Flying Machines
Long before we had aeroplanes, people had been experimenting with different flying machines.Hot-air balloon s pilots steer their aircraft by ascending or descending into air currents that move the balloon.Helicopters first appeared during World War II. A helicopter hasn't got wings, but, like an aeroplane, it's got an engine that makes its blades spin at high speeds.The pilot controls the balloon's movement by heating the air inside the balloon, or by allowing it to cool naturally.Hot-air balloons and gliders use air currents, for movement.A glider also uses air currents to soar and glide.?????????????????????