Author Topic: The Reaction Engines Skylon Master Thread (1)  (Read 746141 times)

Offline KristianAndresen

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Re: Skylon
« Reply #340 on: 07/16/2011 09:04 pm »
And here are my comments:

I don't agree with the suggestion to add solid rocket boosters, but what this guy writes about combining an attached JP-7 based flying wing (could be on remote controlled flyback to launch site) and ending up with a water landing makes a lot of sense to me. I'm just wondering why he is suggesting only 6 inches of water? The Skylon engines are already designed to close off the intakes when the speed gets sufficiently high - the same mechanism can serve to protect the engine from seawater. Plus, a skylon which has emptied its hydrogen fuel tank with nothing but hot gas remaining, and which has delivered the payload to orbit... I suspect it can make a water landing at very low speed and therefore without needing to reinforce the hull. And it cannot possibly sink prior to recovery. The obvious recovery vehicle would be a carrier equipped with a crane and either the American EMALS or the British EMCAT catapult for the next launch.

Offline john smith 19

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Re: Skylon
« Reply #341 on: 07/16/2011 09:54 pm »

"I have read many of the documents at the REL site, but not yet found the documents you refer to that address this and my other points. If you have them handy, please post the links."

There are no documents that discuss you questions from your POV.
Some of your questions indicated you did not understand Skylon's structure. This would be the place to start.
 
http://www.reactionengines.co.uk/downloads/JBIS_v57_22-32.pdf

"Shuttle data gives you good confidence. (But Concorde burst tire data is less rosy.)"
 I fatal crash in 27 years is pretty good by many yardsticks.

"However, in the "commercial" promotional video at the REL web site, they depict a fleet of Skylons at what appears to be a commercial airport - there are A380s there."

REL do not want to *owe* or operate Skylon. It is designed to be *sold* to operators. This has been their position since the start. *Others* buy them, operate them or (if they are rich enough) just leave them on their front yard. It's an *asset*, not a chunk of hardware that gives you a single ticket to ride.

This business model is alien to the space launch business(including the alt-space sector like Xcor or Spacex). REL wanted to make this clear.
MCT ITS BFR SS. The worlds first Methane fueled FFSC engined CFRP SS structure A380 sized aerospaceplane tail sitter capable of Earth & Mars atmospheric flight.First flight to Mars by end of 2022 TBC. T&C apply. Trust nothing. Run your own #s "Extraordinary claims require extraordinary proof" R. Simberg."Competitve" means cheaper ¬cheap SCramjet proposed 1956. First +ve thrust 2004. US R&D spend to date > $10Bn. #deployed designs. Zero.

Offline john smith 19

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Re: Skylon
« Reply #342 on: 07/16/2011 10:58 pm »
It might help you to keep in mind some of the REL ground rules.

No staging

Engines to be testable in the open air.

ITAR free (Even *conversations* with US companies in this area have to be pre-agreed, never mind buying equipment off them).

Normal aircraft operations as far as possible.

The 1200kg of water for the brakes are dumped shortly after a successful takeoff.  Landing gear is sized as a proportion of gross landing weight. Skylon's is no better than that of the B58 Hustler, which is as good as it needs to be.

Between them these cover goatguy's comments.
MCT ITS BFR SS. The worlds first Methane fueled FFSC engined CFRP SS structure A380 sized aerospaceplane tail sitter capable of Earth & Mars atmospheric flight.First flight to Mars by end of 2022 TBC. T&C apply. Trust nothing. Run your own #s "Extraordinary claims require extraordinary proof" R. Simberg."Competitve" means cheaper ¬cheap SCramjet proposed 1956. First +ve thrust 2004. US R&D spend to date > $10Bn. #deployed designs. Zero.

Offline adrianwyard

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Re: Skylon
« Reply #343 on: 07/17/2011 05:57 pm »
John, I'm trying to convince skeptics, so saying Concorde only killed 113 people (averages to only 4 per year) is not going to work. A better answer would be: Yes Concorde had tyre issues (an average of ~2 per year, the majority causing damage to hydraulics, engines, fuel tanks, etc,), but this was fixed by the tyre upgrade after the 2000 tragedy. Evidence? There were no more reported incidents until its retirement. Yes, if Skylon were to have two tyres blow per year this would mean two aborts per year, and yes Skylon has highly loaded landing gear which exacerbates the problem, but it will use modern tyre technology and so this will not be an issue.

