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Old 12th March 2015, 06:53 AM   #1
3point14
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Skylon

I thought I'd start a thread (I couldn't find one) about the potentially marvelous concept that is Skylon and the slightly lesser known and even more conceptual A2


I have been following this since HOTL (too heavy at the back, apparently) and it's looking more and more feasible that an SSTO craft of this nature is possible now that the problem of frost control appears to be actually not a problem at all.

Are there any other comapnies pursuing similar technology? What does the assembled company think the feasibility of the project is?

Also, I get annoyed when the engines are referred to as working as jet engines. As far as I'm aware, they never do, they're always rockets.
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Old 12th March 2015, 08:22 AM   #2
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Been following Reaction Engines and their SABRE engine for a while. Be interesting to see if they can deliver on their promise in a timely manner and for an affordable price.
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Old 12th March 2015, 07:10 PM   #3
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Originally Posted by ohms View Post
Be interesting to see if they can deliver on their promise in a timely manner and for an affordable price.
I'm guessing 'no' at this point....
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Old 12th March 2015, 07:28 PM   #4
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Originally Posted by 3point14 View Post
Also, I get annoyed when the engines are referred to as working as jet engines. As far as I'm aware, they never do, they're always rockets.
When pulling in air to burn fuel, it's a jet; when at high speed/altitude and using oxygen from its tanks, it's a rocket.
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Old 12th March 2015, 07:33 PM   #5
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I'm always skeptical of proposals that have to compare themselves against the worst cost option available to make the proposal appear very cost attractive.

Still, it's very interesting.
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Old 12th March 2015, 08:12 PM   #6
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Originally Posted by Tanalia View Post
When pulling in air to burn fuel, it's a jet; when at high speed/altitude and using oxygen from its tanks, it's a rocket.
I think this device is more spork than fork. The compressor section is not driven by the combustion chamber as a single-shaft feedback loop as in a jet engine but a separate component.

From Reaction themselves:
"The SABRE engine is essentially a closed cycle rocket engine with an additional pre-cooled turbo-compressor to provide a high pressure air supply to the combustion chamber. This allows operation from zero forward speed on the runway and up to Mach 5.5 in air-breathing mode during ascent. As the air density falls with altitude the engine eventually switches to a pure rocket propelling its vehicle (e.g. SKYLON) to orbital velocity (around Mach 25)."
http://www.reactionengines.co.uk/sabre_howworks.html

They're calling it a closed cycle rocket engine + compressor, in effect a rocket with on-board oxygen collection and compression upstream of the combustion chamber; control of the compression stage is discreet from the thrust output and not physically or thermodynamically coupled with thrust output. That detail makes it a spork, a spoon with poking bits rather than an ordinary spoon or traditional fork.

Last edited by Jrrarglblarg; 12th March 2015 at 08:16 PM. Reason: Gettin linky with it
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Old 14th March 2015, 02:21 PM   #7
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Originally Posted by Tanalia View Post
When pulling in air to burn fuel, it's a jet; when at high speed/altitude and using oxygen from its tanks, it's a rocket.
It's never a jet though. It's always rockets it's just, up to mach 5 it scavenges O2 from the atmosphere and injects it into rocket bells (skirts? Exhausts?) along with H. There's never a point at which it uses gaseous air passed straight through the machine.

Is that still a 'jet'?


Or what he said.
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Old 14th March 2015, 10:29 PM   #8
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Last time I looked, the engine seemed fantastically complicated. Unless they come up with something really clever, it has to be an absolute nightmare to maintain.
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Old 15th March 2015, 02:11 AM   #9
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Originally Posted by 3point14 View Post
I thought I'd start a thread (I couldn't find one)
Not about the Skylon, per se but here's a thread I started about the Sabre engine: http://www.internationalskeptics.com...d.php?t=248556
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Old 15th March 2015, 02:45 AM   #10
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They are Jet engines, they use a jet of expanding gas to provide their thrust.

Why do you think Nasa call it the Jet Propulsion Lab?
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Old 15th March 2015, 09:33 AM   #11
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Originally Posted by Captain_Swoop View Post
They are Jet engines, they use a jet of expanding gas to provide their thrust.
so does a 2-stroke chainsaw. Your simplified description fails to account for the actual thermodynamic and engineering differences of rocket and jet engines.
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Why do you think Nasa call it the Jet Propulsion Lab?
Because when the omnisexual crowleyite inventor of the JATO bottle Jack Parsons and his fellow fans of blowing stuff up in the desert were starting JPL the word "rocket" was associated with cartoon science fiction like Buck Rogers. They chose the name to avoid that stain because they wanted the goverenment to take them seriously, firstly in the form of military contracts.

Fun Fact: Jack Parsons has a crater on the moon named for him. It could be accurately described as a pimple on the moon's &&&crack.

Last edited by Jrrarglblarg; 15th March 2015 at 09:34 AM. Reason: larning ta typpe on a new keybord
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Old 2nd November 2015, 04:47 AM   #12
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A bit of an update, BAE has invested a 20m into Reaction Engines. Looks like a good investment for all involved.

http://www.bbc.co.uk/news/business-34694935
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Old 2nd November 2015, 07:33 AM   #13
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Originally Posted by ohms View Post
A bit of an update, BAE has invested a 20m into Reaction Engines. Looks like a good investment for all involved.

http://www.bbc.co.uk/news/business-34694935
Good news, thanks. The only way to kill engineering challenges is to drown them in cash. They don't solve themselves and nobody can afford to do it for free.
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Old 25th October 2019, 07:03 AM   #14
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Now operating at mach 5 conditions.

https://www.theengineer.co.uk/reacti...ecooler-mach5/
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Old 25th October 2019, 07:19 AM   #15
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Is this related to the battery powered pump for use in rockets? I just lately learned that liquid fueled rockets need high pressure pumps.

