Hybrids 2024

[kramer714]

Quartz fibre is better, but FG can be an adequate poor man's alternative. I've been filling composite nozzles with FG and CF for over 25 year for long burn hybrids and continually get multiple burns from them.

TP

with durhams rock hard?

 

[rocket_troy]

with durhams rock hard?

No, Phenolic Resin, but irrespective of the polymer/binder, the longevity of the nozzle is increased significantly will the inclusion of solids. In my case, it's (laid up) CF, and FG, but whether you lay up or cast shouldn't matter much I would've thought. Yes, as you said, there are superior fillers to FG fibre such as quartz fibre or silica that should buy a bit more energy absorption before melting.

TP

 

[kramer714]

No, Phenolic Resin, but irrespective of the polymer/binder, the longevity of the nozzle is increased significantly will the inclusion of solids. In my case, it's (laid up) CF, and FG, but whether you lay up or cast shouldn't matter much I would've thought. Yes, as you said, there are superior fillers to FG fibre such as quartz fibre or silica that should buy a bit more energy absorption before melting.

TP

Agreed for the phenolics, at the day job we used glass reinforced and quartz fiber / silica both as transfer molding and old school compression molding. If it wasnt for the tooling cost, I would transfer mold the nozzles. With the thermosets, the fibers are really important to increase the toughness and to 'hold the parts together' during ablation. Never have done phenolic with carbon-fiber, but LOTS of epoxy CF parts.

I was specially looking at the cast gypsum dextrin ceramic near net cast / final machined nozzles. I have some milled fiberglass, and a little Kevlar pulp. The Kevlar pulp would never wet out well, not a great choice for a water set 'cement'. Im not sure about the fiberglass as a filer in it.

 

[OzHybrid]

Agreed for the phenolics, at the day job we used glass reinforced and quartz fiber / silica both as transfer molding and old school compression molding. If it wasnt for the tooling cost, I would transfer mold the nozzles. With the thermosets, the fibers are really important to increase the toughness and to 'hold the parts together' during ablation. Never have done phenolic with carbon-fiber, but LOTS of epoxy CF parts.

I was specially looking at the cast gypsum dextrin ceramic near net cast / final machined nozzles. I have some milled fiberglass, and a little Kevlar pulp. The Kevlar pulp would never wet out well, not a great choice for a water set 'cement'. Im not sure about the fiberglass as a filer in it.

There's also the possibility of Dental Stone. From memory, it is better at high temperatures, casts well, and is hard. I'll see if I can get some, cast it, and give it a test with a small hybrid.

 

[cfb_rolley]

got my solenoids today and most fittings for the fill and dump part of my ground support. What is best to use for thread sealant (if needed)? I know teflon tape is a no-go due to the potential of debris getting stuck in the solenoids, is loctite fine to use? I have red loctite here but would prefer to use blue in case I need to take anything apart again.

Also, Im keeping my solenoid control fairly simple and plan on just running +12v power through a switch for each solenoid, connecting the ground side of each solenoid to a common ground wire back to battery, and a flyback diode for each solenoid to protect them from a voltage spike. Both solenoids are continuous duty anyway, and I'm only filling a 16" x 38mm motor so can't imagine needing anything much more complex than this to run the solenoids. Is this fine or is there something else to consider?

 

[rocket_troy]

got my solenoids today and most fittings for the fill and dump part of my ground support. What is best to use for thread sealant (if needed)? I know teflon tape is a no-go due to the potential of debris getting stuck in the solenoids, is loctite fine to use? I have red loctite here but would prefer to use blue in case I need to take anything apart again.

Also, Im keeping my solenoid control fairly simple and plan on just running +12v power through a switch for each solenoid, connecting the ground side of each solenoid to a common ground wire back to battery, and a flyback diode for each solenoid to protect them from a voltage spike. Both solenoids are continuous duty anyway, and I'm only filling a 16" x 38mm motor so can't imagine needing anything much more complex than this to run the solenoids. Is this fine or is there something else to consider?

