ap0r

KSP inspired me to design a liquid-fueled rocket engine

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2 hours ago, Kerbart said:

As mentioned before but it cannot be mentioned enough: safety first!

As a rule, any experiment needs to be done in open air. As mentioned by John D. Clarke in Ignition! those who do their experiments indoors “are considered insane, even by rocket scientist standards”


The hell will freeze over twice before I perform a test indoors. I have access to empty land for that.
I got Ignition, reading it now! Amazing book.

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10 hours ago, ap0r said:

I'd imagine you'd reccomend bonding the manifold to the throat with epoxy and then covering the whole thing in 10 mm of fiberglass?

Straight up epoxy should hold. Its ultimate strength is over 100MPa, and your bind area is comparable to cross section, where you will need about 3MPa. Just make sure it is a close fit and coat inner walls of the mouth with epoxy. The only reason you need fiberglass on the rest of it is that walls are going to be relatively thin, compared to relevant cross sections.

 

Oh, and one could absolutely build something like that in their backyard in US. None of the materials are flagged, it is not meant to explode, so it is not a destructive device. And only limitation on hobby rockets is total impulse, which is quite generous. There are additional limitation if you plan to actually fly a high power rocket, but ground tests are fine.

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for fuel piping, I would certainly suggest rubber-type hoses (rubber-type in that the hose is flexible) to help dampen the harm that can come to hoses

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23 hours ago, Sampa said:

for fuel piping, I would certainly suggest rubber-type hoses (rubber-type in that the hose is flexible) to help dampen the harm that can come to hoses

I don't fully understand what did you mean by that. Could you elaborate?

Also, Main post updated. If you're new, start from the beginning of post #1, otherwise scroll down until you find today's date. As always, please do let me know if you find any errors or if you have any suggestion or need clarification about anything.

Thanks

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Pretty much, as I am learning in my AMT (that is: Air Maintenance Technician) school, flex lines, which is what I had intended, are always used where movement is expected.  Movement can include vibrations, such like that would come from a rocket engine, whether it is a gimbaling-type or not, when running.  As I presume you would need to actually feed fuel to the engines, the highest amount of vibrations would be at its source, near the engines.  in the long run, for the rocket's or engine's lifetime (if it is to be reused later) it is naturally unhealthy for rigid fuel lines, which would more than likely be cold-worked by the vibrations and suffer an eventual failure as metal lines have a tendency to become brittle after being flexed enough.  Flexible fluid lines, on the other hand, are capable of sustaining this kind of punishment because of the fact that they are so flexible.  For the amount of pressures you would be seeking, I would presume that a Teflon-line would be the kind of line you would need.

 

Here is a video which, despite being intended for automotive applications, shows the same principles as what I was talking about:

 

 

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Actually, at 248s being high I meant mostly at chamber pressure and the heat produced by combustion for being high for something home made. But in any case, good luck!

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Also, I might suggest you read up on the principles of jet engines.  Rockets work under the exact same principles.

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Hello! Sorry for the long delay, real life has been complicated. I have a short update today, but hey, progress is progress!

As always, start on today's date in the first post of the thread, or, if you're new, start from the beginning of the first post of the thread.

If you have any sort of suggestions, ideas, doubts, or even better, think you've found an error, please, do let me know! Thanks

You rock.

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Hello! It took forever, but finally I got a breather from Real Life Stuff.

As always, start on today's date in the first post of the thread, or, if you're new, start from the beginning of the first post of the thread.

If you have any sort of suggestions, ideas, doubts, or even better, think you've found an error, please, do let me know! Thanks

@K^2 i'd appreciate you checking things over. Your feedback has been real helpful.

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On 6.12.2015 at 4:52 PM, Motokid600 said:

Ha! But.. seriously do you live in a remote area or do you have a bomb range you can try this at? Because I know here in the US you'd be arrested before even getting the chance to fire it. You'd have to wade through a sea of red tape and travel to a very, very remote site.

