Let’s say you’re a country who’s just gotten out of 3rd-world debt and wants to move toward space. Ejector ramjets offer shorter and less expensive development/testing/manufacturing lifecycles than turbojets considering you don’t own any turbojet IP or have any commercial giants (Boeing, Ariane, etc.) clamoring to set up shop in your borders. The fact that turborockets also have yet to ever fly will make them even more costly than ramrockets from scratch – if you’re a brand-new space explorer with zero experience in advanced avionic technology trying to integrate someone else’s proprietary engine without melting it OR violating patents… you see what I mean? Growing your own IP fruit tree will be easier than trying to embed someone else’s turbofan design in it as it grows. As for your reply:

JH: Ramrockets sound like dead easy solutions on the first pass. On the second pass some of the problems start showing up. They would have to be developed from scratch in your scenerio. Straight rockets would be faster and cheaper. You really don’t want to fly them subsonic for any length of time, they use over ten times the fuel of a turbofan in that regime. For a straight climb to 50,000 feet from the runway with a massively overweight bird, maybe. For cruise while playing LOXmaker, no way as you will run out of aircraft fuel well before you get your spacecraft LOXed. In your scenerio, the Microcosm or Beal route would make more sense on the KISS principle.

1 – The whole point of modding a 747 is that they’re everywhere – you only have to ADD to them w/out redesigning the airframe to make them available for air launch – brand-new spacepower nations like Mexico would be able to afford something that easy.

JH: In your original, you suggested massive renovations.

2 – As above – all the “modification and machinery” added is something that has been done for years. The Shuttle Carrier has been extensively modified but remains un-redesigned – it’s still a 747. Simply bolting equipment onto an existing structure that is never expected to pass Mach 1 is a time-honored tradition in avionics; see Boeing 737 AEW&C, etc.

JH: The machinery you suggest has never been demonstrated in flightweight hardware.

3 – You got me – I forgot about the ramrocket oxidizer. You could siphon it in-flight from the LOX-maker or carry another internal tank. The point I was trying to get across is that while ramrockets would SUCK for subsonic flight you’d have massive amounts of fuel (a 747’s-fuselage-worth) just waiting to be burned anyway; the subsonic portion of the flight with the carrier craft DOESN’T MATTER when considering efficiency – it’s not GOING ANYWHERE important, just to the landing runway to be refueled. If you’re Guiana and you’ve just built one of these carrier/orbiters France will start paying through the nose for flights – it doesn’t matter how efficient they are if you can leave the gravity well repeatably and reusably. Once the technology starts rolling then you can kaizen it – it’ll get more efficient over time when you have the money to improve it, plus you’ll OWN it (specs & all) outright.

JH: The fuel use of the carrier aircraft does matter when there is so much of it required that it eats away the payload capacity.

4 – The video of Shuttle Enterprise holding stable and level while the SCA drops off (check wikipedia) sounds a lot louder than all your naysaying about top-mounted air launch. I believe what I see and what I see is a heavy, chunky b*tch of an aircraft with horrible subsonic aerodynamics and poor fuel efficiency just hanging there in glide while the carrier drops away. If NASA can do it… everyone else can do it cheaper.

JH: It can be done yes, but you can’t handwave away the issues involved.

5&6 – It’s cutting edge and complex and added to the subsonic engine cycle because carrying all that hydrogen onboard would be a waste if it wasn’t used to fly the plane. Carrying JP4 (and you’d have to with turbojets/turborockets – H2 embrittlement would kill a turbofan’s alloys, necessitating replacement) would defeat the purpose of stuffing the plane fuselage w/ fuel, which would negate the air liquefier, which would kill in-flight oxidizer loading – which, you have to admit, is a pretty sharp idea.

JH: The carrier aircraft will have to carry the whole mass of the orbiter oxydizer by the time of launch. IMO, it would be more efficient to launch with a full load of LOX as opposed to making it in flight unless there is a long cruise time built into the flight plan. That way your high altitude launch would be with a fully fueled orbiter from an aircraft with just enough fuel to get home on empty and no massive liquification machinery to lift.

