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In steady flight, the sum of thrust, drag, lift and weight acting on an aircraft equals what?

Zero, because the four forces balance out.

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  1. Zero ✔
  2. The aircraft's weight
  3. Twice the lift

Why: In steady, unaccelerated flight the forces cancel, so the aircraft is not speeding up, slowing down or changing direction. Thrust balances drag, and lift balances weight.

Huh, didn't know that: These four forces act on every aircraft in flight, from a jetliner to a powered parachute.

The dad joke
The four forces of flight never argue. They always balance each other out.
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References

Answer: Zero. In steady, unaccelerated flight the forces cancel, so the aircraft is not speeding up, slowing down or changing direction. Thrust balances drag, and lift balances weight.

  1. FAA Pilot's Handbook of Aeronautical Knowledge, Chapter 5 www.faa.gov/sites/faa.gov/files/07_phak_ch5_0.pdf
    There can be no unbalanced forces
    Checked 2026-10-11.
  2. FAA Pilot's Handbook of Aeronautical Knowledge, Chapter 5 www.faa.gov/sites/faa.gov/files/07_phak_ch5_0.pdf
    Thrust, drag, lift, and weight are forces that act upon all aircraft in flight.
    Checked 2026-10-11.

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