Finally finished the machining of the rocket motor! I don't
have a digital camera yet so there's no pictures as
of now. But, the parts look really cool! Now, I need to start
building up test fixtures, etc. Started the design of the test
fixture. The propellant tanks will be pressurized from a helium tank, controlled by
an electric valve. The propellant tank valves will be ball valves controlled
by a pair of air actuators which in turn are controlled by an electric valve.
The propellant tanks will be 4 inch diameter x 0.25 wall 6061 aluminum tubing
welded to a pair of aluminum end plates.
Finished drawings for the latest injector body. Since
C1018 steel is totally unsuitable for LOX service,
I'll be using 304 stainless steel for the injector
assembly. I'd still like to use C1018 steel for the combustion chamber
as it is somewhat easier to machine than the stainless steel.
I got some samples of Grafoil (flexible
graphite) that I'll use to make a gasket between the combustion chamber and
injector. This stuff is really cool. It has a sublimation point
of 6000 deg. F (it never melts). The best part is it cuts just like
I think I finally have all the shop supplies I need to start fabrication
so stay tuned for more progress reports.
Coming up: strength-of-materials calculations for the chamber (fasteners,
wall thickness, etc.), ideas for the regeneratively cooled
I came up with a design for the injector assembly that doesn't
have any joints or seams for the LOX path. The fuel manifold has an
annular ring that feeds the injector holes.
Here are the specs I'm looking at for the uncooled engine:
Liquid Oxygen (LOX)
Mixture ratio: 1.8 (2.24 is ideal
but 1.8 reduces the combustion temp.)
Chamber pressure: 200 psia
Chamber diameter: 2.24 inches
Chamber length: 4.0 inches
Nozzle throat dia.: 0.71 inches
Nozzle exit dia.: 1.23 inches
Injector pairs: 4
Fuel injection dia.: 0.045 inches
Oxidizer inj. dia.: 0.051 inches
Chamber temperature: 5400 Deg R (4940 Deg F)
Specific Impulse: 225 sec
The combustion chamber will be be machined from a solid 3 inch diameter,
C1018 steel bar. I'd love to figure out a better way to fabricate this
and still keep good tolerances.
The propellant tanks will be pressurized by Helium gas.
This test chamber is considered "uncooled", i.e. non-regenerative but to
increase run times, it will be cooled by a few streams of water. I'm
hoping to get at least 5-10 seconds of run time out of it before it melts. The next
version will have internal cooling passages where the fuel will circulate
to keep the chamber and nozzle walls at a reasonable temperature. The
purpose of building and testing the uncooled version first is to get some
of the basic issues out of the way such as:
Ignition and starting
Combustion stability (may require injector changes)
LOX handling, transportation
Data/video system setup and operation
Test stand checkout
High-pressure Helium system checkout