Kim Keller wrote:
wrote in message
ups.com...
But the central CBC on the heavy throttles back much later than
than
the CBC on the single. So you get into the regime where you have
both
a high flow rate and not much liquid in the tank. All the heavy
CBCs
run this way, but the single does not (when the tank is low, it's
running at low flow rates).

The CBC core throttles back later in a mission than a Medium because
it
spends a lot of first stage throttled back to minimum power level
(all the
way from max-q to strap-on sep - a bit over 3 minutes). It has as
much fuel
on hand approaching MECO in Heavy config as it does in Medium; flow
should
be the same.

It has the same amount of fuel, but not the same rate. The single
throttles back to 60% flow when 10% fuel remains, so as not to exceed
5Gs. The heavy keeps full flow till only 2.5% fuel remains, to
minimize gravity losses (the heavier payload ensures it won't exceed
5Gs).

I'm wondering if the Heavy's lower g-levels (4g) are allowing slosh
in the
LO2 tank. Maybe there's enough acceleration in the Medium (5g) to
prevent
it. I dunno, I'm not a rocket scientist, and I don't play one
anywhere.

Even without slosh, in the 10%-2.5% fuel left, there are 3 factors
promoting cavitation. First, less liquid height. Second, less
acceleration (less pressure per height). Third, higher flow rates.
After 2.5% is reached, only the lower acceleration applies.

Also, it's conceivable the roll to wings-level might have an effect.
This puts the oxygen lines on the top, where they will have slightly
less pressure, and the effect is bigger at 4G than 5Gs. But I don't
know if the single does this too.

Lou Scheffer