Is it an actual law? About doing ground tests of liquid fuel rockets and similar stuff. It can hardly qualify as destruktive device. 
Now launching an actual rocket is another issue 

Now in the army we managed to turn an kerosene lamp into an flamethrower by accident, it was an high power type where you pumped air into the fuel tank for over pressure, an spray nozzle would generate droplets who then burned with an mesh a catalyst I think generating more light than an 100 w bulb. 
Well it did not work so we removed the top and mesh, opened it up and activated the ignitor and the flame hit the roof and blossomed everybody was impressed. 

Way worse, as an teen we tried to make an pipe bomb fill with some sort of herbicide and confectioner's sugar, pipe screw on an end cap on both sides one has an hole for the fuse.
Well for being teens we was careful, we knew an remote location out on an field, because of some drainage project they had dug two 3-4 meter deep holes 6-8 meter separated perfect for an test, bomb in one hole, we in the other. 
We waited, the fuse took forever, no bang but an buzzing, the bomb had become an rocket and an pretty smart one, it jumped from its hole down into our hole there it was buzzing around. 
Murphy's laws always win. 

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Well if something goes wrong they can be pretty destructive, but it'd still be classified as an accident because the device was not meant from the get go to explode.

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Hey, finally found a bit of time to update the project. Sorry for the delay but Real Life has to come first. Otherwise i'd starve to death.

As always, start on today's date in the first post of the thread, or, if you're new, start from the beginning of the first post of the thread.

If you have any sort of suggestions, ideas, doubts, or even better, think you've found an error, please, do let me know! Thanks

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So subscribed.

On 12/3/2015 at 7:01 AM, ap0r said:

I've always had a love/hate relationship with maths, i.e, I love the practical science/engineering/bussines applications of it, but it costs me horrors to do anything beyond basic equations.

This sums up my thoughts on math too!  :)

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Took me forever, sorry for the delay, but i've finally cmpleted the chamber and nozzle design. Coming up is cooling system design.

As always, start on today's date in the first post of the thread, or, if you're new, start from the beginning of the first post of the thread.

If you have any sort of suggestions, ideas, doubts, or even better, think you've found an error, please, do let me know! Thanks

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Im not sure if you are, but take note that material strength will change significantly depending on your operating temperature. Im not certain what your anticipated equilibrium temperature of your walls are.

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3 hours ago, A Fuzzy Velociraptor said:

Im not sure if you are, but take note that material strength will change significantly depending on your operating temperature. Im not certain what your anticipated equilibrium temperature of your walls are.

You are absolutely right on that one. Tomorrow I calculate cooling, and depending on the results of that I might recalculate wall thickness.

Thanks.

So obvious... can't believe I would have missed it

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So I finally actually read the whole thing. There are a couple things I noticed.

1) You can actually predict the performance of an idealized one dimensional case for varying O/F ratios. Also the stoichoimetric ratio will the hottest reaction but it may not have the highest exit velocity. For instance hydrolox engines run fuel heavy because the unburnt hydrogen significantly reduces the average molar mass of the products of reaction. A good tool for determining this stuff is NASAcea. You will likely have to follow an iterative process to get the maximum results

2) I notice you vary your units a lot, this can be a significant problem where your numbers can be significantly thrown off. If you are following that first 70pg PDF you found (I forgot the name) some of those equations are empirical equations, and many already have gravitational factors built in and should only be used with English Engineering units and not SI or British Gravitational.

3) How long are you planning on having the engine burn? If the burn is short enough you may be able to use a cheaper material and rely on the thermal mass/thermal inertia for cooling the engine. Otherwise you are significantly complicating your system.

4) Also there are tool available, some of which are free, which can help with that nozzle design, alternatively you could just use a 15 degree conical nozzle which would be significantly easier to machine on your part.

5) Also make sure to figure out how you are addressing your pressurant issue as it will significantly alter the performance and stability of your engine. If you are planning on just using the pressure of the GOx note that pressure will drop along an adiabatic expansion and most fixed injector systems will be very unhappy about that and will suffer from a large drop in combustion efficiency and stability.

Edited by A Fuzzy Velociraptor

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23 hours ago, A Fuzzy Velociraptor said:

So I finally actually read the whole thing. There are a couple things I noticed.

