The video I have, courtesy of Bill Schworer, won't upload to this site. Too big, even the compressed version. I don't have any video editing software on any of my computers at the moment so I can't prune down the length. We'll see.
I launched my first hybrid this past Saturday at FAR. It was a Contrail J246 loaded in the hand me down hardware that I picked up in April. One of the people helping me identified some of the parts as being from Rattworks instead of Contrail as I had originally believed.
It didn't go too well. I had some initial issues with getting the FAR pad boxes to activate the fill and dump solenoids, as well as a few other minor problems. After 30-40 seconds of filling, I didn't see any sign of venting. I thought that with the air conditions there was a chance that it was too dry to produce a cloud, so I decided to just launch and let everyone else get back to doing their stuff. As you can see from the video, there was barely any nitrous loaded, so the motor significantly underperformed.
My friend thinks that the vent restrictor in the forward closure might have been too large. I'm going to try using the Contrail one on my next attempt. I'm also going to rework my GSE setup so that I'm not dependent on the FAR pad boxes. I might just go with long wires and batteries for some tests to make sure that everything works and I can actually get a motor to fill.
I'd also like to look into ways to monitor the actual fill level of the motor. There should be some way to attach a load cell to the launch rail to monitor the rocket weight in real time while filling.
I've certainly done the load cell thing - streaming back (over RF) that with tank temp and pressure on top of all the other stuff I'm transmitting back from my onboard electronics (a lot). For me, it over complicated things and I decided it just wasn't worth the hassle of it all, but that's just my experience from what I was trying to do and how I was doing it.I had considered using a load cell on the rail to monitor the fill, but I have decided to just use remote fill pressure monitoring and a vent sensor to confirm the fill, as well as visual confirmation with binoculars.
I wasn't using a solenoid saver. Some of the pad boxes weren't sourcing enough current to actuate the solenoids, but we were close enough to hear nitrous flowing throughout the fill process.Another thing to look for too: If you're using a solenoid to fill and driving that with a solenoid saver circuit, then be sure the resistor has a low enough resistance to keep the valve open. I've experienced that particular issue myself. The thing would work perfectly for launch after launch, then one day that happened. The cap would open the valve every time, but the resistor wouldn't keep it open which really threw me off the scent because you'd hear the solenoid activate and the hissing of the vent, but it wouldn't be filling beyond the initial squirt. This was also prior to the new rule amendment where research launches needed to set back a level making audible detection and analysis that much more challenging.
How long does it typically take for a J246 to fill in your experience? I was expecting it to be a relatively short process, so I decided to launch after 30 or 40 seconds of filling. I didn't see any sign of liquid nitrous venting, but I had heard that in very dry conditions you might not see the vapor cloud of the vent, so I decided to go for it.All of my flights with 38mm Contrail hardware and J246 reloads have very successful. However, one of the issues I have had with my GSE is that the fill and dump solenoids are quite current hungry. If your battery isn’t very healthy or lacks capacity, then the fill process might be too much for it, particularly if your not using a relay-based pad box with the battery at the pad, and a solenoid saver.
Looking at your video, the launch occurred as soon as the vent tube popped, but I didn’t see much evidence of liquid NOx venting prior to the launch. I would typically wait a couple of seconds after you see a definite vent stream occurring.
I had considered using a load cell on the rail to monitor the fill, but I have decided to just use remote fill pressure monitoring and a vent sensor to confirm the fill, as well as visual confirmation with binoculars.
The tank had a tare weight of 25 pounds. With the solenoids attached, it weighed about 44. I think that means that it had at least 15 pounds of nitrous.How confident are you that you had enough N2O in your supply tank?
With the J246 my fill times are typically 25-30 seconds, but sometimes as low as 20 seconds. It does vary a bit with fill tank pressure and ambient temperature.I wasn't using a solenoid saver. Some of the pad boxes weren't sourcing enough current to actuate the solenoids, but we were close enough to hear nitrous flowing throughout the fill process.
How long does it typically take for a J246 to fill in your experience? I was expecting it to be a relatively short process, so I decided to launch after 30 or 40 seconds of filling. I didn't see any sign of liquid nitrous venting, but I had heard that in very dry conditions you might not see the vapor cloud of the vent, so I decided to go for it.
I am strongly considering using servo actuated ball valves for fill and dump in the future. That should eliminate any problems associated with solenoids, and they should be easy to remote control, for simple field operations.
If it was an engine boosting cylinder, then it should have had a dip tube. From vague memory, they're normally marked with a heavy painted black line down the side of the cylinder to indicate that it's a dip/syphon tube. If it wasn't and you didn't invert the cylinder, that would certainly explain it yes.The tank had a tare weight of 25 pounds. With the solenoids attached, it weighed about 44. I think that means that it had at least 15 pounds of nitrous.
Would it be possible that this could occur if there was no dip tube in the tank? Everything about how it was plumbed and the pressure gauge was oriented seemed to indicate that it was intended to be used right side up, but if it only ever put gaseous nitrous in, that might explain what happened.
I've also experienced conditions (warmer conditions) where venting is very difficult to see with the eye, but that can also depend on your vent and its throughput.I believe that I've confirmed liquid NOx venting visibly in Winter and Summer here. That can be a range of 15 - 35 C, typically. It might also depend on humidity - I'm not sure. Troy might have a better idea here.
I generally keep the fill solenoid on until I press the ignition button.That looks to me about what gas under pressure would do, if it had chilled itself in the tank and therefore took on more density. It definitely didn't look like a normal liquid burn. Very little thrust. Caveat though - I'm more used to looking at higher power hybrids.
Question - Did you attempt to continue fill up until just a second or so before fire? If not, keep in mind that this is an open vent system. Once a tank is full, I pulse the fill solinoid every few seconds to keep the tank topped. Others can tell you what they do.
Is there any chance the vent line was clogged? That would also do it.
If that motor uses multiple injectors, then it is also possible that under the obviously under pressure oxidizer flow, not all the injectors burned through before it was on the way up the rail.
The receiver failsafe is set so that if communication is lost, the servo returns to its close position. Similarly, the purge failsafe position can be set to open. In addition to unintended loss of communication bringing everything back to the safe positions, it means you can also simply turn off the controller to safe all valves (as again, losing communication will make the receiver go its failsafe positions).Cool idea for throttle control in separate tank and combustion chamber but not for fill or purge.
NOS fill systems are to be designed so valves close upon failure.
In your design if a valve is on and you loose communication it would stay on where a solenoid valve requires a constant command to stay open.
I have designed a fill and purge system that meets the NFPA requirements with only a single solenoid valve no servo motors or ball valves.
Lowering the entry cost to do hybrids.
PM me if you want to know more.