What force does an airplane have to overcome in order to stay in flight?

Airplanes have to overcome more than just one force in order to fly. Gravity, of course, is the most obvious one. Drag is another one. The silhouette/cross section/wetted area which the airplane presents to the wind is one obvious form of drag. Then there's induced drag, the friction of the air over the aircraft skin, which increases as the speed of the aircraft increases. There are also incidental sources of turbulence that contribute to induced drag. All of these are overcome with clever design and lots of power.