7 – Air launches are available with completely unmodified aircraft… if you jump from them (ha ha). Seriously though the in-flight oxidizer loading is why I say modify this stuff – simply carrying the orbiter on a (mostly) unmodified jet and tanking it up in-flight with a third aircraft would be troublesome with cryoliquids. Also you’d have another big-ass subsonic craft wanging around your airspace while you try to get something done. In retrospect it’s probably even cheaper overall than in-house development of anything but I am a slave to aesthetics… 1+1 = orbit, no remainder. Also the ramrocket-powered-carrier-craft would be MY next logical step in development after a 3-craft stage anyway, because I am young and have plenty of time for that sort of thing, plus I could live off the IP when I get old.

So you poked really nice holes in my theory, which I wanted. I hope you can get over your own close-mindedness about turbofans – just because everyone is circumcised (i.e. using turbofans) does not make it the most comfortable thing in the world. I was trying to consider what might present the (currently) most easily available AND most easily upgradeable solution to get to orbit for countries “just starting out” in the space race; e.g. what would *I* do if I suddenly had a nation-sized budget for spaceflight and wanted to keep doing it all the time. Developing ramrockets early on would make for savings and simplicity down the road, plus IP you could sell to other nations emerging from terran isolation. I admit I don’t like turbojets but I’d totally consider using them if they weren’t so damn complex mechanically AND intellectually – I could certainly buy an efficient, well-specced P&W turbofan on the cheap but I’d ultimately have to go back to P&W for spare parts, repairs, upgrades, etc. and they’d never tell me exactly how to build my own – that bothers me.

JH: Don’t make the mistake of believing that anyone that disagrees with you has not researched the problem. Used turbofans will be cheaper than ramrockets for the forseeable future. You can’t sell IP (whatever you mean by that) if it is worthless to the potential customers.

Overall I’m sure we can agree that nobody is trying hard enough to get us off this rock…

Some people are trying hard enough, it’s just that the ones that are haven’t been in business for very long, and don’t have the bottomless pockets of the public purse to draw from. The previous government efforts have been like hitting someone with a stick, it hurts but doesn’t stop them, and the bruise will heal. The new space profit based efforts are like hitting them with a virus, they don’t notice until it spreads all over and stops them for the count.

_d

I suppose my post makes more sense if you consider the question to have been “how would *I* get to space” rather than “how would *we* get to space”.

Let’s say you’re a country who’s just gotten out of 3rd-world debt and wants to move toward space. Ejector ramjets offer shorter and less expensive development/testing/manufacturing lifecycles than turbojets considering you don’t own any turbojet IP or have any commercial giants (Boeing, Ariane, etc.) clamoring to set up shop in your borders. The fact that turborockets also have yet to ever fly will make them even more costly than ramrockets from scratch – if you’re a brand-new space explorer with zero experience in advanced avionic technology trying to integrate someone else’s proprietary engine without melting it OR violating patents… you see what I mean? Growing your own IP fruit tree will be easier than trying to embed someone else’s turbofan design in it as it grows. As for your reply:

1 – The whole point of modding a 747 is that they’re everywhere – you only have to ADD to them w/out redesigning the airframe to make them available for air launch – brand-new spacepower nations like Mexico would be able to afford something that easy.

2 – As above – all the “modification and machinery” added is something that has been done for years. The Shuttle Carrier has been extensively modified but remains un-redesigned – it’s still a 747. Simply bolting equipment onto an existing structure that is never expected to pass Mach 1 is a time-honored tradition in avionics; see Boeing 737 AEW&C, etc.

3 – You got me – I forgot about the ramrocket oxidizer. You could siphon it in-flight from the LOX-maker or carry another internal tank. The point I was trying to get across is that while ramrockets would SUCK for subsonic flight you’d have massive amounts of fuel (a 747′s-fuselage-worth) just waiting to be burned anyway; the subsonic portion of the flight with the carrier craft DOESN’T MATTER when considering efficiency – it’s not GOING ANYWHERE important, just to the landing runway to be refueled. If you’re Guiana and you’ve just built one of these carrier/orbiters France will start paying through the nose for flights – it doesn’t matter how efficient they are if you can leave the gravity well repeatably and reusably. Once the technology starts rolling then you can kaizen it – it’ll get more efficient over time when you have the money to improve it, plus you’ll OWN it (specs & all) outright.

