Need help improving design

Discussions about rockets, construction materials, adhesives, nozzles, nosecones and fin design.
BlackAndChrome
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Need help improving design

Post by BlackAndChrome »

Hi, my name is Nick. At my High School I am a member of a team sport called Science Olympiad (in case you've ever heard of it). One of the 20 some odd events is called "egg-o-naut" which is a water rocket building competition designed to launch an egg in the air by means of a water rocket and return it safely to the ground with the longest flight time amongst other things designating the winner. This is my second year in the competition and although I have experimented somewhat with designs I can't seem to get good results. In this competition the two truly significant factors that attribute to success are altitude and time between the apogee and chute deployment. Any advice to improve these would be greatly appreciated.

There are a few rules that have too be followed, the big ones are...
1 carbonated beverage bottle less than 2L no modifications
All energy must originate from the bottle (kills possibility of chemical/electrical/spring deployment)
No factory made model rocket parts (I can make fiberglass nose cones and anything easier anyway)

My design is the following...

I take craft paper and roll a body tube glued with 3M High-strength 90 spray adhesive so that it fits the bottle when inflated with 75 PSI. This is then trimmed flat on both sides and adhered to the bottle. The fins are 3/32 basswood with approximately sanded airfoils on the leading edges. The nose cones are simple conical nose cones made of craft paper with a wooden ring cut with a circle cutter on a drill press. I have dreams of making a fiberglass parabolic nose cone but have little reason considering how easy these are to make in comparison. A picture is attaches as "Rockets".

Considering that there is no stored energy allowed in the deployment segment the deployment method is pretty simple. The tube is trimmed shorter or filled with tissue till the parachute is nearly pushing the nose cone off but is loose enough that if overturned the parachute is free to fall out. Since the nose cone is aerodynamic when the rocket flies into the air the nose cone catches slightly less drag and continues forward further than the body. When the nose cone detaches from the body the hollow cavity in the body catches air and slows down much faster, this causes the cone to pull the parachute out. A picture of the retaining ring on the nose cone is attached as "Cone".

It should be noted that this is the theory... On several instances it appears that the cone falls off prematurely and the body actually flies a good 20 feet higher than the nose cone.

The parachutes are painters plastic. Not the lightest grade because there was too much static cling. At my last competition it appears that I made the parachutes too early and the plastic was crinkled up and did not deploy. I assume that using actual parachute material would assist greatly in this?

This is my design so far, I would like to say that I am not against a complete redesign. Any advice that can be given would be greatly appreciated, constructive criticism is also wanted.

Something that I would like to find... Is anyone aware of a carbonated beverage bottle that is significantly longer and also thinner but still maintains the 2L volume? Remember, no splicing allowed.

I have a competition in one week, a new design would be great if I can get the help.

-Nick Meyer
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Nose cone retaining ring
Nose cone retaining ring
Cone.JPG (982.75 KiB) Viewed 83 times
2 Rockets viewed from side
2 Rockets viewed from side
Rockets.JPG (1000.41 KiB) Viewed 83 times
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Tim Chen
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Re: Need help improving design

Post by Tim Chen »

Hi Nick,

I always wanted to enter in one of these conperitions. Here are a couple of thoughts I've had:

I don't suppose you are allowed to use air pressure from the bottle to control your deploy, are you? You could put a very small diameter hose on the top end of the bottle and have some air pressure flow up into the top of the rocket and use that as deploy energy. I wonder if that would be legal.

Can you use an "air flap" that holds the node in place? That would be another suggestion.

There were other ideas like using a paddle that spins a shaft and releases a nosecone too.

I'm not sure if these are legal. It seems that if you used a spring (like a rubber band) in your system that it would be legal provided that the energy that tensioned it was created by the thrust from the bottle. So, a deploy system that "cocked" like a gun by using a mass inside the rocket which stretched the band during liftoff would seem legal.

Good luck!
Tim Chen
Captain, Team Enterprise
BlackAndChrome
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Re: Need help improving design

Post by BlackAndChrome »

No alterations to the bottle are allowed. Seems that most of the contestants can't do such things properly and wind up hurting themselves. They used to have a trajectory competition that used pneumatics at 60PSI but they stopped a couple years ago. Apparently they had injuries from explosions *rolls eyes* I've made potato guns that withstand 3x that much pressure and never had any problem.

From the information that I have found about airflaps the small rubber band that holds the flap in place qualifies as "stored energy" and therefore disqualifies it as a possibility.

I am not sure what you are designating in the second option. I mean I understand how a turbine like paddle could catch wind and turn a shaft but how could this achieve the energetic ejection of the parachute?

