Author Topic: The Reaction Engines Skylon Master Thread (4)  (Read 339892 times)

Online Chris Bergin

Fourth thread for Reaction Engines/Skylon.

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Offline lkm

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Re: The Reaction Engines Skylon Master Thread (4)
« Reply #1 on: 06/14/2014 07:12 PM »
There's a nice write up of the recent UK launch Symposium here that we were talking about earlier. It talks about Skylon, spaceports and the small sat launcher.

http://seradata.com/SSI/2014/06/uk-launch-symposium-patriotic-rocket-scientists-want-to-put-britain-back-into-launch-business-but-know-that-affordability-is-the-key/

The author's suggesting that REL should design an orbital test vehicle with a small payload rather than Blue Boomerang made me wonder whether that was even possible, given the scaling issues stated what's the smallest engine size the SABRE engine could be reduced to without massive extra development?
« Last Edit: 06/14/2014 07:12 PM by lkm »

Offline john smith 19

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Re: The Reaction Engines Skylon Master Thread (4)
« Reply #2 on: 06/14/2014 08:40 PM »
There's a nice write up of the recent UK launch Symposium here that we were talking about earlier. It talks about Skylon, spaceports and the small sat launcher.

http://seradata.com/SSI/2014/06/uk-launch-symposium-patriotic-rocket-scientists-want-to-put-britain-back-into-launch-business-but-know-that-affordability-is-the-key/

The author's suggesting that REL should design an orbital test vehicle with a small payload rather than Blue Boomerang made me wonder whether that was even possible, given the scaling issues stated what's the smallest engine size the SABRE engine could be reduced to without massive extra development?
I think Hempsell mentioned this with regard to plans for the SCEPTRE engine. They were going with a it being pressure fed because the the development programme for the LH2 turbopump was expected to be 200m alone.

High pressure LH2 pumps scale down badly and you can't do a different design to the full size one otherwise it wouldn't be a test, it'd be a completely different engine. I'm guessing at some point someone had a lightbulb moment and thought "Why bother, let's just build the full scale test engine since most of the cost is in the design the actual mfg is (relatively) an incremental increase."

IIRC Hempsell talked about a pump of 250-500K RPM for a small engine. That is tough (air bearings were hitting 250K RPM in the late 90's).

Listening again to the video he actually refers to two engines on a stand by  2018. 1st flight to orbit 2021.

But at 1:08:00onward he talks about possibilities for "leap frogging" some of the early flight development programme. REL stated the 1st prototype was unlikely to be orbit capable, partly because it would be used for inlet development.

My instinct is that somehow someone has worked out a way to do that process with the ground test engines, so the inlet design is frozen before the first Skylon takes off.

I would also hope that covers the full speed up to the airbreathing to rocket transition, another element that looked to be needing flight test to finally confirm it. 
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Offline lkm

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Re: The Reaction Engines Skylon Master Thread (4)
« Reply #3 on: 06/14/2014 09:28 PM »
There's a nice write up of the recent UK launch Symposium here that we were talking about earlier. It talks about Skylon, spaceports and the small sat launcher.

http://seradata.com/SSI/2014/06/uk-launch-symposium-patriotic-rocket-scientists-want-to-put-britain-back-into-launch-business-but-know-that-affordability-is-the-key/

The author's suggesting that REL should design an orbital test vehicle with a small payload rather than Blue Boomerang made me wonder whether that was even possible, given the scaling issues stated what's the smallest engine size the SABRE engine could be reduced to without massive extra development?
I think Hempsell mentioned this with regard to plans for the SCEPTRE engine. They were going with a it being pressure fed because the the development programme for the LH2 turbopump was expected to be 200m alone.

High pressure LH2 pumps scale down badly and you can't do a different design to the full size one otherwise it wouldn't be a test, it'd be a completely different engine. I'm guessing at some point someone had a lightbulb moment and thought "Why bother, let's just build the full scale test engine since most of the cost is in the design the actual mfg is (relatively) an incremental increase."