4 – The video of Shuttle Enterprise holding stable and level while the SCA drops off (check wikipedia) sounds a lot louder than all your naysaying about top-mounted air launch. I believe what I see and what I see is a heavy, chunky b*tch of an aircraft with horrible subsonic aerodynamics and poor fuel efficiency just hanging there in glide while the carrier drops away. If NASA can do it… everyone else can do it cheaper.

5&6 – It’s cutting edge and complex and added to the subsonic engine cycle because carrying all that hydrogen onboard would be a waste if it wasn’t used to fly the plane. Carrying JP4 (and you’d have to with turbojets/turborockets – H2 embrittlement would kill a turbofan’s alloys, necessitating replacement) would defeat the purpose of stuffing the plane fuselage w/ fuel, which would negate the air liquefier, which would kill in-flight oxidizer loading – which, you have to admit, is a pretty sharp idea.

7 – Air launches are available with completely unmodified aircraft… if you jump from them (ha ha). Seriously though the in-flight oxidizer loading is why I say modify this stuff – simply carrying the orbiter on a (mostly) unmodified jet and tanking it up in-flight with a third aircraft would be troublesome with cryoliquids. Also you’d have another big-ass subsonic craft wanging around your airspace while you try to get something done. In retrospect it’s probably even cheaper overall than in-house development of anything but I am a slave to aesthetics… 1+1 = orbit, no remainder. Also the ramrocket-powered-carrier-craft would be MY next logical step in development after a 3-craft stage anyway, because I am young and have plenty of time for that sort of thing, plus I could live off the IP when I get old.

So you poked really nice holes in my theory, which I wanted. I hope you can get over your own close-mindedness about turbofans – just because everyone is circumcised (i.e. using turbofans) does not make it the most comfortable thing in the world. I was trying to consider what might present the (currently) most easily available AND most easily upgradeable solution to get to orbit for countries “just starting out” in the space race; e.g. what would *I* do if I suddenly had a nation-sized budget for spaceflight and wanted to keep doing it all the time. Developing ramrockets early on would make for savings and simplicity down the road, plus IP you could sell to other nations emerging from terran isolation. I admit I don’t like turbojets but I’d totally consider using them if they weren’t so damn complex mechanically AND intellectually – I could certainly buy an efficient, well-specced P&W turbofan on the cheap but I’d ultimately have to go back to P&W for spare parts, repairs, upgrades, etc. and they’d never tell me exactly how to build my own – that bothers me.

Overall I’m sure we can agree that nobody is trying hard enough to get us off this rock…

_d

It is my opinion that the turborocket based concepts are far superior to the ejector series below mach 2. Above that, you really want to be out of the atmosphere soon enough that the advantage range is quite small. Turbine based systems are actually easier in this field than iaircraft use since we can trade efficiency for simplicity and thrust/weight. From a standing start, I believe that a turbine based system could be fielded faster and cheaper than the ejector series if you factor in testing and vehicle integration.

Another random idea: what about peroxide and subcooled methanol? Methanol is a good coolant and so is peroxide. Peroxide is very dense and methanol is fairly dense. The melting point of methanol is -97C. During airbreathing such an oxygen containing fuel might benefit less from atmospheric oxygen, but because of the more balanced O/F ratio it could allow for better thrust.

So, everyone, I hope these comments haven’t closed, because I just stumbled across them…

After wading through most of this stuff I figured I could just cut to brass tacks as I didn’t see my idea here already.

It’s pretty simple.

JH: not really

“TSTO on the cheap and easy!”:

Step 1 – Strip out interior of a common 747-8 transonic aircraft, including JP4. Inflate in-wing fuel bladders with helium to maintain wing structural integrity. Integrate interior of fuselage with LH2 cryotankage running the length of the aircraft.

JH: You’ve just redesigned the wing and fusilage, that’s going to cost. A new vehicle might be cheaper.