I would personally use Teflon Tape irrespective of debris concerns. You can mitigate that with due care when winding your tape onto the thread eg. try not to overlap over the (wet) end of the thread. You can also add sintered inline filters if it was really concerning you, but it's never been an issue to me. PTFE is N2O compatible, HC organic resins - not so much.

TP

 

[OzHybrid]

got my solenoids today and most fittings for the fill and dump part of my ground support. What is best to use for thread sealant (if needed)? I know teflon tape is a no-go due to the potential of debris getting stuck in the solenoids, is loctite fine to use? I have red loctite here but would prefer to use blue in case I need to take anything apart again.

Also, Im keeping my solenoid control fairly simple and plan on just running +12v power through a switch for each solenoid, connecting the ground side of each solenoid to a common ground wire back to battery, and a flyback diode for each solenoid to protect them from a voltage spike. Both solenoids are continuous duty anyway, and I'm only filling a 16" x 38mm motor so can't imagine needing anything much more complex than this to run the solenoids. Is this fine or is there something else to consider?

Just because the solenoids are continuous duty doesn't mean that's your best option and you're better off using a solenoid saver. It will reduce the size of the battery you need and the temperature of the solenoid. It's really easy to make one.
Like Troy, I use teflon tape. Just make sure it doesn't hang over the end of the threaded male fitting.
No issues.

 

[kramer714]

Just because the solenoids are continuous duty, you're better off using a solenoid saver. It will reduce the size of the battery you need and the temperature of the solenoid. It's really easy to make one.
Like Troy, I use teflon tape. Just make sure it doesn't hang over the end of the threaded male fitting.
No issues.

i use teflon tape, and always use a solenoid saver!

 

[cfb_rolley]

I'm pretty sure one of the solenoids came with a solenoid saver... it's a small black box with 2 wires on each side with labels "DC 12v input", "output" and "energy saving module"... sounds like a solenoid saver to me?

 

[rocket_troy]

I'm pretty sure one of the solenoids came with a solenoid saver... it's a small black box with 2 wires on each side with labels "DC 12v input", "output" and "energy saving module"... sounds like a solenoid saver to me?

Yeah, most solenoid savers are 2 component circuits (a large wattage resistor and a reasonable sized capacitor). Simple stuff. Some of the Chinese N2O solenoid valves might not require savers as they can be pilot type that only draw 1A or so even for large orifices, but as Norm said, it's always good practice to use one.

TP

 

[cfb_rolley]

Yeah really can't see any drawbacks to using solenoid savers. I'm starting to get a excited now, just need a couple more fittings, nitrous bottle, a line to go from the bottle to solenoids. Once that all arrives I'll spend an afternoon putting everything together to test it out, aaaand then I'll be able to fly hybrids! (well... full size ones... micro hybrids are already going up just about every weekend haha)

 

[Voyager1]

I would personally use Teflon Tape irrespective of debris concerns. You can mitigate that with due care when winding your tape onto the thread eg. try not to overlap over the (wet) end of the thread. You can also add sintered inline filters if it was really concerning you, but it's never been an issue to me. PTFE is N2O compatible, HC organic resins - not so much.

TP

Just because the solenoids are continuous duty, you're better off using a solenoid saver. It will reduce the size of the battery you need and the temperature of the solenoid. It's really easy to make one.
Like Troy, I use teflon tape. Just make sure it doesn't hang over the end of the threaded male fitting.
No issues.

I agree with both these recommendations.

I’ve been using Teflon tape for several years on my Nitrous plumbing since I started with hybrids; as Norm suggested, just use it without any loose bits over the front of the connectors.

I’m always using solenoid savers these days. I started with simple RC circuits, but I’m now using active circuits from WFX that allow you to set and optimise the hold current for your particular solenoids.

Just out of curiosity, what are you using for a hybrid launch controller? Wired or wireless? The minimum you will require is a wired relay-based system with a 12V pad battery and field cable back to a remote control unit.

 

[drewnickel]

got my solenoids today and most fittings for the fill and dump part of my ground support. What is best to use for thread sealant (if needed)? I know teflon tape is a no-go due to the potential of debris getting stuck in the solenoids, is loctite fine to use? I have red loctite here but would prefer to use blue in case I need to take anything apart again.

