Energy and Flight
Flying takes a lot of energy. When a bird flies, it uses about fifteen times more energy than when it is still. The fuel that supplies this energy is the bird’s food, which is stored as fat until it is needed.
When a bird takes off and flies, it needs the chemical energy stored in its fatty fuel. The energy is released by chemical reactions that use oxygen from the air. A lot of oxygen is needed to keep
a bird’s muscles supplied with enough energy to keep flying.
Airplanes and rockets have energy needs similar to those of a bird. They carry energy stored in their fuel, and they have to combine the fuel with oxygen to burn it and release the energy. When a jet plane or rocket takes off, chemical energy in the fuel changes to heat energy in the engines. Heat energy changes to the kinetic energy of the hot gas that shoots out of the engines.
Other Forms of Flight Power
There are other ways than using jet fuel to obtain the energy needed for flight. There are electric airplanes powered by propellers driven by electric motors. The electricity is produced by solar cells on top of the wings. Solar cells change solar energy into electrical energy.
There have been experimental nuclear-powered aircraft, too. In the 1950s, nuclear-powered military planes seemed attractive because they could stay in the air for weeks or months. Nuclear-powered jet engines were built, and at least one nuclear-powered aircraft did fly. These planes never went into production, however. It proved to be too hard to protect the crew from the dangerous radiation produced by the fuel. If one of these planes had crashed, it also could have spilled radioactive fuel over a wide area.