good points. if you wanted to close the vent i imagine that a pressure relief value/burst disc would be a safety requirement. that was the set up we had back in my lab days on LN2 LAr2 and LHe2 tanks and carboys. had one go filling an NMR one time due to the helium transfer line losing vacuum...got my heart pounding.
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I've been playing around with vent sensing for a little while and have established a few thresholds for my vent sensor display. I currently use a Wilson F/X hybrid monitor unit that interfaces to my WFX PBU4W-Hybrid pad box. This relays the hybrid status back to the launch control unit (WFX LCU4W-Hybrid). The hybrid status is displayed on the LCU's LCD. I modified the LCU to to display these thresholds with a bright RGB LED to make it easier to determine the status, rather than watching the temperature numbers changing on the LCD.
I performed several tests with my monitor hardware to determine a reasonably reliable and simple means of detecting the venting of liquid N2O with the thermocouple. In these tests I placed the thermocouple approximately 50-100mm away from the vent tube to avoid being too sensitive to a mixture of gaseous and liquid N2O. When the venting is mostly liquid, as (hopefully) evidenced by a solid white plume, the temperature goes down towards -80 C (N2O boiling point ~-88C). You can see in the images below that I have installed an RGB LED above the launch button on my LCU4W-Hybrid panel.
At ambient temperatures >0C, the LED is RED; from <0C to -50C, the LED is BLUE; and then below -50C the LED is GREEN. These thresholds are subject to modification depending on the particular sensor installation. I chose them initially while viewing the venting N2O and making a subjective assessment of the density and visibility of the plume. Not very scientific, but it seems to provide the level of certainty that is required. Of course, installation and ambient conditions will probably affect this, but hopefully, with an optimised setup, it will be reliable. I have much more testing to do, particularly when I finalise the installation. I haven’t yet come up with a final mounting arrangement for the sensor on the launch rail - that is still work in progress. However, it will most likely be a non-contact arrangement that can be appropriately mounted on the rear of the rail with the sensor clear of the rocket body and fins. I have also considered a clip-on sensor that will release from the vent line when the rocket launches.
The image below shows when it is at 9C ambient with no venting of any N2O. Red LED.
This next image is while mostly gaseous N2O is venting, with a very light plume at -21C. Blue LED. There is a short delay between the sensing of the temperature and the display. So, in this case the thermocouple sensed the <-50C temperature while the LCD was still displaying -21C.
The final image is when the N2O plume is a very solid white liquid at -78C. Green LED.
5, 4, 3, 2, 1, launch!
I would be very interested to hear what others have tried for vent sensing, other than just the usual visual clues with the venting plume. I am aware of the prototype system developed by Contrail. There was also another sensor arrangement presented by another forum member some time ago.
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Following on from my previous post, I have now come up with a simple vent sensor installation method. This employs two 3D printed vent tube and sensor mounts that slide onto the rear of the launch rail. The top mount holds the vent tube; the lower mount holds the thermocouple below the vent tube, with the distance between the two variable to optimise the performance. The vent tube slides out of the upper mount very smoothly when the rocket moves up the rail when launching.
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Finally pulled my HyperTEK hammerhead 4630mm M motor out of storage. last flown at my bachelor's launch in 2003. That 10" V2 was one of the original 12 kits Andy Woerner built for the Plaster Blaster 2003 V2 drag race. Those kits basically marked the birth of Polecat Aerospace. Need to update the av bay, source a new M grain, fill stem and GSE.
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The Hypertek M motors were famous for both their performance and their failures. Finding a reload is going to be tricky. I believe they were cast acrylic. You could probably print one in a uv printer using the ABS uv curing resin. Not tried or tested this idea. So buyer beware....It works in MY head. If it works, you might have a niche market....
I’m not very familiar with the Hypertek motors, but I believe they use GOX as well as N2O. You could configure the WFX hybrid controller to activate an extra solenoid for the GOX, if that’s what is required. Additionally, the ignition channel could probably be used to activate an external high voltage module used for igniting the Hypertek motor.
Others with better knowledge can hopefully provide you with more definitive answers here.
