I was just thinking about monopropellants. Most have low ISPs compare to bi-propelleants but can be very dense. ie Peroxide/Alcohol mixes for example.
Since ROTON type engines are self-pressuring, one can build a system with very light weight tanks and high expansion ratio engines. Could the mass ratios of such a design lead to a reasonable TSTO rocket?
Earl_Colby_Pottinger wrote: > I was just thinking about monopropellants. Most have low ISPs compare > to bi-propelleants but can be very dense. ie Peroxide/Alcohol mixes > for example.
> Since ROTON type engines are self-pressuring, one can build a system > with very light weight tanks and high expansion ratio engines. Could > the mass ratios of such a design lead to a reasonable TSTO rocket?
Note that the ROTON engine never got built, so it's difficult to know how practical the concept would have proved in reality. Long time back the US played with a somewhat similar engine to power the XP-79 rocket fighter (in this case the spinning combustion chambers would shaft-drive the engine's fuel pump) and that never was made to work correctly, so it was canceled. Another problem with the ROTON engine could be how burning would behave in the combustion chambers under the centrifugal force of their spinning at high RPM.
On Sep 7, 3:53 am, Pat Flannery <flan...@daktel.com> wrote:
> Note that the ROTON engine never got built, so it's difficult to know > how practical the concept would have proved in reality.
The original ROTON design was a very large design that had to feed two fluids at a time. That is tricky as you can'tt afford one to leak into the other. Instead I am thinking of building a single feed engine that would only be 50 cm in radius or probably less. Seems more do-able.
> Long time back the US played with a somewhat similar engine to power the > XP-79 rocket fighter (in this case the spinning combustion chambers > would shaft-drive the engine's fuel pump) and that never was made to > work correctly, so it was canceled.
Thanks for the pointer.
> Another problem with the ROTON engine could be how burning would behave > in the combustion chambers under the centrifugal force of their spinning > at high RPM.
Did not think of that, but the burning itself may not be the problem but rather the injector design could prove to be a real problem.
>> Note that the ROTON engine never got built, so it's difficult to know >> how practical the concept would have proved in reality.
>The original ROTON design was a very large design that had to feed two >fluids at a time. That is tricky as you can'tt afford one to leak >into the other. Instead I am thinking of building a single feed >engine that would only be 50 cm in radius or probably less. Seems >more do-able.
You still run into the same problem - a ROTON type engine has never been built.
> > I posted here to see if anyone had already done the math and could > tell me how well it could or could not work in theory, that's all.
The problem is that monopropellants tend to have low specific impulses, so although you will be able to make the engine simpler than one using dual propellants, it won't be that good of a engine as far as getting something into orbit via its use goes. If you go over here: http://www.hq.nasa.gov/pao/History/conghand/propelnt.htm ....there is a list of various propellant combinations and their specific impulses on page 44 (note that the list doesn't include LOX/LH2). Nitromethane is the best at 190-230. For comparison to monopropellants, LOX/LH2 has a isp of around 400: http://www.astronautix.com/props/loxlh2.htm There is another monopropellant that's not on that list, and that's Otto fuel II as used in Navy torpedoes: http://en.wikipedia.org/wiki/Otto_fuel_II You can get a isp of near 260 with that: http://www.patentstorm.us/patents/5256220/description.html Unfortunately, the exhaust is going to contain hydrogen cyanide gas, so it's not a friendly thing in the area near the launch site, although the gas is lighter than air and will float off, as the French found out in WW I when they tried to use it to attack the Germans. ;-)
<earlcolby.pottin...@sympatico.ca> wrote: > I was just thinking about monopropellants. Most have low ISPs compare > to bi-propelleants but can be very dense. ie Peroxide/Alcohol mixes > for example.
> Since ROTON type engines are self-pressuring, one can build a system > with very light weight tanks and high expansion ratio engines. Could > the mass ratios of such a design lead to a reasonable TSTO rocket?
> Earl Colby Pottinger
There are many interesting monoprops, but the ISP usually doesn't compare to bi-pop solutions. However, one interesting development in the area of self-pressurizing monoprops recently has been by Firestar engineering. They have come up with a monoprop that can leverage the Vapor-Pressurization (or VaPak) self-pressurization method, which makes for a great (low parts count, zero-g restart, storeable, etc.) solution. They have a working engine (or thruster I should say), and some photos on their website (www.firestar-engineering.com).
I did a lot of work on VaPak when I was at AirLaunch (another Roton- inventor Gary Hudson company). It is not without its pitfalls, but it does have great potential once the kinks are worked out. The Roton engine was clever, but more complex than the VaPak approach, with the added problem of (lack of) stability. As thrust increases, so does spin rate, so does feed pressure to the engine, so does thrust, etc. - some control is required to keep things from running away. VaPak is more stable than that, and has a lower parts count. The physics are complex, but we had just one moving part on our LOX/C3H8 engine (main valve).
