Chapter 4 - Aircraft Stability and Performance

Question 1

What are the three broad classifications of propeller?

Answer 1

Fixed pitch

Variable pitch - driven by a piston engine

Variable pitch - driven by a gas turbine engine

Question 2

Why is the angle of a prop blade reduced towards the tip?

Answer 2

Because the rotational velocity increases as radius increases. Therefore, the twist is required to maintain an efficient AoA across the length of the propeller.

Question 3

What should you do with a windmilling prop in the event of an engine failure?

Answer 3

Feather it (min drag)

Question 4

What affect do compressibility affects have on a prop?

Answer 4

Decrease thrust + increase the rotational drag

Reduces the efficiency of the propeller blade

Question 5

What is the ‘solidity’ of a propeller?

Answer 5

The ratio between that part of the propeller disc which is solid and the circumference.

Question 6

How can we design a propeller to absorb a more powerful engine?

Answer 6

Increase its solidity

Question 7

How can solidity be increased?

Answer 7

Increasing the number of blades (or contra-rotating propellers)

Increasing the chord of each blade (e.g. using paddle blades) - disadv. is that the lower AR of the blades will then cause them to be less efficient.

Question 8

What way does a normal prop rotate?

Answer 8

Clockwise

Torque + slipstream affect will cause the nose to yaw left on takeoff.