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drewnickel
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They have a two part fill stem (sort of akin to a water rocket launcher) that is tethered to the bottom of the motor with a cable tie or strap and slides into the injector: the middle tube loads nitrous into the tank while the outer tube is shorter and wider and bleeds GOX into the combustion chamber. There is an electronic match that lights the fuel grain and the GOX gets the grain burning. Once it's hot enough, the cable tie / strap burns through and releases the rocket, and the fill stem is pushed out of the injector where the nitrous can start flowing into the combustion chamber.
In theory aside from the GOX, the Wilson FX should be fine to run Hypertek GSE. I believe there is an extra channel on the launch controller you could use for the GOX solenoid.
Yes. The second ignition channel can be configured to activate another solenoid.
wasn't an e-match, you actually ran high current creating an arc with speaker wire. always felt inconsistent. the fuel grains are still produced and you can get replacement fill stems. so basically it comes down to replicating the GSE that was discontinued 20 yrs ago.
kramer714
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Not to be that guy... ok so I am that guy...
Think about adding a solenoid saver, a simple R-C Circuit between the Wilson and the solenoids...
kramer714
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Playing with Grain Geometries.
Working on some EX hybrid grains, one version is a nylon grain with a twisted port. I did some simple modeling of the grain erosion, assuming (not a great assumption) uniform erosion plus regression of the grain. Plus I wanted to play with the effective surface area and twist. The O.D. is 40mm to fit into stock PVC pipe as a 'liner' . Here is what I ended up with,
This is the shape pre-burn at the end
This is the port wall pre-burn . hard to see in this render but the port tapers becoming smaller from the top to the nozzle end. and yes it does look like a piece of licorice. The grain length is 230mm. I can a go to 300 mm single piece in my mid sized printer.
Burn Lines these lines represent the 'evolution' of the grain during the burn accounting for regression and corner erosion. I didnt want it to end as a circle, I wanted to have some 'twist' left at the end.
This isnt the grain, is shows how the shape changes over time each color is a 'moment in time' as the grain burns.
I have 3d printed the grain - easy print.
For testing I'm building a simple tie rod test motor using standard 3/4 NF ORB tanks (Oxygen tanks) that screw into the forward plate (green), the outer tube is off the shelf 6061-T6 3.125 inch extrusions. .095 wall. The aluminum tube cost about $5, I plan to reuse them but disposable cheep. The aft plate (magenta) has a bore for the same ID as 38mm motor tube, and has a snap ring cut into it to retain a nozzle. Simplifies the nozzle.
Keeping it simple - cheep, the grain is held in a stock PVC schedule 40 that lives inside the metal outer tube. I'm just using the PVC as a liner / holder for the test, it shouldn't be consumed during test burns.
The vent runs through the threaded boss that screws into the bottles and the is ported out the side with a 10/32 straight thread push to connect. His can also be used to monitor the tank pressure using a 3 way solenoid.
To reduce the number of variables I'm just using a straight injector. The design is easy to mount on a test frame, plus it is VERY easy to change the grain length.
The picture shows the 2.125 OD version on the left, and a 3 inch version on the right. These are shown to scale with M6 cylinders. The system works with M4 or M2 tanks for a smaller fill. The Load cell mount bolts to the aft plate and a simple slider boltsto the forward plate fortesting.
Aluminum tubes are cut, grains printed, ends are on the lathe.
Working on some EX hybrid grains, one version is a nylon grain with a twisted port. I did some simple modeling of the grain erosion, assuming (not a great assumption) uniform erosion plus regression of the grain. Plus I wanted to play with the effective surface area and twist. The O.D. is 40mm to fit into stock PVC pipe as a 'liner' . Here is what I ended up with,
This is the shape pre-burn at the end This is the port wall pre-burn . hard to see in this render but the port tapers becoming smaller from the top to the nozzle end. and yes it does look like a piece of licorice. The grain length is 230mm. I can a go to 300 mm single piece in my mid sized printer.Burn Lines these lines represent the 'evolution' of the grain during the burn accounting for regression and corner erosion. I didnt want it to end as a circle, I wanted to have some 'twist' left at the end.
This isnt the grain, is shows how the shape changes over time each color is a 'moment in time' as the grain burns.
I have 3d printed the grain - easy print.
