Author Topic: Finding the actual speed limit of a conventional ramjet powered vehicle.  (Read 8700 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

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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 »
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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.

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