Back to the bird strike threat: It may be that the odds of any bird strike during its lifetime can be shown to be negligible. However, if it is a perceived risk that needs to be reduced, I did come up with a somewhat crazy idea that would probably work: Robo-raptors! It might be that a fleet of RC-controlled planes painted to look like a Falcon, or other bird-of-prey would be sufficient to keep flocks at bay along the ascent corridor, but by the 2020s we can probably expect some robotics lab to provide something that moves more convincingly...

Again, the person I'm trying to persuade here is currently a fan of big dumb non-reusable boosters. They are correct when they say their solution is more robust on ascent than Skylon, not having to worry about bird-strikes* or burst tyres. My response is that the advantages of the Skylon system as a whole far outweigh the disadvantage of incurring these minimal risks.

____________
* Yes, I know rockets can hit birds too - the Shuttle certainly has - but with Skylon's competitors any bird will likely hit a fairing that will be jettisoned. With Skylon, *any* strike will hit something that's going to orbit, and then experiencing re-entry. I for one, only want to head to 17,500mph with a pristine TPS; would want any strike on the way up to trigger an abort.

PS. I'm aware of their business model. That video implies this new business model, correct. But it also implies Skylon can operated pretty much like an A380F, which was my concern.
PPS. An Air France Concorde had a Deer strike at Dulles in 1979. That's a contingency we can probably agree is truly negligible for Skylon...

Offline yamato

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Re: Skylon
« Reply #344 on: 07/17/2011 05:57 pm »
Did Reaction Engines evaluate the possibility of using some kind of catapult for liftoff? It would work exactly the same way as it works on the aircraft carrier. Would it make some difference in fuel consuption?

Offline deltaV

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Re: Skylon
« Reply #345 on: 07/17/2011 07:31 pm »
Did Reaction Engines evaluate the possibility of using some kind of catapult for liftoff? It would work exactly the same way as it works on the aircraft carrier. Would it make some difference in fuel consuption?
Skylon at takeoff has an ISP on the order of 20 km/s. Takeoff speed is on the order of 0.1 km/s, so fuel burned during takeoff is on the order of 0.5% of takeoff mass. A catapult launch would save carrying that extra fuel, decreasing dry mass by a similar percentage. That's certainly not negligible, but presumably not worth the trouble of designing and building a catapult.

If the catapult supported the vehicle instead of the landing gear one could reduce the size of the landing gear somewhat. This would save a significant amount of dry mass, but why add more risks and development cost for a marginal gain?

Offline yamato

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Re: Skylon
« Reply #346 on: 07/17/2011 07:49 pm »
Did Reaction Engines evaluate the possibility of using some kind of catapult for liftoff? It would work exactly the same way as it works on the aircraft carrier. Would it make some difference in fuel consuption?
Skylon at takeoff has an ISP on the order of 20 km/s. Takeoff speed is on the order of 0.1 km/s, so fuel burned during takeoff is on the order of 0.5% of takeoff mass. A catapult launch would save carrying that extra fuel, decreasing dry mass by a similar percentage. That's certainly not negligible, but presumably not worth the trouble of designing and building a catapult.

If the catapult supported the vehicle instead of the landing gear one could reduce the size of the landing gear somewhat. This would save a significant amount of dry mass, but why add more risks and development cost for a marginal gain?

I agree that these numbers are not interesting. It was just an idea.

Offline deltaV

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Re: Skylon
« Reply #347 on: 07/17/2011 09:41 pm »
Skylon has a few tons of water that it uses to cool the brakes during an aborted takeoff. It dumps that water immediately after takeoff. This seems like potentially a waste the (admittedly small) water tanks that have to be brought to orbit without helping except in emergencies. Here are four different crazy ideas for how to reduce this waste. I suspect that these ideas are bad ones, but they're interesting and might be good ideas so I'm mentioning them anyway.

