The De Laval Rocket Nozzle (Rocket Motor)

In the late 19th century a well known engineer named Carl Gustav De Laval invented the first, practical steam turbine engine, and along with it. the special nozzle used to maximize the speed at which the steam hit the turbine blades. The nozzle’s design was soon adapted by Robert Goddard and other engineers for use in rocket motors, where it became known as the De Laval nozzle.
A De Laval nozzle is made with a precisely engineered venturi shape that maximizes the speed of the motor’s exhaust. Assuming that the other design parameters are fixed, this maximizes the motor’s performance and efficiency. The mathematics of De Laval nozzles are a standard part of all rocket engineering texts. But the narrow neck of the nozzle is very short, and when made of the ceramic mixture described in this topic, it erodes out so quickly during motor operation that all
the design benefits are lost. Knowing that some of the people who read this topic will want to experiment with De Laval nozzles. I spent some extra time during the project, and developed a method of mounting real, stainless steel De Laval nozzles in cardboard tubes. They can be quickly machined by anyone with a metal lathe, and the process of installing one takes less than 5 minutes.
Once the nozzle is in place, the propellant and the other components are loaded in the normal manner. The result is a rocket motor that performs according to classic nozzle engineering principles, and a little more efficiently than a motor with a clay nozzle. Because a De Laval nozzle erodes out only one or two thousandths of an inch with each firing, it can be reused dozens of times. After many firings, when accumulated erosion causes a noticeable drop in motor performance, a small decrease in the propellant’s baking soda content restores performance to its previous level. topic 10 contains complete instructions on how to make and install De Laval nozzles.