Author Topic: The Reaction Engines Skylon Master Thread (5)  (Read 441073 times)

Offline john smith 19

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Re: The Reaction Engines Skylon Master Thread (5)
« Reply #1400 on: 03/23/2016 04:07 PM »

Routing the hot bypass air does sound like the thorniest problem. It may not be worth it, and instead you dump it through bypass doors - a la SR71. But that comes with a performance penalty (no thrust from bypass burners, plus maybe drag) and complexity.
This is the issue.  The problem with it is
a)High volume, so the ducts have large diameters
b)Very hot. so they have to be made in either a high temperature alloy, or something like RCC.

So you've either got a high surface are of a heavy high temperature alloy like Inconel or a high surface area of a very expensive difficult to make (and oxidation pron) semi-ceramic.

Keeping pipe runs short and densities high by using a pre-cooler is part of how SABRE can do a T/W of 15:1 when a SCRamjet can do 2:1.
Quote
It's a good guess that Bond et al considered this sort of configuration in depth after the HOTOL cancellation, before coming up with Skylon.

IIUC the only thing that's a little different now is the temperature/pressure of the cooled air is less extreme with SABRE 4.


You're missing the point.  I wasn't calculating the performance of the vehicle.  I was calculating how badly wrong REL's estimates would have to be to kill their idea completely.  Saying "yes, but their numbers might not be right" doesn't engage the actual question.
In electronic design this is sometimes called a "sensitivity analysis."

Skeptics seem to ignore this, thinking SABRE's payload sensitivity is that of a VTOL SSTO. What it actually shows is REL's calculations and simulations would have to very far out to fail to deliver a working engine or a working vehicle.

They also seem to ignore that unlike other systems SABRE has had independent scrutiny, partly to avoid such mishaps as the X30 PI using the wrong properties for air and deluding himself (and the USAF) that it was possible, when it simply wasn't.
"Solids are a branch of fireworks, not rocketry. :-) :-) ", Henry Spencer 1/28/11  Averse to bold? You must be in marketing."It's all in the sequencing" K. Mattingly.  STS-Keeping most of the stakeholders happy most of the time.

Offline lkm

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Re: The Reaction Engines Skylon Master Thread (5)
« Reply #1401 on: 03/24/2016 03:58 PM »
So according to this account of the 8th of March lecture,
https://www.reddit.com/r/ReactionEngines/comments/48a8uz/at_loughborough_university_on_8th_march_2016/

Skylon is being designed to have a life expectancy of ten years, which isn't something I've heard before.

This would imply a Skylon has a life of 200 launches or 10 years, which ever came first. So unless an operator is launching at least an average of 20 times a year the purchase price will have to be amortized over fewer launches.  An operator launching only 10 times a year would only have 100 launches to recoup the purchase price.
If the launch market is indeed elastic then this would suggest that Skylon operators would be incentivised to lower prices to stimulate launch rates.
« Last Edit: 03/24/2016 04:00 PM by lkm »

Offline RanulfC

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Re: The Reaction Engines Skylon Master Thread (5)
« Reply #1402 on: 03/24/2016 04:44 PM »
Not sure what keeps happening to the page settings but I'm not going to paste quotes and hope to avoid transferring them on :)

AFRL and TSTO: AFRL isn't interested in Skylon because while "nice" to have once someone else develops it, history has shown TSTO vehicles tend to fit their assumptions and requirements more. Hence SABRE as part of a TSTO system in a booster. Considering the militaries operational bias against LH2 for anything they didn't actually HAVE to have I really wouldn't be surprised if trades are still made to try and arrive at a methane/propane or kerosene fueled SABRE with the obvious results :)

Payload: C2 was structurally capable of carrying up to 30mt as designed but was ONLY capable of actually orbiting around 17mt. D1 is structurally capable of only carrying 17mt maximum. In any case part of that has to be an upper-stage to deliver the payload to its actual destination orbit. Currently Skylon couldn't act as a "booster" for an actual TSTO system due to structural and design limits. The main point though is REL is not considering looking at Skylon in any form other than SSTO while others have expressed interest in doing so. Neither approach is "wrong" but I am pointing out that REL itself has done the math that shows (with assumed structural ability) a SABRE powered, sub-orbital booster COULD in fact provide more payload than the basic Skylon to orbit. That's all.

