LOC Graduator Build - "Diomedes"

Hi! This is my first MPR build. I have built about a dozen Estes kits to this point and I'm excited to build a larger rocket that I can bring to local launches. I am hoping that this build will be a good stepping stone towards my L1 Certification and I've chosen the LOC 2.6" Graduator based on recommendations from the forum to build something with thicker walls, plywood fins, and epoxy. I'm going to keep the kit stock for now and fly it on Es and Fs, but I am interested in making it dual-deploy later or maybe just using a chute release to fly it on larger motors and still find it.

The kit just arrived yesterday and I dry fitted the parts together in the garage to get a sense of scale, and admittedly, because I had friends over last night and wanted to show off. Here's a picture of it next to an Estes Patriot and a Viking with a homemade payload bay.


Two things that I could use some help on:
1. Ideas for payload. This rocket has substantial space for payload and I'm open for suggestions. I definitely want to mount a camera to the outside pointing down, I could also include an internal camera as well. I'd love to carry a scientific payload but I don't have a single idea for an experiment, if you have suggestions please comment below.
2. Paint scheme! Here are two options I've come up with so far:

Option 1 (cribbed heavily from Batmite's O motor rocket)

Option 2 (cribbed heavily from Blue Origin's New Glenn rocket)

The scheme for all JCRL rockets is based on the Cascadia flag (you know the made-up country of CA, OR, WA and British Columbia) but I'm having trouble incorporating the green in a pleasing way. Any thoughts are appreciated as I am no artist.

That's all I have for now, I will be updating often as I build out the rocket and hope that you'll comment with advice and expertise if you see me make questionable decisions.

I am, of course, biased toward the first design.

Payloads are not my thing, but people have dropped parachute men from their rockets. Scientific? Someone will come along with ideas.

I started working on the Graduator in earnest this afternoon. One change I made off the bat was how the shock cord attaches to the MMT. The instructions from LOC call for an eyebolt on the inside centering ring. Instead I cut a slot into the centering ring and wrapped the shock cord around the MMT. I removed the glassine layer from the MMT, sanded and fitted the centering rings to finish the assembly.


I slide the MMT assembly into the airframe, making sure that everything fit snuggly but easily. I sanded the root edges of the fins so they will slide through the airframe tube easily when it's time for epoxy. I labeled the fins and the airframe so I won't forget which fin goes where, and then I dry fitted the entire booster.



The last thing I did today was sand, label and fit the payload section. The payload head is slightly smaller than the coupler and it wobbles in the tube. I assume that the epoxy will solve this, but please let me know if I need to do something more to fix the loose fit.


That's all for this weekend

I forgot to mention that a small section (no more than 1/2") of the airframe was crushed and starting to delaminate at the rear of the rocket. I used wood glue to fix it, but please let me know if I'll need to do more to correct this issue (I don't want the airframe to peel apart under thrust).

JCRL said:

I forgot to mention that a small section (no more than 1/2") of the airframe was crushed and starting to delaminate at the rear of the rocket. I used wood glue to fix it, but please let me know if I'll need to do more to correct this issue (I don't want the airframe to peel apart under thrust).

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Whenever I have the edge of a body tube coming apart like that, I take a piece of masking tape and stick it and remove it from the palm of my hand four or five times to weaken the adhesive, and then stick it over the problem section. Then I soak the area from the inside of the body tube with THIN CA so it grabs every layer from behind. Let it sit for a minute or so. It takes some practice to get a feel for how much CA is needed, but if you put just the right amount, you can peel off the masking tape with no problem. Worst case scenario, you'll put too much and some of the masking tape will stick with the CA, but that can be sanded off no problem.

As for payload ideas, I suggest grabbing an altimeter. I personally prefer the Jolly Logic Altimeter 3 which displays the flight data on a nifty graph on your smartphone. Other ideas include weather sensor dataloggers with the sample time set to the absolute lowest interval so you can get data like temperature and barometric pressure changes through the flight, a marshmallow in a clear plastic jar (with vent holes) to measure the expansion of the marshmallow as the air pressure decreases, or a glass microscope slide smeared with some agar in a sealed container that will only open for a short time at apogee in order to collect bacteria samples that you can grow. Keep in mind, most of these payloads would require you to make vent holes in your payload bay to allow for air to equalize in pressure (even the JL Altimeter; it has accelerometers, but it primarily gauges the altitude by measuring the pressure drop). For a rocket that size, three or four holes about 1/16 inch each evenly spaced around the payload bay aligned with wherever your pressure-sensing device is should be fine. The more internal volume of the payload bay you have, the more venting you will need to keep the pressure even.

As you venture further into mid power and especially high power, these vent holes become more important. A nearly airtight rocket can actually experience a premature deployment because the internal air pressure can push the nosecone off as the outside pressure drops at higher altitudes. This is especially bad if you have a two-stage rocket and the sustainer just started and the nose blows off with the rocket under acceleration! Even if you don't have a payload bay or anything on board that senses the air pressure changes, holes in the body to prevent the nose from coming off too early are necessary for bigger rockets hitting higher altitudes.

ebruce1361 said:

As for payload ideas, I suggest grabbing an altimeter. I personally prefer the Jolly Logic Altimeter 3 which displays the flight data on a nifty graph on your smartphone. Other ideas include weather sensor dataloggers with the sample time set to the absolute lowest interval so you can get data like temperature and barometric pressure changes through the flight, a marshmallow in a clear plastic jar (with vent holes) to measure the expansion of the marshmallow as the air pressure decreases, or a glass microscope slide smeared with some agar in a sealed container that will only open for a short time at apogee in order to collect bacteria samples that you can grow.

