Engine Torquemeter Systems: Phase-Shift Torque Measurement Principles

022-01-07Pablo Asensio Martínez2026-03-271 min

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.
Written and reviewed by

Pablo Asensio · 2026-03-27

Aeronautical engineer. Passed the thirteen EASA ATPL(A) theoretical knowledge exams studying from these very notes. Writes and reviews each topic against the Part-FCL Learning Objectives.

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