This is the
talk page for discussing improvements to the
Scramjet article. This is not a forum for general discussion of the article's subject. |
Article policies
|
Find sources: Google ( books · news · scholar · free images · WP refs) · FENS · JSTOR · TWL |
This article is rated C-class on Wikipedia's
content assessment scale. It is of interest to the following WikiProjects: | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
|
Why not give a more descriptive account on the subject. Please fix clarity of topic
For the layman, it would be nice to have a simple summary of the characteristics of a scramjet:
- speed range in mph - operating heights (air densities) - speculation on the sort of craft it might be applicable to.
I think some of these things might be in there, but not for a simple overview for those of us who are not wise in the world of physics.
Can someone please expand on the "obvious" problems with practical/commercial applications of scramjets? What kind of acceleration are we talking about, what would be the maximum practical speeds for passenger aircraft, etc? Speaking as an uninitiated guy, I can't say that I quite understand yet, and a quick two or three sentence expansion on those problems would fix the problem. Now especially relevant, with the hypersonic flight tests back in the news. User:MrZaius 22:54, 16 Nov 2004 (UTC)
Nice Job! Congrats to everybody who helped contribute to this article so far. It was badly needed. Mackerm 23:28, 9 Apr 2004 (UTC)
From the article:
No, a 100% effectivity boost gives 2x efficiency, so 700% gives 8x. Which of "700%" and "7x" is the original figure? Thue | talk 20:48, 15 Jul 2004 (UTC)
They're talking about ISP, I presume. The talk about oxygen is seriously misplaced, so I have edited this down; LOX is dirt cheap; the tankage is extraordinarily lightweight (1% the mass of the contents) and the overall impact of carrying the oxidiser is minor.
The real point of a SCRAMJET is that the higher ISP in the atmosphere reduces the propellent usage enough, and operates to high enough speed that it might enable SSTO.
The problems of SCRAMJETs include that the whole vehicle tends to melt; the engine, tends to melt; and the extra speed it gives is relatively small compared to orbital speed (about mach 25).
You also spend longer in the draggy atmosphere, so you spend more fuel to save LOX. But LOX is dirt cheap ($0.2/kg) compared to hydrogen ($5/kg) or kerosene (<$1/kg).
-- Wolfkeeper 22:33, 21 Aug 2004 (UTC)
High ISP means more mass to orbit for a given vehicle size.
As previously noted, the cost of fuel is much less than the cost of superstructure for a given vehicle. SSTO is a maybe, on one hand you have the cost advantages of reusing a vehicle, on the other hand a reusable vehicle is much more expensive, since leading-edge failures, use of ablatives or even just a hard landing all have to be ruled out, making the vehicle overengineered compared to a single use vehicle. The overall impact of carrying oxidiser is major,
because the same order of magnitude of oxidiser is needed as fuel, and every extra unit of mass costs exponentially if carried on a rocket.
Also Mach 25 is about 7000m/s and an altitude of up to 90km is a significant fraction of orbital speeds. All this means is that a scramjet alone won't do the whole lift to orbit, which we all knew anyway.
some may object to them. i am User:Xmnemonic, though i cant login to wikipedia for various reasons right now. 141.213.39.67 18:27, 17 Nov 2004 (UTC)
addendum
overall, this article is written terribly. it sounds like a dump of vague paragraphs composed of random aerospace trivia. sentences often don't connect, and entire sections are questionably present (this article is titled scramjet, not hypersonic). could people please try to focus on making the prose more intelligible? and with any additions (as opposed to revisions), attempt to reduce your words to the absolute fewest necessary. ✈ James C. 21:06, 2004 Nov 17 (UTC)
"A scramjet is reminiscent of a ramjet. In a ramjet operating supersonically, the supersonic inflow of the engine is decelerated to subsonic speeds and then reaccelerated to produce thrust. This deceleration, which is produced by a normal shock, creates a total enthalpy loss which limits the upper operating point of a ramjet engine. At high speeds, the kinetic energy of the freestream air entering the scramjet engine is large compared to the energy released by the reaction of the oxygen content of the air with a fuel (say hydrogen). Thus the heat released from combustion at Mach 25 may be around 10% of the total enthalpy of the working fluid. Depending on the fuel, the kinetic energy of the air and the potential combustion heat release will be equal at around Mach 8. Thus the design of a scramjet engine is as much about minimising drag as maximising thrust.
Changing from subsonic to supersonic combustion makes the control of the flow within the combustion chamber more difficult. Since the flow is supersonic, no upstream influence propagates within the freestream of the combustion chamber. Thus throttling of the entrance to the thrust nozzle is not a usable control technique. In effect, a block of gas entering the combustion chamber must mix with fuel and have sufficient time for initiation and reaction, all the while travelling supersonically through the combustion chamber, before the burned gas is expanded through the thrust nozzle. This places stringent requirements on the pressure and temperature of the flow, and requires that the fuel injection and mixing be extremely efficient."