Step 2 – Add ramscoops to outside of 747. Connect to a suitable heat exchanger “powered” by the onboard LH2. Add mechanical arrangements to fraction and separate the incoming air (we will use it in step 6).

JH: That’s a lot of modification and machinery thrown out there.

Step 3 – Replace the 747’s 4 turbofans with 6 ramrockets optimised for subsonic flight – ramrockets to be powered by LH2 warmed by the onboard air liquefaction equipment.

JH: Ramrockets are terrible for subsonic flight. Fuel consumption approaches the rocket alone. Plus you would have to develop them from scratch. Also, ramrockets need oxidizer in the rocket side.

Step 4 – Attach some kind of orbiter craft to top of 747, with orbiter to be powered by onboard aerospike engine(s) fueled by carrier-aircraft-made LOX and preloaded LCH4.

JH: See the airlaunch home page for the difficulties of top mounted orbiters.

Step 5 – “Hop” from runway to air with orbiter (full of LCH4 only) attached to 747 (loaded full with LH2), proceed to cruising speed (Mach 0.8).

JH: By hop, do you mean take off?

Step 6 – “Skip” oxidizer loading by cruising at speed with the air-liquifier on; the LOX is diverted to the orbiter tankage (loading it for an insertion burn with the LCH4) while the remaining liquid air fractions (nitrogen, etc.) are used as cold working mass to be injected into the ramrocket engines (I envision little aerospikes in them – the still-liquid air fraction(s) would be injected where the virtual “air spike” is supposed to sit in the inside of an annular rocket-nozzle/hot gas generator, rapidly expanding and improving outbound mass flow – incoming air should keep the “spike” tapered and make a good combustion zone).

JH:You have added a very complex subsonic engine cycle to a cutting edge air liquifier with no visible justification. This is turbofan country at cruise.

Step 7 – “Jump” when the orbiter is full of LOX (and the astronauts of bagels – tee hee) and the 747 reaches a nice altitude like 40,000 ft; separate vehicles at subsonic speed, drop the 747 for the return journey to the runway and light the orbiter’s rockets for a burn to Mach 25 and Low Earth Orbit.

JH: Air launches at 40,000 feet are available with almost unmodified aircraft.

Inspiration: Shuttle Carrier Aircraft + NASA GTX + SpaceShipOne + LACE + Skylon + Black Horse + Pegasus(rocket)

Advantages: “Free lunch” (ha ha) ride for orbiter to 40,000ft and ~500mph, in-flight oxidizer loading utilizing LH2 fuel that will be burned anyway, subsonic vehicle separation (to conserve stability), kickass dead-simple (and relatively cheap) ramrocket engines on the carrier craft that will provide static thrust AND collect both working mass and oxidizer in-flight to improve performance, aerospike (overall most efficient!) rocket engine(s) on orbiter, everything is 100% re-usable.

JH: See above on ramrocket engines.

Disadvantages: Heavy LH2 tankage, heavy orbiter (certainly!), heavy heat exchanger – all things that can be engineered lighter.
Oh, and a jumbo jet full of explosives… like the Shuttle External Tank, but with wings. Don’t be scared.

Am I missing anything?

JH: Simplicity. Calling a complex method simple doesn’t make it so. Complexity is only desirable in direct relationship to it’s advantages.

Oh yeah – I like your turborocket ideas but seriously turbomachinery is heavy, expensive and has zillions more points of failure than a rocket (e.g. thin vanes pulling multiple G at ridiculous temperatures). A rocket with some duct wrapped around it (ramrocket!) is hardly more complex than a rocket alone and can provide static thrust also, plus this particular design will have several metric f*cktons of LH2 available to burn so using fuel-gulping engines means almost nothing. As for the orbiter – if all you can fit on it for cargo (minus pilots) is 1,000kg but you can reach LEO or even geosync each flight (with a fully reusable launch system) you return your bilion+ $ investment in the first system’s lifetime – anyone with something to get into space will buy your services.

JH: Read up on turbines a bit. Fear of turbines seems to be a bad meme in rocket circles.

