Author Topic: The Reaction Engines Skylon Master Thread (5)  (Read 421626 times)

Offline john smith 19

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Re: News
« Reply #360 on: 06/15/2015 02:20 PM »
I wonder if STOIC is still an expansion-deflection nozzle?  I assume so.
According to the REL update at the IAC (IAC-13,D2,4,6,x19609) STOIC is the hot fire version of the STRIDENT cold flow test test chamber, itself developed from the initial STRICT chamber and CFD models calibrated from STRICT tests. All of this is around E/D nozzles.

So yes an E/D nozzle, but incorporating a)Active cooling. AFAIK all  AE engines have been heat sink designs made from big billets of Copper. b) Probably including both air and O2 cooling to simulate the switch over in flight.

Making this the first tri-propellant thrust chamber test in the UK  :)

I've always had a thing about "transitions" in systems. My instinct has always been the air/LOX shift in the chamber and things like the final sealing of the inlet by the spike and its sealing rings would be the place where "unknown unknowns" would be prone to lurk in this system to bite you.

These tests look like they will tackle that issue head on.

If I'm reading the press release correctly STOIC will therefor do a full duration burn (a little over 16 mins) starting in air/H2 and shifting to O2/H2 around 5 mins in.

Sadly I don't think this will include altitude effects but will supply more detailed data to upgrade the CFD for the ground test SABRE.
« Last Edit: 06/15/2015 02:21 PM by john smith 19 »
"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 Citizen Wolf

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Re: The Reaction Engines Skylon Master Thread (5)
« Reply #361 on: 06/16/2015 12:33 AM »
Excellent news. Good to hear that things are hotting up at REL  :)
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Offline Kharkov

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Re: The Reaction Engines Skylon Master Thread (5)
« Reply #362 on: 06/16/2015 06:15 AM »
I seem to recall it being said that the addition of Expansion/Deflection nozzles to SABRE engines means that the required distance to reach takeoff speed, and so the maximum length of the runway allowing abort capability will be reduced to less than the max length of 5,500mtrs, which to my mind has always been a problem. Not a project-stopping problem but a significant PITA.
Would anyone care to speculate, if we take it as read that Expansion/Deflection nozzles are used, what the standard takeoff/max runway length would be?
Even Entropy Isn't What It Used To Be

Offline john smith 19

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Re: The Reaction Engines Skylon Master Thread (5)
« Reply #363 on: 06/16/2015 10:49 AM »
I seem to recall it being said that the addition of Expansion/Deflection nozzles to SABRE engines means that the required distance to reach takeoff speed, and so the maximum length of the runway allowing abort capability will be reduced to less than the max length of 5,500mtrs, which to my mind has always been a problem. Not a project-stopping problem but a significant PITA.
Would anyone care to speculate, if we take it as read that Expansion/Deflection nozzles are used, what the standard takeoff/max runway length would be?
Hempsell mentioned this on a Space Show, but I can't recall which episode.

IIRC this could cut the take off run by 400-500m. As this at full GTOW that would be the part of the runway that has to be extra reinforced.

REL have talked of the runway as a $Bn investment so cutting 1/9 of the heaviest section should be good for saving $90-100m for a new build.

I'll remind people that is only for a full orbit capable runway. A Skylon could be based in its home country at much shorter (lower loading) runways at it'll be 150 tonnes lighter when in air breathing out to Kourou, before LH2 refuel and LO2 on load.
« Last Edit: 06/16/2015 10:59 AM by john smith 19 »
"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 john smith 19

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Re: News
« Reply #364 on: 06/18/2015 05:34 PM »
The SABRE engine requires a novel design of the rocket engine’s thrust chamber and nozzle to allow operation in both air-breathing and rocket modes, as well as a smooth transition between the two. The Advanced Nozzle project is demonstrating the feasibility of this concept and represents a significant technology development effort towards the SABRE demonstrator engine.
Most interesting.

Will the test engine have a name?

"SABRE demonstrator engine" seems a bit unwieldy, or is it so close to a flight model SABRE it's more like SABRE v0.9?
"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 t43562

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Re: News
« Reply #365 on: 06/19/2015 05:02 AM »
Will the test engine have a name?

"SABRE demonstrator engine" seems a bit unwieldy, or is it so close to a flight model SABRE it's more like SABRE v0.9?

"sabre" I imagine.

or "sABRE" :-)  or . . . . . . dare I say it . . . . .. "Light ...er ... SABRE?"

Offline Citizen Wolf

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Re: The Reaction Engines Skylon Master Thread (5)
« Reply #366 on: 06/19/2015 02:58 PM »
It's not a full SABRE, so perhaps it might be referred to as a SABRE lite;
.........or even as t43562 suggests, a lite SABRE.   ::)
« Last Edit: 06/19/2015 02:59 PM by Citizen Wolf »
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Offline Citizen Wolf

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The only thing I can be sure of is that I can't be sure of anything.

