Author Topic: The Reaction Engines Skylon Master Thread (5)  (Read 421113 times)

Offline Jim

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Re: The Reaction Engines Skylon Master Thread (5)
« Reply #1200 on: 01/27/2016 01:33 PM »

Jim pointed out that a layer of paint alone was sufficient to reduce LOX boil off to very  low levels.


Didn't say anything about the boil off.  Just that LOX tanks only have paint and no insulation.  LOX is boiling off and is replenished up to a few minutes before launch.  The open vents are closed but the boil off still causes the vent to open occasionally.

Offline RanulfC

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Re: The Reaction Engines Skylon Master Thread (5)
« Reply #1201 on: 01/27/2016 04:16 PM »
I thought it referred to hydrogen at it's triple-point of 14.01 K
Indeed.

Like many other "grey" areas where people writing the papers don't want to get to specific, "slush hydrogen" tends to be generally described rather than nailed to a specific parameter. My point was simply that it's described as "below-but-above" in a lot of the papers I've read which struck me as odd.

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Randy has pointed out US aerospace R&D seems to have gone off the rails somewhere in the 60's when they became obsessed with SCRamjets.

LACE, now don't forget LACE as well :)

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My feeling is the same applies to their pursuit of "Slush" Hydrogen. It's that same sense of "performance Uber Alles" of pursuing the absolute best performance (in this case in terms of density) regardless of the practical problems, when more viable options, which are simpler to implement, exist.

Actually in most cases it's invoked for the simple reason of trying to reduce the tankage size of an LH2 system. In rarer cases it's used to allow "recycling" of gaseous LH2 into at least a semi-liquid state by running it back through the 'slush' after its used for some cooling purpose. From what I've read it usually isn't worth doing unless there is a very compelling reason, on the gripping-hand though there usually IS a very compelling reason which is why it gets invoked :)

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This is a side point. AIUI the stated concern is that people doubt a Skylon could stay on the runway for 2 hrs without venting.

Actually Jim brought up that LH2 "boils-off" and I 'tried-to-help' and failed miserably :)
http://forum.nasaspaceflight.com/index.php?topic=36826.msg1482971#msg1482971

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I agree that a system that carries out the chill down LH2 sub cooling will need to vent gas to the atmosphere and that will be burnt off.

The question is with all that pre cooled hardware filled with sub cooled propellant resist the heat coming in from the environment long enough to eliminate venting?

"MY" main point was the question of why NOT vents? (Thanks for the calc's JCRM :) )

Randy
From The Amazing Catstronaut on the Black Arrow LV:
British physics, old chap. It's undignified to belch flames and effluvia all over the pad, what. A true gentlemen's orbital conveyance lifts itself into the air unostentatiously, with the minimum of spectacle and a modicum of grace. Not like our American cousins' launch vehicles, eh?

Offline john smith 19

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Re: The Reaction Engines Skylon Master Thread (5)
« Reply #1202 on: 01/27/2016 07:12 PM »
LACE, now don't forget LACE as well :)
Indeed. LACE is the "performance Uber Alles" approach.  SABRE is the "good enough to get the job done" approach.  :)
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Actually in most cases it's invoked for the simple reason of trying to reduce the tankage size of an LH2 system. In rarer cases it's used to allow "recycling" of gaseous LH2 into at least a semi-liquid state by running it back through the 'slush' after its used for some cooling purpose. From what I've read it usually isn't worth doing unless there is a very compelling reason, on the gripping-hand though there usually IS a very compelling reason which is why it gets invoked :)
I don't know about the 60's concepts (IIRC some of Bono's SSTO ideas had it in the small print, along with Beryllium alloy structures) but I get the feeling a lot of the time it comes in when someone has mis-estimated the performance (either engine or structural) of their planned design. 

It's from the same place that caused HOTOL to develop a jet engined takeoff trolley. 

A valuable lesson that (I think) the REL team took to heart.
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"MY" main point was the question of why NOT vents? (Thanks for the calc's JCRM :) )
Well there's the practical and the philosophical.

