Basically, ethanol has much less energy per unit volume than gasoline
so simple chemistry says you have to burn more of it to generate the
same energy as a like amount of gasoline.  I don't remember the exact
numbers, but I think it was in the range of 70-80% compared to
gasoline.  I used to fly a jet that could use about anything that
burned for fuel in an emergency and ISTR that the book limited you to
50% range with alcohol.