Good advice.
I missed one piece of sand once..... never again. Took me an hour to get the parts separated and recover them back to operational. And 2 hours to put together an anodizing tank. One mating part was 1m long. I only had a pot 500mm deep. Had to anodize it in a length of 150mm drain tube vertically then boil it half turn it and boil the other end....
Scott has been helping me along with my experimental hybrid as well. 4' 38mm Skyripper 'clone'. Case has been machined, hopeful to test it out next weekend at our first launch!
)
What thread form did you use for the screw in closure?Over the weekend I cleaned my tanks some more (IPA and DI water), installed the modified pin valve on one and partially filled it with nitrous. The fill tank made a little crackling sound during the fill which made me wary. Turns out the company I got it from turns CO2 tanks into nitrous tanks by adding a new valve to them... they use way too much PTFE tape on the valve threads and get some enough strands of it inside the tank for it to get ripped apart and sucked out when opening the valve (hence the sound). I found some in the valve of my flight tank, yay, fortunately it still seals but it's something that could really cause some problems.
The 54mm motor is also done now, the only parts I still have to machine are spares. I could use the same parts on both the 38 and the 54, but I'd rather have a set for each. Next is printing some ABS grains for next weekend's tests!
(Anodization will follow
For the 54mm I went with a 12mm (a hair under 1/2") nozzle throat and 6 1,5mm (0,06") injector holes which should be right at the maximum flow rate of the modified pin valves.
I'd say it's a cross between metric and unified? So metric 1mm pitch but with rounded crests. I've never had issues with galling but with folded over burrs/chips. Idk if there is a name for that but when cutting fine threads in aluminium and you're getting to the end, doing light passes and the crest is sharp, your chip can form more like a burr and fold over into the the next pitch. It's really easy to miss and will seize threads in an instance if you're unlucky. That's why I start rounding the crest using 4-600grit sandpaper on the final passes.
Hey Matt, fancy seeing you here. I'll try and give you a discord call later today.
Wait you can literally just use printed ASA or ABS chunks as grains? That's cool af!!
You sure can! And 3D printing them makes complex port geometry possible too. I gained a huge leap in performance out of my micro-hybrid just from tweaking the geometry to maximise surface area and mixing in the port. In theory, anything that burns can be used as a fuel grain in a hybrid, but a small amount of energetic material or propellant is often used as a “pre-heater” to provide a heat source that is hot enough to decompose the nitrous oxide and get the motor burning.
Hell yeah. I'll check out the vids. Are micro hybrids any simpler? Or just more convenient because size?
I'm a member of MDRA, and they have a large club so there is bound to be someone flying hybrids. I've only see solid rockets there though... I'll have to check if there are any club rules or restrictions to be safe.
The micro-hybrids can be cheaper and easier not just because of size but also because you don't need any GSE for filling the tank. Problem is most micro-hybrids use steel whippet cartridges, which can't be flown at TRA launches even as an experimental motor, and it can be hard to track down the aluminum cartridges that would be allowed.Hell yeah. I'll check out the vids. Are micro hybrids any simpler? Or just more convenient because size?
I'm in the US unfortunately
Does NAR do the same restrictions for steel carts? I know there are still material restrictions, but I'm wondering if the carts are exempt somehow. Also, what impulse classes do microhybrids span? I only have my L1 at the moment, but am aiming to get my L2 this year as well.
You need to be L2 certified to fly any size EX hybrid.
totally fine.... I will not get to it before getting my L2 anyway. I think this might be something I will explore next year since I have a lot of goals for this year already (plus money doesn't grow on trees... its just made from them and there are only so many trees, but I digress lol)
So at least here in the US, you can order aluminum 8g N2O cartridges. However, I've just asked Demar about these designs and what he thinks regarding the fact that flashback is probably not a concern at this scale, and the cartridges are already pre-loaded with the N2O. He's taken it up with the other TRA folks and we might get a new rule for mini and micro hybrids.
Yeah I found some on Amazon no problem. Does it really only take 8g? or do hybrids use multiple carts if more than that is needed?
The micros use 8g, the minis use 16g!
To the best of my understanding, the injector assembly is sealed, so everything forward of it is the "tank." But yeah, the casing itself is what gets pressurized. Yeah, you'll need electronic recovery.
This seems way more achievable than I thought. I was originally intimidated by the amount of technical challenges I assumed hybrids had. This looks more putting together a reloadable casing than I expected.
Yeah, I keep saying that I feel like I'm being sold a time share. It feels way too good to be true, I'm waiting for the catch hahaha. It seems like the catch is the up-front cost of having to build GSE, but after that.... seems pretty good!
Happy to hear this. Hopefully they'll approve the regular canisters.
They need the "100%" emote reaction or something. Hard agree on the introduction to hybrid rocketry aspect.
Outta curiosity, does this limitation include ground testing? You said “fly”lol
Yes, L2 required to do static firings at a TRA launch.
