Cooling Performance of Reciprocating Aircraft Engines: A Quantitative Analysis of 14 CFR Part 23 Certification Requirements
An analysis of the Federal Aviation Administration (FAA) aircraft certification requirements has revealed a potential error in the temperature correction formula the FAA requires aircraft manufacturers to use to process engine cooling performance data for compliance with Part 23 of Title 14 of the Code of Federal Regulations (14 CFR Part 23). The FAA engine cooling performance temperature correction formula, which predicts the critical temperature of engine components, was quantitatively evaluated using data acquired with a single-engine aircraft powered by a normally-aspirated, air-cooled, reciprocating engine. Previous research has failed to analyze the effect ambient air temperature has on oil temperature and has failed to propose a more accurate model for predicting critical cylinder head and oil temperature. Engine cylinder head and oil temperature data were acquired during FAA-defined cooling performance climbs performed in varying ambient air temperatures. The acquired data revealed the FAA engine cooling performance temperature correction formula, when applied to cylinder head temperature, did not correct data to the most critical test condition, potentially leaving certified aircraft vulnerable to overheating. The acquired data also showed the FAA engine cooling performance temperature correction formula, when applied to oil temperature, underestimated critical oil temperature, again leaving certified aircraft vulnerable to overheating in specific mission profiles. New temperature correction formulas were developed to predict critical engine cylinder head and oil temperature for compliance with 14 CFR Part 23 engine cooling requirements. After further verification, it is hoped the FAA will adopt the proposed temperature correction formulas into 14 CFR Part 23 to ensure engine cooling performance is properly tested and to ensure the safety of general aviation aircraft within the United States.