Ballast and a Minimum Diameter Rocket

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lowga

A.K.A. 'Mr. HoJo'
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I'm working on the build for an L2 certification attempt. I chose a kit from Hawk Mountain Enterprises called the Transonic II. This kit comes in two versions, a single stage--and a longer version designed for dual-deploy that they call Minimum Drift Recovery (MDR). This rocket was chosen based on the survivability of the airframe which is all fiberglass with a molded fin can.

I elected to go with the shorter version and to fly with motor ejection. I'm letting the KISS principle dictate most of my choices. Plan to fly a small J-Motor, and use motor ejection. At apogee, rocket will deploy a small 18" drogue chute along with a larger 30" chute on a Jolly Logic Chute Release. Also on the harness will be a sonic beeper.

At 300' Jolly Logic will release the larger chute. The rocket will also fly a tracker (Eggtimer GPS) in the nose cone avionics bay. There will also be a JL Atlimeter 3 onboard for telemetry.

Just started on the simulations, but it looks like this thing will get out sight pretty quickly. At least 5,500 feet. Hoping to fly at Sky Jam in Harpersville, AL which is a large sod farm field, and a waiver to at least 16,000 feet.

Would love to keep the altitude much lower, and have heard about people flying "ballast" of sand or even water in their rockets. But have no idea how this done from a practical standpoint. My library of high power books has very little on this topic either.

Is this even an option for a rocket like this? It's 54mm minimum diameter type rocket.

I bow to the collective wisdom of the group--and am probably overthinking this. :)
 
Way-under-utilized method of reducing altitude is drag. Make/buy a 54mm-to-75mm centering ring. Notch it to fit either a launch rod (inside notch) or rail (outside notch), and drop it on to where it fits up against the leading edge of the fins. That rocket will slow down fast when the noise-maker in the back stops making noise.

More in tune with your question: Purchase some large, steel washers. Tape them together. Slip them over the lower part of your recovery harness. (It is nylon or better, correct? Not some stretchy stuff?) Tape them in place on the recovery harness - inside the body tube if you have access to the lower attach point and can remove the harness for this.

For both methods, you want to pay careful attention to the body-tube/nose-cone joint. Rapid deceleration or the mass of washers lunging forward at burn-out could cause a pre-mature deployment at high speed.

But enough of this silliness. You want to reduce the altitude?
 
Not sure how seriously to take your reply--but here goes:

1.) Inducing drag certainly would degrade the performance of the rocket, but I worry about stability with a large mass over the fins. Are you being serious?

2.) Yes, using tubular nylon on the recovery harness, so placing a package of heavy washers would be possible.

And yes, I'd seriously like to reduce the altitude.
 
1.) Brilliant! This is a super-easy way to increase drag. A centering ring is not a large mass.

2.) I would be worried about a chunk of mass flying around on a shock cord. Also, a load of washers at the bottom of the airframe would move stability in the wrong direction.

A 54mm min diameter is not a great choice for low-altitude L2, frankly. However, you have dual deploy and a tracker as insurance to let 'er rip.
 
A 54mm rocket is not a good choice for a L2 cert as it is going to go.

Adding an external centering ring will induce drag, but it will also likely change your Cp. you would need to sim this.

Adding weight, if you go this route, may and may not give you the results you want.

Adding mass to the nose cone is a likely location. It will improve the stability margin. Depending on mass it might make it go lower, but it could also make it go higher if the rocket/ motor combo is under ideal mass.

Again you need to sim these sort of things.

My suggestion is to get another section of tubing and build it as a traditional dual deploy. Adds mass. Improves stability. Again- sims.


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You definitely want to sim this. Arbitrarily adding weight to the nose will move your Cg but it will also increase the longitudinal moment and effectively change the lateral natural resonate frequency which can dramatically increase the required rail speed and narrow the window of acceptable wind speeds.

I don’t recommend an exposed bulkhead ring with a notch cut out. It won’t effect the Cp much but will effect the forward drag and do so unevenly causing a forced angle of attack.
 
