Diary of a Pyro

Copyright © 1988 - 2005 John H. DuBois III

Chapter Thirteen

That 4th of July was one of the best ever. I didn't have much time to make stuff because I was working up to the last minute to finish an electronic trigger for my camera of the sort I had jury rigged many years before. This one I did right, and it worked well. It stuck onto the back of my camera with Velcro, and could be set to trigger when a circuit was either opened or closed.

It did have one problem; I discovered that the solenoid slammed the shutter release down so fast (as I wanted it to to take pictures of fleeting events) that the automatic exposure system of the camera did not have a chance to act. Normally, the electronics of the camera is powered up when the shutter release is partially depressed, and by the time the shutter is triggered the illumination on the focal plane has been measured and the shutter speed has been set. In this case, however, the shutter speed always defaulted to one second, which was useless. I got around this by putting a screw cap on the other end of the solenoid that could be screwed down to press in the shutter release just until the electronics were activated. Of course then I had to launch the rocket or do whatever else I was trying to take a picture of quickly since the batteries in the camera would run down.

I managed to find time to refill some commercial miniature finned rockets with a nice flash powder payload, and put launch lugs on them so that I could try out my camera trigger with them. The others had lots of things filled with flash powder and quite a quantity of commercial stuff. Tim, the one I met at St. Francis, arrived as I was finishing the trigger to spend the Fourth with us for the first time.

This time we went straight to the sand plant, which was ideal for our purposes. I started out launching the little missiles with the automatic system before the light faded, and the pictures turned out perfectly.

Laurence and his friend whose father owned the land printed up flyers telling how to get there. We ended up with more than a hundred people. I recall watching the humorous scene as drunken partiers stood around giving lights to people with fantastic fireworks. The occasional load of flash powder lit up the sand plant in a harsh light like an atomic bomb. Some of the people were a problem; most of our fireworks were in boxes and there tended to be a lot of hands reaching toward them when they were opened. Many of mine were stolen.

We set up a large PVC pipe and a cardboard tube, both about five inches (13 cm) in diameter, to launch the skyrockets from. One of Laurence's flash powder rockets exploded in the PVC tube, blasting it in two and sending chunks of plastic flying. I was sitting nearby and was hit by one. Perhaps the rocket blast had bounced off the bottom of the tube and shot up around the rocket, and managed to penetrate some unsealed joint in the warhead. In future years we didn't use PVC tubes for launching rockets. The reputation of Laurence's rockets further declined when one went off in the cardboard tube. It wasn't brittle like the PVC one and just ended up with one side blown open about half way up. This turned out to be convenient as a sort of window to put rockets in without having to reach up to the top. After that people tended to stay away when Laurence launched his rockets.

I took pictures of rockets exiting the launch tube throughout the night. The ones from early in the evening showed just wisps of smoke coming from the tube, which I assumed was the trail left behind as they departed. The later ones actually caught the rockets in flight. This seemed odd, since I was drinking Kahlua and one would expect my reflexes to slow down as I consumed it. It wasn't until the next year that I finally figured out what was going on. The smoke I saw coming from the tube was actually being jetted out by the rocket while still in the tube; since I snapped the picture as soon as I heard the engine thrusting I was getting it before the rocket began climbing out. As the night wore on my reflexes slowed and I began getting the rocket itself. This might seem obvious, but I was so used to rockets that shot off in an instant that it never occurred to me that I might be taking the picture too fast. The pictures suggested that the engines of the commercial skyrockets built up thrust more slowly.

Laurence and Scott set up four mortar tubes for their Festival Balls (they had bought several dozen, and each half dozen came with a tube.) They would load up all four tubes and then twist the fuses together so that they would fire almost simultaneously. The multiple shells bursting overhead was quite a display, and the mortars firing as people ran around reminded me of a war scene. Later in the evening, as the participants became intoxicated, they began doing more dangerous things. It culminated with people taking turns holding a mortar tube in their hands as it fired. I remember watching Luke standing and holding a tube out in front of himself. The billowing flame it produced when it went off was at least twice as tall as he was, and the bottom blew out, directing a smaller flame at his feet. He didn't seem to notice.

Scott took an even greater risk when he held the two pieces of the PVC launch tube together so Laurence could launch one of his larger rockets. Something must have happened to the cardboard one. The ends of the pieces produced when the original tube was fragmented were ragged, so one of the ragged ends was stuck in the ground, and Scott held the smooth ends (what had been the ends of the original tube) together. Of course it had been one of Laurence's rockets that destroyed the tube in the first place, but Scott didn't seem worried. He just grinned and held it. Fortunately the rocket went off safely.

