How about that. Our own Calum Douglas is surely the man to ask - his day job is Mercedes F1 engine design. I just pinged him, fingers crossed.

Funny, that, I was just watching Craig "Scarbs" Scarborough going over the Mercedes design on Peter Windsor's YouTube channel. It would certainly be nice to learn more but understandable if anyone directly involved didn't want to elaborate. The whole thing only seems to have come into light because Pat Symonds, CTO of F1 talked about it publicly.

Somewhat unclear to me what "technology developed by" Reaction Engines means, thermodynamics being universal but use cases not so much. RE might have some proprietary optimization or design software for heat exchangers, most likely this is about applying 3D printing, benefiting packaging, wall thicknesses, flow design and such. Scarbs indicated that there are also other teams who may have similar technology at their disposal, certainly the shaping of Williams' and Aston Martin's cars point to them having possibly adopted Mercedes' intercooler. Apparently Matt Morris, a former McLaren and Sauber designer is now at RE, as engineering director from what I could gather from a haphazard search, so a strong F1 link there.

Haven't kept too close tabs on Reaction Engines recently, perhaps worth a closer look again. Been waiting for them to progress into some kind of real world flight testing for a while.
 
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RE might have some proprietary optimization or design software for heat exchangers, most likely this is about applying 3D printing, benefiting packaging, wall thicknesses, flow design and such.
Their heat exchanger technology is the fundamental breakthrough that makes SABRE plausible. It can cool a hot afterburner exhaust to near-liquid-air temperatures in around 1-2 metres, at supersonic speeds. The manufacturing tech for extremely small tube diameters and wall thicknesses -and the assembly of same into a functional unit - appears to be their principal breakthrough. I think you will find it is a little more than a bit of 3D-printed refinement to current designs.
 
But temperatures in F1 don't really call for braised Inconel HX so the various 3D printed aluminium HXs (still thin wall, much more surface area, lower weight, less cost etc.) from other companies (e.g. Hexcel) are probably a better fit in this application?
 
the various 3D printed aluminium HXs (still thin wall, much more surface area, lower weight, less cost etc.) from other companies (e.g. Hexcel) are probably a better fit in this application?
That's not what the news items report; Mercedes presumably disagree with you.
 
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That's not what the news items report; Mercedes presumably disagree with you.
Everything in the news is always right...

Maybe its simply that REL are busy trying to find other applications for their niche technology and no other companies are that interested in this very niche market? As opposed to technical rationale.
 
Reaction Engines announced today that it is completing the placement of additional ground support equipment at its High Temperature Airflow Test Facility (TF2) in Colorado. The additional modifications to the Reaction Engines test facility will support expanded test envelopes of its revolutionary heat exchanger technology and thermal management solutions that are critical to aerospace, defense, energy, and transportation industries.


 
Talk by RE on the SABRE engine & spinoffs on the 7th June.
A brief introduction to Reaction Engines’ SSTO (Single Stage to Orbit) powerplant concept and a look at some of the recent commercial spinouts. SABRE (Synergetic Air Breathing Rocket Engine) is a class of propulsion system that can span the gap between gas turbines and rocket engines. If realised they could enable a revolution in space access and other high speed flight applications. During development, a number of breakthroughs have been made in lightweight and high temperature capable heat-exchangers, these are now finding applications in a diverse range of areas.

Peter Symes-Thompson is the technical lead for compact heat exchangers at Reactions engines. He has been at Reaction Engines since 2014 with roles in mechanical design, aerothermal analysis and testing of micro-tube heat exchangers on projects in space, motorsport and defence.
 
IIRC, when their capillary heat exchanger proved practicable, they commented that it was potentially as game-changing as the famous 'Lancashire Boiler'. Snag would be persuading potential users that it was worth the trouble...
 
It's just a tubular heat exchanger.

Tubular heat exchangers are the most common heat exchangers in the world, already for many decades. They are available in various sizes and shapes from many heat exchanger companies.

The only difference between REL and those other companies is that REL offers a tubular heat exchanger with 1 mm tubes that has no large scale applications due to it being too flimsy and sensitive to fouling and plugging.

Other companies make a profit by selling their exchangers, but REL can only survive by obtaining money from naive financiers who still seem to think that they are supporting a space company. In reality they are supporting a hopeless heat exchanger company.