(1) Use water to cool the brakes as in the current design. Rather than dumping the water immediately after launch use the water gradually during the air-breathing phase. The water would be boiled and heated to 300C or so, serving as an alternate heat sink for the helium loop. The resulting steam would be dumped in the ramjets for a bit of extra thrust. This would reduce the amount of hydrogen needed as a heat sink as well as the size and weight of the hydrogen/helium heat exchanger. Water is a far worse coolant/propellant combo than the same mass of hydrogen since the water cannot be used as ramjet fuel, but the water is almost free since you already need it for brake cooling. The hope is that replacing a small portion of the bulky hydrogen tanks with an already paid for water tank would make up for the slightly reduced specific impulse and thrust from the ramjet. The steam could potentially be used for curtain cooling the ramjet nozzle, allowing that nozzle to be made from lighter weight materials.

(2) Use LH2 to cool the brakes instead of water. In an emergency something is likely to go wrong and ignite the released GH2, putting the rear of the vehicle inside a hydrogen/air flame. Such a flame has a temperature of around 2210C. For most aircraft this would be problematic, but Skylon is designed for orbital reentry, which involves even hotter gases (albeit at much lower pressures). Skylon's skin presumably cannot tolerate getting anywhere near that temperature, but in a 20 second abort with some radiative cooling the skin might stay below the roughly 800C that it can handle. One could probably design things so that the GH2 and air would would only mix downwind of the wheels, sparing the wheels and brakes from these extreme temperatures.

(3) Use LH2 to cool the brakes on the main gear and water to cool the brakes on the nose gear. The GH2 would be released from the rear gear, which is a ways below the fuselage. The apparent wind will tend to more the flames aft (in the reference frame of the moving vehicle). If the flames rise slowly enough so that they move at an angle less than around 5 degrees above horizontal the flames would never contact the vehicle at all. There being nothing downwind of the rear brakes is why they are better suited for LH2 cooling than the front ones. The LH2 injection would be stopped once the vehicle reaches 20 m/s or so to allow the vehicle to clear the flames before stopping. This loss of cooling at low speeds is less problematic than it seems because the last third of the velocity has only a ninth of the energy.

(4) Use LOX to cool the brakes. One big potential problem is the likelihood of the lubricant burning away from the bearings. Another is the possibility of the asphalt runway burning. Burning fingerprints are probably OK since they wouldn't add significantly to the heat load.


Offline gbaikie

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Re: Skylon
« Reply #348 on: 07/18/2011 12:00 am »
Did Reaction Engines evaluate the possibility of using some kind of catapult for liftoff? It would work exactly the same way as it works on the aircraft carrier. Would it make some difference in fuel consuption?
Skylon at takeoff has an ISP on the order of 20 km/s. Takeoff speed is on the order of 0.1 km/s, so fuel burned during takeoff is on the order of 0.5% of takeoff mass. A catapult launch would save carrying that extra fuel, decreasing dry mass by a similar percentage. That's certainly not negligible, but presumably not worth the trouble of designing and building a catapult.

If the catapult supported the vehicle instead of the landing gear one could reduce the size of the landing gear somewhat. This would save a significant amount of dry mass, but why add more risks and development cost for a marginal gain?

What is the take off speed of Skylon?

What if the "catapult" merely added 60 mph, so as to reduce it's take off speed and distance. Suppose the "catapult" cost a few million?

Have "convoy" of 40 dump truck/lorries which have capacity of 20 ton load, giving total max load of 800 tons [1.6 million lbs]. So a line of 20 trucks and two columns and spaced so their outside perimeter is about 30' and 600' long. Have these vehicles support a deck which also about 30' wide and 600'. Have this deck weight around 100,000 to 200,000 lbs.

Have Skylon on an elevated structure the same height as 40 truck platform. Using tow vehicle used with airline planes, tow the fueled Skylon on to truck platform. Truck platform accelerates to say 30 mph [and continues up to 60 mph] but at 30 mph, Skylon accelerate and takes off around same time truck platform has reaches 60 mph.

This truck platform could about 6' to 8' above the runway. It could be disassembled into say 40' by 40' section and stacked say so each section is 5' high and 6 sections high [about 3 stories high] and taking a area of 80' square [6400 sq ft]. Such platform shouldn't cost much- 1/2 million or less. The trucks would major cost. Somewhere around 1 or 2 million dollars. And storing them would take up a larger area.
One could use rental cars- low height sports cars. Rent 200 of them. Or use employee's vehicles. Attach at wheel hubs- requiring a bearing for each wheel attached to- or spinning axial can extended with deck support member attached with a bearing to the spinning axial.

