The Reaction Engines Skylon/SABRE Master Thread (6)

[Star One]

can anyone see behind this paywall?
http://aviationweek.com/new-space/reaction-engines-refines-hypersonic-engine-demonstrator-plan

Try this link instead.
http://www.nextbigfuture.com/2016/09/fighter-engine-size-hypersonic-ground.html?utm_source=feedburner&utm_medium=feed&utm_campaign=Feed:+blogspot/advancednano+(nextbigfuture)&utm_content=FaceBook&m=1

The NBF article includes nothing about the single-engine demonstrator, it just regurgitates general decade old info about Skylon/SABRE.

[Edit: The key phrase in the pre-Paywalled summary would be "fighter engine-size ground demonstrator" I suspect. In other words, nothing to see here, we already knew they'd do this. The only new info would be an estimated date.]

Though I have an AW login it doesn't unfortunately let me into that article as it's marked as premium content.

[momerathe]

[Edit: The key phrase in the pre-Paywalled summary would be "fighter engine-size ground demonstrator" I suspect. In other words, nothing to see here, we already knew they'd do this. The only new info would be an estimated date.]

What pinged my radar was "fighter engine-size". Firstly because of previous comments on the difficulty of scaling the engine down, and secondly because of my ongoing suspicion that BAE are more interested in a hypersonic bomber than an SSTO.

[Star One]

[Edit: The key phrase in the pre-Paywalled summary would be "fighter engine-size ground demonstrator" I suspect. In other words, nothing to see here, we already knew they'd do this. The only new info would be an estimated date.]

What pinged my radar was "fighter engine-size". Firstly because of previous comments on the difficulty of scaling the engine down, and secondly because of my ongoing suspicion that BAE are more interested in a hypersonic bomber than an SSTO.

I imagine they are interested in providing the engines for something like LM's proposed SR-72 hypersonic global strike/ISR aircraft.

[93143]

previous comments on the difficulty of scaling the engine down

It's not that it couldn't be scaled down at all - just that scaling it down a lot results in a very expensive ultra-high-speed hydrogen turbopump, limiting the cost benefits of going small.  And even that might be subject to finesse if they're after a fighter engine rather than an accurate subscale simulation of a Skylon engine, particularly if they're using the SABRE 4 cycle...

[lkm]

[Edit: The key phrase in the pre-Paywalled summary would be "fighter engine-size ground demonstrator" I suspect. In other words, nothing to see here, we already knew they'd do this. The only new info would be an estimated date.]

What pinged my radar was "fighter engine-size". Firstly because of previous comments on the difficulty of scaling the engine down, and secondly because of my ongoing suspicion that BAE are more interested in a hypersonic bomber than an SSTO.

If you're  only interested in testing the cycle and not actually using the engine in anything then it's actually pretty simple to scale down a SABRE engine, just cut it in half. The engine (SABRE 3 at least)  is designed such that there's 2 of everything past the compressor for safety reasons, so to scale the engine you can easily build it at half scale with only a single set of full sized components attached to a smaller compressor and precooler. But it will lack all the redundancy and safety benefits of a full size engine and be fundamentally less safe.

[Matthew Ak43]

Here's the AFRL paper in full.

[Katana]

[Edit: The key phrase in the pre-Paywalled summary would be "fighter engine-size ground demonstrator" I suspect. In other words, nothing to see here, we already knew they'd do this. The only new info would be an estimated date.]

What pinged my radar was "fighter engine-size". Firstly because of previous comments on the difficulty of scaling the engine down, and secondly because of my ongoing suspicion that BAE are more interested in a hypersonic bomber than an SSTO.

I imagine they are interested in providing the engines for something like LM's proposed SR-72 hypersonic global strike/ISR aircraft.

SR71's proposed suntan project, precursor of RL-10...

[Katana]

Is it possible to have a polite discussion about how SpaceX and Blue Origin affect Reaction Engines without it going off-course into a shouting match about whether SpaceX can't or didn't choose to build a reusable second stage?  I hope so, because I think it's an important issue for Reaction Engines.

The original value proposition of Skylon was versus the old state-of-the-art: expensive, expendable launch vehicles.  Now, the state of the art is changing.  As both Blue Origin and SpaceX move closer to inexpensive, reusable launch vehicles, it erodes the value proposition of Skylon in comparison.  It's one thing to say they want to spend $16 billion to produce a system that reduces launch costs from $250 million per launch to $5 million per launch.  It's a harder sell if the reduction is from $60 million to $5 million.  And even harder when the reduction is from $40 million, then $20 million, and so on.

On the other hand, having other competitors moving toward a low-cost launch system could prove and expand the market, giving investors confidence to invest in REL, particularly if Europe is afraid of the new low-cost launchers and wants its own alternative.

So, which is the bigger effect?  My opinion is that the changes in the market from Blue Origin and SpaceX will have much more of a negative effect on REL than a positive effect.

Not so bad.

Investors in EU could be stimulated by SpaceX /BO and willing to invest on some alternative, regardless of actural technical details (reusable second stage, etc). Somewhat similliar to Rlabs, Firefly, Vector, etc.

