Hybrids 2024

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Solid Recommendations re Propellant Thermochemistry Modeling Software??

I have, and have worked a bit with, various free and paid 'software' for the thermochemical modeling of various propellant formulations. One example would be ProPep3. Can anyone very heartily recommend software - whether freeware or paid - that they truly feel (or, even better, know!!) is excellent and can be relied upon?
RPA (rocket propulsion analysis) is what I use. The free version (1.2.9) has basically all you'd ever need, version 2 limits the number of propellant components but does nozzle geometry and heat transfer, so I recommend 1.2.9 for the most part. If you mean modeling an entire engine burn, there are a couple hybrid spreadsheets floating around and then HRAP (hybrid rocket analysis program) which I developed and posted to GitHub.
 
Working on my Rattworks K240 build again. Also making some improvements to HRAP.
Are you using the 'stock motor' or with changes / improvements?

Using the stock reload and injector? Stock fill line? Stock Preheater? I have wanted to try Pyrodex Pellets for the 'preheater''.

The Ratt K240 is the loudest motor I have ever flown. I clustered 2 of them, 129dB at 100 feet from the pad.
 
Are you using the 'stock motor' or with changes / improvements?

Using the stock reload and injector? Stock fill line? Stock Preheater? I have wanted to try Pyrodex Pellets for the 'preheater''.

The Ratt K240 is the loudest motor I have ever flown. I clustered 2 of them, 129dB at 100 feet from the pad.
Mostly stock aside from the pre-heater (probably along the lines of the new Contrail "Ring of Fire" igniters), I got Dave to make a reload for it a year or so ago. Even stock this rocket is simming to ~12K feet, which is well over half the max altitude any of my local fields could accommodate. Planning to re-fly later on a swirling injector with a shorter ABS grain, which should get it to around a 50% L350, but that'll require a trip out west.
 
NEED Orifice Diameter - Skyripper 38 54. I noticed some gunk / corrosion for the tank vent orifice https://www.mcmaster.com/2712T51/ on my skyrippers. Was going to replace them then I realized I dont know the actual diameter of the orifice. Per Mcmaster Orifice Plugs I can go as low as .010 inch and as high as .063. I was going to guess at .020 inch.

Anyone know the ACTUAL size? FOrthat matter good to know the Ratt 29 - 64 diamters too.

Mike K
 
NEED Orifice Diameter - Skyripper 38 54. I noticed some gunk / corrosion for the tank vent orifice https://www.mcmaster.com/2712T51/ on my skyrippers. Was going to replace them then I realized I dont know the actual diameter of the orifice. Per Mcmaster Orifice Plugs I can go as low as .010 inch and as high as .063. I was going to guess at .020 inch.

Anyone know the ACTUAL size? FOrthat matter good to know the Ratt 29 - 64 diamters too.

Mike K
Or you coould use brass printer nozzles or gas jet nozzles. Brass printer 0.2 mm M6 thread would be 0.01" ish and not $11 each ...
 
Or you coould use brass printer nozzles or gas jet nozzles. Brass printer 0.2 mm M6 thread would be 0.01" ish and not $11 each ...
... but do you know the diameter?

not a bad idea to use a printer nozzle.

Mike K
 
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... but do you know the diameter?

not a bad idea to use a printer nozzle.

Mike K
I can measure the rattworks 29 and 64. Once i can get my hands on my acetylene nozzle cleaners to get a size and find my vermiers. I think Contrail mentioned their vent size before, here. Maybe we should set up a hybrid dropbox and have a single source for useful info.
edit: found Contrail. post #27 half way down

The vent fitting on the Contrail Rockets website has a .028 inch hole. Not sure what size motor/tube that's for. I'd guess 98..
Edit:-----
RattWorks 64mm 0.7mm vent hole for length of 2mm max vent tube 40mm from top of cap internally
Rattworks 29mm 0.3mm vent hole for 1mm max. No vent tube internally, so no ullage....
 