Operations: REL has designed and assumed certain operational parameters for Skylon as an SSTO vehicle. AFRL is looking at a different set of assumptions and requirements. Again neither one is "right" or "wrong" as they are based on different criteria. What we WANT here is enough support for AFRL to at least get someone to build and test a ground-prototype SABRE and put the arguments there to rest. Getting from there to an operational vehicle is another kettle of fish all together.

Can't access the reddit article but stating a "life-expectancy" for an air frame in years is odd to say the least. Even "200 launches" is based on a ton of assumptions and airframe life is most often expressed in hours (of flight time) not years. (BTW? That would be over 80,000 hours :) ) And is dependent on component and materials versus stress and maintenance factors which are not known until you actually do the testing required to gather the data.

The statement would appear to have about as much validity as the claims that the Falcon-9R first stage can fly "10 times" which is unproven and un-provable until after you actually FLY the airframe at least 10 times...

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 A_M_Swallow

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Re: The Reaction Engines Skylon Master Thread (5)
« Reply #1403 on: 03/24/2016 05:26 PM »
{snip}
Can't access the reddit article but stating a "life-expectancy" for an air frame in years is odd to say the least. Even "200 launches" is based on a ton of assumptions and airframe life is most often expressed in hours (of flight time) not years. (BTW? That would be over 80,000 hours :) ) And is dependent on component and materials versus stress and maintenance factors which are not known until you actually do the testing required to gather the data.

The statement would appear to have about as much validity as the claims that the Falcon-9R first stage can fly "10 times" which is unproven and un-provable until after you actually FLY the airframe at least 10 times...

Randy

Expressing the life expectancy of an air frame in years may be odd but it is normal to express the shelf life of silicon chips in years. 10 years is about the maximum shelf life of a Flash Memory.
Ref: http://www.wdc.com/WDProducts/SSD/whitepapers/en/NAND_Evolution_0812.pdf

Whether the entire Skylon needs replacing after 10 years or only its electronics would need investigating. Things like the hydraulics and seals may also need replacing.

Offline lkm

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Re: The Reaction Engines Skylon Master Thread (5)
« Reply #1404 on: 03/24/2016 05:40 PM »
{snip}
Can't access the reddit article but stating a "life-expectancy" for an air frame in years is odd to say the least. Even "200 launches" is based on a ton of assumptions and airframe life is most often expressed in hours (of flight time) not years. (BTW? That would be over 80,000 hours :) ) And is dependent on component and materials versus stress and maintenance factors which are not known until you actually do the testing required to gather the data.

The statement would appear to have about as much validity as the claims that the Falcon-9R first stage can fly "10 times" which is unproven and un-provable until after you actually FLY the airframe at least 10 times...

Randy

Expressing the life expectancy of an air frame in years may be odd but it is normal to express the shelf life of silicon chips in years. 10 years is about the maximum shelf life of a Flash Memory.
Ref: http://www.wdc.com/WDProducts/SSD/whitepapers/en/NAND_Evolution_0812.pdf

Whether the entire Skylon needs replacing after 10 years or only its electronics would need investigating. Things like the hydraulics and seals may also need replacing.

To be clear the exact quote I'm referencing is :

Quote
Mark said they were aiming for 10 year lifespan for Skylon and rapid reuse

Offline RanulfC

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Re: The Reaction Engines Skylon Master Thread (5)
« Reply #1405 on: 03/24/2016 06:06 PM »
To be clear the exact quote I'm referencing is :

Quote
Mark said they were aiming for 10 year lifespan for Skylon and rapid reuse

Thanks. As I noted I couldn't access the article :)
STILL an odd way of putting it.

