Author Topic: Finding the actual speed limit of a conventional ramjet powered vehicle.  (Read 7799 times)

Offline john smith 19

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In different forums and different sites I've seen various claims about the potential speed limit of a sub sonic combustion ramjet.

It is known that the French built a series of 10 missiles that were designed to hit (and did) M5 in the 1960's without needing supersonic combustion and at least one US design has also done so accidentally.

Some have claimed M9+ is possible but it seems no one has actually built a vehicle to test what the limit is.

What I have in mind is sort of like the X1 project. It also would have 1 goal. In this case to keep building vehicles until the internal flow was hitting M0.9-M0.95. Historically it seems most ramjets have been around M0.5 internally so the results should be quite interesting. This is a pure research vehicle to answer a single question. It has no payload (other than the test sensor suite) and is as light and simple as possible. Likewise its radar cross section is irrelevant. An aerodynamically "clean" design should accelerate better to a higher speed while remaining adequately controllable up to that top speed and down to landing speed.

I think it's important to ensure the whole system is reusable to test runs are just a case of loading propellant, not buying more solid rockets.

On this basis 2 architectures seem plausible on a limited budget

#1 would be a single stage vehicle with an "accelerator" engine system and the main ramjet system. The A system's task is to get the vehicle to operating altitude and ramjet ignition speed. "Cleverness" is not   a virtue so I'm thinking either liquid fuel rockets or small turbojets (if anyone still makes pure turbojets that aren't expendable). No launch assist devices. Again, they add complexity, expense and minimal improvement.  :(  [EDIT Today I think a drone or RPV is the way to go. A test pilot would add somewhere between 200-400Kg to a vehicle that's not meant to have any payload]

The upside is this needs a single set of avionics, actuators, landing gear and airframe to be developed or purchased (and AFAP you want to buy most of the systems OTS).
The downside is that airframe has to be designed for the full speed range, so likely to need high temperature (heavy) materials and be larger to accommodate both engine systems at the same time. Without careful management I can see thig resulting in a vicious circle of rising weight needing rising performance resulting in rising weight, killing any cost savings from the single vehicle. 

#2 would use 2 vehicles in a parent/child (or booster/upper stage if you prefer that terminology) design.

Stage 1's task is to get stage 2 to operating height and ramjet ignition speed before separating and returning to base. Concorde demonstrated M2.2 cruise with an Aluminum aircraft is perfectly viable. Drag rises and falls sharply around M1 so the booster stage should accelerate the "upper stage" to at least M1.2 before separation. Personally I'd like it to go closer to the limit speed for unmodified jet engines around M2.2-2.4. Note that like the XS1 stage 1 does not have to cruise at that speed, just get there and release the test vehicle.

While this requires 2 vehicles and hence 2 sets of airframes, actuators, avionics etc it allows each to be optimized for it's task and hence (in principal) to go with smaller, lighter vehicles overall.

Once ignited the ramjet then accelerates the vehicle to the point at which which its internal flow is close to supersonic (after the flow has decelerated from the vehicles airspeed through the inlet) or the vehicles structural thermal limits are close to being exceeded.

The programme ends when you've got internal flow of M0.9-0.95. If the test vehicle airframe temperature limits start to be being hit this is not grounds for giving up. It implies aerodynamic redesign or reimplementation with higher temperature materials.

Cruise is not required. I'd suggest 5-10 secs (at internal flow of M0.9+) would be enough to set the boundary.

I'm interested in wheather this has already been done (and I've never heard of it) or what points I've missed, wheather composites are more viable, airframe shape, how small could you go etc.

Remember the goal is the speed limit of a conventional ramjet inside a suitably designed airframe.
« Last Edit: 08/15/2014 12:21 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 momerathe

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how much - of the initial studies at least - could be done with modern computational fluid dynamics?
thermodynamics will get you in the end

Offline 93143

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Quite a bit.  I could probably figure out a first-order estimate by hand.

Offline aero

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Make it easy. Assume
body drag = 0,
prop is kero,
mdot (air)=1
reaches stagnation pressure within the engine,
then thrust = ram drag = V*mdot (air) and
thrust = ram drag = (mdot(air)+mdot(kero))*Ve and
E = thrust*Ve/2 = 1/2 * total mdot *Ve2

How much kero do you want to burn? Well, you have about 0.2 O2 and if you use a oxygen/fuel mix of, I don't know, 2.2 maybe (for Pc = 25 bar) gives about 0.09 kero. Choose your units, then what is your energy, in Joules =  (watt/sec)? Plug in E and solve for ram drag which gives you velocity. But be sure to observe that Ve /= V.

Oh, I looked it up for you. The heating value of kerosene is 43.1 MJ/kg.

The big problem with this is that drag = 0 (excepting ram drag) is not a valid assumption so you won't get the ~3 km/s velocity this approach produces. Design your engine with a nice low frontal area and a good supersonic coefficient of drag, then extend my little model to account for that drag. Of course now you have to add ram and body drag together to equal thrust.
« Last Edit: 08/14/2014 07:20 PM by aero »
Retired, working interesting problems

Offline john smith 19

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Quite a bit.  I could probably figure out a first-order estimate by hand.
I don't think anyone in their right mind would design a modern flying vehicle without CFD to begin with to converge on roughly what it should look like. One really interesting result of the RAND reviews of the X30 programme was the little factoid that if the CFD model data point count is >=  R ^9/4 (R being the vehicle Reynolds number) you don't need a turbulence model and you can get the results directly.

In an era of GPU's offering power in 1x10^12 FLOPS capacity I wonder if the time has come (at least for small vehicles, which this is meant to be) to brute force the problem? What I'm not so sure about is the number of equations at each point you'd be dealing with and the memory they'd need to store the parameters.

Historically we know of at least 2 designs (the US ASALM and the French M5 ramjet programme) that got to M5+ with fixed geometries [EDIT and subsonic combustion]

Maybe Aero's claim that basic theory will get you to 3Km/s (about M8.8 )   is correct  but given the results of the X30 programme what I'm suggesting is a flight programme.  There just aren't that many (flight) data points for any design going through this range. [EDIT  a page on the Talos missile programme
http://www.okieboat.com/Ramjet%20history.html
stated that later versions switched to what appears to be hydrogenated dimerised JP10 (tetra cylopentadiene). This increased the energy available per (US) gallon of fuel from IIRC 126 to 143 thousand BTU's, about a 13% increase  Called RJ-4]

Note that while I'd prefer to keep things as simple as possible and with most geometry fixed to side step problems with high temperature actuators I think active skin cooling may be a reasonable trade off to lower weight if necessary. However since the goal is research, not an operational vehicle flying a constant dynamic pressure trajectory (IE climbing, not accelerating at a fixed altitude) is the way to go.

I also suspect sub sonic ramjet combustor design has been a rather neglected field and CFD has been not really been used on it.

If I'm right this is an area where substantial improvements should be possible. While the inlet has to handle the full  Mach range of the incoming air stream by the time it hits the combustion section things should be much more constant (after all the goal is to what can be done below M1).

A key element here seems to be the "flame holder." It's been suggested that good designs retain certain combustion products in their lee which are critical to continued stable effective combustion. A similar comment has been made about the injector designs in rocket engines. I'm guessing bad designs end up in combustion cycles of flame outs, fuel accumulation, ignition, resulting in either a pulsing thrust like a series of car engine mis fires or a low efficiency pulse detonation engine if (somehow) you've hit the conditions for deflagration to detonation transition  :( . I think the latter is unlikely but not entirely impossible.

This suggests 2 things. 1) An effective CFD based design must incorporate both the aero thermodynamic and thermochemical  aspects of the problem (including compressibility)  and 2) Most o f the action will take place below M1. That much lower Mach range (and hence Reynolds numbers) coupled with much more powerful modern processing hardware, should make the problem small enough to fit into a relatively small processing environment.

[EDIT
It seems the key task of the flame holder is to ensure complete mixing and combustion of the fuel by slowing down it's passage through the duct by increasing turbulence, giving enough time to complete combustion. In the Talos design this is done by igniting the fuel/air mix and flowing it inward through a truncated perforated metal plate. My guess is that the size and spacing of those holes can make a significant  difference in ramjet performance but IRL (around 1948-1953) they were chosen either by what materials were available or by a cut-and-try process that stopped when they got a result that was good enough to deliver the performance target.

The challenge is to deliver enough delay without increasing the interior drag too much.

AFAIK no ramjet flight vehicles have been built that used the current generation of non invasive diagnostics to measure temperature, pressure and combustion chemistry within the combustor to gather data for a more optimized design.
« Last Edit: 08/17/2014 12:29 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 RanulfC

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Maybe Aero's claim that basic theory will get you to 3Km/s (about M8.8 )   is correct  but given the results of the X30 programme what I'm suggesting is a flight programme.

