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Vibration Analysis in Flight Testing: The Practical Guide

Mar 20, 2026·Written by Nimrod

Why Vibrations Destroy Flights (and Sometimes Vehicles)

Vibration is a silent enemy in every UAV platform. At low levels, it simply blurs camera footage. At moderate levels, it causes the EKF (Extended Kalman Filter) to lose confidence in accelerometer data, producing Lane Switching or even EKF Failsafe—which can lead to complete loss of control.

At high levels, vibration causes structural failure: bolts loosening, solder joints cracking, and carbon fiber mounts fracturing.

Vibration Sources and How to Identify Each

The four primary sources:

  1. Propeller imbalance: Appears in logs as VIBE with frequency matching motor RPM. Example: propeller at 6000 RPM = 100Hz. If VIBE.VibeX shows a peak at 100Hz—it's almost certainly imbalance.
  2. Loose motor mount: Appears as a sub-harmonic—half the propeller frequency. A mount dancing at 50Hz while the prop runs at 100Hz. Harder to identify without experience.
  3. Control surface flutter: Appears at high frequencies (>150Hz) and usually only at high airspeeds. Particularly dangerous because once flutter starts, it's self-reinforcing and can break a control surface.
  4. Structural resonance: The airframe's natural frequency matching a specific RPM band. Solution = change RPM or stiffen the structure.

How to Read VIBE Logs Practically

In ArduPilot, the VIBE message includes three values: VibeX, VibeY, VibeZ. The accepted benchmarks:

  • Below 15 m/s²: Excellent. The vehicle is 'quiet.'
  • 15-30 m/s²: Functional, but monitor closely. Check for Clipping.
  • 30-60 m/s²: Problematic. EKF starts getting uncertain. High probability of altitude estimation errors.
  • Above 60 m/s²: Dangerous. GPS/Baro blending will fail, EKF Failsafe likely.

Beyond the values, check the Clip0/Clip1/Clip2 fields—which show how many times the accelerometer reached saturation. Any Clipping > 0 is a red flag requiring immediate attention.

The Test Pilot Connection: What VIBE Values Don't Tell You

A VIBE value is a time-window average. It doesn't capture transients—vibration that appears only at a specific moment (e.g., one second after a flight mode change, or during strong crosswind). A test pilot feels these transients through the stick and microphone. They can report 'the vehicle vibrated briefly when I entered Loiter'—pointing engineers to the exact timestamp in the log that needs examination.

The combination of quantitative log analysis with subjective observations from an experienced pilot is the only way to build a complete picture of airframe and system health.

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Suspect a vibration problem?

Let's analyze the VIBE logs together, identify the source, and fix it before it gets expensive.

Send logs to Nimrod