On Oct 9, 11:14 pm, void64 <ra...@open-aerospace.org> wrote:
> There are many interesting monoprops, but the ISP usually doesn't > compare to bi-pop solutions. However, one interesting development in > the area of self-pressurizing monoprops recently has been by Firestar > engineering. They have come up with a monoprop that can leverage the > Vapor-Pressurization (or VaPak) self-pressurization method, which > makes for a great (low parts count, zero-g restart, storeable, etc.) > solution. They have a working engine (or thruster I should say), and > some photos on their website (www.firestar-engineering.com).
First, going to the URL you provided the system does not look like a 'true' mono-propellant system. Instead it looks like they used the nitrious-oxide to dissolve the fuel into solution before burning it in the engine. This makes it closer to a hyrid-motor in design. Not that I saying it is a bad design, mind you.
Second, the above makes this a mixed mono-propellant, which is the same as I am looking at to increase the ISP, while I am still trying to nail down that are the ***SAFE*** percentage of alcohol to add to hydrogen peroxide without turning it into an explosive I do remember that ISP above 200secs are possible.
The engine design seems odd to me, It feeds the opposite way that I do in my design. I feed the cold peroxide down first on the outer shell so that it can maintain the full material strenght, then start reacting it on the second chamber using a silver mesh with the completed burning (hopefully) happening in the center chamber which will have a set of flame holders to help combustion.
> I did a lot of work on VaPak when I was at AirLaunch (another Roton- > inventor Gary Hudson company). It is not without its pitfalls, but it > does have great potential once the kinks are worked out. The Roton > engine was clever, but more complex than the VaPak approach, with the > added problem of (lack of) stability. As thrust increases, so does > spin rate, so does feed pressure to the engine, so does thrust, etc. - > some control is required to keep things from running away. VaPak is > more stable than that, and has a lower parts count. The physics are > complex, but we had just one moving part on our LOX/C3H8 engine (main > valve).
I don't get where you think a ROTON design will spin up out of control?
Once the canted motors start the system spinning, the portion of the thrust vector that spins the rotor has the energy that it adds into the rotor system constantly also being taken out to accelerate the fuel going to the motors at the tips. This *always* puts a upper limit how fast the rotor can spin once you know the working ISP of the motors and the angle that the motors are canted at.
I would just like to point out that I am not just asking about ROTON type system for no reason. I am planning to build a test model over the next month or two.
I just finished working/repairs on my cabin and closed it up for the winter. My girlfriend dumped me, and the money that I had set for going on two diffirent cruises was suddenly freed up, so now I have both free time and spare cash (that rarely happens, one or the other but rarely both) that will let me start working on this question.
I am already setting up a system to double vaccum the peroxide in my basement, I should have the silver mesh ordered by the weekend and hopefully should start material work on the rocket engine in the first or second week of November.
If I can get something going soon I will post the pictures in my Flicker account.
PS. All present experiments are to be done with peroxide only! Until I can nail down all the details; mixing alcohol with hydrogen peroxide is too dangerous to be done outside an explosive lab.
Earl_Colby_Pottinger wrote: > I would just like to point out that I am not just asking about > ROTON type system for no reason. I am planning to build a test > model over the next month or two.
Earl,
You might want to ask on the arocketry mailing list:
On Oct 23, 4:12 am, Jim Davis <jimdav...@earthlink.net> wrote:
> Earl_Colby_Pottinger wrote: > > I would just like to point out that I am not just asking about > > ROTON type system for no reason. I am planning to build a test > > model over the next month or two.
> Earl,
> You might want to ask on the arocketry mailing list:
> A number of former Rotary Rocket employees post there.
> Jim Davis
The person you want is Bevin McKinney, he designed the original Roton engine. These days he works HMX together with Gary Hudson (designer of the Roton vehicle). Their website is at http://www.hmx.com/. Bevin's email is zerog(at)centurytel(dot)net He's a very nice guy and won't mind at all if you contact him :).
On Oct 24, 8:11 am, RalphE <ra...@open-aerospace.org> wrote:
> The person you want is Bevin McKinney, he designed the original Roton > engine. These days he works HMX together with Gary Hudson (designer of > the Roton vehicle). Their website is athttp://www.hmx.com/. Bevin's > email is zerog(at)centurytel(dot)net He's a very nice guy and won't > mind at all if you contact him :).
Thank you for the email address, I am on a trip to Florida next weekend so it probably will be a while before I can email him.
At the present moment I am having problems finding a supplier of silver mesh (the company I dealt with before no longer handles it), and I am looking into other designs that can use silver wire available for local jewerly supply companies.
Presently, based on some research I have done it looks like I can make 90% H2O2 breakdown using only the heat generated by it's own decompostion to keep the engine running, but the time this takes requires a total mean path of over 14 inches. (URL to PDF to supply later). This I intend to do by making the entire rotor arms into a regenative motor designs, meaning the rotor needs to 18 inches in diameter..
I will post more after I find out how hard it is to get the silver that I require.
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