IIRC Hempsell talked about a pump of 250-500K RPM for a small engine. That is tough (air bearings were hitting 250K RPM in the late 90's).
As I understand it each SABRE has two sets of turbopumps making effectively two rocket engines fed by one heat exchanger and compressor, could they perhaps at the very least  make a half scale engine with just one set of full size  turbopumps and only two combustion chambers and a half size heat exchanger? That could maybe allow something quarter scale, apart from the fact you've now got a mini HOTOL.

Listening again to the video he actually refers to two engines on a stand by  2018. 1st flight to orbit 2021.

But at 1:08:00onward he talks about possibilities for "leap frogging" some of the early flight development programme. REL stated the 1st prototype was unlikely to be orbit capable, partly because it would be used for inlet development.

My instinct is that somehow someone has worked out a way to do that process with the ground test engines, so the inlet design is frozen before the first Skylon takes off.

I would also hope that covers the full speed up to the airbreathing to rocket transition, another element that looked to be needing flight test to finally confirm it. 

When I heard that what came to my mind was the opportunity of hypersonic testing in USAF wind tunnels as part of a follow on to the CRADA contract. Perhaps they're stuck considering the ITAR implications of that, which is partly why it's only an exciting possibility they can't talk about.
« Last Edit: 06/14/2014 09:40 PM by lkm »

Offline john smith 19

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Re: The Reaction Engines Skylon Master Thread (4)
« Reply #4 on: 06/14/2014 10:03 PM »
As I understand it each SABRE has two sets of turbopumps making effectively two rocket engines fed by one heat exchanger and compressor, could they perhaps at the very least  make a half scale engine with just one set of full size  turbopumps and only two combustion chambers and a half size heat exchanger? That could maybe allow something quarter scale, apart from the fact you've now got a mini HOTOL.
HOTOL did not work largely as a result of having a single engine at the back. The best you could do would be a 1/2 thrust Sklon.

But now you've got to design a new compressor and nacelles and fuselage, just for a test vehicle.

This is the argument for not doing a sub scale SABRE applied to the vehicle as well.  :(
Listening again to the video he actually refers to two engines on a stand by  2018. 1st flight to orbit 2021.

But at 1:08:00onward he talks about possibilities for "leap frogging" some of the early flight development programme. REL stated the 1st prototype was unlikely to be orbit capable, partly because it would be used for inlet development.

My instinct is that somehow someone has worked out a way to do that process with the ground test engines, so the inlet design is frozen before the first Skylon takes off.

I would also hope that covers the full speed up to the airbreathing to rocket transition, another element that looked to be needing flight test to finally confirm it. 
Quote
When I heard that what came to my mind was the opportunity of hypersonic testing in USAF wind tunnels as part of a follow on to the CRADA contract. Perhaps they're stuck considering the ITAR implications of that, which is partly why it's only an exciting possibility they can't talk about.
Possible. And given the huge ability of the US ITAR rules to throw a spanner in the works for sales they should look at such "help" long and very hard.  :(
« Last Edit: 06/15/2014 05:44 AM by john smith 19 »
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Offline lkm

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Re: The Reaction Engines Skylon Master Thread (4)
« Reply #5 on: 06/14/2014 11:25 PM »
As I understand it each SABRE has two sets of turbopumps making effectively two rocket engines fed by one heat exchanger and compressor, could they perhaps at the very least  make a half scale engine with just one set of full size  turbopumps and only two combustion chambers and a half size heat exchanger? That could maybe allow something quarter scale, apart from the fact you've now got a mini HOTOL.
HOTOL did not work largely as a result of having a single engine at the back. The best you could do would be a 1/2 thrust Sklon.

But now you've got to design a new compressor and nacelles and fuselage, just for a test vehicle.

This is the argument for not doing a sub scale SABRE applied to the vehicle as well.  :(

While the HOTOL design did suffer significant problems, as a sub-scale Skylon test bed it would have a pretty big advantage over the original HOTOL in that as an engine test bed it doesn't actually have to work well. The purpose isn't to get lots of mass to orbit but to have an airframe you can stick a test engine to, and if you can practice building it in a similar manner to Skylon then even better and if it can actually make orbit, that's just extra. HOTOL didn't have such conditions.

