phase angle

Definition

In an alternating current (AC) circuit, the angular difference, measured in degrees of a single cycle (0° to 360°), between two related sine waves — typically between voltage and current, or between two voltages or two currents. When voltage and current peak at the same instant, the phase angle is 0° and they are 'in phase.' When one leads or lags the other, the phase angle expresses how far apart in the cycle their peaks occur.

Plain English

How far out of step two AC waves are with each other, measured as part of a full cycle. Zero degrees means they rise and fall together; ninety degrees means one is a quarter-cycle ahead of or behind the other.

Context Anchor

Seen in aircraft electrical-system theory, alternator discussions, and troubleshooting involving alternating-current, or AC, power.

Derivation

From Greek 'phasis' meaning 'appearance' or 'stage,' used in physics to describe a particular point in a repeating cycle. 'Angle' is used because one full cycle of an AC waveform is treated like one full rotation — 360°. So 'phase angle' is literally 'where in the cycle' one wave sits compared to another.

Why Pilots Care

In aircraft AC systems, phase angle affects how voltage and current combine to produce real, usable power. A large phase angle between voltage and current means the system is moving energy back and forth without doing useful work, which reduces efficiency and can stress generators and components.

Analogy

Think of two runners on a circular track. If they run side by side, their phase angle is 0°. If one is a quarter-lap ahead, they are 90° apart — same speed, same track, just offset in the cycle.

Intuition Check

Phase angle is not an angle you see on the airplane structure. It is a way to describe timing difference in a repeating electrical cycle.

Example Sentence 1

In a purely resistive circuit, the phase angle between voltage and current is zero, so the two waveforms peak at the same moment.

Example Sentence 2

A shift in phase angle showed the circuit had developed an unexpected reactive load.

Definition

In propeller synchronization, the angular difference between the rotational position of one propeller's blades and the corresponding blades of another propeller on a multi-engine airplane, measured at the same instant. A synchrophasing system holds this angle at a preset value to minimize cabin noise and vibration caused by the two propellers' pressure pulses combining at the fuselage.

Plain English

It's the difference in where one propeller's blades are pointing compared to the other propeller's blades at the same moment. By keeping that difference at a set value, the cabin gets quieter and smoother because the two propellers' sound pulses don't reinforce each other.

Context Anchor

Seen in multiengine airplane discussions of propeller synchronization and propeller noise reduction.

Derivation