A Cessna 172 Retrofitted with a Rotax 916iS for Training Operations: A Conceptual Study

Flight training in Canada accounts for approximately 30,000 tons of annual CO2 emissions, largely due to the use of legacy aircraft with engine designs from the 1950s. Those engines are often operated with an unoptimal fuel to air ratio that leads to the emission of unburned hydrocarbons. Technologies already adopted and commonly used in the automotive industry would allow non-negligible gains in terms of fuel consumption reduction and environmental impact. The Rotax 912iS/915iS/916iS engine family, able to run on unleaded fuel and ethanol, has introduced new technologies rarely used in the other aircraft engines, such as the FADEC, which reduce the pilot workload and ensure an optimal operation of the engine. This study evaluates the feasibility of retrofitting a Cessna 172, commonly used for training operations, with a Rotax 916iS with both fixed-pitch and constant-speed propellers. First, this article evaluates the impact on the center-of-gravity of replacing the original Lycoming IO-360 with the Rotax 916iS, which is 122 lb lighter. Then the overall performance of the two retofits configurations are presented followed by a mission-level comparison. The results show limited effect on the center of gravity envelope although the engine is 122 lbs lighter. An increase in payload capacity of 13% (120 lb) is also observed due to the reduction of the empty weight. A reduction in terms of fuel consumption between 20% and 30% depending on the propeller configuration for training missions below 3,000 ft is also observed making this aircraft a viable alternative to all-electric aircraft in the short term.