Flight-Validated Digital Filtering for Vibration Mitigation on a 250 kg eVTOL: An FFT-Guided Design Approach

Rotor-induced vibrations corrupt Inertial Measurement Unit (IMU) readings and can destabilize multirotor flight, a risk that grows with vehicle mass. This paper presents a flight-validated, software-only vibration-mitigation strategy for a ~250 kg coaxial quadcopter electric vertical take-off and landing (eVTOL) aircraft. An FFT-guided workflow is used to identify the dominant blade-passage frequency and harmonics, then tune a second-order 30 Hz Butterworth low-pass filter cascaded with two narrow IIR notch filters at 46 Hz and 92 Hz in the gyro feedback path. Indoor hover tests compared mechanically damped, unfiltered, and digitally filtered IMU configurations. The final filter set reduces angular-rate harmonic power by 33.6 +/- 0.97 dB (99.96%), decreases total harmonic RMS angular-rate by 98%, and lowers throttle standard deviation by 60 +/- 10%, enabling repeatable 11-minute stable hovers that were not achievable with unfiltered or mechanically isolated configurations. Stability-margin and latency analysis of an approximate roll-rate loop show that the filter chain preserves gain (16.2 dB ) and phase (93.9 degree) margins within standard rotorcraft criteria, introducing only 16 ms of additional delay, which is less than one quarter of the available time-delay margin. These results highlight the practical impact of digital filtering as a weight-neutral, retrofit-friendly approach that can significantly improve large eVTOL stability and performance.