43. What is the relationship of lift, drag, thrust, and weight when the airplane is in straight-and-level flight?
A) Lift equals weight and thrust equals drag.
When an airplane is flying straight and level at a constant speed, the lift it produces balances its weight, and the thrust it produces balances its drag.
Image Credit: National Air and Space Museum, Smithsonian Institution
"In order to maintain a constant airspeed, thrust and drag must remain equal, just as lift and weight must be equal to maintain a constant altitude."
From: FAA-H-8083-25B "Pilot's Handbook of Aeronautical Knowledge"
Page 5-2, Thrust