Bottle Rocket B

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Re: Bottle Rocket B

Postby Tramsarran » Tue Mar 06, 2012 11:57 pm

Personally I'd say it's less likely for the rocket to catch an updraft than to have its flight disrupted by the wind, but I have very little experience to speak out of. BTW, where do you guys test the rockets? There's no safe place in NYC to do so, and I'm sure that's why the event doesn't run at Regionals.
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Re: Bottle Rocket B

Postby gmui » Fri Mar 09, 2012 1:46 pm

Our regional competition is tomorrow morning and I was wondering what the steps for competing are. Are we expected to fill the water bottles ourselves within the time allotted? Do we also mount the rocket on their launcher? Pull the trigger? I assume they will take care of all the timing...

Also, is it safe to assume that "Sparkling water" bottles are the same as carbonated? I.e. they will qualify for the competition?

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Re: Bottle Rocket B

Postby fishman100 » Sat Mar 10, 2012 1:58 am

gmui wrote:Our regional competition is tomorrow morning and I was wondering what the steps for competing are. Are we expected to fill the water bottles ourselves within the time allotted? Do we also mount the rocket on their launcher? Pull the trigger? I assume they will take care of all the timing...

Also, is it safe to assume that "Sparkling water" bottles are the same as carbonated? I.e. they will qualify for the competition?

I think you're supposed to do everything (fill the bottle, mount the bottle, pull the trigger, etc.) yourselves except for pressuring the rockets and taking the required measurements. Varies competition by competition though, so your regionals might be a little different from my description.
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Re: Bottle Rocket B

Postby Frogger4907 » Sat Mar 10, 2012 2:02 am

gmui wrote:Also, is it safe to assume that "Sparkling water" bottles are the same as carbonated? I.e. they will qualify for the competition?

Yes, they should qualify.
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Re: Bottle Rocket B

Postby UnknownyMous » Sun Mar 11, 2012 3:38 am

If you want to make your bottle go REALLY high, and float down slowly, you SHOULD use a backslider. My competition was in February, and I got 4th. I honestly regret NOT using a backslider because that was what I was gonna do but in the end, decided not to. The people who one first place used a backslider and got around 15-20 sec. (estimating)
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Re: Bottle Rocket B

Postby ls20817 » Tue Mar 13, 2012 3:33 pm

I need help incalculating the center of pressure. I've looked on-line. It doesn't translate well to a cone shaped nose cone. Any advice?

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Re: Bottle Rocket B

Postby jgrischow1 » Tue Mar 13, 2012 6:23 pm

ls20817 wrote:I need help incalculating the center of pressure. I've looked on-line. It doesn't translate well to a cone shaped nose cone. Any advice?


Would something crude like holding it in front of a large fan and seeing where it balances work?

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Re: Bottle Rocket B

Postby fishman100 » Tue Mar 13, 2012 6:32 pm

EDIT: Read that as Center of gravity, not pressure. My bad.
Last edited by fishman100 on Wed Mar 14, 2012 12:31 am, edited 1 time in total.
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Re: Bottle Rocket B

Postby SOCoach » Tue Mar 13, 2012 10:00 pm

I am trying to help my kids prepare for bottle rocket in a few weeks - we have built and tested many rockets but our best time is right around 10 seconds.

We have used plastic flourecent light tubes for the nosecone . . approximately 3 feet . . 450 ml of water, 3 fins, 1 L bottle and the weight of the rocket ends up right around 120-130 grams. Our rockets tend to go fairly high, then fall backwards (straight down, the reverse of how they went up) for about half the height, then level out and backslide the rest of the way.

Are the teams that are getting 15+ seconds using paper nosecones? My kids are getting frustrated and I want to be able to help them but I am running out of ideas.

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Re: Bottle Rocket B

Postby cnapun » Wed Mar 14, 2012 12:28 am

ls20817 wrote:I need help incalculating the center of pressure. I've looked on-line. It doesn't translate well to a cone shaped nose cone. Any advice?

