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-   -   lead weights (http://www.oldrocketforum.com/showthread.php?t=11773)

tbzep 10-24-2012 03:37 PM

Quote:
Originally Posted by tmacklin
Can dried dog $hit smell any worse than black powder residue?

In all seriousness, what I'm looking for is additional mass in order to shift the center of mass forward. By filling the nose cone with epoxy and lead shot, have I not created a solid mass capable of inficting significant damage to any object that it might impact should something go wrong? Additionally, I wouldn't be able to remove this mass should I use a lighter motor.

Why is lead, zinc or other dense material the only option? It seems to me that sand, dry clay or any other natural material either in the nose cone or in a bag would be a viable option. And cheap too!


Because it is dense and can be put at the very tip of the nose cone, allowing you to use less weight overall. If you use material that is less dense, it can't be placed as far forward (fills much more volume, including back toward the CP), requiring you to use much more weight than necessary. Due to it's increased weight and inertia, it could be more dangerous. A nosecone full of sand will rip you a new one just as fast as a nosecone with a little bird shot and epoxy.

ghrocketman 10-24-2012 03:52 PM

The denser the weight, the less will have to be used due to the further fwd. position.
Osmium would be great, but it is not readliy available and would be cost prohibitive due to a cost of about $77/gram.

Bill 10-24-2012 04:36 PM

Quote:
Originally Posted by tmacklin
Anyway, I'm in the process of scratch building a 3" OD x 63" long rocket and it looks like I may need about 3-4 ounces nose weight to obain one caliber on the static CP. So I'm planning on the sandbag trick. I'll probably use a small paper parts bag as it will disintegrate soon after the first rain.



Ted,

You will probably want to wrap your ballast in a sheet of paper or plastic so that it scatters upon ejection. A bag of sand will hurt when it hits.


Bill

tmacklin 10-24-2012 04:50 PM

Quote:
Originally Posted by tbzep
Because it is dense and can be put at the very tip of the nose cone, allowing you to use less weight overall. If you use material that is less dense, it can't be placed as far forward (fills much more volume, including back toward the CP), requiring you to use much more weight than necessary. Due to it's increased weight and inertia, it could be more dangerous. A nosecone full of sand will rip you a new one just as fast as a nosecone with a little bird shot and epoxy.



Understood. But I doubt that the entire nose would need to be filled to accomplish the shift of mass necessary in my particular case. Dry sand weighs about 100 lbs/cubic foot, cast lead about 708 lbs/cubic foot. A small quantity of dry sand in a baggie would strike me as less lethal than a hard slug of lead and epoxy at the point of a nose cone.

Now if GH is willing to be a test subject.....

tmacklin 10-24-2012 04:57 PM

Quote:
Originally Posted by Bill
Ted,

You will probably want to wrap your ballast in a sheet of paper or plastic so that it scatters upon ejection. A bag of sand will hurt when it hits.


Bill


Yes, it would. My idea was to place the sand bag on top of the laundry, leaving the bag folded over only once so that the sand would spill out into the air upon ejection. Were I to have an ejection failure and a ballistic lawn dart, all bets are off anyway and spectators should take cover. I know I sure will!

tmacklin 10-24-2012 05:37 PM

BTW, I've been testing my idea for ballast with powdered dried clay from my land. Really just fine dust. A small ZipLock sandwich bag 1/3 full weighs about four ounces.

Doug Sams 10-24-2012 05:46 PM

Noseweight
 
Re: Noseweight

Here's some stuff I put together on noseweight.

http://www.doug79.com/noseweight/

It presents several methods for having adjustable weight. I prefer the weight to be nearer the aft end of the cone, for safety, but some of my older stuff shown here has it all the way forward.

Nowadays, I prefer to err on the side of safety - ie, to make the nosecones unstable - rather than trying to get minimal mass.

YMMV.

Doug

.

tmacklin 10-24-2012 06:09 PM

Quote:
Originally Posted by Doug Sams
Re: Noseweight

Here's some stuff I put together on noseweight.

http://www.doug79.com/noseweight/

It presents several methods for having adjustable weight. I prefer the weight to be nearer the aft end of the cone, for safety, but some of my older stuff shown here has it all the way forward.

Nowadays, I prefer to err on the side of safety - ie, to make the nosecones unstable - rather than trying to get minimal mass.

YMMV.

Doug

.



Thanks Doug. Those are some pretty nifty solutions to the problem but I'm pretty keen on my sandbag idea. What I really want to do is fill a payload bay with a litter of kittens just to see if they really do come down on their feet. Of course, that might be overkill.

tbzep 10-24-2012 06:25 PM

Quote:
Originally Posted by tmacklin
Understood. But I doubt that the entire nose would need to be filled to accomplish the shift of mass necessary in my particular case. Dry sand weighs about 100 lbs/cubic foot, cast lead about 708 lbs/cubic foot. A small quantity of dry sand in a baggie would strike me as less lethal than a hard slug of lead and epoxy at the point of a nose cone.

Now if GH is willing to be a test subject.....


You are planning to put the ballast in the body tube in front of the chute. That's way down the body, meaning you are going to need a boatload of sand (much more weight) to do the same job as a tiny bit of lead in the tip of the nose. The rocket will be very heavy in comparison. I'll take my chances with a few ounces of lead over a bucket of sand. All safety aside, you're getting into the land of diminishing returns if you add weight somewhere other than the nose. You need more weight....which means you need a bigger motor....which means you need more weight....which means you need a bigger motor. :eek:

Of course, if anybody has any sense, they will just take one step to the side and let the rocket hit the ground harmlessly, whether it has lead or sand as ballast. It's worked for 50 years, and even with very large and dangerous rocket ships. ;)

ghrocketman 10-25-2012 12:55 PM

I'm willing to test-fire the rocket horizontally toward a cinder-block wall to test the penetration of sand vs. lead/epoxy. That's test-subject A-PLENTY !


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