Hybrids 2017

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Speaking for myself only: what they currently do / do not make / sell.

Contrail will pretty much sell everything they have certified. The exception is; If they not currently have hardware on hand, they can make special arrangements to have hardware made in small batches if there is enough interest. Contrail can be ordered through Pratt Hobbies.

RATTWorks & HyperTEK can be special ordered through Black Dog Rocketry, Pratt Hobbies and Star Rocketry:

https://blackdogrocketry.com/

https://www.pratt-hobbies.com/

https://www.starrocketry.com/

This is a quick run down from memory. Do not expect shipments in days, as no one is keeping much in the way of inventory.
 
For me, I want to learn more detail about how they work; what, if anything, can be "fiddled with" on a certified motor without getting into EX territory. What people are doing with EX and hybrids. What the heck is a tribrid?

Etc ...
 
Tribrid vs. Hybrid: normal formula of fuel of t. - the fuel grain has the solid oxidizer and process of burning in the chumber begins with its ignition. After a heat of a grain submission a liquid oxidizer on the hybrid scheme is added. In my "tripropellent" rocket engine the grain is made of a "black" paraffin (with charcoal) and serves for increase in initial temperature and chamber pressure. After a small delay the main oxidizer (NOx), and then liquid fuel (ethylic alcohol, propane) begins to arrive.
 
THRP-1 (Tiny Hybrid Rocket Project version 1); a little more progress. I'm expecting it to be ready to burn in a week or two. That's a valve at the top, not an ejection charge well.

That's a cell phone picture, so not the best. But it should convey the general idea and status.

Remaining to be done:

Machine injector assembly - hopefully tomorrow. This is a small swappable subassembly. This first version is to use three injectors with impinging streams.

Clean THOROUGHLY. Cutting fluids and nitrous unfortunately do mix, and greatly lower the energy needed to get it to go boom. It will get acetone degreasing, then denatured alcohol cleaning, then air drying.

Cast fuel grain. Last needed chemicals arriving Mon or Tu, so should get it done by the weekend.

Cast preheater. It's a chilled nitrous motor, so the preheater is mandatory or it will have good odds of blowing itself out.

Assemble for real, using nitrous safe grease - DuPont Krytox.

Gerald

Somewhat Assembled resized.jpg
 
THRP-1 (Tiny Hybrid Rocket Project version 1); a little more progress. I'm expecting it to be ready to burn in a week or two. That's a valve at the top, not an ejection charge well.

That's a cell phone picture, so not the best. But it should convey the general idea and status.

Remaining to be done:

Machine injector assembly - hopefully tomorrow. This is a small swappable subassembly. This first version is to use three injectors with impinging streams.

Clean THOROUGHLY. Cutting fluids and nitrous unfortunately do mix, and greatly lower the energy needed to get it to go boom. It will get acetone degreasing, then denatured alcohol cleaning, then air drying.

Cast fuel grain. Last needed chemicals arriving Mon or Tu, so should get it done by the weekend.

Cast preheater. It's a chilled nitrous motor, so the preheater is mandatory or it will have good odds of blowing itself out.

Assemble for real, using nitrous safe grease - DuPont Krytox.

Gerald

What are you using for your preheater? Simple AP shot?
 
I'll eventually be providing more details, but probably in the research section. The preheater physically is a grain roughly 2" long in a phenolic 54mm liner, with a thinner web than would be usual for a solid propellant grain. It partially surrounds and extends past the injectors. It isn't the usual solid propellant sort of mix, and it won't have the burn rate.

The preheater serves three purposes here. First is to get the combustion chamber up above the dissociation temp for N2O. Second, since the nitrous is coming in chilled (compared to the usual nitrous hybrid - I'm regulating tank temperature and nitrous density in this motor) I want to boost its temperature as quickly as possible so the motor isn't inclined to blow itself out at startup. In other words, it will need a bit more heating than usual. I need to get the nitrous hot enough to dissociate. The heater won't go out immediately, but instead burn for several seconds. It will be heating the injectors and the nitrous near the injectors. The nitrous flow through the injectors will easily keep them from overheating. I intend the preheater to stop burning before the gas phase burn starts. If it doesn't, well, that might not be pretty... We'll see how that goes. It's going to require some tuning most likely but hopefully it is close enough first burn to be sufficiently functional. I'll start conservative on the short burn side (the safe direction). Third, the preheater will release a catalyst to lower the dissociation temperature and increasing the dissociation rate of the N2O vapor. I don't believe this has been tried before. Think of it as a hot catalytic converter without the solid substrate. It may not achieve much due to the flow rates, but it will at least coat the fuel grain with a light coating of hot catalyst right before the nitrous flow commences. If nothing else, that should help ignition.

There will also be a pyrodex pellet right up near the injectors...

