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1 hour ago, mikegarrison said:

How hot do those engine nozzles get? There is really nowhere for the heat to radiate to in that configuration. (Yes, I know they are cooled by the fuel.)

I assume most of the net total heat is being removed via the exhaust flux.

The nozzles are cooled by the liquid methane which has a MUCH better heat capacity than kerosene AND comes in at a much lower temperature. So if Falcon 9 can handle nine Merlin engines in close proximity, Superheavy can DEFINITELY handle 20 engines in close proximity. The more engines you have in the ring, the less radiative heating there is from one engine to the next.

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16 hours ago, tater said:

That other beam they had on the crane by the launch site was stenciled with text that said:

Working Load Limit

63.77 for fixed configuration

216.57 with sling rigging

 

Makes me wonder what counts as sling rigging (I was assuming it was more of the spiderweb they have used before, but I'm completely clueless about cranes).

I'm not an expert, but it could be the difference between using the beam as a lifting beam compared to using it as a spreader beam.  See https://www.mazzellacompanies.com/learning-center/spreader-beams-vs-lifting-beams-definitions-differences-and-design/

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6 hours ago, sevenperforce said:

The nozzles are cooled by the liquid methane which has a MUCH better heat capacity than kerosene AND comes in at a much lower temperature. So if Falcon 9 can handle nine Merlin engines in close proximity, Superheavy can DEFINITELY handle 20 engines in close proximity. The more engines you have in the ring, the less radiative heating there is from one engine to the next.

Um, no. The more engines, the more heat. This should be pretty obvious.

The radiation is proportional to the surface area, but only the parts of the nozzles that can be seen from outside will be able to radiate. All the other nozzle surfaces will only see nozzles just as hot as they are, so there will be no net radiation. Because the number of engines (and therefore the total heat) is proportional to the area of the circle, but the radiating surface is only proportional to the circumference of the circle, the bigger the circle of engines, the less you can rely on heat being radiated away.

We know it gets pretty hot in there with just three engines. With 30 (or whatever) it's going to be really, really hot in there.

So, like I said, I assume they are relying on ejecting the heat with the exhaust. The mechanism for that is that it goes into the super-cold fuel, which then ultimately gets thrown out the back end. That's potentially going to be an issue for them with soakback, however. When they shut the engines off, does it also shut off the cooling? Or do they keep pumping fuel through them to control the soakback?

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58 minutes ago, mikegarrison said:

Um, no. The more engines, the more heat. This should be pretty obvious.

The radiation is proportional to the surface area, but only the parts of the nozzles that can be seen from outside will be able to radiate. All the other nozzle surfaces will only see nozzles just as hot as they are, so there will be no net radiation. Because the number of engines (and therefore the total heat) is proportional to the area of the circle, but the radiating surface is only proportional to the circumference of the circle, the bigger the circle of engines, the less you can rely on heat being radiated away.

We know it gets pretty hot in there with just three engines. With 30 (or whatever) it's going to be really, really hot in there.

So, like I said, I assume they are relying on ejecting the heat with the exhaust. The mechanism for that is that it goes into the super-cold fuel, which then ultimately gets thrown out the back end. That's potentially going to be an issue for them with soakback, however. When they shut the engines off, does it also shut off the cooling? Or do they keep pumping fuel through them to control the soakback?

"Um, no." These arnt radiatively cooled nozzles, so radiative cooling, by definition, isnt their way to stay cool.

As the person you replied to said, the nozzles have tiny pipes milled into them, with subcooled liquid methane going in one side, and hot methane gas coming out the other, with the nozzles not getting much hotter than the coolant fluid. This used coolant gas is then pumped into the preburners to run the pumps to push more subcooled liquid methane into the nozzle and combustion chamber liner. THEN the exaust enters the main combustion chamber in typical staged combustion fashion.

This is basic stuff. But admittedly not stuff Kerbal teaches us.

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3 hours ago, mikegarrison said:

Um, no. The more engines, the more heat. This should be pretty obvious.

As has been stated, the nozzles aren't hot.

If I were to guess at what sevenperforce means, because each engine is completely surrounded (or at least one engine in the cluster is in each case, F9 and SH) the inverse square law doesn't apply. What counts is the width of the sight angle from the engine head to the exhaust plumes.

This angle can be significantly cut down by placing the engines close together.

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17 minutes ago, RCgothic said:

As has been stated, the nozzles aren't hot.

If I were to guess at what sevenperforce means, because each engine is completely surrounded (or at least one engine in the cluster is in each case, F9 and SH) the inverse square law doesn't apply. What counts is the width of the sight angle from the engine head to the exhaust plumes.

I stated it very poorly, so I fully understand why @mikegarrison was taken aback.

