3D Printing May Be The Key To Practical Scramjets

The first scramjet, an airbreathing jet engine capable of pushing an aircraft beyond Mach 5, was successfully flown in the early 1990s. But while pretty much any other technology you could imagine has progressed by leaps and bounds in the nearly 30 years that have passed, the state-of-the-art in hypersonic scramjets hasn’t moved much. We still don’t have practical hypersonic aircraft, military or otherwise, and any missiles that travel at those sort of speeds are rocket powered.

NASA’s X-43 hit Mach 9.6 in 2004

This is somewhat surprising since, at least on paper, the operating principle of the scramjet is simplicity itself. Air rushing into the engine is compressed by the geometry of the inlet, fuel is added, the mixture is ignited, and the resulting flow of expanded gases leaves the engine faster than it entered. There aren’t even any moving parts inside of a scramjet, it’s little more than a carefully shaped tube with fuel injectors and ignitors in it.

Unfortunately, pulling it off in practice is quite a bit harder. Part of the problem is that a scramjet doesn’t actually start working until the air entering the engine’s inlet is moving at around Mach 4, which makes testing them difficult and expensive. It’s possible to do it in a specially designed wind tunnel, but practically speaking, it ends up being easier to mount the engine to the front of a conventional rocket and get it up to speed that way. The downside is that such flights are one-way tickets, and end with the test article crashing into the ocean once it runs out of fuel.

But the bigger problem is that the core concept is deceptively simple. It’s easy to say you’ll just squirt some jet fuel into the stream of compressed air and light it up, but when that air is moving at thousands of miles per hour, keeping it burning is no small feat. Because of this, the operation of a scramjet has often been likened to trying to light a match in a hurricane; the challenge isn’t in the task, but in the environment you’re trying to perform it in.

Now, both Aerojet Rocketdyne and Northrop Grumman think they may have found the solution: additive manufacturing. By 3D printing their scramjet engines, they can not only iterate through design revisions faster, but produce them far cheaper than they’ve been able to in the past. Even more importantly, it enables complex internal engine geometries that would have been more difficult to produce via traditional manufacturing.

Continue reading “3D Printing May Be The Key To Practical Scramjets”

Engine Hacks: A Pulse Jet UAV By Any Other Name Would Still Be A Cruise Missile

Imagine our surprise when we learned [Bruce Simpson], who made headlines in 2003 with his $5000 DIY cruise missile, is still alive, not illegally interned in a black ops prison, and still doing what he does best: building really awesome remote-control airplanes.

The first successful mass-produced pulse jet aircraft was the German V-1 flying bomb. The V-1 had a very primitive guidance system, but the unmanned pulse jet aircraft quickly evolved into a few target drones used by the US Air Force. There was never any significant advancement towards improving the fuel consumption, noise level, or heat signature of pulse jets, so they were superseded by the superior turbojet. Despite their failings, pulse jets are remarkably easy to build and amazingly fast.

Instead of being antagonized by the New Zealand and United States governments, [Bruce] spends most of his time now working on pulse jet projects. He’s flown quite a few modified R/C planes and has an electronic Engine Control Unit for his jets. One of his most impressive projects is the 100 pound thrust pulse jet that was later attached to a go-kart. His no weld version of a pulse jet can be built in even the most minimalist work shop and is the epitome of an easy-to-build jet engine.

To get an idea of how fast [Bruce]’s planes can be, check out his Long-EZ R/C pulse jet in action after the break.

Continue reading “Engine Hacks: A Pulse Jet UAV By Any Other Name Would Still Be A Cruise Missile”