Ken, can I ask what are the dots seen in the left image in between the
walls, the cutaway of the thrust chamber? They stop where the convergent
throat starts. Are those metal grooves that corkscrew up the engine and we
see them as dots because it's a cutaway?
On Tue, Aug 11, 2020 at 6:09 PM ken mason <laserpro1234@xxxxxxxxx> wrote:
Our group as the RRI back in the 60's built a 400LbF LOx/Ethanol rocket
caller SPARK 1, with the CC/nozzle assembly free floating from the
cylindrical outer wall with only an O-ring sealing the nozzle exit and
outer jacket..The inner wall was attached at the injector end, same point
as the outer wall. This allowed the inner wall to move longitudinally as it
cycled between hot/cold. Other designs like the LR-11, put an expansion
joint built into the outer wall instead of an O-ring. See attached pics.
On Tue, Aug 11, 2020 at 2:32 PM Brian Feeney <alaiadesign@xxxxxxxxx>
wrote:
I've always liked the XCOR (others) Saddle Jacket configuration. As Doug
has mentioned many times through the years, and in at least one paper, it
relieves a lot of the thermally induced stress between the inner and outer
chamber walls.
This question is directed to Doug, but please anyone else chime in. What
do you think the Chamber, injector life may reasonably be for the Saddle
Jacket design in terms of 1 minute or so firing cycles?
Is it possible to see 1000 plus cycles (even 3000 to 5000 cycles) between
overhauls.
While jet engine combustion does not reach the same chamber temperatures,
the air cooling of the walls vs liquid cooling means the wall temperatures
are similar.
It seems to me that a very long life rocket engine that looks to emulate
Aviation level reliability with very low maintenance (which is what I'm
interested in) mainly comes down to better managing the thermally induced
differential stresses between the inner and outer chamber as well as the
injector head assembly.
I believe that XCOR was well on its way to achieving this objective
especially with what I'll call a full free floating inner chamber that has
no hard connection at the injector end and or employs stress relieving
spring style joints.
To Henry's point, I think the independent use of high water cooling
rates, even for a Saddle Jacket, during the development phase is a great
idea.
Many thanks in advance for taking the time to discuss this!
Cheers
Brian Feeney
On Tue, Aug 11, 2020, 4:38 PM Tyler Adkison, <tyler.adkison@xxxxxxxxx>
wrote:
This thread has been fascinating to me as I am on a college team who is
working on a liquid engine project.
I have a few questions for a few specific members:
Ken, do you have any more details on that excellent little ablative
engine you made? Stuff like fuel ratios, pressure, glass orientation, etc?
Did it have some sort of throat insert? I never even considered the
possibility of making one using that particular combination, always
assuming I'd need phenolic to get a usable burn time.
Doug, I think you are onto something with what you said. The LR-101
obviously does work, but I think it might not be the best approach for a
modern amateur who wants to go the regenerative route. However, I have a
few questions about what you said. How important do you think it is to use
C182 over the more common (thus considerably easier to acquire) C110? I
know it has inferior mechanical properties, but it still should be
theoretically good enough for our engines. Does C182 it have any other less
obvious advantages that make it an essential alloy?
Micro-coax looks promising, but I always have trouble pushing it because
my teammates say that it is likely much more work than just doing an
impinging injector.
We are also planning on using CSJ construction, but was wondering if you
have channels cut into your chamber and if so, how did you machine them.
There is a healthy debate over using a 4-axis cnc machine with a standard
endmill or a modified 3-axis machine with a slitting saw. If you managed to
get away without needing channels, that would really simplify
manufacturing.
Finally, did you try to use a bell-nozzle profile or accept the easier
to fabricate conical engine?
Thank you for all of your time and advice.
On Tue, Aug 11, 2020 at 1:15 PM Henry Spencer <hspencer@xxxxxxxxxxxxx>
wrote:
On Mon, 10 Aug 2020, Jonathan Adams wrote:
So my question now is: for a small regeneratively cooled engine (likestresses
the LR-101, mentioned already), with consideration to all the
it must endure, compressive and otherwise, what are some of the more
appropriate options for manufacturing (particularly on a budget)? ...
The most appropriate option is something *you* can afford to do
repeatedly, because you're almost certainly going to need multiple
design
iterations to make it work, and you'll lose chambers while finding out
what changes you need. You need to design with this in mind; if making
(say) ten chambers sounds impossibly expensive, you need to redesign
for
lower cost. Think cheap and easy, not awesome high-tech beautiful.
Is CNC milling/turning a feasible option for this kind of work, or doprocess
chamber geometries complicate this, making another manufacturing
more appropriate?
Others may differ, but my take is that if you even need CNC, you're
thinking too fancy and making overly-optimistic assumptions about how
many
chambers you'll need to make. (Exception: if you have, or plan to
acquire, *your own* CNC machine tools, that's a bit different.)
Preferably you should be able to make it, yourself, with a manual lathe
and mill.
As I said before: people made successful rocket engines before CNC.
That's the example you want to follow, not cost-is-no-object
professionals
on government contracts.
Henry
