Adding nose cone mass

[Gillard]

I'm building a V2 rocket that will need a significant amount of mass for a stable flight (a review on EMRR puts the mass at 25oz) so here's my question:
i'm planning on adding lead shot and epoxy mix to the nose cone. i've done this on sevral smaller rockets that need much less mass, and i'm worried that this amount of epoxy will generate too much heat and possibly melt the nose cone.
i will be sitting the nose cone in a bucket of cold water, but what you you do if you were me? add the mass in one go, or add the mass in 3-5oz lots over several days?

 

[dixontj93060]

I have done this many times. I don't know if it is the best way, but I always do it in one mix. I do set the nosecone in ice though. Also I use a slow epoxy. In addition, you may consider installing a "cross pin" in the area where the epoxy/shot combo is to provide a mechanical hold as epoxy doesn't always adhere well to the inside of a nosecone even after sanding.

 

[Peartree]

I don't know how much of a difference it really makes, but when I have had to put in larger amounts of lead weight (twice) I've used big chunks of lead tire weights instead of lots of little pellets. That way I can drill a hole in a solid NC and insert several ounces at once. Obviously, at 25 oz. you've got a bunch to add so I don't know if it makes a difference whether you use shot or larger fishing weights. I suspect that the shot will pack in more densely.

Naturally, You will need to make REALLY sure that your attachment point is very secure. If a two pound nose cone were to break free of the recovery device... well, I'd really rather not think about it too hard.

 

[Gillard]

Naturally, You will need to make REALLY sure that your attachment point is very secure. If a two pound nose cone were to break free of the recovery device... well, I'd really rather not think about it too hard.

that had me thinking as well, i am toying with the idea of having two smaller parachutes instead of one large one with one of the chutes attached to a different point on the nose cone, just in case one failed.

 

[jcDerRedMax]

I have one of the original LOC pre-production 4" V2 kits, which needed a fair amount of nose weight. First I drilled holes in the nose for the epoxy to 'key' into. I then placed tape over the holes on the outside. I mixed aeropoxy & a heavy mix of chopped fiberglass to add strength. I then poured the epoxy mix into a cup of lead shot which was almost the desired weight, making sure the lead was completely coated. This I poured into the nose. Finally, I added the epoxy mix until the desired weight was obtained.

Having started using Aeropoxy before using other brands, I'd often wondered what these smell and heat problems were that people were discussing with epoxy. When I tried other brands, I found out.

I created 2 slots in the back of the nose, near the shoulder for the tubular nylon to slide through and back out of to create a loop. If I built another, I might imbed the TN into the epoxy/lead slury.

 

[spacecadet]

Amen to the tyre balance weights- they're always falling off and I pick up a fair few off the road. They are of fixed weights too- 20,30,40g, that sort of thing. A pound and a half is a fair amount, though. A box of my rockets doesn't weigh that much.

 

[r1dermon]

i would think that with such a substantial amount of nose weight, in relation to the overall weight of the vehicle, that the nose cone might seperate, due to it's mass, upon realizing negative acceleration. supposing you might need to attach some type of shear pins or something of the sort...anyone want to weigh in on my theory?

 

[stantonjtroy]

You could also use west 106 epoxy base. has a slower cure time and less tendency to exotherm with increased mass.

 

[sylvie369]

i would think that with such a substantial amount of nose weight, in relation to the overall weight of the vehicle, that the nose cone might seperate, due to it's mass, upon realizing negative acceleration. supposing you might need to attach some type of shear pins or something of the sort...anyone want to weigh in on my theory?

Your "theory" is commonly accepted fact. A weighted nose cone definitely requires special attention to attachment for exactly the reason you suggest.

Edit: Just to be clear, r1dermon's suggestion is not about shock cord attachment to the cone, but rather the cone's fit to the body tube (hence the shear pin suggestion).

If you haven't seen it yet, watch what almost happens 9 seconds into this flight:

https://www.youtube.com/watch?v=7mu4u2Lgnic

 

[r1dermon]

well, i've heard it in passing, not to pass it off as my own original thought...just thought it would be of interest to the OP to consider. thanks for the reply.

 

[Adrian A]

When I add lead shot/epoxy or tunsten powder/epoxy to my nosecones I pot in the kevlar shock cord when I get near the top. I protect the cord where it exits the epoxy with some masking tape so that the cord stays epoxy-free and supple all the way to the surface of the potted part.

