26 Propeller Design And Effects

Question 1

How can the amount of power a propeller can absorb be increased?

Answer 1

• Increase the number of blades
• Increase the length of blades
• Increase the chord length of each blade

Question 2

What is the equation for the solidarity of a Propeller?

Answer 2

Solidarity = Propeller blade frontal area / Propeller Disk area

Question 3

Describe the Torque Reaction effect (Right hand prop) and its effect on Take-off compared to inflight

Answer 3

• Due to Newtons 3rd law, a right handed prop will want to make the AC roll to the left. The angular momentum given to the air by the prop reinforces this.
• In the air the AC wants to roll left
• On take-off the increased force on the left wheel generates more drag so the AC yaws to the left
• Most noticeable on powerful single engine AC during T/o roll
• Effect is greater at higher RPM

Question 4

Describe the Slipstream effect (Right hand prop)

Answer 4

• The prop causes the slipstream behind it to rotate in the same direction as the prop is spinning
• This causes the air to hit the fin at an angle (from the left)
• This negative AOA causes the AC to yaw to the left
• The slipstream effect is greatest at low TAS and high RPM

Question 5

Describe the Asymmetric Blade effect / P-Factor (Right handed prop)

Answer 5

• Whilst an AC is climbing or descending, the down going blade is traveling faster than the up going blade
• This increases the amount of thrust being generated on the right hand side of the prop
• This moves the overall thrust line to the right side of the prop
• Causing the AC to yaw to the left
• P-Factor is at it’s greatest at high RPM, high AC AOA and low TAS

Question 6

Describe the Gyroscopic effect (Right hand prop)

Answer 6

• A spinning prop has the same properties as a gyroscope
• When the AC pitches down, this is the same as applying a force to the top of the prop
• Due to procession this force will cause the AC to yaw to the left