[rplst8]

That's a good point. Gasoline engines have come a long way since the days of magneto operation, with variable timing, ignition, and direct injection (of which some piston driven aircraft may already use). Turboprops and turbofans (jets) are already very efficient compared to automotive piston engine aircraft. A 747 for instance gets around 91 mpg/person while buses average around 200 mpg/person - but, the drag forces on an aircraft are I think at least an order of magnitude greater.