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Nozzle and case manufacturing


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#1 JMan

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Posted 08 June 2020 - 10:08 PM

TLDR;
will aluminum nozzles melt with sugar propellants?

Does anyone make good nozzles without a metal lathe?

Why are not official looking things so frowned upon?

Does anyone else here do much data acquisition on their motors?

So, recently, Ive been trying to acquire a lot of data on the rockets I design (sucrose, sorbitol, and erythritol). And, although my motors seem repeatable and well preformed, the data I am getting shows that I have LOTS of room for improvement. The best motor I made (best being rated by specific impulse) was a KNSU end burner. Almost 50 second Isp and 16 N*S (if I remember).

Problem is that these propellants should be getting ISPs of 100 seconds or even a little higher (or at least my goal). I know Estes only gets 80 seconds but I cant find a good source to find theoretical isp of BP motors. So when I tried to push my motors a little harder, I hit the problem I started with years ago, over pressurization and CATO (well, theyre on thrust stands so no take off actually). Which brings me to the thread title (and I have a few points and questions about all of this).

(This was a really long post, but Im shortening it for all your convenience, if you want to know more, let me know).

I have a wood lathe, metal lathes are expensive (and honestly, do not have to be but no true desktop cnc machines exist and I might try to make one if it comes down to it, or a cnc attachment for my wood lathe). So I cannot machine hard metals. I could turn aluminum and graphite. Graphite is too brittle and Id like my nozzles to be threaded (if this is not true and it can be threaded correct me please). Ive heard conflicting things on aluminum (and steel) eroding from sugar propellants. Does anyone know from experience what is true?

Is there an alternative to make good (and reusable) nozzles for reusable cases (not case bonded nozzles like concrete)? It seems like the only way is to machine them.

I also plan on buying aluminum pipe/tubing to make my own cases (that way I can thread them how I want rather than how manufactures do it because they are mildly expensive and do not sell nozzles to go with their cases). So why is it when things like washers (for a nozzle) or a stick taped to a motor are so frowned upon at so many places? Would making my own case (and nozzle) be frowned upon as well?

Most of you people here seem to be into the fire works side of this, I was wondering if anyone is into the data acquisition side like I am? If so, Id love to learn more about it from someone else rather than trial and error. All I have is a thrust stand and a lot of aerospace engineering knowledge right now (love doing the math on all this).

#2 gdeputy

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Posted 09 June 2020 - 10:50 AM

Where are you located?   If in the US, find the nearest Tripoli Prefect and start meeting people.   There is a very active community of motor builders doing design, simulation, data acquisition, etc...  Most folks are using Ammonium Perchlorate Composite Propellant, but sugar motors are also quite common. 

 

You are in a pyro forum, and most rocket motors here are going to be rammed/pressed BP, whistle, etc.    You're getting into the realm of amateur rocketry, you should hit some forums where you'll get better support and find more people into that hobby.  Try www.rocketryforum.com for a starter. 

 

Graphite is ideal for nozzles.     If you want to do threaded retainment, make an aluminum threaded retainer to hold in the nozzle.  Use orings for sealing.   You can also use snap rings for retainment, which reduces the machining complexity considerably.   You can also buy experimental motor hardware, see www.lokiresearch.com for an example.  


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#3 nils

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Posted 09 June 2020 - 10:29 PM

This FB group is helpful, friendly and alive:

Amateur Experimental Rocketry

https://www.facebook...396488870646273

 

Aluminium will melt absolutely. Copper too.

I experimented with reusable nozzle that I made by welding together a steel washer and a steel pipe transition.

https://www.amateurp...eusable-nozzle/

I stopped experimenting with this because I do not have a place to fly big rockets anyway.


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#4 JMan

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Posted 13 June 2020 - 10:07 PM

Unfortunately, those threads are locked for non lvl 2 certified persons. I know a lot of people say its good and go get certified, but my closest club is 3+ hours away and I plan and test stuff more rapidly than once ever few months (or how frequent their launches are). And all of those research threads are locked to even google search so I cant even find useful information very easily if I wanted to.

Anyways, I did make my own case today, threading failed for nozzles, but a second case was made and threaded, and threads provided good holding for a clay nozzle and I achieved 87 seconds Isp (which is weird because if I run it through openmotor, i cant design a rocket in it that gives more than 50 seconds.

Anyways, Id call it a partial success, custom (Reusable aluminum) motor tubes can easily be made, nozzles to fit them may require more machining than I have available right now.

#5 nils

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Posted 16 June 2020 - 09:36 AM

Sugar motors burns at around <1000C. Aluminium melts at 660C. Core burner might work. As I remember, OpenMotor is only for core burner. Original poster mentioned end burner.


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#6 JMan

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Posted 16 June 2020 - 10:52 PM

Open motor does many types of grains, Ive been working on setting up a virtual machine to get propep working. KNER burns at 1210 K so yah, it would melt the throat even assuming temperature drops to half at that point. But clay holds amazingly well to threaded aluminum, Ive gotten it to blow out at 68 atm, Although, typically blowout happens closer to 50-55 atm (these are for end burners so the whole pressure is on the clay).

My thrust stand just quit on me today and I ordered a new load cell so Ill have to wait. Anyways, with propep, Ive been looking at optimal ratios with KNER and nearly 45-55 F-O ratio. Much different than KNSU or SB. Mixed up a batch and it gives stable combustion at atmospheric pressure. Just thought that was interesting.




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