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 A_M_Swallow

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Re: The Reaction Engines Skylon Master Thread (5)
« Reply #1406 on: 03/24/2016 09:56 PM »
{snip}
Can't access the reddit article but stating a "life-expectancy" for an air frame in years is odd to say the least. Even "200 launches" is based on a ton of assumptions and airframe life is most often expressed in hours (of flight time) not years. (BTW? That would be over 80,000 hours :) ) And is dependent on component and materials versus stress and maintenance factors which are not known until you actually do the testing required to gather the data.

The statement would appear to have about as much validity as the claims that the Falcon-9R first stage can fly "10 times" which is unproven and un-provable until after you actually FLY the airframe at least 10 times...

Randy

Expressing the life expectancy of an air frame in years may be odd but it is normal to express the shelf life of silicon chips in years. 10 years is about the maximum shelf life of a Flash Memory.
Ref: http://www.wdc.com/WDProducts/SSD/whitepapers/en/NAND_Evolution_0812.pdf

Whether the entire Skylon needs replacing after 10 years or only its electronics would need investigating. Things like the hydraulics and seals may also need replacing.

To be clear the exact quote I'm referencing is :

Quote
Mark said they were aiming for 10 year lifespan for Skylon and rapid reuse

Car lifetimes are expressed in years and miles.
10 years is the expected lifespan of a modern car. So they are building the Skylons to similar standards.
https://www.cardealpage.com/column14.html

Offline tatarana

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Re: The Reaction Engines Skylon Master Thread (5)
« Reply #1407 on: 03/24/2016 10:04 PM »
I did a little data extracting from   <https://imgur.com/a/F87pA>    and came back with the
following pictures, comparing Isp  and T/W   from several iterations of the SABRE engine.

I call it  SABRE  1/2/3    and   SABRE 4B   (most recent taken from the link above).
There is clearly a dramatic improvement from the first to second group.


Anyone cares to comment ? My technical background is not up to this task.

Tatarana

(edited) I made a mistake and put data for Sabre 4A that was really only an extrapolation from
old data from Sabre 2.  Apologies are due to everybody.   


« Last Edit: 03/25/2016 12:18 PM by tatarana »

Offline francesco nicoli

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Re: The Reaction Engines Skylon Master Thread (5)
« Reply #1408 on: 03/24/2016 10:49 PM »
If I am not mistaken, early figures put Skylon lifetime to 30 years. Has this changed? the implications for the economics of the system are enormous if the expected lifetime is, indeed, only 10 years.

Offline 93143

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Re: The Reaction Engines Skylon Master Thread (5)
« Reply #1409 on: 03/25/2016 01:59 AM »
I did a little data extracting from   <https://imgur.com/a/F87pA>    and came back with the
following pictures, comparing Isp  and T/W   from several iterations of the SABRE engine.

I call it  SABRE  1/2/3    and   SABRE  4A (older data)   / SABRE 4B   (most recent taken from the link above).
There is clearly a dramatic improvement from the first to second group.

Also there is a marked difference between Isp and T/W  from SABRE 4A to 4B.

Where is your older data from?  Aside from Varvill & Bond (2003) and the C1 trajectory spreadsheet, I know of no sources that give (or can be analyzed to give) Isp curves for SABRE.

Offline tatarana

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Re: The Reaction Engines Skylon Master Thread (5)
« Reply #1410 on: 03/25/2016 12:24 PM »
I did a little data extracting from   <https://imgur.com/a/F87pA>    and came back with the
following pictures, comparing Isp  and T/W   from several iterations of the SABRE engine.

I call it  SABRE  1/2/3    and   SABRE  4A (older data)   / SABRE 4B   (most recent taken from the link above).
There is clearly a dramatic improvement from the first to second group.

Also there is a marked difference between Isp and T/W  from SABRE 4A to 4B.

Where is your older data from?  Aside from Varvill & Bond (2003) and the C1 trajectory spreadsheet, I know of no sources that give (or can be analyzed to give) Isp curves for SABRE.


Dear Sir

I made a mistake, already corrected in the original post. Figures were corrected also.
Thank you for your keen attention to details.
I put bellow the figures, again. The first figure is from the link   <https://imgur.com/a/F87pA>,
and the following 2 figures are mine.

