Saturday, February 07, 2009

Great Moments in Aviation, Part III

Lest we think that Western Civilization was having all the fun, we turn our attention to China in the 16th Century. The Chinese had invented gunpowder, and rockets. It's only natural for an inquisitive soul to imagine using rockets' power for flight. But that's a road fraught with peril, as poor Wan Hu found out the hard way.

Gunpowder rockets are, by modern standards, fairly simple devices. But they were absolutely cutting-edge state-of-the-art in the 16th Century. Heretofore, rockets had no use aside from fireworks and antipersonnel artillery, but Wan Hu saw potential in them for something more. As legend has it, he had a grand chair constructed, with forty-seven gunpowder rockets built into the base. One fine morning, he sat himself in the chair, and had his men touch off the rockets, sure he was taking a voyage into history. Well, he did, just not in the way he'd imagined.

There are challenges inherent in using rockets for propulsion. The main problem is symmetric thrust. If you want to fly straight, the axis of thrust MUST pass through the vehicle's center of gravity, or else the vehicle will begin to rotate. And once the vehicle falls even a little bit off vertical, its natural tendency will be to fall even farther off vertical, making a bad problem worse. If you've ever tried to balance a pen or pencil on end, you've seen how this works. Most of the other problems are related to maintaining symmetric thrust. All the rockets must start at the same time, and cut off at the same time, for example. They must produce uniform thrust, if you're using more than one. And they must burn in a stable, predictable fashion.

Well ... Forty-seven being a prime number, it's difficult to imagine a symmetric configuration. And with forty-seven lackeys with torches touching off fuses, it's difficult to imagine all the rockets starting simultaneously. And to top it all off, early gunpowder was notoriously finicky. Two rockets made from exactly the same batch of powder, made by exactly the same craftsman, rarely if ever flew the same.

Wan Hu's ride into history was short, but absolutely action-packed. The chair was consumed in a gigantic explosion, and Wan Hu was nowhere to be found afterwards. I suspect the searchers were looking for an intact body, not the small flaming fragments that poor Wan Hu had been blasted into.

It took hundreds of years of work to get it right, but even today riding into orbit on a controlled explosion isn't what anyone would call safe. Next time you watch a manned space launch, raise a glass in honor of the first poor brave soul to give it a try. He didn't go far, but he was the first, and that's worth something.

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