I think I noted that Glenn Olson (of the old alt-accel website) had spoken to enough ex-ramejt engineers to come away pretty confident that a well-designed subsonic combustion ramjet could reach speeds in a bit excess of Mach-8 and for the most part (unlike many of the folks riding "theory" till it auguered into the ground in the form of the SCramjet :) ) couldn't see many "good" reasons to go faster even if most of them thought Mach-10 was possible given the right propellant and design :)

And really what DOES air-breathing to @Mach-5+ get you if its "cheap" and "easy" enough over the alternatives?

(I'd suggest hitting up the "Ex-Rocketman's Take" blog to see some of the work he's done as one of "those" engineers :) )

Randy
From The Amazing Catstronaut on the Black Arrow LV:
British physics, old chap. It's undignified to belch flames and effluvia all over the pad, what. A true gentlemen's orbital conveyance lifts itself into the air unostentatiously, with the minimum of spectacle and a modicum of grace. Not like our American cousins' launch vehicles, eh?

Offline john smith 19

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Maybe Aero's claim that basic theory will get you to 3Km/s (about M8.8 )   is correct  but given the results of the X30 programme what I'm suggesting is a flight programme.

And really what DOES air-breathing to @Mach-5+ get you if its "cheap" and "easy" enough over the alternatives?

(I'd suggest hitting up the "Ex-Rocketman's Take" blog to see some of the work he's done as one of "those" engineers :) )
I have downloaded the copy of the Glen Olson's site, including the ramjet design tool (although working out how to use it looks tricky. I'm guessing it's imperial units, but I'm not sure  :(  ).

My suggestion is a pure research project to settle an apparently simple question (it's one of the outstanding question's on Olson's site). In the same way the X1 was designed to answer the question "could you build a vehicle big enough to carry a person that could exceed M1".

My impression is that it seems that historically a missile requirement has been stated and people have built a ram jet to meet it but no one seems to checked how fast can such an engine go before you have to start looking at full supersonic combustion or pure rocket systems. In the US upper speeds have only been established by stuck open valves (and I'll note they seem to have been still accelerating so thrust > drag and lift > mass) while the French report you cited indicated that a 10 flight M5 test programme seemed to be fairly straight forward.

Olson suspected the operating range of 3 Mach numbers of most actual missiles was a convenience for the designers (and a perfectly valid trade off in a weapon system). The implication being that with more attention to detail and possibly accepting you'd lose some payload that range could be much wider.

I'll note the Russian/Indian "BraMos" anti ship missile is good to M2.8-3.0 and their planned 2nd generation is to M7. They don't seem to be talking about supersonic combustion to do it but they do seem to want liquid fuel.

As a side note I will note that M7 is 1/4 of the velocity to orbit including losses and M13 (using M1=340 m/s) is about 1/2 to orbital velocity.

If LEO is "half way to anywhere" then I guess at 1/2 LEO velocity you'd be a quarter way to anywhere?

TBH that's beyond what the comments of the people Olson talked to thought possible but the truth is that despite the first one running in the early 1930's we still don't know.  :(
"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 RanulfC

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I have downloaded the copy of the Glen Olson's site, including the ramjet design tool (although working out how to use it looks tricky. I'm guessing it's imperial units, but I'm not sure  :(  ).

I'm still playing with it when I remember I have it :)

Quote
My suggestion is a pure research project to settle an apparently simple question (it's one of the outstanding question's on Olson's site). In the same way the X1 was designed to answer the question "could you build a vehicle big enough to carry a person that could exceed M1".

Ah, yes, this works perfectly! I even have the "moto" we can put on the patch:
"Heus tu Omnis, Vigilate Hoc"
(Actual: "Hey Everyone, Watch This" the "rough" translation would end up being "Hey Y'all! Watch this! ;)) Our Commander was having a bad day and I suggested we needed to create a new squadron patch. I asked him how you say "Hey Y'all, Watch This!" in Latin and he said "NO, just NO!" but walked away laughing. Then my wife asked me "I wonder how DO you say it in Latin" and thus :) )

Anyway, in some of his notes Glenn mentiones that during his research there was enough written data to support the conslusion that "someone" had flown a subsonic ramjet engine at speeds to around Mach-8 and most seemed confident that Mach-10 was possible and still generate thrust. But as you note, we really don't KNOW what the limits are.

Quote
My impression is that it seems that historically a missile requirement has been stated and people have built a ram jet to meet it but no one seems to checked how fast can such an engine go before you have to start looking at full supersonic combustion or pure rocket systems. In the US upper speeds have only been established by stuck open valves (and I'll note they seem to have been still accelerating so thrust > drag and lift > mass) while the French report you cited indicated that a 10 flight M5 test programme seemed to be fairly straight forward.

As far as I know there were only a few actual "test" ramjet vehicles the best known one being the X7. Most engines were "point-designs" specifically designed to operate at a restricted range speeds.

Quote
Olson suspected the operating range of 3 Mach numbers of most actual missiles was a convenience for the designers (and a perfectly valid trade off in a weapon system). The implication being that with more attention to detail and possibly accepting you'd lose some payload that range could be much wider.

I got from his site and other sources that if you're willing to put up with the expense and compelxity of moving inlets and exhaust AND intergrate into the vehicle (the majority of early work concentrated on podded engines as experiance with imbedded jet engines hadn't been as good as hoped, turns out different engines have different operational experiances... Who knew :) ) then you're main barrier should JUST be generating thrust.

Of course that in itself can cause some issues to be worried about... (below)

Quote
I'll note the Russian/Indian "BraMos" anti ship missile is good to M2.8-3.0 and their planned 2nd generation is to M7. They don't seem to be talking about supersonic combustion to do it but they do seem to want liquid fuel.

A LOT of folks "talk" SCramjets but operationally its all been ramjets and everything I've seen so far points to subsonic combustion ramjets being perfectly capable of doing the job.
Quote
As a side note I will note that M7 is 1/4 of the velocity to orbit including losses and M13 (using M1=340 m/s) is about 1/2 to orbital velocity.

If LEO is "half way to anywhere" then I guess at 1/2 LEO velocity you'd be a quarter way to anywhere?

TBH that's beyond what the comments of the people Olson talked to thought possible but the truth is that despite the first one running in the early 1930's we still don't know.  :(

Mach-7 with a subsonic combustion ramjet seems dooable, Mach-13...
The main point as you say is we simply don't know. Designing a vehicle to be able to test up to such speeds isn't easy and the need for variable intake/exhaust system drives up the system cost. I like Glenn Olson's idea of "cheap" testing of subscale ramjets but the need to intergrate them works very hard against the "cheap" part.

Something along the lines of the X7 test vehicle (wikipedia I know but, for general info: http://en.wikipedia.org/wiki/Lockheed_X-7) that's both robust but able to take a variety of engines to test.
(Funny finding, again its wikipedia so take it with a grain of salt but I'd actually heard the "target-drone" version of the X7 was almost impossible to shoot down even with the advanced systems of the day. http://en.wikipedia.org/wiki/AQM-60_Kingfisher)

But probably something more along the lines of the "ASTROX" RBCC booster (http://forum.nasaspaceflight.com/index.php?topic=22610.0) or the more "sugar-scoop" inward-turning design so that the exact nature of the "active" inlet and exhaust systems are less of an overall design issue?

Might be "nice" to have take-off and landing capability but in general I'd settle for the "job" being the main point of the design so "flight" rather than being able to land and take off from a certain point.

Randy
From The Amazing Catstronaut on the Black Arrow LV:
British physics, old chap. It's undignified to belch flames and effluvia all over the pad, what. A true gentlemen's orbital conveyance lifts itself into the air unostentatiously, with the minimum of spectacle and a modicum of grace. Not like our American cousins' launch vehicles, eh?

Offline john smith 19

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I'm still playing with it when I remember I have it :)
Yes it's got a lot of knobs to twiddle. I'm particularly curious if you can replace the 1962 atmosphere model with something else.

Quote
Anyway, in some of his notes Glenn mentiones that during his research there was enough written data to support the conslusion that "someone" had flown a subsonic ramjet engine at speeds to around Mach-8 and most seemed confident that Mach-10 was possible and still generate thrust. But as you note, we really don't KNOW what the limits are.
He mentions that there are enough old documents with graphs running up to M6.5 to suggest someone had flight tested something up to that speed. "Aero" suggested the thermodynamics of the fuel suggested M8.8 was possible (if you ignored drag, which would be a very silly idea). Checking the
Quote
As far as I know there were only a few actual "test" ramjet vehicles the best known one being the X7. Most engines were "point-designs" specifically designed to operate at a restricted range speeds.
That's what I suspected. On the upside it demonstrates that ramjet designs at multiple point speeds and altitudes are viable.
Quote
I got from his site and other sources that if you're willing to put up with the expense and compelxity of moving inlets and exhaust AND intergrate into the vehicle (the majority of early work concentrated on podded engines as experiance with imbedded jet engines hadn't been as good as hoped, turns out different engines have different operational experiances... Who knew :) ) then you're main barrier should JUST be generating thrust.