Already for 33 years REL is fooling their financiers, and REL has become an expert in coming up with misleading propaganda again and again and keeping up appearances.

[Edit - removed some accusations of an unsubstantiated nature about Reaction Engines - Admin]
 
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Feels a bit harsh even for a sceptic like me.

REL primarily founded by people who wanted cheap space access. Had some expertise in thermodynamics and other areas. Invented some IP e.g. HX for high temperature applications. Now the originals folk have retired and the new ones are trying sell their IP to anyone who will listen but no one is buying because it's too niche. But "high speed" is "cool" so relatively easy to get high risk investment. Nothing criminal about it, just optimism / fantasy.
 
A really harsh assessment, I reckon deliberately missing out key achievements to project a negative opinion…. Why do that?

Consider that;-

1. RE have demonstrated a liquid nitrogen (née liquid hydrogen capable) heat exchanger that works with humid air and doesn’t ice up. It’s an achievement which has eluded airbreathing hypersonic engine wannabe’s for decades. Thus enabling hypersonic flight without carrying an oxidiser onboard and with an engine that’ll get to hypersonic without boosting. No one’s even come close before.

2. RE heat exchanger has been demonstrated operating successfully in the harsh environment present within an intake while the vehicle is in hypersonic flight;- another world first.

3 RE are currently developing a lightweight (flight
Worthy) helium turbine which will be demonstrated shortly. When complete yet another world first.

Space X technology rampage has rolled over the world wide launcher business and nobody’s quite sure where it will end up. One missed Starship catch could provide a powerful demonstrate the single point failure of significantly damaging the pad….. which halts the whole business for a considerable time. So it could be game on again for SSTO or maybe the next budding Musk see SSTO easy infrastructure as a way to roll over Space X.

Then there’s air breathing hypersonic’s;- DoD is funding the hypersonic intake demo. With Putin throwing down the hypersonic gauntlet, RE work could become very, very valuable.
 
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This is a technical discussion, and still yet it's running on a very reasonable level, I think.
So, please, wording should be appropriate and not slip into the kind of debate, we know
from political "discussions".
;)
 
Then there’s air breathing hypersonic’s;- DoD is funding the hypersonic intake demo. With Putin throwing down the hypersonic gauntlet, RE work could become very, very valuable.
I think there's definitely some useful spin offs from their IP. Maybe some high speed flight. Maybe some other sectors.

Definitely don't think space access is one of them because there isn't really a viable airframe concept to combine the engine with.
 
That problem with Skylon rear fuselage being destroyed by the engines noise ?
 
A really harsh assessment, I reckon deliberately missing out key achievements to project a negative opinion…. Why do that?

Consider that;-

1. RE have demonstrated a liquid nitrogen (née liquid hydrogen capable) heat exchanger that works with humid air and doesn’t ice up. It’s an achievement which has eluded airbreathing hypersonic engine wannabe’s for decades. Thus enabling hypersonic flight without carrying an oxidiser onboard and with an engine that’ll get to hypersonic without boosting. No one’s even come close before.

2. RE heat exchanger has been demonstrated operating successfully in the harsh environment present within an intake while the vehicle is in hypersonic flight;- another world first.

3 RE are currently developing a lightweight (flight
Worthy) helium turbine which will be demonstrated shortly. When complete yet another world first.

Space X technology rampage has rolled over the world wide launcher business and nobody’s quite sure where it will end up. One missed Starship catch could provide a powerful demonstrate the single point failure of significantly damaging the pad….. which halts the whole business for a considerable time. So it could be game on again for SSTO or maybe the next budding Musk see SSTO easy infrastructure as a way to roll over Space X.

Then there’s air breathing hypersonic’s;- DoD is funding the hypersonic intake demo. With Putin throwing down the hypersonic gauntlet, RE work could become very, very valuable.
1. Did they really?
They pretend they did but I never saw any real proof of that. Also I never heard of other parties trying to replicate that result using the method REL claims makes it possible.
Note also that patents don't prove anything. One can get a patent on any "invention" as long as it does not violate existing patents. One does not have to prove that the "invention" will actually work as advertised.
As a chemical engineer with 30 years of experience in process design I am sure that what they claim is impossible, but I will not bother you all with my technical arguments as I don't think REL believe their own propaganda anymore.
This is a screen shot that I made this morning of the REL website:

SABRE engine precooler.jpg

As everyone can see they don't mention -150 oC anymore but now just talk about cooling down to ambient temperature.

