Threaded nose cone weight (lead or tungsten preferably)

[Steve Shannon]

I don’t wish to dogpile on Eric. He’s a good guy who’s just trying to salvage his L3 rocket. Unfortunately, this is the result of some bad design choices that have stacked up against him. It’s good to understand what those design elements are. I mentioned to him last night that he had designed himself into a corner.

1. The rocket has a long boat tail which reduces base drag, resulting in a CP that moves forward.
2. The fins are mounted ahead of the boat tail. That shifts CP forward a lot.
3. Because a significant portion of his motor mount is cantilevered out behind the fins in the boat tail, his CG is shifted rearward a lot. A heavy motor makes that even worse.

His TAPs gave him the right advice about lengthening the body. I think he’s well on his way to designing his solution. This is what it’s all about, learning by doing.

 

[Steve Shannon]

While I have used the tungsten powder/epoxy mixture [with lead shot to conserve tungsten], Steve Shannon's concerns are valid. A super heavy nose brings it's own problems.

A deployable ballast such as water or dry sand is another strategy. Water makes a nice cloud at apogee and can be dyed for contrast [red works well]. Sand makes something of a 'brown comet' depending on how fast it comes out. Loose tungsten powder would also be a very expensive option.

One might also look at the design to see if the tail needs to be as heavy as it is.

br/

the other Tony

I suggested that if he uses shot he should use bismuth shot which is what many shot shells now use.

 

[School of Rock'et']

The original 12 ft rocket according to rocksim had a raw weight without motor ~84 lbs with motor around 99. Rocksim & Thrust curve screen shots below show 5:1 T/W ratio. Thinking of this "deployable ballast" idea has me rethinking extension of the entire air frame and wondering if I add just a little nose weight and water, can I come out ahead for the certification flight and THEN modify the design to fly larger motors in the future.

 

[prfesser]

14 lb of water would be over a gallon and a half. Sand with just enough water to cover it would be about half that, a bit over three quarts. A fair bit of volume, and I'm not sure how it might be contained so as to not present a hazard on landing. If it's still in the nose on landing, it doesn't make much difference whether it's 14 lb of water or 14 lb of lead, it's gonna hit just as hard. (Ask Galileo about that... )

Best -- Terry

 

[user 30299]

The original 12 ft rocket according to rocksim had a raw weight without motor ~84 lbs with motor around 99. Rocksim & Thrust curve screen shots below show 5:1 T/W ratio. Thinking of this "deployable ballast" idea has me rethinking extension of the entire air frame and wondering if I add just a little nose weight and water, can I come out ahead for the certification flight and THEN modify the design to fly larger motors in the future.

View attachment 431504
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Awesome looking design!

Is the weight based on the actual component weights or did they come from the RockSim library ?

 

[llickteig1]

We see so many rockets ripped apart by inordinately heavy nosecone with a lot of added nose weight tearing up the bullheads and recovery attach points. I'm very surprised to see this being done in a level 3 certification flight.

 

[School of Rock'et']

Awesome looking design!

Is the weight based on the actual component weights or did they come from the RockSim library ?

With the help of the family, we weighed each part and then also simulated the weight of the largest motor to fly to get a sense of what was needed.

 

[School of Rock'et']

We see so many rockets ripped apart by inordinately heavy nosecone with a lot of added nose weight tearing up the bullheads and recovery attach points. I'm very surprised to see this being done in a level 3 certification flight.

Hi Lance. In the process of design planning, I did ask my TAPs about the stress put on the recovery system by the nc weight. Rest assured, I'm looking forward to implementing the most intelligent and cost effective solution just for the cert flight. Any major modification needed to all air frame components can be considered after the successful attempt. Having a deployment baffle system of water and/or sand has me intrigued and should drastically alleviate the stress on the system and the need for future RSO and LCO concerns.

Eric

 

[user 30299]

With the help of the family, we weighed each part and then also simulated the weight of the largest motor to fly to get a sense of what was needed.

That’s good.

 

[School of Rock'et']

All, I'm actually thinking of adding 3 aft fins to the design. Doing so, according to Rocksim gets me a much cheaper solution I believe. As always, feedback is welcome and appreciated.

 

[TonyL]

Just to be clear Terry, I never advocated using "mud" as ballast

The whole point of a fluid based ballast is that it does not come back with the rocket. Bringing back a bucket of mud [or sending it up in the first place] would make little sense .

