Water Rockets

[Andrew_90]

I make these for my grandbuddies (grandchildren). A new batch of grandbuddies is now of suitable age so fun time for them. Just need to make a manual parachute deployment system as these thing come down fast and hard, without parachutes you destroy a parachute per launch.

The basic principle is that the 2l soda bottles are linked in the middle to give 4l total volume. A charge of about 600ml of water is about right to launch the rocket a good couple of hundred meters into the air. I mix red dye in the water for extra effect. The bottom bottle has a Gardena male fitting.

The launcher is a female Gardena that has a rotary action and NOT a pull action. A lever around the bottom Gardena fitting attached to a long piece of string is the "trigger". The bottles are pumped to a couple of bar.

Great fun, I love seeing their reaction.

[Yummyrum]

I like it . Used to do that with my kids . I like the Gardenia idea . The release mechanism was always the curly but .

How do you hold those two bottles together under pressure ?

[Andrew_90]

I put a squeeze of silicone sealer between the opposing bottles just before assembling.

[elbono]

I loved those when I was a kid!

Mine were the dime store version with a hand pump. They had adjustable fins, made it spin on the way down so it wouldn't break. Bend them too much and it wouldn't go very high though. It didn't matter to me I still got wet.

[contrahead]

The bottom bottle has a Gardena male.........The launcher is a female Gardena ..................... The bottles are pumped to a couple of bar.

Of course we now know, that your talking about something like this:

changeshot004.jpg (6.88 KiB) Viewed 2674 times

But as far as I'm concerned, a "Gardena fitting" isn't common language. So I had to look it up. If you Google-up a "female Gardena", then you get a bunch of pictures that look like this.

Of course I knew what you meant by "bar". Barometric pressure (1 bar = 1 atmosphere) approximately . In SCUBA, 2 atmospheres means your body is being squeezed with 2(14.7 lbs / sq.in.) pressure; and that you are about 33.8 feet down.

[You can hang around at that depth as long as you wish or untill your air runs out, which ever comes first. But if you dive down to 4 atmospheres (100' / 30m), you should only stay for less than 19 minutes (any longer requires decompression)].

I looked up barometric pressure to remind myself of a few facts. Everything has gone to metric, which is not welcome, but is no surprise. I don't like pesky “pascals”, just like some children don't like to eat their spinach, or beets or liver. But then a “bar”or a “millibar” which are so common and so frequently mentioned, are not even officially recognized SI units! Pishaw...

1 bar = 100,000 Pa
1 bar = 0.1 MPa
1 MPa = 10 bar

Some newer aneroid barometers don't even sport an "inHg" scale any more.

1 bar = 14.7 psi
A normal (antique) barometer needle should hover between 29.8 and 30.2 inHg (inches in Mercury). Unless a storm is coming.

[Andrew_90]

Embrace metric, I can work in imperial and often due as many of my interests rely on this. Shooting is always in imperial, distilling for the most part etc.

Metric is so easy, to dividing and multiplying by 10 is the easiest thing. Both are valid. With metric you can measure more accurately.

[Ben]

Metric is so easy, to dividing and multiplying by 10 is the easiest thing. Both are valid. With metric you can measure more accurately.

You telling me a set of SAE micrometers are less accurate than a set of metric micrometers? Fallacy.

[NormandieStill]

Metric is so easy, to dividing and multiplying by 10 is the easiest thing. Both are valid. With metric you can measure more accurately.

You telling me a set of SAE micrometers are less accurate than a set of metric micrometers? Fallacy.

Actually your set of SAE micrometers were ultimately calibrated against a metric standard.

[BourbonStreet]

I used to have a toy similar to this when I was young. It was basically a bicycle pump with a hollow plastic rocket on the end. I haven’t seen them for sale in a long time. I guess they got pulled off the market like lawn darts did.

[Ben]

Metric is so easy, to dividing and multiplying by 10 is the easiest thing. Both are valid. With metric you can measure more accurately.

You telling me a set of SAE micrometers are less accurate than a set of metric micrometers? Fallacy.

Actually your set of SAE micrometers were ultimately calibrated against a metric standard.

No shit? And how does that effect accuracy?'

Here, I will answer for you: It doesn't. The little number that is engraved on the side of any measuring device is just a number. It doesn't matter if it is SAE, Metric, API, whatever. The same with a volumetric flask, a scale or balance. It's just like switching your digital calipers from standard to metric, switching to standard doesn't mean they are automatically inaccurate, the accuracy of the instrument does not change, only the competence of the operator.

[NormandieStill]

Sorry. Didn't mean for you to take that seriously. Obviously your imperial micrometer is just as accurate as a metric one. I just find it amusing that for some time the ultimate measurement of accuracy has been a metric standard.

And 1/32" provides slightly greater precision than a millimeter.

I don't think either is inherently more accurate. I do think that when the rest of the world and the entire global scientific community has embraced a standard, it might be time to accept it and move on. This comes from being raised in the UK where I was taught in metric, but expected to know imperial. Where I was sold vegetables by the pound by paid per kilo. And where I measured distances in meters but all the signs had miles on them. The metric versus imperial argument feels like it should have been over some 40 years ago already.

[Setsumi]

In 1970 when South Africa changed to metric from imperial properties got 2.5 times smaller, distances increased almost double, fuel per volume quadrupled and credit repayments doubled. Maths did get easier though....

Edit, forgot to include... produce weights more than halved.

[jonnys_spirit]

What about 1000'ths of an inch?

https://en.wikipedia.org/wiki/Thousandth_of_an_inch

Accuracy isn't the accurate term here - Tolerance might be more precise?

Cheers,
j

[elbono]

The U.S. is going metric, inch by inch...

[BourbonStreet]

The US was the first with metric money, everyone forgets that.

There’s a crazy legend about the US not using metric measurements: supposedly, Thomas Jefferson wanted to go metric during his presidency, and asked for a sample kilogram from France. It was sent via ship, but the ship was captured by pirates and never got to America.

[ShineonCrazyDiamond]

Please keep this off topic, on topic .

Thanks.

[cranky]

I can't believe how this one went so off topic so quickly...that said I feel the need to say

I'LL NEVER UNDERSTAND THIS DECIMAL NONSENSE IF I LIVE TO BE C!!!

Andrew_90 Great idea bolting the two bottles together I might have to try that.

When I was young I loved those store bought water rockets. I bought them frequently (whenever I could get to the store that sold them) because they would get taken away because I would shoot them at my brothers