For testing I'm building a simple tie rod test motor using standard 3/4 NF ORB tanks (Oxygen tanks) that screw into the forward plate (green), the outer tube is off the shelf 6061-T6 3.125 inch extrusions. .095 wall. The aluminum tube cost about $5, I plan to reuse them but disposable cheep. The aft plate (magenta) has a bore for the same ID as 38mm motor tube, and has a snap ring cut into it to retain a nozzle. Simplifies the nozzle.
Keeping it simple - cheep, the grain is held in a stock PVC schedule 40 that lives inside the metal outer tube. I'm just using the PVC as a liner / holder for the test, it shouldn't be consumed during test burns.
The vent runs through the threaded boss that screws into the bottles and the is ported out the side with a 10/32 straight thread push to connect. His can also be used to monitor the tank pressure using a 3 way solenoid.
To reduce the number of variables I'm just using a straight injector. The design is easy to mount on a test frame, plus it is VERY easy to change the grain length.
The picture shows the 2.125 OD version on the left, and a 3 inch version on the right. These are shown to scale with M6 cylinders. The system works with M4 or M2 tanks for a smaller fill. The Load cell mount bolts to the aft plate and a simple slider boltsto the forward plate fortesting.
Aluminum tubes are cut, grains printed, ends are on the lathe.
So you're printing nylon? And putting inside a PVC liner? Inside an aluminium pressure vessel?
WF/X does have solenoid savers that are connected between the relay output and a solenoid. These allow high current to flow during activation and will decrease current after around 2 seconds to the hold current.
A solenoid saver circuit (made from a bunch of storage capacitors and a limiting resistor) stores the additional energy required to pull in the solenoid coil. Then limits it with the limiting resistor.
The Wilson Fx circuit, pulse width modulates the full current to the solenoid.
The difference is subtle but significant.
Both methods are valid. The PWM method will generate more electrical noise. I'm not sure if that's been tested or quantified.
My preference would be the resistor capacitor bank solenoid saver circuit.
YMMV.
You could always use the old incandescent bulb if you wanted to go old school.... I designed the circuit saver to limit the amount of wasted current.
ContrailRockets
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It is on a 6AN tee right after solenoid manifold
It sits vertical so will not fill with liquid.
I use the old style purge solenoid valve on vent line. It is opened and closed using same circuit power as fill solenoid valve. I just install a cube plug to power both.
When you’re done filling your done venting. The fill line is the pressure relief as it is rated at 1750 psi burst and motor is designed for 3000 psi burst.
Tom
kramer714
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yes, yes I am....
So here is the logic, and this is important, I designed this to be able to test motors, flight hardware will be related. but different.
I looking at (3) different grains types for testing plus (1) a baseline
- Spiral port - 3d printed
- Spiral port, porous - 'wax' impregnated 3d printed
- Wax with a 3d printed 'rebar' skeleton
- BASELINE Schedule 80 PVC
Sample 1, trying test for the regression rate and also how uniform the burn is. For the initial test I don't want to burn all the way through the grain, i want to see how uniform the grain is eroding. I could just 3d print a larger grain, throw away the OD, or.... use cheep PVC as a liner (call it a spacer) print a smaller OD grain press fit, and test. If I do burn through the grain, I still have the PVC to give me more time. Plus, I can buy PVC pipe cheaper than buying phenolic motor liners.
Sample 2 and Sample 3 For these I plan on using a PVC liner for flight, with the 3d printed parts 'vacuum wax cast' into the PVC. Easy to seal, easy to make. the test motor configuration also lets me get a chance to do some testing of the seal method I plan to use.
Sample 4, just open up the ends of schedule 80 slips right onto the fixture.
Mike (it is hard to be this cheap) K
P.S. one of the bigger challenges for my 50 year old lathe is threading. I was able to use a 3/4 UNF die an make the bottle threads.
