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Modal Parameter Extraction via Propeller-Driven Vibration Testing

Gabriele Dessena, Alessandro Pontillo

Abstract

Ground Vibration Testing (GVT) supports aircraft certification but often requires lengthy and costly campaigns. Propeller-driven Vibration Testing (PVT) is assessed here as an output-only alternative, in line with Operational Modal Analysis approaches such as Taxi Vibration Testing and Flight Vibration Testing. A cantilever Aluminium 7075-T6 wing spar is instrumented with seven accelerometers and excited by an outboard electric motor and propeller. Seven runs are carried out: a motor-off baseline, five constant-throttle cases, and a manual up-down throttle sweep. The acquired spectra indicate that the dominant resonances remain observable under propeller excitation, while low-throttle conditions introduce narrowband harmonics that may mask structural peaks; the sweep reduces persistent overlap. Modal parameters are identified for the baseline and sweep cases using the Natural Excitation Technique with the Loewner Framework (NExT-LF). The first two modes remain closely matched (Modal Assurance Criterion (MAC) > 0.99), whereas the third mode shows reduced repeatability (MAC = 0.827) and a larger frequency shift, consistent with propeller-induced bending--torsion coupling and non-ideal sweep control. Overall, PVT provides a viable complement to GVT for extracting low-frequency modal information and motivates pursuing future work on automated throttle scheduling and coupling-aware test planning.

Modal Parameter Extraction via Propeller-Driven Vibration Testing

Abstract

Ground Vibration Testing (GVT) supports aircraft certification but often requires lengthy and costly campaigns. Propeller-driven Vibration Testing (PVT) is assessed here as an output-only alternative, in line with Operational Modal Analysis approaches such as Taxi Vibration Testing and Flight Vibration Testing. A cantilever Aluminium 7075-T6 wing spar is instrumented with seven accelerometers and excited by an outboard electric motor and propeller. Seven runs are carried out: a motor-off baseline, five constant-throttle cases, and a manual up-down throttle sweep. The acquired spectra indicate that the dominant resonances remain observable under propeller excitation, while low-throttle conditions introduce narrowband harmonics that may mask structural peaks; the sweep reduces persistent overlap. Modal parameters are identified for the baseline and sweep cases using the Natural Excitation Technique with the Loewner Framework (NExT-LF). The first two modes remain closely matched (Modal Assurance Criterion (MAC) > 0.99), whereas the third mode shows reduced repeatability (MAC = 0.827) and a larger frequency shift, consistent with propeller-induced bending--torsion coupling and non-ideal sweep control. Overall, PVT provides a viable complement to GVT for extracting low-frequency modal information and motivates pursuing future work on automated throttle scheduling and coupling-aware test planning.
Paper Structure (8 sections, 5 figures, 3 tables)

This paper contains 8 sections, 5 figures, 3 tables.

Table of Contents

  1. INTRODUCTION
  2. MATERIALS AND METHODS
  3. RESULTS
  4. CONCLUSIONS AND FUTURE WORK

Figures (5)

  • Figure 1: PLANFORM GEOMETRY OF THE FLEXIBLE WING SPAR (RETRIEVED FROM BannehekaNavaratna2022).
  • Figure 2: EXPERIMENTAL SETUP. APPARENT GEOMETRIC DISTORTIONS IN THE IMAGE ARE ATTRIBUTABLE SOLELY TO CAMERA LENS EFFECTS. (RETRIEVED FROM Dessena2025b).
  • Figure 3: ANPSD COMPARISON ACROSS ALL TEST CASES (IMPULSE BASELINE AND PVT). ADAPTED FROM Dessena2025b.
  • Figure 4: STABILISATION DIAGRAMS OBTAINED VIA NEXT-LF FOR CASES (I) AND (VII).
  • Figure 5: MODE SHAPES $\boldsymbol{\phi}_{1-3}$ IDENTIFIED VIA NEXT-LF FOR CASE (VII).