从无到有 建立水火箭

火箭首先我购买了一个轮胎，用轮胎的嘴子做水火箭的喷嘴如下图：

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2^#发表于 2010-11-24 05:23 | 只看该作者





Making the hole, method 1:
I find it easier to get a hole centered by starting with a small bit to make a pilot hole, then enlarging it with larger bit.  Here the pilot bit is 1/8 inch, the final bit 3/8 inch.  The bottle gives me something to hold onto while the drilling is done.  Yes, this is a crude method.  Stay tuned for a better one.
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3^#发表于 2010-11-24 05:23 | 只看该作者




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4^#发表于 2010-11-24 05:23 | 只看该作者





A sharp knife is used for gross enlargement of the hole.  It is then smoothed-up with a piece of 320 grit wet-or-dry paper rolled around a pencil.  High tech.
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5^#发表于 2010-11-24 05:23 | 只看该作者





The valve stem should be a tight fit.  Fortunately, the neoprene covering tapers a bit from the threaded tip up to where the bulb used to be, so we make the cap-hole just big enough for the skinny end to fit into, and the fatter end will almost not pull out of.
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6^#发表于 2010-11-24 05:32 | 只看该作者Cutting the valve stem
I start by cutting the neoprene around the brass core with a sharp knife, then hacksaw through the core.  Yes, you can just hack through the rubber too, but the knife cuts it more cleanly.  The sawed end is rough, but it is soft brass and surrounded by firm rubber.  It is reasonably finger-friendly, so I resist the urge to true it up.






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7^#发表于 2010-11-24 05:32 | 只看该作者





Note that there are two sizes of valve stems.  Either will work, but the longer size ("2 inch") is much better.  It gives me something to grab when attaching the valve to the air pump.
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8^#发表于 2010-11-24 05:32 | 只看该作者Test-fitting the valve stem.
I smear a little grease on the valve-stem every time it is inserted.  This makes the release much more consistent, I think.  Palmer's Coco Butter skin cream is my favorite.  Slick, non-toxic, and smells good.  Vaseline works fine too.






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9^#发表于 2010-11-24 05:32 | 只看该作者






So now we have a pressure-valve.  Time to test it.
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10^#发表于 2010-11-24 05:33 | 只看该作者I fill the bottle about 1/2 full of water, screw on the plugged cap and attach the valve-stem to an air pump.  The bottle is pointed bottom to the sky, the pump is started and the operator moved to a safe spot.
Well, the first of these was launched without any stabilizer.  It went flooey and flew all over.  Good thrust, no stability, so the next one got a stick.  It went fairly straight, but not very far.  Got caught in a rocket-eating tree and is still there after two months.  Stick heavy.  Bad aerodynamics.  Need a better stabilizer.




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12^#发表于 2010-11-24 05:33 | 只看该作者


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13^#发表于 2010-11-24 05:33 | 只看该作者Also notice how nicely the trailing end of the stick is streamlined.  Wish I had a wind tunnel!  Here is Bottle 1 going together:






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14^#发表于 2010-11-24 05:34 | 只看该作者




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15^#发表于 2010-11-24 05:34 | 只看该作者





Bottle 1 worked OK (as we shall see in the videos) but the weight of the fins suggested a larger motor would be of benefit.  So I broke down and bought a 2-liter bottle of caffeinated sugar water, and drained it.  Oh, the trials of rocketry.
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16^#发表于 2010-11-24 05:34 | 只看该作者


Bottle 1 had complained a lot while I was assembling it, flexing, creaking, groaning and whining while I squeezed and twisted it to get the fins on.  So Bottle 2 was bloated with water making it much stiffer while the fins were attached.  That helped.  More recently, I have been using the valve/nozzle and inflating the bottle with a few psi of air to make it stiff - this works even better.
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17^#发表于 2010-11-24 05:35 | 只看该作者







The finsticks are taped on with a single strip of ... Duct Tape!  My deepest apologies to all the Red Green fans out there, but this one is mine!
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18^#发表于 2010-11-24 05:35 | 只看该作者




One little strip gets them all in place, then two long ones cinch them down, but not before:
The launch lug.
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19^#发表于 2010-11-24 05:35 | 只看该作者 I looked all over for a sturdy straw but had suffered a cleaning frenzy over Christmas break and thrown everything useful out.  But there was still a broken arrow in my quiver.  It had been lost in the field for a couple of years, no doubt stepped on by the Belgian mare a few times before the tractor found it.  But a little manual straightening, trimming and sanding improved it a lot, and it is going to get covered with duct tape anyway.  It's still kind of ugly.  Sorry I showed it to you.