Skylon is moved after propellant load to its start point on the runway.  Yes you could run some kind of flexible vent pipe to a burn off stack but imagine how clumsy that would be  :(

Option b would be to stick vent system on the vehicle.  H2 is very light and would disperse very quickly but I'm not sure that would be enough to convince the CAA it would not need some kind of burn off system.

Then there's the philosophical point. IE the COP.

Aircraft don't have flare stacks for fuel vapors from their tanks.  VTO  ELV's do.

AFAIK the nearest they get are Nitrogen generators, to purge fuel tanks on large aircraft of explosive vapors, are quite a recent feature (although IIRC SOP for military aircraft)
« Last Edit: 01/27/2016 07:13 PM by john smith 19 »
"Solids are a branch of fireworks, not rocketry. :-) :-) ", Henry Spencer 1/28/11  Averse to bold? You must be in marketing."It's all in the sequencing" K. Mattingly.  STS-Keeping most of the stakeholders happy most of the time.

Offline john smith 19

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Re: The Reaction Engines Skylon Master Thread (5)
« Reply #1203 on: 01/27/2016 07:12 PM »
Didn't say anything about the boil off.  Just that LOX tanks only have paint and no insulation.  LOX is boiling off and is replenished up to a few minutes before launch.  The open vents are closed but the boil off still causes the vent to open occasionally.
Noted.

"Solids are a branch of fireworks, not rocketry. :-) :-) ", Henry Spencer 1/28/11  Averse to bold? You must be in marketing."It's all in the sequencing" K. Mattingly.  STS-Keeping most of the stakeholders happy most of the time.

Offline RanulfC

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Re: The Reaction Engines Skylon Master Thread (5)
« Reply #1204 on: 01/27/2016 07:50 PM »
LACE, now don't forget LACE as well :)
Indeed. LACE is the "performance Uber Alles" approach.  SABRE is the "good enough to get the job done" approach.  :)

I'm not so sure it's actually "performance-et-al" really because it's quite clear the people working on the "problems" were in many ways going out of their way to "work" the problems even when there was evidence (but none they were paying attention to) of a "simpler" way to do things. Maybe more the allure of the "perfect" system approach, with eyes fixed firmly on the "prize" with all the blinders that implies :)

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Actually in most cases it's invoked for the simple reason of trying to reduce the tankage size of an LH2 system. In rarer cases it's used to allow "recycling" of gaseous LH2 into at least a semi-liquid state by running it back through the 'slush' after its used for some cooling purpose. From what I've read it usually isn't worth doing unless there is a very compelling reason, on the gripping-hand though there usually IS a very compelling reason which is why it gets invoked :)
I don't know about the 60's concepts (IIRC some of Bono's SSTO ideas had it in the small print, along with Beryllium alloy structures) but I get the feeling a lot of the time it comes in when someone has mis-estimated the performance (either engine or structural) of their planned design. 

It's from the same place that caused HOTOL to develop a jet engined takeoff trolley.

Actually I was thinking of Bono's case specifically and the fact it had to "fit" into what was supposed to be a "basic" S-IVB stage :) There simply wasn't room to fit the needed amount of LH2 in any form BUT slush... 

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"MY" main point was the question of why NOT vents? (Thanks for the calc's JCRM :) )
Well there's the practical and the philosophical.

Skylon is moved after propellant load to its start point on the runway.  Yes you could run some kind of flexible vent pipe to a burn off stack but imagine how clumsy that would be  :(

Option b would be to stick vent system on the vehicle.  H2 is very light and would disperse very quickly but I'm not sure that would be enough to convince the CAA it would not need some kind of burn off system.

Then there's the philosophical point. IE the COP.

Aircraft don't have flare stacks for fuel vapors from their tanks.  VTO  ELV's do.

AFAIK the nearest they get are Nitrogen generators, to purge fuel tanks on large aircraft of explosive vapors, are quite a recent feature (although IIRC SOP for military aircraft)

I'd actually rather face the truth you're working with hydrogen and face the issues :)

In either case though it still doesn't make that much sense as these "issues" were faced when there was consideration of using LH2 to power aircraft, but I suspect the main issue is the amount of LH2 involved and the more advanced knowledge of dealing with its vapors in an operational manner.

The reading is confusing as for the most part most VTO and all HTO designs using LH2 don't seem to be concerned with LH2 venting and/or leakage in operations. Yet VTO rocket operations on a pad it's an assumed requirement.