I didn't catch that this was an L3 certification flight. I would not particularly recommend water ballast for a cert attempt.

As far as 'reference designs', I was not the first to try it and there are no 'instructions'. I make the drogue chute invert the water chamber and empty it, not much to it. I have had the best success keeping the recovery section separate from the water section, and beware drag separation. A smooth nose and draggy fins is not as good as smooth fins and a draggy nose...

br/

the other Tony

 

[Steve Shannon]

All, I'm actually thinking of adding 3 aft fins to the design. Doing so, according to Rocksim gets me a much cheaper solution I believe. As always, feedback is welcome and appreciated.
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View attachment 431534

Good thinking! That definitely will help stability, but those aft fins look susceptible to flutter. Be sure and analyze that as well.

 

[manixFan]

If you do end up with a lot of nose weight, I still strongly suggest brining the nose down separately from the rest of the rocket. That's what I did with my level 3 that had a lot of nose weight. While that does introduce another layer of complexity, it reduces the odds of a recovery failure due to the shock of such a heavy load. And of course Steve is right about those new fins - rectangular is the shape most likely to flutter. Worse, they would likely break on landing which would disqualify your flight. The shape of your main fins is the way to go if you do add the second set of fins.

And Steve - have you priced bismuth shot? Yikes!


Tony

 

[Ez2cDave]

Anyone ever need ~ 14lbs of nose weight for stability? I'm looking for either a great idea on how to make a lead mold that won't crack during drying or fail when pouring lead or a 1/4 threaded rod insert (billet) solution of lead or tungsten carbide that can be epoxied in place.

Trying to figure out what the best option is to allow a magical O5280x flight in the near future.
Thanks in advance for the assistance ALL!

In my opinion, the wisest course of action is to "shelve" the current design and create a new design, specifically for Level 3 Certification on a "Baby M".

You need light weight, strong construction, and reliability for any Cert flight. Once you "punch you ticket", then you can design for "magical O5280X" flights, later.

Simplest approach - 3 or 4 FNC, 7.5" diameter, 10 - 12 feet long, keep the mass low, avoid Boat-Tails, do not exceed 950 fps ( sub-transonic ), use a 75mm "Baby M" . . .

Punch it into the air, deploy the Drogue ( no zipper ), descend under Drogue, deploy the Main ( no zipper ), No Landing Damage . . . Get certified and then build whatever you want !

Below are "rough sims" for such a rocket with a "dry weight" ( "all up" w/o Motor ) of 30 lb. , 35 lb, & 38 lb, respectively. The 2nd Column is airspeed at the top of a 10 ft Rail.

Dave F.

30 LB.



35 LB.



38 LB.

 

[Steve Shannon]

If you do end up with a lot of nose weight, I still strongly suggest brining the nose down separately from the rest of the rocket. That's what I did with my level 3 that had a lot of nose weight. While that does introduce another layer of complexity, it reduces the odds of a recovery failure due to the shock of such a heavy load. And of course Steve is right about those new fins - rectangular is the shape most likely to flutter. Worse, they would likely break on landing which would disqualify your flight. The shape of your main fins is the way to go if you do add the second set of fins.

And Steve - have you priced bismuth shot? Yikes!


Tony

You’re right! No, I hadn’t. My thought was that it would be cheaper that tungsten which someone else had mentioned.
Tungsten shot (real tungsten, not alloyed) is over $100/lb.
Tungsten alloy shot sells for $34/lb.
Bismuth shot varies from $15/lb to $17/lb.

 

[Zbench]

Lead is less than $1/lb. Steve, what’s your aversion to lead?

 

[rharshberger]

Its interesting people are concerned about lead in rocketry...even on a ballistic recovery how much lead gets left unclaimed? I have dropped the noseweights that are made with lead shot and epoxy into a melting pot (in a very well ventilated location like outside) and the lead and epoxy can be separated for re-use, it takes a little work, but if people are responsible about it recovering the stuff and recycle and reuse it shouldn't be a big deal.

 

[Steve Shannon]

Lead is less than $1/lb. Steve, what’s your aversion to lead?

Environmental groups are pursuing lawsuits targeting lead contamination. It’s easy to anticipate that landowners including the BLM would quickly revoke permission to launch if they discover that lead contamination was a risk that could involve them in litigation. Second, lead shot in is banned in California for hunting because of the risk to birds. I wouldn’t want to see rocketry incur greater regulations as a result of something that’s avoidable.

