Figure 6-6 demonstrates the basic principles of gas turbine operation.

A blown-up balloon (fig 6-6 view A) does nothing until the trapped air is released. The air escaping rearward (fig 6-6 view B) causes the balloon to move forward (Newton's third law). If we could keep the balloon full of air (fig. 6-6 view C), the balloon would continue to move forward.

If a fan or pinwheel is placed in the air stream (fig 6-6 view D), the pressure energy and velocity energy will rotate the fan and it can then be used to do work.

Figure 6-7.-Turbine operating theory.

Figure 6-8.-Practical demonstration of turbine operating theory.

By replacing the balloon with a stationary tube or container and filling the tube with air from a fan or series of fans, we can use the discharge air to do work by turning a fan at the rear of the tube (fig 6-7 view A).

If fuel is added and combustion occurs, we greatly increase both the volume of air and the velocity that propels it over the fan. This increases the horsepower the fan will produce (fig 6-7 view B). The continuous pressure created by the inlet fan, or compressor, prevents the hot gases from going forward.

Next, if we attach a shaft to the compressor and extend it back to a turbine wheel, we have a simple gas turbine. It can supply power to run its own compressor and still provide enough power to do useful work, such as to drive a generator or propel a ship (fig 6-8, view A). By comparing view A with view B in figure 6-8 you can see that a gas turbine is very similar to our balloon turbine.