How do you compute endurance and range from usable fuel and throttle settings?

• A. Endurance = usable fuel × consumption rate; Range = TAS + endurance
• B. Endurance = consumption rate / usable fuel; Range = TAS × endurance
• C. Endurance = usable fuel − consumption rate; Range = TAS − endurance
• D. Endurance = usable fuel / consumption rate (hours); Range ≈ TAS × endurance, adjusted for headwind/tailwind

Answer: (D)

Endurance measures how long the airplane can stay in the air on the usable fuel at the current throttle setting, so the fuel burn rate (how much fuel is used per hour) and the amount of usable fuel are the key ingredients. If you have usable fuel in gallons (or kilograms) and a burn rate in gallons per hour (or kilograms per hour), the time you can fly is simply usable fuel divided by the burn rate. That gives you endurance in hours.

To get range, multiply that endurance by your speed. Using true airspeed (TAS) is standard for planning, so range is TAS × endurance. Wind changes how far you actually travel over the ground, so you adjust the result for headwinds or tailwinds; with no wind, TAS × endurance is the precise range.

Other formulations don’t fit because they mix units incorrectly (adding or subtracting fuel, speed, or time) or use operations that don’t yield a meaningful duration or distance.