NASA Whoosh Rocket

I'm 66, and when I myself was 10 or 11 my friends on my street and I were completely obsessed with the Estes rocket and Cox .049 U-control scenes. Most of us were lucky enough to have engaged fathers and once the standard craft were assembled and flown, we all browbeat them mercilessly for more information for mods, shortcuts, hacks etc. My dad grew very wary of the 'Why can't we' type questions. I had modified a C-type engine Big Bertha rocket with an extra long transparent payload module which set the stage for various kidnappings of lizards, frogs, praying-mantises, eggs, multiple 1 and a quarter inch sockets, etc (all returned to earth unharmed, if not un-rattled). The nichrome wire igniters were troublesome for most of the kids. Bulky and expensive (for 4th graders) lantern batteries were hard to come by. We found we could steal D-cells from flashlights, hack cardboard tubes from paper towel rolls, reinforce with electrical tape, and make passable energy sources from that, etc. But all of that required questions from the closest available parent about voltage and series/parallel connections, as well as other questions about CG when modding the rockets themselves, etc. I think your STEM comment is very much on-point. None of my friends thought we were learning anything at the time. We were mostly just jazzed about doing fun stuff that had the potential for tearing itself apart in mid-air. I know the advent digital everything makes modeling systems for kids [Kerbal,etc] probably pretty trivial now, but actually crashing things in spectacular fashion IRL had/has it's own visceral rewards.

What went wrong?

Is this you? https://i0.wp.com/makezine.com/wp-content/uploads/2016/03/Sc...

My high school chemistry teacher did this a few times with a water cooler bottle. In fact, the morning of our graduation, we were having breakfast at the school when he walked on stage holding a water cooler bottle and a lighter. I think he must have used too much alcohol that time because it blew out the bottom of the bottle and the rest of it shot several feet in the air.

I'm not sure it is a good idea to do that indoors.

Water bottle rockets have a surprising amount of energy. I managed to hit myself in the chest with one, after only a couple of pumps, and it fair knocked the wind out of me.

We also did some messing around with coke/butane rockets. These could easily knock teeth out and I made my son wear his full face cycling helmet before handling them.

Model rockets with solid fuel motors obviously require an even greater level of respect.

That is pretty impressive. Large empty spaces like that are a bit hard to come by in the UK.

Two or three drops of fuel!

The stoichiometric AFR for isopropanol is 10.4:1 according to the sources I found. For 1g of fuel you need 10.4g of air which at SSL[1] corresponds to around 8.5L. One drop of fuel does consume several liters of air to burn. The volume difference is really that huge --- and the higher the AFR, the bigger the difference; gasoline engines are around 14.7:1, and diesels go much higher when idling or under light load.

Relatedly, fuel economy expressed as an area: http://theskepticalzone.com/wp/weirdly-fuel-efficiency-can-b...

[1] https://en.wikipedia.org/wiki/Standard_sea-level_conditions

> I also seem to recall a type of toy vehicle that was propelled by some compressed gas as it slid, suspended along a horizontal wire/string, but I'm drawing a blank regarding the type of propellant right now. It seemed safe enough to use indoors, especially considering the constrained pathway.

I've heard of using ordinary rubber party balloons for this.

It looks like a pretty fun demo to do for students: https://youtu.be/xZ3hRrdj7Y0?t=445

Only one way to find out !

Soda bottles are surprisingly strong. Even if one fails, I think it would probably split, rather than creating dangerous shrapnel (citation needed).

TFA warned against using bottles other than soda because soda bottles are made to withstand a lot of pressure. Others may or may not.

I don't imagine ANY plastic bottle survives too many lift-offs.

I think so:

1. It's only a drop out two of alcohol

2. Carbonated drinks are at a very high pressure already.

I could, if I wasn't feeling lazy right now, do the math to compare the two pressures. Its easy stuff - two drops of alcohol combusted + assumption all the combustion products are ideal gases vs Henry's law for CO2. This last one will require looking up how much co2 is dissolved in the product, but thats not too hard.

But, like the other commentator pointed out.... there's only one way to find out.

Reading this in the UK, I'm not sure if "walking to school on your own" is supposed to be a safe or unsafe reference point.

I thought that children walking to school is unthinkable in the US because everything is designed for cars and public transit is inadequate/nonexistent. Made worse by endless suburbia stretching for miles. Someone please prove me wrong...

Almost certainly. But it might need to be printed out of something with moderate heat resistance.

I would think the next logical step would be pressurizing a stainless steel thermos with liquid methane and mating it to a 3d printed copper prototype manifold and turbine pump.