Author Topic: The Reaction Engines Skylon Master Thread (5)  (Read 420057 times)

Offline Ravenger

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Re: The Reaction Engines Skylon Master Thread (5)
« Reply #1180 on: 01/17/2016 08:55 PM »
I found this old article from 2008 that that's got a very high-resolution cut-way CAD rendering of the sabre engine which I've not seen before. This was used to produce the 1/6th scale model for use at airshows, etc.

http://www.engineeringcapacity.com/news101/business-news/it_is_rocket_science_from_gemini

I think this makes the layout much clearer than other cut-aways I've seen.

It's new to me, so apologies if it's been posted before in the many previous Skylon threads.



Offline adrianwyard

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Re: The Reaction Engines Skylon Master Thread (5)
« Reply #1181 on: 01/17/2016 09:13 PM »
Can anyone discern any thirst vector control hardware for those nozzles? To the untrained eye they appear locked in place by the structure.

Offline NovaSilisko

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Re: The Reaction Engines Skylon Master Thread (5)
« Reply #1182 on: 01/17/2016 09:49 PM »
I'll attach it here, just in case that article ever blows up for whatever reason.

Offline Soundbite

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Re: The Reaction Engines Skylon Master Thread (5)
« Reply #1183 on: 01/18/2016 10:48 AM »
I have just come across an interesting report by Purdue University, published in July 2015, to study a design of a SABRE cycle based engine that is capable of powering a modified X-43 at Mach 5, so that they can test the performance of a modified X-43 when cruising at Mach 5 as well as the performance of the pre-cooler, see http://www.slideshare.net/JulianWang2/aae537sabrefinalreportdocx.

Just note that it takes a few seconds for all the tables and images to load.

What do you all think?

Offline adrianwyard

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Re: The Reaction Engines Skylon Master Thread (5)
« Reply #1184 on: 01/18/2016 03:21 PM »
It has been stated in a couple of places that the axisymmetric inlet on the SABRE/Skylon - ingesting mostly uninterrupted free stream air - simplifies its design, so fitting SABRE to a rectangular inlet behind a forebody will involve some work. Mind you, if it only has to work at M5 (and not M0-M5 as on Skylon) perhaps thats doable.

X-43 is expendable, so somebody's going need a healthy budget to make this happen...

Offline adrianwyard

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Re: The Reaction Engines Skylon Master Thread (5)
« Reply #1185 on: 01/18/2016 03:53 PM »
Orbitec (now owned by SNC, of Dream Chaser fame) has received a NASA grant that amongst many other things looks at rocket-based combined cycle engines. And one of their partners is Purdue...

http://orbitec.com/documents/ORBITEC_RTAPS_2_contract_announce_pr_12.8.2015.pdf

Offline adrianwyard

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Re: The Reaction Engines Skylon Master Thread (5)
« Reply #1186 on: 01/19/2016 10:50 PM »
Here's a SABRE brain teaser: will flying through heavy rain and/or ingesting spray kicked up from the nose gear be any cause for concern?

In a generic turbojet the compressor blades have to deal with rain drops, but by the time you get to the back, high pressure stages I think the water has evaporated so you just pass humid air to the combustion chamber. But in Skylon the rain/water has to pass in-between the precooler tubes before it hits the compressor. Looking at that exploded diagram it's hard to tell what will happen. Will most of the rain (relatively dense) fly past the pre cooler into the bypass ducts? Or does it get sucked through the precooler? And if the operating pressures are high enough ahead of the compressor then perhaps it just evaporates before it's of any concern?

This is the sort of thing they could test with their current precooler setup - if it wasn't too risky.

Offline pippin

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Re: The Reaction Engines Skylon Master Thread (5)
« Reply #1187 on: 01/20/2016 12:56 AM »
Didn't they already test this?

Offline adrianwyard

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Re: The Reaction Engines Skylon Master Thread (5)
« Reply #1188 on: 01/20/2016 01:14 AM »
They certainly tested humid air - as demonstrating frost control was a key goal. But I'm not sure if that was just ambient humidity, or if they went on to chuck actual raindrops/spray in the front end.

Offline SICA Design

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Re: The Reaction Engines Skylon Master Thread (5)
« Reply #1189 on: 01/20/2016 08:24 AM »
Here's a SABRE brain teaser: will flying through heavy rain and/or ingesting spray kicked up from the nose gear be any cause for concern?

In a generic turbojet the compressor blades have to deal with rain drops, but by the time you get to the back, high pressure stages I think the water has evaporated so you just pass humid air to the combustion chamber. But in Skylon the rain/water has to pass in-between the precooler tubes before it hits the compressor. Looking at that exploded diagram it's hard to tell what will happen. Will most of the rain (relatively dense) fly past the pre cooler into the bypass ducts? Or does it get sucked through the precooler? And if the operating pressures are high enough ahead of the compressor then perhaps it just evaporates before it's of any concern?