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Yes Contrail Rockets vent fitting has a .028 hole. You can see it on website. For some of the other vents we have used as in the recent internal vented 54mm motor I machined a .028 hole. Years ago the Trojan line was all machined .028 holes. Tooling and jigs make it so I can drill 100 vent fittings without breaking a bit.
 
I can measure the rattworks 29 and 64. Once i can get my hands on my acetylene nozzle cleaners to get a size and find

Yes Contrail Rockets vent fitting has a .028 hole. You can see it on website. For some of the other vents we have used as in the recent internal vented 54mm motor I machined a .028 hole. Years ago the Trojan line was all machined .028 holes. Tooling and jigs make it so I can drill 100 vent fittings without breaking a bit.
I got you beat, I can drill 100 vent fitting hols and break many bits....
 
I got you beat, I can drill 100 vent fitting hols and break many bits....
Stop hand drilling them...... :) . Printer nozzles look like a good easy option to me.
Below are Oxy Acetylene nozzle cleaners/reamers. $5 for a set on Ebay. You could easily use them to ream from a 0.6mm to 0.7mm. Or see how long it takes to fill with a 0.6 vent. The reamers are too large for the 0.3mm vent in RattWorks 29mm, but you can buy a 0.3mm printer nozzle
https://www.ebay.com.au/itm/374973720074?

1714858100965.png
 
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Printer nozzles are a great option, but idle jets for carburetors also do the trick! They're available in a ton of different thread sizes and shapes, from hex to slotted head and so on. They're also available in a wide range of sizes, sometimes in 0.01 mm / 0.5 thou increments, but usually in 0.05 mm / 2 thou increments. I've thought about using them for injectors as well as you could machine one injector body and test different size orifices by changing the jets, without having to machine multiple tiny holes.
 
Ended up just drilling .028 holes using tungsten carbide PCB drills with expanded shanks into real 1/8 npt hex plugs.

Printer heads were tempting but the straight thread on them isn't really meant to be a high pressure gas sealing surface. Made a simple drill jig on the lathe for putting the holes in the caps.

https://www.mcmaster.com/products/plugs/pipe-size~1-8/drive-style~hex/?s=1/8+npt+plug

The plugs seat in well 1715007622472.jpeg
 
I just got my West Coast Hybrids I110 ready for the weekend and it was also missing the vent but I had a bunch of idle jets left over from tuning my motorbike. Made an adapter from 1/8" NPT to M5 thread, one side gets the jet (0,42mm) the other a small fitting for 3mm PA hoses (roughly 1/8). Can't wait to fly it :) I'll burn my last original (PVC) grain first and I have an optimized ABS grain for another flight.
 

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I just got my West Coast Hybrids I110 ready for the weekend and it was also missing the vent but I had a bunch of idle jets left over from tuning my motorbike. Made an adapter from 1/8" NPT to M5 thread, one side gets the jet (0,42mm) the other a small fitting for 3mm PA hoses (roughly 1/8). Can't wait to fly it :) I'll burn my last original (PVC) grain first and I have an optimized ABS grain for another flight.
M5 and 1/16 npt pretty much fit each other....
 
M5 and 1/16 npt pretty much fit each other....
Not really, 1/16 has an OD of 7,89mm and a pitch of 0,941mm vs 5mm and 0,8mm for M5. The threads on the WCH parts are 1/8" and the fittings for 5/32" / 4mm fill hose have the right ID so you can just tap a M5 thread in them.
 
Pretty easy to make the proper vents, the 1/8 npt hex plugs are about a 1$ each, using the PCB drill (about a $1/drill) a few seconds a piece to drill the brass.

As far as straight threads vs pipe threads, straight threads dont actually seal
Not really, 1/16 has an OD of 7,89mm and a pitch of 0,941mm vs 5mm and 0,8mm for M5. The threads on the WCH parts are 1/8" and the fittings for 5/32" / 4mm fill hose have the right ID so you can just tap a M5 thread in them.
Might be ok but.....

Tapered plug in tapered hole will really seal. Straight threads don't really seal, even a straight thread in a tapered hole. Straight threaded fittings use another feature for the gas seal. Plus, wrong thread may not be able to come out without damaging the hole.