Of course that in itself can cause some issues to be worried about... (below)

A LOT of folks "talk" SCramjets but operationally its all been ramjets and everything I've seen so far points to subsonic combustion ramjets being perfectly capable of doing the job.
Well the BrahMos design is described as a ramjet but checking their website they say the "BrahMos II" design will be a SCramjet, which they claim will be in service by 2017. I'm doubtful but who knows?
Quote
Mach-7 with a subsonic combustion ramjet seems dooable, Mach-13...
The main point as you say is we simply don't know. Designing a vehicle to be able to test up to such speeds isn't easy and the need for variable intake/exhaust system drives up the system cost. I like Glenn Olson's idea of "cheap" testing of subscale ramjets but the need to intergrate them works very hard against the "cheap" part.

Something along the lines of the X7 test vehicle (wikipedia I know but, for general info: http://en.wikipedia.org/wiki/Lockheed_X-7) that's both robust but able to take a variety of engines to test.
(Funny finding, again its wikipedia so take it with a grain of salt but I'd actually heard the "target-drone" version of the X7 was almost impossible to shoot down even with the advanced systems of the day. http://en.wikipedia.org/wiki/AQM-60_Kingfisher)

But probably something more along the lines of the "ASTROX" RBCC booster (http://forum.nasaspaceflight.com/index.php?topic=22610.0) or the more "sugar-scoop" inward-turning design so that the exact nature of the "active" inlet and exhaust systems are less of an overall design issue?

Might be "nice" to have take-off and landing capability but in general I'd settle for the "job" being the main point of the design so "flight" rather than being able to land and take off from a certain point.
The designs I suggested in the OP were just outlines. My starting view would be a "simplest possible" approach with fixed geometry, which got the French and the US designs to M5. My instinct is for a reusable design to allow (relatively) gradual expansion of the flight envelope and the ability to reuse the basic structure. OTOH a fully expendable design skips the landing gear and could be built more lightly. I think modern materials open up some interesting options. PICA demonstrates high temperature entry. There are also various ceramic materials that can offer light weight(ish) high temperature protection.
« Last Edit: 08/25/2014 09:30 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 Cherokee43v6

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Finding the actual speed limit of a conventional ramjet powered vehicle.


Sorry, but the clarification must be asked...  African or European?  :P
"I didn't open the can of worms...
        ...I just pointed at it and laughed a little too loudly."

Offline RanulfC

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Finding the actual speed limit of a conventional ramjet powered vehicle.


Sorry, but the clarification must be asked...  African or European?  :P

Well African of course they start OUT with more payload capability!

He (Olson) mentions that there are enough old documents with graphs running up to M6.5 to suggest someone had flight tested something up to that speed. "Aero" suggested the thermodynamics of the fuel suggested M8.8 was possible (if you ignored drag, which would be a very silly idea). Checking the...

You seem to have cut off there :)
 
Quote
That's what I suspected. On the upside it demonstrates that ramjet designs at multiple point speeds and altitudes are viable.

Specifically if the vehicle is cheap enough and adaptable enough :)

Quote
The designs I suggested in the OP were just outlines. My starting view would be a "simplest possible" approach with fixed geometry, which got the French and the US designs to M5. My instinct is for a reusable design to allow (relatively) gradual expansion of the flight envelope and the ability to reuse the basic structure. OTOH a fully expendable design skips the landing gear and could be built more lightly. I think modern materials open up some interesting options. PICA demonstrates high temperature entry. There are also various ceramic materials that can offer light weight(ish) high temperature protection.

One of the reasons I mentioned the X7 was when looking at the "inward-turning" ASTROX design I noted the twin "horns" on the front an thougth "a duel spike X7" and imagined a very robust "recoverable" test vehicle using the X7 landing method :)

Randy
From The Amazing Catstronaut on the Black Arrow LV:
British physics, old chap. It's undignified to belch flames and effluvia all over the pad, what. A true gentlemen's orbital conveyance lifts itself into the air unostentatiously, with the minimum of spectacle and a modicum of grace. Not like our American cousins' launch vehicles, eh?

Offline john smith 19

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You seem to have cut off there :)
True. And I'm not sure where my chain of thinking was going.  :(
 
Quote
One of the reasons I mentioned the X7 was when looking at the "inward-turning" ASTROX design I noted the twin "horns" on the front an thougth "a duel spike X7" and imagined a very robust "recoverable" test vehicle using the X7 landing method :)
It's possible.

My problem is astrox have done lots of design studies.  :(

I want to see an actual flight vehicle to anchor some of those CFD predictions.
« Last Edit: 08/27/2014 07:05 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 R7

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I want to see an actual flight vehicle to anchor some of those CFD predictions.

No super-/hypersonic wind tunnel tests in between?
AD·ASTRA·ASTRORVM·GRATIA

Offline john smith 19

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I want to see an actual flight vehicle to anchor some of those CFD predictions.

No super-/hypersonic wind tunnel tests in between?
I'll quote 2 data points on that.
1)The Navaho cruise missile was designed to fly with a pair of 40 000lb ramjets in cruise at M3 in the late 1950's. IOW the people of the time were confident enough of their ability to deploy this tech that they could fit it to a large operational vehicle and make it work.

2) According to a history of the Johns Hopkins APL they were working on SCramjets in the early 1960ss and (in a wind tunnel) "proved" it could work.

The first actual SCramjet vehicle producing net thrust did not take place (IIRC) until 2004.

I think wind tunnel tests up to about M3 should be used to test the separation dynamics but I think by then the test ramjet should also have ignited.
"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 RanulfC

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I want to see an actual flight vehicle to anchor some of those CFD predictions.

No super-/hypersonic wind tunnel tests in between?
I'll quote 2 data points on that.
1)The Navaho cruise missile was designed to fly with a pair of 40 000lb ramjets in cruise at M3 in the late 1950's. IOW the people of the time were confident enough of their ability to deploy this tech that they could fit it to a large operational vehicle and make it work.

And lest we forget there was PLUTO :)
(http://www.merkle.com/pluto/pluto.html)

Unshielded nuclear reactors at 300ft AGL at Mach-3 for the win! (And by "win" I mean in the same sense anyone "wins" a game of Nuclear War :) )
Quote
I think wind tunnel tests up to about M3 should be used to test the separation dynamics but I think by then the test ramjet should also have ignited.

Seperation of what? And where?

Randy
From The Amazing Catstronaut on the Black Arrow LV:
British physics, old chap. It's undignified to belch flames and effluvia all over the pad, what. A true gentlemen's orbital conveyance lifts itself into the air unostentatiously, with the minimum of spectacle and a modicum of grace. Not like our American cousins' launch vehicles, eh?

Offline john smith 19

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And lest we forget there was PLUTO :)
(http://www.merkle.com/pluto/pluto.html)
Unshielded nuclear reactors at 300ft AGL at Mach-3 for the win! (And by "win" I mean in the same sense anyone "wins" a game of Nuclear War :) )
Good point. It takes a confident design team to propose a turboramjet to fly M3+ at 60 000 ft+ but a team of epic cojones boldness to do the same at near tree top height (not that many trees will be left standing once they've been hit by a M3 pressure wave  :( )
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Seperation of what? And where?
One of the outlines in my OP was the idea of a 2 stage Parent/Child design. The parent being a small RPV designed specifically to carry the test vehicle (whatever it turned out to be) to launch height, accelerate to launch speed and release it.

The firebee supersonic drones showed that if your thurst is more like 50% of your GTOW rather than 30% powering through the sound barrier is not that difficult. What I have in mind is a small vehicle big enough to carry the main test vehicle whose design is driven by the requirements to make it easy to control (especially during the separation phase) with AFAP minimal danger of the test vehicle hitting any control surfaces.

Things like sustained high speed, endurance and low RCS are not really relevant in this context. No canted in rudders for example (very cool to look at  however :)  ) but I'm thinking something more like that of the Shuttle Carrier Aircraft or the An 225, if that can work at M1+.

conceptually  I'm thinking of a low supersonic White Knight 2, although I'd expect the actual layout to be very different.  No crew should allow significantly larger payloads or smaller engines (as an aside does anyone make pure turbjets these days which aren't for expendable drones or missiles?) and only enough structural endurance to survive at M1+ (probably nearer M2) to get the ramjet firing and separated.

I'll note that WK2 has had quite a successful life hiring out to various people who want to drop test stuff off it. Perhaps VG are already in profit on their operations?  :) Sadly I doubt the ramjet carrier would be so popular.  :(
"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 Asteroza

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So something like a scaled down Crossbow air launch carrier? That's got a strongback design  to keep the ventral/aft clear for a drop with easy load/access on the ground. No weird side drop like a B-52, no dorsal launch like a SR-71. Structure is fairly simple and strong (joined box wing), aside from the landing gear arrangement.