Also, Im keeping my solenoid control fairly simple and plan on just running +12v power through a switch for each solenoid, connecting the ground side of each solenoid to a common ground wire back to battery, and a flyback diode for each solenoid to protect them from a voltage spike. Both solenoids are continuous duty anyway, and I'm only filling a 16" x 38mm motor so can't imagine needing anything much more complex than this to run the solenoids. Is this fine or is there something else to consider?

Teflon is the standard, but really for gasses you want something called oxygen tape. It's still teflon, but you'll usually see it dyed green and it's a higher quality/density teflon:
https://www.amazon.com/Gasoila-Dens...ords=oxygen+teflon+tape&qid=1710517534&sr=8-3

I normally use Krytox TS-4, which is a very viscous paste you can apply to threads as a sealant. It's expensive but way easier to put on and tends to get a better seal (no gaps between wraps of tape, it's a continuous seal). Despite the cost, you only need a pea sized blob for each joint, so it lasts a very long time.

 

[kramer714]

wireless

 

[drewnickel]

wireless
View attachment 635575View attachment 635578View attachment 635576

Are you using Xbee or LoRa for communications?

 

[kramer714]

Are you using Xbee or LoRa for communications?

LoRa

 

[cfb_rolley]

Just out of curiosity, what are you using for a hybrid launch controller? Wired or wireless? The minimum you will require is a wired relay-based system with a 12V pad battery and field cable back to a remote control unit.

I’ll use a wired setup for now. Is there a reason relays are used for sending 12v to the solenoids? I’m already using 12v ignitors anyway so my whole system can run on the one 12v circuit.

I can do a wireless setup later but I’d be building my own for that too, and although I have wifi working on one of my flight computers now I wouldn’t say I’ve mastered it enough yet to apply it a launch controller.

Teflon tape seems to have this weird paranoia in the motor racing world, but I always thought it may stem from care not being taken, and I guess Teflon tape getting stuck in a nitrous solenoid can lead to a very expensive engine rebuild.

 

[Voyager1]

I’ll use a wired setup for now. Is there a reason relays are used for sending 12v to the solenoids? I’m already using 12v ignitors anyway so my whole system can run on the one 12v circuit.

Yes, there is a reason to use a relay-based system. If you’re using a long field cable to control your pad box, particularly for a hybrid, and you have high currents flowing to igniters and solenoids, you can waste a significant amount of your battery power over the long field cable. Using relays at the pad box, you can limit the high current wiring to a couple of meters, rather than 30, 60 or 90m. Your field cable only needs to be a low current circuit back to your control box.
Remember, over a long cable there can be a significant voltage drop that reduces the available power for the igniters and solenoids.
If you would like to review a design for a wired relay-based hybrid controller, then please PM me.

 

[cfb_rolley]

Fair point, I guess I've never needed to consider the voltage drop before now because the controller I currently use is just meant for low and mid power rockets, and the length of the ignitor lead isn't that long in comparison. I'll take you up on the PM later, that would be greatly appreciatted, thank you.

*Also going to add a note here regarding micro hybrids for anyone stumbling across this thread - While the laws where I live allow me to fly them, this might not be the case in other states as pointed out by OzHybrid. Ages ago, I went on a deep dive before buying one and long story short, QLD's explosives laws define HPR motors differently to NFPA codes, so there is sometimes a little bit of confusion about what rules apply and when.

-QLD laws define HPR motors only by propellant weight and thrust. Rocket motors under these limits are defined as model rocket motors, and are unrestricted.
-NFPA defines all hybrids as high power rocket motors, regardless of propellant weight and thrust.
-QLD laws obviously must be abided by in QLD, but NFPA doesn't relate to our laws.
-NFPA does however relate to clubs that have adopted the codes, as it defines their rules on top of the laws.

This means that where I live, you can fly any type of rocket motor privately as long as it's got less than 62.5g of propellant and has a max total impulse under 160Ns, but you would still need appropriate certification before you're allowed to fly hybrids with a TRA sanctioned club. This may not be the case for all places, just where I live. Also don't annoy CASA and fly it where you're not supposed to. You still need to contact them to privately launch if the rocket weight is over 1500 grams, even if the installed motor is G impulse or below.

