Zoooosh
Shirley the first rule should be that the hull is based on a commercially available fizzy-drink container?
Our report yesterday that a water rocket formed from "2 x 2l fizzy drink bottles" may have ripped past an Airbus A321 departing Birmingham airport last year prompted some readers to mull the possibility of having a pop at the water rocket world altitude record. The current "Class A" (single stage) record stands at 825m (a …
They were talking about it's length rather than width. We already have appropriate measurements for this. It would have, of course, been significantly better if they had reported the distance travelled accurately though. This sloppy journalism mathematics isn't appropriate for El Reg.
I have kept all to 4 decimal places for ease of typing. As the rocket was travelling at 550km/h (or 152.7778 m/s) in 0.75s it will have covered 114.5833m.
A ruby pitch is between 112m and 122m, this article is suggesting that the speed could have been anywhere between 537.6km/h and 585.6km/h. Accuracy is key. It would have been much more appropriate to have stated that it would have covered a distance of 15 double decker buses (or 1 Brontosaurus) in a princely time of 0.9051s.
I wonder why El Reg even maintains its conversion page, I really do.
By any mode of transit, fucking aaaaaaaaaages. The roads go round and round the mountains, the trains are non-existent except up the coast if you don't mind them being some miniature gauge, the bus follows the road, on foot you'll be cold, miserable and exhausted (see mountains), by air you have to go up and up to avoid the mountains and the rain clouds... really, it's not worth even setting out.
Back in the day when a standard type valve from a bike tyre was just the right size to jam into the nozzle of a washing up liquid bottle, Fairy Liquid being the best, and everyone had a bike pump, it was easy enough to make your own at no cost. Lego or meccano was useful for building launch towers too. It worked best with an adapter and dads car foot pump.
It wasn't exactly predictable when it would launch since it depended how hard the valve was jammed in.so there were one or two "rapid unexpected dis-assemblies". In my defence, I was only about 9 at the time.
"featherweight record-breaking rocket that is 2.68m tall yet weighs less than 1.5kg"
"The rocket produced 550kg of thrust – enough to lift a small car off the ground – and blasted off to 550km/h in under 0.5 seconds"
I am guessing the 1.5kg weight is without fuel - even so, 0 - 550km/h in 0.5s sounds like way too fast too soon. Wouldn't you be better off distributing that thrust over a longer time? Are they not wasting a lot of DV trying to go too quickly through the atmosphere?
Using a lower acceleration means that you're wasting impulse lifting the remaining mass of your fuel for a longer time, hence you'll get a lower altitude. Blasting it out all at once means that more of that potential energy stored as pressure is used to push the vehicle alone, getting you to a higher altitude.
As long as you're not worried about the effects of too-rapid acceleration on fragile payloads (Fleshy water-bags like passengers, say) you're best off using as much of your launch fuel as possible to accelerate you as quickly as possible as early as possible in your flight.
Note: I am not a rocket scientist.
Draw a graph of atmospheric pressure over altitude. Is the line straight or curved?
http://www.engineeringtoolbox.com/air-altitude-pressure-d_462.html
It's curved. Ergo, expending all your thrust at launch is not the most efficient way to gain altitude.
According to that graph, at 1km up (Which is how high the vehicle got), there is ~2.3% less pressure than at sea level.
"Using a lower acceleration means that you're wasting impulse lifting the remaining mass of your fuel for a longer time, hence you'll get a lower altitude. Blasting it out all at once means that more of that potential energy stored as pressure is used to push the vehicle alone, getting you to a higher altitude."
If you expend 100% of your fuel in the first 1% of altitude, it means that you have to travel the remaining 99% (Through the least efficient part of the graph) with no power at all, and that you have way less inertia. So expending all the fuel at the start is not all good - there are up-sides and down-sides.
How do you propose to distribute the thrust?
The only way to distribute the thrust is to reduce the pressure (so the water takes longer to be spat out of the 'fire end'). And that reduces the energy stored.
Additionally, distributing the thrust means that you have to lift some of your reaction mass (water) - whereas dumping it all in the first 0.1s means that none of it is lifted beyond about 4-5m of the ground. That leads directly to more energy in the rocket.
Yes, the atmosphere is a bit of a pain - I wonder if they can take a water rocket with them to the moon next time - see how well it goes there ;)
D'Oh - of course you are right - that is the way to distribute the energy.
My brain got stuck on the new Ro-Kit I got for the kids (cough) recently.
But on the basis that all the serious (single stage) rockets still use very short "burn" times, I'll stand by my suggestion that lifting the reaction mass is probably a bad idea.
"The water rocket competition is very exciting, as it uses only water and air – very environmentally friendly"
Technically speaking, the Space Shuttle Main Engines only used water (well, its component parts anyway). Wouldn't call it environmentally friendly though.
More than enough to lift a Fiat 500 (the original): 499kg, 118.80952 jubs. It would also easily, although briefly, significantly increase its acceleration*.
* They're remarkably spiffy when fitted with a Moto Guzzi engine, but still sluggish compared to a Goggo with a 9 cylinder radial.
Fiat 500 - one of my favourites. The Abarth versions move very nicely, too. The Fiat 500 Giardiniera is the original minivan IMO.
There is one original Fiat 500 that was recently converted to accommodate a V12 Lamborghini motor. Bit of an abomination, but fast...
http://www.spiegel.de/auto/fahrkultur/fiat-500-getunt-mit-einem-motor-aus-einem-lamborghini-murcielago-a-901161.html
Rust is pretty close to half as heavy again as bare steel, until it falls off that is.
Per unit volume, that is. But if you let a piece of steel turn to rust, it'll still contain the same number of Fe atoms, plus the now added O, so the total weight will have increased.
Its weight will indeed be lower when it falls off, but only during the fall.
I'd budget at least £20,000 in manufacturing costs to build a rocket to *perhaps* beat the current water rocket record; a filament wound carbon fibre or aramid pressure vessel is almost certainly needed to contain the pressure and keep the weight down, given the thrust to weight ratio needed. That figure assumes the design is done for free, and that someone is available who is capable of designing the nozzle for the waterjet, which is really a job for an expert in the field.
Not sure about your pricing. Carbon fibre is really quite a home tech thing, you can buy a 2kg reel of carbon fibre string for 80 quid, a bucket of epoxy would hardly break the bank. There's some tricky tooling and you'd probably need to be able to borrow a decent lathe for the nozzle and cone, but again possible for most students although harder for the rest of us.
I also wonder about the nozzle, given the reaction mass is an incompressible fluid is there very much you can do with it?