Modal Parameter Extraction via Propeller-Driven Vibration Testing

TL;DR

This paper evaluates Propeller-driven Vibration Testing (PVT) as a cost-effective, output-only alternative to Ground Vibration Testing for aircraft, demonstrating its ability to reliably extract low-frequency modal parameters under various excitation conditions.

Contribution

It introduces PVT as a novel, practical approach for modal analysis in aircraft structures, utilizing the Natural Excitation Technique with the Loewner Framework for data interpretation.

Findings

Propeller excitation maintains dominant resonances in spectra.

Low-throttle conditions introduce masking harmonics.

PVT reliably identifies modal parameters with high repeatability.

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.