Alternative would be something like the bee-plane...

http://www.bee-plane.com/

Offline RanulfC

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Seperation of what? And where?
One of the outlines in my OP was the idea of a 2 stage Parent/Child design. The parent being a small RPV designed specifically to carry the test vehicle (whatever it turned out to be) to launch height, accelerate to launch speed and release it.

Oh sure, like "I" ever read what you actually wrote.. ;)
My bad I missed that. Beside one of the reasons I keep bringing up the ex-rocketman's blog is he's done a lot of work, (given it was his "real" job for a long time) on hybrid rocket-ramjets using solid boosters inside the ramjet that transition to ramjets engines using liquid fuel for the rest of the flight.

And my own idea was that the vehicle could be launched using a liquid/solid/hybrid booster vertically before switching to ramjet power.

The above mentioned Crossbow ALV isn't a bad idea for something of a similar nature:
http://thehuwaldtfamily.org/jtrl/research/Space/Launch%20Vehicles/Air%20Launch/Air%20Launch%20To%20Orbit%20-%20ALTO%20-%20Crossbow-concept,%20MSFC.pdf

Your main issue is going supersonic with a combined structure, though the more I've thought about it the more something like a combination "B-58" with box-wings might make a lot of sense.

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The firebee supersonic drones showed that if your thurst is more like 50% of your GTOW rather than 30% powering through the sound barrier is not that difficult. What I have in mind is a small vehicle big enough to carry the main test vehicle whose design is driven by the requirements to make it easy to control (especially during the separation phase) with AFAP minimal danger of the test vehicle hitting any control surfaces.

"Biggest" issue for seperation is the carrier vehicle having a postive lift factor after release, the more the better which argues towards something like a box or joined wing. Since the ramjet is just running flat-out (pun-intended) there's no need for fancy manuevers at seperation.

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Conceptually I'm thinking of a low supersonic White Knight 2, although I'd expect the actual layout to be very different.  No crew should allow significantly larger payloads or smaller engines (as an aside does anyone make pure turbojets these days which aren't for expendable drones or missiles?) and only enough structural endurance to survive at M1+ (probably nearer M2) to get the ramjet firing and separated.

Subsonic would require some sort of booster to get the ramjet up to speed I'm thinking. (And "yes" technically the ONLY folks that make small jet engines these days make "pure" turbojets but they're pretty much all centrifugal compressors and turbines coupled with one or more "fan" blades for added cruise efficiency. The problem is they are all pretty small and what you'd need comes closer to a small fighter engine like a J85 or some such: http://en.wikipedia.org/wiki/General_Electric_J85. However I'll point out there are a number of studies on usign the "standard" cruise missile type engines, the F107/F112 types, http://en.wikipedia.org/wiki/Williams_F107/http://en.wikipedia.org/wiki/Williams_F112, and fitting them with afterburners to get supersonic performance out of them similar to early centrifugal turbojets)

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I'll note that WK2 has had quite a successful life hiring out to various people who want to drop test stuff off it. Perhaps VG are already in profit on their operations?  :) Sadly I doubt the ramjet carrier would be so popular.  :(

Depends on what people want to use it for :) The ALTO/Crossbow study mentioned above was partially refined and driven by the idea of an RPV space launch vehicle after all according to some folks here :)

Randy
From The Amazing Catstronaut on the Black Arrow LV:
British physics, old chap. It's undignified to belch flames and effluvia all over the pad, what. A true gentlemen's orbital conveyance lifts itself into the air unostentatiously, with the minimum of spectacle and a modicum of grace. Not like our American cousins' launch vehicles, eh?

Offline john smith 19

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Oh sure, like "I" ever read what you actually wrote.. ;)
My bad I missed that. Beside one of the reasons I keep bringing up the ex-rocketman's blog is he's done a lot of work, (given it was his "real" job for a long time) on hybrid rocket-ramjets using solid boosters inside the ramjet that transition to ramjets engines using liquid fuel for the rest of the flight.
Interesting thought but AFAIK the SoA in this area is a solid booster and solid fuel ramjet (or fuel rich gas generator as it seems to be called).
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And my own idea was that the vehicle could be launched using a liquid/solid/hybrid booster vertically before switching to ramjet power.
I'm a big fan of the KISS principle. I think the carrier aircraft should be as simple as possible, if you're going with a 2 stage design, which I prefer. If it's correct that modern turbofans are good to M2.4  as long as the engines are big enough the design should be fairly simple, although I suspect the inlet and (possibly) the exhaust systems will need to be fairly dynamic. For this mission (since oribit is not the goal) an HTOL system with a runway is viable, but a VTOL and approach similar to a launch assist platform is viable. 
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The above mentioned Crossbow ALV isn't a bad idea for something of a similar nature:
http://thehuwaldtfamily.org/jtrl/research/Space/Launch%20Vehicles/Air%20Launch/Air%20Launch%20To%20Orbit%20-%20ALTO%20-%20Crossbow-concept,%20MSFC.pdf
This makes interesting reading.  :)  I think the 2 takeaways from it were the CX120 (Just such a clever idea. A standard cargo container idea years ahead of what became the ISO container standards. Sadly AFAIK it's only outing was in the Jerry Anderson movie "Doppleganger"  :(  ). The other was the detail that the main reason for the Pegasus's wings (and most of its structure) is to be strong enough to execute the 45 deg pullup manoeuvre. So in principal an aircraft that can make a 45 deg pull up can simplify the launch vehicle design considerably,   with lighter structure and hence higher payload.
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"Biggest" issue for seperation is the carrier vehicle having a postive lift factor after release, the more the better which argues towards something like a box or joined wing. Since the ramjet is just running flat-out (pun-intended) there's no need for fancy manuevers at seperation.
Interesting point. I think flying the mission would be easier if the ramjet trajectory is flown at constant dynamic pressure. AIUI as the ramjet picks up speed the trajectory should get shallower due to the exponentially falling atmospheric pressure graph.
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Subsonic would require some sort of booster to get the ramjet up to speed I'm thinking. (And "yes" technically the ONLY folks that make small jet engines these days make "pure" turbojets but they're pretty much all centrifugal compressors and turbines coupled with one or more "fan" blades for added cruise efficiency. The problem is they are all pretty small and what you'd need comes closer to a small fighter engine like a J85 or some such: http://en.wikipedia.org/wiki/General_Electric_J85. However I'll point out there are a number of studies on usign the "standard" cruise missile type engines, the F107/F112 types, http://en.wikipedia.org/wiki/Williams_F107/http://en.wikipedia.org/wiki/Williams_F112, and fitting them with afterburners to get supersonic performance out of them similar to early centrifugal turbojets)
Too bad.  :( While I'd like to keep the overall vehicle sizes (of both) fairly small to keep the budget down if you could get a better deal on small bigger engines than the minimal size needed that would seem to be a simpler option.
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Depends on what people want to use it for :) The ALTO/Crossbow study mentioned above was partially refined and driven by the idea of an RPV space launch vehicle after all according to some folks here :)
Fair point. I did not know this about Crossbow.  :( It still looks like a sub sonic vehicle. I think the goal in this thread can be met with a much smaller vehicle than Crossbow.
« Last Edit: 09/06/2014 04:09 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 Katana

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Maybe Aero's claim that basic theory will get you to 3Km/s (about M8.8 )   is correct  but given the results of the X30 programme what I'm suggesting is a flight programme.

I think I noted that Glenn Olson (of the old alt-accel website) had spoken to enough ex-ramejt engineers to come away pretty confident that a well-designed subsonic combustion ramjet could reach speeds in a bit excess of Mach-8 and for the most part (unlike many of the folks riding "theory" till it auguered into the ground in the form of the SCramjet :) ) couldn't see many "good" reasons to go faster even if most of them thought Mach-10 was possible given the right propellant and design :)

And really what DOES air-breathing to @Mach-5+ get you if its "cheap" and "easy" enough over the alternatives?

(I'd suggest hitting up the "Ex-Rocketman's Take" blog to see some of the work he's done as one of "those" engineers :) )

Randy

Ramjets could reach speeds of Scramjets, restrictions on fuel energy density to max velocity of 3km/s are basically same. Main difference is ramjet burns hotter, Scramjets has low mixing efficiency.

The concept of Scramjet is over hyped over ramjets, on a false compare between engines with very different levels of construction technology.

On the side of low cost, French STX got to M4.9 with simple and cheap stainless tubes, also compatible to standard balloon tank rocket airframe.

Going above M5 need to increase cost on airframe, M8 needs heavy TPS or regen cooling of airframe.

So that for launch vehicles it maybe wise to cutoff at M5, similar to Skylon.

Offline john smith 19

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The concept of Scramjet is over hyped over ramjets, on a false compare between engines with very different levels of construction technology.
Agreed.
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On the side of low cost, French STX got to M4.9 with simple and cheap stainless tubes, also compatible to standard balloon tank rocket airframe.

Going above M5 need to increase cost on airframe, M8 needs heavy TPS or regen cooling of airframe.