Instead of building a very high performance 54mm minimum diameter rocket for your L2 cert and then trying to figure out how to keep it from going too high, how about just building a bigger rocket. A 4" diameter would probably go about the altitude that you are trying to shoot for with a J motor. And without any extra weights or drag inducing devices.
 
I thought long and hard about my options for an L2 Certification attempt. In the end, I weighted decisions heavily on building the most robust rocket possible. A fiberglass airframe, and molded fin can certainly fit the bill. As a lifelong amateur radio operator (N1LF) I'm very comfortable with trackers--and confident in my ability to recover the rocket despite the altitude. I'm running lots of simulations in RockSim now, and making allowances for various wind speeds, etc.

I opted against dual-deploy for the same reason. K-I-S-S. This combination is simple and reliable. The only checks in the "CONS" column are that it will quickly fly out of sight, and recovery could be challenging. "Low and slow" is certainly a good option, but there are lots of things that can go wrong with that kind of attempt as well.

In the end, like all engineering challenges, it comes down to trade offs.

Ballast was mentioned in passing to me a couple of times, and I wanted to at least consider it. Shifting CG's, unnatural angles of attack---all of that sounds scary--and even with simulations, very unpredictable. Think I'll take my chances with the tracker.

Advice is much appreciated. Thanks for helping me to whiteboard the problem.
 
One factor you are not considering is that using an altimeter is probably more reliable than using motor ejection. It is certainly more accurate at detecting apogee.




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Excellent point, Mark. But there are also quite a few things that can wrong with dual-deploy. I weighted complexity vs. reliability pretty heavily--and opted for the K-I-S-S approach. My logic may be flawed, but it's consistent throughout the design and build.
 
For my L2 I used an altimeter for apogee deployment along with the JLCR and then just left the motor ejection charge unfurled for redundancy. That method might not work for you as it requires the motor delay to be longer than your expected time to apogee. I usually find the delays too short in most commercial motors for my MD rockets and have always had to use DD. Double check your sim and make sure your motor choice will not deploy too early.
 
You call it KISS- that does not make it the best choice- not by a long shot. At a certain power/performance point what is kiss is not the same thing it was at lower power levels.

Unless you are flying at a really massive launch site popping the chute at apogee on this almost guarantees a really long walk. Where are you flying this?

Have you ever looked at winds aloft? Have you considered that winds aloft are always considerably faster than they are at ground level? There is a reason that a considerable number of folks fly dual deployment all the time. You seem to like details- I suggest you look into the prevailing winds for your projected launch site for the time of year you will be flying. This historical data exists and can be really useful.

You are already talking about trying to add weight to reduce performance. Traditional dual deploy will help a bit there and get you landing closer than popping the main at altitude.






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The OP is using a JLCR for dual deploy and A3 for data. People seem to like this combo, but I don't think multiple electronics is KISS. A single, conventional, dual-event altimeter will accomplish all tasks, is more versatile, more reliable for apogee ejection, and costs $100-$200 less than the combined price of the two JL products.

The JLCR is not fool-proof. Dual-event altimeter ejections are not that daunting, either. In fact, it uses the concepts you are already familiar with in motor ejection: igniting a black powder charge to pressurize a volume. If you trust the motor ejection, then why not trust the altimeter to do the same thing? Yeah, you need to obtain ematches and BP and do a little more ground testing, but hey, you are an L2 rocket scientist, right?
 
The OP is using a JLCR for dual deploy and A3 for data. People seem to like this combo, but I don't think multiple electronics is KISS. A single, conventional, dual-event altimeter will accomplish all tasks, is more versatile, more reliable for apogee ejection, and costs $100-$200 less than the combined price of the two JL products.

The JLCR is not fool-proof. Dual-event altimeter ejections are not that daunting, either. In fact, it uses the concepts you are already familiar with in motor ejection: igniting a black powder charge to pressurize a volume. If you trust the motor ejection, then why not trust the altimeter to do the same thing? Yeah, you need to obtain ematches and BP and do a little more ground testing, but hey, you are an L2 rocket scientist, right?

