h a l f b a k e r y"Look on my works, ye Mighty, and despair!"
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Recently I was pondering a middle school rocket contest. Rules: propulsion is 75 psi air + water from an unperforated 2L soda bottle. Rockets are judged by total air time. They cannot change conformation in air: no chute deployed etc. The idea is that they tip on their side at apogee and this slows
their fall.
I wonder about a spiral kite rocket. This would be made of 2 enormous hoops. Kite nylon, possibly in multiple "blades" wraps up from the bottom to the top. The rocket bottle is placed horizontally on the hoop. On deploying the rocket spins the hoops which screw themselves upwards into the air - similar to the fireworks in which a bottle rocket "motor" is affixed to a round alumunum circle with fins.
This would not go very high but would fall very slowly as it spun on descent. Also it would be very cool.
I wonder about rocket nozzle differences - it seems to be that an optimal nozzle for pure altitude might not be optimal for spinning a structure like this - a tighter nozzle with a more measured output might do better, with less risk of the horizontal rocket bottle breaking off and entering the crowd at velocity.
By itself, the spiral kite might be thrown like an aerobie. I thought I had seen something like this before but did not turn it up on google.
Bottle rocket rules
http://www.soinc.or...ly%20Sheet%20v6.doc
[bungston, Jan 10 2011]
helical fireworks
helical_20fireworks
shameless self promotion [xaviergisz, Jan 10 2011]
Maple seeds and animals exploit the same trick to fly (w/Video)
http://www.physorg.com/news163948977.html
A technical description of the helicopter configuration with video [CwP, Jan 12 2011]
Spiraling Flight Of Maple Tree Seeds Inspires New Aerial Surveillance Technology
http://www.scienced...10/091020162007.htm
Spiraling Flight Of Maple Tree Seeds Inspires New Aerial Surveillance Technology. Does not follow the need rules but does show others who are making powered versions. [CwP, Jan 12 2011]
[link]
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However, if you want duration, I would have thought a
bottle-powered glider would be more effective. If in doubt,
compare the unpowered glide rates of a helicopter and a
glider... |
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I suggested a glider to the folks fooling around in with the bottle in the field. They told me that the ascent rate tore off the wings. I suggested affixing a slow rocket to a very large balloon which would act as a parachute and was told that this too would be torn off. |
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Again I think the problem is ascent rate. Their rocket did go up impressively fast, maybe reaching a height of 60-70 feet to my eye. I think the nozzle was the unmodified neck of the bottle. I have seen a fair # of middle-school type demonstrations showing that the radio between air and water is important but not much on nozzle diameter and shape. |
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Well, if you're going to include a radio... |
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I suspect nozzle shape does matter when you get near
optimal. I also suspect that the use of technical-grade
Sellotape would hold the wings on. Why not start with a big
radio-controlled glider, rip out the radio and shove in the
bottle? Your weight penalty will be higher than ideal, but
those things can survive quite vigorous launches. |
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If the ability to hold things on is a consideration, the cheater might suggest holding on a number of helium ballons with some sort of industrial-strength glue. |
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More seriously, I wonder if one could get effective results with a helix in which the rocket was the vertical axis, rather than providing side propulsion. One would get similar slower descent, but possibly a higher ascent. |
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[bungston] - how were you planning to get the thrust to go tangential? Bottle at the edge of hoops, or across the center with a deflector of some sort? |
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/tangential/
Bottle at edge of hoops, possibly inclined 15-30 down from horizontal. Ideally there would be a matched bottle 180 across the hoop, to balance. |
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I think the helical fireworks are meant to put on a pretty show, not be more efficient. I am not seeing this as a good idea. It would be pretty, but not contest winning. It isn't efficent as either rocket or aircraft. |
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Wings should be long and thin for best efficiency. A spiral of fabric isn't the best lift/drag design. |
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Generally a rocket works best if it goes off as quickly as possible--think of it as holding itself up in a hover, and you'll see that you want to get things over with as quickly as possible, not waste around spinning hoops. |
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If I was going to put a hoop and fabric rig on a water rocket, I'd put a light skirt on it with a hoop to barely hold it open. When the rocket was moving fast, the hoop would flex back and reduce drag. When the rocket emptied and slowed down the hoop would open the skirt again and provide drag for the descent. |
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You'd need to get the hoop right and convince the judges you were not changing conformation. |
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The above suggestions seem to be on the right track. |
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Rule [3.f: Fins and other parts added to the bottle are 6cm above the level of the bottles opening] prohibits many designs but there are a number of designs in nature that promote slow decent. These range from a shuttle cock configurations, umbrella configurations, and helicopter configurations. |
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Shuttle cock and umbrella/parachute configurations would radically slow assent unless the configuration changed which would violate the rules. |
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The helicopter configuration might be a good choice because it leverages off the inherent change in weight and balance of water rockets that expend most of their mass on assent. Examples in nature include some winged creatures but, of static configuration, the common Maple tree seed demonstrates a reasonable approach. |
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The Maple tree seed should exhibit lower resistance to air flow during assent, yet higher resistance on decent due to the natural shift in weight and balance. It would have to be launched wing first. As mentioned in earlier posts, keeping the large wing on during assent might be the biggest challenge but, once met, the wing could provide other advantages like spin on assent. |
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I have provided some links on the subject. |
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I can make a wedge airplane that will reliably fly
from the nosebleed seats of the Superdome at
the 50, cross the field, and land on the other side
in the stands. |
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It was a design that OMNI magazine published in
the 70's. It looks like it wouldn't fly at all, but it's
balanced so that it won't stall. |
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If it were properly weighted, you could probably
get it pretty high before it leveled out. |
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This reminds me of Simpsons episode "Homer's Enemy" wherein Frank Grimes tricks Homer into entering a contest for children, and Homer wins it and the esteem of his co-workers which was exemplified by Lenny when he repied to Grime's statement "He's in a contest for children" with "And he's beating their brains out!". |
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Way to go [bungston]! Beat those kids' brains out. |
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I don't know about 'five'...teens maybe. |
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I like the wedge shape itself becoming a maple seed on the way down thing. If that same wedge were weighted a bit differently I bet you could get it to see-saw more like a feather.
Not sure which one would stay up longer though. A spinning feather? |
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Maybe someday, someone will read something I write on the halfbakery, try it, then email me to say "That was a good idea!", or "I lost my thumb but had fun doing it!". When I run into problems or projects like this contest, my mind wrangles over it indefinitely. Somehow depositing my ideas on the HB satisfies that part of my brain that the problem has been dealt with. |
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CWP: I like very much the maple seed idea. You could make it out of racing bike parts. A rigid fin ascending edgewise would present little resistance and no conformational change would be needed at apogee to switch to helicopter. |
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//I can make a wedge airplane// link? |
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Using the wing as the lead element will take careful consideration due to the steering effect it will have. My early exposure to rocketry has always led me to use blunt nose cones. Later, I found out why when NASA published information about the merits of blunt vs. sharp nose cones. The blunt ones form a natural and balance pressure wave that helps guide ballistic objects which is a plus for non-ballistic projectiles too. |
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Given that weapons shooting projectiles moved away from sharpen bullets early in history likely indicates there is a lot of analysis on the subject (mostly empirical.) |
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That would be a good video: a marksman firing variously modified bullets with analysis of spread. Blunt nose, sharpened nose, hollowpoint, cross cut into silver bullet..etc. |
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[MB] I looked and looked. I'll have to make a
tutorial of some kind. |
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Later - Check the email listed on your profile - My
daughter and I made a video of the plane folding. |
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