Propellers

Question 1

ATM and CTM

Answer 1

ATM - Increasing the blade angle

CTM - fining force - try to align the mass of the blade around the pitch point - uses centrifugal force

Question 2

Blade angle definition

Answer 2

Angle between the plane of rotation and the chord line

Question 3

Why is the spinner orientated slightly right on a right hand tractor

Answer 3

To control asymmetric, p factor and torque factor

Question 4

Washout/ aerodynamic washout

Answer 4

Reducing the AoA and the thickness to reduce the amount of vortices at the tip

Question 5

Where is most of the thrust produced on a prop

Answer 5

70% of the blade

Question 6

Efficiency in the cruise - prop

Answer 6

85%

Question 7

Sole purpose of a spinner

Answer 7

Reduce drag

Question 8

The hub is connected to

Answer 8

The drive shaft or crankshaft of the engine either directly or through a series of gears

Question 9

Reduction gear box purpose

Answer 9

Reduces the prop RPM to maintain the optimum engine RPM - while trying to maintain optimum prop RPM

On a fixed pitch prop - neither the prop or the engine are operating at optimum rpm

Question 10

Common prop construction

Answer 10

Simplest are made from wood

Most are made from metal alloys

Some are made from steel composite

Question 11

Torque drag

Answer 11

Aerodynamic force acting against rotation motion

Question 12

2 types of pitch control units

Answer 12

Single acting

Double acting

Question 13

Single acting PCU - SEP

Answer 13

Uses BFO - big spring and oil pressure moves a piston which then moves the prop

Safest place to fail is in the fine posn - so oil is fed to the piston for coarsening - if it is lost or fails - CTM will cause it to fine - assisted by a spring for low RPMs

Question 14

Single acting PCU - light twin

Answer 14

Opposite to the SEP - want the prop to go to coarse when the engine fails - spring makes it coarse and oil makes it goes fine

Question 15

Double acting PCU

Answer 15

Oil in both sides of the piston - hydraulic lock is formed

Directly related to rpm - prop going too slow - bob weight will relax inwards - push the landed valve downwards - oil pressure is sent to fining the blade - when rpm stabilises - landed valve shuts - hydraulic lock forms on the pistons to keep them in place

Overspeed - opposite - bob-weights flyout

Question 16

Prop lever

Answer 16

Sets the base for which the rpm stabilises - varies the speeder ring - dictates engine rpm

Fully fwd = fully fine

Question 17

In order to increase power (rev up)

Answer 17

RPM goes up first then throttle - MAP also goes up

Question 18

In order to decrease power (throttle back)

Answer 18

Throttle goes down first then RPM

Prevents “over gearing”

Question 19

CSU checks

Answer 19

After engine start - operate the rpm lever to exercise the CSU and encourage oil to flow - check RPM rise and fall

Question 20

Alpha range - prop

Answer 20

The flight range

Question 21

Beta range

Answer 21

Range of pitch angles below flight idle

Controlled by weight on wheels

Torque drag increases rapidly the further the blade moves into the beta range - req more reverse thrust req more engine power - only turboprops have the engine power to do true beta ranges

Question 22

Underspeed governor

Answer 22

In the beta range - power lever directly controls blade pitch angle - prop rpm is maintained at safe levels by an underspeed governor

Question 23

Synchrophasing unit

Answer 23

Adjusts the prop blade phase - allows for a more constant/calmer noise through the fuselage

Props can also be synchronised at the same rpm

Question 24

Methods of indicating power - fixed pitch

Answer 24

Amount of thrust is proportional to engine rpm - req power is set as an rpm

Set by a function of mass flow through the engine - MAP

Question 25

Methods of indicating power - turboprops

Answer 25

Measure of power = torque

Measures the twisting of the shaft - how much mechanical work the engine is doing - can be done electronically or by measuring oil pressure