Desperate goalpost moving and back-pedalling at Aulis

[JayUtah]

What ka9q said.

In the V-2, the alcohol fuel was just sprayed down the inside of the thrust chamber.  In some engines the outside rim of the injector plate has a different impingement pattern.  It creates a shear layer of cooler exhaust that still mixes with the main flow before exit but, for the length of the thrust chamber, provides the same effect as classic film cooling.

[JayUtah]

It is piped to the side of the engine nozzle through large ducts ...

There's a heat exchanger in there too somewhere.  The turbine and pump assembly on the F-1 is quite impressive.

Rocketdyne thrust chambers and nozzles are built as a single regeneratively-cooled set of Inconel tubes brazed together.  The F-1 was too big for the entire nozzle to be built this way, so the rest of the nozzle -- the nozzle extension -- was a bolted-on assembly.  This means it can't have shared the same regenerative cooling pathways and had to be cooled a different way: in this case, the cooling film from the turbine exhaust.

[Sus_pilot]

Thank you!  I knew for years it had something to do with how the fuel was burned, but could never come up with anything that made sense. I always thought it was something esoteric in the chemistry, not something this straightforward.

[DD Brock]

Ahh, ok thanks. So basically a little gas goes out the tailpipe to keep the nozzle cool, and the burning of the cooling film causes the black exhaust. Makes sense. I'm assuming then since this unburned fuel doesn't enter the combustion chamber, it does not effect the actual thrust of the engine?

[ka9q]

The black exhaust is the cooling film. It's black because it was produced by the gas generator with an extremely rich mixture ratio, so there's lots of unburned fuel. Actually, it's unburned carbon -- black smoke -- because the excess fuel decomposes in the heat.

You are correct that the propellants feeding the gas generator and turbine do not contribute significantly to the thrust. This does lower efficiency, and it's a reason for more complex engine designs such as "staged combustion" used in the SSME (space shuttle main engine) and others. In the SSME, all (not just some) of the hydrogen is mixed with a small amount of oxygen in a "preburner", producing a lot of hot hydrogen (plus a little steam) to drive the turbines.

Instead of being dumped overboard (which would waste all of the hydrogen!) the turbine exhaust is then fed into the rocket combustion chamber where it meets the rest of the liquid oxygen and burns much more completely. (The mixture ratio is still a little rich, so some of the hydrogen still comes out unburned in the plume. This actually improves efficiency at the same time it lowers the temperatures that must be tolerated by the engine.)

[Zakalwe]

Ahh, ok thanks. So basically a little gas goes out the tailpipe to keep the nozzle cool, and the burning of the cooling film causes the black exhaust. Makes sense. I'm assuming then since this unburned fuel doesn't enter the combustion chamber, it does not effect the actual thrust of the engine?

Here's an excellent article of the engine cooling and thrust chamber:
http://heroicrelics.org/info/f-1/f-1-thrust-chamber.html

I can recommend this book on the development of the F-1 engine:
http://www.amazon.co.uk/Saturn-F-1-Engine-Powering-Exploration/dp/0387096299/ref=sr_1_1?ie=UTF8&qid=1419773431&sr=8-1&keywords=F-1+engine

[JayUtah]

Anything injected into the divergent part of the nozzle doesn't contribute materially to propulsive effect.  In some vehicle designs the turbine exhaust is vented through vectored nozzles for steering -- chiefly roll control.

[JayUtah]

http://airandspace.si.edu/collections/artifact.cfm?object=nasm_A19751580000

Here's a cutaway of the turbopump assembly.

[JayUtah]

Actually, it's unburned carbon -- black smoke -- because the excess fuel decomposes in the heat.

And it really soots up the turbines and exhaust system.  That's why you can't run an RP-1 engine with gas-generator cycle for more than a few minutes total before you'd have to tear down and rebuild everything south of the combustors.

[DD Brock]

That actually makes sense to me. Never really understood how any of it worked. Thank you all for the explanations and answers, learn something new every day!

[Bob B.]

The black exhaust is the cooling film. It's black because it was produced by the gas generator with an extremely rich mixture ratio, so there's lots of unburned fuel. Actually, it's unburned carbon -- black smoke -- because the excess fuel decomposes in the heat.

Is it really black or does it just look black on film because it is under exposed next to the bright exhaust?  Kind of like how sunspots look black even though they're not black at all.  I've always thought the turbine exhaust was orange* but often looked darker because of its contrast with the bright exhaust and the need of the camera to stop down.

(ETA)
* To clarify, I mean the area of dark coloration immediately aft of the nozzle looks orange, not necessarily the turbine exhaust itself.

[Bob B.]

There's a heat exchanger in there too somewhere.

Just to elaborate on this a little bit...

The heat exchanger surrounds the exhaust duct and is located just aft of the turbine (it looks like a thickened section of duct).  Its purpose is to heat up gaseous oxygen and helium that is then used to pressurize the propellant tanks.  As liquid propellant is drawn from the tanks, the resulting empty volume has to be filled with something to allow a smooth continuous flow.  Hot GOX from the heat exchanger is piped to the LOX tanks, and hot helium is piped to the RP-1 tank.  Heating the gas increases its volume, thus it takes a smaller mass of hot gas to bring the tanks up to the required pressure than it would if cold gas were used.

[JayUtah]

Reminds me of the elusive "Dr. David Groves"...