I'm still debating which ignition sequence to use. Ignite the pyrodex first, or ignite the preheater first and let that ignite the pyrodex when it is up to temperature. I'll likely cheat and coat the preheater with a pyrodex slurry as I really want both to go off at nearly the same time. Otherwise the fuel (a heterogeneous blend of a number of things) is going to get one of its components above its softening temperature. That might hard start, or even CATO, if it was heated for too long before the nitrous flow starts.

That wasn't a consideration in the original design. But I've spent a fair bit of time in PEP code analyzing different fuel blends and the one I'll be using has that issue. The originally intended fuel was essentially immune to temperature issues. But the change ups the ISP notably so I think it worth the challenge. This particular blend has probably not been done before. Heck, it is not all that common to even find one key ingredient.

A goal of this motor is to pack as much total impulse into the volume as I can, using N2O as the oxidizer, and NOT adding an oxidizer to the fuel. It is still a lot longer than an equivalent solid propellant motor would be, but shorter than usual for the expected delivered total impulse for an N2O based hybrid. But even chilled a bit, N2O isn't very dense. It can't compete with a solid oxidizer in that regard. But it's what we're allowed to use.

So, this motor is a bit more EX than usual... Hopefully it doesn't achieve the other meaning of EX!

If it works well, then I have a much more elegant mechanical design to accomplish all the above, provided the motor is scaled up from here. If I did that, then I'd probably want to fly it at Black Rock, but I have no way of managing the logistics. It is not as easy as for a solid.

Gerald
 
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PS - Succeed or fail, I intend to post pics and video when the first test is made. I'll try to remember to take assembly pics.

Mostly I'm hoping to get some good data from the first burn.

What is the regression rate of the fuel? I can adjust the composition to alter the O:F balance in the combustion. If it's not right, ISP drops. That's one reason for the formula change. It is readily tunable being a mix of three different primary fuels with radically different properties.

Does the ignition sequence work? Or does it blow itself out?

Is the combustion stable?

Are there any issues with the valve chosen on the tank with the cold nitrous flow? If it freezes open, well, there won't be a burn... It's not supposed to, but, well, this is rocket engineering... It hasn't been proven to work yet.

Did I design the injector correctly to achieve roughly the target burn time? If not, the chamber pressure is going to be +/- the intended pressure range. That would necessitate either an injector assembly change (it is a swappable unit so not that big a deal just a bit of machining for the new injector assembly) or sinply accepting the observed nitrous flow rate and making a new nozzle.

Does it appear the fuel is getting burned efficiently in the combustion chamber, or am I blowing it out the nozzle and burning it where it doesn't do any good?

Etc.

Mechanically, everyting is done now except for making the first injector assembly. The metal I need isn't here yet - probably tomorrow. But the rest of the machining should be done by sometime this coming weekend.

So, it's about ready to burn.

Gerald
 
1.jpg2.jpg3.jpg4.jpg5.jpg6.jpg

Unlike my usual posts, more pictures less text. Machining the replacable injector assembly. Injectors are not there yet, but you can see what it is, and where it goes. The part it is plugged into is the coupler between the flight tank tube and the combustion chamber tube. In the full motor picture a few posts back, it is the joint above the fins with the bolt circles.

The last picture shows the assembly from the precombustion chamber side, with its liner. The preheater will be cast onto that liner.

Gerald

PS - Injector assembly is flipped end for end in the lathe chuck between the first picture and the second. The first picture shows the conical face which will have the impinging injectors added, perhaps tomorrow.

PPS - The pictures show better if you click on each one individually, then click on the picture that comes up.
 
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Slowly begun machining the parts for some 75mm hybrid motor testing, goal will be to develop a system similar to the rattworks tribrid... has anyone else come up with a dual phase system like that? Unfortunately Nitrous Oxide is a lot more expensive here in NZ compared to the USA and UK. Do I need to be a payed subscriber to the forum to upload images these days?

IMG_20170212_203826.jpg
 
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There is another here who is doing an EX tribrid. He'll chime in if he wants to.

Monotube is definitely simpler than what I'm doing. I'll not make another motor quite this way again. Too much work.

Gerald
 
Here is a pre-filled showerhead injector.

The first is for an 88mm case. This is a showerhead system for a prefilled tank. Attached the tank to the forward closure, open the valve and the pyrovalve is ready to go. The motor used 3 50 caliber pyrodex pellets to start it. Flew this three times, then developed a bit better method instead of using BP to hold back the pyrovalve. This showerhead is my preferred injector style for hybrids. Easy to machine and atomizes the nitrous oxide very well. Also the showerhead impinges directly on the fuel grain and it also breaks it up further.

