"HellFire" Baby J, J1600 build

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3stoogesrocketry

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You cannot tease us like that lol. Let's see the grains . Knowing what I do , what's your burnsim theoretical KN? 25:1 is fun .
 

PayLoad

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Burnsim doesn't work well on long, thin motors - it does not take into consideration erosion burning down the core. The cores are 1/8th up to 3/8ths, with a large throat on the nozzle. I'll video & post burn here.
 

timbucktoo

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Let’s at least see a pic or your grains!
 

PayLoad

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29mm by 76cm Hellfire "Baby J" Ready to fire. Video Forthcoming

If she explodes, I will officially give up building motors. (she won't)

IMG_8914.JPG
 

timbucktoo

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why don't you bury it it the ground instead of using that crazy tripod in case something goes wrong?
 

PayLoad

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Easy Answer - What could possibly go wrong?
Real Answer - Worst case scenario is blowing out either the fore or aft seals, which will either plant it to the ground or make it a very bad rocket.

Besides, I'm a huge fan of lighting tripods

EDIT - Plus there is a whole 1.6 seconds of burntime.
 
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3stoogesrocketry

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Burnsim doesn't work well on long, thin motors - it does not take into consideration erosion burning down the core. The cores are 1/8th up to 3/8ths, with a large throat on the nozzle. I'll video & post burn here.
True , but also mixing up fuel types and sharp stepped edges will shear AP just as easily. I would round over your edges on all your grains.
Easy Answer - What could possibly go wrong?
Real Answer - Worst case scenario is blowing out either the fore or aft seals, which will either plant it to the ground or make it a very bad rocket.

Besides, I'm a huge fan of lighting tripods

EDIT - Plus there is a whole 1.6 seconds of burntime.

1.6 second burn J1600? What grain formula(s) from RCS are you using ? What holds the tripod in place ? Your neighbors may not like a J motor flying thru their yard if a leg pops and it turns into a land shark.
 

rocketkyle

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impossible. 1600 x 1.6 = 2560Ns which would be a full K/baby L. and that is just simply not happening. how did you come up with those numbers?
 

Antares JS

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impossible. 1600 x 1.6 = 2560Ns which would be a full K/baby L. and that is just simply not happening. how did you come up with those numbers?
Going to have to agree with this - the 1.6 second burn time raised an eyebrow here. I really doubt you're going to get that slow a burn out of a motor with this extreme long and thin geometry. Assuming your 1600 N average thrust is correct, the longest it could burn and still be a J is 1280 Ns on a full J/1600 N average thrust = 0.8 seconds.
 

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True , but also mixing up fuel types and sharp stepped edges will shear AP just as easily. I would round over your edges on all your grains.

Agreed & already done

1.6 second burn J1600? What grain formula(s) from RCS are you using ? What holds the tripod in place ? Your neighbors may not like a J motor flying thru their yard if a leg pops and it turns into a land shark.
BurnSim says 1.6, I mistakenly used that number. It will be less than a second, is my guess, but we'll see
 
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neil_w

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It is amazing to me that you can make a properly functioning motor in that aspect ratio. Look forward to seeing the test burn.
 

boatgeek

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Silly question: how do you get an igniter into a 1/8" core that far up a motor?

I'm also looking forward to videos/data from the test.
 

PayLoad

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Silly question: how do you get an igniter into a 1/8" core that far up a motor?

I'm also looking forward to videos/data from the test.
Not a silly question at all, it was a big concern of mine - Igniters that come with Aerotech 29mm H & I reloads are long enough with 6 inches to spare. I was prepared to "build around an inserted igniter" but that was not necessary - marked on the wire how far it had to go in, and it went all the way in first try, much to my surprise.
 

boatgeek

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Fail. Kablam. I'm done
Before you bail completely on making motors, can you do something less ambitious (say 1-2 grains of the same approximate size)? My understanding is that it takes the pros a long time to work up to a 30:1 motor like this one.
 

DeeRoc29

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Payload, how long have you been making motors? The motor you attempted here is a very challenging one to get right, even for experienced research flyers.
 

PayLoad

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Before you bail completely on making motors, can you do something less ambitious (say 1-2 grains of the same approximate size)? My understanding is that it takes the pros a long time to work up to a 30:1 motor like this one.
Perhaps (no, really?) I bit off more than I could chew. I don't think I will try again, as my main purpose was making the largest 29mm I could.

Payload, how long have you been making motors? The motor you attempted here is a very challenging one to get right, even for experienced research flyers.
Been making motors/explosives since before there was a Tripoli. I've learned that I don't know everything, clearly.
 

3stoogesrocketry

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Perhaps (no, really?) I bit off more than I could chew. I don't think I will try again, as my main purpose was making the largest 29mm I could.



Been making motors/explosives since before there was a Tripoli. I've learned that I don't know everything, clearly.


You had the master of length to diameter make you the case , message him about orange sunset
 

ksaves2

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I did a high L/D 24mm diameter motor 12 inches long. Snap ring with graphite nozzle. Prefect had a couple of lathes. The wall diameter of the aluminum was rather thick as compared to a commercial motor.
I did stepped grains and after the test fire, which burned rather fast and forcefully, the case was hotter than Hades, the forward snap ring was bowed outwards and likely would have failed if the burn was longer and the graphite nozzle was so brittle, it was single use.
Needless to say, I never tried another motor like this again.
I mean that case was so blankety blank hot it was ridiculous.
Getting high L/D motors to work so they are not single use takes a different skill set and formulas to make doable. (Which I haven't mastered mind you.)
Make sure you video the test. I was too young and stupid to video mine as I thought naturally it would work!! Burnsim isn't everything!

Kurt
 

AtomicStorm

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I would look at this as a learning experience. Learning experiences are mandatory for long term success. Alot of times the problem is much bigger then the solution. I am getting back into rockets after taking a break from large 50cc gas 3d airplanes and i can tell you right now that i have had my fair share of learning experiences where the problem cost me hundreds if not thousands and the solution was less than $1. Examples like heat shrink or a little extra glue or epoxy, or thin cheap insulation. Im to the point now where i will research what im doing religiously before i even take the first step on the project. Just keep on keeping on, go slow, research, experiment, test and never give up. Also start recording these test and make you a youtube channel. You'd be surprised how many people enjoy seeing stuff shoot in the air and blow up. That grain you had could have paid for itself multiple times with the views it would get. Check out ElementalMaker on youtube if you haven't already, he makes and test rocket motors and different types of propellants for really cheap, maybe you could learn a few things. Keep them coming payload, we're here if you need help! Post pics of damage if you have them.
 
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PayLoad

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Well, hell, I had one more un-cut fuel grain & another set of hardware, let's try a different cut & fire her up Saturday
IMG_8919.JPG
 
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