A quadcopter has a manufacturer maximum takeoff weight of 4.4 pounds and an empty weight of 2.9 pounds with battery. What is the maximum payload that may be carried?

Payload capacity is the difference between the maximum takeoff weight the manufacturer certifies and the weight of the aircraft as it sits ready to fly. Maximum takeoff weight is a structural and performance limit covering everything that leaves the ground: airframe, battery, and anything attached to it. Because the stated empty weight already includes the battery, the subtraction is direct: 4.4 pounds minus 2.9 pounds leaves 1.5 pounds available. Exceeding that figure does not merely reduce endurance — it lengthens the stopping distance in a descent, cuts the margin the motors have to arrest a gust, and can push the aircraft past the 55-pound line that separates Part 107 from other rules, though not at this scale.

Subtracting the 2.9-pound ready-to-fly weight from the 4.4-pound maximum takeoff weight leaves 1.5 pounds of payload. Because the battery is already counted in the empty weight, no further deduction is needed.

Manufacturers publish a maximum takeoff weight that bounds total mass at liftoff. Remote pilots compute available payload by subtracting the ready-to-fly weight, and must account for whether the published empty weight already includes the battery.

Max Minus Ready equals Room to Carry. If your answer is bigger than Max, you added when you should have subtracted.

Read whether the stated empty weight includes the battery. When it does, subtract once; when it does not, the battery comes off the payload allowance too.

• •Adding the two weights instead of subtracting
• •Reporting the maximum takeoff weight as the payload
• •Deducting the battery twice when it is already in the empty weight