2. No they did not.
That "hypersonic" test was an even bigger farce. All they did was blow 1000 oC gas (jet engine exhaust) into a precooler that was cooled by atmospheric water inside the tubes. I don't think that the metal of the precooler got any warmer than 250 oC at the "hot" side and not colder than 100 oC at the "cold" side, while the pressure inside the tubes was only atmospheric. A far cry from the conditions the precooler metal would experience during actual hypersonic flight, which I estimate to be 950 oC at the hot side, -200 oC at the cold side, 200 bar inside, if the air would be cooled to -150 oC.
This test was just keeping up appearances. It had nothing to do with hypersonic.

3. A turbine is a turbine is a turbine.
It is irrelevant which gas runs through the turbine. The thermodynamics and mechanics are the same for every gas.
You should ask yourself: why is REL developing their own turbine? Why not outsource that to the professionals?

The same applies to the precooler: why is this company, that was founded 33 years ago to build a Skylon spaceplane, only tinkering with parts of the engine?
When Lockheed or Northrop or Boeing or Airbus design a new plane they don't design the engines themselves, they leave that to specialised companies like P&W, GE, RR, .... They certainly don't spend 33 years on merely some engine parts while the rest of the plane remains fiction.

REL has dragged this on for 33 years now without much to show for it, and they will drag it on another 33 years if given the chance by the financiers.
 
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It's just a tubular heat exchanger.

Tubular heat exchangers are the most common heat exchangers in the world, already for many decades. They are available in various sizes and shapes from many heat exchanger companies.

The only difference between REL and those other companies is that REL offers a tubular heat exchanger with 1 mm tubes that has no large scale applications due to it being too flimsy and sensitive to fouling and plugging.
Other companies make a profit by selling their exchangers, but REL can only survive by obtaining money from naive financiers who still seem to think that they are supporting a space company. In reality they are supporting a hopeless heat exchanger company.

Already for 33 years REL is fooling their financiers, and REL has become an expert in coming up with misleading propaganda again and again and keeping up appearances.

It is time that the financiers finally wake up and start a serious investigation into REL.
Such audit should not involve fanboys who will swallow any BS that REL feeds them, but be done by experienced design engineers who (like me) don't believe any of the REL propaganda, and (like me) are very suspicious about the real intentions of REL.

If such audit were conducted properly I suspect that it could be followed by a criminal investigation into the REL management, resulting in jail sentences, like Bernie Madoff after his Ponzi scam imploded.
Tubular heat exchangers with small diameters are beeing used quite succsessfully in racecars, millitary vehicle and some aircraft applications:


These coolers seem to be pretty robust, the question is how to get rid of the ice. Maybe they use a divece to scrap it off (a plate with little holes for the pipes), they reheat a segment of it or thy shake it somehow.

I'm not saying it will work or not..
 
I fear that our Dagger is overly blunt, in more ways than one.
Our admins got the worst hate speech redacted, but the zealous antagonism remains.
At a technical level, being a comical engineer does not qualify one in meteorology. Take for example that first claim, that "ambient" is a far cry from -150 deg C. SABRE's hypersonic regime with extreme intake heating will not begin until perhaps 40,000 ft (15 km). Here is a graph of atmospheric temperature with height. Note that at these heights ambient temperature falls to around 220 K, which is near enough -50 deg C. Of course, numbers such as these can only ever be approximate and some design margin is needed, so in cooling from 1,000 deg C, a safe design target of an additional 10%, i.e. around -150 deg C, is entirely consistent with "ambient".
486px-Comparison_US_standard_atmosphere_1962.svg.png


The rest of their little rants are filled with similar blunders, but I tire of this garbage.
 
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Ice free cryo heat X
1. Did they really?
They pretend they did but I never saw any real proof of that.
As a chemical engineer with 30 years of experience in process design I am sure that what they claim is impossible.

