How does a blimp stay in the air?
A blimp is an airtight bag that is able to rise in the air because it is filled with light gases. A blimp is a small, balloon-like airship. Unlike the heavier-than-air airplane, the blimp remains aloft because it is lighter than air. It needs only small motors to push it forward. Blimps are descendants of the simple balloon . The blimp’s lift comes from a lighter-than air gas that raises the blimp in the same way a balloon is lifted.
A balloon rises because the gas inside the balloon is much lighter than the air round it, and so it floats in the atmosphere, in much the same way a ship floats on water. The gas inside the blimp expands and fills out the blimp. Its gasbag has no framework inside, and collapses when the gas is taken out.
Some airships, such as the dirigible, have an inside framework that supports the sides, and do not depend on the pressure of the lifting gas to maintain their shape. During World War II, blimps protected ships by spotting enemy submarines. They were also used for observation, photographing enemy positions and for rescues at sea and on land. Today, blimps with signs painted on their sides are used mostly for advertising and sightseeing. – Dick Rogers