So that for launch vehicles it maybe wise to cutoff at M5, similar to Skylon.
There are 2 parameters. The absolute top speed a (subsonic combustion) ramjet can reach and the operating range it can do.

AFAIK the usual rules of thumb for ramjets have been a) No more than 3 Mach numbers of acceleration and b) Slow the flow inside the combustor to about M0.5

These seemed to have been arrived at as empirical rules, not absolute limits.

So I wondered if you you slowed the flow down less how fast could you go EG M0.9 in the combustor. And at what point do the subsonic design rules break down (I'm pretty sure it's below M1 in the combustor,, but what is it?)

Likewise if you have different injector sets within the combustor, or avoid a conventional flame holder, and use "thermal choking" to create "virtual" variable geometry withing the ramjet, how high could you go?

On the materials side you could have relatively cheap spray coated ceramic layers inside to handle the heat, going on up to full superalloys.

The driver for this BTW was the notion of a "launch assist" architecture, where every Mach number you can add to the operating Mach range means a larger payload for the terminal rocket powered stage.

Increasing the Mach range from 3 (IE M2.2 to 5.2) to say 5 (M2.2 to M7.2) would definitely be worthwhile.

Hence my question what if you ran an X programme just to find those limits.
"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 Katana

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Make it easy. Assume
body drag = 0,
prop is kero,
mdot (air)=1
reaches stagnation pressure within the engine,
then thrust = ram drag = V*mdot (air) and
thrust = ram drag = (mdot(air)+mdot(kero))*Ve and
E = thrust*Ve/2 = 1/2 * total mdot *Ve2

How much kero do you want to burn? Well, you have about 0.2 O2 and if you use a oxygen/fuel mix of, I don't know, 2.2 maybe (for Pc = 25 bar) gives about 0.09 kero. Choose your units, then what is your energy, in Joules =  (watt/sec)? Plug in E and solve for ram drag which gives you velocity. But be sure to observe that Ve /= V.

Oh, I looked it up for you. The heating value of kerosene is 43.1 MJ/kg.

The big problem with this is that drag = 0 (excepting ram drag) is not a valid assumption so you won't get the ~3 km/s velocity this approach produces. Design your engine with a nice low frontal area and a good supersonic coefficient of drag, then extend my little model to account for that drag. Of course now you have to add ram and body drag together to equal thrust.
The temperature rise during inlet compression is restored during nozzle expansion. So the flight velocity may exceed 3km/s If effective energy release is greater than drag loss.

However with practical total thermal efficiency less than 50% (already better than best car engines), flight velocity is generally limited below 3km/s.

At high speed, subsonic combustion ramjets suffer from high temperature chemical disintergration of air (N2 and O2 to N, O ,NO). If recombination is not complete during nozzle expansion, efficiency drop.

Scramjets reduce temperature by only partly convert kinetic energy to heat. But low efficiency of mixing (of air and fuel) at supersonic conditions becomes a bigger problem, long and thin flow path is required, with large drag loss.

The timescale of macroscopic mixing is much larger than chemical recombination of air molrcules. So the problem of air disintergration is easier than the problem of fuel mixing.

Low efficiency of supersonic mixing (slow growth rate of supersonic shear layer) is fully understood until CFD tools of late 1990s made X-43 possible (after failure of X-30). Already too late that Scramjets attracted too much attention over ramjets.

Offline Katana

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Quite a bit.  I could probably figure out a first-order estimate by hand.
I don't think anyone in their right mind would design a modern flying vehicle without CFD to begin with to converge on roughly what it should look like. One really interesting result of the RAND reviews of the X30 programme was the little factoid that if the CFD model data point count is >=  R ^9/4 (R being the vehicle Reynolds number) you don't need a turbulence model and you can get the results directly.

In an era of GPU's offering power in 1x10^12 FLOPS capacity I wonder if the time has come (at least for small vehicles, which this is meant to be) to brute force the problem? What I'm not so sure about is the number of equations at each point you'd be dealing with and the memory they'd need to store the parameters.

Historically we know of at least 2 designs (the US ASALM and the French M5 ramjet programme) that got to M5+ with fixed geometries [EDIT and subsonic combustion]

Maybe Aero's claim that basic theory will get you to 3Km/s (about M8.8 )   is correct  but given the results of the X30 programme what I'm suggesting is a flight programme.  There just aren't that many (flight) data points for any design going through this range. [EDIT  a page on the Talos missile programme
http://www.okieboat.com/Ramjet%20history.html
stated that later versions switched to what appears to be hydrogenated dimerised JP10 (tetra cylopentadiene). This increased the energy available per (US) gallon of fuel from IIRC 126 to 143 thousand BTU's, about a 13% increase  Called RJ-4]

Note that while I'd prefer to keep things as simple as possible and with most geometry fixed to side step problems with high temperature actuators I think active skin cooling may be a reasonable trade off to lower weight if necessary. However since the goal is research, not an operational vehicle flying a constant dynamic pressure trajectory (IE climbing, not accelerating at a fixed altitude) is the way to go.

I also suspect sub sonic ramjet combustor design has been a rather neglected field and CFD has been not really been used on it.

If I'm right this is an area where substantial improvements should be possible. While the inlet has to handle the full  Mach range of the incoming air stream by the time it hits the combustion section things should be much more constant (after all the goal is to what can be done below M1).

A key element here seems to be the "flame holder." It's been suggested that good designs retain certain combustion products in their lee which are critical to continued stable effective combustion. A similar comment has been made about the injector designs in rocket engines. I'm guessing bad designs end up in combustion cycles of flame outs, fuel accumulation, ignition, resulting in either a pulsing thrust like a series of car engine mis fires or a low efficiency pulse detonation engine if (somehow) you've hit the conditions for deflagration to detonation transition  :( . I think the latter is unlikely but not entirely impossible.

This suggests 2 things. 1) An effective CFD based design must incorporate both the aero thermodynamic and thermochemical  aspects of the problem (including compressibility)  and 2) Most o f the action will take place below M1. That much lower Mach range (and hence Reynolds numbers) coupled with much more powerful modern processing hardware, should make the problem small enough to fit into a relatively small processing environment.

[EDIT
It seems the key task of the flame holder is to ensure complete mixing and combustion of the fuel by slowing down it's passage through the duct by increasing turbulence, giving enough time to complete combustion. In the Talos design this is done by igniting the fuel/air mix and flowing it inward through a truncated perforated metal plate. My guess is that the size and spacing of those holes can make a significant  difference in ramjet performance but IRL (around 1948-1953) they were chosen either by what materials were available or by a cut-and-try process that stopped when they got a result that was good enough to deliver the performance target.

The challenge is to deliver enough delay without increasing the interior drag too much.

AFAIK no ramjet flight vehicles have been built that used the current generation of non invasive diagnostics to measure temperature, pressure and combustion chemistry within the combustor to gather data for a more optimized design.

When flight mach nuber approaches upper limit, subsonic mach number inside combustor reduces (behind stronger shockwave) to ~0.15. Engine performance and stability becomes more forgiving to flameholder, while inlet and nozzle supersonic losses and shockwawe stability go critical and require good CFD.

Talos style flameholder can't survive heat of M5, French STX used a simple fingured shape similar to early cobra burner test vehicles in 1946 before Talos.

Offline Katana

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The concept of Scramjet is over hyped over ramjets, on a false compare between engines with very different levels of construction technology.
Agreed.
Quote
On the side of low cost, French STX got to M4.9 with simple and cheap stainless tubes, also compatible to standard balloon tank rocket airframe.

Going above M5 need to increase cost on airframe, M8 needs heavy TPS or regen cooling of airframe.

So that for launch vehicles it maybe wise to cutoff at M5, similar to Skylon.
There are 2 parameters. The absolute top speed a (subsonic combustion) ramjet can reach and the operating range it can do.

AFAIK the usual rules of thumb for ramjets have been a) No more than 3 Mach numbers of acceleration and b) Slow the flow inside the combustor to about M0.5

These seemed to have been arrived at as empirical rules, not absolute limits.

So I wondered if you you slowed the flow down less how fast could you go EG M0.9 in the combustor. And at what point do the subsonic design rules break down (I'm pretty sure it's below M1 in the combustor,, but what is it?)

Likewise if you have different injector sets within the combustor, or avoid a conventional flame holder, and use "thermal choking" to create "virtual" variable geometry withing the ramjet, how high could you go?

On the materials side you could have relatively cheap spray coated ceramic layers inside to handle the heat, going on up to full superalloys.

The driver for this BTW was the notion of a "launch assist" architecture, where every Mach number you can add to the operating Mach range means a larger payload for the terminal rocket powered stage.

Increasing the Mach range from 3 (IE M2.2 to 5.2) to say 5 (M2.2 to M7.2) would definitely be worthwhile.

Hence my question what if you ran an X programme just to find those limits.
M0.9 in combustor goes to M1 thermal choking after little amount of heat addition (either subsonic flow or supersonic flow goes near to M1 with heat added), and you can't add heat anymore.

