Visual rotor blade inspection: methodology and defect classification

What is inspected?

The visual rotor blade inspection covers all three rotor blades of a turbine. Per blade, four surfaces are captured: leading edge, trailing edge, suction side and pressure side. With three blades per turbine that gives 12 blade surfaces per inspection. All images overlap at the edges so no area remains unrecorded.

Image resolution and camera setup

For visual inspection DDI uses a high-resolution DJI camera drone, a camera system designed for detail imagery in industrial inspection. It makes it possible to document even small defects reliably. Details on the hardware can be found under /en/technik/hardware.

Automated flight paths per turbine type

DDI carries out a survey flight per turbine, during which the turbine is measured live. From this an automated inspection flight path is generated, ensuring constant distance, optimal image quality and reproducible results. This creates comparable benchmark results within a wind farm and across multiple inspection cycles.

Defect classification by standardised scale

Images are evaluated by independent experts who assign each finding a defect class according to the standardised defect classification:

• Class 1: Cosmetic, no action required
• Class 2: Monitor at next inspection
• Class 3: Repair at next opportunity
• Class 4: Repair promptly required
• Class 5: Immediate action / shutdown

Every classification includes position on the blade (blade surface, radius, distance from root), size of the finding and a concrete recommended action.

Evaluation by independent experts

The visual inspection reports are produced by independent experts, not by drone pilots. The pilots provide the high-resolution imagery and flight documentation; evaluation and defect classification is carried out by qualified professionals with experience in rotor blade assessment. Professional responsibility lies with the independent expert. The result is suitable for expert reports and insurance purposes.

Drone vs. rope access for visual inspection

Rope access can capture damage visually but cannot precisely locate it. The RTK positioning of the drone provides centimetre- accurate geolocation of every finding, as the basis for precise maintenance workflows and directly comparable follow-up findings.