Tatarana

Offline lkm

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Re: The Reaction Engines Skylon Master Thread (5)
« Reply #1411 on: 03/27/2016 10:30 PM »
New Skylon article with some  details on the test program at the end.

http://epizodsspace.no-ip.org/bibl/inostr-yazyki/aerospace-america/2016/3/8-11.pdf

Offline oddbodd

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Re: The Reaction Engines Skylon Master Thread (5)
« Reply #1412 on: 03/28/2016 03:18 AM »
News at 11: Researchers competing for aerospace R&D dollars have pessimistic view of alternatives to their own research!

Seriously? How long and how much have these people (plus all the other scramjet researchers) spent on scramjet tech? Rhetorical question; since the 50's and billions (probably more than the entire Skylon projected budget) And what have they delivered so far? A space launch system? Nope. A practical usable atmospheric vehicle? Nope. So far (IIRC correctly) we have a small vehicle that needs to be pre-boosted using rockets to get it up to a significant Mach number, then ignites the scramjet and gets up to something like Mach 5-8, flies for a max of 3 minutes, and is then dumped in the ocean. A launch vehicle with scramjets would not only need pre-boosting, but it would also need "something else" engine-wise to achieve orbit because the scramjet alone can't achieve it. And yet they get asked to comment on the SABRE engine? Why? You might as well ask the oil companies to comment on the viability of electric cars.

Disclaimer: I'm a Brit so, as well as a little bit of national pride, I also tend to root for the underdog, so I'm doubly invested in seeing Skylon succeed.

2nd disclaimer: Yes, I'm fully aware that scramjets are much further along in real terms than SABRE, but until the scramjets achieve reuse, testing will continue to be crazy expensive and slow. A key trait of the SABRE (in comparison) is that a great deal of the engine modes and cycles can be tested on the ground. Provided REL/SABRE isn't starved of cash and there are no "unknown unknowns" in the design I think the SABRE engine (not Skylon) could overtake (pun intended) scramjets in the not too distant future.

Offline Oli

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Re: The Reaction Engines Skylon Master Thread (5)
« Reply #1413 on: 03/28/2016 10:16 AM »

A scramjet can go up to Mach 10.

Mach 5 you can do with a turboramjet, to my knowledge.

Both have very bad thrust-to-weight ratios, but that's not a showstopper for atmospheric flight. Space launch is hardly a relevant market at this point.

Offline Paul451

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Re: The Reaction Engines Skylon Master Thread (5)
« Reply #1414 on: 03/28/2016 02:55 PM »
New Skylon article with some  details on the test program at the end.
http://epizodsspace.no-ip.org/bibl/inostr-yazyki/aerospace-america/2016/3/8-11.pdf

Looks like they are planning a single engine suborbital test vehicle. Props to AM_Swallow for predicting this.

EN: "The first flight test vehicle, with its  single  engine, would look more like a missile than a space plane, [Richard] Varvill [REL chief designer] says. It would be built to test the initial stage of a flight to space — taking off from the ground and accelerating to about Mach 5 with air-breathing engines — and then the engine would shut off and the air-craft would glide back to the ground."

As I said before, the company is clearly more flexible than people trying to "defend" the company.

Offline oddbodd

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Re: The Reaction Engines Skylon Master Thread (5)
« Reply #1415 on: 03/28/2016 03:47 PM »

A scramjet can go up to Mach 10.


Yeah, I didn't do enough searching when I wrote that, but to be fair, it only traveled at that speed for 10 seconds and that was way back in 2004. Since then as far as I could see lower speeds with longer durations have been the norm.


Mach 5 you can do with a turboramjet, to my knowledge.

Both have very bad thrust-to-weight ratios, but that's not a showstopper for atmospheric flight. Space launch is hardly a relevant market at this point.

Which was the main point of my post. The scramjet research and the people involved have no sensible bearing on space launch, so why the hell ask them to comment on SABRE?

Offline john smith 19

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Re: The Reaction Engines Skylon Master Thread (5)
« Reply #1416 on: 03/28/2016 05:13 PM »
I'll note that people who love the SCRamjet concept never talk about it's T/W or the very large system needed to get it up to operating speed.