BTW the 747 was a suggestion – you could also try an AN-225 or something else with sufficient lift capacity (ha!).

_d

P.S. – Criticize me! I am an ignorant youth. Also I want feedback.

JH: Part of being an innovator is the requirment for a thick skin AND open ears. You will need to be able to hear critisizm without taking it personally, and the ability to filter the wheat from the chaff. Innovators without the thick skin give up too quickly. Innovators that don’t listen get killfiled as it’s a waste of time explaining to them. The middle of the road is a difficult path, but the most rewarding if you can hack it. Watch people shred my ideas to see what I mean. The ones ready for immediate use would be going to my friends in the industry direct instead of free on a blog.

So, everyone, I hope these comments haven’t closed, because I just stumbled across them…

After wading through most of this stuff I figured I could just cut to brass tacks as I didn’t see my idea here already.

JH: All these ideas have been tossed out individually from time to time. What kills most of them is the cost, risk, and complexity. If it is difficult to get one of them at a time funded, how hard do you think it wil be to get all of them at once done?

It’s pretty simple.

“TSTO on the cheap and easy!”:

After wading through most of this stuff I figured I could just cut to brass tacks as I didn’t see my idea here already.

It’s pretty simple.

“TSTO on the cheap and easy!”:

Step 1 – Strip out interior of a common 747-8 transonic aircraft, including JP4. Inflate in-wing fuel bladders with helium to maintain wing structural integrity. Integrate interior of fuselage with LH2 cryotankage running the length of the aircraft.

Step 2 – Add ramscoops to outside of 747. Connect to a suitable heat exchanger “powered” by the onboard LH2. Add mechanical arrangements to fraction and separate the incoming air (we will use it in step 6).

Step 3 – Replace the 747′s 4 turbofans with 6 ramrockets optimised for subsonic flight – ramrockets to be powered by LH2 warmed by the onboard air liquefaction equipment.

Step 4 – Attach some kind of orbiter craft to top of 747, with orbiter to be powered by onboard aerospike engine(s) fueled by carrier-aircraft-made LOX and preloaded LCH4.

Step 5 – “Hop” from runway to air with orbiter (full of LCH4 only) attached to 747 (loaded full with LH2), proceed to cruising speed (Mach 0.8).

Step 6 – “Skip” oxidizer loading by cruising at speed with the air-liquifier on; the LOX is diverted to the orbiter tankage (loading it for an insertion burn with the LCH4) while the remaining liquid air fractions (nitrogen, etc.) are used as cold working mass to be injected into the ramrocket engines (I envision little aerospikes in them – the still-liquid air fraction(s) would be injected where the virtual “air spike” is supposed to sit in the inside of an annular rocket-nozzle/hot gas generator, rapidly expanding and improving outbound mass flow – incoming air should keep the “spike” tapered and make a good combustion zone).

Step 7 – “Jump” when the orbiter is full of LOX (and the astronauts of bagels – tee hee) and the 747 reaches a nice altitude like 40,000 ft; separate vehicles at subsonic speed, drop the 747 for the return journey to the runway and light the orbiter’s rockets for a burn to Mach 25 and Low Earth Orbit.

Inspiration: Shuttle Carrier Aircraft + NASA GTX + SpaceShipOne + LACE + Skylon + Black Horse + Pegasus(rocket)

Advantages: “Free lunch” (ha ha) ride for orbiter to 40,000ft and ~500mph, in-flight oxidizer loading utilizing LH2 fuel that will be burned anyway, subsonic vehicle separation (to conserve stability), kickass dead-simple (and relatively cheap) ramrocket engines on the carrier craft that will provide static thrust AND collect both working mass and oxidizer in-flight to improve performance, aerospike (overall most efficient!) rocket engine(s) on orbiter, everything is 100% re-usable.

Disadvantages: Heavy LH2 tankage, heavy orbiter (certainly!), heavy heat exchanger – all things that can be engineered lighter.
Oh, and a jumbo jet full of explosives… like the Shuttle External Tank, but with wings. Don’t be scared.

Am I missing anything?