 

[G_T]

Teflon is the standard, but really for gasses you want something called oxygen tape. It's still teflon, but you'll usually see it dyed green and it's a higher quality/density teflon:
https://www.amazon.com/Gasoila-Dens...ords=oxygen+teflon+tape&qid=1710517534&sr=8-3

I normally use Krytox TS-4, which is a very viscous paste you can apply to threads as a sealant. It's expensive but way easier to put on and tends to get a better seal (no gaps between wraps of tape, it's a continuous seal). Despite the cost, you only need a pea sized blob for each joint, so it lasts a very long time.

Thanks for the link to the tape. I hadn't run across it before. Ordered some... TS-4 in small quantities (2 oz) seems harder to find!

Gerald

 

[cfb_rolley]

Thanks for the link to the tape. I hadn't run across it before. Ordered some... TS-4 in small quantities (2 oz) seems harder to find!

Gerald

I wish there was a less "extremely expensive" alternative to krytox GPL206 too haha. I know you can get 205 in small quantities usually sold for keyboard switches but I don't think it has the right properties, seems very similar but temperature tolerance is lower.

 

[OzHybrid]

I wish there was a less "extremely expensive" alternative to krytox GPL206 too haha. I know you can get 205 in small quantities usually sold for keyboard switches but I don't think it has the right properties, seems very similar but temperature tolerance is lower.

I doubt there is much compositional difference between one ptfe tape and another. For the oxygen safe one, you're paying for the certification. The gas and non gas ones primarily vary in thickness. And the colour of the dye used to make them green/blue/yellow. The colour just gives a ready indication to choose the correct tape.

 

[hybridfreak]

Speaking of PTFE what a cheap segway but here's what I did yesterday, pins (with thinner pins/stems) for the paintball pin valves:



The original piston is a cylindrical piece (not hexagonal) that has lots of play in the valve body for the fluid to go around it. The play between the actual pin (on the piston) and the valve body is pretty small to keep the piston somewhat centered in the body. That play also defines the smallest crosssection for nitrous to flow through and is way too small for our application. So I picked hex stock of the right diameter, so that the edges center the piston with little play and I can make the pin very thin (1,5 mm instead of 4 mm) and have some usable cross section. It will probably still max out at ~200 g/s, so maybe 500N, which is more than enough for me

On the left is the first iteration that leaked because I couldn't part the PTFE (there it is!) sealing off good enough and had to remove a burr by hand and... well it didn't work well enough for me. I ended up using the o-ring that came in the valve originally. Initially I didn't want to because it ment trepanning (making an axial groove) a recess into the front of the piston but that was actually easy. Also turning the stainless pin and press fitting it in was no big deal, so for now I've found the best solution for these parts!

I also started working on a test stand, it will be quite simple and have a 1000N load cell, an Arduino and a HX711 (@90sps) to measure thrust.

 

[cfb_rolley]

I also started working on a test stand, it will be quite simple and have a 1000N load cell, an Arduino and a HX711 (@90sps) to measure thrust.

Be sure to post a video of it on the test stand, I look forward to it!

 

[hybridfreak]

Got a few more ducks in a row for hybrids and related projects.

- got a used precision level and leveled and aligned my lathe properly

- cleaned the CO2 tanks for use with nitrous. I soaked them in water with cleaning solvent over night, rinsed them multiple times and dried them using a heater blowing at the tank while an aquarium air pump flushed them by pumping air through a syringe filter and a hose into the tank.
Did the same again but used acetone instead of water/solvent. One of the paintball tank had quite some gunk in it...

- finalized the code for the Arduino teststand. Would've taken me forever but a friend suggested I'd use ChatGPT which worked quite well. Translating "human" requirements like "measure thrust and safe that in a file on an SD card" to code has never been easier I guess... Interesting, convenient and somewhat frightening.

And I put the freshly leveled lathe to use and started making parts for a 54mm motor. The casing is 258mm (just over 10") long and should house enough fuel to get it into the K range.