HTX
2. No they did not.
That "hypersonic" test was an even bigger farce. All they did was blow 1000 oC gas (jet engine exhaust) into a precooler that was cooled by atmospheric water inside the tubes. I don't think that the metal of the precooler got any warmer than 250 oC at the "hot" side and not colder than 100 oC at the "cold" side, while the pressure inside the tubes was only atmospheric. A far cry from the conditions the precooler metal would experience during actual hypersonic flight, which I estimate to be 950 oC at the hot side, -200 oC at the cold side, 200 bar inside, if the air would be cooled to -150 oC.


3. A turbine is a turbine is a turbine.
It is irrelevant which gas runs through the turbine. The thermodynamics and mechanics are the same for every gas.
You should ask yourself: why is REL developing their own turbine? Why not outsource that to the professionals?

The same applies to the precooler: why is this company, that was founded 33 years ago to build a Skylon spaceplane, only tinkering with parts of the engine?

1 Ice free Cyro heat X
Video of test below;- I’ve spoken with people who witnessed the test and confirmed it was liquid nitrogen in the pre cooler tube and no ice.

View: https://m.youtube.com/watch?v=wxdXLl9P62M


Why would they tell a competitor their commercial secrets? Just doesn’t make any sense.

It’s not the first time seriously clever folks have proven career professionals wrong.

2 HTX testing
Please find linked the HTX progress report.


On page 6 it clearly states that the heat ex test article is supplied with cold helium at 200 bar while subjected to 1800F air. It describes how the hot He (up to “950K”)then goes into a water boiler as a heat sink, even with photo’s of the equipment.

To support your watery claims, please provide any documentary evidence.

3. He Turbines are the same as any other.
Wrong again I’m afraid. The blade aspect ratio to permitted leakage is unique and more demanding by about one order of magnitude. The very few nuclear He turbines have used massive structures to maintain the necessary sealing gaps. RE have a number of former RR turbine designers on staff and now have access to RR via the joint venture

And finally no, Reaction Engines limited was never established to develop Skylon, there’s a clue in their name which should be very obvious.

About 25 of their 33 years was spent as 5-6 guys in a shed solving the pre cooler icing problem without which they had nothing.
 
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Aww, c'mon. The test report was a blatant forgery by Alan Bond's 12-year-old great nephew, the "photos" were produced by feeding a Tom Gauld cartoon through a 3D visualiser, and we all know that superfluid helium plasma turbines are in every interstellar drive.
Just you wait 'til I peel off my human exoskin and reveal my true lizard self. Then you'll be sorry! :p
 
I fear that our Dagger is overly blunt, in more ways than one.
Our admins got the worst hate speech redacted, but the zealous antagonism remains.
At a technical level, being a comical engineer does not qualify one in meteorology. Take for example that first claim, that "ambient" is a far cry from -150 deg C. SABRE's hypersonic regime with extreme intake heating will not begin until perhaps 40,000 ft (15 km). Here is a graph of atmospheric temperature with height. Note that at these heights ambient temperature falls to around 220 K, which is near enough -50 deg C. Of course, numbers such as these can only ever be approximate and some design margin is needed, so in cooling from 1,000 deg C, a safe design target of an additional 10%, i.e. around -150 deg C, is entirely consistent with "ambient".
486px-Comparison_US_standard_atmosphere_1962.svg.png


The rest of their little rants are filled with similar blunders, but I tire of this garbage.
I had not yet noticed that my original post has been edited.
As far as I can remember a line is removed in which I kind of advised the financiers to initiate an audit, not by gullible fanboys that will believe anything, but by experienced design engineers who, like me, don't believe what REL claims.
Don't really understand why that would be insulting towards REL, but even if so, I have seen worse criticism towards companies in other topics. As long as I don't insult members (which I won't) the Admin could be more tolerant, but he is the judge so I will not protest in this case.

Strange though that you seem to have permission from the Admin to insult me, calling me a comical engineer, implying that I don't know what atmospheric conditions exist up there, et cetera.

Your statement that -150 oC is entirely consistent with ambient is very funny. I had to laugh for hours.

I intend in future to post much more detailed argumentation why the claims and tests by REL are nonsense. Not suitable for fanboys, so you better not read them.
 
That's quite unnerving, because they invented Skylon in the first place to solve HOTOL CoG issues - the heavy engine in the back played havoc with stability and payload.
So they went with Skylon in 1989, putting two engines on the wingtips. Only for thermal issues to become a PITA instead.
 