These paragraphs are not clear to me. It's unclear when we are talking about conventional ramjets and when we are talking about scramjets.-- Gbleem 02:02, 19 Nov 2004 (UTC)
The page claims that the Concorde was the only "production supersonic airliner" to have been operated, yet the Concorde's own page states that it was "one of only two supersonic passenger airliners to have seen commercial service." The supersonic transport page states that the other is the Tupolev Tu-144, which only flew commercially from 1975 to 1978. Perhaps the Tu-144 should be noted? -- LostLeviathan 15:41, 19 Nov 2004 (UTC)
During the Hyper-X tests, there was much talk about the potential for scramjet technology to operate using "practically no fuel" once at hypersonic speed. I don't see any mention of this in the article, though, and I'm hardly an expert-- does anyone know anything about this? siafu 1 July 2005 20:00 (UTC)
Two of the links in the "references" section are now broken:
Can suggest the latter should be replaced with something appropriate near http://hapb-www.larc.nasa.gov/, but I don't have the subject expertise to select one. I have too little Wikipedia mileage or personal time to know the best action for flagging the first (seems deleting it might be missing an opportunity to replace it). Huge Bananas 11:18, 9 November 2005 (UTC)
An obvious question is what's the lowest workable Mach number for a scramjet. This impacts the type and amount of performance boost needed to reach scramjet operational speed. E.g, if it's Mach 2 that's reachable with a turbojet. If it's above Mach 3 that likely requires a ramjet or variable cycle engine. If it's Mach 5, that might require rockets. I looked around the net but don't see authoritative information on that. Maybe a more knowledgeable person can comment/add that info? Joema 19:53, 19 December 2005 (UTC)
The reason it's not there, is that the minimum Mach number is unclear. The minimum Mach number is limited by the fact that the compressed flow must be hot enough to burn the fuel, and of high enough pressure that the reaction is finished before the air moves out the back of the engine. (When a supersonic flow is compressed it slows down). It is clear that a pure scramjet can operate at Mach numbers of 6-8, but in the lower limit, it depends on what you're allowed to call a scramjet. Certainly there are designs where a ramjet transforms into a scramjet over the Mach 3-6 range. In this range however, the engine is still receiving significant thrust from subsonic combustion of "ramjet" type. On second thoughts, maybe I'll just add this explanation. AKAF 08:05, 20 December 2005 (UTC)
You can clearly accelerate to and fly at Mach 1.5 without afterburners, since the F/A-22 already does that. Some believe the YF-23A could fly at Mach 1.8 without afterburners, but it's classified so we don't know for sure. The Concorde definitely cruises at Mach 2 without afterburners, although it uses them to reach that.
Re being far away from a supersonic airliner, because of complex airline economic issues, it's likely the next civilian supersonic transport will be a business jet. BTW the Cessna Citation X has marginal supersonic ability right now, but they're prohibited from using that since the plane's FAA certification doesn't allow it. Joema 04:08, 21 December 2005 (UTC)
Appreciate the dialog on this. My recommendation would be to say something like "Similar to a ramjet, scramjets have a minimum functional speed. This speed is uncertain due to the largely classified nature scramjet research. However it's likely to be at least Mach 4 for a pure scramjet, with higher Mach numbers more likely. A hybrid ramjet/scramjet would have a lower minimum functional Mach number, and some sources indicate the NASA X-43A research vehicle is a hybrid design."
Stating this at least gives casual readers the concept, without being inaccurate. Because of the wide Wikipedia audience, it's possible by stating this you'll get expert feedback with more definitive sources.
The changes look great, thanks for doing that. Joema 16:28, 23 December 2005 (UTC)
Hi everyone. I am from Australia and not Yankee bashing...but....shouldn't metric equivalents of units in this article be provided (if even in brackets)? especially since the recent test was done in Australia which uses metric units? english units can be useful eg. when discussing height of people etc, but for scientific articles, i would think that SI units should be used.
Yes, so add it, anyone can edit. Please remember to keep significant figures approximately the same, so 11000 ft is probably best translated as 3300m or 3400m, depending if you think the original number was rounded or truncated (11000.0 ft =3352.8m). If you feel that you'd like to spend more time at wikipedia, you can create an account, which lets you keep track of things you like, and what you've done. Even if you don't create an account, please sign your posts by typing four tildes (~~~~), which will automatically link to your username. AKAF 08:45, 29 March 2006 (UTC)
I made a number of edits to Scramjet lately, trying to do a bit of a cleanup of the whole article. I would appreciate your input. One of the things I did was to split off a page about scramjet programs, since it seems like there might be enough programs for a general overview page. I'd appreciate it if that page could be looked at a bit.