This is the sort of thing they could test with their current precooler setup - if it wasn't too risky.

I remember this answered by Alan Bond at one of the talks I attended (apologies I can't remember which) when the apparent fragility of the pre-cooler was questioned. He stated first that the HX is much stronger than it looks when pressurised, but (more importantly) the airflow makes a sharp 90deg turn to enter the HX whereas debris (and liquid? - not sure if this was mentioned specifically) would continue past to the RAMjets.

Offline adrianwyard

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Re: The Reaction Engines Skylon Master Thread (5)
« Reply #1190 on: 01/20/2016 06:06 PM »
Thanks for that. What I find interesting is how unaerodynamic the precooler looks to the untrained eye. At low speeds (say take off speed of 0.5M) it appears as though debris and rain will hit the front edge of the third and fourth precooler ring head on. (While some will fly past towards the bypass burner inlets.)

My guess is it's incorrect to imagine rain drops flying into the precooler/bypass at high Mach because by then the temperatures and pressures inside the engine will vaporize them in short order.

I'm not sure if air is intended to be drawn into the side of the precooler rings that face the airstream, if not then you could easily imagine ramps added designed to deflect light debris/spray away from the rings, and out the bypass ducts.

Please don't think I'm suggesting REL haven't considered this - just curious about how it's all supposed to work.

Offline Lars-J

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Re: The Reaction Engines Skylon Master Thread (5)
« Reply #1191 on: 01/21/2016 05:33 AM »
Can anyone discern any thirst vector control hardware for those nozzles? To the untrained eye they appear locked in place by the structure.

I'll attach it here, just in case that article ever blows up for whatever reason.

Yes, that is a good question. There must be some thrust vector control/gimbal ability, otherwise there is no engine out capability and *very limited* control authority outside the atmosphere. The only way I can see it is if the entire "purple plate" that holds the four engine chambers gimbals, but that does seem very complex.

I certainly look forward to seeing a an actual working SABRE engine, that would go a *long* way towards making me a Skylon believer. But this design image must be hiding or obfuscating quite a few details, because as-is it seems more like a "rube goldberg machine" than a practical engine.
« Last Edit: 01/21/2016 05:34 AM by Lars-J »

Online Hankelow8

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Re: The Reaction Engines Skylon Master Thread (5)
« Reply #1192 on: 01/25/2016 04:22 PM »
Just noticed Alan Bond does not appear on the Reaction Engines web site board of directors or their executive
leadership team.

Anyone know anything about this ?

Offline Jim

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Re: The Reaction Engines Skylon Master Thread (5)
« Reply #1193 on: 01/25/2016 04:38 PM »
are people going to carry on accepting the necessity of falling COPVs?
The COPV for the F9 stage was inside the tank most of the time.
I was thinking of the hairy black space balls that farmers come across from time to time

Those are not launch vehicle specific.  They are in spacecraft too and no different than other space hardware that returns.  Reusable launch vehicle are not going to change this

Offline Jim

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Re: The Reaction Engines Skylon Master Thread (5)
« Reply #1194 on: 01/25/2016 04:39 PM »

No boil off means no burn off.


No such thing with hydrogen.  There is always boil off.

Offline john smith 19

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Re: The Reaction Engines Skylon Master Thread (5)
« Reply #1195 on: 01/25/2016 06:58 PM »

No boil off means no burn off.


No such thing with hydrogen.  There is always boil off.
AFAIK all LH2 work has been done at NBP.  I'm also not sure how these systems are pre cooled, or wheather they have just flushed the system and let it flash boil to GH2 before venting.

I think this has a lot to do with design decisions made in the 1960's. IIRC the SLS LH2 delivery system will cut the H2 waste by 50%.

My instinct is the key issues are a)Precooling all the hardware down to be the precooled level b)Precooling the LH2.

REL plan to operate around 16-18K, rather than 20K+

what has been done is not the limit of what can be done.
« Last Edit: 01/25/2016 06:59 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 RanulfC

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Re: The Reaction Engines Skylon Master Thread (5)
« Reply #1196 on: 01/25/2016 07:16 PM »

No boil off means no burn off.


No such thing with hydrogen.  There is always boil off.
AFAIK all LH2 work has been done at NBP.  I'm also not sure how these systems are pre cooled, or wheather they have just flushed the system and let it flash boil to GH2 before venting.

I think this has a lot to do with design decisions made in the 1960's. IIRC the SLS LH2 delivery system will cut the H2 waste by 50%.

My instinct is the key issues are a)Precooling all the hardware down to be the precooled level b)Precooling the LH2.

