Editing Flight (section)

=== Energy efficiency ===
{{Main|Propulsive efficiency}}
To create thrust so as to be able to gain height, and to push through the air to overcome the drag associated with lift all takes energy. Different objects and creatures capable of flight vary in the efficiency of their muscles, motors and how well this translates into forward thrust.

Propulsive efficiency determines how much energy vehicles generate from a unit of fuel.<ref>[http://www.hq.nasa.gov/pao/History/SP-468/ch10-3.htm ch10-3 "History."] ''NASA.'' Retrieved: May 6, 2012.</ref><ref>Honicke et al. 1968 {{Page needed|date=May 2012}}</ref>