FAA Aviation Mechanic Powerplant (AMP)PropellersEasy
A mechanic is explaining propeller theory to a student. The student asks how 'effective pitch' differs from 'geometric pitch.' Which statement correctly describes effective pitch?
- AThe distance from the blade tip to the center of the hub measured along the blade
- BThe actual distance the propeller advances through the air in one revolution, accounting for slip
- CThe angle between the chord line of the blade and the plane of rotation
- DThe theoretical distance a propeller would advance in one revolution if there were no slippage in the air
Show answer & explanationAnswer & explanation
Correct answer: B. The actual distance the propeller advances through the air in one revolution, accounting for slip
Effective pitch is the actual forward distance the aircraft travels per propeller revolution, which is always less than geometric pitch because air is not a solid medium and some slippage occurs.
Why the other options are wrong
- A. This describes blade length/radius, not pitch.
- C. This describes blade angle, a different concept.
- D. This describes geometric pitch, not effective pitch.
Effective Pitch
The actual distance a propeller advances through the air in one revolution, which is less than geometric pitch due to slippage.
- Always less than geometric pitch
- Difference between the two is called 'slip'
- Affected by blade angle, RPM, and forward airspeed
Memory trick: Geometric is the goal, Effective is what's real