REL plan to operate around 16-18K, rather than 20K+

what has been done is not the limit of what can be done.

I think Jim's point was that "boil-off" isn't something you can prevent due to the nature of LH2. Doesn't matter what temps REL is planning on working with as long as it's lower than ambient the propellant WILL boil, the question is at what rate. REL "planning" on having zero-boil off is part of the reason folks don't accept they fully understand what they are talking about :)

Hint: 16-18K simply means you have from there to 20K before boil off becomes serious, and you "vent" in fact to help keep the propellant cool :)

I'll admit that line struck me as odd as well:
"However REL's COP is to load and launch within 2 hrs or recycle the propellants to long term storage. By pre cooling the hardware and the propellants they expect zero boiloff under normal operation."

Load and launch in two hours is pretty strict timing and by "pre-cooling" the hardware they are in essence planning on flowing large amounts of LH2 THROUGH the system and a large percentage of it is going to be fully gaseous and either need to be recycled or dumped until the system is fully cooled and even THEN the on-board LH2 is going to be trying to boil unless they are constantly cycling propellant through the tanks. (And all that piping is NOT going to be as insulated as the tanks are btw)

Simply put, until REL shows a zero-boil off storage tank made of flight-weight materials and shows no "boiling" for two full hours no one who has worked with LH2 on a consistent basis is going to take the assumption seriously.

I for one have noted that REL seems to be confusing/conflating "pre-cool" with "sub-cool" of the LH2 which btw runs into "slush-hydrogen" operations which seems to be what they are talking about rather than "pre-cooling".

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 RanulfC

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Re: The Reaction Engines Skylon Master Thread (5)
« Reply #1197 on: 01/25/2016 09:33 PM »

I think Jim's point was that "boil-off" isn't something you can prevent due to the nature of LH2. Doesn't matter what temps REL is planning on working with as long as it's lower than ambient the propellant WILL boil, the question is at what rate. REL "planning" on having zero-boil off is part of the reason folks don't accept they fully understand what they are talking about :)
Wikipedia tells me Hydrogen won't boil off below 20K. But the manual doesn't claim zero boil off, it only has zero venting (minimising boil off would help with that)

That's the confusing part for most folks as venting is required unless there's no boil off and hence no need for venting :)

The problem is that LH2 still heats up to ambient and wants to boil off. The only way to prevent this is to keep the LH2 colder than 20K and THAT isn't easy or cheap. (And mind you, this does not address the fact that LH2 LEAKS even if when liquid, it slips right out of ANY closed system and that's something no one has every managed to prevent)

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I'll admit that line struck me as odd as well:
"However REL's COP is to load and launch within 2 hrs or recycle the propellants to long term storage. By pre cooling the hardware and the propellants they expect zero boiloff under normal operation."

Load and launch in two hours is pretty strict timing
Fuel loading is 40 minutes, followed by 24 minutes of towing and final checks, followed by a hold time of up to two hours, during which time the temperature rises in the foam insulated tanks inside a nitrogen purged atmosphere inside layers of Mylar, inside the ceramic shell. If the temperature gets above 20K, then the pressure in the tank will start to rise - I don't know if that's accounted for in the concept design, but these people have spent decades working with the thermodynamic properties of hydrogen If it's not gone in that time it needs to be towed back

Uhm, yes and while they have spent decades working with the "thermodynamic properties" of hydrogen they are far from the only ones :) And yes they are planning on what amounts to a series of super-insulated "shells" to hinder the boil off of the LH2, but the fact they are counting on "zero-boil-off" after having spent "decades" working with the thermodynamic properties of hydrogen is something others who have been working for decades with the thermodynamic properties of hydrogen question since having no vents means you can't relieve the pressure build up in the tanks if you DO run into problems.

On the other hand let me add that there ARE in fact 'vents' in the design in that they can "vent" through the engines themselves but REL isn't planning it seems to follow any of the normal procedures for working with quantities of liquid hydrogen which is why there are questions from those who have also "yadda-yadda-decades-working-hydrogen" that don't seem to be addressed.

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and by "pre-cooling" the hardware they are in essence planning on flowing large amounts of LH2 THROUGH the system and a large percentage of it is going to be fully gaseous and either need to be recycled or dumped until the system is fully cooled and even THEN the on-board LH2 is going to be trying to boil unless they are constantly cycling propellant through the tanks. (And all that piping is NOT going to be as insulated as the tanks are btw)
* Install pipes and run LN2 through
* Connect to liquid Helium source and fill to cool.  Drain and recover helium
* Connect LH2 and LO2 pipes and fill.  Fill to 95% then top off

I'm assuming "Draw vacuum in filler tube [...] Tank chill down (H2 boils off until tank is cold)" refers to the storage tank where they sub-cool the hydrogen, otherwise cooling Skylon with helium seems like an unneeded step.

