A few HPR questions...

K'Tesh

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As much time I've spent researching model rockets, I have a few HPR questions that I've yet to wrap my head around. I'll admit, I've not spent much time trying to answer these questions myself (I'm really sleep deprived right now).

I know that NAR frowns on metal being used for model rockets, but at what point of certification does that go by the wayside? I've seen HPR builds with sharp pointy metal nosecones, I've seen BBs mixed with expoxy to create noseweight... When is that OK, and you're not voiding your protection (insurance coverage) with using them?

Why do I ask? I've got a 4" design (a stubby pencil design) that I'd like to use an empty metal cigar tube (Cuban of course) to form the "point" of the pencil. I could use the handle of a broom for it, but that would be harder, stronger, and heavier than this little lightweight piece of aluminum.

I realize that the 5:1 nosecone refers to a ratio... I'm presuming 5 (whatever the units are) to 1 (whatever the units are. Is the 1 the radius? or the diameter? Basically, how long would a 4" OD 5:1 (ogive) nosecone be? 20"? 10"?

Now, it's time for bed.

Thanks!
 

Steve Shannon

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I won’t answer for NAR. Tripoli says lightweight metals (non-brittle) are okay when they are structurally needed. A lot of people push that further than they should by adding aluminum tips to nosecones even though unnecessary or building aluminum rockets.
The ratio is length to width, which is usually diameter.
 

Bat-mite

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It is a reasonable question. The rules say "no significant metal parts," and yet we have aluminum fin cans, aluminum AV bay lids, aluminum NC tips, aluminum retainers, etc. "Significant" is a relative term. Unless the rules are modified to state a weight, ratio, proportion, something scientific, then it is an open book.
 

BABAR

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Some of the Estes Motor Hooks for low power have the aft "Prong" pointed straight down/aft with pointy edges. I always bend this upward or at least medially/sideways, so that if it lands on anybody or somebody tries to catch the rocket on descent (catching being a violation of the HIGH Power Safety code [trying to catch a high power rocket on descent is also a potential Darwin Award Nomination], but is NOT a violation of the Low Power safety code) they don't get cut by the end of the hook.

When I downsize the "chimney" for long gap stage rockets (e.g., 24mm engine with a BT-20 chimney internally to guide the gases up the tube to the sustainer) I routinely put in a piece of rolled up aluminum can just forward of the engine block. Keeps the ejection gases from the larger motor from roasting the smaller chimney just in front. Der MicroMeister, God Bless Him and I miss him, would get all bent out of shape over improper use of metal with this.
 

DavidMcCann

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Considering an Alpha III will penetrate 1/2" plywood...
and materials like fiberglass and carbon fiber are really really strong (in highly technical terms)

Basically anything we put in the air will kill you and destroy whatever it hits.

Banning one material or another is absolutely pointless.
 

g.pitts

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Considering an Alpha III will penetrate 1/2" plywood...
and materials like fiberglass and carbon fiber are really really strong (in highly technical terms)

Basically anything we put in the air will kill you and destroy whatever it hits.

Banning one material or another is absolutely pointless.

I agree with you philosophically, but recall that we live in a very litigious society, so any harm caused by construction techniques that fall “outside the norm” (as determined by a jury of his or her peers) will imperil the builder.
 

Steve Shannon

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I agree with you philosophically, but recall that we live in a very litigious society, so any harm caused by construction techniques that fall “outside the norm” (as determined by a jury of his or her peers) will imperil the builder.

And possibly invalidate insurance.
 

mikec

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There's a lot of apples to oranges, HPR vs LPR, discussion in this thread. I thought the OP was asking about HPR.

I'd start by reading https://www.tripoli.org/Portals/1/Documents/Safety Code/Metal in Rocket Construction v2.0.pdf which is TRA's official statement from 2015 on the use of metal in rocket construction. But at the end of the day this is all very subjective. FWIW, I don't think an aluminum-tipped nose cone is substantially more dangerous than a composite-tipped one when it has multiple pounds of airframe and spent motor behind it.
 

Steve Shannon

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If a big HPR comes down ballistic it's not going to make any difference whether the nose tip is aluminum or fiberglass. The important thing is to make sure that it doesn't come down ballistic.

