Liquid-Fuel Engine Design and Implementation

Area66 said:

In a system like Contrail, you never get close to the rocket when it's fill with nitrous, you have to purge if you want to get near the pad. I'm interested in your system as I want to make ground static test, but I don't see why it will be better than an Hybrid System.

How you plan to purge the mixture of Fuel and Nitrous in case it fail to ignite ?

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Launch control equipment can be programmed to dump the excess n2o in the plumbing on command if the controller receives a "failure to ignite" signal. This removes the pressure from the system and does not contaminate the launch pad area with excess hydrocarbon fuel. There are many contingency plans that can be resolved using microcontroller programming instead of hardware solutions.

I need to design a flame redirect system which keeps the initial burst of fuel off the pad. I am thinking a baffle system like the US Navy uses for their ship launched missiles. Also a good way to keep the non-ignited fuel from scattering everywhere.

billspad said:

I don't think this approach has even the slightest chance of working unless you can demonstrate a working engine. For the NAR or TRA to do this means bringing in front of the NFPA. This is a long and involved process. You'd have to convince the the NAR and/or TRA that enough of their membership want this for them to go through the effort.


I think as a personal project what you want to do is cool. As a commercial venture, I'm really skeptical.

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Challenge accepted.

The whole point is to make a functional motor. If I can demonstrate sufficient safety, reliability, and mitigation of known and potential unknowns, then the question becomes "why not?". Will people be willing to drop $$ on a motor that offers a 3rd (or 4th) route for the hobby? Maybe. But I would like to build something, put it out there, and get a response.

https://www.rocketryforum.com/showthread.php?21102-Liquid-Fueled-Model-Rockets

https://www.rocketryforum.com/showthread.php?38875-Why-does-nobody-use-Liquid-Propellant-rockets

There is interest. The only question is how much and is it enough.

bobkrech said:

A few things to point out in the review. The simple rocket for this motor weighs 7.1 kg. and the motor has an average thrust of 260 N. The initial thrust to weight ratio of the rocket supplied with the motor is 260 N / 7.1 kg *9.81 m/s2 = 3.73 providing an acceleration of only a = T/W - 1 = 3.73 -1 = 2.73 g. This is very marginal and only acceptable with a very long launch ramp in winds less than 3 mph or 5 kmh.

The review also claims the motor is base on the one used in the German Tailfun Missile that used a Nitric Acid / hypergolic hydrocarbon liquid propellant that produced 7.84 kN thrust. https://www.astronautix.com/lvs/taifun.htm It is not even a close comparison as the German motor used a hypergolic bipropellant system that produced 30 times higher thrust. The rocket weighed 20 kg and carried 10 kg of propellant burning at a specific impulse of 200 s for 2.5 seconds. The initial acceleration was a = 7840 / (20 x 9.81) = 39 g and a burnout acceleration of 7840 / 10 x 9.81 = 79 g! The comparison of the Tailfun missile to the System Solaire rocket is like comparing a race car to a rickshaw, or not even close.

Bob

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The consensus on this system seems to be, politely, a thumbs down.

The current design I am working on reduces mass by eliminating the excess oxidizer storage locations. I need to keep an eye on how much the hardware weighs and what the end thrust actually is. If I have to increase the thrust in order to maintain system stability, that's what needs to be done. As it is, given the current size requirements of the combustion chamber based on the thrust specs, I am at the bottom of the scale for the size of the motor. I can really only go up from here, and that may offer some solutions in itself.

How about a monotube using N2O and CH3OH? Have a floating piston separating them, fittings on either side with check valves leading into the combustion chamber. The pressure of the N2O will feed the liquid propellants, and the check valves will prevent blowback. The key word here is "functional", rather than
"optimal".

innkeeper said:

Challenge accepted.

The whole point is to make a functional motor. If I can demonstrate sufficient safety, reliability, and mitigation of known and potential unknowns, then the question becomes "why not?". Will people be willing to drop $$ on a motor that offers a 3rd (or 4th) route for the hobby? Maybe. But I would like to build something, put it out there, and get a response.

https://www.rocketryforum.com/showthread.php?21102-Liquid-Fueled-Model-Rockets

https://www.rocketryforum.com/showthread.php?38875-Why-does-nobody-use-Liquid-Propellant-rockets

There is interest. The only question is how much and is it enough.