Offline simonbp

Re: The Reaction Engines Skylon Master Thread (4)
« Reply #6 on: 06/15/2014 03:54 AM »
Possible. And given the huge ability of the US ITAR rules to throw a spanner in the works for sales they should look at such "help" long and very hard.  :(

Maybe. The tunnel that comes to mind is at AEDC in Tullahoma, which does have have decades of experience in testing engines and satellites for non-US companies. Including once sticking an entire Alpha Jet (sans wings) in the big supersonic tunnel and turning its engines on.

That's not to say it would be easy, but ITAR does make it much easier to bring technology into the US than to remove it. So, bringing a SABRE to the US for testing wouldn't be that hard. Returning the test data to the UK so REL can use it would be the paperwork nightmare.

Offline john smith 19

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Re: The Reaction Engines Skylon Master Thread (4)
« Reply #7 on: 06/15/2014 06:27 AM »
While the HOTOL design did suffer significant problems, as a sub-scale Skylon test bed it would have a pretty big advantage over the original HOTOL in that as an engine test bed it doesn't actually have to work well. The purpose isn't to get lots of mass to orbit but to have an airframe you can stick a test engine to, and if you can practice building it in a similar manner to Skylon then even better and if it can actually make orbit, that's just extra. HOTOL didn't have such conditions.
Actually he's advocating a sub orbital test vehicle that can be extended to an orbital vehicle, so yes it does matter.

The problem is that SABRE has some parts that are difficult to sub divide. The front end compressor being the big one.

Previously REL had considered a sub orbital Nacelle Test Vehicle for fine tuning the nacelle, inlets and (I think) the ramjets. It was a scaled down Skylon but purely rocket driven. That AFAIK has been superseded by the Valkyrie test vehicle to confirm nozzle flow and thermodynamics over a critical part of the speed/altitude profile (it can't test all of it because that would make an orbital vehicle in its own right). I would presume that's because their confidence levels in their understanding of those issues has risen to the point where they feel the uncertainties can be coped with on a full size vehicle.

The idea of building a small size SABRE/Skylon sounds good but you get all of the trajectory problems (in fact you get a few more as some drag terms scale badly with reducing size) but only a fraction of the revenue.  :(

Even if you succeeded in chopping a full SABRE in half you've got to design a vehicle around it. That's a lot of work to run over the full trajectory.  :(

But REL don't want to design a vehicle around it. They want to be in the engine business. :(

I suggest  you start a new thread about making a small launcher (RLV or ELV). Doing so you'd have to keep in mind a couple of things.

1) The article suggests people would pay no more than $5m a launch but IIRC prices for secondary payloads on Ariane 5 are around $100k for a single 100Kg slot.
2) Historical data suggests it won't launch more than 1-2 times a year.
3) LH2 is not a good choice for small vehicles. It's an extreme cryogen. 
4) Historically range costs have been fixed regardless of launcher size.
5) Hypergols have gotten much more expensive (last time I checked the Hydrazines were around $60/lb) but it's all their associated costs. Comm sats use them and have sunk the costs of using them, but small sats don't.

It's a tough problem in its own right. Basically anyone seriously looking at this has to start from the price and work backward. The key point is that with such low prices and launch rates your development programme has to be very low cost. How you do that is highly non trivial.

 [EDIT It can often take a lot of very clever analysis to show that something that looks stupidly primitive will actually work. Mass wise the electronics is the easy bit. My instinct is to use clusters of largish diameter plastic pipe (flanged for simplicity, flat ended for cheapness) but that has LOX compatibility issues (NOX? HTP?), common bulkheads, common propellants. Flanges mean you can bolt stuff together (and bolt the engine on the bottom tank). Frankly I'd look at the kind of strapping they use to hold tarpaulins on flat bed trucks to keep it together.  Crude, primitive, OTRAG like, but cheap  :( and anyone who wants to do this had better have that word at the front of their minds. Likewise anyone thinking "solid fuel" should know they are at the mercy of the solids mfg for pricing. I think there might be room for a powdered coal (in binder) / liquid oxidizer hybrid as well (burns pretty clean).  :(  But again this doesn't really have anything to do with Skylon so better in another thread.]