IMG_1876[1].jpg
IMG_1878.jpg
IMG_1879.jpg
IMG_1880.jpg

Edward

P.S. This will be for sale, along with a case in the Yard Sale section.
 
Here is another injector, for a 75mm case.

This injector is what I termed my annular injector. The nitrous flowed around a central piston through a gap and into the chamber. This had a servo controlled plug valve to initiate flow. It works very well, the flow impinged on the surface of the grain and atomized. The downside to this injector was making all the pieces line up together to provide an equal gap.

IMG_1892.jpgIMG_1893.jpgIMG_1894.jpgIMG_1896.jpgIMG_1897.jpg

Edward

Now for sale in the Yard Sale section, if you can find it. Includes casing and nozzle.
 
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I've been working on upscaling the RATTWorks tribrid. So far I have a clone of the motor and I've made some modifications to it to make it easier to machine. Dave's machining is very elegant, but not all of us have an aerospace shop to machine parts. I have made the mid-bulkhead that separates the nitrous and fuel chamber two pieces. I have a traditional U/C injector on the bottom. The top part contains the 1/8" fitting and fits with a snap ring into the bottom piece. This way I can adjust the drilled holes for nitrous flow easier. I have also removed the burst tube that holds the alcohol in favor of a piston system. After the nylon fill tube burns though, it pulls the piston out of the alcohol fitting as it is ejected. The alcohol is released nearly instantly, so the hybrid phase of the motor lasts tenths of seconds and then it transitions to liquid mode while still on the pad.

Edward
 
Edward, all I can say is after you are done, these could be used to make quite interesting ornamental fountains! Nice work!

Gerald
 
  • Convection cooling for the Nitrous Tank (I fly in South Carolina so Nitrous Tank temps get dicey in the July and August)

Hey, I may have seen one of your launches! Did you have a kiddie pool underneath to reduce the risk of fire?

I'm the guy with the twins.
 
All - here is a link to the 54mm as well as the basic parts list. I'm still working on getting all the CAD consistent and on the same sheets. Once I get that done I'll publish that PDF as well.

Download Here

Edward
 
I have an in-house draftsperson ( the missus' day job ).

Let me know if you'd like some tidying / sheet sets / normalizing done.
 
Edward,

What materials did you use for the burst disk. Plus does it burn through or burst?

Mike K
 
I have an in-house draftsperson ( the missus' day job ).

Let me know if you'd like some tidying / sheet sets / normalizing done.

Thank you for the offer - I work all day in CAD as well so I just need to find the time.

Edward
 
Machining is now complete for my EX M hybrid, for the motor itself. I plan to machine the mandrel for casting the fuel grain tomorrow, and get started on cleaning/prep for assembly. T-2 weeks for the static test, at Battle Park launch. At least that's the tentative plan of the moment - still working out the details.

Pictures of the injector block in place in the coupler (injectors removed), and a bag of the injectors. One can see the convergence pattern of the three injectors by the angles of their threaded holes. The picture flattens the appearance of the surface where the injectors mount. It is somewhat conical rather than flat. One can also see there is a bit of volume available for precombustion after the injectors. That picture is shown with the precombustion chamber liner removed.

The injectors are single use for this iteration - as is done for the Contrail motors. When prepped, there will be a long loop of tubing connecting a pair of the injectors, and a tube in the third injector which is the fill line. Venting is via automatic valve at the top of the tank which regulates the tank pressure.

Gerald

injector side of coupler.jpg

tank side of coupler.jpg

injectors.jpg
 
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1.22 pounds/sec, 3x ~1/8" injectors. 1.4" initial port diameter. I've send you a design spreadsheet on the motor. It isn't accurate for the current design but was the starting point. As built, the oxidizer mass is a bit greater, as is the fuel mass through increased density. The theoretical ISP of the fuel is also quite a bit better with N2O at the target combustion pressure. Regression rate and O:F ratio, well, we'll see in two weeks, weather permitting.

Gerald
 
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For me, I want to learn more detail about how they work; what, if anything, can be "fiddled with" on a certified motor without getting into EX territory. What people are doing with EX and hybrids. What the heck is a tribrid?

Etc ...

Tribrid vs. Hybrid: normal formula of fuel of t. - the fuel grain has the solid oxidizer and process of burning in the chumber begins with its ignition. After a heat of a grain submission a liquid oxidizer on the hybrid scheme is added. In my "tripropellent" rocket engine the grain is made of a "black" paraffin (with charcoal) and serves for increase in initial temperature and chamber pressure. After a small delay the main oxidizer (NOx), and then liquid fuel (ethylic alcohol, propane) begins to arrive.
This is the open propulsion forum. Discussion of propellant formulations is not permitted.

Discussions of research rocketry belongs in the research forum, not in propulsion. Gerald and Edward, it's time to move your discussions to the research forum.
 
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