Deceleration Splike
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Deceleration Splike
I was pondering how I should recover my latest rocket. If you looked at the Ozone Probe Two Stage post the rocket was in one of the pictures. I don't have a servochron and I can't seem to find any Tomy timers right now. Would a deceleration spike be the way to go. Pretty much just a wooden or fiberglass (or metal against general recommendation) spike that stabs into the ground on impact. It would slow the fall like a dart. It would have to be attached securely so it doesn't break off. There aren't really anyone at the park except me and a few other members of the crew. What do you guy think. Air.Command gave the suggestion. do you guys think its too dangerous or would it work nicely.
Water Rocket Expert
I'm 20
Maryland
"Anyone who has never made a mistake has never tried anything new." -Albert Einstein
I'm 20
Maryland
"Anyone who has never made a mistake has never tried anything new." -Albert Einstein
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Re: Deceleration Splike
Why don't you go for a back glider?Water Rocket Expert wrote:I was pondering how I should recover my latest rocket. If you looked at the Ozone Probe Two Stage post the rocket was in one of the pictures. I don't have a servochron and I can't seem to find any Tomy timers right now. Would a deceleration spike be the way to go. Pretty much just a wooden or fiberglass (or metal against general recommendation) spike that stabs into the ground on impact. It would slow the fall like a dart. It would have to be attached securely so it doesn't break off. There aren't really anyone at the park except me and a few other members of the crew. What do you guy think. Air.Command gave the suggestion. do you guys think its too dangerous or would it work nicely.
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Re: Deceleration Splike
That "Franks Water Rockets" video on YouTube does a really good job of explaining how they work, so it should be very easy for any rocket to be configured that way.Reptiglorandrockets wrote:Why don't you go for a back glider?
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Re: Deceleration Splike
I looked on YouTube and saw it but don't understand how it works. Can you explain?
Water Rocket Expert
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Maryland
"Anyone who has never made a mistake has never tried anything new." -Albert Einstein
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Maryland
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Re: Deceleration Splike
Long skinny rockets that are tail heavy will fly stable and will try to fall backwards after apogee, but the fins will catch air and slow the back end causing the nose to tilt over and the rocket will fall sideways nice and slowly.Water Rocket Expert wrote:I looked on YouTube and saw it but don't understand how it works. Can you explain?
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Re: Deceleration Splike
I would backglide it. A big stick on the top is a bad idea. You could kill someone with a stick out the top of your rocket.
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Re: Deceleration Splike
Okay I will try that. Air command recommended the lawn dart idea but the back glide sounds better. Can you tell me how I can know if my rocket will back glide, I don't want to spend hours building it and then have that not work and turn into a lawn dart.
Water Rocket Expert
I'm 20
Maryland
"Anyone who has never made a mistake has never tried anything new." -Albert Einstein
I'm 20
Maryland
"Anyone who has never made a mistake has never tried anything new." -Albert Einstein
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Re: Deceleration Splike
For a rocket made out of 6 spliced and coupled 1 liter bottles with a nozzle like antigravitys booster nozzle do the trick or is it not enough thust. I don't want to do full bore. I can add boosters though that have a full bore.
Water Rocket Expert
I'm 20
Maryland
"Anyone who has never made a mistake has never tried anything new." -Albert Einstein
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Maryland
"Anyone who has never made a mistake has never tried anything new." -Albert Einstein
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Re: Deceleration Splike
Here is a good link that shows how to backglide a rocket: Back Gliding Rocket.
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Re: Deceleration Splike
But it doesn't tell the exact weight ad stuff and cg and stuff so I can't take the risk of my rocket being a lawn dart and ruinign itself
Water Rocket Expert
I'm 20
Maryland
"Anyone who has never made a mistake has never tried anything new." -Albert Einstein
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Maryland
"Anyone who has never made a mistake has never tried anything new." -Albert Einstein
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Re: Deceleration Splike
I'm probably wasting my breath, but here goes. To make a water rocket that has a backgliding configuration you must work out the positions of three significant points along the long axis of the rocket: the centre of gravity CG, the centre of pressure CP and the centre of lateral area CLA.Water Rocket Expert wrote:But it doesn't tell the exact weight ad stuff and cg and stuff so I can't take the risk of my rocket being a lawn dart and ruinign itself
As you know already - having built successful high-flying rockets - a stable rocket has the centre of gravity ahead of the centre of pressure, and this helps to restore the rocket's heading when it is deflected by a gust of wind. No doubt you already know how to determine these two points.
