Combustion engines have been used on aircraft ever since the Wright brothers' first flight in 1903. Though their design has changed over the years, all combustion engines still work by burning a mixture of fuel and air to generate thrust. While the fuel is loaded on the plane already at the right consistency for use, the air which the engine collects needs to first be compressed. To use only as much fuel as necessary, airplane combustion engines rely on high powered compressors which condense the air they take in, making for an oxygen-rich fuel-air mixture that can be ignited with ease. Though there are many different compressors to choose from, most can be divided into two major categories: centrifugal and axial.