Ramjet vs SABRE engine?

[Idobox]

I'm not sure, thermal damage is tough problem.

Look at the thermal protection tiles of the Space Shuttle: basically ceramic bricks, it was extremely expensive to maintain. If you have to change the skin after every flight, it might not be competitive at all.

The longest burn in flight for a scramjet in about 6 minutes, I couldn't find a figure for wind tunnels. I'm not sure how the X51 works, but for this kind of time, you can use simple cooling systems. Sure, that's a good 6 minutes longer than any Sabre engine ever ran, but I'm not aware of any air-augmented rocket using a scramjet having ever flown either.

Scramjet is definitely the way to go for single use, and that's why Boeing wants to put them on missiles. I can also imagine a space launch system where the combustion chamber would be changed after each flight.

For repeated use, it will all depend on how complex Sabre maintenance is compared to Scramjets, and right now, we don't know. Also, RAL is developing the Sabre, working on the Scimitar as well allows to greatly widen the potential market and reduce risk for a limited cost. I'm not sure anybody in the world as as much incentive to work on civilian scramjet augmented rockets, even if it actually was a better solution.

[Wahgineer]

Personally, I think that Scimitars are the way to go. While LH2 does require a high volume and is volatile, it is very easy to produce and can be bought in bulk cheaply (correct me if I'm wrong). The whole complexity thing isn't a problem, either: we make jet engines that are just as if not slightly more complex than a Scimitar. And that's not counting rocket engines. Also, Scimitars have the advantage of being operational at any speed, where as scramjets are dead weight for a good part of the flight (takeoff, acceleration, deceleration, landing).

[sgt_flyer]

For the 'density' problem of LH2, they plan to turn it into an asset. The increased size needed will allow Skylon much less aggressive reentrys than a space shuttle. (Skylon's bigger than the space shuttle, yet it's lighter than it when it's fuel tanks are empty) the less agressive reentry profile allows to use much more standard thermal protection than the space shuttle - further decreasing the weight of the system, and the maintenance costs on the thermal protection (although they still use active cooling on leading edges for reentry, thanks to the lh2)

Basically, due to skylon being bigger, air drag starts to have a significant effect at higher altitudes than the shuttle.

In a jet fuel based system, you would end up having a much more compact system, which will require higher quality TPS to survive reentries.

[K^2]

Again, we aren't talking about SABRE on Skylon. We are talking about Scimitar on an airliner, where low density of LH2 certainly is going to be a disadvantage.

[Idobox]

awsumindyman, sabre and scimitar are very complex, and nobody is even sure RAL will actually manage to make them work.

The precooler is the most complex part, and the rest is basically a rocket AND a turbojet AND a ramjet engines mashed together, so it's fair to assume it's also quite more complex than a typical jet engine.

The concept is promising, and I love it, but it will be expensive and require a lot of maintenance.

[Seret]

The concept is promising, and I love it, but it will be expensive and require a lot of maintenance.

That's a reasonable assumption. This is the first generation of a complex machine that does something new. They reckon they've nailed the precooler, and that's the most challenging single component, but that still puts you a long way short of a working, reliable, economical production engine. The jury's still out on SABRE and any allied technologies like Scimitar at least until they've built and flown a prototype and got some data back. Given the exceptionally long gestation time of the HOTOL/Skylon/whatever it's called this decade I'm not holding my breath, although the fact they've now got government funding is promising.

[Idobox]

Having a complete, working engine, even if only on a test bench would already be a huge step forward.

Once you have proved you can build the engine, that it performs as expected and is reliable enough, getting funding and manpower to finish building the Skylon or whatever design has replaced it is easy.

[nhnifong]

K-2, What is a combustion camera? Just a camera with a view of the combustion chamber?

[K^2]

K-2, What is a combustion camera? Just a camera with a view of the combustion chamber?

Sorry, Russian for "camera" and "chamber" is the same, and I've learned most of I know about conventional rocket propulsion from Soviet texts.

[Idobox]

camera comes from the Latin (or maybe Italian, not sure) 'camera obscura', which means 'dark room'.

In the old times, some painters would sit in a black box with a pinhole acting as a lens and projecting a view on a canvas they would then paint over. This evolved into modern cameras, and the name stuck, and you will find the word pop up here and there in different areas to mean room, chamber, space ...