As I have mentioned before, I have seen several very experience folks have failures with the JLCR. It is not bullet proof. I also would not be doing my first dual deploy on my L2 cert flight.

I strongly suggest the traditional dual deploy be done a couple times successfully before the L2 cert. This is a hobby, not a race to obtain certifications, at least in my opinion. Take your time, learn the skill you need before moving up in power level.


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You mentioned flying at an event. Do you have experience flying your eggtimer GPS in a crowded RF environment? Have you previously had success flying the eggtimer GPS with regards to switches, batteries, and other stuff that likes to fail in rockets? If your relying on the tracker definitely make sure it’s right.
 
This is a hobby, not a race to obtain certifications,

There does seem to be an uptick in this activity on the forum. Not sure why. Yes, I get the sense of accomplishment, but think about the practical aspects of the certification. Bottom line, L2 lets you buy motors J-L. Is that you want to do? I guess L2 allows you to RSO and LCO at club launches and sign off on others certification flights. Some people like the volunteer aspect of that, some probably like the power trip. However, do we really want somebody with a grand total of two HPR flights judging other people's rockets?

Sorry for the hijack. Back to your regular programming. Yes, adding mass may actually increase your altitude, depending on where you are on the optimal mass curve for your rocket/motor combo. I like the added drag with the centering ring idea. I recall that Igotnothing fooled us before with that "MD" trick in another thread!
 
There does seem to be an uptick in this activity on the forum. Not sure why. Yes, I get the sense of accomplishment, but think about the practical aspects of the certification. Bottom line, L2 lets you buy motors J-L. Is that you want to do? I guess L2 allows you to RSO and LCO at club launches and sign off on others certification flights. Some people like the volunteer aspect of that, some probably like the power trip. However, do we really want somebody with a grand total of two HPR flights judging other people's rockets?

Sorry for the hijack. Back to your regular programming. Yes, adding mass may actually increase your altitude, depending on where you are on the optimal mass curve for your rocket/motor combo. I like the added drag with the centering ring idea. I recall that Igotnothing fooled us before with that "MD" trick in another thread!
That rear mounted CR on outside the airframe might be better called a "drag plate" or some such.
 
I'd want it behind the fins, not in front of them. Sandwiched between the thrust ring and the MMT would probably be best, and it's nice and removable.

Should be able to sim the base drag using the 3:1 massless polished cone to get the added stability in the right ballpark.
 
Just curious, what motors did you simulate to get your 6000ft? Have you looked at the possibility of using a smaller , 38mm motor?
Remember if you drift out of the designated recovery area, you fail the cert.
As others have said, the JLCR is not perfect. I destroyed what was intended to be my L2 cert rocket flying a test flight on and I-motor when the chute didn't deploy. CR released, but things didn't go as planned. This would also fail the cert. Make sure you practice with the CR and get a handle on what works for you and your situation.
I understand the desire for a robust rocket, but there are other options out there which may be better suited to your desired outcome.

At the same time, if you like it, and are comfortable with what you are doing, go for it! It is all about having fun, not bending to others opinions.
 
Seems like half of the replies here are telling the OP he's not "doing it right." There's lots of "right" ways to set up and fly a rocket. The JLCR is a proven product. Not bulletproof but neither is DD, since most failures are not related to the hardware but the set-up. So in the spirit of trying to advise the OP on how to make his "right" approach safe and reliable, here's my two cents:

(1) I helped a friend put a JLCR and a 36" chute into a 54mm airframe last weekend, it was a tight fit and we had to use a long/thin burrito to get it in there. 30" is probably going to be much easier depending on the packing volume of the chute. And we could have reverted to dog barf and less nomex if needed. Before you head to the field, work on your packing method so you are confident you can get everything into the airframe, it's protected, and the main with the JCLR is not jammed too tightly in there.