I often fly with 50+Gs and once flew to 125 Gs and never had a problem with the nose weight coming loose, despite the fact that I never did any special preparations. Several square inches of good epoxy bond means several thousand pounds of strength.

 

[powderburner]

If you set the ballast into epoxy in the front end of the NC, you always run the risk (small risk?) of the epoxy de-bonding and rattling around loose. (One hard impact on concrete can crack the epoxy bond.) At that point, the ballast/epoxy would no longer be secured in the proper location to function as ballast.

Instead of epoxy, why not foam? You would not have problems with epoxy getting hot, and if you put in enough foam to fill the rest of the NC, the ballast will be locked forever in the tip.

You can use the fancy hobby foams (two-part stuff, high quality) but the hardware store insulation foam-in-a-can will work just fine. You could probably also use Gorilla glue.

Or you could use a threaded rod through the base of the NC (double-nut into position), screw various amounts of ballast on the front end of the rod, and still be able to remove/adjust if necessary. Requires no epoxy at all-

 

[troj]

Instead of epoxy, why not foam? You would not have problems with epoxy getting hot, and if you put in enough foam to fill the rest of the NC, the ballast will be locked forever in the tip.

The reaction of the foam is exothermic, as well.

You can use the fancy hobby foams (two-part stuff, high quality) but the hardware store insulation foam-in-a-can will work just fine. You could probably also use Gorilla glue.

Do not use the foam-in-a-can -- it requires atmospheric moisture to cure, and will not reliably cure inside a nosecone.

Stick the nosecone in a cup of water (cold tap water is fine) and you won't have any issues. If it's a plastic nosecone, then follow John's recommendation of foam (use two-part foam) to fill the rest of the nosecone, so that the epoxy cannot pop loose.

My preferred method is different -- I use a piece of all-thread down the center of the nosecone, and use washers on the front of it to get the desired weight, then a bit of epoxy. The recovery system gets attached to the all-thread, so there's no risk of the nosecone not handling recovery loads, or weight popping loose.

-Kevin

 

[Gillard]

My preferred method is different -- I use a piece of all-thread down the center of the nosecone, and use washers on the front of it to get the desired weight, then a bit of epoxy. The recovery system gets attached to the all-thread, so there's no risk of the nosecone not handling recovery loads, or weight popping loose.

-Kevin

after alot of thought i'm going with the above suggestion, with a slight change.
i'm bedding in a M8 bolt in a slurry of lead BB and epoxy in the tip of the nose.
on this bolt there is a M8 nut joiner.
this will thread onto a length of threaded M8 bar.
at the base of the nose cone the bar ends on another joiner, which then joins onto a M8 eye bolt going through the base of the nose cone
the advantage of this is that i can remove the bar from inside the nose cone and add and subtract as many M8 washers as i need for stability (2 washers = 1oz).

 

[troj]

after alot of thought i'm going with the above suggestion, with a slight change.
i'm bedding in a M8 bolt in a slurry of lead BB and epoxy in the tip of the nose.
on this bolt there is a M8 nut joiner.
this will thread onto a length of threaded M8 bar.
at the base of the nose cone the bar ends on another joiner, which then joins onto a M8 eye bolt going through the base of the nose cone
the advantage of this is that i can remove the bar from inside the nose cone and add and subtract as many M8 washers as i need for stability (2 washers = 1oz).

I'd lose the joiners.

Instead, place a piece of allthread in the nosecone, embedded in epoxy, and use a fender washer and a nut to hold a bulkhead in place at the end of the nosecone.

If you can't easily see the joiners, it's possible for them to not properly engage the threads, which will cause you problems....

-Kevin

 

[Gillard]

I'd lose the joiners.

Instead, place a piece of allthread in the nosecone, embedded in epoxy, and use a fender washer and a nut to hold a bulkhead in place at the end of the nosecone.

If you can't easily see the joiners, it's possible for them to not properly engage the threads, which will cause you problems....

-Kevin

valid point, but i've cut a hole in the shoulder of the nosecone, which is directly opposite the joiner, so i can see if everything is linked up.

 

[troj]

valid point, but i've cut a hole in the shoulder of the nosecone, which is directly opposite the joiner, so i can see if everything is linked up.

The trick is knowing how many threads are engaged. Putting a mark of some sort on things will help.

-Kevin