Wednesday, May 13, 2015

Homemade jet engines, then and now

True story: as a fifth-grader, I and a classmate built a rudimentary jet engine for a science fair*.

OK, OK... maybe "rudimentary" is being a little complimentary. And in reality, it was more of a motorjet, which was cutting edge in the late 1930s. But still. A jet. I assume the Parents of the Blog have a picture somewhere, but since I don't have one in hand, I'll just describe it to you.

It was a coffee can with both ends removed.

The beginnings of an engine.

Inside the can was mounted a smaller can--I think it once held tuna. The lid was removed and a hole about 1/3 the diameter was cut in the bottom.

The ignition system.

At one end was a two-stroke model airplane engine with a two-bladed propeller.

This would be the "motor" part of a motorjet.

Inside the tuna can was a wad of steel wool mixed with wood putty--the ignitors. I won't even try to find something to illustrate that. But the point was that after experimenting with a bunch of different flammable things, we discovered this mixture would maintain an open flame in high winds... like those generated by a model airplane engine.

Finally, a tiny hole in the top of the coffee can admitted a tiny straw, which was attached to a can of WD-40. This was the fuel system.

You started up the prop in the front, started spraying fuel, and whoosh: a jet. The tuna can compressed the air inside the coffee can enough that, combined with the heat of WD-40, you actually got a little thrust. We never tested it, but I suspect it would have, say, accelerated a skateboard pretty nicely.

What made me think of this? Well, I saw today that GE just produced a rudimentary jet engine of its own. Except this one was more or less 3D-printed. And it's quite a bit more powerful. Check it out:

It's a really cool application of a technology that is still evolving in interesting ways. Just a couple of years ago, 3D printing was basically something you used to make toys or plastic parts. Now you can, in theory, simply command a computer to make a jet engine.

I think even adjusted for inflation, my production costs were much lower. But measured in skateboard thrust units, GE's version of a cheap jet engine blows mine away.

*Our jet came in second, to a "microwave that cools things down." It was a box with a fan in it.

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