If a person is struck then you’re right, that person will probably suffer the same injuries.
But, if a lawsuit happens and a lawyer seeks punitive penalties because that nosecone had a “penetrator tip” the jury may be more likely to award a penalty (and possibly higher penalties) to a person struck by the metal tipped nosecone. The flyer or the organization could be adversely affected more as a result.
 

micro

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It's very subjective. Consider that nearly all motor casings are metal. Motor retention- metal. Nose weight- metal. Eye bolts, links, swivels- metal. Just use as little as necessary.
 

mikec

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If a person is struck then you’re right, that person will probably suffer the same injuries.
But, if a lawsuit happens and a lawyer seeks punitive penalties...
Certainly. But upthread you suggested that inappropriate use of metal could invalidate insurance. If that's the case, then TRA needs to have a much less ambiguous stance on the use of metal than the official 2015 document on the TRA website that I linked to.

At the end of the day, if one wants zero legal exposure, the only solution is to get out of the hobby.
 

Steve Shannon

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Certainly. But upthread you suggested that inappropriate use of metal could invalidate insurance. If that's the case, then TRA needs to have a much less ambiguous stance on the use of metal than the official 2015 document on the TRA website that I linked to.

At the end of the day, if one wants zero legal exposure, the only solution is to get out of the hobby.

Nobody realistically expects zero exposure. The key is to figure out how much exposure we can afford without actually testing it. We’ve done a great job the last few years and our insurance rates reflect that. But we don’t want to take unnecessary chances. People just need to think of these things as they make design choices. A big heavy rocket doesn’t need a metal tip. A Mach 3 minimum diameter rocket could probably be defended. Adding metal just because it looks cool, is not smart.
 

mikec

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A big heavy rocket doesn’t need a metal tip.
You might want to take that up with the vendors. As far as I can tell, FWFG cones with composite tips are not even an option from Madcow in diameters above 4 inches.

I don't prefer metal because it looks cool, I prefer it because it breaks off less easily than composite if I hit the tip when I'm loading the rocket into my car, the rocket falls over in my garage, lands on cement, etc. If it's official TRA policy that this isn't a good enough reason, tell me now so I can react accordingly.
 

Steve Shannon

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You might want to take that up with the vendors. As far as I can tell, FWFG cones with composite tips are not even an option from Madcow in diameters above 4 inches.

I don't prefer metal because it looks cool, I prefer it because it breaks off less easily than composite if I hit the tip when I'm loading the rocket into my car, the rocket falls over in my garage, lands on cement, etc. If it's official TRA policy that this isn't a good enough reason, tell me now so I can react accordingly.

It’s not official policy; nor is it directed towards you personally. I hope I didn’t make you feel that way. It’s just an ongoing concern I have and I want people to understand it. It seemed appropriate to express given the nature of questions the op asked. You linked to the only official policy.
I have a couple of nosecones with broken tips also. The damage in transporting is a real thing and I choose fiberglass rather than cardboard (and certainly rather than phenolic) for that very reason. At least with aluminum tips, or removable tips of other non-metal materials, a person can reattach the tip.
The manufacturers started adding aluminum tips in response to demand several years ago and even though you don’t choose aluminum tips because they look cool, I’ve seen people expressing that as a sentiment. You may have seen that also.
 

mikec

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Thanks for the reply, Steve. All of us should always keep safety paramount in our minds, because the hobby is one major accident away from not existing. That said, the only reason I am comfortable flying at all is the insurance, and I'm paranoid about any hint or suggestion that my insurance could be voided because I violated some unwritten rule.
 

Steve Shannon

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Thanks for the reply, Steve. All of us should always keep safety paramount in our minds, because the hobby is one major accident away from not existing. That said, the only reason I am comfortable flying at all is the insurance, and I'm paranoid about any hint or suggestion that my insurance could be voided because I violated some unwritten rule.

Mike,
I don’t think you have any reason to worry. You seem like a very responsible flyer. Nobody on the board, including me, is interested in trapping someone using unwritten rules. There are none. Unfortunately, some of the written rules are not as clearly stated as we would like. They just don’t lend themselves to creating perfectly quantified rules. Don’t let that put you off.
 