Mike (previously pressure vessel designer) K.
 
Pretty easy to make the proper vents, the 1/8 npt hex plugs are about a 1$ each, using the PCB drill (about a $1/drill) a few seconds a piece to drill the brass.

If using brass fittings, if you were worried about drilling it with a sub-mm diameter drill bit, then you can always drill a larger hole into the brass with a slightly larger counterbore in the back and fill enough of that with solder, then drill the vent orifice into that. Brass isn't the toughest material to cut though.

TP
 
Pretty easy to make the proper vents, the 1/8 npt hex plugs are about a 1$ each, using the PCB drill (about a $1/drill) a few seconds a piece to drill the brass.

As far as straight threads vs pipe threads, straight threads dont actually seal

Might be ok but.....

Tapered plug in tapered hole will really seal. Straight threads don't really seal, even a straight thread in a tapered hole. Straight threaded fittings use another feature for the gas seal. Plus, wrong thread may not be able to come out without damaging the hole.

Mike (previously pressure vessel designer) K.
You're just not using enough teflon tape Mike...... :) Now you're thinkin to yerself, "did he tap this 1/4 BSP or 1/4 NTP..... Do ya feel lucky?"
 
If using brass fittings, if you were worried about drilling it with a sub-mm diameter drill bit, then you can always drill a larger hole into the brass with a slightly larger counterbore in the back and fill enough of that with solder, then drill the vent orifice into that. Brass isn't the toughest material to cut though.

TP
Also the vent restriction is not just about the diameter, it's about the length it applies.
 
Pretty easy to make the proper vents, the 1/8 npt hex plugs are about a 1$ each, using the PCB drill (about a $1/drill) a few seconds a piece to drill the brass.

As far as straight threads vs pipe threads, straight threads dont actually seal

Might be ok but.....

Tapered plug in tapered hole will really seal. Straight threads don't really seal, even a straight thread in a tapered hole. Straight threaded fittings use another feature for the gas seal. Plus, wrong thread may not be able to come out without damaging the hole.

Mike (previously pressure vessel designer) K.

No worries, it's all sealed where it needs to be 😉 the 1/8" --> M5 adapter is tapered, there is a aluminium washer on the idle jet has and the 1/8" hose fitting comes with an O-Ring.
 
Well it was a good weekend 😀 flew the 54mm prefilled motor with the bigger tank to 1443m and the WCH I110 one time on PVC (1073m) and once on a more complex ABS grain (only 853m, same rocket). All flights were successful but the lower altitude on the WCH ABS flight means I have to put it on the teststand... Oh no ;)
 

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Just want to confirm with the legends here that Krytox 215 is safe to use? Reason I ask is that I’m now able to obtain it for free if I want and it appears to be listed as oxygen safe like the rest, but the sheet does mention that it contains molybdenum disulphide - and not sure if that’s an issue
 
Just want to confirm with the legends here that Krytox 215 is safe to use? Reason I ask is that I’m now able to obtain it for free if I want and it appears to be listed as oxygen safe like the rest, but the sheet does mention that it contains molybdenum disulphide - and not sure if that’s an issue
Yes, it's safe. But it's going to be messier......
Molybdenum disulfide does not react with oxygen. The other components of the grease are fluorinated synthetic which are oxygen safe.
And of course, Nitrous oxide is not as reactive as pure oxygen. There are cheaper oxygen safe greases such as Crystalube used for dive equipment. But the Krytox range has better high and low temp performance.
Although Krytox205 is expensive, you don't need to use much, so a tube lasts a long time.
Norm

https://www.krytox.com/en/-/media/files/krytox/krytox-gpl-105-205-215-225.pdf?
 
Awesome, thanks for that. I had found Tribolube from a dive shop at a fairly good, but I also crew on a race car and just found out that we go through heaps of 215 all the time as that’s the high pressure lube our clutch bloke uses. Since we already go through tons and the quantities I’d be using is tiny by comparison, they’re happy for me to take what I need - hard to beat that price!
 
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