Hi All,
Well, I survived my many and varied adventures in Thailand and Japan, in fact I thrived on them, and I wanted to report on those parts of my journey that bear on rocketry. If anyone's interested in the rest of my travels I'll be happy to fill you in, but in this (probably rather long) note I'll limit myself to rocketry-related issues. Well, on second thought, I can't resist sharing a few quick high points:
-I participated in the national water fight they have in Thailand to celebrate the new year. This is the most fun I've ever had on a holiday. Thai people really know how to have a good time. (There's simply no way this could work in America: fights would erupt, people would get shot, lawyers and insurance companies would ensure that no one had any fun the next time.)
-I ate bugs. Ants and ant larvae, to be precise. Delicious.
-I learned to count to 20 and beyond, say "thank you," "delicious," and "goodbye" in Thai, and to name several kinds of food, particularly the myriad variations of noodle soup, which was ubiquitous, delicious, and cheap (about a dollar). However, people always giggled at me when I said anything. Those tonal languages are a bitch for Americans...you may THINK you're saying "thanks for the delicious noodles" but you're probably saying something like "wooden water buffalos think furiously."
-I was a guest in a Japanese home for a night: tatami mats, shoji screens, beautiful wood joinery, o-furo (japanese bath), futon, yukata (cotton robe), and a japanese breakfast (fish, miso soup, rice, seaweed, squid, pickled radish, and yes, a fried egg). A real treat.
OK, back to rockets:
THAILAND
Thailand was devoid of water rockets, as far as I could tell, but I did go to a rocket festival in a small village in the northeast. There's a big and famous rocket festival that happens in mid-May, but there are also several smaller, regional ones that happen on any old holiday. The one I went to was on the second day of Songkran, the Thai new year.
The rockets were huge versions of the "bottle" rockets we all know and love. (Not PET bottles, I mean the rockets that look like a firecracker tied to a stick, that you launch FROM bottles.). In this case, the "engine" was constructed from 2 1/2" PVC pipe about 3 feet long: we're talking several kilograms of gunpowder here. And then the engine was strapped to a bamboo stick that was perhaps 12 feet long. These are truly enormous rockets, in my eyes, though apparently at the big national rocket festival they get much, much bigger. Here we see a rocket being readied for launch.
The guy in the next shot was in charge, and very serious about his rockets. (Cultural note: I made a major faux-pas in my excitement: In Thai culture, the feet are considered dirty, and it's a serious insult to sit with your feet towards someone or to step over them. In my zeal for pictures, I stepped over a rocket once rather than walking around it. Bad idea. Loud exclamations erupted, lots of dirty looks from the rocket men, etc. I immediately realized my mistake, acknowledged it, and bowed and scraped and apologized my way back to forgiveness. I was, after all, just a silly ignorant American, and my obviously intense and admiring interest in their rockets made up, I think, for my boo-boo. I was very careful after that.)
These suckers are hung on a big timber framework, and ignited electronically. They take off with a deafening roar and a huge plume of smoke, and achieve altitudes of thousands of feet (see below). Burn times are long, on the order of 15 seconds, but it seems that after the first 5 or so, the thrust tails off a lot. Most of them flew very straight at first, then did crazy jigs all over the sky after they were way up there. I don't know if this was intentional or not, but it was really cool. Some did nice spirals, some traced out seemingly random wanderings, and there was one that took periodic hard left turns: it would fly straight for a while, then suddenly turn hard to the left, then fly straight again, then turn again, etc. Weird.
Of the six rockets I saw launched, only one blew up on the pad. It was a very good day for the rocketeers :-) Apparently the usual ratio is much worse.
The only other thing worth mentioning about Thailand and rockets is that there's a wonderful pop bottle size in Thailand: it's a 500 ml bottle that is similar to the 20 oz. and 24 oz. here, the ones with the bulge at the top and bottom. But the Thai version has only very slight bulges (about 1/16") and is otherwise nice and thin (2.5"). I brought back a dozen, and the customs guy was a bit flummoxed by someone bringing a bunch of "trash" home from Thailand...