DavidMcCann

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If a person is struck then you’re right, that person will probably suffer the same injuries.
But, if a lawsuit happens and a lawyer seeks punitive penalties because that nosecone had a “penetrator tip” the jury may be more likely to award a penalty (and possibly higher penalties) to a person struck by the metal tipped nosecone. The flyer or the organization could be adversely affected more as a result.


We've seen that happen in other sports...yes. However in those cases, the Tips are designed to cause more damage and advertised as such. They're chosen to be dangerous.

In our sport, metal tips are not advertised nor designed to cause damage. It's a simple way to solve a lot of building problems and open up some options for retention, storage of electronics, etc. They're also so prevalent as to be considered a standard option.

So I don't think we'd see the same type of litigation results. (Just don't name the rocket 'Black Talon')

Now....People going on and on about rockets surviving a ballistic return with no damage....a smart lawyer could use that as unjustified overbuilding.
 

Andrew_ASC

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About Lead shot BB’s epoxied... No RSO complained when I stated it has a pound of counterweight in the nose since it was a scale missile and it has a unsafe negative stability margin without the counterweight. As long as you sand the living crap out of the internal nose so the shot epoxy goop doesn’t move there won’t be a issue with most RSO as long as your rocket really needs the extra nose weight for flight stability safety. Nobody wants you to fly something with negative stability. My argument was rocket is much safer with noseweight for stable vertical tracking flight than without and looping Lol.


In all super seriousness there was one guy I can’t recall but his argument against the epoxied lead shot was if a motor severely CATO’d it could cause a claymore or shotgun effect through the nose and shoot pellets all over the place. If I had to do lead shot again I’d pick a larger shot pellet size to minimize the amount of fragments of said failure scenario. He still sided with its better to have a stable rocket with counterweight than to launch something not stable at all.

If anyone wants to suggest the tips as bad I’d redirect their attention to it’s a thermal heat sink really for supersonic flight. These things aren’t tungsten penetrators designed to kill military tanks. Although some lawyer type may construe such crapola if anyone’s head got penetrated by a bad launch.
 

Andrew_ASC

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What bothers me more than tip material is ballistic entry does happen and there is high levels of energy. The kinetic energy transfer I’ve seen L1 rockets pierce 8” of hard ground. I’ve seen large L3’s go into ten feet of a salt flat. A hole with three fins. The L3 was nearly invisible coming down from so high. Thank god someone with epic eyesight caught it visually last minute and warned others. Either case I’d argue the kinetic energy transfer involved would be deadly to humans.
 

Rocketjunkie

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If you're worried about lead toxicity, there is lead free (bismuth) shot, bird shot anyway. Go to reloading store.
 

dhbarr

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What bothers me more than tip material is ballistic entry does happen and there is high levels of energy. The kinetic energy transfer I’ve seen L1 rockets pierce 8” of hard ground. I’ve seen large L3’s go into ten feet of a salt flat. A hole with three fins. The L3 was nearly invisible coming down from so high. Thank god someone with epic eyesight caught it visually last minute and warned others. Either case I’d argue the kinetic energy transfer involved would be deadly to humans.
You can't eliminate all hazard when slicing skytunnels. This is why we have process controls as well as engineering controls.
 

prfesser

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What worries me, is 1 lb of lead shot relying on only the epoxy bond to the inside of a well sanded NC.. I would insist (and expect) some mechanical means of securing the mass.

Agreed. Back when I was foolish enough to say "Yeah, I'll be president", I got a call. Seems that someone had poured LOOSE shot into the nose of the rocket, and yes, A Very Bad Thing happened. Several pounds of loose shot landing on I-don't-know-how-many cars....

Best -- Terry
 

Buckeye

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An empty, aluminum cigar tube is far more weak and crushable than any proper model rocket nosecone. Just do it.
 

stevemco

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I have never built a high power rocket that didn't have metal in it. At a minimum I connect the centering rings with threaded rods and use thread ed rods to hold the ebay together. Plus u-bolts for every shock cord attachment. My L3 project had plenty of metal in it and the Tripoli TAPs didn't complain. I have never used a metal tipped nose cone but realistically, if a 20lb rocket comes in ballistic and hits you, it may very well kill you. We need to use good common sense but it isn't possible to put up big rockets with zero risk.
 

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