 The velocity inside combustor is inverse related to velocity outside. If the engine starts at M2.5 with M0.3 inside, when flying to top speed of M5, the velocity inside falls to ~M0.15.

For thermal choking to occur with suitable amount of fuel, Internal velocity should lies between M0.1 to M0.5, normally M0.1 to M0.3

Relatively higher internal velocity M0.3~M0.5 at startup may widen the total operating range. Need to startup with lean fuel and have inlet and nozzle designed for a range of conditions instead of fixed design point.

For launch assist applications, reduce startup velocity may be more benificial, for low boost fuel consumption and low TPS weight. Maybe M1.5 to M5.5, even M0.8 to M4.
« Last Edit: 01/31/2017 02:25 AM by Katana »

Offline Archibald

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trying to help here. The Lockheed X-7 reached Mach 4.31 in 1960 with the same ramjets as the BOMARC (XRJ-43 Marquardt)

The ONERA Stataltex may have broken that record and flew at Mach 5 but it remains unclear.
http://xplanes.free.fr/stato/stato-17.html
https://archive.org/stream/nasa_techdoc_19670008070/19670008070_djvu.txt

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Four missiles reached a flight speed of nearly 4,600
feet per second, i.e., about Mach 5, between the altitudes
of 40,000 to 115,000 feet.

what is sure is that Mach 5 - Mach 5.5 remained unbroken until the 90's at least, and then it was "supersonic combustion" (Kholod, HyFly and on)
« Last Edit: 01/31/2017 07:26 AM by Archibald »

Offline Hobbes-22

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The approach with a carrier vehicle seems overly complicated. As an alternative, you could attach a rocket booster to get the ramjet up to any speed you want. 

The Royal Navy used to use the Sea Dart ramjet-powered missile. It had a small solid booster.
IMO, this would be a good starting point for an expendable trials system. Enlarge the booster for higher speeds. Replace the warhead and seeker with instrumentation.

Offline john smith 19

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When flight mach nuber approaches upper limit, subsonic mach number inside combustor reduces (behind stronger shockwave) to ~0.15. Engine performance and stability becomes more forgiving to flameholder, while inlet and nozzle supersonic losses and shockwawe stability go critical and require good CFD.
So for a higher peak velocity you need a combustor design that starts with an internal mach number of (say) M0.9 and drops to Mach 0.5-0.3 at peak velocity?
Quote
Talos style flameholder can't survive heat of M5, French STX used a simple fingured shape similar to early cobra burner test vehicles in 1946 before Talos.
There has been some comments about a "dump combustor" that seems to have good properties in this area.
The temperature rise during inlet compression is restored during nozzle expansion. So the flight velocity may exceed 3km/s If effective energy release is greater than drag loss.
Which I presume is where we enter SCramjet territory.
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However with practical total thermal efficiency less than 50% (already better than best car engines), flight velocity is generally limited below 3km/s.

At high speed, subsonic combustion ramjets suffer from high temperature chemical disintergration of air (N2 and O2 to N, O ,NO). If recombination is not complete during nozzle expansion, efficiency drop.
I think it's usually referred to as dissociation. The NN and OO bonds are broken but the atoms are intact.
Quote
Scramjets reduce temperature by only partly convert kinetic energy to heat. But low efficiency of mixing (of air and fuel) at supersonic conditions becomes a bigger problem, long and thin flow path is required, with large drag loss.

The timescale of macroscopic mixing is much larger than chemical recombination of air molrcules. So the problem of air disintergration is easier than the problem of fuel mixing.

Low efficiency of supersonic mixing (slow growth rate of supersonic shear layer) is fully understood until CFD tools of late 1990s made X-43 possible (after failure of X-30). Already too late that Scramjets attracted too much attention over ramjets.
Do you mean "was not fully understood" before CFD in the late 90's?  I can certainly believe that.
M0.9 in combustor goes to M1 thermal choking after little amount of heat addition (either subsonic flow or supersonic flow goes near to M1 with heat added), and you can't add heat anymore.

 The velocity inside combustor is inverse related to velocity outside. If the engine starts at M2.5 with M0.3 inside, when flying to top speed of M5, the velocity inside falls to ~M0.15.
That's a key factor that will set a ceiling on maximum Mach in a design. How high can you start, how low can you go.
Quote
For thermal choking to occur with suitable amount of fuel, Internal velocity should lies between M0.1 to M0.5, normally M0.1 to M0.3

Relatively higher internal velocity M0.3~M0.5 at startup may widen the total operating range. Need to startup with lean fuel and have inlet and nozzle designed for a range of conditions instead of fixed design point.
Ideally a fixed geometry design is best but beyond that a moving spike inlet seems mechanically the next simplest, although having different sets of fuel injectors would need multiple valves to modulate the fuel flow and where the fuel, and hence heat, is injected.
Quote
For launch assist applications, reduce startup velocity may be more benificial, for low boost fuel consumption and low TPS weight. Maybe M1.5 to M5.5, even M0.8 to M4.
M0.8-0.9 put it in in range of conventional turbofans but that would not give you any new capabilities for an application.

The original concept that sparked this was a Launch Assist Platform carrying turbojets or pre cooled turbofans to get to M2.2 (IE Concorde speed) then RP1 (allowing common tankage) fueled ramjets mounted on the wing tips of a winged rocket stage. At M5.2 the ramjets are jettisoned for later recovery and reuse. The goal was a fully reusable design with all stages operating over speed ranges for which there is solid (decades in the case of Concorde, but also various bombers and fighters) operating experience. This thread however was to see what you could get as a pure X programme, where there is no goal except go as fast as possible or go over as many Mach numbers as possible.

Widening the operating Mach range of the ramjet component seemed the best simple way to raise payload on the final stage, by cutting the delta V it has to supply. Lowering the starting velocity to M0.8-0.9 would widen the range of available jet engines but give you no increase on the top speed, which is what this concept would need to either lighten the final stage or raise the payload it could carry to orbit.
"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 Katana

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There has been some comments about a "dump combustor" that seems to have good properties in this area.
Dump combustor is easy to achieve good combustion, but runs very hot. They are favored on early scramjet test models with combustion difficulty, but not necessary for high mach conventional ramjets where combustion occurs very easy in slow (<M0.15) and hot(>1000K) inflow.

For compatibility to fast (~M0.5) and cool (~300K) inflow during start, recent derivatives of dump combustor and conventional flameholder called "trap vortex combustor" works better.

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Which I presume is where we enter SCramjet territory.
Conventional ramjet is more efficient than SCramjet, though hotter and require better material / cooling.

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I think it's usually referred to as dissociation. The NN and OO bonds are broken but the atoms are intact.

Do you mean "was not fully understood" before CFD in the late 90's?  I can certainly believe that.
Yes.

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That's a key factor that will set a ceiling on maximum Mach in a design. How high can you start, how low can you go.
Ceiling of internal mach number of existing ramjets range from M0.2~0.3, going down to bottom of M0.1~0.15. Theoretical max ceiling is M0.5~0.7, above M0.7 the airflow could accept little amount of heat and produce no useful thrust.

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Ideally a fixed geometry design is best but beyond that a moving spike inlet seems mechanically the next simplest, although having different sets of fuel injectors would need multiple valves to modulate the fuel flow and where the fuel, and hence heat, is injected.
Moving spike inlet are widely used  in 1960s. While fixed inlet have stability problem of wide range operation, modern CFD and automatic optimization technique may help.

Multiple injection afterburning in high expansion nozzle could replace adjustable nozzle at low flight mach number. It's the ramjet version of TAN in rocket nozzle, but backpressure of afterburning reduce nozzle throat flow speed to subsonic and produces sonic outflow (local M=1 at high temperature, near 1000m/s). No supersonic combustion efficiency problem.

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M0.8-0.9 put it in in range of conventional turbofans but that would not give you any new capabilities for an application.

The original concept that sparked this was a Launch Assist Platform carrying turbojets or pre cooled turbofans to get to M2.2 (IE Concorde speed) then RP1 (allowing common tankage) fueled ramjets mounted on the wing tips of a winged rocket stage. At M5.2 the ramjets are jettisoned for later recovery and reuse. The goal was a fully reusable design with all stages operating over speed ranges for which there is solid (decades in the case of Concorde, but also various bombers and fighters) operating experience. This thread however was to see what you could get as a pure X programme, where there is no goal except go as fast as possible or go over as many Mach numbers as possible.

Widening the operating Mach range of the ramjet component seemed the best simple way to raise payload on the final stage, by cutting the delta V it has to supply. Lowering the starting velocity to M0.8-0.9 would widen the range of available jet engines but give you no increase on the top speed, which is what this concept would need to either lighten the final stage or raise the payload it could carry to orbit.

Using supersonic carrier aircraft (F-15?) is generally too expensive for either budget of small test program (private funded or SBIR) or meaningful satellite launcher (size of Concorde needed).

