Building a rocket to loft water?

[GL-P]

Anyone build a rocket to lift water for a contest? I am limited to 32ns. Any ideas?

 

[wwattles]

What are the other requirements and restrictions? Also, what is the objective? If it's altitude, treat it like the bowling-ball launches. If it's duration, run it like an egg-loft. If it's the most amount to break 1000 ft, set it up with sims and play with the thrust options and burn times for the weight.

Give us some more specifics, and we can be more helpful.

WW

 

[GL-P]

It's really a mix of both. Height and duration, etc

the pdf has the details. I have the previous scores

 

[edwardw]

Could you give us an idea of the scores in the past. 30 seconds isn't that big of a problem at all. I think the main thing is containing your water (I would heat seal it into bags) and having a nice single stage rocket with high thrust. Also, if possible I would tube launch it so that you can gain some additional umph from the tube. Three C11's and a B6 would be right at 32 N total. And you would have 39 N of thrust at the get go (maybe a little more) that is about 8.79 lbs so you could get a 2 lb rocket off the ground safely. Overchute it so that you get the 30 second hang time and you are good to go.

Edward

If you are really crazy you could cluster 12 A10's for 120 N thrust at the start. But there you are leaving 2 Ns on the table unused (30 instead of 32) and you have to light 12 motors at the same time.

 

[bobkrech]

Originally posted by GL-P
Anyone build a rocket to lift water for a contest? I am limited to 32ns. Any ideas?

It appears there is no advantage (points gained) to exceed a 30 second flight, so it would appear that you should add a slight margin and design for a 30+ second flight.

It would appear that a cluster of (2) D12-3s in a 50 mm diameter rocket weighing 650 gram at launch deploying a 1200 mm diameter chute would stay in the air for about 30.8 seconds.

Each motor weight ~42 grams each, and if you keep the rocket light you should be able to lift about 500 grams of water.

Good luck.

Bob Krech

 

[GL-P]

https://home.cogeco.ca/~r_c_k/contests.html

The rules have been changed tho.

I keep having the idea of freezing the water instead (which is not disallowed in the rules) Of course ice has a slightly higher volume than water but that means no leakage.

edwardw: That sounds like a good mix. Slap on some elliptical fins and there I go! I might just try that!


bobkrech: two D12s would put it over the limit according to thrustcurve.org

 

[bobkrech]

Originally posted by GL-P
bobkrech: two D12s would put it over the limit according to thrustcurve.org [/B]

Absolutely right. I misread it.

There is a large 25 point penalty (read 25 gram water) for each second under 30 seconds, so you want to make sure you go over 30 second. That appears to be the correction in the rules from previous years.

650 gram is still about the right weight and ~500 gram water payload is possible with lightweight construction. Motors willweight ~120-130 gram. Use 0.7 mil polyethylene painters drop cloth for the parachute to make it really light.

Good motor combinations are:

(1) D12-3 for recovery and (7) A10-3s (either kicked or vented)

(3) C11-3s for recovery and (2) A10-3s (either kicked or vented)

(7) B6-4s

https://webalt.markworld.com/multistage.html is a useful calculator for this.

Bob Krech