Propellors

Question 1

Purpose of propellor

Answer 1

Turn engine torque into forward thrust
F = MASS X ACCELERATION
HP = TORQUE X RPM/33,000

Question 2

Type of materials

Answer 2

● Wood
Light weight
5-9 layers laminated together
Lamination problems
Cloth covering on tips as well as metal leading edges protect the propeller
●Metal
Lighter than wood (thinner)
1 piece
●Composite
Lightweight

Question 3

Taper of blade

Answer 3

Designed by engineers to enhance:
- propeller efficiency
- force distribution
- shock wave formation
- etc

Question 4

Blade twist

Answer 4

Compensates for the fact that the outward part of the blade travels a greater distance through the air than the hub of the blade does.

Question 5

Propellor efficiency

Answer 5

•Slip
•Geometric Pitch-Effective Pitch
•Geometric Pitch
•Screw in wood
•How far the prop should move in one revolution

•Effective Pitch
•Non solid medium
•How far the prop actually moves in one revolution

Question 6

Types of pitch props

Answer 6

Fixed pitch, different pitches are available
●climb prop
●cruise prop
●Anywhere in between

Adjustable - crew changes on the ground

Controllable - change in the air

Question 7

Fixed vs constant speed

Answer 7

Fixed
●AOA changes with airspeed

Constant Speed
●AOA remains the same at all airspeeds

Question 8

Prop governor

Answer 8

•Governor is hooked to the accessory drive assembly to “monitor” rpm of engine
•Flyweights - spin due to linkage through gears to the camshaft
•Speeder spring - sets fly weights to position representing rpm desired
•prop control - sets speeder spring - therefore determines rpm
•pilot valve - allows oil either to go in or out of the hub depending on flyweights position

Question 9

Aerodynamic factors

Answer 9

Centrifugal Force - tries to pull blade out of hub.
Thrust Bending Force - bends tips forward
Torque Bending Force - bend prop. opposite the direction of rotation
Aerodynamic Twisting Moment - tries to twist blade to higher angle.(feathered)
Centrifugal Twisting Moment - tries to twist blade to lower angle

Question 10

Prop blade terms

Answer 10

Blade Path - always opposite relative wind
Relative wind - changes due to Forward Velocity and Rotation Velocity
Blade Angle - angle between the chord line of the blade and the plane of rotation.
Angle of Attack - difference between chord line and relative wind.

Question 11

How angle of attack changes

Answer 11

Forward Velocity - increase in speed means decrease in angle of attack
Rotational velocity - increase in rotational velocity (increase in rpm) - increase angle of attack
Blade Angle - increase in blade angle increase angle of attack.