Hybrids 2024

[cfb_rolley]

Hey, is someone able to confirm the diameter of the o-ring groove on 38mm contrail nozzles for me? mine are measuring up at 28mm while the bulkheads both had a diameter of 27.5mm - as a result, none of my nozzles are fitting in to my motor during assembly as the nozzle o-ring is getting stuck at the snap-ring groove

 

[Voyager1]

My 38mm nozzle o-ring groves are 27.5mm.

 

[cfb_rolley]

My 38mm nozzle o-ring groves are 27.5mm.

cheers - might have to email Contrail about it. I did end up managing to get the nozzle in but not without a ton of effort. Definitely not ideal, I'm concerned the o-ring will slice on the snap ring groove with that much force needed. Also tried to do a fill and dump test to see if my ground support is all good, but the fill hose burst within about 3 seconds of opening the fill solenoid - maybe I just got unlucky and had a dodgy fill hose but the bottle pressure is definitely not above the burst pressure of the hose.

On the up side, at least I know the electrical side of the ground support works perfectly and the fill solenoid flows more than enough - just need to get this motor filled So I can test the dump solenoid!

 

[Voyager1]

cheers - might have to email Contrail about it. I did end up managing to get the nozzle in but not without a ton of effort. Definitely not ideal, I'm concerned the o-ring will slice on the snap ring groove with that much force needed. Also tried to do a fill and dump test to see if my ground support is all good, but the fill hose burst within about 3 seconds of opening the fill solenoid - maybe I just got unlucky and had a dodgy fill hose but the bottle pressure is definitely not above the burst pressure of the hose.

On the up side, at least I know the electrical side of the ground support works perfectly and the fill solenoid flows more than enough - just need to get this motor filled So I can test the dump solenoid!

I assume that you were using synthetic M1 grease on the nozzle and o-ring? Where did the fill line burst? At the injector; the solenoid manifold; or the main hose connection onto the motor fill hose? Did you check all the quick fits for proper connection?
What was your bottle pressure at the time?

 

[cfb_rolley]

I assume that you were using synthetic M1 grease on the nozzle and o-ring? Where did the fill line burst? At the injector; the solenoid manifold; or the main hose connection onto the motor fill hose? Did you check all the quick fits for proper connection?
What was your bottle pressure at the time?

Yeah used synthetic grease on the nozzle. The bulkheads went in without an issue, half a millimeter is a pretty big difference though.

The line burst just below the injector, my first thought when it happened was that it sheared off where the teeth of the fitting dig in to the hose, because I’ve seen that happen before. but was surprised to find it definitely burst the line below the injector rather than a shear. it's a reasonably cool night so the bottle pressure was under 850psi.

 

[Voyager1]

Yeah used synthetic grease on the nozzle. The bulkheads went in without an issue, half a millimeter is a pretty big difference though.

The line burst just below the injector, my first thought when it happened was that it sheared off where the teeth of the fitting dig in to the hose, because I’ve seen that happen before. but was surprised to find it definitely burst the line below the injector rather than a shear. it's a reasonably cool night so the bottle pressure was under 850psi.

Do you have a pressure gauge on the bottle side of the solenoid manifold? I've never had my bottle pressure anywhere near 850psi; more like 650-750psi, depending on the ambient temperature.

 

[cfb_rolley]

Do you have a pressure gauge on the bottle side of the solenoid manifold? I've never had my bottle pressure anywhere near 850psi; more like 650-750psi, depending on the ambient temperature.

Hmm, interesting. The gauge is on the bottle side. It was just filled today, don’t know if that would have anything to do with it but I’ll grab another gauge from the workshop tomorrow to see what that reads. Seeing as this is the first time this equipment has been put together and used there is always a chance something is amiss. This is the reason for testing, right!

 

[sjsyracuse]

3D Printing of Hybrid Rocket Fuel (Polymer) Segments or Elements.

I would like to see what some others are doing, or have done, re direct 3D Printing of fuel segments. Irrespective of the Polymer used, if someone wouldn't mind sharing some images, I'd be very grateful!

Thanks,
Steve

 

[cfb_rolley]

3D Printing of Hybrid Rocket Fuel (Polymer) Segments or Elements.

I would like to see what some others are doing, or have done, re direct 3D Printing of fuel segments. Irrespective of the Polymer used, if someone wouldn't mind sharing some images, I'd be very grateful!

Thanks,
Steve

Here's a variety of grain geometries I've printed for my micro hybrid. I form the 3d model by creating a 2d shape for the port, then use the sweep tool to extrude the shape with a twist, then subtract it from a cylinder. I can also further tweak the shape in the slicer through scaling, line width, outer wall inset, horizontal hole expansion (or contraction if you use a negative value) etc. So far the grains with a 720 degree twist have outperformed everything else and the regression is quite even throughout the length of the grain, whereas previous straight port grains regressed much more in the middle and less on the top and bottom.

Do you have a pressure gauge on the bottle side of the solenoid manifold? I've never had my bottle pressure anywhere near 850psi; more like 650-750psi, depending on the ambient temperature.

Must've just been a damaged fill hose, I was able to do 2 fill and dump tests today with no problem at all. Extremely happy about that! Also emailed Contrail about the nozzle o-ring grooves so hopefully will have some info about that this week some time, and I put the last touches on the rocket and flight computer today too. Fingers crossed I can get this thing up in the air within the next couple of weeks.

 

[hybridfreak]

Contrail uses different o-rings on different parts afaik (more expensive nitrous safe o-rings where they are in contact with it and cheaper O-Rings where they aren't). Maybe they are a bit different in size as well?
I always fill the snap ring groove completely with grease and I find it helps a lot for getting the o-rings past undamaged. You can also sand a little radius on the inside edge of the groove to facilitate things, just don't sand the edge that the snap ring sits against.

 

[OzHybrid]

Contrail uses different o-rings on different parts afaik (more expensive nitrous safe o-rings where they are in contact with it and cheaper O-Rings where they aren't). Maybe they are a bit different in size as well?
I always fill the snap ring groove completely with grease and I find it helps a lot for getting the o-rings past undamaged. You can also sand a little radius on the inside edge of the groove to facilitate things, just don't sand the edge that the snap ring sits against.

You could probably 3D print a split snap ring filler. Kind of like a piston ring.... ish Make sure it fits with a slight gap so you can remove it afterwards. This weeks free idea.....
edit... I've just checked my 54mm case and there is a chamfer on the snap ring groove internally in the direction you would be pushing the o-ring seal at both ends of the casing. There is no chamfer in the direction the load would be acting on the snap ring. ie the outer face of the snap ring groove.

 

[hybridfreak]

Spent half an hour latheing yesterday and made a new nozzle for my West Coast Hybrids I-motor. Won't call it an I110 anymore because it will not run at 110N avg. thrust anymore
Standard nozzle is 8mm/0.315" and the ferrule (?) compresses the fill hose to ~2mm/0.078" giving it an Ae/At of ~1:16. When using a push fitting instead, the full ID of the fill hose (2.7mm) is used, i.e. injector area increases quite a bit. Also the high Ae/At gives it quite low chamber pressure so I went for a 10mm/0.39" throat giving an Ae/At of 1:13.7 which should increase chamber pressure a little. ABS grains will be printed tonight and hopefully my solenoid will arrive before the weekend so I can fire this on sunday!