It's also not really SABRE/Skylon related anymore.
« Last Edit: 06/16/2014 10:13 AM by john smith 19 »
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Offline RanulfC

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Re: The Reaction Engines Skylon Master Thread (4)
« Reply #8 on: 06/16/2014 01:55 PM »
I wrote:
Quote
The "math" says that a rocket-powered SSTO vehicle will (without some sort of "cheat" involved) be capable of putting less than 1% of its Gross-Lift-Off Mass (GLOW) into orbit. That's if everything works exactly right. Skylong "cheats" by being airbreathing and not having enough "thrust" under the pure-rocket powered equation. But because it IS airbreathing but does NOT have as much "penalty" mass as a mixed or duel mode power system it is supposed to get a much higher mass fraction overall. Multiple stage vehicles can always get more mass to orbit simply because they ARE multiple stages, and expendables more-so because they are in fact expendable and don't carry any mass penalty for recovery systems.

Uccello wrote:
Quote
Nonsense. REL is paradigm shifting. Is not spike-SSTO, it is something different. If the heat exchanger works properly, the vehicle works. If sabre doesn't work as advertised, then we have another engineering dud.

While I agree that what REL is doing IS a "paradigm" shift in many ways, I'm afraid the "math" still applies and is not nonsense :) SABRE and Skylon are going to take a bit more work to "fit" into the rocket-equation, however as JohnSmith 19 notes in their case how they fit it take some work. In one respect the fact that SABRE is in fact an "airbreathing" rocket engine makes some of it easier, but in most cases the need to know at each step what the air-conditions are and how they effect engine operations is quite a pain.

As John Smith 19 points out (and as I've pointed out to him and others on the thread over an over again) "airbreathing" SSTO's of both vertical and horizontal nature have been proposed before and in most cases the "airbreathing" system was partially or fully seperate from the rocket system. In most cases where they were "combined" into Rocket Based Combined Cycle engines the rockets were still fed from tanks of stored propellant and for the longest time the only "answer" seen was to turn part of the "processed" air for these engines into "Liquid-Air" (Liquid Oxygen actually) during flight to restore and replenish the stored LOX in the system.

It made "sense" since you were using Liquid Hydrogen and the deep cooling "sink" it provided could liquify the oxygen out of air easily... A bit less so when you're travelling at Mach-5, but realtivly...

The entire idea was to allow the use of future "super-high" pressure injection rocket engines that were being discussed at the time. "Normal' compression whether ram or turbine would not be enough and in order to use "highs-speed" rocket turbopumps the "fluid" had to be liquid.

Along with the "assumptions" about how easy it would be to build operational SCramjets, the problem with the Liquid Air Cycle Engines (LACE) was that they tended to be heavy, complicated and prone to operational break down. Worse, to get proper "LACE" operations turned out to require more Liquid Hydrogen than had been assumed and since it was to much to "burn" in the engines that meant dumping it over-voard and "wasting" it...

RELs major "idea" was figuring out that the supposed "pressure" issue wasn't nearly as bad as it had been thought to be. Turned out that "liquid" rocket engines work best when the propellants are at or near a "gasous" state when they are injected into the combustion chamber. And if you don't assume that super-high injection pressure is required you don't need to have a "liquid" to compress and can actually inject dense AIR into the combustion chamber! Suddenly you have what no previous rocket engine designer had thought possible:
You've got an actual "Airbreathing" rocket motor! If that same motor will run on both Liquid Hydrogen and Air and LH2 and LOX then you have a SINGLE engine that is capable (in theory) of running from ground to orbit with almost NO "extranious" mass! Super-huge "shift" in how the rocket equation "works" at this point.

Randy
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Offline RanulfC

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Re: The Reaction Engines Skylon Master Thread (4)
« Reply #9 on: 06/16/2014 02:04 PM »
Avron wrote:
Quote
Wondering why SSTO has anything to do with Skylon.. all the maths etc and VTOL are irrelevant, I just don't see any relationship

First of all the Skylon is a "Single-Stage-To-Orbit" vehicle so the math does matter since it has to go to orbit using a modified rocket-equation. What doesn't "matter" as much is VTOL/HTOL etc as major factor.

