ROTON type engines and liquid monopropellants

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

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.

Pat

On Sep 7, 3:53 am, Pat Flannery 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.

Earl Colby Pottinger

Earl_Colby_Pottinger wrote:

On Sep 7, 3:53 am, Pat Flannery 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.

You still run into the same problem - a ROTON type engine has never
been built.

D.
--
Touch-twice life. Eat. Drink. Laugh.

http://derekl1963.livejournal.com/

-Resolved: To be more temperate in my postings.
Oct 5th, 2004 JDL

On Sep 14, 1:32 pm, (Derek Lyons) wrote:

You still run into the same problem - a ROTON type engine has never
been built.

And how is this a good reason to not try and make a smaller mono-
propellant version now?

After-all http://www.peroxidepropulsion.com/ne...est-of-our-rot
or-tip-rocket-system
was able to use the same principles to drive thier autogyro.

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.

Earl Colby Pottinger

Earl_Colby_Pottinger wrote:


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 he
http://www.hq.nasa.gov/pao/History/c...d/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/52...scription.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. ;-)


Pat

On Sep 5, 6:38 pm, 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?

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).

Ralph

---
Dream of Space? Make it Real.
www.open-aerospace.org

On Oct 9, 11:14 pm, void64 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.

Earl Colby Pottinger

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

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:

http://www.arocketry.net/

A number of former Rotary Rocket employees post there.

Jim Davis