I do like the last idea though and combined with the airflap idea I think it may be applicable although it would be a pain to pull off. Basically it is a reversal of the airflaps that I saw elsewhere. The body tube (something other than paper) is split in two and hinged on the bottom closer to where it connects to the bottle. A conical fishing weight is attached to a light rubber band so that it points down, the other end is attached to the side of the flap. The weight is inserted into a kind of Chinese finger trap that sits below the flaps running down the side of the rocket (clever cutting of a straw may actually suffice). That seems like it would actually work great but keeping it from deploying prematurely still remains a problem. I should be able to devise a way to make it so that the flaps lock in the nose cone like jaws then make air flaps on the nose cone that is supported by rubber bands. Airspeed pulls the flaps over the jaws holding them down then when it slows down it releases the jaws... I like the 2 part body tube/flap idea but the way of holding them in not so much... I attached a crappy paint render of the self priming idea but need to improved a way of locking them down.

As far as increasing altitude what would you suggest? Since the impulse is so high it seems like a heavier rocket would go higher (to a certain extent). What about water volume? I went through several simulators but never got consistent results. And I really would like to see a 3 foot long 2L bottle, that would be so awesome.

Thanks,
-Nick
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Sketch
Sketch
Design.jpg (17.68 KiB) Viewed 77 times
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Spaceman Spiff
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Re: Need help improving design

Post by Spaceman Spiff »

I think given your time frame you should look into making your parachute as big as possible. If you have problems with the material you have you can try some nylon. I use garbage bags myself with good luck that seem similar to what you use. One tip is to sprinkle talcum powder on the parachute. It will lubricate and keep it from sticking together.

Have you tried a design where the parachute is just draped over the top of the rocket and air pressure keeps it on top until the rocket falls backward where it inflates?

One more idea would be to create a parachute that is bundled in a way that it takes a long time to unwrap and inflate and just have the parachute launched at the same time the rocket launches. Just sit it on the ground beside the rocket. If you come up with a way to delay the inflating of the parachute by coiling the string around it you can get really high before it pops.
Spaceman Spiff
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rockets-in-brighton
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Re: Need help improving design

Post by rockets-in-brighton »

Hi Nick

Science Olympiad is really strict, isn't it? If it helps, I think you have a pretty good system there already. You'd like to improve the overall flight time, but as you haven't said what you are getting at the moment it is hard to advise. We'd also need to know total weight and launch pressure.

You are already using a simulator to optimise stuff like the water fill? In addition to the chute how about making the rocket itself a backglider, which increases the fall time and gives you a backup if the chute fails to deploy. Adjust the centre of gravity to lie between the centre of lateral area (the centre of gravity of the rocket's "shadow") and the Barrowman centre of pressure.
Cheers
Steve
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Re: Need help improving design

Post by WRA2 »

Given the time frame you have to work within you might just want to improve your "nose off at apogee" system. I would suggest experimenting with different weight nosecones. By changing the weight you will change when the nose comes off. Your nose that comes off early is too heavy (the nose has more inertia then the drag on the rocket and causes it to come off early.

Another thing you could try is to put the parachute on the egg only and have the rocket "toss it" . To recover the rocket you would need to make what is called a "side gliding" rocket (see this example provided by one of our members) by making a long paper or cardboard tube to fit over the bottle.

http://www.wra2.org/forum/download/file.php?id=643
Lisa Walker,
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Ripper
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Re: Need help improving design

Post by Ripper »

Dave Johnson, the inventor of the airspeed-flap release also worked on a self-cocking flap that was legal for science olympiads.
you can check it out here:
http://dogrocket.home.mindspring.com/Wa ... lease.html

I'm not sure how well it works, but the idea seems fine to me.
Christian
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BlackAndChrome
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Re: Need help improving design

Post by BlackAndChrome »

I think I'm going to go with one of my originally rockets and a rough prototype for the new one. I'll see how things work out and post results/times.

The rules for Science Olympiad are really unspecific in the elastic department. Considering how just about anything can be considered a semi-elastic it's hard to say where they will draw the line. By the time I bent the two halves of the bottle down they had enough spring to them I don't even think the band system is needed.

-Nick
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Spaceman Spiff
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Re: Need help improving design

Post by Spaceman Spiff »

Ripper wrote:Dave Johnson, the inventor of the airspeed-flap release also worked on a self-cocking flap that was legal for science olympiads.
you can check it out here:
http://dogrocket.home.mindspring.com/Wa ... lease.html

I'm not sure how well it works, but the idea seems fine to me.
Hi Christian,

Thanks for posting the source for the self arming flap. I knew I saw that somewhere before and I couldn't find the reference when I tried to look for it.
Spaceman Spiff
"What goes up, must come down"