JAPAN
One of the major reasons I went to Japan at all was to meet with Shushi Shiota and other water rocketeers, and I'm happy to report that this "First International Water Rocketry Conference" was a resounding success. We laughed a lot at my bad japanese and their bad english (I took Japanese classes years ago, so I can sometimes actually construct understandable sentences, but my "toolbox" of verbs and nouns is woefully inadequate for discussing anything but eating and sleeping :-) Their english was actually very good, though they didn't think so). Much consulting of dictionaries ensued when trying to explain delicate technical points. Much information was transmitted, in both directions. (See a few Quicktake photos of the event taken by Shiota-san here). Here's the group: note the table cluttered with McDonalds take-out food and nose cones :-) Shiota-san is at the top right, in the yellow shirt.
Water rocketry is very popular in Japan: there are 6 books on the topic that I saw (I got 5 of them: I can't read them but the pictures are nice) and there are hundreds of entries in the regional contests they have: the usual event is maximum distance, and the rules carefully specify such things as legal materials for construction, etc., so everyone is on equal footing. To give you an idea of the scale, in a recent contest there were 267 entries, 230 of which actually launched. 171 of those stayed in bounds and were measured. The winner achieved 127.33 meters. Also see the pictures from a Japanese water rocket "idea" contest that Shushi sent me.
Here are some shots of the many rockets that Orii-san (our host, seated on the right in the above picture) had in his office. The "whimsical" rocket in the second shot was never launched, to my knowledge, but sure was cool. Note the little man inside the clear section near the top.
I was also treated to videotape from a couple TV shows, some of which was very interesting. In particular, a gentleman named Hiyashi-san is a physics teacher and something of a "water rocket genius" and he had a 3 stage rocket with two attached "boosters." Here's a photo of Hiyashi's big rocket scanned from a Japanese science magazine:
The "standard" Japanese water rocket is made from 1.5 liter bottles, a very common size in Japan. There is one pressure tank, and a second bottle is used to extend the length of the rocket. The fins, 4 of them in a clipped delta configuration, are also made from PET cut from a bottle. ALL Japanese water rockets use plastic hose quick-connects as launchers, so all of them have choked-down nozzles as well. PCAJ (PET bottle Craft Association, Japan) sells two "kits." One, the rocket kit, consists of a green foam rubber nose cone and a male quick-connect nozzle with threads that fit a bottle neck. The second is a launcher kit that is simply a plastic quick-connect (the female, mechanical part) and a tire valve to attach to it. You can build your own "stand" for the connector, and launching is usually by hand: your arm gets wet :-)
They also sell fancier launchers, a molded plastic one (below) and a deluxe one that looks like a camera tripod. Both have a sort of shelf support to help get the rocket off the launcher straight. They used to include remote-control triggers, made from bicycle brakes, but there was apparently an accident (one kid fooling with the release while another was in front of the rocket) so the PCAJ no longer recommends remote release.
There are two parachute systems in wide use. One is Orii-san's invention, a "set the top part on the bottom part and launch" system, where air pressure and/or acceleration keep that two sections together until near apogee (remember that all japanese rockets are "nozzled down" so the acceleration is smooth and slow). There are some nice refinements here: the top section is long, more than just the nose, and there are two parachutes, one for each section. At the joint, each section is wrapped once with weather stripping. This provides a nice resilient "shelf" at the joint, which (I think) really helps them stay together. Here's a line drawing of this system, scanned from one of my Japanese water rocket books:
The other is much more mechanically involved. There is a spring-biased hatch near the tail of the rocket that contains the parachute. It is latched closed with a rod that extends through a hole in the latch. The rod is mounted parallel to the body of the rocket, and has a sliding weight, a fishing weight, on it. When the rocket tips at apogee, the weight slides forward, hitting a stop on the rod and thus pulling the rod forward a bit, enough to release the hatch, and thus the parachute. Here's a diagram, again scanned from a book:
I presented my airspeed flap parachute system, and once I got the basic idea across, they seemed to like it. I kicked myself for not bringing one along, it would have packed very small in my suitcase, and would have made explaining it MUCH simpler. Nothing I saw in Japan was airspeed-sensitive, only pressure or "tipping" sensitive, and we talked for a while about the various possible "triggers" on a water rocket: pressure reduction, airspeed reduction, and attitude change (like tipping at apogee). Can you guys think of any other changes during flight that could be used to trigger an action? I can't...
