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The piston engine of the training aircraft Utva-75 malfunctioned during the flight mission due to the cracking of its cylinder head. After successful forced landing, the damaged cylinder assembly was removed from the engine and sent to the lab for forensic expertise. Fractographic examination of the mating fracture surfaces revealed that the fatigue was the main cause of the cylinder head failure. The metallography examination has shown that the fatigue was promoted from pre-existing material defect due to an elevated presence of porosity forms at the crack initiation zone. The finite element method, utilized to determine the stress state of the cylinder assembly, confirmed that the crack origin was located at the most stress area.

The impact of geometric parameters of teeth and lubricating oils to the efficiency of involute internal spur gears, when the transverse contact ratio is 2 < εα ≤ 3, has been analyzed in this paper. The mathematical model and computer program for determining the current and the effective value of the efficiency have been developed. The influence of the character of load distribution and energy losses due to heating effects during the meshing period is included in the factor of load distribution. The results of computer simulation are given in the form of a diagram of the current values of the efficiency during the meshing period. Also, the values of effective efficiency for the considered cylindrical gear pairs have been calculated. [ABSTRACT FROM AUTHOR]