It isn't necessary to delve into the intricacies of thermodynamic theory to
get my point across about it not being so simple to actively cool a flame
bucket. By "Significant" I mean it can get into the 90% within one nozzle
diameter of the exit,so 90% of 4400 psi is a lot. So no matter how you
slice it, the water has to be introduced inside the impinging plume, it
won't simply entrain like I used to believe until I tried it. It wasn't so
easy, I found.
I used to operate a Linde Jet Piercing torch at CSD/UTC in San Jose to
test ablative materials for rocket and ramjet motor development.motors.
The test specimen would be placed in the shock studded supersonic jet and
rapidly ablate away the surface. Silica filled EPDM rubber was a test
standard.
The LJPT burned GOx and kerosene at approx 100 psi chamber pressure and was
water cooled. The water exiting the cooling jacket was discharged into the
cutting area which would easily spall solid rock..They use(d) these torches
in quarries. I think now they use aluminum/oxygen lances to cut rock like
in those bank heist movies.
Fun stuff.
Ken
On Fri, Apr 21, 2023 at 3:37 AM Ben Brockert <wikkit@xxxxxxxxx> wrote:
Though you don't define "significant percentage", I don't think the
math is as simple as you imply by quoting the chamber pressure.
Stagnation pressure increases with the square of mach number, but mach
number (here effective exhaust velocity) doesn't increase very quickly
with chamber pressure. You can get 250s out of a low pressure methane
engine running at a few hundred psi vs. the 327s claimed for Raptor,
but the ratio of the squares of those as exhaust velocities says that
all else being equal the Raptor would have less than twice the
stagnation pressure of a low pressure engine.
I've bored through a reinforced concrete pad with a rocket engine
before, it doesn't take a high pressure engine to do it. Once there's
a hole a fairly small amount of pressure will float out quite large
material, as seen in the huge slabs of material flying around on the
webcast.
On Fri, Apr 21, 2023 at 12:23 PM roxanna Mason
<rocketmaster.ken@xxxxxxxxx> wrote:
inside the flame/plume impingement area because as I mentioned
OK so it's just a plain spike, with a water outlet at the top, dump a
squillion tonnes of water out the top of an 8ish meter high spike (to
fit under the OLM) that has a nice radiused curve into being level with
the ground.
Actually that won't work Jake, the water needs to be injected directly
earlier the stagnation pressure is a significant percentage of thechamber pressure which is ~ 300Bar or 4400psi. Just squirting water outside
one place won't translate to the entire flame impingement area. This is why
water cooled test stand flame buckets have 1000's of orifices throughout
the entire steel plate with water injected at higher pressures than the
stagnation pressure. Of course the farther from the nozzle exit plane the
lower the pressure but SpaceX launch stanch lacks the luxury of vertical
height with the aforementioned high water table. If you look at the Saturn
5 flame diverter/splitter it sits free standing on the ground/concrete
flame trench. I don't know what the distance or F-1 nozzle diameters it was
to the flame diverter but it wasn't too great from looking at old photos.
SpaceX sure looks like they're locked in to whatever height they havewith that 'Chop Stick' grabber being a height limiter without major surgury.
I bet they find a quick fix though knowing they're past performance.dmarc-noreply@xxxxxxxxxxxxx> wrote:
Time will tell.
Ken
On Thu, Apr 20, 2023 at 10:25 PM Jake Anderson <
separate.
On 21/04/2023 8:47 am, Keith and Mary Stormo wrote:
There is very little distance from the surface to the water table.I want to see a "reverse aerospike" as the diverter.
That makes a trench unlikely. It is likely that they will have some
type of above ground diverter system. They seem to have some parts and
components for a diverter on site to install after this flight.
Keith
At 02:00 PM 4/20/2023, you wrote:
I continue to be baffled- Why not a flame trench or two?
The amount of energy- thermal, radiative, acoustical and inertial-
that is forced to bounce back and forth between the 33 motor array
must be staggering.
Even the latest refractory concrete, it seems, cannot survive. How
can the motors?
I think that is a lot of undue stress applied to those raptor IIs
that are already trying as hard as they can to melt and rip
themselves apart.
I guess there must be a reason, but I can't figure it out.
It's also hard to imagine that NASA at Kennedy in florida is going to
tolerate all the flying junk that seems to result from such powerful
launches, even if the ships them selves are super-reliable.
OK so it's just a plain spike, with a water outlet at the top, dump a
squillion tonnes of water out the top of an 8ish meter high spike (to
fit under the OLM) that has a nice radiused curve into being level with
the ground.
Wouldn't catch all the engine plumes before they hit but it'd at least
let you give them an idea about which way to be heading and hopefully
allow the water layer to become film cooling for the pad. If you can put
the tip of the spike up far enough that the plumes from the centre
engines don't hit it at ignition even better.
Probably also replace the concrete pad directly under the ring with a
nice bit of full thickness welded 6" plate steel. You might erode it
some but if there's no edges you won't get under it to do that lifting
and excavation that happened.
For the surrounding concrete make it like a spillway, they have
interlocking joints that are angled to prevent high speed water getting
under an edge. Seals to prevent water pressure pushing into a joint and
vents so that if water does get behind a block it's able to drain before
building pressure.
The concrete just outside the ring that wasn't *lifted* seemed to
survive fairly intact so it doesn't look like they are actually far from
having a working solution, just with this much energy even a small
problem (concrete cracking and letting pressure build behind it) leads
to dramatic outcomes.
That said, I'd bet a coke that at least some of the problems they had
were due to acoustic bashing on engine components. That spin manoeuvrer
is going to be really sensitive to residual thrust. One valve not
closing allowing methane to vent through an engine would probably
explain the ongoing burn after the MECO call and the inability to