I made an edit to the section on advantages and disadvantages of airbreathing engines, but that whole section still just doesn't seem right. I would like some discussion of the sort to be on the Scramjet page, but it's very confusing, because the arguments are handwavey, without numbers. This lack of numbers mean that it's hard for a layman to understand the arguments presented, and to weigh the advantages and disadvantages. It's even harder because, as for the minimum Mach number discussion, the severity/advantage of some of the options are also not well understood. For instance the fuel density problems and coking due to cracking for active cooling are not discussed, and could probably do with a page for themselves.
I have tried to bring in a realistic example, with some numbers, to try and illustrate the arguments, but the whole section still reads a bit scrappily.
My favourite options here (in order) would be:
1. Make a good quality page on this argument, along the lines of a short review of Heiser and Pratt's "Hypersonic Airbreating Propulsion", with some equations and estimates of the possible ranges of each of the advantages and disadvantages.
2. Reduce the section to a table of advantages and disadvantages plus a case study
3. Try to rewrite the section, somewhat longer, as prose, with a but more discussion of areas of research which apply to the field (materials, fuels, structured, MHD, SSTO, etc)
I make edits to the "recent progress" section to try to get away from nationalistic arguments. I can fully appreciate why these might be attractive, but they were leading to a scrappy article. Any suggestions would be appreciated.
AKAF 07:13, 24 April 2006 (UTC)
Do you have a cite for the Ariane 5 ECA figures improvement if a scramjet was used? Specifically it contains the phrase "immediately increasing the total payload by a factor of 16". WolfKeeper 07:33, 25 April 2006 (UTC)
It's not a cite, it's a calculation. I was trying to make the point that in the _ideal_case_ (which we don't have) that the mass which is now liquid O2, in the main stage, would all be payload. Ideally I'd like to make the following argument:
(Scramjet benefits)= (A+B+C) - (X+Y+Z) (+-) (I+J+K)
Where
A,B,C are the benefits (positive ISP, easier transfer to polar orbit, supersonic cruise etc)
X,Y,Z are the negatives (complexity, drag, new materials, etc)
I,J,K are the unknowns (system performance, system weight, environmental impact, SSTO, etc)
And give some discussion of each of these to illustrate the degree of uncertainty for each.
It's not original research. Having the equation (maximum new payload ignoring all negatives)=(old rocket weight)-(LOX weight), is the statement of barest fact based in physics. In fact what is currently completely missing from this section is any statement of fact. The section is currently unreferenced. There are vague arguments, but not even the vaguest estimates for their relative importance. AKAF 07:25, 26 April 2006 (UTC)
In the Arianne example, I'm making the comment that the boosters and top stage are irreplaceable, so an estimate for the value of the positive benefits is 16 times the payload. The last paragraph is then leaving space for a discussion of the estimated size of the negatives. The reason for this, is that essentially a lot of aerospace "experts" make arguments like in this section that the engines are "very" heavy, when the question as to whether scramjets will ever be practical is very much a question of the hard numbers of exactly _how_heavy_, or that the heating problems are fixable by one method or another without discussing the technical problems of such a system.
I think that any arguments (both positive and negative) need to be very clear as to how important they are. You may believe from my writing that I fall generally on the positive side, but I want a discussion of all sides. I _do_ have a serious problem with handwavey arguments, and arguments which are mathematically dubious. In the category of handwavey would be all sentences including the following: "seems to", "very", "may be" and a whole stack of other weasel words, which you'll notice I've also used :-). I think that these are illustrative of the imprecision of the current section.
An an example of a mathematically dubious argument, consider the paragraph on Lower thrust-weight ratio, which only talks about the engines. I think it is simply silly to talk about (rocket engine vs scramjet engine) when the point that you're trying to make in this section is (rocket vehicle vs scramjet vehicle). Thus, (in the idealised case) you would need to compare (total thrust)/(total weight), where a discussion of the range of values of each of those variables would be beneficial.
