Hybrids 2022

[G_T]

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.

 

[Neutronium95]

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.

 

[rocket_troy]

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.

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.

TP

 

[Voyager1]

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.

 

[rocket_troy]

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'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.

TP

 

[Neutronium95]

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.

TP

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.

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.

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.

 

[rocket_troy]

How confident are you that you had enough N2O in your supply tank? Also, how hot were the conditions?

TP

 

[Neutronium95]

How confident are you that you had enough N2O in your supply tank?

TP

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.

 

[Voyager1]

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.

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 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.

 

[rocket_troy]

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.

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.

On really hot days, your N2O supply can go beyond its critical point ie turning all to gaseous state. That requires cooling to bring it down below critical state which is generally paid for with wasted N2O out your vent unless you're externally cooling it. 30-40 seconds of fill isn't a significant amount of waste by any measurement though.

TP

 

[rocket_troy]

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'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.

TP

 

[maddmaxx11]

It really looked like the tank may not have had a dip tube. The solenoids pull about 15 amps at first to open so you need a good battery and a GSE that can handle the current.

 

[maddmaxx11]

We’re you using a vent sensor? Just wondered why the vent tube is so long?

 

[G_T]

I wouldn't worry about too large a vent in the flight tank - within reason of course! That would mostly just lower the temperature and pressure of the nitrous once it is filled. You'd end up with more mass of nitrous loaded, but a little lower combustion pressure.

It does sound like a supply-side problem. If you still have the tank and GSE, rig it up like you did, tie off the fill line to something like a post, instead of connecting it to a rocket, and cycle the solinoid. See what happens. You should get a strong flow out the tube. If not, try it again with the cylinder inverted. If that doesn't do it, I'd suggest looking for a flow restricter in there somewhere (such as wrong valve on the tank) or a problem with the solinoid.

You can test for restriction on the tank by cracking the valve open with nothing attached - outdoors, and wear leather gloves. If the tank won't vent strongly by itself, there's your problem.

You can work through it one step at a time, as long as you still have nitrous.

 

[rocket_troy]

Looking at the video, it doesn't quite look to me like it was only running on straight gas. I'm still curious on the temperature conditions during the fill/launch?

TP

 

[G_T]

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.

 

[Voyager1]

As a comparison, here is a image of one of my launches with a Contrail J246 motor alongside yours. The rocket is an extended RW Double Shot sustainer that I modified for the hybrid motor. The length is about 220 cm (~87"), so the flame length is approximately 60-70 cm, about 1/4 - 1/3 of the rocket length. I have no idea of the size of your rocket, but the flame is quite short. This would suggest that you hadn't achieved a very complete fill, or combustion was less than optimal.

In my case, the flight under-performed a little with altitude, so I suspected at the time that even though I observed a healthy liquid venting, it wasn't an optimal fill at the time. However, there could have been many other reasons.

 

[Voyager1]

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.

I generally keep the fill solenoid on until I press the ignition button.

The J246 motor only uses a single 3/16" injector. It also requires a medium nozzle.

 

[reddrock]

I used to launch many hybrids, mostly Rattworks and HyperTEK. I was also at FAR and saw your launch. You definitely did not have a full flight tank. Temps were at least high 80s when you launched. While I wasn't looking close enough to tell for sure, I did not see liquid coming out. The flight itself was confirmation. Under those conditions I would have been cooling the tank. Also, you need to determine if there is a dip tube in your supply tank.

Once I used an ice bath in a cooler with a 150 lb supply tank and got the pressure down to 750 psi when the temps were 115 in the shade. So it can be done. I've also used a towel "condom" over the tank and soaked it in cold water. That works well to a point. You can tell by monitoring the pressure.

Years ago there was someone on the east coast selling a simple electric device using a thermocouple and bright LED that was battery driven. The thermocouple sits under the vent tube and senses when gas turns to liquid, and turns the LED on. It was easy to see from 500' away. It might not be too hard to reinvent that sensor.

 

[ContrailRockets]

I have been busy with Spaceport America and then COVID-19. It has slowed me down. Many of the original solenoid valves are not designed for continuous duty. They have a five minute on cycle. That being said when you are filling you are cooling the valve and coil which extends the on cycle. Damage occurs when a fill or purge valve is left on without flow for more than 5 minutes. Coils smoke making for a bad day. The Pratt hobbies purge valve draws 34 watts at 12 volts. the BFV draws 38 watts at 12 volts. The amp draw increases as the coil temperature increases but NOS flow offsets the increase in temperature. The new CFF draws 11 watts and is continuous duty. Unless you are filling larger motors the traditional valves work. I have been using them for 15 years without solenoid savers and without frying the coils. I filled the O-6300 using twin NOS cylinders and two BFV fill solenoid valves. If someone has a bad valve PM me about getting it repaired.

