Page 142 - Understanding Flight

CH05_Anderson 7/25/01 8:58 AM Page 129

Airplane Propulsion 129

Fig. 5.7. How a piston engine converts chemical
energy to propeller rotation.

One way to overcome the power loss with altitude is to add a pump
to the air intakes to increase the amount of air in the cylinders. There
are two common methods for doing this. The first is called
turbocharging. A turbocharger makes use of the energy expelled in the
exhaust to run a small pump in the air intakes. A “supercharger” is
another method to pump additional air into the cylinders. A
supercharger can be powered mechanically through a belt on the engine
shaft, or with an electric motor. The purpose of both is the same, to
increase the amount of air (oxygen) in the cylinders at higher altitudes
where the air is less dense. The result is that a turbocharged or
supercharged engine can maintain constant power up to a higher
altitude. Above that altitude the pump can no longer maintain sea-level