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Yep. you've pretty much nailed the design, other than the fuel. I though of alcohol, but kerosene is a bit energy denser. I have a Mk2 set of ideas rolling around for that, but I would like to get a good design prototyped before I try to move on to that. I have definitely discovered that better is the enemy of good.

I need to get some more screenshots of the CAD models I have. The one I posted was pretty lacking.

I did get the news that my printed models of the chamber, nozzle and nozzle support are done, so I should have pics of those this weekend.

More detail that the first screenshot I posted. The servo and the valves are there for location spacing only. I am working on getting the plumbing done. None of these models have the entire set of nuts and bolts added in, yet. Many parts need to come together still.

innkeeper said:

Thinking on the certification issue more tonight, I realized that this might be an opportunity to come up with a set of regulations that can be brought to NAR/Tripoli in order to facilitate a certification process. As we are a self-regulating hobby, this would be a prime example of working from the bottom up in order to put guidelines and regulations in place before they are further imposed on us. Yay... another section in my binder.

Any tank that is going to be certified DOT is going to be hefty. Contrail Hybrids are DOT certified. "These motors are a case contained grain system but uses DOT certified Nitrous Aluminum Nitrous flight tanks" https://www.contrailrockets.com/

Thank you all for the info and challenges.

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The AeroTech hybrids also used DOT approved tanks with pin valves similar to Paint Ball tanks. They could be filled at home and transported to the launch site. When attached to the propellant part of the motor the pin valve opened and the pressure was held in check by a pyro valve, (a black powder pressed pellet and a plastic disk) that burned through upon ignition and released the Nitrous into the motor. The flow was adjusted by plugging a different number of ports in the adapter for each size motor. The nitrous flowed through a small ACPC grain that acted as a preheater before it entered the main propellant chamber.
AT used some fuel grains that were plain paper wrapped and glued into a thick cylinder, others were combinations of the paper tube and standard APCP grains while some used just the standard APCP and used the extra oxygen to increase performance.

Sailorbill said:

The AeroTech hybrids also used DOT approved tanks with pin valves similar to Paint Ball tanks. They could be filled at home and transported to the launch site. When attached to the propellant part of the motor the pin valve opened and the pressure was held in check by a pyro valve, (a black powder pressed pellet and a plastic disk) that burned through upon ignition and released the Nitrous into the motor. The flow was adjusted by plugging a different number of ports in the adapter for each size motor. The nitrous flowed through a small ACPC grain that acted as a preheater before it entered the main propellant chamber.
AT used some fuel grains that were plain paper wrapped and glued into a thick cylinder, others were combinations of the paper tube and standard APCP grains while some used just the standard APCP and used the extra oxygen to increase performance.

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The aerotech motors were just an HTPB rubber in the chamber weren't they? I didn't think they added AP to hybrid grains, or just not much?

edwinshap1 said:

The aerotech motors were just an HTPB rubber in the chamber weren't they? I didn't think they added AP to hybrid grains, or just not much?

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A friend of mine has flown the AT M-845HW hybrid which uses the two grain 98MM L952W-P motor with the Nitrous fed through it to increase power. I seem to remember there was a K motor too that I think was a J415 White Lightning motor with a different nozzle and Nitrous added. I flew a J-390HW Turbo AT Hybrid that had two grains of White Lightning plus a paper grain in a 1280 case.

I think your estimated costs on your indegogo page are underestimating the project costs a bit.

Those micromills and microlathes are pretty cool pieces of machinery. However, they struggle to do anything other than light cuts on soft metals. So boring operations, or if anything on your engine is made from steel or nickel alloys you will have a really tough time of it. If you were making one of these you could probably with enough patience, determination, and cleverness; get those microlathe/mills to make all your parts for you. They would be of marginal quality or have taken you a very long time to make since the bed on those microlathes will flex if you take too aggressive of cuts.
If you are intending to use them as production machines you will probably wear them out rather quickly and it will take you several weeks at least to machine each rocket motor.

I spent about 40 hours of pure machine time to make the fincan for my last rocket. It didn't have what I would call very complicated machining processes. I am definitely slower than a professional machinist but still not too far off what a real shop would do it for you. Remember machine shop time usually is $100-$200+ an hour. So that fincan that I made would cost ~$4000-$8000+ for a professional shop to manufacture.

