Author Topic: Finding the actual speed limit of a conventional ramjet powered vehicle.  (Read 7188 times)

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.
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.
"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

Quote
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.
Quote
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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