The difference between the propeller's geometric pitch and its effective pitch is called

The difference between the propeller's geometric pitch and its effective pitch is called

• A. Pitch error
• B. Propeller slip
• C. Blade twist
• D. Gear ratio

Answer: (B)

The main idea is the difference between what the propeller would theoretically advance in one rev if the air didn’t swirl, and what it actually advances in flight. Geometric pitch is that nominal distance—the pitch written on the blade—assuming the air is pushed straight back with no swirl. In real operation, the blades impart energy to the air and create swirl, so the air exits with a tangential component and the craft moves forward by less than the geometric pitch. The actual forward distance per revolution is called the effective pitch, and the shortfall between geometric and effective pitch is the propeller slip. This slip can be expressed as a percentage of the geometric pitch: slip = (geometric pitch − effective pitch) / geometric pitch × 100. The other terms don’t describe this difference: pitch error isn’t the standard term for this, blade twist is about how blade angle changes along the span, and gear ratio relates to engine-to-prop rpm, not the forward advance per revolution.

The main idea is the difference between what the propeller would theoretically advance in one rev if the air didn’t swirl, and what it actually advances in flight. Geometric pitch is that nominal distance—the pitch written on the blade—assuming the air is pushed straight back with no swirl. In real operation, the blades impart energy to the air and create swirl, so the air exits with a tangential component and the craft moves forward by less than the geometric pitch. The actual forward distance per revolution is called the effective pitch, and the shortfall between geometric and effective pitch is the propeller slip. This slip can be expressed as a percentage of the geometric pitch: slip = (geometric pitch − effective pitch) / geometric pitch × 100. The other terms don’t describe this difference: pitch error isn’t the standard term for this, blade twist is about how blade angle changes along the span, and gear ratio relates to engine-to-prop rpm, not the forward advance per revolution.