Loki graphite nozzles

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littlemisterbig

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Hello everyone,

I was wondering if loki nozzles could be used in a hybrid motor, more specifically a GOX/Acrylic motor? And if i was to use different propellants in it such as Paraffin wax or PVC, would i need to buy a different nozzle for the higher impulse?

Thanks, David
 
David... I really hope you are not doing EX motors...
 
Hybrids run at much lower pressures than AP motors, so I suspect they'll work fine. I believe some commercial hybrids use graphite.

But you have to make sure that you never use it for a normal AP motor with any not-fully-fluorinated grease, or you may have a sudden disassembly on your hands.
 
There are some quirks about it. A hot highly oxygen rich environment and hot graphite mix rather well, if you want to burn off the surface of your graphite! You want to have enough fuel regression rate to achieve a slightly reducing atmosphere at the nozzle surface thereby protecting your graphite.

If you are not familiar with O:F ratios, and haven't researched regression rates of various fuels, then I figure you're not ready to do this experiment. The question about nozzles vs impulse indicates to me that you don't know enough about hybrids yet. I'm thinking the question isn't quite put in the appropriate terms (not grammer; physics) for hybrids. Please research them some more!

But as a generic answer - yes, with any rocket motor, if you change some characteristic somewhere, then likely a change of nozzle is in order.

I'm not sure I'll answer further on this thread.

Gerald

PS - I apologize for being a bit abrupt in my answer. We get lots of questions asking about something a bit advanced, where the nature of the question indicates the person isn't quite ready to try it yet. This is also the open forum where we tend not to discuss too much about motors, sorry to say.
 
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Hybrids run at much lower pressures than AP motors, so I suspect they'll work fine. I believe some commercial hybrids use graphite.

But you have to make sure that you never use it for a normal AP motor with any not-fully-fluorinated grease, or you may have a sudden disassembly on your hands.

So what fully-fluorinated grease would you recommend?
 
Probably not the best project for a 14 year old but your going to have to do some extensive research before you attempt to build anything.
 
What are some good resources for hybrids?

I relied extensively on Rocket Propulsion Elements by George Sutton when I first started working with hybrids in high school. Here are some excerpts from the "Why Not Hybrids?" thread I posted a while back:

- I used to build hybrids (a picture of one is in the middle of https://www.buyrocketmotors.com/about-me/) and it was fun. I still have the parts but never had the time to actually configure it into something I could fly. A decent metal working setup with a lathe, mill, etc. are a huge plus. Otherwise, building from scratch is a difficult proposition although possible but probably very limited.

- I used Fundamental of Hybrid Rocket Combustion & Propulsion quite bit about 13 years ago. Before that was George Sutton's Rocket Propulsion Elements that had a chapter dedicated to hybrids. The version I have is whatever was current in '95 or so. I remember taking it to my high school math teacher looking for some help with, well, the math. AIAA has a bunch of technical papers on hybrids but they can be costly and it's hard to know just how useful they'll be until you buy them. That's the way it was many years ago so things may have changed.

- I'm not familiar with the book Hybrid Rocket Combustion, but knowing nothing about it I would still buy it based on the title alone if I was still knee deep in design.

In the end, it's time to pick up some books and dedicated quite a bit of time reading and working through some basic design calcs. Then, cross the hardware bridge when you get to it.

Hope this helps.
 
I use cheap graphite for my hybrids. The nozzles last forever.. or until I loose the rocket.

--MCS

.
 
David, I highly suggest if you plan on doing this to make a few successful burns with a heavy, overbuilt, static model without a nozzle. Get a working hybrid that has no possibility of making thrust and work up from there. Its better to be overbuilt than underbuilt with something like this.
 
The heavy, static, overbuilt recommendation could be a mistake if one switches to N2O instead of O2 for the oxidizer. In the catastrophic situation where the N2O goes monoprop in the tank, having a heavier wall tank may just be equivalent to creating higher pressure before it bursts. Sometimes it's better for some parts of hardware not to be overbuilt. For instance, one wants to design so that a nozzle blows out as the first failure point for a solid propellant motor. That's just an example. Consider the types of failures which might occur, and then design for either eliminating them, or for how those failures shall occur if they cannot be eliminated. A failure that occurs in a controlled fashion is generally preferable to an uncontrolled failure.

If I'm recalling correctly, I remember a story about a solidly overbuilt motor static test where a bulkhead ended up embedded in concrete half a mile away. The motor was large but within the realm of what a dedicated hobbyist could produce. Rocket motors are high power devices. It is something worth keeping in mind.

I do like that "without a nozzle" suggestion though. However it significantly changes the dynamics as the pressure differential through the injectors will be much greater than the nominal 150-200psi for a reasonable burn.

There is actually a great deal of research and information available now on hybrids. Not nearly as much as other forms of rocket propulsion, but enough to spend quite a bit of time absorbing! The fundamental design factors are a bit different for a hybrid than a solid, as the hybrid is halfway towards a full liquid system. It contains elements of both types of systems.

