Here at the model rocket site, we love rockets. But we also love learning about them and how they work. Often we get asked what is in those rocket engines?
Rocket Model engines are made from cardboard, plastic and black powder (Gun powder). The three most important ingredients are charcoal, potassium nitrate, and sulphur. Most small model rocket motors are single-use engines, with cardboard bodies and lightweight moulded clay nozzles, ranging in impulse class from fractional A to G. B
Bigger rocket engines typically use composite propellants including ammonium perchlorate, aluminum powder. They also have a rubbery binder substance encased in hard plastic. The propellant is not as fragile as black powder, increasing motor reliability and resistance to fractures in the propellant.
What’s the difference between Liquid Rocket engines and Solid?
Although not as widely used as the solid rocket engines, there are liquid motors as well. The fuel source in a liquid rocket mixes with the oxidizer (Oxygen) in a chamber in the nozzle. They are stored separately inside the engine until launch.
Liquid rockets use liquid fuel, such as liquid hydrogen or a hydrocarbon fuel such as RP-1, and a liquid oxidizer, such as liquid oxygen.
Solid Rocket Engines come pre-mixed. So the propellant and the oxidizer are already mixed together inside the engine. This makes them safe and easy to transport, they do not ignite under normal temperature environments. At launch, an external source of heat is provided by the launcher and that starts the engine. Once the solid propellant starts burning it will continue until all of the material is burnt up. This provides the force to launch the rocket.
How Do Model Rocket Engines Work?
Black Powder Engines
The most common model rocket engines are small, black powder motors like these ones on Amazon. I had these as a kid, and they are still what we use today in most situations.
Black powder model rocket engines are made of a paper tube with a clay nozzle, a solid pellet of black powder propellant, a smoke/delay charge, and an ejection charge as shown in this figure.
These black powder model rocket engines are typically made with a solid black powder propellant, a clay nozzle, and ejection charge and a smoke/delay charge. Booster Engines are basically the same but they lack the Smoke/Delay and ejection charge.
The engine is ignited by inserting an igniter into the clay nozzle which in turn connects it to the propellant. When the launch happens there is an electric current that goes through the igniter, lighting up the powder and boom, rocket launches.
Many of the model rocket kits come with a launcher, but if you are looking for one this Estes one on amazon does the trick. It will guide your rocket up and also has the igniter.
Thrust comes from burning the propellant.
After the powder is completely burned up the smoke charge burns to produce a trail of smoke. This allows you to not only follow the flight path, but it also allows the rocket to slow down before it activates the ejection charge releasing the parachute.
Single Use Composite Engines
Composite engines come in two main forms. The single-use form is made of high-temperature plastic and the fuel is a rubbery material that is used in space ships. This fuel is three times more powerful than the black powder, allowing them to be significantly smaller in size.
The internals of the composite engines is much the same as the black powder motors except that the nozzle and body of the engine are moulded from a high-temperature plastic. The engine body contains the fuel, a smoke/timer charge, and the ejection charge.
Reuseable Composite Engines
Reuseable composite engines are the same as the single-use engines. The biggest difference is that they are in an aluminum case. After the reusable case has been cleaned it can be reloaded. To reload it you will need a new nozzle, fuel, delay charge and ejection charge, and used again.
The chief benefit of reloadable engines is that they are less expensive than single-use composite engines. And, it is fun to build your own engine before a launch.