I don't think anyone has said that 1 horsepower = 746 watts. Of course nothing is 100% efficient -- electric motors are typically 85-92% efficient, so if your motor is 85% efficient, then you need 877.65 watts to produce 1.0 horsepower. Note: in the metric system, watts are used as the unit for mechanical power as well as electrical power. I am also a pilot and retired electrical engineer. I've been going to Oshkosh since 1974.