 

[Steve Shannon]

Its interesting people are concerned about lead in rocketry...even on a ballistic recovery how much lead gets left unclaimed? I have dropped the noseweights that are made with lead shot and epoxy into a melting pot (in a very well ventilated location like outside) and the lead and epoxy can be separated for re-use, it takes a little work, but if people are responsible about it recovering the stuff and recycle and reuse it shouldn't be a big deal.

That’s the key - “if people are responsible”
Unfortunately, there are many examples where people are not.

 

[OverTheTop]

All, I'm actually thinking of adding 3 aft fins to the design.

Just remember that fins towards the rear are more prone to damage on landing.

 

[BABAR]

While I have used the tungsten powder/epoxy mixture [with lead shot to conserve tungsten], Steve Shannon's concerns are valid. A super heavy nose brings it's own problems.

A deployable ballast such as water or dry sand is another strategy. Water makes a nice cloud at apogee and can be dyed for contrast [red works well]. Sand makes something of a 'brown comet' depending on how fast it comes out. Loose tungsten powder would also be a very expensive option.

One might also look at the design to see if the tail needs to be as heavy as it is.

br/

the other Tony

I have always wondered about using water as a forward ballast, especially if you could deploy it (oh heck, just “dump it.”) at apogee.

Potential issues I could see (not all inclusive, suspect more that I DON’T see)

Container needs to be resistant to G forces. Might be suboptimal (although entertaining) to watch a red dyed water ballast load start “bleeding” from the nose from the moment it leaves the pad

Even if it makes it to apogee, any “dump” mechanism could be problematic if it dumps the water on the electronics, the chute, or any non-fiberglass portions of the rockets, particularly paper.

Recovery system needs to be reinforced in case “dumping” fails and the rocket recovers with the full load intact.

Best of luck!

 

[BABAR]

Second, lead shot in is banned in California for hunting because of the risk to birds.

.....................um, the State of California has determined (after considerable and costly investigation, I would guess) that the use of lead shot in hunting causes a “risk to birds”...........? I thought that was the point.

Or are they going to ban it from Police bullets too, because it is a hazard to criminals?


Addendum: apparently the danger of CHRONIC lead poisoning is NOT to the target birds (who are extremely susceptible to “acute” lead poisoning, but that is sort of the expected and indeed intended.) The risk is to UNRECOVERED target birds that are eaten by condors and vultures. I still thought it sounded funny, but kudos to California for figuring it out and solving it.

https://www.nrdc.org/onearth/hunter-asks-why-are-lead-bullets-still-thing

 

[cwbullet]

Lead poisoning is not as large risk as you might think. I have a large bullet collection from antique projectiles from 1800-1900. I have been tested quite a but. My lead levels have never gone up. The key is not eating them or licking them.

 

[BABAR]

The key is not eating them or licking them.

I commend you for your restraint!

 

[TonyL]

So the water does not 'bleed' until around burnout [remember your free body diagram, fluid is still a 'free body']. The same is true for sand. Drag pushes everything inside forward [technically pulls the body back and the insides try to keep going...]. This does make drag separation a concern. Also in free fall there is not so much 'dumping onto things' as much as 'spraying everywhere'. I protected my electronics with from the water that runs down the outside, but it is not very much water and the wind tends to blow it back, not into things.

My best result was in a cardboard rocket [painted cardboard is sufficiently water resistant]. I used a heavy duty trash bag [leak tested] taped inside the tube and reinforced the water chamber to take the hydrostatic loads [not that hard with Kevlar tape]. The nose cone perched on top of the chamber and naturally came off when it was hanging nose down under the drogue. I have only done this in rockets 8 inches to 12 inches in diameter

In reality it is nothing like that. When a rocket separates at apogee it often gets pulled around violently, which also gets the nose off & water out in short order. Unless you have a cotton parachute, they don't seem to care about water mist.

br/

the other Tony

 

[Zbench]

Environmental groups are pursuing lawsuits targeting lead contamination. It’s easy to anticipate that landowners including the BLM would quickly revoke permission to launch if they discover that lead contamination was a risk that could involve them in litigation. Second, lead shot in is banned in California for hunting because of the risk to birds. I wouldn’t want to see rocketry incur greater regulations as a result of something that’s avoidable.