[K^2]

"Camera" does mean "chamber" in Latin, yes. Both words came to Russian from Latin. As did a lot of other roots, and most of the grammar.

[Seret]

Having a complete, working engine, even if only on a test bench would already be a huge step forward.

Indeed, however this engine operates through a pretty extreme range of conditions compared to an aircraft power plant. To fully validate the design you'd need to run it up to high altitude, get up to Mach 5, transition from air breathing to rocket, and do restarts at speed and altitude. The amount you could simulate at ground level in a wind tunnel is limited.

Once you have proved you can build the engine, that it performs as expected and is reliable enough, getting funding and manpower to finish building the Skylon or whatever design has replaced it is easy.

I think the Sabre/Scimitar technology is a lot more commercially viable than the Skylon. Even if the Sabre exceeds expectations and goes into production (or gets licensed to others) there's no guarantee the Skylon will ever get built.

Edited February 23, 2014 by Seret

[K^2]

You can simulate most of the conditions in the wind tunnel. It's not a replacement for flight tests, but it's a difference between going off figures on paper alone and basing your performance estimates on actual data. So when they get a working prototype on the ground, I'm willing to accept it as a working engine and not just a cool idea.

As I've pointed out, I don't think Scimitar has much of a future, but I'm completely with you on SABRE. If they make it work, it has a potential to be a component of many future spacecraft regardless of how well the Skylon does against the competition.

[Idobox]

By the time they have a working engine, they will probably have redesigned, and possibly renamed the Skylon.

Also, if their engine is that great, I can totally see other players building the ship and buying the engines, or making some kind of joint venture. Making a working Sabre would be impressive, but building a SSTO ship probably requires different skills.

And I sure hope UK doesn't drop funding again, or if they do, that somebody else, like ESA or EADS cough the dough.

[Thiel]

As I uderstand it Reaction Engines is making a pretty penny on their cooler fabrication tech.

[Seret]

As I uderstand it Reaction Engines is making a pretty penny on their cooler fabrication tech.

Well, they've got to make money somehow, they'd be mad not to capitalise on their IP. Likewise if they manage to get SABRE into production I suspect they'll go looking for buyers straight away, and use that money to fund further SABRE & Skylon development.

[MrZayas1]

Ramjets are a much older idea, and are likely to (in my view at least) die a painful death after the SABRE variants are ready to fly.

I agree with that because SABRE jets are much more efficient and awesome lol!

[Wahgineer]

Once the SABRE goes public, I'm pretty sure the US will order a couple of them. They'd then reverse engineer them, build their own, and most likely improve upon them exponentially, considering the same thing happened to the jet engine and steam engine.

[sgt_flyer]

Well, US air force already signed a cooperative research and devellopment agreement with reaction engines ltd - so the us are already looking into the sabre engine

www.reactionengines.co.uk/news_updates.html

[Seret]

Once the SABRE goes public, I'm pretty sure the US will order a couple of them. They'd then reverse engineer them, build their own, and most likely improve upon them exponentially, considering the same thing happened to the jet engine and steam engine.

The critical technology, such as the precooler, is already patented. REL might allow people to produce their stuff under licence, but anyone that tried to copy it would get the pants sued off them.

[problemecium]

Is it possible to make a Scrabjet? As in a SABRE with a scram intake.

[SargeRho]

The SABRE is already designed for up to mach 5 or so. So it already has a supersonic-capable intake.

[Idobox]

Is it possible to make a Scrabjet? As in a SABRE with a scram intake.

But it's not Scram, it slows down air to subsonic speeds before entering the combustion chamber.

I don't see why you couldn't do it, but then you would have the same issue as normal ram and scramjet : they have zero thrust at low speeds.

[EatVacuum]

The SABRE is already designed for up to mach 5 or so. So it already has a supersonic-capable intake.

More accurately and so the entire point of SABRE - it goes up to Mach 5 or so in air breathing mode. Then it switches over to close cycle mode and uses liquid oxygen instead of air to get out of the atmosphere and to orbital velocity. So it's truer to say it is designed for Mach 20 or so.

[Nuke]

once the intake closes the point is moot. its a rocket at that point. saber will run up to mach 5, and i dont think they need to use scram tech to accomplish that. sabre essentially solves the major issue with scram, that it only operates in a vary narrow flight regime. you might be able to use scam in other closed cycle designs, but no point using it in sabre, since much of the design work is already done.