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A water rocket is a type of model rocket using water as its reaction mass. The pressure vessel (the engine of the rocket) is constructed from thin plastic or other non metallic materials (usually a used plastic soft drink bottle) weighing 1,500 grams or less. The water is forced out by compressed air. It is an example of Newton's third law of motion.

My best WRONG reading?

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My best WRONG reading?

Post by Braaainz » Fri Sep 14, 2018 7:17 pm

I'm using a Jolly Logic Altimeter 2.
Altitude 376
49 mph top speed
1.40 thrust time
Peak acceleration 12.5 g's
Average acceleration 8.4g"s
Coast at apogee 3.6 seconds
Ejection 342
Duration 31.7
Descent 6
Apogee ejection

Does this look correct? I don't have a computer to run a simulator.
Seems way too high to me.

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Re: My best WRONG reading?

Post by anachronist » Wed Feb 06, 2019 12:30 am

I'd have replied sooner but for some reason all the WRA2 email notices were ending up in my spam folder, and I just noticed it now.

If you provided some additional information, I could run it on my simulator.
  • What is the total volume of the pressure vessel? (e.g. 2 liter bottle, whatever)
  • How much did you fill it?
  • How much air pressure did you pump into it?
  • What is the diameter of the nozzle?
  • What is the weight of the rocket before filling with water?
Quick and dirty calculation, assuming constant 8.4G acceleration for 1.4 sec:
8.4G = 8.4*9.8 = 82.3 m/s/s
v = a*t = 82.3 * 1.4 = 115.2 m/s = 257 mph, which is way off the top speed recorded.

I'm skeptical of that thrust time if it's a bottle, typically the thrust is over after about 0.1 sec, not 1.4 sec.
Need more info.

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