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Two or three drops of fuel! That's a very counterintuitive contraption! I would really be reluctant as a teacher to bring a flame near something made entirely o

Two or three drops of fuel! That's a very counterintuitive contraption! I would really be reluctant as a teacher to bring a flame near something made entirely of plastic... and with no fins or guidance control on a ballistic trajectory? I mean it's an air-filled soda bottle, but still. 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 loved water rockets as a kid and I also enjoyed actual model rocketry, except they seemed too hazardous for me to find a launch area where bystanders felt completely safe. Model rocketry is sometimes 90% modeling, and 10% launching them. Estes can make some really precious designs that fly horribly but look great in a Plexiglas cube on your shelf. I lost most of the ones I built due to poor launch conditions, and while I chose deserted school campuses during vacation or weekends, I didn't make any friends with security patrols there!

kelseydh 2y ago
It looks like a pretty fun demo to do for students: https://youtu.be/xZ3hRrdj7Y0?t=445 https://youtu.be/xZ3hRrdj7Y0?t=445
tbrownaw 2y ago
> 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.
userbinator 2y ago
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-be-expressed-as-an-area/comment-page-1/ http://theskepticalzone.com/wp/weirdly-fuel-efficiency-can-b... [1] https://en.wikipedia.org/wiki/Standard_sea-level_conditions https://en.wikipedia.org/wiki/Standard_sea-level_conditions

kelseydh 2y ago

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

tbrownaw 2y ago

> 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.

userbinator 2y ago

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-be-expressed-as-an-area/comment-page-1/ http://theskepticalzone.com/wp/weirdly-fuel-efficiency-can-b... [1] https://en.wikipedia.org/wiki/Standard_sea-level_conditions https://en.wikipedia.org/wiki/Standard_sea-level_conditions