What is specific range and how is it calculated?

• A. Specific range is distance per unit of fuel; calculated as range divided by fuel weight or fuel burn rate.
• B. Specific range is speed per unit altitude; calculated as speed divided by altitude.
• C. Specific range is weight per distance; calculated as weight divided by range.
• D. Specific range is lift per drag; calculated as L/D times weight.

Answer: (A)

Specific range is a measure of fuel efficiency expressed as the distance you can fly for each unit of fuel consumed. It can be calculated from how far you actually fly (range) divided by the amount of fuel used (fuel weight on board), giving a distance-per-unit-of-fuel figure such as nautical miles per pound of fuel. It can also be expressed as cruise speed divided by the fuel flow rate (V divided by q), since distance equals V times time and fuel equals q times time, so the time cancels out and you get distance per unit of fuel. This concept captures how efficiently the airplane converts fuel into distance. Other descriptions mix different quantities (speed per altitude, weight per distance, or lift-to-drag) and do not reflect distance per unit of fuel, which is why they’re not the correct definition.