We didn't over 1000 firings on one film cooled engine. Once you have
start/stop sequences working and the engine is demonstrated to run fine at
thermal steady state, the only limit to life is the durability of the
fabrication methods (i.e. do welds crack or any other fatigue paths from
thermal cycling) or you run it out of fuel and don't shut it off fast
enough.
I still prefer regen for performance reasons and more benign failure modes,
but it's certainly faster to build a film cooled engine if you're early in
a vehicle development program or are aiming for cheap one-off units. You
can still hit 90% c* efficiency, and I've seen worse than that on pure
regen engines with excessively low L* because they were concerned about
cooling area.
Ben
On Friday, February 23, 2018, Henry Vanderbilt <hvanderbilt@xxxxxxxxxxxxxx>
wrote:
Armadillo did a lot of work with film cooling, and seemed to have it
working pretty well for them in some long-life engines. Hard to say how
much technical detail is available at this point, though.
Henry V
On 2/23/2018 4:43 PM, Brian Feeney wrote:
It has been discussed previously how XCOR (Doug Jones et al)
achieved long engine life particularly with the Saddle Jacket (SJ) engine
design -- hundreds of cycles on a given engine with lots of apparent life
left after engine tear down.
How does a Film Cooled (FC) engine compare to the SJ design in terms of
longevity. Clearly the SJ has a higher Isp all other factors the same. The
FC engine is somewhat simpler in design and fabrication and does not appear
to have the degree of inner surface to outer surface thermal stress that
you get with a traditional regeneratively cooled non SJ engine design.
Is the FC engine chamber and nozzle essentially undergoing the same /
similar lower thermal stress on the inner chamber as the SJ engine and
therefore would have a longlife?
In this case I am choosing to rate longevity as a higher priority over
Isp performance for suborbital flights as opposed to more recently
discussed orbital efforts.
The SJ is somewhat more complex with added failure and maintenance modes
compared to an FC design. Maybe I'm overstating it in the context of the
overall complexity of the full rocket system?? That said, it's never a bad
idea to reduce part count, complexity and failure modes, especially in a
complex system if one can afford the performance drop off.
I appreciate all comments... Thank you.
Cheers
Brian Feeney