(2) Best place to carry ballast is usually up high. Best way to carry it is very securely. Have you simmed the amount of mass that you are going to have to add? Are we talking about a handful of large fender washers, or a small bag of sand, or what? Hypothetical -- if you could fit the right amount of sand into a zip-lock bag, rolled up so it would fit into the tube with some room to spare -- you could attach the package to the top of the shock cord with a buttload of duct tape. Encase it completely in duct tape so that the plastic won't tear (until you remove it, but that's after you have achieved your L2) :) There are other ways to attach this mass object, depending on how much you are going to need and how the rocket is configured. This way just assumed that you are working with a single tube, you don't want the mass shifting during boost, and at apogee deployment you are not worried about keeping the NC attached (like you are with a DD setup).

(3) When you start adding a lot of mass, drag separation is something to consider, so you might want to think about putting a couple of shear pins in the NC. Which brings up another thing to think about - does the motor have enough BP to pop the NC if you have it pinned. With DD setups, we ground test the charges...if you haven't made the DD leap yet, it might be a hassle to get your hands on BP, and e-matches to do any real testing. But if you know how much is in the motor, and talk to some experienced fliers, you might get a sense of whether it's "plenty" or "hmmm...?".

(4) If the 30" main is the right size, I'm wondering about that 18" drogue. I use a crappy flat 18" parachute on a rocket that is around 10 pounds after the propellant is spent. It descends at around 65-70fps, which is the slowest I'd want to go if the rocket is going really high. If you can get drag coefficient info for your chute, or sim it in the tools, I would recommend targeting a higher descent rate (75-80fps, or higher) to get it down quickly.

(5) Re: your main deployment setting on the JCLR. I think that 300 feet is fine for a light mid-power rocket. But for heavier fiberglass rockets, I would recommend setting a higher deployment altitude. If anything gets fouled, you are giving it more time to get straighten out. And if for any reason things don't go exactly as planned, you've got a lot more time to sound the alarm if it is coming down near people. I was at a launch where the flier had set the JCLR to 300 feet, and the parachute didn't inflate right away. It did finally inflate at around 100 feet, but it was far too close for comfort in my opinion, given that the rocket was a fiberglass and weighed around 5 pounds. If the main event was set to 800 feet, we would have had several more precious seconds to evaluate the situation and alert people in the vicinity.

So there's my two cents. I didn't start out to write an essay, but I guess this suggests one more thing -- the OP wants to K.I.S.S his L2 flight. But K.I.S.S. is relative. L2 and L3 certs are more than just merit badges -- they are recognition that the cert holder understands the risks of our hobby, and actively mitigates them to keep themselves and everybody else at the range safe. So I completely support the OP's KISS approach - he is using proven systems, is seeking information on how to set up the rocket to achieve his personal objectives (which are different than yours or mine) while keeping the flight as safe as possible (given that we are hurling chunks of fiberglass into the sky--what could possibly go wrong?)
 
In my personal experience the JLCR has been less reliable than traditional dual deploy. I have had two flights in which the JLCR released the rubber band but the chute failed to open. In one case with a 15 lb rocket and a 48" chute the JLCR released but the chute stayed in its burrito wrapped Nomex protector for 500 ft.

It would be nice to have some real statistics about JLCR failures.
 
I have two JLCRs which I fly with an altimeter for apogee eject as well as motor eject. I also fly traditional dual deploy and although the number of my JLCR flights are much less than my traditional DD flights I would say that both are reliable, both have pluses and both are susceptible to failure due to user issues. So far I have mitigated my JLCR flights to a few thousand feet and I have done this because I have it in my head that there is an increased possibility that the JLCR bundle could let lose on decent resulting in a long recovery. However this is just instinctual and I know that there are some who have flown to relatively high altitudes without any issue using the JLCR.

One thing I would caution the OP of using motor eject for, is longer higher flights. The flight time may exceed the delay time and keep in mind that delays can vary +- X number of second/s. So if you want to use motor eject on a higher flight just make sure you get your sims down. Besides that I say go for it as it is all part of the learning curve. I think eventually you will decide that these flights are better serviced by an altimeter.
 