AKAF 09:26, 25 April 2006 (UTC)
I think it's fair to say rather than "all the figures" is "all the projections", since they are all talking about projections based on an array of assumptions. As an example, I've seen figures between 0.2g (Harry Spencer) to 0.5g (Robert Zubrin) to 10g (Fred Billig) for scramjet acceleration. Now, since only one of those three figures was experimentally measured by an expert in the field, I know which one I believe, but I think that the section deserves some discussion of the sort. Especially as to which set of numbers leads to which projection. I think that something like the discussion at Drake Equation would be appropriate. AKAF 07:25, 26 April 2006 (UTC)
I'll dig out some books. I've got copies of [ [5]], [ [6]], [ [7]] and [ [8]] and I guess a few dozen papers on the whole-systems design, and about the same on each of the subsystems. I guess if we start with Heiser and Pratt, they go through some reasonable discussion of parameters. If you already have a couple of these, then I can concentrate on the remaining. I'll look at it in the next couple of days. AKAF 07:25, 26 April 2006 (UTC)
would the person that wrote this section use proper scientific language instead of the ambiguous tripe that is currently in that section,
i am assuming you are refering to the use of a converging - diverging pasage. and anothere thing the working fluid dose not 'become even hotter and more compressed' due to combustion, it may get hotter and expand, unless of course you are talking about some sort of detination of the fuel then there may be some sort of pressure rise any way sorry to bitch, will try and carm down and start a more civilised edit ric
Does anyone else think it would be more logical to have the advantages separated some the disadvantages for clarity? For the most part it is fairly easy to tell which is an advantage or disadvantage, but there are a few places where this could be confusing for some readers. Johnwwatson 12:57, 5 August 2006 (UTC)
This section read "The shockwave of the vehicle itself compresses the expanding gasses..." I don't know much about scramjets, but I went ahead and changed that to "The shockwave of the vehicle itself compresses the inlet gasses..." I reasoned that earlier in the article, at "Simple description" is was discussed that the underside of the vehicle forms the intake and nozzle for the engine. I suspect that both of these versions are true, as the shape of the bottom of the X-43A would seem to indicate that. The engine is not placed on the back of the vehicle, but in the middle. It seems to use the front to compress the inlet gasses into the engine, and then the shockwave and the back may be used to direct the exhaust gasses. That should produce lift from deflection at both stages, and get pretty high efficiency by minimizing the size of the engine. I changed it because in the "History" portion it was noted that the pressure inside the engine must be fairly high in order to have combustion before the gasses leave the nozzle. This seems to indicate that a scramjet has a nozzle, but would probably need the front of the aircraft to produce the necessary compression, hence, it's the front half (the compressing of gases) that wouldn't be performed by the engine. However, it could probably be reasoned either way, so if you know a lot about scramjets, I'd appreciate it if you could expand upon that section. - NorsemanII 07:41, 2 October 2006 (UTC)
I've add the Unreferenced, which may be a bit unkind to some of the article, but not to some key sections. Erich ( talk) 11:02, 19 June 2008 (UTC)
I've reverted the edit to reaction times, because it missed the point. Although the full reaction takes microseconds, modeling the reaction requires that all partial reactions are also modeled. The chain branching reactions are particularly sensitive to small amounts of H and O, and these are self-catalysing reactions, meaning that a very small timestep is required for direct modeling. Exactly what timestep is required, will depend on the modeling scheme, but I think that 10e-19 is a good reference number for simple reactions. Consider for example the H+H+M and O+O+M reactions (NASP 10+12), which are exponential for small quantities of mixed fuel. In this case a good fit or small timestep is required for direct modeling, making the chemical reactions "stiff". AKAF ( talk) 08:36, 26 June 2008 (UTC)
When scramjets burn the air-fuel mixture at supersonic speeds, is it still a deflagration process or is it now a detonation process? -- Pavithran( talk) 06:32, 06 January 2009 (UTC) —Preceding unsigned comment added by 202.169.31.178 ( talk)
Deflagration. GreyTrafalgar ( talk) 22:00, 30 June 2010 (UTC)
I've reverted the minimum Mach number comment for several reasons. Firstly, there have been several successful experiments of both net thrust producing scramjets and supersonic combustion at Mach 6 (for fully aerodynamic engines). See the NASA/CIAM tests (eg AIAA 2002-4128) and the tests using Borane-based fuels by Billig et al (AIAA 93-2329). So Mach 7 is obviously too high for an absolute minimum, and since there are no production engines of this type, its also probably unfounded to say Mach 7 is some kind of functional minimum. The minimum Mach number is very much a function of the fuel and engine design. It may be that Dr Paull's caveats for the Mach 7 number were not fully explained. As far as I know he's only looking at "green" engine designs (= Hydrocarbon or hydrogen). I think this is a far too complex problem to be fully referenced by a single popular science show. AKAF ( talk) 08:07, 16 March 2009 (UTC)
Under this section and subcategory "Propellant" one could read the following.
"An advantage of a hypersonic airbreathing (typically scramjet) vehicle like the X-30 is avoiding or at least reducing the need for carrying oxidizer. For example the space shuttle external tank holds 616,432 kg of liquid oxygen (LOX) and 103,000 kg of liquid hydrogen (LH2). The shuttle orbiter itself weighs about 104,000 kg (max landing weight). Therefore 75% of the entire assembly weight is liquid oxygen."
It is very wrong to say that the oxygen makes up 75% of the space shuttle since nothing is said about the normal takeoff weight of the orbiter (only maximum landing), nothing is said about the weight of the Solid Rocket Boosters that are needed to get the assembly of the launch pad and not even the weight of the external tank that holds the liquid oxygen and liquid hydrogen is taken into consideration.
Of the true "entire assembly" at takeoff the liquid oxygen is much less than 75% of the weight. The external tank weight is either 26,500 kg, 30,000 kg or 35,000 kg depending on tank version used. Each of the two Solid Rocket Boosters weight is 590,000 kg and the orbiter weight with payload is at maximum 109,000 kg with a maximum payload of about 25,000 kg depending on the specific orbiter used.