Sounds interesting. Nylon is expensive though. As you're using a pvc liner, which does not melt and collapse to compensate for that like the rattworks Polypropylene grain with the floating piston, have you considered ABS as the fuel grain? Got a good ISP rating in the k240 rattworks tests. 213?
very clever. love to get some pics of your set up.
btw...any plans for a 98mm 10k Ns >90% M? otherwise no way to touch the M record without finding a 5478cc hypertek tank and a perfect weather day in Blackrock.
is their a performance table yet for all the printable thermoplastics? I'll have to revisit the Cesaroni fuel grains but IIRC they are ABS or ABS+Al powder injection molded with a phenolic nozzle insert. the Ns per cc NOS output of those motors were impressive. Not needing a metal case for the fuel grain kept the weight down.
as per US5893266A Kline et al, eAC (licensed to CTI) carbon-filled ABS, GE T-4500 CYOLAC resin
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kramer714
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The injector had a lot to do with the performance. As far as the plastic motorcase, I saw too many catos of m grains.....
never saw a single a cato of a new M grain. lot of people made the mistake of trying to fly them twice. the j/k grains you could, but not the L/M grains.
and I agree the injector design also contributes as does the combustion chamber design and the diameter of tank orifice.
to be clear, atm i'm focused purely on altitude
I’ve used both solenoid saver techniques but now use the WFX active electronic module in my hybrid pad box. Yes, there is a little PWM noise. However, the convenience of a small size, and a programmable output that optimises the power profile delivered to each solenoid, works well for me.
The DSO screen shot below displays the solenoid saver output at the final hold-in state. In this case, the output starts at 12V @ 2.4A for a couple of seconds, then ramps down to the programmed hold-in set point of about 3.4V @ 0.7A.
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ContrailRockets
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38 mm HP uses 1 inch schedule 200 pipe from Home Depot as liner
54 mm BG or SP uses 2 inch ABS sewer pipe from Home Depot as liner
The EX 54 mm uses SDR 21 PVC as liner. Harder to find but thinner wall than ABS.
Have white and purple.
Purple is for pleats as in 13 point star grain.
Massive surface area increases.
Tom Sanders
Contrail Rockets
For a liner plastic, there are basically 3 strategies.
1 Use Polypropylene or another low melting plastic as the full fuel grain which a floating piston. When the grain gets close to the pressure vessel case wall it's hot enough to melt, collapse the grain enough to seal the burnt rough and keep performing at a slightly lower thrust.
2 Use a melting liner with a higher performance core fuel grain. You burn through the main fuel grain and then start melting the liner. Hopefully the liner collapses as above.
3 Use a non melting liner, design so you don't burn through.
PVC, burns well, but does not melt well. When hot, it maintains a lot of its structural integrity. This can prevent it from collapsing and self sealing. I've had a motor burn through because of that. So I'd be unlikely to do that again.
You can of course design your fuel grain heavier, so you're not getting that close.......
if going the non-melting liner route, i'd try going to RCS source...their pricing seems steep for the phenolic liners. best i can tell the paper-phenolic is Latimex Grade XXX by Franklin Fibre. https://www.franklinfibre.com/phenolic-paper-tubes-x-xx-xxx.
cfb_rolley
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Increasing surface area with pleats and twisted ribs etc has yielded massive performance boosts in micro-hybrids, I'm pretty excited to upscale some of the grains I made for micros and try them out with the new 38mm tank when it arrives.
I can only imagine that pleated BG or SP grains would be even more of a performance boost over my ASA grains with that kind of geometry!
ContrailRockets
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We do leave a bit of fuel that acts like an insulator. In addition since we make grains like the 8 inch PVC in 38 mm that can be used in the 20 inch, 28 inch, 36 inch and 48 inch case the fuel left behind is greater in shorter cases. Our motors are certified for only firing a grain once. In the PVC grain the surface area created by the continuous thread is burnt away. This greatly reduces performance if a flyer attempts a second flight when using a shorter case for both attempts. Again we do not recommend a second flight as motor failure from burn through and unknown thrust profile make this unsafe.
Our Hybrid motors are tested vertically so the total Newtons of thrust. This does not factor into account the impulse needed to lift the weight of the motor case, the fuel grain and the loaded Nitrous Oxide. This deviation in actual impulse versus measured impulse increases with motor burn time.
Horizontal testing seen in AP motor testing gives total impulse. The weight of the case and fuel have no impact on the motors total impulse.
Tom Sanders
Contrail Rockets
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