Analysis of Adhesive Disbond Occurrences in Rotor Blades of Mi-2 Helicopters

Polish Air Force Institute of Technology (AFIT) is responsible for delivery service life extension program for the main rotor blades of multiple helicopters in the Polish Air Force (such as Mi-2, Mi-8/17, Mi-14, Mi-24). Due to the operational profile, certain number of blades got decommissioned when the calendar service life is reached, while the accumulated flight hour count is still below the hourly service limit. This is why a dedicated research program, as well as inquiry into the usage and technical condition of the blades is necessary. To maintain such a program, regular inspections of the blade structure are required.

In the paper, the Mi-2 (hoplite) service life extension program findings are presented. The Mi-2 rotor blade service life extension program has been implemented in three phases, and life extension of 42 months was achieved. The program is based on detailed non-destructive tests. Inspection procedures include verification of the spar structure (corrosion, cracks) as well as the verification of adhesive bonded joins between various elements of the blade (skin and spar, skin and core, etc.). The inspection is performed with the use of automated NDE systems with C-Scan data presentation possibility. Because adhesive disbonds are the main reason for component rejection and decommissioning, they are the main focus of the paper. A study of more than hundred non-destructive inspections is included in the paper. The inspection methodology is presented, as well as the statistics and distribution of the blade failure modes. The adhesive disbonds are also characterized. The study aims to determine the factors that drive the disbond process, and environmental factors are taken into account.