It took me years to discover the current expected T/W for a SCRamjet is about 2:1. That's less than the combined J58/nacelle combination (and the combination was key to making the system work) for the SR71 in the mid 1950's.

6 decades of effort (starting roughly in 1960 at Johns Hopkins APL) has produced this.

Historically fixed geometry ramjets have been good for a an operating Mach range of about 3 IE M1-M4 M2-M5 at most disregarding the weight of the rocket (including propellant) or air breathing engines to get it there.

SABRE design (as it was planned to from day one) covers the whole range from 0 to M23. The downside is it's poor (but only  by rocket standards) T/W ratio (which is 50% better than state of the art turbofans).

SABRE buys a huge propellant tank (provided by the airflow through it) and that makes it's relatively poor IE T/W ratio 7x better than SCRamjet, performance, coupled with it's excellent air breathing Isp good enough to get the job done.
"Solids are a branch of fireworks, not rocketry. :-) :-) ", Henry Spencer 1/28/11  Averse to bold? You must be in marketing."It's all in the sequencing" K. Mattingly.  STS-Keeping most of the stakeholders happy most of the time.

Offline A_M_Swallow

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Re: The Reaction Engines Skylon Master Thread (5)
« Reply #1417 on: 03/29/2016 12:24 AM »
New Skylon article with some  details on the test program at the end.
http://epizodsspace.no-ip.org/bibl/inostr-yazyki/aerospace-america/2016/3/8-11.pdf

Looks like they are planning a single engine suborbital test vehicle. Props to AM_Swallow for predicting this.

EN: "The first flight test vehicle, with its  single  engine, would look more like a missile than a space plane, [Richard] Varvill [REL chief designer] says. It would be built to test the initial stage of a flight to space — taking off from the ground and accelerating to about Mach 5 with air-breathing engines — and then the engine would shut off and the air-craft would glide back to the ground."

As I said before, the company is clearly more flexible than people trying to "defend" the company.

A good sign that they are actually bending metal.

Offline 93143

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Re: The Reaction Engines Skylon Master Thread (5)
« Reply #1418 on: 03/29/2016 05:41 AM »
As I said before, the company is clearly more flexible than people trying to "defend" the company.

No one ever complained about test vehicles.

The issue is that some feel the full DDT&E/certification program for a full-size commercial TSTO would be a waste of time and money, because it could easily cost as much or more to develop as Skylon without being nearly as cheap or easy to use (it might very well not be competitive with SpaceX, assuming F9 reusability goes well), and if SABRE works as expected and the airframe technology development doesn't trip over any major oversights, the technical risk associated with SSTO isn't high enough to make up the difference.  It's the same reason nobody is proposing a 3STO nowadays.

But it is hard to tell from the armchair, and there's still room for various opinions on this matter.

I tried to do some figuring on a SABRE-based TSTO one time.  As I recall, the numbers looked surprisingly bad, due in part to the extra hydrogen required for first-stage RTLS...  but maybe my design assumptions needed tweaking...
« Last Edit: 03/29/2016 10:21 AM by 93143 »

Offline Star One

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The Reaction Engines Skylon Master Thread (5)
« Reply #1419 on: 03/29/2016 06:52 AM »
Seems like REL may have some competition in this area & LM hope to fly their demonstrator by 2018.

Quote
That is according to Skunk Works head Rob Weiss, who confirmed that it would be an unmanned vehicle, at least at first. Hewson says the company’s long-term ambition is to “enable hypersonic passenger flights and easier access to space”.

Quote
Hewson, while displaying an artist’s rendering of the SR-72, said it would cost “less than $1 billion” to develop and fly a demonstrator aircraft the size of a the company's F-22 Raptor.

Quote
[In] 2016 [there] will be a decision on winners; more than one, likely, on one or both programmes,” says Weiss, adding that flight tests are planned for 2018.

https://www.flightglobal.com/news/articles/lockheed-pushing-1-billion-mach-6-airbreather-423198/
« Last Edit: 03/29/2016 06:54 AM by Star One »

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