SpudFiles

Hey everyone, I have a little challenge. The concept is to get a model rocket to fill up a balloon when it lands. The reason for this, is that many times model rockets will land in corn fields or the likes, and dissappear entirely. Even with the most advanced tracking, such as GPS and all, you can only get accuracy to 30-50', and that is nowhere close enough to find a rocket in tall grass.
The idea is, that when the parachute pops out, a balloon also pops out, and starts filling with some gas lighter than air. Then, when it hits down, the balloon will be floating a good 10' off the ground, where it will be very easy to spot, no matter how high of grass or corn or what ever it lands in.

How to actually get that to happen is far more complex though. The way I see it, there are two ways to go about this: store a compressed gas, and use a chemical reaction. The problem with a compressed gas, is that rockets need to be very light in order to fly, and the pressure in the tank would have to be such that the weight of the tank would be a serious issue. A chemical reaction on the other hand, such as lye+aluminum to produce hydrogen gas, could work, but could get very messy.

Obviously the bigger the rocket, the less of a difficulty both of these issues would be, but I want to see how small this could be done.

Any and all comments greatly appreciated.

You could have a small pvc air chamber pumped up with very low pressure helium in the back of the rocket then a small hose going up to the top of the rocket and attach a 1/4 BV then have a short peice of hose going to a ballon at the top.

When the rocket lands it would land nose first right? the BV would be sticking out the front and the impact of the landing would turn it open. The helium goes from the chamber through the open BV and fills up the balloon.

Well the question is just how to get enough helium into the rocket. I am looking at something in the 1-2" diameter, probably not more than 1-1.5' long. I am sure that I could find a way to get the ejection charge to open a valve, that is not the issue, so much as designing a very light way to contain the gas in the first place.
A 1' long section of 1" sch40 pvc pipe is most likely too heavy. We are talking about rockets that weight less than a pound, including parachutes, engines, and everything.


edit: I did find US patent #3930448 which seems ti be kind of sort of what I am looking for, but I can't really figure out how it works.
http://www.google.com/patents?vid=USPAT3930448

Those rocket motors have quite high thrust it could easily lift PVC i think....

The simple chemical generation of hydrogen is probably your best bet, a liquid that is mixed with a solid when the rocket goes from vertical to horizontal flight.

Ok, qwerty so you are somewhat missing the point. While in theory, I could get motors powerful enough to heft some heavy pvc pipe, the point of this device would be to not lower the efficiency of the rocket too much, by keeping the weight down as much as possible. If I add too much heft to the rocket, then there will be no need for the balloon recovery system, as it won't go over 300 feet ever. I am thinking of something more on the range of going a mile up, hopefully on something in the range of a G engine, so I have to keep the weight to a minimum. I realize that this may be stretching it, but lets see what we can come up with.

edit: damn posts while I was posting...
that comment was directed at qwerty, not you jsr

@jsr: that is basically what I was thinking. there is just no way to get helium as dense as a solid and liquid. I do realize that there are biproducts of the reaction, so it won't be as efficient, but chances are it will still be better.
The next question is how do you get the gases into a balloon that has to be a good 10' above the rocket. Its not like you can just have a hose running up to it, nor could the balloon support the weight of the biproducts, so you can't hang the whole mechanism from the balloon...
Maybe there is some way to have the liquids drain? Other possibility is to have the balloon fill up during the decent, and as soon as it hits the ground, the impact could be used (or in worst case scenario, you could use an altimeter, but I would rather avoid more electronics, and complications and all) that would then separate the balloon from the filling chamber, and let it float up on the string. You would need some sort of auto-shutoff, but that could be figured out.

Did you already thought of how to fill the balloon?

I think that your idea is to fill the balloon and it flies up on a string?
The ballon would need a kind of light weight check valve and a mechanism that let it go when filled up. Everything would happen during the flight on the parachute and then you have no guarantee that the balloon doesn't get stuck under the parachute.

On the 2nd thought you could use the balloon to pull out the parachute but then you need a hole new release concept for the parachute and if the balloon fails the parachute fails aswell.

