By Jim Bowery
Copyright 2002
Why should anyone care about ultracentrifugal engine technology?
If it fulfills its potential, it will open up space as the primary habitat
for technological civilization. For a more extensive explanation, see Ultracentrifugal
Engine Import.
Did the engine prototype work?
No. The initial friction of the silicon nitride bearings was larger than anticipated
and the test stand did not have a starter assembly that could externally rotate
the engine to get it started.
Why haven't you tested more prototypes with a starter assembly?
The patent application process has dominated our available resources.
What is the status of your patent?
Patent #6,212,876 has been issued by the US Patent office. Patent filings have been made in all Patent Cooperation Treaty countries plus
Taiwan, however lack of funding has resulted in expiration of most of the patent filings.
Why hasn't anyone thought of this before?
The general idea of a rotating combustion chamber that could self-pressurize
via cooling channels and enhance combustion was thought up by Robert Goddard
in the 1930s, unsuccessfully tested at Jet Propulsion Laboratory in during WW
II in their Centrojet project, and extensively patented
by Goddard's estate posthumously.
So what is new here?
Primarily the recognition that ultracentrifugal forces are required to realize
the potential of Goddard's idea, and the innovations necessary to support such
an ultracentrifugal structure. Secondarily, the availability of better bearings
and seals.
Why isn't NASA doing this?
Working on "old" technologies that haven't been proven, but which
could visibly fail in a short period of time, is bad politics.
Why aren't private concerns doing this?
We are. The reason there isn't more private backing for this development work
is that the market for launch services appears unpromising to many investors
subsequent to Iridium's failure in the marketplace, and even more so subsequent to the tech downturn of 2001.
How much does a small engine cost?
The first prototypes cost under $1000 per engine to fabricate using the commercial
services of a professional machine shop, and this was largely setup cost. The
materials were less than $200 per engine, including the commercially supplied
silicon nitride bearings and cryogenic seal.
What is the thrust to weight ratio?
Around 100 to 1.
Why are the cooling channels so far apart? Won't the engine melt down?
When the thermodynamic equations told us how thick we could make the aluminum,
we found it hard to believe. Aluminum has a very high heat conductivity and
was used by Robert Goddard in his early engines. Even so, to do a sanity check
we ran an acetylene cutting torch at full throttle against a tube of aluminum
whose walls were nearly an inch thick. By running a minimal stream of water
through the tube, heat transport was fast enough that there was no effect on
the aluminum. The large distance between channels remained a concern of
mine and I suggested more channels. This was rejected due
to the fact that it was already problematic to get the injector holes small enough
in such a small engine. I had Roger partially fabricate a larger model with a continuous
disk rather than discreet impeller channels but this prototype was never completed and
thus not tested. The idea there was to let the turbulence from heating accellerate
the liquid in the disk and then possibly have some sort of structure at the injector inlet
to capture additional ram pressure (possibly even allowing it to cavitate for some distance behind the structure). If this worked,
this could be a simpler structure to fabricate and provide more effective cooling (with
correspondingly stronger material) as well as heading off certain hypothetical
instabilities that can arise if the pressurization on one side of the wheel starts to
exceed the pressurization of the other side.
Won't any imbalance in the wheel assembly result in the whole thing failing?
Yes. Ultracentrifugal wheels must be carefully balanced. This is within the
capability of high performance automotive machine shops.
Toroidal chambers have historically had problems. How do you addess those?
By making the major diameter to minor diameter ratio smaller, decreasing
the ratio of chamber volume to throat area and rotating the engine fast so that
Coriolis effects and centrifugal separation of fluid fractions makes "race
track" instabilities fall apart before they can complete once round the
inside of the torus.
Send your questions to Jim Bowery.