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 (4)
« Reply #10 on: 06/16/2014 04:00 PM »
I wrote:
Quote
Again, "worthwhile" payload comes with a lot of baggage attached, and is especially dependent on what that baggage is  300lbs to orbit doesn't "sound" worthwhile but consider the first specified requirements for an "operational" aircraft were not much different it suddenly doesn't seem quite as bad

John Smith 19 wrote:
Quote
Well in a lot of cases that would have been one man and no sandwich.
Quote

 :) Well, no actually it was something like "two-men" and a hundred pounds of gear. Basicly pilot, observer and their "kit" as the definition of "worthwhile" payload... But I suspect you get my meaning :)

I wrote:
Quote
But then again I'm one of the folks who believes that access will cause major changes in "paradigms" more than any particular system. Having something launched into orbit every day for a year, whether it was in the "perfect" launch system or one that "gets-by" would be just about as world changing as Skylon IMHO!

John Smith 19 wrote:
Quote
The trouble is the first customers want something that can do what they already do, whereas that approach requires establishing a market, which makes investors very nervous.

Maybe. I'd say the way has been paved for more "experimentalism" in approaches but the economy still has to bounce back enough for their to be lots of "spare" money to get some of the wilder ideas going :)

john smith 19 wrote:
Quote
I think you're right. If someone could demonstrate the claim "This RLV can put X Kgs into an A Km orbit at the launch site inclination, X - f(inclination) Kg in an equatorial inclination and X - f2(inclination) Kg in a polar orbit with N ground crew to turn it round in D days when you like" as long as X was not too  small and the price not too large quite a lot of people would be interested.

Putting actual numbers on X, D, f() and f2() that customers would accept is however hard  .

If it delivers what a sufficient group of customers consider "reasonable" regardless of implementation they'd buy one. But my instinct is this is so phenomenally risky by VC standards no one would touch it with a barge pole.  You'd have to fund it yourself.

Spacex's business plan is sort of 50% of this. Any launch site you like as long as long as it's on a US launch range and they do the actual launching on their schedule.

And I'm still thinking that "worthwhile" payload for demonstration purposes may not be as "big" as most people think :)

john smith 19 wrote:
Quote
I'm a bit slow and it's just occurred to me that all current LV's are railways, not ships (which can go to any suitable port, or even piece of coast line in a pinch). You start from stations (launch sites) you hand yourself or your "luggage" over to them and from then on you have no say in how it gets where you want it to go.

But Skylon would be a car.

No I'm afraid it would still be a "train" mostly due to the lack of "locations" it can go and how it has to adhere to a schedule... But it will be a much more often "aviailable" train with a larger schedule at least and with a much higher level of "user" input :)

Car and Plane "personal" transportation is still quite a good ways off :)

Randy
« Last Edit: 06/16/2014 04:02 PM by RanulfC »
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 Space OurSoul

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Re: The Reaction Engines Skylon Master Thread (4)
« Reply #11 on: 06/16/2014 05:45 PM »
On a completely different and very, very serious note:

While reading Alastair Reynolds' sci-fi ("Redemption Ark", in this case), I noted that his "lighthuggers" bear a strong resemblance to our favourite ship. See attached.

The engines are known as "Conjoiner drives" ("Conjoiners" referring to the faction who built the drives, not referring to how they work). The Conjoiners guard the secret of the drives most closely, and I couldn't help but smile at the similitude with REL's guarding of the frost-control mechanism, and at the notion of "conjoiner" referring to the melding of a rocket and an air-breather.

That is all. As you were.

A complete OurSoul

Offline lele

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Re: The Reaction Engines Skylon Master Thread (4)
« Reply #12 on: 06/16/2014 06:02 PM »
Does the new joint venture between Airbus and Safran to develop Ariane 5ME and Ariane 6 mean that they aren't interested in manufacturing Skylon ?

Offline john smith 19

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Re: The Reaction Engines Skylon Master Thread (4)
« Reply #13 on: 06/16/2014 07:56 PM »
Does the new joint venture between Airbus and Safran to develop Ariane 5ME and Ariane 6 mean that they aren't interested in manufacturing Skylon ?
Interesting question.