I think this idea is simply not reliable enough and takes to much extra weight.

No, the parachute (or streamer, as high altitude, light rockets can't have a parachute and be expected to land on the same continent...) will be deployed normally, and the balloon won't get caught on it, I can guarantee you.

I just did the math. A 1'x1" pipe would have to be under aproximately 600psi to fill a 9" (spherical for the easy math) balloon. Not completely unreasonable, but still... It is well within the limits of copper. That still leaves the issue of getting the helium up to the balloon though.

Another thought...
Why not making the parachute the balloon?

Kite surfing kites for example have air chambers so that they don't go down when they land in the water.

A chemical reaction within the parachute could provide the light gas to inflate it.

Interesting concept...

I did some more looking around at lighter than air gases, too. Both methane and Ammonia popped up. I have been getting somewhat mixed signals about ammonia, but it seems as though it could be absolutely ideal. Were I to keep it cold before hand, (maybe on dry ice? the boiling point is -33c) and then stick it in the balloon before launch, it would stay mostly liquid for a while, because of the high energy required for vaporization. Then, in theory, as the (black or dark) balloon lay out in the sun, it would start to boil off, and inflate. Eventually, the balloon would be fully inflated and floating over your rocket.

Are there any other lighter than air gases that liquify at reasonable temperatures and pressures?

Why not have a small amount of sodium hydroxide in a container, with aluminum foil around it.

Then, in a similar way to a soda extinguisher is activated the small container would be opened when the rocket impacts (nose first) with the earth?

You may see on old fire extinguishers that use sodium bicarbonate and sulfuric acid that the instructions tell you to turn the extinguisher upside down and bang it on something before use.

That's how I'd do it, all you need is a larger container (with the Al foil), with a small container held inside containing HCl or NaOH that has a loose fitting bung. It's held in place by gravity/acceleration until impact with the earth, the bung is then released and hydrogen is produced. Simply have a balloon/bag over the top of the chamber to catch it.

Hmm... Let's think outside the square here for a moment. Take a look at this parachute test NASA performed for the Ares rocket.

Now, you will have noticed that when the parachutes are first deployed a cable system keeps the 'neck' of the parachute closed quite small, and the entire chute somewhat resembles a balloon.

How about for your rockets you work this concept slightly in reverse. Have a somewhat 'hot air balloon' shaped chute, and have a slip knot or drawstring type system on the opening. Once the chute deploys and fills hopefully you can make the opening constrict, resulting in your rocket hanging off a balloon of sorts. Of course some system would need to be figured out to make it airtight, perhaps a rubber band that is somehow triggered could hold the air for long enogh to find the rocket.

I think a system along those lines would be better than a chemical solution as it should be lighter, and would also be able to replace the current parachute system, reducing weight furthur. Basically, tweak somthing you already have rather than adding more stuff to the rocket.


Just my $0.02

EDIT: If you made the balloon out of lightweight black plastic and it was of sufficient size, it would start to act like a solar balloon in the sun and rise above the rocket... Hopefully not dragging or lifting the rocket away from where it landed. I can just imagine a too-large balloon flying away with your rocket after a flight. So much for a 'recovory' system!

As he's already said, if you use much more than a ribbon or streamer to recover very small rockets you will never find them. I believe this would have similar results.

Perhaps, but I can't see a fairly small balloon slowing it down too much (a balloon shape is obviously not an ideal shape for a parachute). I suppose the main issue is that only very large solar balloons have enough lift to work, and we need a small parachute/balloon. Oh well. I wonder if some sort of system to cool off the ejection charge gasses, along with a small check valve would work. A small balloon ought to work as a recovory system... but then again, I doubt the ejection charge gives lighter-than-air gasses. Hmmm. This is a tricky little problem.

could you not just put a small-but-strong, pre-filled helium balloon in above the parachute/streamer attached by cotton thread or similar, that way the balloon is simply pushed out with the 'chute and floats above it. it just seems that it may be a lot easyer thinking simple, rather than overcomplicating things