This website is awesome, given that you have a conventional design http://physics.gallaudet.edu/tools/rocketcop.html

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Re: Bottle Rocket B

Postby Lady Epidemic » Thu Mar 15, 2012 12:02 am

SOCoach wrote:I am trying to help my kids prepare for bottle rocket in a few weeks - we have built and tested many rockets but our best time is right around 10 seconds.

We have used plastic flourecent light tubes for the nosecone . . approximately 3 feet . . 450 ml of water, 3 fins, 1 L bottle and the weight of the rocket ends up right around 120-130 grams. Our rockets tend to go fairly high, then fall backwards (straight down, the reverse of how they went up) for about half the height, then level out and backslide the rest of the way.

Are the teams that are getting 15+ seconds using paper nosecones? My kids are getting frustrated and I want to be able to help them but I am running out of ideas.

Maybe you're using too much water - we use about 200-250 ml of water for our 1-liter bottles. When you launch, look and see it the water comes almost glugging out, as opposed to in a spray - that can indicate if you're using too much water, which can weigh the rocket down on the way up. Center of balance and fin size might also be an issue, so I'd also check that. There should be some tips on that further down the posts.
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Re: Bottle Rocket B

Postby SOCoach » Thu Mar 15, 2012 9:07 pm

Okay, I've been coaching 17 years and never seen this . . . .

Our team tested their rocket today. It weighed 119 grams, 105 cm long, we used 375 ml of water, 4 fins and I even had the kids determine the CLA, CG, and CP. According to their calculations there is about 20 cm between the CLA, CG, and CP (although the CP is nearly at the end of the bottle.)

1st flight, went high leveled out and backslid beautifully (we only tested with 250 ml of water on that flight) 11 seconds.

2nd flight (350 ml of water) it went up very high and then straight down, but not nose first . . . . bottle end first. Kind of like someone hit the rewind button . . . straight up, straight down.

3rd flight exact same thing as the second flight . . .

We tried adding clay to the front (very little) and it nose dived. Took the clay off . . . . same as before, straight up . . straight down.

Are our measurements off? (CP and CG) are they that close together that the smallest amount of clay overcorrects it?

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Re: Bottle Rocket B

Postby fishman100 » Thu Mar 15, 2012 10:27 pm

SOCoach wrote:Our team tested their rocket today. It weighed 119 grams, 105 cm long, we used 375 ml of water, 4 fins and I even had the kids determine the CLA, CG, and CP. According to their calculations there is about 20 cm between the CLA, CG, and CP (although the CP is nearly at the end of the bottle.)

If the CP is at the end of the bottle, and if all 3 points are within 20 cm of each other, then that means all of the points are located near the nose of the rocket. If they are all located near the same area, the rocket will be unstable. I've heard that having the CG close to the tip of the rocket is the best, but IDK for sure. Another thing I'm not too sure about is that if the rocket is nosediving, then that means you're on your way to having a good backslider.

Play around with the locations of the CG, CP, and CLA, and use a simulator to predict the flight of your rocket.

Here are some things that will change the CP/G/LA:

1) Add mass to the front (moves CG forward)
2) Decrease mass in the back (moves CG forward)
3) Increase fin size (moves CP & CLA backward)
4) Increase number of fins (moves CP backward with little effect on CLA)
5) Move fins further back (moves CP and CLA backward)
6) Lengthen rocket (moves CP back in relationship to CLA)
7) Check Body Alignment (Cone, Extension, Pressure Vessel)
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Re: Bottle Rocket B

Postby SOCoach » Thu Mar 15, 2012 10:43 pm

Thanks!

If their calculations are correct . . . the 3 (CLA, CG and CP) are fairly spread out which is why I can't figure out why adding so little clay to the front caused it to nosedive. We only added at most 2 grams of clay to the front . . . I guess we will go with 1 gram and see what happens.

I'd just never seen a rocket act so much like a pogo stick . . . straight up and down.

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Re: Bottle Rocket B

Postby ls20817 » Fri Mar 16, 2012 2:53 am

How are you doing the calculations. I have tried to download one and put in the numbers and it didn't work. I am using a cone shaped rocket. Do you need to figure in the shaping at the end near the nozzle. Can any one recommend a good simulation site? Any help would be appreciated.


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