What causes P-factor in a multi-engine aircraft?

P-factor, or asymmetrical thrust, occurs when a propeller generates different amounts of thrust based on its angle of attack, especially during climbs or when the aircraft is in a bank. In multi-engine aircraft, when the aircraft is operating with one engine at a higher power setting than the other, the propeller on the more powerful engine will produce more thrust. This differential thrust leads to a yawing moment towards the less powerful engine.

The difference in angle of attack of the individual propeller blades is significant because, as the propeller rotates, the blades moving into the relative wind (on the ascending blade side) experience a greater angle of attack compared to those moving away (on the descending blade side). This results in unequal lift generated by the blades, leading to the P-factor.

The other options do not accurately describe the cause of P-factor. For instance, differences in fuel flow between engines affect performance but do not specifically account for the yawing moment associated with P-factor. Similarly, propeller diameter and altitude are not primary factors in generating the asymmetrical thrust observed in P-factor behavior. Understanding P-factor is crucial for multi-engine pilots, particularly for maintaining control during critical phases like takeoff and climb, especially with asymmetric thrust conditions.