Venting. I have found that a black plate mounted to the launch rail that is adjustable up and down on the 1010 rail works well. I always put my vent on the same side in comparison to the launch lugs and drill the 1/8 inch hole so it sprays at a 45 degree up the black plate. This method allows for easy viewing and is adjustable for longer or shorter rockets. The 75, 98, and 152 motors all were certified with an internal vent out the combustion chamber. When the motor ignites it severs both the fill lines and the vent line. I have bee using this method for over 15 years. At the request of a flyer I developed both a 54mm and 38mm internal vented motor. This allows the vent line to be placed where it is highly visible or you can hook up to a vent detector. This internally vented process allows any vented NOS to be used in the combustion process not just being dumped overboard until motor burnout. This process increases combustion pressure and reduces the speed that the NOS tank vent as it is venting into a pressurized combustion chamber not the atmosphere.

I do not have parts for other hybrid manufactures. Some flyers have used Contrail Rockets internals in other hybrid mono motor tubes. They were not certified that way but many say that they work the same except they are not black. Contrail Rockets website is being updated having 3 other designers work on the site I have finally had to assume that responsibility as well. If you see an error on the website PM me so I can address it.

NOS prices are all over the place. The cheapest I have found is buying a 56 pound steel NOS k cylinder at under $5 a pound and transferring it to smaller 20 pound aluminum NOS cylinders for use in the field. Retail prices without an account were $14+ a pound or more. What is worse is that there was no NOS available at my gas plant in Lake Havasu City or in Kingman 60 miles away even Las Vegas did not have any Racing NOS available before I went to Spaceport. I was able to secure 4 K cylinders in Las Cruces NM. With this I will be able to fill all my cylinders and still have cylinders left for my next major launch.

 

[SentinelNorth]

Dunno why I never posted it here before, but here's a guide on making a cheap and reliable servo-actuated ball valve:
https://www.halfcatrocketry.com/sabv

Pair it with an RC controller for a really simple off-the-shelf control system:

https://www.halfcatrocketry.com/rcfs

 

[ContrailRockets]

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.

Tom

 

[SentinelNorth]

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.

Tom

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).

 

[ContrailRockets]

Fail to safe works.

About 7 years ago I built a 54mm 48 inch NOS tank and a 28 inch Combustion chamber for Yale University. In between was 3/8 NPT for a valve to throttle the hybrid motor. Years ago the Rocketmen in the UK took three 75mm L2525BG and split the NOS Tank and the combustion chamber so that they could have the tanks vertical while the car was on an incline. Not much more would have been required to install a valve to control NOS flow.

 

[Dave A]

I thought about a throttling valve a while on here. An admin told me to move the research section.
You can do a lightweight racing nitrous controller. The system that pulses it like a car efi but fully programmable to any flow rate curve.

 

[DabCat]

I just received a micro hybrid from a member on here. It came with some paper reloads that I'm thinking about flying next Wednesday. Just to clarify a little, this is my first hybrid. I am lightly experienced with larger hybrids, having a fellow club member explain a bunch of it and show me a few of his own flights, but I have no experience with these micro hybrids. They seem pretty easy, and I've made sure to thoroughly read through the instructions. I love the instructions that come with it. I'm not new to research motors.

I'm already thinking about making some custom fuel grains for it, so I have a few questions. I don't think this warrants the research form, but I could be very wrong.

I want to be able to 3d print grains for it, since that seems very convenient. I know that 3d printing fuel grains has been done before, so for those who have, which filament is best? What print settings works best? How does the performance compare to other types of fuel grains?

And one last quick question about the preheater grain. The instructions don't specifically recommend an exact propellant, but suggest using an Aerotech grain that has no special effects. I assume this is referring specifically to white lightning. I have some extra white lightning which can be used, but I also have a ton of extra redline in grains that are too short for motors. Would redline work too? I don't see why it wouldn't, but I could be wrong. It would be more convenient for me to use redline because my excess redline is never used. I always use my excess blue thunder and white lightning for lighting my normal motors.

I have another question about mixing stuff into a poured and casted grain to add special effects like smoke and sparks, but I assume that would need to be on the research forum, right?

 

[rocket_troy]

I can't see any reason why redline wouldn't work. I probably wouldn't recommend white lightening for small preheaters only because you'll only be using part of a grain for your preheating needs and the small AT White Lightening propellant grains don't store well unless in sealed packaging.

TP

 

[maddmaxx11]

Redline will work just fine. I have tested a 3d printed ABS grain in a 29mm SkyRipper motor and it worked and preformed like the factory grain. the weight was even within a gram of the factory grain as well. As far as the micro hybrid a person on here even made a fuel grain for a micro hybrid with Pringles chips and wax. It had a great looking burn with several Mach diamonds but not sure of a thrust profile compared to a stock grain.

 

[G_T]

From Potter, zoomed in on some pictures taken by James Fields. THRP-1. Pic shows cryovent open. Using a cryovalve makes venting very obvious, once the tank has chilled down. The other pic shows the motor at full burn. That's about 8' of flame. Cool mach diamonds. I'll put some pics in the THRP-1 thread as well.

It's too bad the poor motor startup wasted about half the nitrous.

Gerald

 

[Troy3003]

Anyone planning on bringing a hybrid to Airfest? I am hoping to fly mine but as of now I still don't have access to an available launch controller.