F-1 Exhaust on Saturn V

It probably won't you folks long to come back with the explanation,
but my google searches have come up with nothing . . .

What is the explanation for the dark band in the exhaust of the five
F-I engines of the Saturn-V? It almost seems to look like a band of
dark static smoke which makes no sense to me. It appears to be opaque
and dark where you might expect the exhaust to be the brightest. I
don't remember ever seeing this on the exhaust of any other engine.

Thanks in advance for any (reasonable) explanation.

John Pelchat

"John Pelchat" wrote in message
om...
|
| What is the explanation for the dark band in the exhaust
| of the five F-I engines of the Saturn-V?

That's the preburner (or gas generator, if you prefer) exhaust. It's being
used for film-cooling the nozzle.

The gas generator is what powers the pumps and other mechanical systems of
the engine. A portion of the fuel and oxidizer is diverted to a small
burner where it is ignited and used to drive a turbine. This turbine is
geared to the fuel pumps, etc. This gas generator is run significantly
fuel-rich in order to keep the combustion temperature down (at a cost, of
course, of suboptimal combustion). As you can guess, if you burn kerosene
without enough oxygen, you get a very sooty combustion product. And, of
course, a cooler gas. If memory serves, it's around 700 F.

So after it has driven the turbine, what to do with it? In other engines
it's simply dumped overboard from an auxiliary exhaust port. It's
relatively non-propulsive.

In the F-1 engine, however, it was injected into the nozzle as a form of
film cooling. Film cooling is where you arrange for a layer of cooler gas
to form between the hot principal combustion products and the inner surface
of the nozzle. This reduces the heat loading on the nozzle by making a sort
of boundary layer. The preburner exhaust doesn't seem cool at 700 F, but
compared to the primary gas, it's quite cool enough.

The flow of this cooler (and less incandescent) boundary layer remains
annular for several feet after it leaves the nozzle until turbulence causes
it to mix with the hot inner core of the plume.

--
|
The universe is not required to conform | Jay Windley
to the expectations of the ignorant. | webmaster @ clavius.org

"Jay Windley" wrote in message ...

snipped to save bandwidth

So after it has driven the turbine, what to do with it? In other engines
it's simply dumped overboard from an auxiliary exhaust port. It's
relatively non-propulsive.

Thanks for a great reply, one follow-one: Part of your reply spoke of
dumping exhaust overboard. In photos of some launch vehicles, you see
a rather non-propulsive flame to one side of the engine exhaust,
especially the older Atlas vehicles . . . is that the same exhaust?

Thanks

John Pelchat

In article ,
John Pelchat wrote:
Thanks for a great reply, one follow-one: Part of your reply spoke of
dumping exhaust overboard. In photos of some launch vehicles, you see
a rather non-propulsive flame to one side of the engine exhaust,
especially the older Atlas vehicles . . . is that the same exhaust?

No, the side flames on the old Atlases (there are two, 180deg apart) are
its vernier engines, used for roll control after booster-engine jettison,
and for final velocity trim after sustainer-engine cutoff. They fired
continuously for the same reason that Atlas used its 1.5-stage trick,
jettisoning two booster engines midway up: because it was designed at a
time when igniting rocket engines at high altitude was somewhat of an
unknown, so having all engines running before takeoff was a design goal.

The vernier engines were always less fuel-efficient than the main engines,
and as part of the design cleanup that produced the commercial Atlas II,
they were deleted. Since the modern Atlases always fly with an upper
stage, there is no need for the Atlas proper to do velocity trim, and roll
control after booster-engine jettison could be done by a small thruster
package on the interstage ring. (Even that became superfluous when
re-engining produced Atlas III, because now it has two engines(*) and no
jettison events, and can do its own roll control throughout.)

(* The RD-108 is best considered a two-engine cluster. Counting engines
by chambers rather than by pump sets introduces fewer contradictions.)
--
MOST launched 30 June; first light, 29 July; 5arcsec | Henry Spencer
pointing, 10 Sept; first science, early Oct; all well. |

John Pelchat wrote:

Thanks for a great reply, one follow-one: Part of your reply spoke of
dumping exhaust overboard. In photos of some launch vehicles, you see
a rather non-propulsive flame to one side of the engine exhaust,
especially the older Atlas vehicles . . . is that the same exhaust?