The 3rd point - the centre of lateral area - approximates the centre of pressure under special conditions: when the rocket is flying completely sideways. You can easily work out the position of this point by drawing a side profile of your rocket as if it was casting a shadow, cutting this out as a cardboard silhouette and balancing it on the edge of a ruler. The CLA is the balance point. Now, if you arrange your rocket so that the centre of gravity is located ahead of the centre of pressure but behind the centre of lateral area, you have a backglider. It will be stable in flight, and will tumble sideways on descent.
Often the easiest way to achieve this configuration is to simply elongate your rocket body, because doing this tends to bring the CG and CLA closer to each other - the longer the body, the smaller the effect of fins and nosecone on both lateral area and CG, but centre of pressure still tends to be further towards the fin-end.
If you don't want to bother with the calculations, you could just follow the pattern that Robert Youen's devised in his "Coney" rocket. If you roll your own, be prepared for some disappointments because what you are aiming for is "marginal stability", and that means almost unstable. Lots of things can go wrong and lead to hard landings.
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Re: Deceleration Splike
So, you may have heard of a game called Jarts? If not, you should search for info on the web about why they were recalled.
Almost all of the rockets I built last year were built around what I called Non Ballistic Recovery. Which is just where the rocket naturally falls sideways. Altimeter readings showed the peak rate of descent was just under the 30m/s limit. And that was with camera and altimeter onboard.
I didn't do any calculations. I just made my fins out of something stiff and heavy, like 1/4" plywood. And made them small. For shorter rockets, I used water ballast that dumped at apogee but my longer Modular Rocket didn't need any ballast.
IMHO, it takes a lot of stress out the launches and makes it less likely you'll find your rocket hanging from a tree or buried in the ground.
Bugwubber
Almost all of the rockets I built last year were built around what I called Non Ballistic Recovery. Which is just where the rocket naturally falls sideways. Altimeter readings showed the peak rate of descent was just under the 30m/s limit. And that was with camera and altimeter onboard.
I didn't do any calculations. I just made my fins out of something stiff and heavy, like 1/4" plywood. And made them small. For shorter rockets, I used water ballast that dumped at apogee but my longer Modular Rocket didn't need any ballast.
IMHO, it takes a lot of stress out the launches and makes it less likely you'll find your rocket hanging from a tree or buried in the ground.
Bugwubber
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Re: Deceleration Splike
I don't know how to find cg or anything else.
Water Rocket Expert
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Maryland
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Maryland
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Re: Deceleration Splike
Try these:Water Rocket Expert wrote:I don't know how to find cg or anything else.
http://www.grc.nasa.gov/WWW/k-12/rocket ... ket/cg.htm
http://txsnapper.eezway.org/txsnapper/stability.html
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Re: Deceleration Splike
You can take my easy method and just make the rocket as long as possible, and put a good set of fins on it. I make my fins 2x as wide as the rocket diameter and 4x as long as the diameter. This is not based in science I just do it because it looks good that way and never bothered to calculate the limits, since what looked good worked for me.Water Rocket Expert wrote:I don't know how to find cg or anything else.
The trick is that if you load up your rocket with your payload and measure the halfway point along the fuselage and try to balance on the halfway point, if the rocket tilts toward the fins it will side glide and if it tilts nose down it will take a nosedive. The more it tilts to the fins the better.
Remember: The suggestions for this design only works as long as you launch straight up. If the rocket flies like an arch shaped path, it will not turn on the side, no matter how well you calculate the parameters.
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