I also saw several staging machanisms, one of which impressed me with the simplicity of it's basic operation. First, the more complex one:
It used a quickconnect to hold the sustainer on, and some sort of piston (the details aren't entirely clear) that was hooked into the booster's pressure tank to hold the quick-connect closed. When the pressure in the booster is reduced enough, the piston lets go and the quick-connect is allowed to release.
The other one is based on a beautifully simple idea, though realization is a bit tricky, as you'll see: Basically a piece of rubber hose several inches long that just fits into the nozzle of the sustainer is connected to the top of the booster, plugged at its top end, and inserted up into the sustainer. As the booster is pressurized, the rubber hose expands, locking the sustainer to the booster. Beautiful, no? But if you think about it a bit there are complications: one obvious one is how is the sustainer pressurized?
Well, there's a lovely solution to that one: japanese bicycle valves. These are unique: the internal bit is a cylindrical piece of steel (actually slightly conical, but that's an unimportant detail for now). A hole is in one end ("upstream"), and the exit for that hole is out the SIDE of the cylinder. A small piece of rubber tube is stretched over the outside of the cylinder, covering the exit hole, resulting in a special kind of one-way valve that won't allow air to pass at all in one direction, and in the other will only allow air to pass if the difference in pressure between the two sides is large enough to lift the rubber tube. One of these valves is used to plug the end of the rubber tube up inside the sustainer. So as the booster is pressurized, the rubber hose swells first, then as the pressure inside the hose becomes enough greater than the pressure inside the sustainer, the valve bleeds air into the sustainer.
The valve seems to maintain a pressure difference of 15-20 psi. I'm sure this can be modified with different kinds of tubing. In fact, the little valve inserts I bought in Japan came with 4 different pieces of tubing, I'm not sure why but maybe it's for this reason.
Here's where things get a bit fuzzy, though. According to Shushi, a second valve is also required, pointing the other direction, back into the booster. Otherwise, he says, the sustainer lets go too soon. This makes sense: unless there's something holding the pressure in the tube, then as soon as the pressure in the booster is reduced by the valve differential (20 psi) the tube will un-swell and the sustainer will let go. But if there's a second valve pointing into the booster, then pressurizing as above won't work. I have some drawings of one system that involves three different sizes of tubing and two valves and some other piece I can't identify, I've stared at it at length and can't quite get it. Then there's a web page, in japanese, at http://www.na.rim.or.jp/~kazushig/wr/wr_4.html, about muliti-stage rockets with several drawings, and this one I think I understand, only because I have a few of the valves in hand. I believe the valve can be modified to allow air to pass unimpeded "backwards", while still performing it's valve function in the normal "forward" direction. One of these valves installed on the booster side should do the trick: while pressurizing, air passes unimpeded backwards, but but is then trapped "upstairs" unless the pressure in the sustainer (and thus the rubber tube) is 20 psi greater than that in the booster.
OK, enough detail on that. The basic idea is excellent, I think: a rubber hose that expands inside the sustainer, thus locking it on. The details look tricky, but are, I think, easier to deal with than many of the other staging ideas we've had, and probably MUCH easier to build without specialized tools.
BTW, I'm not sure but perhaps shrader valves can work the same way? High pressure on one side will let air through? And then there are the "presta" valves on European bikes, I don't know how they work but I want to look into it. I think that the Japanese valves may be tough to find in the US. I believe English bikes use the same valve, if that helps any.
There are several commercial water rocket toys avalable in Japan as well, I bought one with a parachute system. Launch report to come, as soon as I've launched it (it's been too windy here lately).
OK, I'd better go, this took longer than I anticipated to type up/put together.
Dave
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