Geometric Pitch

Question 5

Fine vs Coarse

Answer 5

Fine: good for slow TAS, TO. Has low pitch
Coarse: good for high TAS, cruise. Has high pitch

Question 6

Prop Types (3)

Answer 6

Fixed Pitch
Two Pitch
Constant Speed

Question 7

Prop AoA and Reverse Thrust

How does TAS / RPM Affect it? How to obtain reverse thrust?

Answer 7

TAS+ -> AoA-
RPM+ -> AoA+
Reverse thrust = high TAS, low RPM
until TAS becomes small enough to obtain thrust again

Question 8

Blade Angle

Constant?

Answer 8

Varies along propeller length. Pitch decreases to keep AoAp constant, because linear velocity increases near blade tips.

Question 9

Constant Speed / Variable Pitch Propeller

What does it do? What if you increase throttle?

Answer 9

Keeps RPM constant
if throttle increase, RPM wants to increase -> coarse
if throttle decreases, RPM wants to decrease -> fine

Question 10

Engine Failure

Prop positions names (3), parasite, torque, rank lowest to highest drag

Answer 10

Seized engine: highest parasite drag, no torque
Windmilling engine: high parasite, torque in direction of prop
Feathered: low parasite, no torque

Question 11

Propeller efficiency
Worst to best efficiency by prop type (3)
Efficiency calculation (2)?

Answer 11

Fixed pitch: worse
Two pitch: decent, fine/coarse setting
Constant speed: best
Efficiency = output / shaft input 
or = thrust power / shaft power