For a small test program, French Stataltex launch from ground and reach maximum speed with minimum cost up to now, though boosted to M3 with solid rocket.

For practical launcher, air-breathing propulsion with VTVL architecture is optimal. Low minimum speed allows for direct rocket boost without turbojet/turbofan engines. At external speed M0.8 the internal speed could be M0.3, rising to M0.5 when multiple shockwaves establish at M1.5, and drop to M0.15 at near M5.
« Last Edit: 02/01/2017 03:19 PM by Katana »

Offline colbourne

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Pulse detonation jets can be more efficient than other jets as a higher compression ratio can be obtained. I dont know if they are suitable for such high speeds.  In June 2008, the Defense Advanced Research Projects Agency (DARPA) unveiled Blackswift, which was intended to use this technology to reach speeds of up to Mach 6.

https://en.wikipedia.org/wiki/Pulse_detonation_engine
« Last Edit: 02/02/2017 04:29 AM by colbourne »

Offline Katana

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Pulse detonation jets can be more efficient than other jets as a higher compression ratio can be obtained. I dont know if they are suitable for such high speeds.  In June 2008, the Defense Advanced Research Projects Agency (DARPA) unveiled Blackswift, which was intended to use this technology to reach speeds of up to Mach 6.

https://en.wikipedia.org/wiki/Pulse_detonation_engine
No practical PDE exist up to now.
The best flight one: long-EZ test platform with PDE modified from automobile engine front end
http://www.airliners.net/photo/Untitled/Rutan-61-Long-EZ-PDE/4179773

Offline john smith 19

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Pulse detonation jets can be more efficient than other jets as a higher compression ratio can be obtained. I dont know if they are suitable for such high speeds.  In June 2008, the Defense Advanced Research Projects Agency (DARPA) unveiled Blackswift, which was intended to use this technology to reach speeds of up to Mach 6.

https://en.wikipedia.org/wiki/Pulse_detonation_engine
No practical PDE exist up to now.
The best flight one: long-EZ test platform with PDE modified from automobile engine front end
http://www.airliners.net/photo/Untitled/Rutan-61-Long-EZ-PDE/4179773
I think the impressive thing about the PDE demonstration was how it was relatively easy to get it working.
"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 Katana

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Pulse detonation jets can be more efficient than other jets as a higher compression ratio can be obtained. I dont know if they are suitable for such high speeds.  In June 2008, the Defense Advanced Research Projects Agency (DARPA) unveiled Blackswift, which was intended to use this technology to reach speeds of up to Mach 6.

https://en.wikipedia.org/wiki/Pulse_detonation_engine
No practical PDE exist up to now.
The best flight one: long-EZ test platform with PDE modified from automobile engine front end
http://www.airliners.net/photo/Untitled/Rutan-61-Long-EZ-PDE/4179773
I think the impressive thing about the PDE demonstration was how it was relatively easy to get it working.
This demonstration model go no further, while first ramjet demonstration model (even more easier) evolved to Mach 2 in a year.

http://www.designation-systems.net/dusrm/app1/ptv-n-4.html
The first 15.2 cm (6 in) diameter ramjet model, named Cobra, was made of out a P-47 exhaust tube and first tested in early 1945. The initial Cobras used only dummy ramjets and evaluated launching and flight stability issues. Later that year, development had progressed to larger vehicles with live ramjets, and in October 1945 a 25 cm (10 in) diameter model reached a speed of 2250 km/h (1400 mph) at an altitude of about 6000 m (20000 ft).

Offline colbourne

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The point is that pulse detonation engines are potentially more efficient. They might not be easy but the future savings in fuel costs will provide an incentive for research.

Offline john smith 19

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The point is that pulse detonation engines are potentially more efficient. They might not be easy but the future savings in fuel costs will provide an incentive for research.
My actual point was that once someone had decided to commit to a PDE building it was fairly straightforward, and IIRC it operates from zero speed, something no ramjet can do.

It just feels like a system that's going to be intrinsically easier to test in prototype.

My instinct is however that to do so will mean a collection of US institutions acknowledging that SCRamjets are basically a research curiosity and the several $Bn that has been spent on them has not been a very good use of resources.
"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 RanulfC

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>snipping my quote :)<

Ramjets could reach speeds of Scramjets, restrictions on fuel energy density to max velocity of 3km/s are basically same. Main difference is ramjet burns hotter, Scramjets has low mixing efficiency.

SCramjets however have a much greater "new-shiny-research-grant-getting" efficiency which is why subsonic combustion ramjets keep getting ignored :)

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The concept of Scramjet is over hyped over ramjets, on a false compare between engines with very different levels of construction technology.

You must be rather 'new' around here NOT to have run into one or more of my rants on just the subject :) SCramjets "promise" has always been wrapped up in weapons delivery despite their overuse in all manner of launch and air travel vehicle concepts. For weapons delivery they have distinct, (but difficult and expensive) advantages but for almost every other application their use comes at to high a cost in vehicle and systems design.

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On the side of low cost, French STX got to M4.9 with simple and cheap stainless tubes, also compatible to standard balloon tank rocket airframe.

And the ASALM with a 'simple' fixed inlet optimized for a narrow Mach range was pushing past Mach-5.5 when it ran out of fuel so yes ramjets are pretty low cost and high utility IF you can keep someone from slapping SCramjets onto the concept :) Note the ASALM was a internal solid booster which converted after burnout to a ramjet and flight operation was solid boost to around Mach-1+ at which point it burned out and both the main chamber nozzle (converting it to a ramjet nozzle) and inlet cover were ejected, at which point the vehicle accelerated to cruise speed of Mach-4. Unless the fuel valve sticks :)

Though it's a bit more complicated than that, (again the blog "An Ex-Rocketman's Take" is an excellent source of actual ramjet experience and wisdom :) ) as to get the best performance you need to optimize different factors and take into account the need to get the ramjets up to operating speed. GW Johnson of the afore mentioned blog prefers mixed solid/ramjet hybrid boosters for a combined SRB/Ramjet accelerator concept so as to avoid a heavy inlet/exhaust system, I prefer something closer to the Supercharged-Ejector-Ram-Jet, (SERJ) though it's more complex and heavy because it's got a much higher turn-around and therefore duty cycle.

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Going above M5 need to increase cost on airframe, M8 needs heavy TPS or regen cooling of airframe.

So that for launch vehicles it maybe wise to cutoff at M5, similar to Skylon.

This IS pretty much what every study shows though depending on the assumed bias' behind the study's many will justify and hand-wave to get speeds as high as Mach-10, (got to justify that SCramjet money you know :) ) in order to get the 'most' out of air-breathing propulsion but it's rather obvious that going that fast IN the atmosphere isn't going to be COST effective let alone as efficient as suggested. You pretty much wipe out any of the aircraft-legacy 'advantages' once you go beyond Mach-5 and if you do THAT the whole idea and justification of using an air-breathing stage/booster pretty much falls apart.

trying to help here. The Lockheed X-7 reached Mach 4.31 in 1960 with the same ramjets as the BOMARC (XRJ-43 Marquardt)

The ONERA Stataltex may have broken that record and flew at Mach 5 but it remains unclear.
http://xplanes.free.fr/stato/stato-17.html
https://archive.org/stream/nasa_techdoc_19670008070/19670008070_djvu.txt

ASALM was going Mach-5.5 and STILL accelerating when it ran out of fuel. In addition it was widely noted by the Marquardt BOMARC engine engineers, (oral and anecdotal not it should be noted anywhere 'official' :) ) that the engines themselves could probably reach a much higher total speed than the airframe could possibly stand. Boeing had certified the airframe to speeds up to Mach-6 before failure so...

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what is sure is that Mach 5 - Mach 5.5 remained unbroken until the 90's at least, and then it was "supersonic combustion" (Kholod, HyFly and on)

It was 'supersonic combustion' long before the 90s as the book "Facing the Heat Barrier" shows clearly. By the early 60s the "math" said that there was no upper limit to the speeds possible once combustion when supersonic in a 'ramjet' engine so the SCramjet became a 'thing' which even then was touted as coming "in just a few more years" despite the inability to figure out how. We've been chasing an operational SCramjet ever since

Randy
From The Amazing Catstronaut on the Black Arrow LV:
British physics, old chap. It's undignified to belch flames and effluvia all over the pad, what. A true gentlemen's orbital conveyance lifts itself into the air unostentatiously, with the minimum of spectacle and a modicum of grace. Not like our American cousins' launch vehicles, eh?

Offline RanulfC

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M0.8-0.9 put it in in range of conventional turbofans but that would not give you any new capabilities for an application.

The original concept that sparked this was a Launch Assist Platform carrying turbojets or pre cooled turbofans to get to M2.2 (IE Concorde speed) then RP1 (allowing common tankage) fueled ramjets mounted on the wing tips of a winged rocket stage. At M5.2 the ramjets are jettisoned for later recovery and reuse. The goal was a fully reusable design with all stages operating over speed ranges for which there is solid (decades in the case of Concorde, but also various bombers and fighters) operating experience. This thread however was to see what you could get as a pure X programme, where there is no goal except go as fast as possible or go over as many Mach numbers as possible.

