www.pulse-jets.com

I'm posting this in valveless, but it's relevant to valved as well. I could have put it in Mark's youtube thread in offtopic, but I think it's good enough to merit its own thread. Basically, what we have here is a guy filming a big clear spudgun in extreme slow motion, and although he's not (entirely) looking for it, it has a lovely film of kadency in action.

Enjoy.

http://www.youtube.com/watch?v=_TNSUIsjdpY

There was one critical viewer comment about the video worth noting. Tough crowd out there. To be honest, I would have liked to seen multiple tests with the speed of the projectile. I wonder what the ideal combustion chamber to barrel length would be? And what would the ideal diameter of combustion chamber to barrel ratio be for something around the size he was using?

Mike Meyer3 days ago
+SmarterEveryDay I hate to pick nits, but I think you fell just short of doing science here. Not that this isn't cool, and fun, and informative - but you fell just one notch short of what I'd call science. Your hypothesis is that igniting in the middle will work better (which we can loosely define is giving your potato a higher exit velocity), and you designed an experiment that created the two conditions you wanted to compare - but you didn't measure anything that would tell you whether or not the hypothesis was right! You just trusted your intuitive interpretation of what the gas flow - which you cleverly and neatly made visible - was doing.Part of the issue is that my intuition - which comes from sail and wing airflow analysis, and is certainly not as good as yours - is that the middle ignition will spend more energy doing things that don't help your cause, so the middle ignition will be worse, not better. So I want some kind of measurement of the end result so I can compare things quantitatively. Say, measure the potatoes movement between the last two frames before it exits the barrel, or the time from ignition to exiting the barrel, or something to give you a quantitive measure of how well you did? It's that step - moving from your intuition (and I don't trust mine, so you'll forgive me if I don't trust yours) to a comparison of measurements that transforms it from cool messing around to science.
I mean, he started down the path of the scientific method, with a hypothesis and and experiment designed to test it. He just didn't show the measurements that would have demonstrated the truth or falsity of the hypothesis and thus completed this science.

And there was this.

kuroibuta3 days ago (edited)
I'm sure if he did what you ask, it would be a long and boring video. He is just trying to teach us something and give us entertainment. Not make a PHD.
Reply3
Mike Meyer
Mike Meyer3 days ago
+kuroibuta In that case, he should wear a T-shirt about infotainment, not one about science. And change the name of the channel from "SmarterEverDay": to "EntertainedEveryDay".But I think you're wrong on both counts. I think doing a single measurement on one or two examples and an explanation would add maybe a minute, so not long. And I'd be interested in seeing it, so not boring. It would be no worse than taking the time he took to explain his hypothesis.

Awesome camera work catching that. Thanks tufty.

would be awesome if someone in the forums could run a few experiments

what material is this exactly?

clear rigid PVC?

Yep, that's clear pvc.

IIRC Mark had a bunch of borosilicate tubing a while back, but going from "bits of clear tubing" to "clear pulsejet" is a far from easy step. Even if it's only going to run for a few pulses at a time. Not sure if Nick didn't do something, waaay back when in the days of the old old forum, with a clear wall on a square section jet.

I've probably got the names mixed up, though.

At first I thought this was a fancy quartz window but as you see it isn't.
https://www.youtube.com/watch?v=cS1_1GkeTnI