for the people who are interested in seeing the scientific aspect of propellers. on page 21 you can clearly see how our experience of diameter and blade speed are similar. https://www.mh-aerotools.de/company/paper_15/Hepperle%20-%20Elektrisches%20Fliegen%20Stuttgart%202015.pdf
Many ask me why I do not fly with 20 or 24 cells in series batteries? That’s easy to explain. It would not change the overall wattage. It is also easier to design a motor in the 3.5 kg range which has a maximum efficiency of around 50-60 volts. If you would wind the motor so that it needs 100 volts or more to reach the speed, it is very many extra thin windings then only half of the amperage may get. that’s the technical side to it. a very crucial point is that there is a limit of 60 volts for battery-powered applications in europe, which can come into contact with people. If you had wet fingers and touched a 100 or more volts battery on the + and - cables, it could very quickly kill you or cause your heart to fail. It is DC with an incredibly high pulse rate. that means very fine muscle and nerve cells respond immediately if you do not wear protective gloves. I know people who have made special courses to properly understand e-cars in case of repair or accident damage with regard to the voltage of the individual battery modules. If you were to touch the voltage at the input of the controller of an e car, it would be deadly immediately. Everything is possible to build. you just have to do everything right. then it is ok, of course.