Failure analysis of the engine cylinder of a training aircraft

Two-blade aircraft propellers, designed to be powered by a small engine, were improved with engines used in three-blade aircraft propellers. As a consequence, the new engines revealed pressure losses, crack formation, and recurrent fracture, approximately after every 600 h of flight. This paper analyzed one of the failed engines; the engine has six cylinders manufactured in aluminum alloy. Optical microscopy and scanning electron microscopy were used for microchemical and microstructural analyses. Cracks were identified by using liquid penetrant between two cooling fins in the exhaust port and around the exhaust port, at the exhaust valve seats. Shrinkage micropores were found in the aluminum alloy forming cracks in the exhaust port.