Several people in the U.K. attempted diligently to locate "David Groves, PhD."  The best we could manage is mention of his name as a principal in a company that advertised digital 3D contour extraction from photographs.  The company has been defunct for well over a decade, and -- to anyone's best research -- never existed beyond a listing in a directory.

As with many of the claimants purporting to have advanced academic degrees, by their fruits we know them.  The experiments attributed to Groves in Bennett and Percy's work display an appalling ignorance of even basic physics or experimental method.  And Percy himself flip-flops over the faux doctor's claims.  For his own purposes, for example, Percy claims you can't discern contour on the lunar surface from photographs, so the explanation that surface variation causes "improper" shadow casting can't possibly be correct.  But then in the appendix, his "expert" Groves not only maintains that contour can be discerned from photographs, he even proposes a (simplistic) method for quantifying it and uses it in "analyzing" -5903 to conclude artificial light must have been used.

...and the outright fraud, "Dr." Ken Johnston.

And the equally fraudulent Maurice Chatelain.  Chatelain claimed to be "Chief of NASA Communications Systems."  In fact he was a low-level electronics technician who may have briefly worked as an installation contractor at one of the NASA centers.

Johnston was outed by James Oberg as little more than a shipping clerk.  As I recall, Hoagland and company had to rewrite Johnston's bio on the subsequent editions of their various books to downplay the earlier claim that he was a "Director" of the Apollo mission photography archives.

What puzzles me is how these people think they can get away for very long with making such easily-checked and clearly exaggerated claims?  Do they not understand that, at least in the case of NASA, what people were "directors" of this or that throughout the agency's entire history is a matter of very easily verified fact?

Then there's the guy who was custodian of Ralph Rene's work ... I should look into that, since my home base is in that area.

Yes, you probably should.  Chances are he was a graduate teaching assistant or some such thing during his own doctoral work.  Doctoral candidates are presumed to want to continue in academia.  That means it's valuable to have practical teaching experience.

Then there's the mysterious "Bill Wood". I'm not sure that's even his name and that maybe he just stole the name of a couple of important people at NASA.

I really think that's what happened.  Bennett and Percy rely on a cast of characters, some easily verified like Jan Lundberg of Hasselblad, and others simply names they throw out there without providing enough information to verify the foundation of the alleged expertise.  "Una Ronald" is alleged to be an eyewitness, but Bennett and Percy say that's not her real name.  They have given her a false name, allegedly to protect her identity.  But then Percy shows her face on his video!  Great way to protect her identity there, Percy.

Ditto "Bill Wood."  They give him a name that would survive perhaps a cursory web search -- "Oh, look, there's someone with that name legitimately associated with NASA" -- but again his story is suspicious.  After "Bill" spilled the beans to Bennett and Percy, he was allegedly taken so ill that he was unable to participate in any more evidentiary discussions.  There's the insinuation that he was "silenced," but then again he really wasn't.  The only thing that's silenced is his critics' ability to test his expertise and claims for validity.  But then again, his face appears on Percy's film.  So is Percy responsible for the "silencing" of the witness by exposing his face?

I doubt that anybody with only a bachelor's degree is considered a "highly qualified scientist".

Correct.  In fact, given the clearly bogus claims of Percy's on-screen witnesses and his flagrant fabrications elsewhere in his work, I wouldn't be surprised if those people are just actors Percy hired to portray his fictional "witnesses," claiming expertise or other standing, but simply reciting the script Percy wrote for them.

[JayUtah]

Is it really black or does it just look black on film because it is under exposed next to the bright exhaust?

A little of both.  By itself it would look like the dirty exhaust of a big diesel.  But we can't deny that the only way we see it in this context is in film records where we can plausibly suspect the exposure has been set to allow such things to be visible even if, to the naked eye, they would be unbearably bright.

We know the turbine exhaust contains particulate carbon.  Film cooling generally invokes two methods.  First, the annular film is engineered to move very much more slowly than the main flow.  This creates a fluid shear a few centimeters inboard of the inner surface of the nozzle.  Fluid shear is the generalized form of wind shear, or simply the concept that adjacent layers of any fluid can be made to move at vastly different speeds.  This generally inhibits mixing the two flows for a time, and in the case of a rocket engine prevents the main flow (very hot) from physically touching the nozzle surface and transferring heat to it.  So the entire convective-conductive heat transfer scenario is engineered to minimize transfer of heat to the nozzle.

But to return to the carbon, the other heat transfer mechanism you have to inhibit is radiation.  The main flow is very hot and radiates heat via electromagnetic energy that would be absorbed in the nozzle.  If the cooling film is opaque to those wavelengths, it effectively shades the inside of the nozzle from that influx.  Some cooling films are suitably opaque and the chemical level.  But the LOX/RP-1 cooling film is additionally opaque at the physical particulate level.  The fluid is composed of gaseous products as well as particulates of carbon compounds entrained in the flow.

So effective was this eventual design that it was contemplated that even bigger and more powerful engines (e.g., the M-1) could be built by scaling up the qualitative design features of the F-1.

[ka9q]

But to return to the carbon, the other heat transfer mechanism you have to inhibit is radiation.  The main flow is very hot and radiates heat via electromagnetic energy that would be absorbed in the nozzle.  If the cooling film is opaque to those wavelengths, it effectively shades the inside of the nozzle from that influx. 

If the cooling film is black, wouldn't it then absorb radiation from the main flow and be heated by it?