Skylon Aerodynamics and SABRE Plumes, AIAA 2015-3605, page 18, section IV. Takeaway: "The highly innovative Skylon concept has the potential to evolve into an operational reusable launcher for a viable transport to LEO. The ultimate goal would be a SABRE-propelled SSTO RLV. However, the fallback or near-term objective should be a TSTO system. This system would comprise a SABRE-powered reusable launcher
(first stage) and an expendable or reusable second stage that would be staged at approximately at 7.16 km/s. This staging velocity could allow the first stage to go around the world and return to the launch site and could lead to the second stage to be small enough to be carried in the payload bay of the first stage."

I don't think that particular configuration is an optimal configuration by any stretch, but the basic idea to use SABRE (if it ever works as an integrated engine system) for the propulsion of a hypersonic booster stage carrying a rocket powered orbiter seems in principle a (comparatively) sensible alternative approach.
 
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Yup. According to Mitchell Burnside Clapp, air launching at Mach 5.5 (Sabre top speed) removes 3000 m/s out of ascent to orbit 9000 - something. It is from this moment air launch really starts to pay. Even if that's "only" 33% of the delta-v and an even smaller amount of the energy to orbit (never get the proper adjective for it: inertial energy ? potential energy ? kinetic energy ?)
 
It is useful to distinguish between general design issues with spaceplanes and those specific to SABRE. Skylon was fundamentally a marketing vehicle to promote SABRE. RE are not air/space craft designers and it bombed. A shame, as it rather defeated the object of pushing for the NASA study, which fundamentally was to evaluate SABRE and not to evaluate the Skylon configuration per se.
For what its worth, the Skylon engine positioning was doubly flawed. NASA picked up on the exhaust plume, but the outboard location is unworkable if safety certification in commercial airspace is required; it is not feasible to meet the single-engine-out safety condition. The Shuttle engines' location and thrust line alignment through the centre of mass bears close consideration.
Put SABRE in a viable spaceplane airframe, give up on SSTO and instead go with say a two-stage mothership-plus-orbiter, and you might just have a launch platform (see what I did there) after all. RE's more recent puff seems to be accepting this modest climbdown, which has to be a Good Thing.

This system would comprise a SABRE-powered reusable launcher (first stage) and an expendable or reusable second stage
...
I don't think that particular configuration is an optimal configuration by any stretch, but the basic idea to use SABRE (if it ever works as an integrated engine system) for the propulsion of a hypersonic booster stage carrying a rocket powered orbiter seems in principle a (comparatively) sensible alternative approach.
One of SABRE's unique abilities is to shut down the airflow and operate as a pure rocket. Indeed, once the heat exchanger makes it into plain airbreathing jets (as is the current spinoff plan), that is about SABRE's only USP. The ABR bit does after all stand for Air Breathing Rocket. Recall that the Shuttle orbiter carried one unused main engine as dead weight into orbit. Carrying SABRE's thermodynamic gubbins instead might be equally feasible. I am less sure that SABRE will make for an efficient low-speed, low-altitude heavy-lifter. Maybe sticking SABRE in the orbiter is the better idea.
Personally I'd start with a Mk. I/IA three-stage system with a turbofan mothership, carrying a SABRE sub-orbital spaceplane, whose Mk. IA payload is a pure rocket orbiter. Then build out the Mk II two-stager from proven tech.
 
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Travelling and extremely distracted by other matters, so please forgive omissions, repetitions, and outright mistakes.

BAE Systems released this (terrible CGI) promo a while back. The vehicle is not orbital and 'only' Mach 5 capable. Considering that everything aft of the compressor is liquified, it seems that the concept has all the cooling and compressing hardware in the nose and the rockets in the tail, with the two connected by what is essentially plumbing rather than ducts. This might solve the balance and thermal problems.

View: https://www.youtube.com/watch?v=XVBHs-aS9WU


RE's LAPCAT A2 concept, also 'merely' hypersonic, has four proportionally smaller, engines based on SABRE, so such a configuration might address the engine-out and certification problem (let's just add 'perhaps' to every statement I make).


Skip back to here, and there's discussion and pics:


'Classic' Skylon may be little more viable than HOTOL in the end, but the first stage of a 2STO system using SABRE for the first stage in the new configuration shown - the engines hung under a rear delta seems to be where thought was headed four years ago now (!).