1) You can actually predict the performance of an idealized one dimensional case for varying O/F ratios. Also the stoichoimetric ratio will the hottest reaction but it may not have the highest exit velocity. For instance hydrolox engines run fuel heavy because the unburnt hydrogen significantly reduces the average molar mass of the products of reaction. A good tool for determining this stuff is NASAcea. You will likely have to follow an iterative process to get the maximum results

2) I notice you vary your units a lot, this can be a significant problem where your numbers can be significantly thrown off. If you are following that first 70pg PDF you found (I forgot the name) some of those equations are empirical equations, and many already have gravitational factors built in and should only be used with English Engineering units and not SI or British Gravitational.

3) How long are you planning on having the engine burn? If the burn is short enough you may be able to use a cheaper material and rely on the thermal mass/thermal inertia for cooling the engine. Otherwise you are significantly complicating your system.

4) Also there are tool available, some of which are free, which can help with that nozzle design, alternatively you could just use a 15 degree conical nozzle which would be significantly easier to machine on your part.

5) Also make sure to figure out how you are addressing your pressurant issue as it will significantly alter the performance and stability of your engine. If you are planning on just using the pressure of the GOx note that pressure will drop along an adiabatic expansion and most fixed injector systems will be very unhappy about that and will suffer from a large drop in combustion efficiency and stability.

Hey! Thanks for yout toughts, much appreciated! In response to your points,
1) Yes you can but the math is horrible. About o/f ratios, I mention that " There is an exception to that if running fuel-rich reduces the molecular weight of your exhaust, such as in hydrogen burning engines, but that is honestly beyond the scope of this discussion " so maybe you missed that part :)
But really, I'm not aiming for max performance. I'm aiming for simplicity.

2) All relevant calculations are performed with EE units. I use metric in my head, so I usually convert back and forth, but yes, I have taken the empirical nature of the equations that you mention into account.

3) I'm designing for indefinite run time, with a cooling jacket, but will operate it in 5 second increments, up to a max of 30 seconds when I have done many many test firings. Surely that is overkill, but then again, i'm not aiming for a lightweight engine here.

4) It surely would be easier to design, but I worry about the angle on the throat, where the nozzle and inlet are joined... A sharp corner there seems like it would be counterproductive? This requires more tought.

5) That is already taken into account, I will use pressure regulators to get constant oxidizer and fuel pressures despite variations in tank supply pressure with expansion.

Once again thanks for the feedback, it sure is appreciated! Thanks!

AndThanks Basto to you too :D  

Edited by ap0r

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1 hour ago, ap0r said:

1) Yes you can but the math is horrible. About o/f ratios, I mention that " There is an exception to that if running fuel-rich reduces the molecular weight of your exhaust, such as in hydrogen burning engines, but that is honestly beyond the scope of this discussion " so maybe you missed that part :)
But really, I'm not aiming for max performance. I'm aiming for simplicity.
4) It surely would be easier to design, but I worry about the angle on the throat, where the nozzle and inlet are joined... A sharp corner there seems like it would be counterproductive? This requires more tought.

1) Yes, I expect I did. I didn't intend for you to do the math by hand which I why I dropped you the link to NASAcea which can do that. For one you could do your own system which could be safer and cheaper than GOx Methonol. GOx also requires special fittings which are quite a bit more expensive.

4) A 15 degree conical nozzle doesn't have a sharp corner at the throat, it is still rounded there.

From braeunig:

fig1-04.gif

Edited by A Fuzzy Velociraptor

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23 hours ago, A Fuzzy Velociraptor said:

1) Yes, I expect I did. I didn't intend for you to do the math by hand which I why I dropped you the link to NASAcea which can do that. For one you could do your own system which could be safer and cheaper than GOx Methonol. GOx also requires special fittings which are quite a bit more expensive.

4) A 15 degree conical nozzle doesn't have a sharp corner at the throat, it is still rounded there.

From braeunig:

fig1-04.gif

1) I tought about using compressed air, as oxidizer, but that is not fun imho. All the GOX fittings, pressure regulators, etc, only have to be bougth once, and are then installed in my "test stand" and can be utilized in future designs.
4) I will redesign the nozzle/chamber assembly. Same inner dimensions and wall thickness (pending cooling review), but with this simpler geometry.

Thanks for your toughts and feedback, it really is appreciated.

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