In my personal experience the JLCR has been less reliable than traditional dual deploy. I have had two flights in which the JLCR released the rubber band but the chute failed to open. In one case with a 15 lb rocket and a 48" chute the JLCR released but the chute stayed in its burrito wrapped Nomex protector for 500 ft.

It would be nice to have some real statistics about JLCR failures.

Sounds like the JLCR functioned fine, the problem is elsewhere.
 
Sounds like the JLCR functioned fine, the problem is elsewhere.

Yes, the problem is the chute and how it is wrapped. Some stayed bundled and never unfurl (think Estes parawad). Even a nomex burrito-wrapped chute ejected from a traditional dual-deploy tube can remain bundled, especially if the chute is rather plastic-y. I stopped doing this.

I'll probably get a JLCR for MPR, but I'll stick with two compartment DD for HPR.
 
Yes, the problem is the chute and how it is wrapped. Some stayed bundled and never unfurl (think Estes parawad). Even a nomex burrito-wrapped chute ejected from a traditional dual-deploy tube can remain bundled, especially if the chute is rather plastic-y. I stopped doing this.

I'll probably get a JLCR for MPR, but I'll stick with two compartment DD for HPR.

I burrito wrap my JLCR chutes the same way I wrap my dual deploy chutes and I only have problems with the JLCR. And my chutes are all FruityChutes, made of non plastic-y nylon. I suspect that being tightly bound by a rubber band for 30 minutes or more in cold weather may be making the Nomex burrito less likely to open up.
 
My two pennies with all this...I think you are on the right track provided you take the time to really learn how to work the JLCR. I dislike traditional dual deploy set ups, I think they are tedious and fiddly and don't enjoy setting them up at a launch. When the JLCR came out I knew I had found the prefect solution for me. Up until that point I just flew a flight profile that makes people cringe and shake their heads. I routinely flew past 4-5K feet with apogee deploy relying on a bad to the bone tracker system to get my junk back.

Now I do the same thing with a JLCR with a much shorter walk. My current go to rocket is similar to what you are building, a 54mm body tube with a single break. It's a Nuke Pro Max that I did my level 2 flight with. The light weight cardboard rocket has been used to test several dual deploy set ups from a traditional dual break to a single break with a cable cutter and now a JLCR. I think now it's the best it's ever been as the payload bay has been shortened up a bit and there is very little wasted space inside. I haven't flown it on a J since the refit but have little doubt it will soar past it's best altitude of over 7K'. It has been up on H's and I's and gets going in a hurry.

Every one of my 20ish flights with the chute release in several different kits have all been flawless. I believe the secret sauce is the setup (duh). I found that flat panel chutes from Top Flight work best for me and no longer use my expensive Fruities. Wile the Fruits are very nice, I can get a much tighter pack job with the panel chutes. I will never be able to describe how I fold my chute because words just don't paint the proper picture but I get the chute as skinny as possible then Z-Fold it then place the JLCR centered on the chute bundle. When I test it, it explodes open like it has somewhere else to be. No way it won't open in flight. I also make sure the whole shooting match is fully enclosed inside a nomex with the ends folded up over the shock cord so it will be pulled open after the nose separates. Make sure the whole thing fits easily inside the body tube and is not too tight as it is likely not to come out in flight otherwise.

So while I feel I have the system dialed pretty good, I want to try a small drogue attached to the forward payload section. I feel stabilizing the descent will let it come down vertically instead of drifting a long way drogueless.

Personally I wouldn't worry about adding drag or weight to limit your altitude. If you have the means to track it and feel comfortable doing so then let it rip on a small J and see what happens. Fiberglass rockets are pigs and are heavy enough as it is. Fly it a couple times on a large H or I to sort it out and then punch it.
 
In my personal experience the JLCR has been less reliable than traditional dual deploy. I have had two flights in which the JLCR released the rubber band but the chute failed to open. In one case with a 15 lb rocket and a 48" chute the JLCR released but the chute stayed in its burrito wrapped Nomex protector for 500 ft.

It would be nice to have some real statistics about JLCR failures.


Did you have your chute wrapped up in the nomex with the JLCR holding the nomex closed?
 
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