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20^#发表于 2010-11-24 05:35 | 只看该作者




The Pump



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22^#发表于 2010-11-24 05:36 | 只看该作者




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23^#发表于 2010-11-24 05:36 | 只看该作者




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24^#发表于 2010-11-24 05:36 | 只看该作者




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25^#发表于 2010-11-24 05:37 | 只看该作者



This funnel fits between the fins so nicely I should patent it.  The bottle is filled about 1/3 full of water and the cap with blowout valve screwed on tight.  Notice the mismatched cap color.  There is a reason for that (see below.)  The rocket is set upright on a model-rocket launch rod stuck into the ground and the pump connector attached.  Here I am using the short valve stem because that's what I had.  The long ones are much better - they give me something to hold onto while attaching the pump
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26^#发表于 2010-11-24 05:37 | 只看该作者 本帖最后由 rocketry 于 2010-11-24 05:38 编辑

The aluminum pan is the "blast deflector" and serves the purpose of keeping the pump dry.  It sort of works, but after awhile the pump stopped working.  I had to disassemble it and clean the mud out of it.  Ever since I have been throwing a cover over it.
So here, finally, are some launches.  Not all are good ones.  Each video is 1.4 megs for 15 seconds of video, much of which is the sound of the pump running.






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27^#发表于 2010-11-24 05:38 | 只看该作者 本帖最后由 rocketry 于 2010-11-24 05:39 编辑


I heard large vehicles driving up to my house, then a horn.  Out of water anyway, I picked up the pieces and headed back.  It was the tree-trimmers hired by our local power company.  They were scouting the easements getting ready to thrash the brush back from the power lines.  I showed them the water rocket.  They were intrigued. I fired it a few times.  One guy was particularly interested, and suggested using PVC pipe.  I thought to myself:  No, that's too heavy.  Even for thinwall, if you could find thinwall big enough for a drink bottle to fit into...  Bing!  The light comes on.  I am thinking airframe, he means pressure vessel.  Just add fins and the vessel becomes the airframe.  I just might have to experiment with that option soon
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28^#发表于 2010-11-24 05:39 | 只看该作者In the meantime, here are a few gratuitous shots from the field:






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29^#发表于 2010-11-24 05:40 | 只看该作者

Another little revelation:  I have been assuming that my off-vertical launches were the result of a poorly-centered nozzle hole in the cap.  But during testing, I noticed that some rockets flew funny every time, always arced in the same direction, and using a different nozzle-cap made little difference.  Now I believe that some PET bottles have off-center necks, or perhaps are not straight.  These defects aren't obvious from a casual visual inspection, so I choose my bottles more carefully now.
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30^#发表于 2010-11-24 05:40 | 只看该作者Caps Revisited
The Dasani problem:  An alternative to drilling
Notice that the bottle caps used in Bottle Rockets 1 and 2 are all blue.  That is because the nozzle holes are drilled, and I have found only one brand that has caps suitable for drilling:  Dasani bottled water.  Dasani caps do not have a gasket.  Coke, Pepsi, and all their siblings have a thin, soft plastic gasket inside the cap which provides the seal.  Remove the gasket and they leak.  Drilling destroys the gasket.  So if you are going to drill, get caps from Dasani bottles even if your tap water is good.








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32^#发表于 2010-11-24 05:41 | 只看该作者




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33^#发表于 2010-11-24 05:41 | 只看该作者




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34^#发表于 2010-11-24 05:41 | 只看该作者




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35^#发表于 2010-11-24 05:41 | 只看该作者




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36^#发表于 2010-11-24 05:42 | 只看该作者Water-Rocket Cap Holing JigAllows much better-centered nozzle holes.
Plus it is much quicker - I can crank out 2 or 3 nozzle-caps per minute.
To make the jig, a PET bottle neck is cut off just below the flange.
Since the hacksaw invariably angles, the base is sanded flush to the flange.
Using a better saw might eliminate the need for sanding.




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37^#发表于 2010-11-24 05:42 | 只看该作者

A PVC pipe fitting is used to complete the jig.  It is a 1/2 male threaded adapter.  The other end is 1/2 inch female slip, but that doesn't matter.  The male threaded portion happens to be a snug fit into the bottle neck, providing good centering.  Notice that there are two PVC adapters.  One has hexagonal flanges, the other a knurled exterior.  For my purposes, the flat hex flanges are better by far, fitting the flat jaws of my drill-press vise well, so that is the one I will use




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38^#发表于 2010-11-24 05:42 | 只看该作者

The bottle-neck is fastened to the PVC fitting with 5-minute epoxy.  Yes, I know.  Epoxy is not the best glue for either of these plastics.  But this is a low-stress application. Epoxy is quick, easy, and more than adequate.






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39^#发表于 2010-11-24 05:43 | 只看该作者 Here is the first of these (left) and today's project (right.)  Notice the sloppy glue-job on the first one.  I got in a hurry.  Serves me right.  Works OK anyway.


Mounting the jig.  Here I have cut the head off a 3/8 inch steel bolt and mounted it in the drill-press chuck.  The plastic jig is clamped in the vise, centered under the bolt, and tightened down.  Precise centering is difficult.  This is where a good indexing vise would be helpful.  Guess I ought to buy one.




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42^#发表于 2010-11-24 05:44 | 只看该作者




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43^#发表于 2010-11-24 05:44 | 只看该作者




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44^#发表于 2010-11-24 05:44 | 只看该作者




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40^#发表于 2010-11-24 05:43 | 只看该作者Since semi-retiring my 4x4 airframes, they have found many uses.  This one the torch bearer.  It serves most proudly.






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