The Astrium "roadmap" for Ariane 5 Midlife Evolution & Ariane 6 ends at 2024

Given that A6 is meant to be made up mostly of 4 identical solid stages capped with a Vinci upper stage (3rd or 4th stage, depending on how you number them) it will share with A5ME I'm guessing that should happen  within 3 years.

Retiring A5 leaves AIr Liquide (who do a lot of the cryogenic work on A5) out in the cold.

This joint venture could be viewed as tidying away all the Astrium A5 stuff into the new joint venture (BTW while this might look sort of like the ULA, it isn't as Saffran is not the A5 prime contractor (That's "ELV Spa.") Although both Astrium and Saffran are trying to buy Avio Spa, who are a major subcontractor to ELV.

But let's say Saffran buys Avio that leaves the rest of Astrium free to look at "new business" as the A5 stuff winds down.

so we have staff with LV construction and design skills (not dedicated to A5) and a company with a large cryogenics facility in Kourou at a loose end.

Personally my instinct is that no company has experience with these airframe materials, but an airframe, rather than a VTO LV company would be a better bet.

So at the very least we have Air Liquide as a possible French supporter looking to get the tank and cryo management work, Astrium neutral or positive (as they've hived off A5 to the subsidiary) and DLR who like the Skylon aerothermodynamics and have significant RCC experience.

2024 is looking to be quit an interesting year.
BFS. The worlds first Methane fueled FFORSC engined CFRP structured A380 sized aerospaceplane tail sitter capable of flying in Earth and Mars atmospheres. BFR. The worlds biggest Methane fueled FFORSC engined CFRP structured booster for BFS. First flight to Mars by end of 2022. Forward looking statements. T&C apply. Believe no one. Run your own numbers. So, you are going to Mars to start a better life? Picture it in your mind. Now say what it is out loud.

Offline john smith 19

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Re: The Reaction Engines Skylon Master Thread (4)
« Reply #14 on: 06/16/2014 08:19 PM »
Worse, to get proper "LACE" operations turned out to require more Liquid Hydrogen than had been assumed and since it was to much to "burn" in the engines that meant dumping it over-voard and "wasting" it...

RELs major "idea" was figuring out that the supposed "pressure" issue wasn't nearly as bad as it had been thought to be. Turned out that "liquid" rocket engines work best when the propellants are at or near a "gasous" state when they are injected into the combustion chamber. And if you don't assume that super-high injection pressure is required you don't need to have a "liquid" to compress and can actually inject dense AIR into the combustion chamber! Suddenly you have what no previous rocket engine designer had thought possible:
You've got an actual "Airbreathing" rocket motor! If that same motor will run on both Liquid Hydrogen and Air and LH2 and LOX then you have a SINGLE engine that is capable (in theory) of running from ground to orbit with almost NO "extranious" mass! Super-huge "shift" in how the rocket equation "works" at this point.
I think REL may have come at it from the other end. Bond worked on the Rolls Royce RZ20, a LO2/LH2 engine (which also replaced the hand brazing of the Gamma 8 with furnace brazing, at much more reliable quality, a lesson the RL10 builders apparently never learned).

He was probably also aware that real engines (outside text books) do use supercritical injection, in temperature, pressure, or both. Likewise when you look at the heat of vaporization for air (compared to how much energy you have suck out to get it to  the vaporization temperature (or the liquefaction temperature of coming at it from the vapor direction) you realize it's huge just at sea level (and only going up as the speed climbs toward M5)  :( This suggests a few design directions.

1) Never liquify, deeply cooled is good enough.
2) Not liquifying cuts the excess LH2a lot. So why in fact try to do anything with all that GH2 you've created at all?

But the joker in the pack is frost, because as any child with a grade school Physics education can deduce any heat exchanger with LH2 in its pipe being hit by moist air will instantly freeze solid. QED Idea is DOA.  :(

The difference between the superficial understanding of frost formation and what really happens is the difference between giving up before starting and pursuing a 30 year quest (the HOTOL lab work was done in the early 80's) to make the precooler work. :(

A little theory is a very dangerous thing, in the hands of the clueless.  :(
« Last Edit: 06/16/2014 08:27 PM by john smith 19 »
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Offline Jim

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Re: The Reaction Engines Skylon Master Thread (4)
« Reply #15 on: 06/16/2014 08:37 PM »

I think REL may have come at it from the other end. Bond worked on the Rolls Royce RZ20, a LO2/LH2 engine (which also replaced the hand brazing of the Gamma 8 with furnace brazing, at much more reliable quality, a lesson the RL10 builders apparently never learned).


you don't know that.  You don't know all the reasonings going into RL-10 production decisions.
Also, You have a habit of using hindsight to criticizing decisions made by others years ago. 


