Easy workaround for Delta-IW heavy problem?

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.

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.

-Kim-

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.

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.

-Kim-

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

In article ,
Kim Keller wrote:
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...

Higher acceleration doesn't particularly tend, in itself, to suppress
slosh. But it does change the slosh frequencies, and that can matter.
--
"Think outside the box -- the box isn't our friend." | Henry Spencer
-- George Herbert |

In article .com,
wrote:
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...

Not unless there's an attempt being made to exploit aerodynamic lift,
which is unlikely. The rocket is in free fall except for its engine
thrust, so the roll angle doesn't change the pressure in the oxygen lines.
--
"Think outside the box -- the box isn't our friend." | Henry Spencer
-- George Herbert |

Henry Spencer wrote:
In article .com,
wrote:
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...

Not unless there's an attempt being made to exploit aerodynamic lift,
which is unlikely. The rocket is in free fall except for its engine
thrust, so the roll angle doesn't change the pressure in the oxygen
lines.

That makes perfect sense, except Av Week stated:

"Roll maneuver. At 2 min. 33 sec., the vehicle began a 50-sec. "roll to
wings level" maneuver, which if viewed as an airplane, put the liquid
strap-ons parallel to the flight path angle. This was done to place the
large oxygen feed lines on the exterior of the vehicle out of the
high-velocity airflow."

So if one side of the vehicle is in the aerodynamic shadow, and the
roll affects this, then it seems to me it must be flying at some
non-zero angle of attack. This is also indicated by the fact that the
roll "puts the strap-ons parallel to the flight path angle". (If the
flight path angle was identical to the vehicle angle, roll would have
no effect). This means there must be aerodynamic forces, and some
pressure gradient across the rocket. This is probably not a very big
effect since the deviation from the velocity vector could only be a few
degrees at most, and the rocket is not very wide, but every little bit
helps (or hurts).

Lou Scheffer

In article .com,
wrote:
Not unless there's an attempt being made to exploit aerodynamic lift,
which is unlikely. The rocket is in free fall except for its engine
thrust...

...if one side of the vehicle is in the aerodynamic shadow, and the
roll affects this, then it seems to me it must be flying at some
non-zero angle of attack...

Hmm, yes, does sound like it.
--
"Think outside the box -- the box isn't our friend." | Henry Spencer
-- George Herbert |