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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.

Time to re-think the class D World Record Category?

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mac_xpert
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Time to re-think the class D World Record Category?

Post by mac_xpert » Tue Nov 13, 2018 6:48 am

Apologies for the controversial title to this post!

As a newbie to the water bottle record world, it seems like the class D title is currently unbeatable unless you can travel to a launch location that is at high altitude with warm weather. The online calculators all seem to say that the current record is well beyond expected altitude for the constraints.

Its difficult to see how 417 feet (127.1 meters) could be beaten with a 100Psi / unmodified 2L bottle limit? (apologies if i'm missing something!)

Am i the only person who thinks this? Am i missing the point? I'm not sure if you're trying to encourage people to have a go or just display the one highest record for ever...

I'm not trying to rock the boat, but i'm just putting over the point of view that as a newcomer i certainly don't feel that its worth even attempting to try and beat it, as i can't see any angle for experimentation or development.

Perhaps some other classes need to be added that people can attempt (I note class E is currently not claimed).

If i'm stirring things up i could comment that the current class C record is also held by someone with access to a hot climate and thermals to launch into... just saying!

Apologies if this all comes across as a bit negative, but the rules for the latter, unmodified, classes all seem to start by saying they are great for groups to try out, but as a newbie reading them i just think - that's not even worth trying to beat. I don't think i'm the only one?



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Re: Time to re-think the class D World Record Category?

Post by WRA2 » Tue Nov 13, 2018 7:04 pm

Hello mac_xpert.

There are more ways to go higher then just launching in warm weather. How about a lighter payload bay, or what about a lighter bottle or a more aerodynamic shape bottle? World records are supposed to be hard to achieve and usually stand for a while (which makes the effort to achieve one worth it) until someone else comes up with a "better mouse trap". The class A record was held by one team for 10 years before another team beat it.

As you mentioned, there are several classes that do not have records yet. Why not go after one of them.

The pressure limit and volume limit for the Class D was put in place to keep cost of participation in check.

Also numerical simulations do not tell the whole story about how high a rocket will fly (especially if you do not "tune the simulation" to an actual flying rocket. In other words, fly a rocket and record the altitude, pressure, weight, etc. and then input the numbers into the sim. Then play with the values like drag until the simulated flight matches the actual flights.

Hope that helps. Good luck with whatever class you attempt and please fill out the membership application.
http://www.wra2.org/WRA2_Membership_Application.php

Once you complete the application, you will be granted access to "members only" content in this forum and be eligible to compete for the records.


Lisa Walker,
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:WRA2:The Water Rocket Achievement World Record Association :WRA2:

mac_xpert
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Re: Time to re-think the class D World Record Category?

Post by mac_xpert » Wed Nov 14, 2018 6:18 am

Thanks for the reply,

I take your points, but the limitations of 100Psi AND unmodified bottle AND 2L limit, there is very little room to try the things you mention. e.g. More aerodynamic is unlikely to be achieved in unmodified, commercial bottles.

Have you considered classes with only a pressure limit, or only a volume limit? that would keep costs down (pressure being the biggest cost factor), but allow much more space for experimentation and different ways of tackling the same problem.

Another thought would be a dual requirement, e.g. smallest / highest rocket where it 50% weighted on the physical volume and 50% on the height achieved?

Just some thoughts for categories that might encourage participation?



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Re: Time to re-think the class D World Record Category?

Post by anachronist » Wed Feb 06, 2019 12:44 am

Hi mac_xpert. If you look at the threads here over the past couple of years (in many cases initiated by me) we had extensive discussions about revamping the rules, which was done last year. A new "anything goes unreinforced" class E was created out of that, replacing the reinforced bottle class that nobody had entered.

Yes, there is a theoretical limit for what you can do with 100 psi and 2 liters of volume. The current record has not reached that limit, according to my calculations.

Temperature and altitude are a factor, yes, so those who live in, say, Colorado in the summertime have an advantage over those who live in Canada.

However, aerodynamics matter a lot too. The current record holder managed (unofficially) to break 500 feet with just a 1 liter bottle, because he found a bottle with the perfect aerodynamic shape.

I'm confident I can beat the class D record based on my own experiments and calculations, although at the moment class C is intriguing. Sadly, I did not get to work on rocketry AT ALL last summer. But I've always wanted to try a rocket glider with wings that deploy at apogee. I've got some ideas.



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