The injector assembly will be the same as on the 38mm so parts are interchangeable. I have some more machining to do before my club's hybrid test day in two weeks but I'm pretty sure I can get it done

 

[OzHybrid]

Got a few more ducks in a row for hybrids and related projects.

- got a used precision level and leveled and aligned my lathe properly

- cleaned the CO2 tanks for use with nitrous. I soaked them in water with cleaning solvent over night, rinsed them multiple times and dried them using a heater blowing at the tank while an aquarium air pump flushed them by pumping air through a syringe filter and a hose into the tank.
Did the same again but used acetone instead of water/solvent. One of the paintball tank had quite some gunk in it...

- finalized the code for the Arduino teststand. Would've taken me forever but a friend suggested I'd use ChatGPT which worked quite well. Translating "human" requirements like "measure thrust and safe that in a file on an SD card" to code has never been easier I guess... Interesting, convenient and somewhat frightening.

And I put the freshly leveled lathe to use and started making parts for a 54mm motor. The casing is 258mm (just over 10") long and should house enough fuel to get it into the K range.

View attachment 639212

View attachment 639211

The injector assembly will be the same as on the 38mm so parts are interchangeable. I have some more machining to do before my club's hybrid test day in two weeks but I'm pretty sure I can get it done

If you're threading mating parts, you must anodize them. Otherwise, you'll get galling on the threads and they'll bind horribly. Then, you'll wish you had anodized them...

Anodising is easy to do at home for small parts and clear anodising is super easy. Clean part, finish with a dip in sodium hydroxide solution to remove last of grease. Anodise for 20 mins, boil for 20 mins. Job done.
Distilled water is ideal to use, but you'll get results with non distilled water, boil it first to get rid of the majority of any temporary hardness. Should still be ok.
I use a 12v battery charger and it works well. There's lots written on ideal current levels, but again don't worry too much, just do it.
WEAR PROTECTION ON HANDS AND EYES/FACE. SULPHURIC ACID IS BAD FOR EYES......AND OTHER BITS.

 

[G_T]

Acetone is NOT the last step in prepping tanks for oxidizer service. Acetone is a fuel and can leave oily residue.

I'd suggest following the acetone with denatured alcohol, and ideally following that with hydrogen peroxide of successively increasing percentages. That takes care of any remaining organics.

Anyway, you can probably find better advice.

Gerald

 

[hybridfreak]

If you're threading mating parts, you must anodize them. Otherwise, you'll get galling on the threads and they'll bind horribly. Then, you'll wish you had anodized them...

Good tip! I'm aware of the issue but haven't had any problems with similar parts so far but I also always lubricated them. I plan on anodizing them at some point, just haven't decided on a pretty color yet

Acetone is NOT the last step in prepping tanks for oxidizer service. Acetone is a fuel and can leave oily residue.

I'd suggest following the acetone with denatured alcohol, and ideally following that with hydrogen peroxide of successively increasing percentages. That takes care of any remaining organics.

Anyway, you can probably find better advice.

Gerald

Also good information! I've found the field of "oxygen safe cleaning" to be a bit... well not so straight forward I've started reading into it in diving forums and some standards like AIGA 012/04. In forums you'll find anything from dish soap to toluol and so on. According to the AIGA standard acetone is fine as long as you can remove all of it. I'll give the tanks another flush with IPA, then hot water and air them out properly using the hose/pump/heater method again.

 

[drewnickel]

Also good information! I've found the field of "oxygen safe cleaning" to be a bit... well not so straight forward

General process is to scrub with a strong de-greaser like simple green, rinse in de-ionized water and then finish with isopropyl alcohol (so it evaporates and the part doesn't stay wet). Just soaking a part in a solvent doesn't mean when it evaporates that it'll take the contaminant with it. You can check cleanliness with a wet out test: if water beads on the surface anywhere, there is probably grease. Also after cleaning you should wear gloves or there isn't really a point to the cleaning (finger prints are inherently greasy). A UV flash light can sometimes pick up other contaminants.

 

[G_T]

Also using a pump to run air through can also deposit an oil film from the pump.