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Thank you for advice on the damaged BT @ebruce1361 , I'll take a look at this tonight. Also I really love your idea about collecting bacterial samples at altitude. Could I speak with you in greater detail about how to design a sealed container that will open at apogee? The payload section is roughly 10" by 2.6"

Sure! You can send me a message via the "Conversations" option, or you can email me at ebruce1361@gmail.

One quick suggestion, and hopefully it is not too late, but you are going to need to shock cord from ejection gasses (first picture in post #3). The way you have it there, it wont last but 3 or 4 flights before it snaps.

One way would be to use a nomex sleeve and slide it over your elastic cord being sure to secure it on the mmt side so it doesnt slide up the cord exposing the end your trying to protect. The other, and this might take some doing now, would be to use an 18" piece of 1/4" or 1/2" kevlar, then attach your elastic to that.

...and be warned, many will tell you that elastic is a bad idea, and give you funny anecdotes as to where it "belongs." I wouldn't worry, I have used it for decades in similar builds with zero issues.

Thanks for the tip @Theory ! I haven't glued anything together yet so there's still time to make changes. The elastic shock cord came with the kit, so I wasn't aware that it wouldn't last very long. I'm hoping to fly this one often so changing out the shock cord seems like a good investment.

ebruce1361 said:

can email me at

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May want to break up or sudo that email address. Don't want it to be picked up my spam/advertisers

I’m curious as to why you aren’t using the eyebolt to secure the shock cord?

Nytrunner said:

May want to break up or sudo that email address. Don't want it to be picked up my spam/advertisers

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Well, too late for me to edit it now. No worries, I got in contact with JCRL via the conversation feature, so I'll just send everything I get to spam except for addresses I already have saved.

JCRL said:

Thanks for the tip @Theory ! I haven't glued anything together yet so there's still time to make changes. The elastic shock cord came with the kit, so I wasn't aware that it wouldn't last very long. I'm hoping to fly this one often so changing out the shock cord seems like a good investment.

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no need to switch it all out, just add the piece of Kevlar to the mmt end and tie your elastic to the other end

Scott_650 said:

I’m curious as to why you aren’t using the eyebolt to secure the shock cord?

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The plan is to wrap the shock cord around the MMT instead of using the eye bolt was at the suggestion of Mike Westerfield in his book Make: High Power Rockets. My understanding is that way the force pulling the shock cord is spread across the entire centering ring, rather than focused on the eyebolt.

Theory said:

no need to switch it all out, just add the piece of Kevlar to the mmt end and tie your elastic to the other end

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I ended up picking up a nomex sleeve for the shock cord at my local hobby store.

I didn't get any work done on the rocket this weekend because I was working on another related project: a folding workbench for my garage! Also moved an electrical outlet because it would have been blocked and now it's easily accessible. I've been working off a banquet table I set up in the garage, but now I'll have a dedicated workspace and my wife can still park her car. I'll be putting up pegboard over the window and storage over the workbench this winter.

Going back to choosing a paint scheme for the rocket, here option 3:

NC and Payload section in glossy blue; Booster section in polished aluminum or stainless steel; Fins in glossy green; Lettering, and "Doug" logo in matte green.

The temperature has plummeted to near freezing here, my garage isn't heated, and the epoxy won't work at this temperature so progress is halted until it warms up again. It's unfortunate because the skies have been perfect for rocket launches.

JCRL said:

The temperature has plummeted to near freezing here, my garage isn't heated, and the epoxy won't work at this temperature so progress is halted until it warms up again. It's unfortunate because the skies have been perfect for rocket launches.

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Do like I do except for painting, take over the dining or breakfast table, cover with newspaper and go for it.

@John Taylor that's what I'm going to have to do...as soon as the wife okays it

JCRL said:

@John Taylor that's what I'm going to have to do...as soon as the wife okays it

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LOL! I understand. However I AM THE MAN OF THE HOUSE!!

As long as it's ok with my wife.

Question for the group: Does this MMT need an engine block at the end? The kit didn't come with one and the instructions don't mention one, but what's to stop the motor ripping through the nosecone on ignition?

You don't need an engine block. There isn't one provided and it's not needed. You probably do want an engine retainer. I used the AeroPack Quick-Change 29mm on my Graduator and I'm very pleased with it. Estes makes a plastic 29mm retainer which works pretty well if you want plastic, and LOC also sells 29mm motor retainers so there are several options you can choose from.

~dave~

Thank you @ChicagoDave I have a really nice AeroTec retainer that I'll be using on the build. I guess I'm just paranoid.

The only reason to add a block is to us BP motors that lack a thrust ring. Instead of the block you can make a thrust ring from tape If you use BP motors . Or just not use BP motors.

ChicagoDave said:

The only reason to add a block is to us BP motors that lack a thrust ring. Instead of the block you can make a thrust ring from tape If you use BP motors . Or just not use BP motors.

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I will be using BP motors and that was the reason for my concern. My local launch site doesn't have a HPR waiver so F is as big as I can push it.

Got ‘ya.

BTW, I love flying the Graduator on a F52 Aerotech reload which is a great motor and should get you just about 1,000' apogee.

Also check out Thrustcurve.org for some ideas about what motors work well with the Graduator: https://www.thrustcurve.org/motorguide.jsp?rocket=5025 and see what it says and sim a few of them to see if they'd work for your rocket and field.

Thanks for your advice @ChicagoDave

X2 on the F52

its a very solid (and inexpensive) motor - great for small fields

Here's my Graduator on a G40-7 in October. Don't know what happened to the sound on this video.