In other words the oxygen weight is only 30% of the entire space shuttle stack at liftoff.
JasonCW - 15:49, 14 November 2009 (CET) —Preceding
unsigned comment added by
JasonCW (
talk •
contribs)
Someone try to work this in. Scramjets can't achieve orbit alone because the final orbital insertion maneuver must occur beyond the atmosphere. Suborbital flight is obtainable and theoretically interplanetary flight but not orbital insertion. Any closed orbit (elliptical or circular) will always return the vehicle to the altitude of the last maneuver. If the final maneuver was in the atmosphere then you will reenter the atmosphere. Unless you reach escape velocity you won't be able to stay in space. Circuitboardsushi ( talk) 08:57, 29 June 2019 (UTC)
Beginning to reorganize, clarify, cite, update, etc.... entire article. If it seems that I'm removing relevant info or links, it's likely they're just temporarily removed as I go from section to section.
Please leave comments, suggestions, criticisms, etc.
The tags have been on the page for over a year in some cases, without the taggers actually bothering to explain on the talk page what they consider the problem. I think that there is some basic minimum assumption that all pages can/should be edited, so the tags are not useful as a general warning. Moreover, the page ratings of >4.0 show that those rating do not feel that the tags are justified. AKAF ( talk) 16:34, 20 September 2011 (UTC)
I removed the phrase from the intro which said the top speed "is near orbital velocity". There are multiple things wrong with this:
There's also the issue that a scramjet must have a maximum altitude limit, because it's air-breathing. And a stable orbit is inversely limited: it won't do any good to reach "orbit" at too low an altitude, because air drag will quickly kill it.
Bottom line is, there are so many variables involved, that any meaningful statement comparing the scramjet's top capability to orbit would involve original research, unless some reliable source makes it. JustinTime55 ( talk) 16:34, 16 January 2012 (UTC)
In the article is assumed thrust-to-weight ration about ~2.0 I don't believe that it is really so low. If I compare with current turbojet engines ( 4.0-7.0 ) and ramjets according to this page ( http://airindustriesresearch.com/siram/ramstats.htm ) could have thrust-to-weight ratio about 30.0 While ramjet/scramjet are both in principle just a specially shaped shock-wave-forming tube with no moving parts the thrust-to-weight of scramjet should be for sure higher than in turbojet and similar to ramjet at its peak of optimal working conditions. While there is no citation of "thrust-to-weight ration about ~2.0" reference, I suspect that this number is misinterpreted - for example it could be thrust-to-weight ratio of the whole airplane ( not just the engine ), or thrust-to-weight ratio at not optimal conditions ( too high or too low velocity ).
As can be seen from the page ( http://airindustriesresearch.com/siram/ramstats.htm ) the thrust-to-weight ratio of this type of engines very much depend on velocity. It could be as low as 7.0 at 0.5 Mach and as high as 30.0 at 3.0 Mach — Preceding unsigned comment added by ProkopHapala ( talk • contribs) 15:03, 8 May 2013 (UTC)
Hello fellow Wikipedians,
I have just modified one external link on Scramjet. Please take a moment to review my edit. If you have any questions, or need the bot to ignore the links, or the page altogether, please visit this simple FaQ for additional information. I made the following changes:
When you have finished reviewing my changes, please set the checked parameter below to true or failed to let others know (documentation at {{
Sourcecheck}}
).
This message was posted before February 2018.
After February 2018, "External links modified" talk page sections are no longer generated or monitored by InternetArchiveBot. No special action is required regarding these talk page notices, other than
regular verification using the archive tool instructions below. Editors
have permission to delete these "External links modified" talk page sections if they want to de-clutter talk pages, but see the
RfC before doing mass systematic removals. This message is updated dynamically through the template {{
source check}}
(last update: 18 January 2022).
Cheers.— cyberbot II Talk to my owner:Online 01:39, 1 April 2016 (UTC)
Under "basic principles", the article states that scremjets slow the incoming air down, before speeding it back up through combustion heat transfer and a diverging nozzle.
Scramjets do slow the air down before the inlet, but Mach numbers converge towards unity, ie M=1, whenever heat is added. See Rayleigh flow. This is important, as that's what the diverging nozzle at the end is for, to speed the flow back up relative to the new speed of sound.
In other words, the flow does indeed accelerate through the combustor and the nozzle, but the Mach number does not continue to increase. The temperature will increase, so the speed of sound will increase, but Mach number also relies on total velocity.