Otherwise, four engines rather than two or somehow splitting the heavy bits between nose and tail as the BAE bomber concept in the video has it?

The heat exchanger was always the core of RE's um, wibble, bah, whatever, and that's what the MoD and BAE are looking at, per this press release. Note the concept aircraft image. Probably just indicative.


Thermal management is identified as a critical issue for next generation fighters as the article linked here shows, and there's no reason that RE doesn't apply its particular expertise to that.


Looks like RE will continue to be viable as a technology development company for propulsion, maybe as a subcontractor to BAE & RR, not a launcher developer, but I think that was not too far from their original aim anyway.

So, yeah, um, whatever.
 
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If you can keep the combined two upper stages below 250 metric tons, Stratolaunch might just have the turbofan mothership for you :D.

Skylon C1 was 275 mt, so close enough. Make it suborbital, cut some prop weight and, hurrah ! It fits !
 
Even if SABRE is a viable propulsion system, in over 30 years no one has yet thought of a viable airframe concept to integrate it with. Which means its probably not going anywhere.

VL-VL TSTO reusable rocket appears to be the lowest risk, most efficient (cost) option.

VL-HL TSTO reusable winged rocket if you want greater cross range at the expense of efficiency.

Its really difficult to see the additional advantages of HL-HL spaceplanes e.g. basing flexibility translating into the real world when you consider things like noise, runway lengths, strengths, safety zones etc.
 
in over 30 years no one has yet thought of a viable airframe concept to integrate it with.
Nonsense. HOTOL was a viable airframe concept. It would also have made a useful second stage, and BAe teamed up with Antonov to push the idea. That Alan Bond's engine was an idea before its time was no fault of BAe's. The only problem since has been a lack of airframe design expertise and over-exposure to marketing graphics.
 
Even if SABRE is a viable propulsion system, in over 30 years no one has yet thought of a viable airframe concept to integrate it with. Which means its probably not going anywhere.

VL-VL TSTO reusable rocket appears to be the lowest risk, most efficient (cost) option.

VL-HL TSTO reusable winged rocket if you want greater cross range at the expense of efficiency.

Its really difficult to see the additional advantages of HL-HL spaceplanes e.g. basing flexibility translating into the real world when you consider things like noise, runway lengths, strengths, safety zones etc.
Not if you use MIPCC-jets on one end of the ascent to mach 4.5, and suborbital refueling on the other end. Oh well...
 
Nonsense. HOTOL was a viable airframe concept. It would also have made a useful second stage, and BAe teamed up with Antonov to push the idea. That Alan Bond's engine was an idea before its time was no fault of BAe's. The only problem since has been a lack of airframe design expertise and over-exposure to marketing graphics.

The inability to trim and hence fly at a range of fuel states was why they moved to the Skylon configuration which has its own issues.
 
The inability to trim and hence fly at a range of fuel states was why they moved to the Skylon configuration which has its own issues.

Firstly, if you abandon the SSTO hubris then the trim problem becomes more manageable.

Secondly, there are many conventional solutions. Here are a few:
  • A second, aft hydrogen tank allowing fuel-pumping, as widely practiced (e.g. Concorde).
  • Move the airbreathing bits of the engines forwards and accept a small increase in duct losses when in airbreathing mode.
  • Deepen the wing roots to more of a blended form, so more stuff can lie close to the CG. (Reduces wetted area and structural weight at the expense of frontal area). Pioneered on the Saab Draken and seen on many hypersonic/lifting-body designs.
  • Add a (larger) lifting-canard foreplane to extend the stable trim range.
I see no reason why these should all prove inapplicable.
 
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I see no reason why these should all prove inapplicable.

Yes they are sensible but the devil is in the details as the design is in a corner point where small differences in drag, mass, thrust etc make very large differences on performance.
 
I see no reason why these should all prove inapplicable.

Yes they are sensible but the devil is in the details as the design is in a corner point where small differences in drag, mass, thrust etc make very large differences on performance.
I'd say that successful engineering is ensuring the overlap of the least unviable with the least impossible.
 
Now, the all rocket DLR Spaceliner—if funded…might that be a testbed?

If the engine doesn’t work out, you still have something. Put an engine on a stage for high speed tests?
 