Liquid helium would be the only substance COLDER than LH2 so if they cool to Liquid Helium temperatures but that's a lot of helium to be running through the system and then recycling. And it still only delays the boil off. Enough to meet their ops deadline? Maybe, that's what REL thinks but others don't see it that way.

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Simply put, until REL shows a zero-boil off storage tank made of flight-weight materials and shows no "boiling" for two full hours no one who has worked with LH2 on a consistent basis is going to take the assumption seriously.
It's conceptual operations of a conceptual vehicle. If a top-up and vent hose had to be used, no one would have batted an eyelid - but these people who have spent decades working with the thermodynamic properties of hydrogen seem to think it wont be needed - if it turns out they're wrong they have egg on their face, ConOps needs revising, infrastructure costs go up, and some mass margin is lost - but the vehicle concept probably remains valid.
I guess that's a step along from no-one taking the idea seriously because intake air would be too hot, or no-one taking the idea seriously because precoolers are too slow, or no-one taking the idea seriously because precoolers are too heavy, or no one taking the idea seriously because undercarriage would be too heavy.

That's actually part of the problem as a whole, it IS a "conceptual" operations suggested for a "conceptual" vehicle and it's the fact that with all their experience working with the thermodynamic of hydrogen they are suggesting none of the proven and trusted technological solutions from "decades of practical work with the thermodynamics of hydrogen" are applicable to their concept :) Specifically it's "our design is so different" that has people worrying over their design as if it's that different it should be "provable" with a working prototype. They did it with the heat exchangers did they not?

Given that the outcome of an unvented tank with "boiling" cryogenic fluid in it is a bomb waiting to go off it's not unreasonable to want to see a working example before you commit to accepting the statement.

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I for one have noted that REL seems to be confusing/conflating "pre-cool" with "sub-cool" of the LH2 which btw runs into "slush-hydrogen" operations which seems to be what they are talking about rather than "pre-cooling".
REL or commentators?
My understanding is they precool Skylon, before filling it with sub-cooled hydrogen, where sub-cooled means significantly below the boiling point of hydrogen, but above freezing.

"Below the boiling point but above freezing" is in fact the usual definition of "slush" hydrogen used in most cases hence my question.

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 #1198 on: 01/25/2016 11:41 PM »
"Below the boiling point but above freezing" is in fact the usual definition of "slush" hydrogen used in most cases hence my question.
That is a very suspicious definition.  :(

"Slush" Hydrogen is a very specific term for a 2 phase mix of liquid and solid Hydrogen, IE Hydrogen below the melting point of Hydrogen. IE c14K. IOW like a slush puppy desert.

"Sub cooled" Hydrogen would be LH2 cooled below it's normal (IE 1 atm pressure) boiling point, but remaining single phase.
A system "pre cooled" would be a system flushed with a cold fluid to bring the system down to the LH2 storage temperature. If the system is sealed then while it's quite high volume the fluid can be recovered and re-circulated.
Obviously GHe is the choice for this fluid but making it possible for a re-circulation path to cool the whole of the system is a design issue, not exactly cutting edge thermodynamics.

Of course it will take good HX design to cool the He, but since that's REL's core skillset I think that won't be a problem.

Please note Skylon propellant tanks are designed to be suspended from low themal conductivity and fixed at one end, so they can grow and contract with minimal structural resistance, and minimal heat leaks into the tanks.

Anyone who wants to know the scale of the problems shoudl figure what it takes to lower several tonnes of Aluminum alloy (or several tonnes of inconel, to represent the engines) to the necessary temperature, and once there how fast it would heat up.

BTW NASA have done a number of studies on Zero Boiloff Tankage.

IIRC the key issue was ensuring the inlet spray bars remained submerged to avoid either +ve or -ve pressure spiked (IE tank collapses).
"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 #1199 on: 01/26/2016 08:24 PM »
I thought it referred to hydrogen at it's triple-point of 14.01 K
Indeed.

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.

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.

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.

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?

I'll note a few points.

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

Alan Bond noted that LH2 has a SHC 4xs that of water (already excellent, given most chemicals with its molecular weight are either gases or low BP liquids).

Those extra degrees of sub cooling give a large cushion (coupled with the heat the hardware would have to absorb before it gets to the propellant. Call it 2GJ before LH2's heat of vaporization would be needed to vaporize and the pressure rise, excluding similar benefits due to sub cooling LOX.

Leaving cryogenic tanks sealed indefinitely without active cooling would clearly be very difficult but that is simply not the case here.  The time frame is very tightly limited. With enough thermal mass it sounds very unlikely to me that a 2 hr hold on runway would not be possible.
"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.

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