Propeller Vibration After a Blade Repair

The vibration is strongest at 2,200 rpm and varies with power but never disappears, which rules out a simple resonance that would appear only in a narrow band. Candidate sources:

1. Propeller imbalance or track error after refit - the highest-probability cause. The propeller was removed and refitted, the spinner was changed, and no track or balance check was done afterwards. A spinner that is not seated or is mismatched to the hub can create imbalance on its own. A blade angle or track difference between blades produces a once-per-revolution vibration that is felt strongly through the airframe and changes with rpm.
2. Blade repair geometry - if the repaired blade's mass or contour changed, the original balance is invalid even though it was balanced before removal. A repair that altered the blade tip or leading edge is a plausible source.
3. Engine-related vibration - a rough-running engine, failed mount, or exhaust issue. Less likely here because the vibration appeared after propeller work and varies with power in a way consistent with propeller loading, but it must be excluded.
4. Hub or mounting hardware - incorrect torque, missing shims, or a damaged hub flange from the strike.

The history strongly favours a propeller balance or track problem, but the engine and mounts must be checked because a power-related vibration can mimic a propeller fault.

Decision: not until basic on-site checks are done. A vibration of unknown origin on a propeller that has just been repaired after a strike is not something to fly with. However, if the on-site checks show only a track or spinner seating problem that can be corrected, a cautious ferry to a base with balancing equipment may be acceptable.

On-site checks:

• Inspect the spinner for correct seating, missing screws, and evidence of rubbing.
• Check blade track with a simple track gauge or a fixed reference; a difference of more than a few millimetres between blades is significant.
• Check blade angle at a fixed station on both blades to confirm they match.
• Inspect hub bolts and mounting flange for correct torque and for damage from the strike.
• Check engine mounts and exhaust for security, and do a mag check and ground run to exclude engine roughness.
• Confirm the propeller logbook records the repair and refit correctly.

Ferry criteria:

• If a spinner seating or track fault is found and corrected, and a ground run shows the vibration is gone or clearly reduced, a ferry flight at reduced power to a base with balancing equipment is reasonable, with the maintenance organisation's agreement.
• If the vibration persists or track cannot be corrected, the aircraft stays until balancing equipment or a replacement propeller is brought in. Flying an unbalanced propeller after a strike risks hub and crankshaft loads.

Balance is a property of the assembled rotating system: hub, blades, spinner, and attachment hardware. Removing the propeller, repairing a blade, and fitting a different spinner changes the mass distribution, so a balance certificate from before removal does not apply to the new assembly. Even if every part were identical, refitting changes the angular position of components relative to the hub, and the balance correction depends on that position. This is why track and balance are normally rechecked after any propeller removal or blade repair.

The engineer's assumption that the earlier balance carried over is the root of the problem, and it is a common one.

Records to update:

• The propeller logbook: blade repair details, refit date, and the fact that track and balance were not performed at refit.
• The engine/airframe log: the vibration report, the on-site checks, and the outcome.
• The maintenance release: any ferry approval and its conditions.
• A note for the base to perform dynamic balance and record the result.

Accurate records matter here because if the vibration later causes damage, the history shows what was and was not done, and it prevents the same assumption being repeated.