Offline RanulfC

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Re: The Reaction Engines Skylon Master Thread (4)
« Reply #16 on: 06/16/2014 08:49 PM »
I think REL may have come at it from the other end. Bond worked on the Rolls Royce RZ20, a LO2/LH2 engine (which also replaced the hand brazing of the Gamma 8 with furnace brazing, at much more reliable quality, a lesson the RL10 builders apparently never learned).

Being "fair" the folks that build the RL-10 never really HAD to "learn"  differently as there wasn't a great demand for the RL10 even when there is :) The Gamma-8 on the other hand was "supposed" to be mass-producable which is a "lesson" that most American aerospace has never bothered to learn because it is never supposed to happen :)

Quote
He was probably also aware that real engines (outside text books) do use supercritical injection, in temperature, pressure, or both. Likewise when you look at the heat of vaporization for air (compared to how much energy you have suck out to get it to  the vaporization temperature (or the liquefaction temperature of coming at it from the vapor direction) you realize it's huge just at sea level (and only going up as the speed climbs toward M5)  :(

Again being fair pretty much everyone who supported or worked on LACE systems was well aware of the injection interface of a rocket engine, the problem is they weren't LOOKING at the process at that point but further back at the point where everything goes through the TURBOPUMPS which, (again TBH) was liquid in every circumstance.

The "assumption" that baised all that research and study was simply one of those little "paper-viruses" that crop up when no one takes the time or effort to "question" the "expert" opinions of the time.

Quote
1) Never liquify, deeply cooled is good enough.
2) Not liquifying cuts the excess LH2a lot. So why in fact try to do anything with it at all?

"The" problem of course is hind-sight is alway so perfect but IN that time/place not so much :) Turbo-compression was never going to get into the ranges that were being discussed for LH2/LOX rockets for SSTO flight so there was no thought of using the LH2 to simply "deep-cool" the air. That wouldn't have worked to get it to the level needed so a turbopump could compress it properly... Which of course is all fine, dandy, and makes logical sense as long as you make that nice simiple "basic" assumption the the oxydizer has to be compressed by a turbopump...

And you "use" the LH2 because it was always assumed you'd have only ONE fuel (and that would be Liquid Hydrogen) on-board so it SHOULD be used for everything... As I recall one scientist was specifically quoted as saying "Once we have hydrogen fueled rockets we can do anything!" despite its well known, (even then) issues involved. Bias can be blinding if one isn't careful :)

Quote
But the joker in the pack is frost, because as any child with a grade school Physics education can deduce any heat exchanger with LH2 in its pipe being hit by moist air will instantly freeze solid. QED Idea is DOA.  :(

Actually while its a "joker" its not a show-stopper because it CAN be done. That was proven in the 1960s during the original LACE work, more so now with RELs method. Frost is a problem for many cryo systems not just LH2 so "QED" isn't always the best argument to have :)

Randy
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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 (4)
« Reply #17 on: 06/16/2014 09:16 PM »

I think REL may have come at it from the other end. Bond worked on the Rolls Royce RZ20, a LO2/LH2 engine (which also replaced the hand brazing of the Gamma 8 with furnace brazing, at much more reliable quality, a lesson the RL10 builders apparently never learned).


you don't know that.  You don't know all the reasonings going into RL-10 production decisions.
Also, You have a habit of using hindsight to criticizing decisions made by others years ago.

