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10#
发表于 2010-11-24 05:33
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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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19#
发表于 2010-11-24 05:35
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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
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25#
发表于 2010-11-24 05:37
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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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27#
发表于 2010-11-24 05:38
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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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29#
发表于 2010-11-24 05:40
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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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40#
发表于 2010-11-24 05:43
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Since semi-retiring my 4x4 airframes, they have found many uses. This one the torch bearer. It serves most proudly.
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