Skylon Aerodynamics and SABRE Plumes, AIAA 2015-3605, page 18, section IV. Takeaway: "The highly innovative Skylon concept has the potential to evolve into an operational reusable launcher for a viable transport to LEO. The ultimate goal would be a SABRE-propelled SSTO RLV. However, the fallback or near-term objective should be a TSTO system. This system would comprise a SABRE-powered reusable launcher
(first stage) and an expendable or reusable second stage that would be staged at approximately at 7.16 km/s. This staging velocity could allow the first stage to go around the world and return to the launch site and could lead to the second stage to be small enough to be carried in the payload bay of the first stage."

I don't think that particular configuration is an optimal configuration by any stretch, but the basic idea to use SABRE (if it ever works as an integrated engine system) for the propulsion of a hypersonic booster stage carrying a rocket powered orbiter seems in principle a (comparatively) sensible alternative approach.

Intrestingly in the April 2022 edition of Spaceflight Mark Hempsell discuses a VTOHL two stage to orbit Heavy Lift launcher called Cormoran.

Piggy back second stage with both stages standard rocket engines IIRC

2022-07-18 15_39_01-Cormoran VTOHL two stage heavy lift vehicle  -  Compatibility Mode - Word.png
 
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Update regarding SABRE.


Reaction Engines is proud to announce the completion of a critical subsystem, integral to air-breathing rocket engine technology development for space access. At Reaction Engines’ UK headquarters, our skilled team has successfully integrated our high performing HX3 heat exchanger and advanced Hydrogen Preburner modules to form the ‘Integrated Preburner System’, part of our advanced engine cycle development.

Background
The “Integrated Preburner System” provides a controllable heat source within an air-breathing SABRE engine cycle to enable flight at low speeds and low altitudes. This system allows the overall engine to bridge the gap between low and high-speed operation, generating and harvesting heat to power various internal components at low-speed conditions.

The Preburner component is a lean hydrogen-air combustor that can be throttled to generate varying amounts of thermal energy. The HX3 is a unique extreme-temperate heat exchanger. HX3 transfers thermal energy from the Preburner into a helium loop for powering adjacent subsystems within the system. The hot gas produced from hydrogen-air combustion in the Preburner generates temperatures up to 1450K. HX3 extracts energy from the hot combustion gas via heat transfer using Reaction Engines’ innovative heat exchanger design.

The design, manufacture and testing of this technology is a great example of how the team at Reaction Engines is progressing air-breathing technology, integration and testing represents an important milestone in overall development. This step also serves to show the strength of the UK in researching, designing and manufacturing unique forward-looking aerospace propulsion technology. The learning received in the development of this technology will also be applied to spin-out opportunities adjacent to space access and will advance thermal management capability for use within other applications and industries.

Extreme Temperature Heat Exchanger
The fully Integrated Preburner System is possibly the most extreme heat exchanger that has ever been developed. Its combustion temperatures can reach over 1450K (1100° C), which is enough to melt gold and at 100% throttle, generates approximately 2.5MW of energy. For a sense of scale, the volume of the matrix performing the thermal heat transfer could fit in an airplane suitcase.

Sam Fox, Senior Systems and Test Engineer, had this to say about the successful integration of the HX3 and Preburner subsystems: “Successful assembly of such an advanced system does not come without challenges. Our team of highly experienced engineers and technicians did a fantastic job to coordinate and manage this activity, demonstrating again the strong assembly, integration, and testing capabilities within the Company.

Ground Testing
The full Preburner System has been transported to Cotswold Airport where we will once again be working with our UK partners S&C Thermofluids to conduct this testing campaign. The system is now in the process of being integrated into the test site with ground support equipment, full control systems, and data acquisition systems. Integration will be followed by the official commissioning of the full test site arrangement configuration, with testing due to commence in July. The results of this test campaign will provide demonstration of the Preburner System design concept and valuable learning for system performance and operation that will be fed directly into future development.

Shaun Driscoll, Programme Director of Reaction Engines had this to say about the milestone: “The successful design, build and integration of the HX3 and Preburner subsystems represents a phenomenal effort from the Reaction Engines’ team. The Preburner System provides quite astonishing capability and is a vital element of an advanced engine cycle like SABRE. I am excited to see it perform in testing!”

If you would like to find out more about our air-breathing rocket technology and the ground testing of the Preburner System, come and meet us at Farnborough International Airshow, July 18-22 in the Space Zone.
 

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