The textbook Mechanics and Thermodynamics of Propulsion by Hill & Peterson (1992) has a lot of detail explaining these mechanisms, but I suggest that explanation be edited to be accurate. 128.227.158.246 ( talk) 00:51, 29 April 2020 (UTC)
Why there is no mentions Russia in this article? Russia has plethora of different missiles, in operation today. Calimero ( talk) 07:35, 10 July 2022 (UTC)
Chemists and physicists predominate but the biological effects of technology makes frequent news. Reusable can of course be multiple or single STO. Electric flight including the atmosphere breathing variety has no mention but examples of both are in service and operate in regimes where rockets are wasteful. Increase in the use equals small scram, small rocket. Operators in a listicle needs linked. Nesshunter ( talk) 21:23, 10 December 2023 (UTC)
This is the
talk page for discussing improvements to the
Scramjet article. This is not a forum for general discussion of the article's subject. |
Article policies
|
Find sources: Google ( books · news · scholar · free images · WP refs) · FENS · JSTOR · TWL |
This article is rated C-class on Wikipedia's
content assessment scale. It is of interest to the following WikiProjects: | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
|
Why not give a more descriptive account on the subject. Please fix clarity of topic
For the layman, it would be nice to have a simple summary of the characteristics of a scramjet:
- speed range in mph - operating heights (air densities) - speculation on the sort of craft it might be applicable to.
I think some of these things might be in there, but not for a simple overview for those of us who are not wise in the world of physics.
Can someone please expand on the "obvious" problems with practical/commercial applications of scramjets? What kind of acceleration are we talking about, what would be the maximum practical speeds for passenger aircraft, etc? Speaking as an uninitiated guy, I can't say that I quite understand yet, and a quick two or three sentence expansion on those problems would fix the problem. Now especially relevant, with the hypersonic flight tests back in the news. User:MrZaius 22:54, 16 Nov 2004 (UTC)
Nice Job! Congrats to everybody who helped contribute to this article so far. It was badly needed. Mackerm 23:28, 9 Apr 2004 (UTC)
From the article:
No, a 100% effectivity boost gives 2x efficiency, so 700% gives 8x. Which of "700%" and "7x" is the original figure? Thue | talk 20:48, 15 Jul 2004 (UTC)
They're talking about ISP, I presume. The talk about oxygen is seriously misplaced, so I have edited this down; LOX is dirt cheap; the tankage is extraordinarily lightweight (1% the mass of the contents) and the overall impact of carrying the oxidiser is minor.
The real point of a SCRAMJET is that the higher ISP in the atmosphere reduces the propellent usage enough, and operates to high enough speed that it might enable SSTO.
The problems of SCRAMJETs include that the whole vehicle tends to melt; the engine, tends to melt; and the extra speed it gives is relatively small compared to orbital speed (about mach 25).
You also spend longer in the draggy atmosphere, so you spend more fuel to save LOX. But LOX is dirt cheap ($0.2/kg) compared to hydrogen ($5/kg) or kerosene (<$1/kg).
-- Wolfkeeper 22:33, 21 Aug 2004 (UTC)
High ISP means more mass to orbit for a given vehicle size.
As previously noted, the cost of fuel is much less than the cost of superstructure for a given vehicle. SSTO is a maybe, on one hand you have the cost advantages of reusing a vehicle, on the other hand a reusable vehicle is much more expensive, since leading-edge failures, use of ablatives or even just a hard landing all have to be ruled out, making the vehicle overengineered compared to a single use vehicle. The overall impact of carrying oxidiser is major,
because the same order of magnitude of oxidiser is needed as fuel, and every extra unit of mass costs exponentially if carried on a rocket.
Also Mach 25 is about 7000m/s and an altitude of up to 90km is a significant fraction of orbital speeds. All this means is that a scramjet alone won't do the whole lift to orbit, which we all knew anyway.
some may object to them. i am User:Xmnemonic, though i cant login to wikipedia for various reasons right now. 141.213.39.67 18:27, 17 Nov 2004 (UTC)
addendum
overall, this article is written terribly. it sounds like a dump of vague paragraphs composed of random aerospace trivia. sentences often don't connect, and entire sections are questionably present (this article is titled scramjet, not hypersonic). could people please try to focus on making the prose more intelligible? and with any additions (as opposed to revisions), attempt to reduce your words to the absolute fewest necessary. ✈ James C. 21:06, 2004 Nov 17 (UTC)
"A scramjet is reminiscent of a ramjet. In a ramjet operating supersonically, the supersonic inflow of the engine is decelerated to subsonic speeds and then reaccelerated to produce thrust. This deceleration, which is produced by a normal shock, creates a total enthalpy loss which limits the upper operating point of a ramjet engine. At high speeds, the kinetic energy of the freestream air entering the scramjet engine is large compared to the energy released by the reaction of the oxygen content of the air with a fuel (say hydrogen). Thus the heat released from combustion at Mach 25 may be around 10% of the total enthalpy of the working fluid. Depending on the fuel, the kinetic energy of the air and the potential combustion heat release will be equal at around Mach 8. Thus the design of a scramjet engine is as much about minimising drag as maximising thrust.