Technically, SABRE engines may power some VTVL first stage either. But this is Not the right story to tell now.

[john smith 19]

Here's the AFRL paper in full.

Thanks. That will give a lot of food for thought.

SR71's proposed suntan project, precursor of RL-10...

No. The Martin "Suntan" was the official winner of the competition. Lockheed (they were 2 separate companies) lobbied hard and eventually the A12 design got accepted.

Suntan provided the Hydrogen turbo pump for what became the RL10.

If you're  only interested in testing the cycle and not actually using the engine in anything then it's actually pretty simple to scale down a SABRE engine, just cut it in half. The engine (SABRE 3 at least)  is designed such that there's 2 of everything past the compressor for safety reasons, so to scale the engine you can easily build it at half scale with only a single set of full sized components attached to a smaller compressor and precooler. But it will lack all the redundancy and safety benefits of a full size engine and be fundamentally less safe.

That gives you an engine that's got the thrust of just 2 1/4 Trent 900's (one engine option for the A380).

The problem is the Hydrogen turbo pump and especially the chamber pressure. 

Pump designers talk in terms of the static head. How high would a column of the fluid need to be to exert the same pressure as the pump at the base. LH2 columns are measured in kilometres. REL's view has always been why speed a disproportionate amount of money for what is essentially a 1 shot engine.

[Archibald]

Here's the AFRL paper in full.

thank you for the paper, an interesting read, but I'm still not convinced at all.
- The 5000 Ibs payload / expendable stage brings nothing when compared to the all rocket DARPA XS-1.
- As for the 20 000 pounds payload AND reusable upper stage - well, SpaceX in 2011 showeved a reusable stage 2 but since then it has been buried indefinitively. Whatever way is used to recover stage 2 there is a serious weight penalty that eat the payload (even worse when the stage is made winged)

By the way, the document CGI was rather crappy. It looked like CGI from the late 90's.

[john smith 19]

I've just had a first look at the report. I'll be updating my spread sheet with the data from the upper stage options.

As always the devil is in the details. In this case the assumptions you start the various pieces of software running with.

"Engines were sized for a takeoff T/W of 0.7" Why ?

Historically engine thrust has been about 1/3 GTOW for HTOL vehicles.  Concorde (with reheat at takeoff) was about 0.37 and the Firebee drones did supersonic cruise with T/W at 0.5. That makes a huge difference in engine weight. Given the opacity of the "Mass Estimating Relationships" used (Might have been the USAF program, might not) it's unclear what knock on effects this would have had. I'd guess they would be substantial. 

So why assume a HTOL booster needs so much more T/W?

As for the propellant mass fraction being lower than a rocket well it's not a rocket, it's an aircraft. So how does that compare with big aircraft? In fact why is it important?

Incidentally I did not know that "pleny" is actually a word.

[Jim Davis]

No. The Martin "Suntan" was the official winner of the competition. Lockheed (they were 2 separate companies) lobbied hard and eventually the A12 design got accepted.

No, Suntan (the Lockheed CL-400 design) was a Lockheed design. Kelly Johnson quickly realized that LH2 was not ready for prime time and offered to design a "conventional" design in its place. This design eventually became the A-12.

You may be thinking about another, earlier, competition that Lockheed managed to wrest away from its nominal winner. Bell won the competition for a high altitude reconnaissance aircraft with a twin engine design which was designated the X-16. Lockheed, represented by Kelly Johnson, kept pushing for its own design which was a single engine design that looked like an F-104 with high aspect ratio wings. This design eventually prevailed and became the U-2.

[john smith 19]

No. The Martin "Suntan" was the official winner of the competition. Lockheed (they were 2 separate companies) lobbied hard and eventually the A12 design got accepted.

No, Suntan (the Lockheed CL-400 design) was a Lockheed design. Kelly Johnson quickly realized that LH2 was not ready for prime time and offered to design a "conventional" design in its place. This design eventually became the A-12.

You may be thinking about another, earlier, competition that Lockheed managed to wrest away from its nominal winner. Bell won the competition for a high altitude reconnaissance aircraft with a twin engine design which was designated the X-16. Lockheed, represented by Kelly Johnson, kept pushing for its own design which was a single engine design that looked like an F-104 with high aspect ratio wings. This design eventually prevailed and became the U-2.

I think I've comflated Lockheed's behavior in the first with that of the second.

[john smith 19]

I've now had a chance to read the report and added the numbers for the upper stage and fully reusable versions to my spreadsheet on additional worksheets. As before I've related the raw numbers to percentages of GTOW or gross weight of stage and of dry weight of stage. My original reservation about why they made the T/O Thrust to Weight so high and mentioned the propellant mass fraction was low compared to a VTO ELV remain.

As before I calculated values for numbers which should have been derived by summing items higher up the charts as a sanity check . The results are somewhat worrying.

For the expendable option the Dry Weight is 88lbs lighter than the number given, as is the inert weight. Using the listed numbers for inert weight added to propellant masses, payload and payload adapter gives a number that's 630lb too small.