So if you intend for a professional shop to make any parts for you keep in mind it is not going to be cheap, and if you do, have them make several for you since the setup time is a pretty significant part of the process. So you could probably have them make 10 for not all that much more than it would cost to make 1. (depending on the part of course)

You didn't include the cost of tooling for your machining equipment. The tooling costs add up fast when cutters run $20-50+ a piece and you break a few and usually you need a different tool for each machining operation. You will also want some precision measuring equipment like micrometers, and feeler gauges to help setup the machines, which also aren't cheap. I don't know how extensive your existing set of tools is, but don't discount things like files and the metal finishing equipment.


Next question is your test stand equipment. I don't know what test stand equipment you have on hand but dataloggers, pressure sensors, and thermocouples also cost a pretty large amount of money, Not to mention the test stand itself. If you are intending to certify these motors to sell them, you will probably want this motor pretty well characterized with pressure sensors, accelerometers, and temperature sensors. That way you can detect things like high frequency combustion instabilities, hard starts (unless its hard enough to blow it up of course, then its pretty obvious even without sensors), and also see how much your combustion chamber and nozzle is being heated. You want to find the kinds of things that will cause bad things to happen later on. Your rocket probably could operate with a fair amount of combustion instability. But if you intend to sell these to people, those are the kinds of things if undetected that will come back to bite you in the butt later on.

Since you are using an arduino I am assuming your price point for microcontrollers includes all of the misc. wiring, power regulation and other electronic components as well. I'd probably recommend having some sensor setup on-board to confirm motor ignition. That way you don't pour all of your fuel onto the ground on a failed ignition, or it doesn't attempt to use the igniter if your chamber is full of fuel.

Keep in mind weight, a 42% I motor like I195J weighs about 1.3 lbs. So you probably want to keep the weight of the system under 5 lbs at max, which will be a bit of a challenge with all the tankage, valves, and other heavy object that are required.

All in all if you intend to make this a certified consumer product, I'd guess in the end you will probably spend about $30,000 - $60,000 at least to get a quality product out and ready for general consumption.
If you only want to make 1 or 2 for your own purposes and to say that you did it, then the $6,000 - $10,000 range that you are currently at is a reasonable assumption, depending on how good your bargain hunting skills are, and how well you can talk free services out of people.

There is no way that you will be able to sell these for $1,000 unless you intend to run your business as a charity, since your raw component cost is already over $1,000.

So for your indegogo, if you already have made the motor, and had at least a prototype done and working so you were aware of all the difficulties that you never can think of ahead of time. It might be reasonable to ask people for money to fund it. As it stands you aren't really taking much of a risk in this endeavor and instead attempting to get everyone else to take the risk. Which likely why no one has stepped up some funding for it.

I'd say your highest chance of success on this is to put your bargain hunter hat on to find you components, then it gets even easier since you are a student. There is money existing for undergraduate research projects at just about every university. Most of the time all it takes is figuring out who to talk to. So I'd definitely try to get a research grant from your school to fund something like this, $5000 is not all that much money to get out of even a public university.

Doesn't your school have a machine shop?

So once you get a prototype done, which your school would be more OK with since you arn't trying to use their resources for commercial purposes. You then can come back and much more accurately estimate the real costs to make these motors a commercial product.

There is some content here that might be of some use. (Link)

Eric

[email protected] said:

There is some content here that might be of some use. (Link)

Eric

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On that link...yes! I'm helping with a liquid rocket at FAR that's been a project for a group of guys for a few years now, and there are so many little things that need to be figured out. If a solid lights, it lights, but when the valves on a hypergolic engine are opened, they must be opened enough to get a high enough flow for a high enough M:W or it'll go off the rail and be unstable, so checks and safeties need to be put in place to reduce the chances of failure.

On a side note I went to a talk that Tom Mueller did about his time at RRS, and he brought along the parts for his "smallest liquid rocket ever". He started plugging the injector holes to see how few it could safely run on. Once he got down to 1 he found out the answer..

That would be what Tom called the Micro-scud. I managed to find a photo of it taking off. Somewhere I have photo's of the internals, I'll see if I can find that. If I had to guess this rocket was about 4" diameter maybe a little less. All the valves where pyro actuated.



