# Engine Torquemeter Systems: Phase-Shift Torque Measurement Principles

> Study torquemeter operation in propeller and turboprop aircraft, including torque units, power relationships, and phase-shift electronic sensing architecture.

- **Subject:** 022 — Instrumentation
- **Section:** 022-01 — Sensors and Instruments
- **Topic code:** 022-01-07
- **Last reviewed:** 2026-03-27
- **Author:** Pablo Asensio Martínez
- **HTML version:** https://pilotsyllabus.com/en/instrumentation/sensors-and-instruments/engine-torquemeter/

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Torquemeters are used primarily on propeller-driven and turboprop aircraft to measure the turning force applied to the propeller shaft.

## Definitions and Units
*   **Torque (Moment):** A force that causes rotation about an axis.
*   **Unit:** The **Newton-meter (Nm)**. 1 Nm represents a force of 1 Newton applied to a lever arm of 1 meter. ($T = F \times d$)
*   **Power:** Work done per unit of time.
    *   Formula: $P = Torque (T) \times RPM (n)$
    *   *(Requires unit conversion, e.g., RPM to rad/s).*

## Operating Principle (Electronic)
First-generation electronic torquemeters use a **phase-shift** method.
*   **Construction:** Two concentric shafts connect the engine to the gearbox: a **Torque Shaft** (load-bearing) and a Reference Shaft (no load).
*   **Measurement:** Each shaft has a serrated ring and a magnetic pickup. With no load, signals are in phase. Under power, the torque shaft **twists** very slightly, creating a phase difference between the signals.
*   **Display:** The system converts this phase shift into a torque indication (Nm, ft-lb, or % Torque). Modern systems may use strain gauges.

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