BTW the Mass Growth Allowance is 650 lb yet this seems to be factored in to Dry Weight and is 20lbs too big to account for the discrepancy.

This suggests a) there is an 650lb item left off the BoM for some reason. b) someone cannot seem to add up, or c) can't get a spreadsheet to add it up for them. 

The 20 000lb "fully reusable " is very low resolution. There is no mass break down and it's RP1, despite authors saying it would probably use LH2 as well. The GTOW given is bigger than the sum of the stage gross weights by over a 1/4 of a million lbs.

Incidentally using the Upper Stage Gross and dry weights shows a design with a structure that is under 16% of fully fueled mass (it's just under 3.8% of the GTOW if you use the reports figure of 1 300 000lbs). Skylon is 16% without consumables and reserves, about 18% with (giving what the expendable stage figures calls the "inert" weight).

Perhaps these weights are not meant to be calculable by adding up previous items. Perhaps there has been a "reserve pile up" as levels of "growth allowance" have been applied one atop the other. Perhaps an intern mis-keyed some numbers on their calculator (but if so why were they using a calculator to begin with?)

Maybe the graphs are more accurate because they were produced by programs in their development framework. I'm still not clear why a 5g turn is needed in the flight path, nor why the booster doesn't run in airbreathing up to the full M5.5. Because the computer says it's not optimal,  apparently.

Some of the conclusions are quite baffling. "SABRE is a unqiue cycle that will require significant development to mature." Left out is the fact most of that can be achieved in a ground facility without building a full size flight vehicle.

"conformal LH2 tanks used in the nose and aft body sections of the booster are also in need of technology maturation and represent a risk item." Then why were they chosen? The report does not say.     It implies they would be composite but one of the often forgotten facts of the X33 programme was that an Aluminum conformal tank was made that was the same mass as the problematical composite tank. However a former Boeing engineer (I'm not sure who he was working for) testified before Congress this would eliminate the audit trail between the X-33 and the supposed commercial "Venturestar" LV.  NASA and LM accepted this with results that are now history. 

As for another trade study between SABRE, Rocket, RBCC, TBCC and SCRamjet well consultancy firms always want another trade study. Either you want to do this or you don't and you want to do it because SABRE gives you unique advantages over other engines and you already know this, otherwise you wouldn't have chosen it in the first place, would you?

With the switch to the SABRE 4 cycle and its (presumed) lower chamber pressures using Methane might now be in the range of possible changes.

I think this study has reassured people that if SABRE meets it's performance objectives then a system could be built round it that did not have to be SSTO to work. 

And they managed to avoid adding a SCramjet to the design as well.

[Asteroza]

5G turn was to simplify return to runway, as it would be a straight shot in to CCAFS shuttle runway. I guess somebody really did not want to do low speed turns to do a runway alignment like the old shuttle HAC.

[t43562]

This is available now:

http://m.aviationweek.com/technology/reaction-engines-refines-hypersonic-engine-demonstrator-plan

[john smith 19]

This is available now:

http://m.aviationweek.com/technology/reaction-engines-refines-hypersonic-engine-demonstrator-plan

Funny I could have sworn something like this was listed a week or two ago under "premium content."

Just to give some scale a full size SABRE thrust is about 4 1/4x that of a Trent 900, the usual engine on an Airbus 380. Roughly 80 000lb thrust.  "Fighter size" is more like 10-20 000lb thrust or RL10 size, which is an appropriate metric here.  Using the USAFRL model of T/W of 0.7 that would be a flight vehicle of about 57 000lb, but that would be the TSTO with the ELV. Not going to do anywhere near 5 000lb to orbit. 

[t43562]

They say 44,000lb thrust for the fighter-sized engine which is about the same as an F-136 (and F-135, sorry)  with afterburner - at least according to wikipedia. 

[CameronD]

This is available now:

http://m.aviationweek.com/technology/reaction-engines-refines-hypersonic-engine-demonstrator-plan

Funny I could have sworn something like this was listed a week or two ago under "premium content."

Just to give some scale a full size SABRE thrust is about 4 1/4x that of a Trent 900, the usual engine on an Airbus 380. Roughly 80 000lb thrust.  "Fighter size" is more like 10-20 000lb thrust or RL10 size, which is an appropriate metric here.  Using the USAFRL model of T/W of 0.7 that would be a flight vehicle of about 57 000lb, but that would be the TSTO with the ELV. Not going to do anywhere near 5 000lb to orbit.

I read that article as meaning they were planning to build a ground demonstrator the same physical size as a fighter engine.  It would not necessarily be the same thrust, but perhaps if it was (or better!) they could break into another market.

[Rocket Science]

A few years back I mentioned that they should test a "scaled down" engine as was done with with NASA/Lockheed Martin Linear Aerospike SR-71 Experiment (LASRE) and was told that it was not needed. I'm glad the Air Force agrees with me. Hopefully it will lead to an inflight test as well...
http://www.nasa.gov/centers/dryden/history/pastprojects/SR71/Lasre/index.html