If using dump truck/lorry one could do more customizing, allowing  their height to be lower and thereby also lower the platform height. Such major modification could add another  million dollars to cost. And one could design these truck be always be attached to the deck and be stacked with decks when stored.
Oh, these vehicles would controlled remotely.
« Last Edit: 07/18/2011 02:57 am by gbaikie »

Offline sitharus

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Re: Skylon
« Reply #349 on: 07/18/2011 04:18 am »
Have "convoy" of 40 dump truck/lorries which have capacity of 20 ton load, giving total max load of 800 tons [1.6 million lbs]. So a line of 20 trucks and two columns and spaced so their outside perimeter is about 30' and 600' long. Have these vehicles support a deck which also about 30' wide and 600'. Have this deck weight around 100,000 to 200,000 lbs.

Have Skylon on an elevated structure the same height as 40 truck platform. Using tow vehicle used with airline planes, tow the fueled Skylon on to truck platform. Truck platform accelerates to say 30 mph [and continues up to 60 mph] but at 30 mph, Skylon accelerate and takes off around same time truck platform has reaches 60 mph.

[cut]

Oh, these vehicles would controlled remotely.


For some reason I'm reminded of the first episode of Thunderbirds, though that was landing, not takeoff.

Also that's a lot of things to go wrong for a small fuel saving.

Offline gbaikie

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Re: Skylon
« Reply #350 on: 07/18/2011 08:20 am »
Have "convoy" of 40 dump truck/lorries which have capacity of 20 ton load, giving total max load of 800 tons [1.6 million lbs]. So a line of 20 trucks and two columns and spaced so their outside perimeter is about 30' and 600' long. Have these vehicles support a deck which also about 30' wide and 600'. Have this deck weight around 100,000 to 200,000 lbs.

Have Skylon on an elevated structure the same height as 40 truck platform. Using tow vehicle used with airline planes, tow the fueled Skylon on to truck platform. Truck platform accelerates to say 30 mph [and continues up to 60 mph] but at 30 mph, Skylon accelerate and takes off around same time truck platform has reaches 60 mph.

[cut]

Oh, these vehicles would controlled remotely.


For some reason I'm reminded of the first episode of Thunderbirds, though that was landing, not takeoff.

Also that's a lot of things to go wrong for a small fuel saving.

I think of the "Mythbusters".
Not Brit, used lorry cause Brit spaceplane- I didn't see the Thunderbirds

Not a faithful follower of Skylon, don't know what it's take off speed is suppose to be. But it seems it would require quite a bit of speed to get airborne. If Skylon has no problem taking off, then not any need of such things.
Such a thing I mentioned, could be altered. You could use electric powered vehicle, along the line of Tesla Roadster- obviously no need to be pretty. But for short distance, it more than enough horse power, and could be really low to ground. You make go faster- say 100 mph. Might make it bit longer and wide. But it's a few million. And if getting enough speed for take off was a concern, it might be worth it.
« Last Edit: 07/18/2011 08:25 am by gbaikie »

Offline 93143

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Re: Skylon
« Reply #351 on: 07/18/2011 09:40 pm »
What is the take off speed of Skylon?

our rotation speed is around 590 km/hr

Offline RobLynn

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Re: Skylon
« Reply #352 on: 07/19/2011 07:34 am »
Skylon at takeoff has an ISP on the order of 20 km/s. Takeoff speed is on the order of 0.1 km/s, so fuel burned during takeoff is on the order of 0.5% of takeoff mass. A catapult launch would save carrying that extra fuel, decreasing dry mass by a similar percentage. That's certainly not negligible, but presumably not worth the trouble of designing and building a catapult.

It's more than that.  The C1 configuration burns about 2tonnes of LH2 getting to rotation speed (40 seconds 50kg/s).  That is about 30m³ or ~3% of the 1100m³ propellant volume and probably costs about 500kg of dry mass to contain.
The glass is neither half full nor half empty, it's just twice as big as it needs to be.

Offline 93143

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Re: Skylon
« Reply #353 on: 07/19/2011 07:49 am »
HOTOL had a launch trolley, which disappeared for some reason when it morphed into Skylon.  IIRC Mr. Hempsell has expressed strong distaste for the concept...

