Propeller Effects And Designs

Question 1

What do we assume about propellers movement

Answer 1

Moves clockwise direction

Question 2

Methods to increase power absorption of propeller

Answer 2

Increase propeller diameter
Increase propeller solidity (surface area)
Increase blade chord
Increase number of blades
Use contra rotating propellers

Question 3

What is propeller solidity

Answer 3

Propeller blade frontal area
—————————————
Propeller disk area

The ratio of propeller blade frontal area to propeller disc area. Greater the solidity the greater potential for power absorption.

Question 4

Torque Reaction what is it

Answer 4

Propeller rotates clockwise of a small mass but large angular velocity

Aircraft rotate anti clockwise opposing the clockwise momentum

Rolling tendency to the left or left yaw on ground

Question 5

What increases torque reaction/How can it be reduced

Answer 5

Greater power setting/faster RPM more roll left

Contra rotating propellers reduce the effect

Question 6

Slipstream Effect What is it

Answer 6

Propeller creates slipstream under fueselage hit tail from left to create AOA and creates sideway force around CG

Moves tail right creating a left yaw

Question 7

What factors increase slipstream effect

Answer 7

Slow airspeed and high power setting

Question 8

Asymmetric Blade Effect What Is it

Answer 8

At high AOA the right hand propeller produces more than left half resulting in thrust line being offset to the right.

Causes ac to yaw left

Known as P factor

Question 9

Why does asymmetric blade effect occur

Answer 9

Down going blade travel a further distance in one rotation therefore faster RAF and more lift

Question 10

Gyroscopic Effect - pitch up/down what happens

Answer 10

Force acts 90 degrees to force applied
Occurs in pitch or yaw

Pitch Up = Yaw to the right
Pitch Down = Yaw to the left

Yaw to the right = Pitch down
Yaw to the left = Pitch Up

Question 11

Why does the gyroscopic effect happen

Answer 11

Mass has rigidity and therefore will process and move as though force displace by 90 degrees

Question 12

What are the limits to propeller tip speeds

Answer 12

Above Mach 0.85 drag increases rapidly as shockwaves begin

Question 13

Propeller effect T/O

Answer 13

Torque effect - yaw left
Slipstream effect - Yaw left
Gyro - yaw left

Question 14

Propeller effect - Rotation

Answer 14

Gyro effect - Yaw right
Torque reaction - roll left

Question 15

Propeller effect - Initial Climb

Answer 15

Asymmetric Blade Effect (slow/high AOA) - Yaw left

Question 16

Propeller effect - Go Around

Answer 16

Flaps reduce alphas - reduction in p factor (less left yaw)
Gyroscopic yaw to right (pitch up)
Slipstream - yaw to left at high power setting
Torque reaction from applied thrust (left yaw)

All propeller effects can be expected during go around!

Question 17

What is the negative effect of increasing blade chord

Answer 17

Reduce in aspect ratio of blade more wing tip vortices less efficient

Question 18

Variable pitch propeller during takeoff (blade angle)

Answer 18

Increases as forward velocity increases

RPM up - AOA up
Velocity up - AOA Down - therefore governor will coarsen the pitch to maintain optimum AOA

Question 19

Most favourable situation in failure of a twin engine aeroplane

Answer 19

Failure of the right engine if both engines are counter rotating inwards

Inwards = both arms closer to CG