Widening the operating Mach range of the ramjet component seemed the best simple way to raise payload on the final stage, by cutting the delta V it has to supply. Lowering the starting velocity to M0.8-0.9 would widen the range of available jet engines but give you no increase on the top speed, which is what this concept would need to either lighten the final stage or raise the payload it could carry to orbit.

Using supersonic carrier aircraft (F-15?) is generally too expensive for either budget of small test program (private funded or SBIR) or meaningful satellite launcher (size of Concorde needed).

For a small test program, French Stataltex launch from ground and reach maximum speed with minimum cost up to now, though boosted to M3 with solid rocket.

For practical launcher, air-breathing propulsion with VTVL architecture is optimal. Low minimum speed allows for direct rocket boost without turbojet/turbofan engines. At external speed M0.8 the internal speed could be M0.3, rising to M0.5 when multiple shockwaves establish at M1.5, and drop to M0.15 at near M5.

Actual the ORIGINAL, orginal idea I think was a concept that expanded on a multi-engine turbojet launch assist system based on an original concept by Dani Edar when he was working at Boeing:
http://yarchive.net/space/launchers/jet_first_stage.html
http://forum.nasaspaceflight.com/index.php?topic=25095.0
https://en.wikibooks.org/wiki/Space_Transport_and_Engineering_Methods/Human_Transport

Which used them in a VTVL configuration, again originally as booster pods and later as a "ring-wing" stage in and of itself to boost a TSTO configured vehicle to Mach-2 and 100,000ft. NASA-Dryden re-packaged (and patented)the concept in 2013 (https://www.nasa.gov/offices/ipp/centers/dfrc/technology/DRC-010-039-Ram-Booster.html) and added a ramjet second stage and a Centaur based third stage. My personal addition was the inclusion of Mass-Injection-Pre-Compressor-Cooling (MIPCC) to significantly increase the turbofan thrust though it also made it "possible" to raise the maximum Mach to around 4 I wasn't sure it would be worth the extra engineering for the LV though the Dryden concept uses the ramjet for Mach-2 through 4 acceleration so it seems like it would still work. As MIPCC LOX injection later in flight to stabilize the combustion chamber combustion and temperature it's baseline to operate to a bit above 100,000ft anyway so this cuts out the Dryden ramjet stage entirely. (Unless someone wants to use it to get from Mach-4 to higher speeds but again, air breathing past Mach-5 is problematical anyway...)

"Ex-Rockteman's" take was to avoid the use of turbojets at all and go with integral solid/liquid hybrid ramjet booster pods from zero-to-around-Mach-4 as per ASALM which are recovered down-range. I'll point out there's no reason you couldn't use hybrid solid/liquid ramjets in a 'stage' somewhat similar to the Dryden concept as well. (Again eliminating the turbofans entirely)

Of course the nice thing about the turbofan-stage is you get high-use/fast turn-around RTL-VTVL out of it where as down-range recovery requires getting the boosters back to the launch site for refurbishment/reuse. Edar/GW Johnson's pods didn't require much more than a couple of guys and a truck with a small crane, (assuming down-range land-landing which was predicted to be within a pretty small area, you can't of course recover turbofans in the ocean but you can the empty ramjets so it's similar in that respect) but the pods could be spread over the area and individual recovery would take some time. Recovering a large "stage" would of course require more infrastructure and personnel.

Of course Edar, GW Johnson, and I are fine with VTVL architecture but a lot of people over the years have made convincing arguments for both VTHL and HTHL concepts as well so YMMV as per usual :)

PDW engines haven't been seen in the 'white' aerospace world because they are not as efficient or as easy to control as they were thought to be. Again, that's at least as far as the public record has it :) They were supposed to have a higher operating range than a 'standard' turbojet because they relied less on intake air but they were also supposed to be efficient 'ejector' engines which turned out to not be so true which called into question their actual utility as proposed. Like SCramjets they appear to have a lot of promise they haven't lived up to yet. (And "Blackswift" has been proposed with every type of advanced engine from PDW's to dual-mode-SCramjets and isn't even a real project as of yet so I wouldn't hold my breath :) )

Randy
From The Amazing Catstronaut on the Black Arrow LV:
British physics, old chap. It's undignified to belch flames and effluvia all over the pad, what. A true gentlemen's orbital conveyance lifts itself into the air unostentatiously, with the minimum of spectacle and a modicum of grace. Not like our American cousins' launch vehicles, eh?

Offline john smith 19

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Actual the ORIGINAL, orginal idea I think was a concept that expanded on a multi-engine turbojet launch assist system based on an original concept by Dani Edar when he was working at Boeing:
http://yarchive.net/space/launchers/jet_first_stage.html
http://forum.nasaspaceflight.com/index.php?topic=25095.0
https://en.wikibooks.org/wiki/Space_Transport_and_Engineering_Methods/Human_Transport
True.
Quote from: RanulfC
Which used them in a VTVL configuration, again originally as booster pods and later as a "ring-wing" stage in and of itself to boost a TSTO configured vehicle to Mach-2 and 100,000ft. NASA-Dryden re-packaged (and patented)the concept in 2013 (https://www.nasa.gov/offices/ipp/centers/dfrc/technology/DRC-010-039-Ram-Booster.html) and added a ramjet second stage and a Centaur based third stage. My personal addition was the inclusion of Mass-Injection-Pre-Compressor-Cooling (MIPCC) to significantly increase the turbofan thrust though it also made it "possible" to raise the maximum Mach to around 4 I wasn't sure it would be worth the extra engineering for the LV though the Dryden concept uses the ramjet for Mach-2 through 4 acceleration so it seems like it would still work. As MIPCC LOX injection later in flight to stabilize the combustion chamber combustion and temperature it's baseline to operate to a bit above 100,000ft anyway so this cuts out the Dryden ramjet stage entirely. (Unless someone wants to use it to get from Mach-4 to higher speeds but again, air breathing past Mach-5 is problematical anyway...)
This architecture was suggested to avoid as many unnecessary development risks as possible, keeping everything within the known SoA AFAP. Although eliminating the ramjets would have eliminated the ramjet pod recovery as well.
Quote from: RanulfC
"Ex-Rockteman's" take was to avoid the use of turbojets at all and go with integral solid/liquid hybrid ramjet booster pods from zero-to-around-Mach-4 as per ASALM which are recovered down-range. I'll point out there's no reason you couldn't use hybrid solid/liquid ramjets in a 'stage' somewhat similar to the Dryden concept as well. (Again eliminating the turbofans entirely)
TBH That would pretty much answer the core of this thread.  :)

Build a bigger, better instrumented  ASALM with more fuel storage and just see how fast it can go before the structure failed. Then maybe used the data obtained to see if there were any (simple) changes you could make that would either push it higher still or lower its fuel consumption. 

Going the other way would also be interesting IE could you get to M5 with the booster only going to a bit over M1 to get past transonic drag and start getting decent compression.

BTW I notice that weapons that use ramjets seem to have standardized around solid/solid designs, although liquid sustainer fuel should give better performance. The last one I can recall was the BAe "Odin" ramjet on one of their seaborne missile systems.
Quote from: RanulfC
Of course the nice thing about the turbofan-stage is you get high-use/fast turn-around RTL-VTVL out of it where as down-range recovery requires getting the boosters back to the launch site for refurbishment/reuse. Edar/GW Johnson's pods didn't require much more than a couple of guys and a truck with a small crane, (assuming down-range land-landing which was predicted to be within a pretty small area, you can't of course recover turbofans in the ocean but you can the empty ramjets so it's similar in that respect) but the pods could be spread over the area and individual recovery would take some time. Recovering a large "stage" would of course require more infrastructure and personnel.

Of course Edar, GW Johnson, and I are fine with VTVL architecture but a lot of people over the years have made convincing arguments for both VTHL and HTHL concepts as well so YMMV as per usual :)
True. This is one where the next level down in lowering pod recovery costs is to eliminate the process and crew needed to do it.
Quote from: RanulfC
PDW engines haven't been seen in the 'white' aerospace world because they are not as efficient or as easy to control as they were thought to be. Again, that's at least as far as the public record has it :) They were supposed to have a higher operating range than a 'standard' turbojet because they relied less on intake air but they were also supposed to be efficient 'ejector' engines which turned out to not be so true which called into question their actual utility as proposed. Like SCramjets they appear to have a lot of promise they haven't lived up to yet. (And "Blackswift" has been proposed with every type of advanced engine from PDW's to dual-mode-SCramjets and isn't even a real project as of yet so I wouldn't hold my breath :) )
PDW still has some attractions if it can deliver that from a standing start, something no ramjet can. A PDE that could accelerate to M5 eliminates both the turbofan and the ramjet. If it could deliver better than say 10:1 T/W that would be worth it. 
"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.

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