Changing from subsonic to supersonic combustion makes the control of the flow within the combustion chamber more difficult. Since the flow is supersonic, no upstream influence propagates within the freestream of the combustion chamber. Thus throttling of the entrance to the thrust nozzle is not a usable control technique. In effect, a block of gas entering the combustion chamber must mix with fuel and have sufficient time for initiation and reaction, all the while travelling supersonically through the combustion chamber, before the burned gas is expanded through the thrust nozzle. This places stringent requirements on the pressure and temperature of the flow, and requires that the fuel injection and mixing be extremely efficient."
These paragraphs are not clear to me. It's unclear when we are talking about conventional ramjets and when we are talking about scramjets.-- Gbleem 02:02, 19 Nov 2004 (UTC)
The page claims that the Concorde was the only "production supersonic airliner" to have been operated, yet the Concorde's own page states that it was "one of only two supersonic passenger airliners to have seen commercial service." The supersonic transport page states that the other is the Tupolev Tu-144, which only flew commercially from 1975 to 1978. Perhaps the Tu-144 should be noted? -- LostLeviathan 15:41, 19 Nov 2004 (UTC)
During the Hyper-X tests, there was much talk about the potential for scramjet technology to operate using "practically no fuel" once at hypersonic speed. I don't see any mention of this in the article, though, and I'm hardly an expert-- does anyone know anything about this? siafu 1 July 2005 20:00 (UTC)
Two of the links in the "references" section are now broken:
Can suggest the latter should be replaced with something appropriate near http://hapb-www.larc.nasa.gov/, but I don't have the subject expertise to select one. I have too little Wikipedia mileage or personal time to know the best action for flagging the first (seems deleting it might be missing an opportunity to replace it). Huge Bananas 11:18, 9 November 2005 (UTC)
An obvious question is what's the lowest workable Mach number for a scramjet. This impacts the type and amount of performance boost needed to reach scramjet operational speed. E.g, if it's Mach 2 that's reachable with a turbojet. If it's above Mach 3 that likely requires a ramjet or variable cycle engine. If it's Mach 5, that might require rockets. I looked around the net but don't see authoritative information on that. Maybe a more knowledgeable person can comment/add that info? Joema 19:53, 19 December 2005 (UTC)
The reason it's not there, is that the minimum Mach number is unclear. The minimum Mach number is limited by the fact that the compressed flow must be hot enough to burn the fuel, and of high enough pressure that the reaction is finished before the air moves out the back of the engine. (When a supersonic flow is compressed it slows down). It is clear that a pure scramjet can operate at Mach numbers of 6-8, but in the lower limit, it depends on what you're allowed to call a scramjet. Certainly there are designs where a ramjet transforms into a scramjet over the Mach 3-6 range. In this range however, the engine is still receiving significant thrust from subsonic combustion of "ramjet" type. On second thoughts, maybe I'll just add this explanation. AKAF 08:05, 20 December 2005 (UTC)
You can clearly accelerate to and fly at Mach 1.5 without afterburners, since the F/A-22 already does that. Some believe the YF-23A could fly at Mach 1.8 without afterburners, but it's classified so we don't know for sure. The Concorde definitely cruises at Mach 2 without afterburners, although it uses them to reach that.
Re being far away from a supersonic airliner, because of complex airline economic issues, it's likely the next civilian supersonic transport will be a business jet. BTW the Cessna Citation X has marginal supersonic ability right now, but they're prohibited from using that since the plane's FAA certification doesn't allow it. Joema 04:08, 21 December 2005 (UTC)
Appreciate the dialog on this. My recommendation would be to say something like "Similar to a ramjet, scramjets have a minimum functional speed. This speed is uncertain due to the largely classified nature scramjet research. However it's likely to be at least Mach 4 for a pure scramjet, with higher Mach numbers more likely. A hybrid ramjet/scramjet would have a lower minimum functional Mach number, and some sources indicate the NASA X-43A research vehicle is a hybrid design."
Stating this at least gives casual readers the concept, without being inaccurate. Because of the wide Wikipedia audience, it's possible by stating this you'll get expert feedback with more definitive sources.
The changes look great, thanks for doing that. Joema 16:28, 23 December 2005 (UTC)
Hi everyone. I am from Australia and not Yankee bashing...but....shouldn't metric equivalents of units in this article be provided (if even in brackets)? especially since the recent test was done in Australia which uses metric units? english units can be useful eg. when discussing height of people etc, but for scientific articles, i would think that SI units should be used.
Yes, so add it, anyone can edit. Please remember to keep significant figures approximately the same, so 11000 ft is probably best translated as 3300m or 3400m, depending if you think the original number was rounded or truncated (11000.0 ft =3352.8m). If you feel that you'd like to spend more time at wikipedia, you can create an account, which lets you keep track of things you like, and what you've done. Even if you don't create an account, please sign your posts by typing four tildes (~~~~), which will automatically link to your username. AKAF 08:45, 29 March 2006 (UTC)
I made a number of edits to Scramjet lately, trying to do a bit of a cleanup of the whole article. I would appreciate your input. One of the things I did was to split off a page about scramjet programs, since it seems like there might be enough programs for a general overview page. I'd appreciate it if that page could be looked at a bit.