Offline Crispy

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Re: Skylon
« Reply #354 on: 07/19/2011 09:00 am »
Operational simplicity was judged to be more important. A kilometers long powered launch trolley is not simple or cheap.

Offline john smith 19

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Re: Skylon
« Reply #355 on: 07/19/2011 10:35 am »
Google for the International Bird Strike Committee to get a feel for the scale of the problem. File name IBSC26 WPSA1.pdf

Summary 1912-2002
42 accidents killing 231 people over a period of 90 years.
of which
10  airliners/executive jets >5700Kg killed 164 people and destroyed 30 aircraft.
Airplanes <5700Kg 42 aircraft destroyed of which 27 had fatalities totaling 58 people.

Most through engine ingestion. Most of the rest through hitting the windshield, which Skylon does not have.

I think a bird strike triggering an abort is an *assumption* on your part. the skin has a certain amount of give on its mountings. It could bend rather than break. Also note. Skylon will have taken off 10s, if not 100s of times in tests *before* it carries a payload.

Benefits of the Skylon approach over BDB.

Vehicle that flies is vehicle that's been (thoroughly) tested.
Intact abort during *any* stage of the mission.
Down mass = up mass. No separate capsule needed.
It delivers an ELV payload fraction with SSTO simplicity (Shuttle managed the *reverse*, which is an impressive feat but not in a good way).
Unless 2nd stage is *very* like 1st stage project cost *doubles* (key finding of BAC cost model of late 1960s for project MUSTARD). Keeping stages very similar has been a key feature of Spacex's approach which has served them very well so far, hope they will keep it up in F9H.
C 3000Km cross range gives it near hemispherical landing options (virtually empty so tire loading issues don't matter)
Design can self ferry in one piece (empty payload bay, no Oxygen loaded) by atmospheric flight only, eliminating exotic transport requirements (renting a barge, world's biggest transport aircraft etc)

Bottom line. If you do things the same way they've always been done you'll get what you've always got. 10-15000$/Kg to orbit and a 1 in 50 loss of vehicle rate (which is what ELV's have converged on and is about what Shuttle managed), because you build something as complex as a passenger jet and throw it away after 1 flight

The goal is lowering the cost of space access, making it a place not a programme. I admire what Elon Musk has done with Spacex and I really hope OSC will deliver Taurus II/Cygnus to compete. If Musk achieves reuseability for Falcon (something OSC are not even considering) that should radically lower his recurring costs but that's still a long way in the future

I'm a pragmatist. TSTO works, but at terrific cost, and the world has enough TSTO designs in production. A new ELV design (which I presume your friend is looking at)  offers *no* track record just a *promise* of lower costs. The customers will say "So what?"

The last *actual* clever take on this I've seen was the Loral pressure fed H2/O2 design (with Sea Dragon style launch) looking to go SSTO for delivery to a depot in LEO for ISS supplies. They made a good point. Why sweat 5 9s reliability to deliver water, ready meals or toilet paper? It goes bang, order up another. Personally I thought with modern manufacturing methods they'd have trouble getting their reliability *down* to 70%.

Ultimately RE have pursued this concept for nearly 30 years. Their view of it's success will be if you or I or our children hop on one to go to orbit.





MCT ITS BFR SS. The worlds first Methane fueled FFSC engined CFRP SS structure A380 sized aerospaceplane tail sitter capable of Earth & Mars atmospheric flight.First flight to Mars by end of 2022 TBC. T&C apply. Trust nothing. Run your own #s "Extraordinary claims require extraordinary proof" R. Simberg."Competitve" means cheaper ¬cheap SCramjet proposed 1956. First +ve thrust 2004. US R&D spend to date > $10Bn. #deployed designs. Zero.

Offline gbaikie

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Re: Skylon
« Reply #356 on: 07/19/2011 11:15 am »
Operational simplicity was judged to be more important. A kilometers long powered launch trolley is not simple or cheap.

The longest airports are 4-5 km. And you need room to abort a take-off, so you got about 2 km to take off. The higher the elevation of runway the higher the stall speed and longer runway needed.

