Rita F. Ricketts, age 10, of Staten Island, New York, for her question:

How long have jet planes been flying?

The first aircraft driven by a machine got off the ground in 1903. For many years, a machine driven aircraft needed a propeller on its nose to cut a path through the air. But as long ago as 1909, a few designers began dreaming of another way to drive an airplane. , It could, they thought, be shoved from behind by a strong jet of air. However, no one could figure a practical way to make the jet push work.

At last, in 1930, Frank Whittle of England solved the problem and designed a jet propelled plane. However, it was not tested until seven years later in 1937, the same year that Germany began testing jets. The first successful flight of a plane with a turbo jet engine was made by the Germans in 1939. The world soon learned that jet engines can drive aircraft faster and farther and that jet fuel saves money. In a few years, jets began replacing propellers on all large aircraft. Today, a large airplane with propellers looks relatively old fashioned.