Coke bottle rocket

I'm going to have a look at LaTex, but for simpler solutuion, which actually does the arithmetic for you as well see SmathStudio. Alternative (and might be better) is MathCad 14, which seems now to be a free download

Thanks Dave, all explained. I had just wondered if there a version of LaTeX which converted from DVI to jpg directly . The developers of this excellent code will get a well deserved rest at the 762nd point of Pi - 999999 and so on....

Rob

In the bottle rocket,the way I see it is the mass of the expelled fluid relative to the mass of the projectile tells the tale;water shoves it along quite nicely,but when just air is released,the bottle hardly notices it,couldn't care less,really.Enter Murphy's third law"If one Can get wet,one Will get wet"Someone might try Coca Cola as a working fluid,as things go better with Coke.

I've looked at this. While the speed of the gases is 1.25 to 1.75 times the speed of the projectile, the weight of the gases is the weight of the propellant . 35-70 grains compared to ~200 for the bullet (to keep mike happy) so the kick from the gases will be smaller (say 1/2 to 1/4) than the kick from the bullet.

Sorry to be a nerd!

It's ok but I think it depends upon the specifics of the charge and bullet combination how efficiently all of the energy is transferred to the projectile. I think it probably depends on the comparative length of the barrel to the calibre - relatively long barrels with small light projectiles will tend to have less secondary recoil.

I agree with your gas weight but I think that your gas speed may be a bit low in some cases but the major missing effect is that there will also be a time factor in operation. I think it's quite likely that the gasses will continue to escape for some time after the bullet has left the barrel and the charge gets completely burnt. In effect the charge may be acting like a rocket motor for some time for relatively short barrel lengths or high calibre/mass projectiles.

Muzzle brakes were designed specifically to reduce the magnitude of the secondary recoil and have no impact on the primary. I think they were first used on the 25 pounder FG but could be wrong.

My gut feeling is that if the secondary recoil was always only relatively small compared to the primary they would have negligible effect and wouldn't get used much but that's clearly not the case. They even get used on handguns to limit muzzle lift, AK47's and and .50 calibre sniper rifles.

This may be interesting... **LINK**

Jon

Thanks for the pointers Duncan, I'll have a look at those. A easy to use package that does the sums as well as display the formula would be rather useful.

latex is aimed at a rather different target. It's for producing publication quality maths papers, theses, books, and articles etc. As such it does various standard maths publication formats extraordinarily well, but it can't crunch numbers itself. I use it the old-fashioned way with a text-editor: but there's TexMaker and TexStudio if you want a GUI with advanced features.

Open Office and Word both have maths extensions that can produce many of the symbols, but the typist has to arrange the formatting himself. Fine for small examples but a real pain writing a big document.

My own usage is far more likely to be on a small scale than big, so thanks again for the suggestions.

Dave

Wikipedia looks to have a good overview of recoil. I haven't had time to read it properly or to try and redeem my shattered reputation. Somehow I've lost momentum on this one...

Dave

All my shooting experience is with airguns, I don't really have the practical experience to go further, but it's an interesting diversion!

Neil

As the thread is about Coke Bottle Rockets, I wonder if the group could put their minds to optimising CBR performance? For starters:

• What's the burst pressure of a 2L coke bottle?
• What's the optimum ratio between water and compressed air?
• What's the maximum height and time of flight that could be achieved on earth?
• What's the most efficient way of releasing the rocket once operating pressure is reached?

Could be the new IMLEC!

Cheers,

Dave (who should be cleaning aluminium out of clogged files)

Well I'd consult NASA... **LINK**

Yes, really

Jon

You can check this with our aeromodelling colleagues. 2L coke bottles used to be used as gas tanks for CO2 motors. I don't recall the figure but it was very much higher than I expected.

Dave

Thanks Jon, very useful link!

As guidance it suggests a distance of 102m at 80psi, also that bottles should never be pressurised above 90psi. (As there are children involved, I assume this implies a safety factor of 2 or 3, and that bottles will fail somewhere between 200 & 300psi )

I'm just off to see if I can get the simulator to work: it appears to be the last word on bottle rockets.

Dave

Duncan,

Many thanks for the link to SmathStudio which has filled a gap in my software armoury.

It fired up straight out of the box on Windows 10 and experiments with it have all been very positive. Not too difficult to drive and it even does units. If only such a thing had existed when I was struggling with maths at school - mankind has come a long way from my error-prone fights with a slide-rule and 4-figure Tables.

For linux fans, it runs as a mono application. Ubuntu 16.04 automatically downloaded and installed the mono run-time but then SmathStudio crashed with an exception equivalent to 'missing DLL'. This was easily fixed by manually installing the complete mono package with 'sudo apt-get install mono-complete' Limited testing hasn't found anything wrong with the mono version on Ubuntu.

The chief shortcoming is that the display is utilitarian. Perfectly understandable but nowhere near as good looking as latex. The two complement each other though: do the sums with SmathStudio, and type them up with latex when you need publication quality.

Thanks again,

Dave

More basic and very little precision,

I made this bottle launcher for the children, a little while ago

Not quite ready for a moon trip yet . . .

Like it!

The great Aeromod Doug McHard used to wrap his bottles in fibreglass tape before installing them inside model aircraft.

Neil

SoD,

I'm glad you founf SMath useful, Mathcad gives better presentation, and draws graphs, which SMath seems to struggle with. If you're really into it it can do programming as well, but that makes my head hurt, I'd switch to C for that

On the coke bottle front, several clubs have in the past had a competition for how far you can get a rail vehicle to travel with the stored energy inside a coke bottle. The pressures quoted frightened the life out of me! Plenty of scope for reaction rockets, little air motors whatever

Cripes !! Those kids haven't got eye protection or hard hats !! And the rocket' going to hit the upper window!

Edited By Hacksaw on 12/10/2016 22:21:00

"Made the launcher for the children"......I've used that excuse too!