Randy
From The Amazing Catstronaut on the Black Arrow LV:
British physics, old chap. It's undignified to belch flames and effluvia all over the pad, what. A true gentlemen's orbital conveyance lifts itself into the air unostentatiously, with the minimum of spectacle and a modicum of grace. Not like our American cousins' launch vehicles, eh?

Offline Asteroza

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Re: The Reaction Engines Skylon Master Thread (5)
« Reply #1205 on: 01/28/2016 12:55 AM »
Hrm, if one were committed to flaring off somehow, how about a hobby/micro gas turbine with a shaft motor/generator to regulate the RPM'S? Keep the compressor turning hard enough to heat air to autoignite any vented hydrogen gas flushed into the combustor. Piping to the rear near the SOMA engines, plus maybe five kilos worth of gear?

Vehicle self-flaring would avoid hydrogen umbilicals after tanking...

Offline john smith 19

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Re: The Reaction Engines Skylon Master Thread (5)
« Reply #1206 on: 01/28/2016 08:32 AM »
It would be about 30 tonnes of hydrogen that would need to be evaporated to chill (my estimate of) 180 tonnes of fuel. That's a lot to burn, even if one was happy to just throw it away. On the other hand, it's a lot to pressurise and store - so  who knows what actual operational procedure would be.
The usual figures for Skylon are it holds about 150 tonnes of LO2 and about 60 tonnes of LH2.

John Whitehad's team estimated LV propellant tanks are about 1% of contents weight except for LH2, when (IIRC) it's nearer 12% (Shuttle ET H2 is about 1/8 mass of LH2 it holds).
That's about 9 tonnes of Aluminium to cool down. With engines being roughly 24 tonnes of superalloy.

Assuming the drain and fill pipes are well located it should be possible to re-circulate Helium through the whole system to give good coverage of all the pipes and tanks. 

Note that LN2 is the cheapest bulk cryogen (described as being cheaper than "A quart of milk" in tanker car quantities) and with a delta t of 2deg (demonstrated by the X33 sub cooler HX) that would get the whole structure (and contents) to 79K (quite how SX get their LO2 tank to 65K remains something of a mystery to me).

Beyond that you'd need to run LH2 to cool the GHe further. Sub cooling LH2 either takes lots of LHe or sub atmospheric boiling of some of the LH2 to cool the rest. This was how the the X33 programme did it.
"Solids are a branch of fireworks, not rocketry. :-) :-) ", Henry Spencer 1/28/11  Averse to bold? You must be in marketing."It's all in the sequencing" K. Mattingly.  STS-Keeping most of the stakeholders happy most of the time.

Offline hkultala

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Re: The Reaction Engines Skylon Master Thread (5)
« Reply #1207 on: 01/28/2016 01:40 PM »
It would be about 30 tonnes of hydrogen that would need to be evaporated to chill (my estimate of) 180 tonnes of fuel. That's a lot to burn, even if one was happy to just throw it away. On the other hand, it's a lot to pressurise and store - so  who knows what actual operational procedure would be.
The usual figures for Skylon are it holds about 150 tonnes of LO2 and about 60 tonnes of LH2.

John Whitehad's team estimated LV propellant tanks are about 1% of contents weight except for LH2, when (IIRC) it's nearer 12% (Shuttle ET H2 is about 1/8 mass of LH2 it holds).
That's about 9 tonnes of Aluminium to cool down. With engines being roughly 24 tonnes of superalloy.

The shuttle tank also contains 630 tonnes of O2, the 26 tonne total weight the total weight of the O2+H2 tanks.

So your 12% number is total rubbish.

Offline SICA Design

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Re: The Reaction Engines Skylon Master Thread (5)
« Reply #1208 on: 01/28/2016 02:30 PM »

The shuttle tank also contains 630 tonnes of O2, the 26 tonne total weight the total weight of the O2+H2 tanks.

So your 12% number is total rubbish.