Oh yeah – I like your turborocket ideas but seriously turbomachinery is heavy, expensive and has zillions more points of failure than a rocket (e.g. thin vanes pulling multiple G at ridiculous temperatures). A rocket with some duct wrapped around it (ramrocket!) is hardly more complex than a rocket alone and can provide static thrust also, plus this particular design will have several metric f*cktons of LH2 available to burn so using fuel-gulping engines means almost nothing. As for the orbiter – if all you can fit on it for cargo (minus pilots) is 1,000kg but you can reach LEO or even geosync each flight (with a fully reusable launch system) you return your bilion+ $ investment in the first system’s lifetime – anyone with something to get into space will buy your services.

BTW the 747 was a suggestion – you could also try an AN-225 or something else with sufficient lift capacity (ha!).

_d

P.S. – Criticize me! I am an ignorant youth. Also I want feedback.

Bob Clark

— On Sat, 8/1/09, Robert Clark wrote:
> From: Robert Clark
> Subject: Re: [AR] Another prize suggestion – Re: Hypersonic ‘WaveRider’ poised for test flight.
> To: “arocket”
> Date: Saturday, August 1, 2009, 6:59 AM
>
> There seem to be a million dozen different ways of doing
> the turbine-free air compression for jet engines. But it
> seems like all the jet engine and aircraft manufacturers are
> only focused on improving turbine engines. Why?
> Perhaps because turbine engines in their view are already
> good enough, at least on the measure we’re trying to improve
> on: thrust/weight. For while a rocket engine might have a
> T/W of 70:1 and a jet engine might only be 6:1, because of
> lift, where a typical jet aircraft might have a lift-drag
> ratio of 12:1, the T/W for the jet becomes effectively 72 to
> 1.
> What the jet engine professionals are very interested in
> is improving fuel efficiency since fuel costs are a big part
> of airlines profit margins. The methods suggested of doing
> away with compressors/turbines look like they will actually
> make fuel efficiency worse, such as the ejector ramjet for
> example, the exact opposite of what the jet engines pro’s
> are majorly focused on.
> But how about the rocket guys? They’re focused on getting
> to orbit and what happens at quite high Mach numbers. What
> happens at subsonic speed to low supersonic speed holds very
> little interest.
> So if this is going to be done, it looks like we’re going
> to have to be the guys to do it.
>
> And here’s another one of the million dozen different
> ways:
>
> I just saw this on Selenian Boondocks:
>
> Rotary PDE
> Nov 23rd, 2008 by johnhare
> guest blogger john hare
> http://selenianboondocks.com/2008/11/rotary-pde/
>
> Hare suggests using multiple combustion chambers within a
> rotating torus. He suggests this for rocket engines using
> pulse detonation propulsion. But the idea would also work
> for jet engines and you don’t need to use detonation
> for the method. Regular combustion would work.
> Detonation propulsion still is not well understood. Hare
> was suggesting the detonation wave to provide the
> compression, but you could just have the rotating torus
> generate the compression required for a jet engine by
> centrifugal force. The force to rotate the torus would be
> provided when each combustion chamber released its exhaust
> in turn.
> As Hare mentions, this idea for the rocket case is
> analogous to Gary Hudson’s rotary rocket, at least in the
> second incarnation where Hudson made the rotating
> engines be internal rather than on external rotors.
> Hudson then might be a good one to ask about its
> feasibility for the jet engine case.
>

John Hare discusses a variant of the Gary Hudson Rotary Rocket to get high thrust for the thrust provided by the rockets at the rotor tips here:

Roton Revisit.
Nov 5th, 2008 by johnhare
http://selenianboondocks.com/2008/11/roton-revisit/