Steve, not to dismiss your concern, but always seemed silly to me all the hyperbole about lead and how we don't want to "contaminate" the ground. Lead is mined and comes from the ground, usually found with silver and gold deposits. So, by that logic, wasn't the ground contaminated to begin with?

In light of all this, seems like the most environmentally friendly (and cheap) weight is regular old mild steel. Density of mild steel is 4.54 ounces/cubic inch. That's 30% less dense than lead, but you could easily get some mild steel rod in 2 or 3" cross sections, saw it, face and bore it on a lathe and use it in stackable weight fashion holding it all together with a long threaded eye bolt. Advantage would be no need to melt or cast it, and if you made the plates uniform and of various thicknesses, you could vary the nose weight easily to suit various motor configurations.

 

[Steve Shannon]

Steve, not to dismiss your concern, but always seemed silly to me all the hyperbole about lead and how we don't want to "contaminate" the ground. Lead is mined and comes from the ground, usually found with silver and gold deposits. So, by that logic, wasn't the ground contaminated to begin with?

In light of all this, seems like the most environmentally friendly (and cheap) weight is regular old mild steel. Density of mild steel is 4.54 ounces/cubic inch. That's 30% less dense than lead, but you could easily get some mild steel rod in 2 or 3" cross sections, saw it, face and bore it on a lathe and use it in stackable weight fashion holding it all together with a long threaded eye bolt. Advantage would be no need to melt or cast it, and if you made the plates uniform and of various thicknesses, you could vary the nose weight easily to suit various motor configurations.

Your logic could also apply to arsenic, uranium, and any of a number of other minerals that are considered hazardous. Seldom are any of those materials found just lying on the surface or buried just beneath and when they are fences get erected to prevent human access. Figuring out what to do with used material is a constant problem.

But my concern is about losing access to launch sites. You can justify any practice you wish, but I’ve dealt with BLM and FAA for a launch site with a 52,000 foot waiver for eighteen years. One screwup with a bunch of fishing weights or lead shot that results in an incident that someone formally complains about and we would almost certainly lose our launch site. Launch site access is declining as it is. Thirty states have regulations about the use of lead shot. The federal government did too for about a day (enacted on the last day of President Obama’s term - cancelled by the new Interior Secretary within hours of being sworn in). So we would be foolish to ignore the regulatory threat.
Steel is specifically forbidden except in small quantities and where necessary by all of our Safety Codes.

 

[Zbench]

Steve,

Again, not to diminish your concern, but seeking to understand.

So, consulting the periodic table, Zinc is about the same density as steel and could be cast into shapes that would work as it melts at around 800 degrees F. Since people actually eat powdered forms of zinc in the belief that is prevents or lessens the common cold, I would presume that the toxicity aspect is not an issue.

I see Rotometals actually sells zinc discs in various diameters at about $3/lb. Additionally, Zinc is now used in place of lead on wheel weights, even in the state of California. Would that pass all concerns, other than putting that much weight in the nose of a rocket?

 

[School of Rock'et']

Steve,

Again, not to diminish your concern, but seeking to understand.

So, consulting the periodic table, Zinc is about the same density as steel and could be cast into shapes that would work as it melts at around 800 degrees F. Since people actually eat powdered forms of zinc in the belief that is prevents or lessens the common cold, I would presume that the toxicity aspect is not an issue.

I see Rotometals actually sells zinc discs in various diameters at about $3/lb. Additionally, Zinc is now used in place of lead on wheel weights, even in the state of California. Would that pass all concerns, other than putting that much weight in the nose of a rocket?

Good question.

IF I hadn't had explored other options, zinc was on my list of questions as well.

 

[Steve Shannon]

Steve,

Again, not to diminish your concern, but seeking to understand.

So, consulting the periodic table, Zinc is about the same density as steel and could be cast into shapes that would work as it melts at around 800 degrees F. Since people actually eat powdered forms of zinc in the belief that is prevents or lessens the common cold, I would presume that the toxicity aspect is not an issue.

I see Rotometals actually sells zinc discs in various diameters at about $3/lb. Additionally, Zinc is now used in place of lead on wheel weights, even in the state of California. Would that pass all concerns, other than putting that much weight in the nose of a rocket?

I think it might.
But keep in mind that I’m not making rules here. With the exception of those times where I point out that something violates the Safety Codes, I’m stating my opinions.