The aim of this paper is to show that the gains, technical and/or economical, from the use of ethanol as fuel in agricultural aviation may be even greater if the aircraft engine is specially designed for that purpose. A specific design is also necessary if it is intended to achieve a truly "green" engine, neutral regarding carbon emissions. Using available technologies, computational tools, development methods and project management methods (Reference Model for Agricultural Machinery Development Process (RM-AMDP), the engine can be fully developed to be used specifically as an agricultural aircraft propellant operating with ethanol. In Brazil, the current fleet of agricultural airplanes has around 1500 aircrafts and almost all operating with AvGas (Aviation Gasoline). There is already in Brazil a "green" airplane, manufactured by Neiva, a subsidiary of the aircraft manufacturer Embraer. This model uses a conversion kit on the original engine to use ethanol as fuel. The use of ethanol has great technical and economical feasibility when compared to AvGas, even with the low efficiency of the current application. Operational improvement and gains with cost reduction can be already observed. However, with a specific engine design those gains could be more expressive due to increased fuel efficiency and power.