Offline t43562

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Re: The Reaction Engines Skylon Master Thread (5)
« Reply #368 on: 06/23/2015 05:59 PM »
I have been reading over on the pprune forum (military aviation) several posts in praise of the use of a ski jump to launch the Harrier and the upcoming F35-B.   "It's like having a free 1.5km runway in the sky".

A question was asked about why they are not used on land as well - and here is a video of that happening:

https://vimeo.com/lmaeronautics/review/131439135/07c088ad82

The answer was generally that they weren't so critically important when there was enough runway space as you do find on land.  They are also inconvenient if you want to use the runway to land in the opposite direction (if I understand correctly).

I was just thinking about whether Skylon could make use of a ramp?

I couldn't immediately see if this had been discussed before - perhaps long ago or with different words than I searched for.  Sorry if I missed it.

Presumably the gradient would have to be much lower for such a long vehicle and perhaps the landing gear might not survive it. 
I am sure there must be other objections but I thought it might make the very expensive runway a bit shorter.

I suppose to be fair it wouldn't remove the need for a long of free space after the end of the runway for a Skylon to pass over as it builds up to flying speed but you would not, perhaps, have to build anything on it.

I suppose there is also the thought that Skylon doesn't have any kind of thrust vectoring and I'm not sure how much that affects the usefulness of a ramp.  Wikipedia tells me that the Su-33 doesn't appear to use vectoring but I have seen the ramps on Russian carriers.

Offline john smith 19

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Re: The Reaction Engines Skylon Master Thread (5)
« Reply #369 on: 06/23/2015 06:29 PM »
I suppose there is also the thought that Skylon doesn't have any kind of thrust vectoring and I'm not sure how much that affects the usefulness of a ramp. 
I thin k you'll find that SABRE does do thrust vectoring, but on the whole engine, rather than something smaller.
"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 93143

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Re: The Reaction Engines Skylon Master Thread (5)
« Reply #370 on: 06/23/2015 08:57 PM »
I thought it was just the chambers/bells that were supposed to gimbal.  And not by much; this isn't a Harrier here...

Offline Kharkov

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Re: The Reaction Engines Skylon Master Thread (5)
« Reply #371 on: 06/24/2015 05:07 AM »
@t43562

I think you'll find that Skylon's takeoff speed is around Mach 0.5. I'm not an engineer but I really wouldn't want to hit even a very modest ski jump at anything like that speed...

Having said that however, would it help matters - shorten the takeoff run a bit & get Skylon into the air quicker - if at around Mach 0.45, the forward undercarriage extended its length by another metre or so, raising the nose and increasing the angle of attack on the wings?

I suspect you'd need to gimbal the thrust somewhat to avoid melting bits of the runway...
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Offline john smith 19

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Re: The Reaction Engines Skylon Master Thread (5)
« Reply #372 on: 06/24/2015 09:42 AM »
I thought it was just the chambers/bells that were supposed to gimbal.  And not by much; this isn't a Harrier here...
It's a tricky point. Early US engines (and I think the Russians?) pivoted their thrust chambers only, but the US started pivoting their whole engines from quite early on, presumably feeling pivoting about the fairly low pressure feed lines from the tanks were going to be a lot easier than moving the TC, need flexible couplings capable of staying leak proof at 10s (100's for the SSME) of atms.

You're right about the gimbal angles, IIRC even the Shuttle only did +/- 7.5 deg on any axis, which is well within the range of a flexure bearing (which can be made very strong)
"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 t43562

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Re: The Reaction Engines Skylon Master Thread (5)
« Reply #373 on: 06/24/2015 10:49 AM »
@t43562

I think you'll find that Skylon's takeoff speed is around Mach 0.5. I'm not an engineer but I really wouldn't want to hit even a very modest ski jump at anything like that speed...

I'm also a layman but from what I read, the aircraft leaves the ramp at less than flying speed - otherwise the ramp wouldn't actually be serving any purpose.  It's the fact that it has space and time (thanks to the vector given to it by the ramp) to accelerate in the air and reach flying speed without it's wheels having to be on tar that gives you the advantage of a shorter runway.

M 0.5 is about 600kmh and googling leads me to believe that the Harrier stalls at roughly 270kmh.  I suppose the harrier number is rather a rough guess and would be very variable depending on takeoff weight anyhow.  Nevertheless it's indicative of the relative difference - maybe Skylon need to travel about 2X faster.

Perhaps any ramp would have to be correspondingly 2X more gentle and would then need to be very very long and very very strong and would end up being more expensive than the extra runway.  It's gradient would also be limited by how much Skylon could tip before the tail touched the ground and as you said the effect of the engines on the runway.
 