When the engines are firing, they are regeneratively cooled, so they aren’t hot. If kerosene-regenerative cooling can handle nine Merlin engines, methane-regenerative cooling can definitely handle the full array under Superheavy.

My point with respect to the outer ring was separate (and, again, poorly-phrased). The only time the engines are not regeneratively cooled is during the retropropulsive burn, when the outer engines are just sitting there and the inner engine(s) are roaring. There is more physical distance between Superheavy’s outer ring and its core cluster than there is between Falcon 9’s outer ring and its core engine, so the heat flux from the core exhaust plume to the outer ring of Raptors will be lower than from the core Merlin to the outer ring of Merlins. Thus the larger the outer ring of engines, the less heat those outer engines receive from  the overall thermal environment.

But, again, very poorly phrased. Mea culpa.

Edited by sevenperforce
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1 minute ago, GuessingEveryDay said:

I haven't seen this yet on the forums, but:

So I guess in the future:

5igfxz.jpg

That TFR has always been there, simply they hadn't renewed it yet in the last three days. The testing TFR is much higher

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4 hours ago, Rakaydos said:

"Um, no." These arnt radiatively cooled nozzles, so radiative cooling, by definition, isnt their way to stay cool.

As the person you replied to said, the nozzles have tiny pipes milled into them, with subcooled liquid methane going in one side, and hot methane gas coming out the other, with the nozzles not getting much hotter than the coolant fluid. This used coolant gas is then pumped into the preburners to run the pumps to push more subcooled liquid methane into the nozzle and combustion chamber liner. THEN the exaust enters the main combustion chamber in typical staged combustion fashion.

This is basic stuff. But admittedly not stuff Kerbal teaches us.

 

2 hours ago, RCgothic said:

As has been stated, the nozzles aren't hot.

 

1 hour ago, sevenperforce said:

When the engines are firing, they are regeneratively cooled, so they aren’t hot.

I am pretty damn sure those nozzles are hot. Yes, yes, I know they are cooled. I already said that several times. But I've worked around engines my whole career, and my guess is that they will cool the nozzles to just a little bit under the point where they start running into problems.

You've seen the videos from inside the engine bay, right? Has there been a flight where you didn't see flames in there? That's a hot environment, and that's just with three engines. With 30 engines, it's going to be a very hot environment.

If one of you can find some data on what the temperatures are like in there, I would be interested to see it. But I'm pretty sure it's very hot.

Edited by mikegarrison
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15 minutes ago, mikegarrison said:

 

 

I am pretty damn sure those nozzles are hot. Yes, yes, I know they are cooled. I already said that several times. But I've worked around engines my whole career, and my guess is that they will cool the nozzles to just a little bit under the point where they start running into problems.

You've seen the videos from inside the engine bay, right? Has there been a flight where you didn't see flames in there? That's a hot environment, and that's just with three engines. With 30 engines, it's going to be a very hot environment.

If one of you can find some data on what the temperatures are like in there, I would be interested to see it. But I'm pretty sure it's very hot.

Hot for a flesh and blood individual, sure. But at no point are the bells going to be hotter than the melting point of copper, which is what they build those channels out of. The outside of the bell, made out of sterner stuff, is going to be cooler than that, and the outside of the next bell over, if it doesnt have a flame running, will be cooler still.

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34 minutes ago, mikegarrison said:

 

 

I am pretty damn sure those nozzles are hot. Yes, yes, I know they are cooled. I already said that several times. But I've worked around engines my whole career, and my guess is that they will cool the nozzles to just a little bit under the point where they start running into problems.

You've seen the videos from inside the engine bay, right? Has there been a flight where you didn't see flames in there? That's a hot environment, and that's just with three engines. With 30 engines, it's going to be a very hot environment.

If one of you can find some data on what the temperatures are like in there, I would be interested to see it. But I'm pretty sure it's very hot.

I can't speak for the Raptor specifically, but the RS-25's and RL10's exterior definitely get downright chilly when firing.

Spoiler

819px-Shuttle_Main_Engine_Firing_in_Gimb

686px-Common_Extensible_Cryogenic_Engine

 

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3 minutes ago, Silavite said:

I can't speak for the Raptor specifically, but the RS-25's and RL10's exterior definitely get downright chilly when firing.

  Hide contents

819px-Shuttle_Main_Engine_Firing_in_Gimb

686px-Common_Extensible_Cryogenic_Engine

 

Yep! Those icicles on the outside of the RL-10 are just incredible.

Of course, the RL-10 uses an expander cycle so it has to suck every last Kelvin it can out of that engine bell in order to function. And while the RS-25 doesn’t need the heat to operate since it uses a staged-combustion preburner, it is also using liquid hydrogen, which has a much greater heat capacity than liquid methane.

Even so, the heat capacity of subcooled liquid methane should be plenty to keep the Raptors chilled.

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