In the comments section on this page, Wayne Gramlich also pointed to a page on an internal type of rotary rocket engine by Roger Gregory:

halfwaytoanywhere.com rotary rockets.
http://www.halfwaytoanywhere.com/

These are rocket engines. I wanted to investigate the case for airbreathing propulsion.
John Hare in responding about the Gregory rocket engine noted it might be dangerous to have the engine be rotating at ca. 600 m/s rim speed while at high pressure, 10,000 psi chamber pressure, and at the high temperature of combustion chambers.
This would be a problem in the airbreathing case as well. You might want to use the high velocity rotating torus just for compression and not have the combustion there. Firstly, how fast would you need to rotate it to get the ca. 10 to 20 bar compression typical of turbojets? Perhaps someone can give the equations for centrifugal compression of a gas given rotation speed and radius.
As a first guess I’ll estimate it by what happens with ramjets. Ramjets get good compression and thrust and Isp when the aircraft is flying in the range of Mach 2 to Mach 3, about 650 m/s to 1,000 m/s. I mentioned before a case of a ramjet able to get a thrust/weight ratio of 40 to 1 using hydrocarbon fuel. So we could get likewise good compression, thrust, and Isp if our rotating chamber encounters the air, when still as at start or when moving as when flying subsonically, at a rotating rim speed of 650 – 1,000 m/s. There are flywheel rotors that can rotate at these speeds, though I believe 1,000 m/s is near the edge of what is currently being done.
But this would be a problem if we made the high temperature combustion chamber be rotating at this speed. The highest rim speed flywheels use for example carbon fiber or synthetic fibers such as Kevlar to withstand the tensile stresses at these speeds. The chamber pressure when using air would not be nearly as high as the Gregory rocket case of 10,000 psi using liquid fuel and LOX. But still the materials used for fast flywheels could not withstand the temperatures of combustion.
Perhaps regenerative cooling could be used as for rockets. But the allowed temperature would be significantly lower for the flywheel materials compared to the metals used for rocket engines.
A few other possibilities. Use two torii, one for the combustion chamber, one for the compression chamber. The compression chamber torus may compress the air by encountering the incoming air at supersonic rim speed, as happens with ramjet compression, or just by using centrifugal compression. Using centrifugal compression, with the air introduced at the hub, might be preferred since you don’t have to deal with the shock waves or the heating from the low altitude, high density air suddenly encountering an inlet at supersonic relative speed. In any case, once the air is sufficiently compressed it would then be presented to the combustion chamber.
The combustion chamber would be rotating as I suggested before due to exhaust vented from nozzles around the toroidal chamber, as with Hero’s engine (like a lawn sprinkler.) Note in this scenario, unlike what I first proposed in a prior message, the compression is NOT provided by the rotation here. So you don’t need high rotational speed and can use higher temperature resistant metals. You convert this low speed rotation of the combustion chamber into high speed rotation of the compression chamber by principles of mechanical advantage, such as with gears, levers, etc.
Note you also have some flexibility with this combustion chamber. You might be able to get better efficiency and have lesser technical complexity if the combustion chamber does not rotate. Instead it could be a standard fixed combustion chamber but you could have some of the exhaust bled off to connect to a Hero’s engine, for lack of a better term. Or you could have instead use a heat eschanger to heat hydrogen using the heat only from the combustion chamber to thereby drive the Hero’e engine. Since hydrogen is of low molecular weight you wouldn’t need to get very high temperatures here to get high velocity exhaust from the nozzles of the Hero’s engine. As before the rotation of the Hero’s engine would be used to drive the rotation of the compressor torus.
There are several other variations. For instance instead of a toroidal compression chamber you could have a piston and cylinder arrangement driven by the Hero’s engine, as the piston is seen here driven by a flywheel:

Energy Storage II.
http://zebu.uoregon.edu/2001/ph162/l10.html

The jet engine would likely have to be pulsed in this case but we could emulate continous operationn by having two or more pressure cylinders operating sequentially.
As a variation on this idea we could use fan blades, cupped or flat, that drive the air for compression as suggested by John Hare here:

Cagejet Turborocket
Oct 17th, 2008 by johnhare
http://selenianboondocks.com/2008/10/cagejet-turborocket/

This would look analogous to a paddlewheel on a steamboat. The advantage of using this or of the piston and cylinder is that you wouldn’t need very high rotation or lateral speeds, just sufficient force to compress the large volume of air. Again this could be done by using methods of mechanical advantage, driven by the Hero’s engine.

Bob Clark

Bob Clark