Power Required (Level Flight)

In steady level flight, an aircraft is not accelerating up, down, or along its path, so the engine only needs to supply enough power to balance the aerodynamic drag. Since power is the rate of doing work and work against drag equals force times distance, multiplying drag by true airspeed gives the rate at which energy must be delivered to the airflow. This is why higher drag or higher speed both increase the required power.

Use this when analyzing an aircraft in steady, level cruise or any situation where lift balances weight and thrust balances drag. It is especially useful for estimating engine power demand, comparing cruise speeds, or finding how changes in drag affect fuel use.

• Using indicated airspeed instead of true airspeed
• Forgetting to convert the answer from watts to kilowatts when needed
• Applying the formula to climbing or accelerating flight without accounting for extra power requirements