So far as "jet" vs "rocket", they both use a jet of reaction mass. The axial turbine engine uses heated air as a reaction mass. The rocket uses on board mass. I doubt that whether pumps or compressors make the distinction. Is it important how you power the pumps?
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Old 25th October 2019, 07:32 AM   #16
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Aside- craft design- Swing wing? Maybe with wings that fold totally into the body. This would lessen drag at the time when lift supplied by the wings does not offset the friction of the wings, once in thin air and 'rocket' mode? And canards for trim because folding the wings will change lift/load balance point. Later fold the canards into the body too.

The change in air density makes for an interesting dynamic as the craft morphs from plane to missile.
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Old 25th October 2019, 07:32 AM   #17
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Originally Posted by casebro View Post
Is this related to the battery powered pump for use in rockets? I just lately learned that liquid fueled rockets need high pressure pumps.

So far as "jet" vs "rocket", they both use a jet of reaction mass. The axial turbine engine uses heated air as a reaction mass. The rocket uses on board mass. I doubt that whether pumps or compressors make the distinction. Is it important how you power the pumps?

How you power the pumps is huge chunk of rocketry. Efficiencies to that process are the main reason the Raptor is such a good engine. (This is the everyday astronaut talking about it. https://www.youtube.com/watch?v=LbH1ZDImaI8)


This isn't related to that though. Conventional jet engines tend to melt at around mach 3 and there's nothing that can reasonably be done about it.

This engine force cools incoming hypersonic air so it can be used as oxidiser for what is effectively a rocket engine.



EDIT: All of the above is my pretty shonky knowledge and subject to correction if someone who knows what they're talking abut turns up.
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Old 25th October 2019, 08:32 AM   #18
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Did I read it cools the compressed air in 1/20th of a second? At mach 5, that is 1,000 feet. Seems like a long unwieldly craft.
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Old 25th October 2019, 08:36 AM   #19
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Originally Posted by casebro View Post
Did I read it cools the compressed air in 1/20th of a second? At mach 5, that is 1,000 feet. Seems like a long unwieldly craft.



The theorised prototype, Skylon, is long and thin and, predictably, looks part way between a rocket and a plane:

https://meflyrocket.files.wordpress....sus_orbit2.jpg

As I understand it, REL aren't pursuing the Skylon concept initially and are looking at two stages to orbit with the first stage using the Sabre and the second stage conventional.
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Old 25th October 2019, 08:39 AM   #20
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Originally Posted by casebro View Post
Did I read it cools the compressed air in 1/20th of a second? At mach 5, that is 1,000 feet. Seems like a long unwieldly craft.
Don't know what you read but the proposed length is 280ish feet. And that, not 1,000 feet, is approximately how far something moving at Mach 5 moves in 1/20th of a second.
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Old 25th October 2019, 03:53 PM   #21
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Originally Posted by casebro View Post
Did I read it cools the compressed air in 1/20th of a second? At mach 5, that is 1,000 feet. Seems like a long unwieldly craft.
The idea is to cool the air as it compresses it and slows it to subsonic speeds so it can be piped around and injected into the combustion chamber on the rocket end of the engine. SABRE would do this by feeding it through a heat exchanger composed of 16800 tubes with 30 micron thick walls that circulate helium chilled by the liquid hydrogen fuel. The helium drives the turbopumps pumping the fuel in the process.

The required temperature drop means liquid hydrogen is the only usable fuel, since it doubles as coolant. In Skylon, it would also have been used to cool leading surfaces during the slow ascent at high supersonic speeds. Between the fantastically complicated engines and the huge tanks needed to hold the liquid hydrogen, "unwieldy" is a pretty good word.

I think Skylon was Alan Bond's baby. Since his retirement, the website's been scrubbed of all references to it apart from some pretty concept art. They don't mention even tentative plans of building any actual vehicles themselves any more, and seem to be trying to sell the engine as something for others to build vehicles around. Given the likely cost and fragility of something that complex...good luck.

For space launch: liquid oxygen is cheaper than dirt, liquid oxygen tanks are a small contributor to vehicle dry mass, and conventional rocket engines easily produce the thrust to lift the needed oxygen while being cheaper than SABRE could ever dream of being. I doubt you'll ever see a SABRE-based launch vehicle, it's better suited to craft that cruise at high supersonic speeds than to those that are trying to accelerate out of the atmosphere.
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Old Yesterday, 01:11 AM   #22
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Originally Posted by 3point14 View Post
It's never a jet though. It's always rockets it's just, up to mach 5 it scavenges O2 from the atmosphere and injects it into rocket bells (skirts? Exhausts?) along with H. There's never a point at which it uses gaseous air passed straight through the machine.

Is that still a 'jet'?


Or what he said.
There is a difference though, an engine that uses the atmospheric air as reaction mass must expell that mass from the nozzle at a higher velocity than the vehicle is travelling for that mass to contribute to thrust, an engine that uses on board oxidiser doesn't have that limitation.
As the speed of an air breathing engine increases it would have to increase its exhaust velocity to maintain its thrust, not so with engine running on carried oxidiser.
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