Here is Tom working on the BFR project. This is what he was working on at the time Elon met with him and SpaceX was born. This was to support a 10-15K lbf thrust motor we called the BFR. Tom's installing the thrust structure here.



Eric

He said you guys found an old titanium pressure vessel at a junk yard, and the owner was doing the math on the weight, and you guys were praying he wouldn't figure out where it came from/how much it was worth.

The micro-scud was an IRFNA hypergol I think?

Tom's micro-scud was a LOX/Kerosene rocket using helium as a pressurant. It was 74 inches tall, 3 inches in diameter, had an empty weight of 7.6 lbs, a propellant load of 1.5 lbs and a burn time of about 6.2 sec. It's max altitude was 7950ft agl as measured by a Transolve altimeter. A very cool piece of engineering!

Jason328K said:

Tom's micro-scud was a LOX/Kerosene rocket using helium as a pressurant. It was 74 inches tall, 3 inches in diameter, had an empty weight of 7.6 lbs, a propellant load of 1.5 lbs and a burn time of about 6.2 sec. It's max altitude was 7950ft agl as measured by a Transolve altimeter. A very cool piece of engineering!

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Ah, I'm thinking of the wrong rocket then. He claimed he built the smallest cryo and hypergolic rockets in the amateur community, but the hypergol was really small, 1.5" or so I think.

I'd love to make an attempt at something that small, but that's some damn high precision requirements.

edwinshap1 said:

Ah, I'm thinking of the wrong rocket then. He claimed he built the smallest cryo and hypergolic rockets in the amateur community, but the hypergol was really small, 1.5" or so I think.

I'd love to make an attempt at something that small, but that's some damn high precision requirements.

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Tom flew both. I recall helping him fuel that little hypergolic rocket. It was tiny. It also made a rather interesting noise on launch due to some combustion instability. My memory is fuzzy on that flight but I think it didn't recover normally and was destroyed or partially destroyed on impact with the desert.

Eric

edwinshap1 said:

He said you guys found an old titanium pressure vessel at a junk yard, and the owner was doing the math on the weight, and you guys were praying he wouldn't figure out where it came from/how much it was worth.
?

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I do recall that story. Tom was at a scrap yard and found a couple really nice titanium pressure spheres. Knowing their worth he asked the scrap dealer how much.. The scrap guys said something along the lines of "Those are titanium and thats X dollars a pound". So Tom told him to put these feather weight spheres on the scale and walked out with a total steal. I hate to think what they cost originally.

Eric

That sounds like a much more interesting scrap yard than any I've visited!

Gerald

G_T said:

That sounds like a much more interesting scrap yard than any I've visited!

Gerald

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Haha, every scrapyard in the Mojave I've seen has had at least something surprising (like jet fighter parts) in it visible from the road; I imagine you can find just about anything in a scrapyard in SoCal if you know where to look!

Xrain said:

I think your estimated costs on your indegogo page are underestimating the project costs a bit.

There is no way that you will be able to sell these for $1,000 unless you intend to run your business as a charity, since your raw component cost is already over $1,000.

So for your indegogo, if you already have made the motor, and had at least a prototype done and working so you were aware of all the difficulties that you never can think of ahead of time. It might be reasonable to ask people for money to fund it. As it stands you aren't really taking much of a risk in this endeavor and instead attempting to get everyone else to take the risk. Which likely why no one has stepped up some funding for it.

I'd say your highest chance of success on this is to put your bargain hunter hat on to find you components, then it gets even easier since you are a student. There is money existing for undergraduate research projects at just about every university. Most of the time all it takes is figuring out who to talk to. So I'd definitely try to get a research grant from your school to fund something like this, $5000 is not all that much money to get out of even a public university.

Doesn't your school have a machine shop?

So once you get a prototype done, which your school would be more OK with since you arn't trying to use their resources for commercial purposes. You then can come back and much more accurately estimate the real costs to make these motors a commercial product.

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School's good with machining, currently. The only issue with everything else about u-grad and grant is that I graduated on Sunday, and my school is/was not a research institute. They do not give money to students for projects.

As for costs:

If a machine shop cannot machine down a 6" length of aluminum pipe and thread it for less than $4K, I need to find a better machine shop.