Yes, that is indeed the turbopump exhaust. Saturn I's could really shoot out some
serious turbopump exhaust also.

Pat

Henry Spencer wrote:

In article ,
John Pelchat wrote:


Thanks for a great reply, one follow-one: Part of your reply spoke of
dumping exhaust overboard. In photos of some launch vehicles, you see
a rather non-propulsive flame to one side of the engine exhaust,
especially the older Atlas vehicles . . . is that the same exhaust?



No, the side flames on the old Atlases (there are two, 180deg apart) are
its vernier engines, used for roll control after booster-engine jettison,
and for final velocity trim after sustainer-engine cutoff.


I think he was referring to the big flame from the turbopump exhaust, it was very noticeable on Atlas; speaking of which, was it Jupiter that swiveled the turbopump exhaust pipe for roll control? I know some launch vehicle did this.

Pat

(Henry Spencer) wrote in message ...
In article ,
John Pelchat wrote:
Thanks for a great reply, one follow-one: Part of your reply spoke of
dumping exhaust overboard. In photos of some launch vehicles, you see
a rather non-propulsive flame to one side of the engine exhaust,
especially the older Atlas vehicles . . . is that the same exhaust?

No, the side flames on the old Atlases (there are two, 180deg apart) are
its vernier engines, used for roll control after booster-engine jettison,
and for final velocity trim after sustainer-engine cutoff. They fired
continuously for the same reason that Atlas used its 1.5-stage trick,
jettisoning two booster engines midway up: because it was designed at a
time when igniting rocket engines at high altitude was somewhat of an
unknown, so having all engines running before takeoff was a design goal.

The vernier engines were always less fuel-efficient than the main engines,
and as part of the design cleanup that produced the commercial Atlas II,
they were deleted. Since the modern Atlases always fly with an upper
stage, there is no need for the Atlas proper to do velocity trim, and roll
control after booster-engine jettison could be done by a small thruster
package on the interstage ring. (Even that became superfluous when
re-engining produced Atlas III, because now it has two engines(*) and no
jettison events, and can do its own roll control throughout.)

(* The RD-108 is best considered a two-engine cluster. Counting engines
by chambers rather than by pump sets introduces fewer contradictions.)

Sorry, I was not as clear as I meant to be. I was not talking about
the two verniers on the lower side of the vehicle, but rather the
flame from the base but not the nozzle. However, I did wonder about
the lack of verniers in later versions of the Atlas. Thank you.

John Pelchat wrote:


Sorry, I was not as clear as I meant to be. I was not talking about
the two verniers on the lower side of the vehicle, but rather the
flame from the base but not the nozzle. However, I did wonder about
the lack of verniers in later versions of the Atlas. Thank you.

That's the turbopump exhaust.

Pat

I would say that the answers to this man's question was rather
"exhausti-ive" in nature :0)
"Pat Flannery" wrote in message
...


John Pelchat wrote:

Thanks for a great reply, one follow-one: Part of your reply spoke of
dumping exhaust overboard. In photos of some launch vehicles, you see
a rather non-propulsive flame to one side of the engine exhaust,
especially the older Atlas vehicles . . . is that the same exhaust?




Yes, that is indeed the turbopump exhaust. Saturn I's could really shoot
out some
serious turbopump exhaust also.

Pat

In article ,
John Pelchat wrote:
Sorry, I was not as clear as I meant to be. I was not talking about
the two verniers on the lower side of the vehicle, but rather the
flame from the base but not the nozzle.

Yep, any flame on the base that isn't one of the three main nozzles is
turbopump exhaust. It comes out as sooty gas, but usually gets ignited
fairly promptly by one of the main plumes, and thereafter is a flame.
(I'm told that there was one Atlas launch where it somehow persistently
failed to ignite, so the Atlas went up with a little smoke trail behind.)
--
MOST launched 30 June; first light, 29 July; 5arcsec | Henry Spencer
pointing, 10 Sept; first science, early Oct; all well. |