As a quick example, the scaling factor Kn for a solid propellant motor (which many are familiar with; certainly all EXers) which is the ratio of the burning surface area of propellant to the nozzle throat area would be replaced by a different scaling factor which is the ratio of the effective injector surface area to the nozzle throat area. Though, I'm over-simplifying it of course.

If that last paragraph isn't totally obvious to a person, then that person is nowhere near ready to start designing hybrids!

Ultimately, the research tends to leave a person with more ideas and more questions. But they are more practical, more interesting ideas and questions!

Gerald
 
The heavy, static, overbuilt recommendation could be a mistake if one switches to N2O instead of O2 for the oxidizer. In the catastrophic situation where the N2O goes monoprop in the tank, having a heavier wall tank may just be equivalent to creating higher pressure before it bursts. Sometimes it's better for some parts of hardware not to be overbuilt. For instance, one wants to design so that a nozzle blows out as the first failure point for a solid propellant motor. That's just an example. Consider the types of failures which might occur, and then design for either eliminating them, or for how those failures shall occur if they cannot be eliminated. A failure that occurs in a controlled fashion is generally preferable to an uncontrolled failure.

If I'm recalling correctly, I remember a story about a solidly overbuilt motor static test where a bulkhead ended up embedded in concrete half a mile away. The motor was large but within the realm of what a dedicated hobbyist could produce. Rocket motors are high power devices. It is something worth keeping in mind.

I do like that "without a nozzle" suggestion though. However it significantly changes the dynamics as the pressure differential through the injectors will be much greater than the nominal 150-200psi for a reasonable burn.

There is actually a great deal of research and information available now on hybrids. Not nearly as much as other forms of rocket propulsion, but enough to spend quite a bit of time absorbing! The fundamental design factors are a bit different for a hybrid than a solid, as the hybrid is halfway towards a full liquid system. It contains elements of both types of systems.

As a quick example, the scaling factor Kn for a solid propellant motor (which many are familiar with; certainly all EXers) which is the ratio of the burning surface area of propellant to the nozzle throat area would be replaced by a different scaling factor which is the ratio of the effective injector surface area to the nozzle throat area. Though, I'm over-simplifying it of course.

If that last paragraph isn't totally obvious to a person, then that person is nowhere near ready to start designing hybrids!

Ultimately, the research tends to leave a person with more ideas and more questions. But they are more practical, more interesting ideas and questions!

Gerald


I believe he's using neither of those as oxidizers and rather GOX, I believe....
 
The heavy, static, overbuilt recommendation could be a mistake if one switches to N2O instead of O2 for the oxidizer. In the catastrophic situation where the N2O goes monoprop in the tank, having a heavier wall tank may just be equivalent to creating higher pressure before it bursts.

Like this?

https://www.rocketryforum.com/showthread.php?89139-RATTWorks-K240-CATO

attachment.php
 
The heavy, static, overbuilt recommendation could be a mistake if one switches to N2O instead of O2 for the oxidizer. In the catastrophic situation where the N2O goes monoprop in the tank, having a heavier wall tank may just be equivalent to creating higher pressure before it bursts. Sometimes it's better for some parts of hardware not to be overbuilt. For instance, one wants to design so that a nozzle blows out as the first failure point for a solid propellant motor. That's just an example. Consider the types of failures which might occur, and then design for either eliminating them, or for how those failures shall occur if they cannot be eliminated. A failure that occurs in a controlled fashion is generally preferable to an uncontrolled failure.

If I'm recalling correctly, I remember a story about a solidly overbuilt motor static test where a bulkhead ended up embedded in concrete half a mile away. The motor was large but within the realm of what a dedicated hobbyist could produce. Rocket motors are high power devices. It is something worth keeping in mind.

I do like that "without a nozzle" suggestion though. However it significantly changes the dynamics as the pressure differential through the injectors will be much greater than the nominal 150-200psi for a reasonable burn.

There is actually a great deal of research and information available now on hybrids. Not nearly as much as other forms of rocket propulsion, but enough to spend quite a bit of time absorbing! The fundamental design factors are a bit different for a hybrid than a solid, as the hybrid is halfway towards a full liquid system. It contains elements of both types of systems.

As a quick example, the scaling factor Kn for a solid propellant motor (which many are familiar with; certainly all EXers) which is the ratio of the burning surface area of propellant to the nozzle throat area would be replaced by a different scaling factor which is the ratio of the effective injector surface area to the nozzle throat area. Though, I'm over-simplifying it of course.

If that last paragraph isn't totally obvious to a person, then that person is nowhere near ready to start designing hybrids!

Ultimately, the research tends to leave a person with more ideas and more questions. But they are more practical, more interesting ideas and questions!

Gerald

Just to clarify my previous comment, What I meant by over built was to make it so that you eliminate as many variables as you can. Make it stronger than it needs to be so it won't fail, not to just build it strong without doing the math and actually thinking through the process. I also agree with you that anything can happen on motors like this so no amount of over building can substitute proper safety. I don't build motors so this is just my two cents but I just wanted to clarify so there's no misunderstanding.
 
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