Wikipedia gives the (SLWT) dry ET mass as 26.5T
1% of the LO2 mass would be 6.3T
12% of the 106T LH2 mass would be 12.7T (1/8th would be 13.3T)
This leaves 6.9 - 7.5T for the intertank and other miscellaneous

Given the limited info, 12% seems plausible to me - and certainly doesn't deserve to be called "total rubbish".

Offline Asteroza

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Re: The Reaction Engines Skylon Master Thread (5)
« Reply #1209 on: 01/28/2016 10:19 PM »
Would an engineered aluminum material be worth the weight/expense to avoid the thermal conductivity? Say a 3D printed tank wall that was actually two aluminum face sheets and cubic octet truss honeycomb?

Offline AnalogMan

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Re: The Reaction Engines Skylon Master Thread (5)
« Reply #1210 on: 01/28/2016 10:45 PM »

The shuttle tank also contains 630 tonnes of O2, the 26 tonne total weight the total weight of the O2+H2 tanks.

So your 12% number is total rubbish.

Wikipedia gives the (SLWT) dry ET mass as 26.5T
1% of the LO2 mass would be 6.3T
12% of the 106T LH2 mass would be 12.7T (1/8th would be 13.3T)
This leaves 6.9 - 7.5T for the intertank and other miscellaneous

Given the limited info, 12% seems plausible to me - and certainly doesn't deserve to be called "total rubbish".
12% seems to be stated a little too precise given the way it was estimated. No need, however for the LWT:
Quote from: http://science.ksc.nasa.gov/shuttle/technology/sts-newsref/et.html
Liquid Hydrogen Maximum 227,641 pounds
[...]
The liquid hydrogen tank is 331 inches in diameter, 1,160 inches long, and has a volume of 53,518 cubic feet and a dry weight of 29,000 pounds
or 12.74%
Now, Skylon's tanks aren't structural, so it may be lighter - but they're less optimally shaped, so it's probably a good estimate.

Disappointingly, the SHC of aluminuim is ridiculous at cryogenic temperatures, with just 0.055 J/g to raise its temperature from 16 to 22 K and its thermal conductivity remains high at 27W/m K - so it wont be doing much to slow the temperature rise,

And this is the description given for the SLWT:

The liquid hydrogen tank is a semi-monocoque structure designed to contain 227,641 pounds of propellant fuel; it measures 1160.75 inches long with on outside skin diameter of 331 inches, has a total volume of 53,518 cubic feet, and its empty weight is approximately 23,600 pounds.

[Taken from "Space Shuttle External Tank - System Definition Handbook SLWT, December 1997"]

So about 10.4% for the lighter version

Offline SICA Design

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Re: The Reaction Engines Skylon Master Thread (5)
« Reply #1211 on: 01/29/2016 08:38 AM »
A ?new? promotional puff:

http://www.msn.com/en-us/video/t/the-new-engine-that-could-revolutionise-aviation/vp-BBoFjko
"destroy all the other naysayers that say this can;t be done"

This piece implies that BAe's interest is more in LAPCAT/Scimitar - media bias, perhaps?

Offline SICA Design

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Re: The Reaction Engines Skylon Master Thread (5)
« Reply #1212 on: 01/29/2016 10:07 AM »
This piece implies that BAe's interest is more in LAPCAT/Scimitar - media bias, perhaps?
Scimitar is a better missile engine? Four hours to Australia is of more interest to the general public than space access? (weird right? but then the general public watch Big Brother and the X Factor)

'Fraid I'm guilty with the X Factor - honestly guv, my wife makes me!

Offline john smith 19

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Re: The Reaction Engines Skylon Master Thread (5)
« Reply #1213 on: 01/29/2016 08:54 PM »
A ?new? promotional puff:

http://www.msn.com/en-us/video/t/the-new-engine-that-could-revolutionise-aviation/vp-BBoFjko
"destroy all the other naysayers that say this can;t be done"

This piece implies that BAe's interest is more in LAPCAT/Scimitar - media bias, perhaps?
The LAPCAT stuff was a fairly small part of the report I thought. LAPCAT remains a very different engine from SABRE.  The joker in the pack remains coping with the prolonged heating on a fuselage during cruise.
"Solids are a branch of fireworks, not rocketry. :-) :-) ", Henry Spencer 1/28/11  Averse to bold? You must be in marketing."It's all in the sequencing" K. Mattingly.  STS-Keeping most of the stakeholders happy most of the time.