While I tend to agree with the second part of the first statement, and agree with second part of your statement I believe that JS19 has a point about the "mentality" behind the decisions on manufacturing differences between the RL10 and Gamma-8 being pretty obvious. (Even though I'd question the basic comparision between an H2O2/Kero and LOX/LH2 engines as working with LH2 as a "fluid" is far more difficult that either H2O2 or Kerosene)

The British started with the "assumption" that thier rockets were going to be "industrial" produced items where in the US the "decision" was made to build and assemble rockets as "specialty" items even when  produced in quantity. The difference in manufacturing and design criteria are obvious and quite startling to examine closely. The Brits set out to mass produce rockets while the US was going to apply "industrial" methods to producing high performance rockets. A subtle but definate differenace that shows in subsequent production.

As far as I'm aware the "decision" to hand-braze the RL10 is STILL not questioned beyond the possible "switch" to 3D printing should production continue, but the last I'd heard is that even IF production continues it will probably REMAIN hand-brazed as production would never justify the "switch" to 3D printing.

On the other hand the production decision on the Gamma-8 was to SWITCH as soon as a more practical method was found because hand-brazing was man-hour intensive and the fact that furnace-brazing was found to produce a higher quality, fewer defect product was a secondary bonus.

"Maybe" furnance brazing isn't a "choice" available to someone working on an LH2/LOX engine, maybe... But maybe not and besides what evidence is there that hand-brazing is the ONLY technique that works with LH2.LOX engines? This is far from the only example where decisions that effect "rocket" engineering seem to be biased towards making production "harder" than it has to be and it is an obvious trend in American aerospace itself that remains unquestioned on many levels.

No we do not in fact "know" what drives each decision made, but maybe its time the "reasons" WERE questioned and maybe some bias' and assumptions exposed to the light of day?

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 (4)
« Reply #18 on: 06/16/2014 09:35 PM »
you don't know that.  You don't know all the reasonings going into RL-10 production decisions.
Also, You have a habit of using hindsight to criticizing decisions made by others years ago.
REL staff participated in the RZ20 programme. It's mentioned on some of their later presentations.
The use of furnace brazing and the view that it was a great advance over the hand brazing used to construct the combustion chamber earlier engines is also mentioned in the presentation.

Prefacing a comment by the words "I think" and "apparently" imply I'm making a qualified statement. AFAIK (that's also a qualification, or would you prefer "IMHO" ? ) the RL10 is still made by hand brazing the tubes. Yes I am aware that a skilled panel beater with a wooden mallet can mfg the fenders (indeed most of the body work) of a Morgan sportscar.

And 20 years ago they did.

Today they are laser cut and blown up using a superplastic forming process.

Morgans are low volume and high cost luxury items but they have moved on.

Just as a skilled panel beater could wrap those tubes round a former and make a chamber.
Now in 1959 I'm sure the choices were not so clear. Fair enough.

Historically the aircraft industry has moved from a "shim to fit" approach (some people call it "coach building") where in fact all the copies of a particular model were just a little different to one where parts are made with tight enough precision that you really can take the wings off one and fit them to another. That did not happen overnight but has evolved through generations of vehicles.

This "old school" style construction came back to bite the British big time when they decided to rebuild their Nimrod aircraft and decided to use the first rebuild to setup the jigs for the rest.

None of them matched and the project has been a very expensive fiasco.  :(

Which suggests (that's another qualification word BTW)  the RL10 is a 1950's designed engine that's made in a 1950's way.

At 2014 prices.  :(
BFS. The worlds first Methane fueled FFORSC engined CFRP structured A380 sized aerospaceplane tail sitter capable of flying in Earth and Mars atmospheres. BFR. The worlds biggest Methane fueled FFORSC engined CFRP structured booster for BFS. First flight to Mars by end of 2022. Forward looking statements. T&C apply. Believe no one. Run your own numbers. So, you are going to Mars to start a better life? Picture it in your mind. Now say what it is out loud.

Offline SteveKelsey

Re: The Reaction Engines Skylon Master Thread (4)
« Reply #19 on: 06/16/2014 09:36 PM »
I am conscious of the expertise and experience owned by the members of this thread and so ask this question aware that it may be naive, however, isn't the descision to furnace braze a given in that the sheer number of joints on the heat exchanger module and the fine size of the tubes make hand brazing impossible, or at least impossibly expensive?
2001 is running a little late, but we are getting there.

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