« Last Edit: 06/24/2015 10:54 AM by t43562 »

Offline SICA Design

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Re: The Reaction Engines Skylon Master Thread (5)
« Reply #374 on: 06/24/2015 06:10 PM »
The real killer for this idea is that a large proportion of the runway is for abort contingency, where Skylon cuts off the engines and slams on the (water cooled) brakes.

Bang (crash, bang, wallop) goes the intact abort option when you fall off the end of the ramp while braking...

Offline john smith 19

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Re: The Reaction Engines Skylon Master Thread (5)
« Reply #375 on: 06/24/2015 06:59 PM »
Given Reaction Engine's approach of having as few unconventional technologies as possible, I suspect launch ramps are something that may not be considered for the first wave.
Welcome to the site.

Yes, I've never heard of a land runway with ski jump. It's a clever idea but aircraft carriers have (essentially) a cliff the aircraft falls off if takeoff fails. That's not the case for normal airports.
"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 t43562

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Re: The Reaction Engines Skylon Master Thread (5)
« Reply #376 on: 06/24/2015 09:01 PM »
The real killer for this idea is that a large proportion of the runway is for abort contingency, where Skylon cuts off the engines and slams on the (water cooled) brakes.

Bang (crash, bang, wallop) goes the intact abort option when you fall off the end of the ramp while braking...

One of the great things about the internet is the way that you get to talk to all sorts of people you'd never otherwise meet.  I asked John Farley, one of the most famous Harrier test pilots, about it on pprune and his objection was that the T/W had to be over 0.85 roughly.   My very dodgy guess at Skylon's T/w is 0.26.

As for abort.....obviously that does present a serious problem but I suppose it might be worth trying to think about that some other way if a ramp was actually worthwhile in the first place.
« Last Edit: 06/24/2015 09:02 PM by t43562 »

Offline Asteroza

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Re: The Reaction Engines Skylon Master Thread (5)
« Reply #377 on: 06/24/2015 11:23 PM »
Possible arrangement of a ramped runway is an otherwise long and flat conventional runway with an overrun extension leading up an embankment to an elavated (relative to main runway elevation) runout extended overrun area exclusively for Skylon. If the embankment change in elevation is roughly equivalent to traditional 100ft obstacle clearance spec and is a appropriate upward curve for the expected speed, normal airplanes will have no issue (though pilots will get creeped out by the ground following them up). The annoyance is the overrun area is where approach lighting equipment is normally located (and the inner marker beacon?) so how one would set that up flush in the overrun is a bit of a problem. That achieves the hump with no cliff dropoff, and no downhill component for a inserted hump in a runway complicating emergency braking.

In retrospect, I suppose the humped aspect could be better achieved with a single contiguous runway with the hump near Skylon Vto, so the overall runway looks like a flattened S shape. This avoids the overrun design issues. Many existing runways have non-flat profiles due to local topography (and cost cutting avoiding the earthworks to build a flat runway), though I think of those, most tend to have a V profile? Though that depends on local terrain being helpful to keep costs down.

Offline 93143

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Re: The Reaction Engines Skylon Master Thread (5)
« Reply #378 on: 06/25/2015 09:29 PM »
My very dodgy guess at Skylon's T/w is 0.26.

C1 was around 0.45-0.47 during the takeoff roll, and peaked (for the airbreathing segment) at roughly 0.8 just past Mach 2.  The D revision has some substantial differences from the C designs, including larger wings and a more efficient engine cycle, so there might be some modest changes in those numbers.

Offline lkm

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Re: The Reaction Engines Skylon Master Thread (5)
« Reply #379 on: 06/26/2015 07:59 PM »
I've been thinking about the differences between the SABRE 3 and SABRE 4 cycles since the patents became available to read.
I think it's interesting that where as the former was designed as an integrated engine which was an excellent rocket and an adequate air breather the later seems to be a much less integrated engine designed to be an excellent rocket and and a good air breather and that this disintegration of the engine modes has resulted in a much more flexible design.

Historically all attempts at combined cycle engines seem to be about finding the right balance between performance and integration of different engine cycles and it seems REL have moved in the direction of more performance and less integration.

An interesting result of this is that where as previously the SABRE engine could be said to be not much good for anything other than SSTO that's no longer strictly true for the SABRE 4 cycle. Its equivalence ratio of 1.2 is not far off Scimitar's EQ of  0.7959 and the patent allows for a variant to run at the same EQ by adding another recuperation stage and lower pressure combustion chambers, further the only thing that is shared with the rocket mode is the nozzle so it would seem possible to easily remove all the pure rocket components to make a pure air breathing SABRE variant with reasonable fuel consumption only without the high life cycle and subsonic efficiency of Scimitar.

This begs the question, given the USAF interest in SABRE, have REL  decided in order increase their addressable market  to develop a duel purpose engine design that both satisfies their design needs for SSTO but also allows for an easily achievable variant that satisfies USAF desire for hypersonic flight and when they talk about SABRE, is this the SABRE they're talking about?   

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