Offline Star One

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Re: The Reaction Engines Skylon Master Thread (5)
« Reply #1214 on: 01/29/2016 11:07 PM »

A ?new? promotional puff:

http://www.msn.com/en-us/video/t/the-new-engine-that-could-revolutionise-aviation/vp-BBoFjko
"destroy all the other naysayers that say this can;t be done"

This piece implies that BAe's interest is more in LAPCAT/Scimitar - media bias, perhaps?
The LAPCAT stuff was a fairly small part of the report I thought. LAPCAT remains a very different engine from SABRE.  The joker in the pack remains coping with the prolonged heating on a fuselage during cruise.

I think it's above eight minutes and the skin of the craft tears off.

Offline Robotbeat

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Re: The Reaction Engines Skylon Master Thread (5)
« Reply #1215 on: 01/29/2016 11:57 PM »
Make 'er out of Titanium, then...
Chris  Whoever loves correction loves knowledge, but he who hates reproof is stupid.

To the maximum extent practicable, the Federal Government shall plan missions to accommodate the space transportation services capabilities of United States commercial providers. US law http://goo.gl/YZYNt0

Offline Star One

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Re: The Reaction Engines Skylon Master Thread (5)
« Reply #1216 on: 01/30/2016 12:00 AM »

Make 'er out of Titanium, then...

I think even that has its issues at hypersonic speeds as the craft starts to stretch, the old SR-71 used to and that was only doing Mach 3.

Offline SICA Design

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Re: The Reaction Engines Skylon Master Thread (5)
« Reply #1217 on: 01/30/2016 03:30 PM »
A ?new? promotional puff:

http://www.msn.com/en-us/video/t/the-new-engine-that-could-revolutionise-aviation/vp-BBoFjko
"destroy all the other naysayers that say this can;t be done"

This piece implies that BAe's interest is more in LAPCAT/Scimitar - media bias, perhaps?
The LAPCAT stuff was a fairly small part of the report I thought. LAPCAT remains a very different engine from SABRE.  The joker in the pack remains coping with the prolonged heating on a fuselage during cruise.

I agree; more than 75% of the piece was dedicated to SABRE and reusable space vehicles. However my point was based on the last minute where the video and talk appeared all about LAPCAT, with the quote at 3:51 -

"The project [LAPCAT visuals playing] received a huge boost at the end of 2015: a $100M investment from BAe Systems and the British government" followed shortly after at 4:06 -

Varvill: "When that day happens and that AEROPLANE [my emphasis] rolls out on the tarmac will be a pretty emotional moment..."

Hope I'm wrong...

Offline Star One

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Re: The Reaction Engines Skylon Master Thread (5)
« Reply #1218 on: 01/30/2016 06:59 PM »

A ?new? promotional puff:

http://www.msn.com/en-us/video/t/the-new-engine-that-could-revolutionise-aviation/vp-BBoFjko
"destroy all the other naysayers that say this can;t be done"

This piece implies that BAe's interest is more in LAPCAT/Scimitar - media bias, perhaps?
The LAPCAT stuff was a fairly small part of the report I thought. LAPCAT remains a very different engine from SABRE.  The joker in the pack remains coping with the prolonged heating on a fuselage during cruise.

I agree; more than 75% of the piece was dedicated to SABRE and reusable space vehicles. However my point was based on the last minute where the video and talk appeared all about LAPCAT, with the quote at 3:51 -

"The project [LAPCAT visuals playing] received a huge boost at the end of 2015: a $100M investment from BAe Systems and the British government" followed shortly after at 4:06 -

Varvill: "When that day happens and that AEROPLANE [my emphasis] rolls out on the tarmac will be a pretty emotional moment..."

Hope I'm wrong...

And what's wrong with that?

Offline Stormbringer

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Re: The Reaction Engines Skylon Master Thread (5)
« Reply #1219 on: 01/31/2016 12:16 AM »
http://nextbigfuture.com/2016/01/charles-bombardier-has-improved.html

to quote daffy duck when he is about to be in a lot of pain:  "mother"

When antigravity is outlawed only outlaws will have antigravity.

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