An artifical satellite revolves in the orbit around the Earth without using any fuel. But an aeroplane requires fuel to fly at a centain height. Why ?

Explanation

Air is necessary for the areoplane to fly. Therefore, the aeroplane requires fuel against the frictional force due to air. The satellite orbits around Earth at such a heigher height where air is very much rarer and its friction is nearly negligible. The centripetal force necessary for orbital motion of satellite is provided by the gravitational pull exerted by Earth on the satellite.