At higher rpm, the valve opens to allow more exhaust flow for increased boost.

The propelling nozzle is a critical part of a ramjet design, since it accelerates exhaust flow to produce thrust.

At high speeds, the flap would stay open, decreasing resistance and increasing exhaust flow.

By contrast, the new system allows exhaust flow through a straight pipe that creates no back-pressure at all.

Often, cool air is deliberately injected into the exhaust flow to boost this process.

The exhaust flow of these fans was also controlled by dampers in the ducting.

The space for the exhaust flow was also somewhat restricted, so the exhaust passages were tall and narrow in some locations.

It incorporated a rim and capuchon to control exhaust flow into the atmosphere.

This is done to prevent turbulence to the exhaust flow and reduce total back pressure in the exhaust system.

They have an advantage in being able to handle small, medium and large exhaust flows.