Before revision: The Oswald efficiency, similar to the span efficiency, is a correction factor that represents the change in drag with lift of a three dimensional wing or airplane, as compared with an ideal wing having the same aspect ratio and an elliptical lift distribution.Raymer, Daniel P., Aircraft Design: A Conceptual Approach, Section 12.6 (Fourth edition) Definition The Oswald efficiency is defined for the cases where the overall coefficient of drag of the wing or airplane has a constant+quadratic dependence on the aircraft lift coefficient where {| border="0"|-| || is the overall drag coefficient,|-| || is the zero-lift drag coefficient,|-| || is the aircraft lift coefficient,|-| || is the circumference-to-diameter ratio of a circle,|- | || is the Oswald efficiency number|-| || is the aspect ratio|} For conventional fixed-wing aircraft with moderate aspect ratio and sweep, Oswald efficiency number with wing flaps retracted is typically between 0.7 and 0.85.
After revision: The Oswald efficiency, similar to the span efficiency, is a correction factor that represents the change in drag with lift of a three-dimensional wing or airplane, as compared with an ideal wing having the same aspect ratio and an elliptical lift distribution.Raymer, Daniel P., Aircraft Design: A Conceptual Approach, Section 12.6 (Fourth edition) Definition The Oswald efficiency is defined for the cases where the overall coefficient of drag of the wing or airplane has a constant+quadratic dependence on the aircraft lift coefficient where {| border="0"|-| || is the overall drag coefficient,|-| || is the zero-lift drag coefficient,|-| || is the aircraft lift coefficient,|-| || is the circumference-to-diameter ratio of a circle,|- | || is the Oswald efficiency number|-| || is the aspect ratio|} For conventional fixed-wing aircraft with moderate aspect ratio and sweep, Oswald efficiency number with wing flaps retracted is typically between 0.7 and 0.85.