Apparently the Skylon has take off speed of about 220 mph- similar to Concorde, and 747 is about 180 mph fully loaded.
http://en.wikipedia.org/wiki/List_of_longest_runways
And:
http://www.aerospaceweb.org/question/performance/q0088.shtml
In last link shows that aircraft keep on the runway for about 3/4 distance after they reach merely the stall speed of aircraft [for various reasons]. It may be that Skylon stall speed is around 220 mph and would need to go much faster to takeoff [safely].

So Skylon is about twice the weight of Concorde. And probably needs a higher speed for take off.
If you reduce load of landing wheels by making it have effective take off less than 180 mph you putting it in the realm of 747 take off speed and lower the risk tire blow out at take off.
If take upper limit of say 300 mph, if using trolly which reaches 120 mph, you having effective take off of 180 mph from the trolley.
It take about 200 meters of distance to brake if traveling 120 mph in car- which also means you could accelerate faster unless wheels are spinning like a drag racer:).
More realistic would be say about 400 meters distance for trolley to reach 120 mph [192 kph, 53 m/s]
Can we suppose Skylon gets say 7 m/s/s?
If so in 10 second it will be going 70 m/s [156 mph] and takes 350 meters of distance. Giving total speed of 276 mph.
And need trolley length of about +350 meters- 1100'.
So for total take off distance you have 400 + 350 meters. Since have at least 1-2 km you could decrease the acceleration needed for the trolley.
If Skylon had faster than 7 m/s/s you have shorter trolley and if slower acceleration than 7 m/s/s need a longer one.
« Last Edit: 07/19/2011 11:17 am by gbaikie »

Offline john smith 19

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Re: Skylon
« Reply #357 on: 07/19/2011 11:36 am »
Skylon takeoff speed was quoted at 597 Km/hr IE 163 m/s

RE looked at this in the early 90s (see the report in Spaceflight) and as Hempsell mentioned the last iteration was a trolley with some RB211 jet engines (and no doubt substantial tankage) on it. The wheels would have also been non trivial.

They concluded cost (and complexity) was not worth performance gained. I suspect operationally they did not like the idea of yet *more* specialised hardware having to be installed on a launch runway (not "Aircraft like") and are in the launch vehicle business, not the high speed jet (or rocket) powered trolley building business. 
MCT ITS BFR SS. The worlds first Methane fueled FFSC engined CFRP SS structure A380 sized aerospaceplane tail sitter capable of Earth & Mars atmospheric flight.First flight to Mars by end of 2022 TBC. T&C apply. Trust nothing. Run your own #s "Extraordinary claims require extraordinary proof" R. Simberg."Competitve" means cheaper ¬cheap SCramjet proposed 1956. First +ve thrust 2004. US R&D spend to date > $10Bn. #deployed designs. Zero.

Offline Hempsell

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Re: Skylon
« Reply #358 on: 07/19/2011 01:39 pm »

Other question: What about transferring heat from the heated (post-precooler) helium to the high pressure (pre-turbine) hydrogen via another heat exchanger? The idea is to allow far higher hydrogen outlet temps, and thus allow less of it to be used.

I am afraid (like your previous proposal) without diagrams I am not quite sure what you mean.  The hydrogen does not drive the main compressor turbine (it did in the old HOTOL RB545 engine).  It does drive its own (i.e. the hydrogen pump) and the He circulation pump; an arrangement that means the engine can be started (which we judged to be an important feature of a operational engine). But this is already after we have exchanged heat with the helium.

Well, let me describe it in detail.

After the turbine, the helium passes through a heat exchanger that heats the hydrogen. The hydrogen exits this heat exchanger at a certain temperature.

The idea is actually quite simple, at least in theory (though I am sure not in practice). The idea is that some of the helium (instead of entering the turbine) is shunted into another heat exchanger and then into the last He compressor stage. This heat exchanger heats the hydrogen a second time. The hydrogen then enters its turbine in the usual way.

The net result is that some more heat is shunted from the air to the same amount of H2 -> less H2 needed for a given cooling effect ->higher Isp.

I do not think this would help any. Just before the turbine we have heated the helium (HX3) to give it the energy required to drive the turbine.  Having just added the energy taking it away again before its done its job seems a bit silly.

Offline Hempsell

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Re: Skylon
« Reply #359 on: 07/19/2011 01:40 pm »

Suppose the ramjet Isp turned out to be better than expected. What would be the improvement in payload?

The improvement would be in the order 100 kg on the delivered payload

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