For most people, a jet is a jet. But there are several different kinds of jet engines, depending on how they operate. You frequently hear about ramjets, scramjets, and even turbojets. But there is another kind — a very old kind — called a pulsejet. [Integza] shows how he made one using 3D printed parts and also has a lot of entertaining background information. You can see the video below. (Beware, there is a very little bit of off-color language and humor in the video, so you might not want to watch this one at work.)
They are not ideal from a performance standpoint, but they are easy to make. How easy? A form of pulsejet was accidentally discovered by a young Swiss boy playing with alcohol in the early 1900s. Because of their simplicity, they’ve been built by lots of different people, including rocket pioneer Robert Goddard, who mounted one to a bicycle.
Tesla — the inventor, not the car — invented a lot of things, including a one-way valve design with no moving parts. A pulsejet expels exhaust and intakes air through the same hole, so good ones use a one-way valve. Tesla’s is interesting because it is nothing more than a shaped channel that has low resistance to flow in one direction and higher resistance in the other direction. The trick is in a teardrop shape that is thin on the inlet side and fat on the outlet side. It isn’t perfect, but it does provide a basic and mechanically reliable one way action.
The biggest problem, of course, with a 3D printed jet engine is that the engine gets hot and plastic likes to melt. [Integza] used lost PVA casting with plaster which worked well. There were still plastic parts melting, though. He used a high tech PLA, but we wondered if PETg or nylon would have been better choices for heat resistance.
It took several iterations, but he finally got some pretty impressive results. Well, impressive when you consider what he’s working with. We aren’t sure you’d ever want to use a 3D printed pulsejet in an actual project, but if models like this help you understand the principles, it might lead to a more practical engine somewhere down the road.
If you think Goddard’s bicycle idea was cool, here’s a more recent attempt. If a bicycle isn’t your thing, a jet sled is a possibility. We’ve seen other attempts to make jets with at least some 3D printed parts.