Retaining threaded rod in plastic nose cone

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I am looking for suggestions for a way to mount/retain a threaded rod inside a 5.5 inch plastic nose cone. The threaded rod will be used for an adjustable nose weight system and possibly an avionics/GPS sled.

I have previously used John Coker's brass rod technique to retain nose weight and it worked really well.
John's Nose Cone Mods

I am wondering if John's technique could also be used to retain a threaded rod that is epoxied into the tip of the nose cone. Possibly using 4 brass rods that are spaced wider apart so the threaded rod can fit through the middle.

I have sketched what this would look like.

UBL3-Nose-Cone.png


Front end detail:
UBL3-Nose-Cone-Tip.png


Rear end detail:
UBL3-Nose-Cone-Base.png


Has anybody tried something similar or got a better idea for securely mounting a threaded rod?
 
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jimzcatz

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Please forgive my ignorance, but why? Not once in all my years have I ever put weight in the nose of my rockets.
 

Kelly

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I've thought about doing something like this several times, but then I think about the possibility of the rocket coming in ballistic, and nothing but a thin shell of plastic between a steel rod traveling hundreds of MPH and whoever/whatever it's pointed at, and I decide against it.

My best alternate solution to date is using large steel washers (which settle in the nose so they don't move side-to-side), and something like a pool noodle cut to length in between the washer(s) and the NC base to hold them in place.
 

jmasterj

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I've thought about doing something like this several times, but then I think about the possibility of the rocket coming in ballistic, and nothing but a thin shell of plastic between a steel rod traveling hundreds of MPH and whoever/whatever it's pointed at, and I decide against it.
Is that really different from an aluminum tip of an FG nose cone coming in ballistic?
 

Kelly

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In ballistics, an important concept is "sectional density" (SD). This is the mass of the projectile, divided by its cross-sectional area. The SD, along with velocity, determines how well a projectile can penetrate. So a heavy, thin object - like a 12" long steel rod, coming in lengthwise - has a huge SD. An aluminum tip - which probably weighs much less, due to the size of the tip and density of aluminum - and has a wider cross section (well, once you get past the point!) probably has a much lower SD. But, there's people here who will claim that aluminum tips are unsafe, too; and I think there are ranges that ban them.

I don't think aluminum tips nor steel rods violate any safety codes, so I'm just stating my opinion: Steel rods in nosecones give me the willies. They're not so bad in bays, where at least you have a significant 'crumple zone' between the rod and the target.
 

Kelly

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Yeah, we might be debating different levels of "dead". :oops: You're not going to survive a rocket coming down on your head, whether it has steel rods or not.
But, there's also the issue of a nosecone coming down ballistic by itself - a FG NC alone might not be so bad, but with a steel rod in it, could be a different story. Land sharks come to mind also. 🤷
 
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Yeah, we might be debating different levels of "dead". :oops: Your not going to survive a rocket coming down on your head, whether it has steel rods or not.
But, there's also the issue of a nosecone coming down ballistic by itself - a FG NC alone might not be so bad, but with a steel rod in it, could be a different story. Land sharks come to mind also. 🤷

I mostly agree.

This is a 20lb rocket so if the whole thing comes in ballistic the inclusion of a single threaded rod is not going to change anything.

I guess an empty nose cone coming down ballistic by itself is "less bad", but it could still be traveling incredibly fast.

This rocket will have dual deploy with a primary and back up altimeters, so 4 chances for a chute to deploy.

The Apogee newsletter 329 has instructions for installing 2 threaded rods with an air cavity at the tip of the nose cone. This is a sort of crumple zone, but it is suggested as a way to reduce the amount of epoxy (and weight) required rather than as a safety feature.
Screen-Shot-2022-04-15-at-7-20-12-am.png
 
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For those worried about a metal rod, don't use one. Use a nylon threaded rod instead. You can affix it into the nose cone the same as a metal rod (epoxy and cross rods - I don't use brass, just 16 penny nails that I drill holes for, insert, then cut off the ends with a Dremel) and can still add washers for weight and hold them in place with a nylon nut).
 
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