View Single Post
  #8  
Old October 20th 09, 01:02 AM posted to sci.space.tech
Earl_Colby_Pottinger
external usenet poster
 
Posts: 7
Default ROTON type engines and liquid monopropellants

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