Some of the equipment we brought was burned or otherwise destroyed. Laurence blew up a garbage can with one of his larger flash powder devices. Towards the end, a plastic chair was tossed on the bonfire along with everything around that was made of wood. The most spectacular event of the night was the annihilation of the fire itself. Laurence tossed an item containing a large quantity of flash powder in it. When it went off, most of the coals in the fire were turned into dust which was blasted into the air where it combusted furiously, producing an enormous incandescent cloud at least twenty feet across. A plate-shaped sheet of flame flowed out under the main fireball, from which sparks and coals spiraled, and at it base it was complemented by flying sand. As it dissipated an immense column of sparks rose into the sky. When it was done the sand was littered with glowing coals over a large area. As people wandered through them they gave an impression of walking among the stars.

After the successful test of my camera trigger on the Fourth, I tried taking pictures of even more fleeting events, like exploding firecrackers, popping balloons, and piles of burning flash powder. I wrapped a piece of thin wire around a firecracker, and set the camera to trigger when it was blasted in two. For the balloons, I first tried drawing a line of conductive paint on the surface, with the expectation that it would be torn in half when the balloon popped. However, the paint seemed to give some strength to the balloon and held that part together. I ended up putting a strip of foil around the balloon, and pressed it against contacts so that when the balloon burst and began to contract the contact would open. To get a picture of the flash powder, I put a thin piece of foil through it so that it would be melted by the intense heat.

Unfortunately, the trigger proved too slow for all but the flash powder. I got back slides that just showed bits of firecracker and balloon rubber flying out of the frame. Though the trigger system responded in a fraction of a microsecond, the time it took the solenoid to press down the release and the shutter to open was too long.

That fall we got into rocketry in a big way. We started with Luke and Scott finally refilling some of the practice missiles they had picked up at Fort Ord. They filled one with polyurethane fuel, one with Pyrodex (a type of smokeless powder made for guns), and one with PETN, the high explosive from the other missile warheads. They didn't expect the last two to work, but thought they were worth a try. We brought them to the High School grounds and tried launching them from a tube. The Pyrodex rocket exploded (as might be expected), and blew the end off of the tube. One of the others managed to barely make it out of the end and then flopped on the ground. The final one just sat in the tube and fizzled.

After that, we began using ordinary model rocket engines. The hobby shop happened to have some E and F engines, which are much larger than the usual engines that only go up to D. They were rather expensive (the F's cost $5 apiece), but were a lot of fun. Luke put an F100 engine his Mars Lander model, which is supposed to be propelled by a D12 with one eighth of the thrust. It couldn't handle it and gyrated wildly just over our heads. He and Scott made some other very large rockets that worked better. On liftoff, the more powerful engines we were using tended to burn right through the blast deflector of Luke's launch pad.

These rockets accelerated very fast, and the few tens of milliseconds delay of the camera trigger caused some problems here too. The launch lug began the sequence when it knocked the clip off of the top of the launch rod. The rockets were several feet above the rod by the time the shutter opened. I wanted to catch them closer to the ground, so I came up with another scheme that satisfied this requirement. I made a different clip that closed a circuit when it shut. I then fastened the trigger cable to the ground, and clamped the clip onto a fin of the rocket. The fin held the clip (and circuit) open. When the rocket launched, the fin pulled out of the clip and triggered the camera. This method proved very reliable and versatile, since I could vary the height at which the fin pulled out.

I also found a faster way of making rockets than tediously gluing the fins and other parts on with white glue. I got some thick cyanoacrylate glue and accelerator from the hobby shop. I stuck parts together with the glue, and then sprayed it with the accelerator to harden it in seconds. Once the parts were gathered, a rocket took minutes to make instead of hours. This made them even more expendable, which was fortunate since the larger engines tended to make them disappear into the heavens. No local site was really large enough; the rockets drifted down slowly on their parachutes and were carried far by the wind. I had recovered only a few rockets since my days at St. Francis, which had plenty of land.

Because of this, once when we made a particularly large batch of unusual rockets we went to launch them at the Carmel Middle School which was in a wide-open area. I had a rocket that used a couple of toilet paper tubes glued on the sides instead of fins. It worked perfectly, but the ejection charge failed (the first time that had ever happened to any of us) and it slammed into the ground nose first when it came down. I later managed to fix it by cutting off the part of the rocket tube that had been “accordionized”. All of our other rockets were double-stagers, which with D, E, and F engines sent them so high that we lost most of them despite the large grounds.

The next year I finally figured out how to take really fast pictures, at least under controlled conditions. I made a different trigger system, which instead of releasing the shutter activated the flash. I could set up a picture using the same triggering schemes I had before, turn out the lights, open the shutter, and then pop the balloon or light the firecracker. When the flash was triggered it responded in a few microseconds, freezing the scene at the critical moment. The pictures showed firecrackers bursting open and balloons looking oddly contorted as their sides ripped open and they began to deflate.

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