You have hit the nail on the head WRT the prototype, though. Lack of anything in my hand is a big turnoff. I need to get a Mk1 made for show and tell, which covers most of the test equipment and initial setup. Just means I have to be a better sell to the GF about the shop equipment I need to get. At least being graduated means I can work and pay for the equipment, though.

Driving cost down has been a big part of this whole thing. Find a valve here for $90. Ouch, but it works. Hey look, here's one for $50. Ouch, but less so.

A lot of these issues have come up as I go through the system with a coworker, or telling a forum of rocket enthusiasts. Its all very recursive, but that's kinda the point. If I end up going in front of the NFPA or anyone else who has a stake in an attempt to certify, and all of the questions have answers, then it all goes that much better.

innkeeper said:

.....A lot of these issues have come up as I go through the system with a coworker, or telling a forum of rocket enthusiasts. Its all very recursive, but that's kinda the point. If I end up going in front of the NFPA or anyone else who has a stake in an attempt to certify, and all of the questions have answers, then it all goes that much better.

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I don't want to discourage your enthusiasm but the proposed rocket motor is not presently certifiable because it does not fall into any existing certifiable NFPA model or high power rocket motor categories. Please go to the NFPA website and read NFPA 1125 Code for the Manufacture of Model Rocket and High Power Rocket Motors. The codes are free to read.

You will have to convince NFPA that a new category of hobby liquid rocket motors are safe to operate and will not present a significantly higher risk than solid fuel and hybrid rocket motors, and you would also have to convince NAR and/or TRA as well. IMO it is highly unlikely that without the endorsement of a National Hobby Rocketry Organization that you can even get NFPA to consider it.

If you manage to get it certified, IMO you might be likely to sell a few dozen motors, but not much more, as the extra complexity when compared to a hybrid, which is more complex than a solid, will discourage most users. Note: Once the BATFE APCP lawsuit was decided in hobby rocketry's favor, the number of hybrid flights plummeted, and most hybrid manufacturers went OOB.

Without certification, there is no commercial market. Realistically you might expect a handful because without certification as a model or high power rocket motor, the motor can not be flown at any NAR launches or Commercial TRA launches. With the permission of the TRA BOD, it might be possible to launch it at a TRA Research Launch but that might be a stretch under the existing TRA research launch rules. You might be able to convince an indy group to let you launch it if you have TRA L2 certification. The user as an individual can launch independently if they can find a land owner who does not require liability insurance from the flyer and they can obtain a waiver from the FAA. IMO both will be difficult in most parts of the country.

Bob

bobkrech said:

I don't want to discourage your enthusiasm but the proposed rocket motor is not presently certifiable because it does not fall into any existing certifiable NFPA model or high power rocket motor categories. Please go to the NFPA website and read NFPA 1125 Code for the Manufacture of Model Rocket and High Power Rocket Motors. The codes are free to read.

You will have to convince NFPA that a new category of hobby liquid rocket motors are safe to operate and will not present a significantly higher risk than solid fuel and hybrid rocket motors, and you would also have to convince NAR and/or TRA as well. IMO it is highly unlikely that without the endorsement of a National Hobby Rocketry Organization that you can even get NFPA to consider it.

If you manage to get it certified, IMO you might be likely to sell a few dozen motors, but not much more, as the extra complexity when compared to a hybrid, which is more complex than a solid, will discourage most users. Note: Once the BATFE APCP lawsuit was decided in hobby rocketry's favor, the number of hybrid flights plummeted, and most hybrid manufacturers went OOB.

Without certification, there is no commercial market. Realistically you might expect a handful because without certification as a model or high power rocket motor, the motor can not be flown at any NAR launches or Commercial TRA launches. With the permission of the TRA BOD, it might be possible to launch it at a TRA Research Launch but that might be a stretch under the existing TRA research launch rules. You might be able to convince an indy group to let you launch it if you have TRA L2 certification. The user as an individual can launch independently if they can find a land owner who does not require liability insurance from the flyer and they can obtain a waiver from the FAA. IMO both will be difficult in most parts of the country.

Bob

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Or FAR/RRS. Some Navy students have come as far as Annapolis to test their liquids. However I don't see myself driving from Maryland to California to fly an engine somebody else designed and machined.