I made an edit to the section on advantages and disadvantages of airbreathing engines, but that whole section still just doesn't seem right. I would like some discussion of the sort to be on the Scramjet page, but it's very confusing, because the arguments are handwavey, without numbers. This lack of numbers mean that it's hard for a layman to understand the arguments presented, and to weigh the advantages and disadvantages. It's even harder because, as for the minimum Mach number discussion, the severity/advantage of some of the options are also not well understood. For instance the fuel density problems and coking due to cracking for active cooling are not discussed, and could probably do with a page for themselves.
I have tried to bring in a realistic example, with some numbers, to try and illustrate the arguments, but the whole section still reads a bit scrappily.
My favourite options here (in order) would be:
1. Make a good quality page on this argument, along the lines of a short review of Heiser and Pratt's "Hypersonic Airbreating Propulsion", with some equations and estimates of the possible ranges of each of the advantages and disadvantages.
2. Reduce the section to a table of advantages and disadvantages plus a case study
3. Try to rewrite the section, somewhat longer, as prose, with a but more discussion of areas of research which apply to the field (materials, fuels, structured, MHD, SSTO, etc)
I make edits to the "recent progress" section to try to get away from nationalistic arguments. I can fully appreciate why these might be attractive, but they were leading to a scrappy article. Any suggestions would be appreciated.
AKAF 07:13, 24 April 2006 (UTC)
Do you have a cite for the Ariane 5 ECA figures improvement if a scramjet was used? Specifically it contains the phrase "immediately increasing the total payload by a factor of 16". WolfKeeper 07:33, 25 April 2006 (UTC)
It's not a cite, it's a calculation. I was trying to make the point that in the _ideal_case_ (which we don't have) that the mass which is now liquid O2, in the main stage, would all be payload. Ideally I'd like to make the following argument:
(Scramjet benefits)= (A+B+C) - (X+Y+Z) (+-) (I+J+K)
Where
A,B,C are the benefits (positive ISP, easier transfer to polar orbit, supersonic cruise etc)
X,Y,Z are the negatives (complexity, drag, new materials, etc)
I,J,K are the unknowns (system performance, system weight, environmental impact, SSTO, etc)
And give some discussion of each of these to illustrate the degree of uncertainty for each.
It's not original research. Having the equation (maximum new payload ignoring all negatives)=(old rocket weight)-(LOX weight), is the statement of barest fact based in physics. In fact what is currently completely missing from this section is any statement of fact. The section is currently unreferenced. There are vague arguments, but not even the vaguest estimates for their relative importance. AKAF 07:25, 26 April 2006 (UTC)
In the Arianne example, I'm making the comment that the boosters and top stage are irreplaceable, so an estimate for the value of the positive benefits is 16 times the payload. The last paragraph is then leaving space for a discussion of the estimated size of the negatives. The reason for this, is that essentially a lot of aerospace "experts" make arguments like in this section that the engines are "very" heavy, when the question as to whether scramjets will ever be practical is very much a question of the hard numbers of exactly _how_heavy_, or that the heating problems are fixable by one method or another without discussing the technical problems of such a system.
I think that any arguments (both positive and negative) need to be very clear as to how important they are. You may believe from my writing that I fall generally on the positive side, but I want a discussion of all sides. I _do_ have a serious problem with handwavey arguments, and arguments which are mathematically dubious. In the category of handwavey would be all sentences including the following: "seems to", "very", "may be" and a whole stack of other weasel words, which you'll notice I've also used :-). I think that these are illustrative of the imprecision of the current section.
An an example of a mathematically dubious argument, consider the paragraph on Lower thrust-weight ratio, which only talks about the engines. I think it is simply silly to talk about (rocket engine vs scramjet engine) when the point that you're trying to make in this section is (rocket vehicle vs scramjet vehicle). Thus, (in the idealised case) you would need to compare (total thrust)/(total weight), where a discussion of the range of values of each of those variables would be beneficial.
AKAF 09:26, 25 April 2006 (UTC)
I think it's fair to say rather than "all the figures" is "all the projections", since they are all talking about projections based on an array of assumptions. As an example, I've seen figures between 0.2g (Harry Spencer) to 0.5g (Robert Zubrin) to 10g (Fred Billig) for scramjet acceleration. Now, since only one of those three figures was experimentally measured by an expert in the field, I know which one I believe, but I think that the section deserves some discussion of the sort. Especially as to which set of numbers leads to which projection. I think that something like the discussion at Drake Equation would be appropriate. AKAF 07:25, 26 April 2006 (UTC)
I'll dig out some books. I've got copies of [ [5]], [ [6]], [ [7]] and [ [8]] and I guess a few dozen papers on the whole-systems design, and about the same on each of the subsystems. I guess if we start with Heiser and Pratt, they go through some reasonable discussion of parameters. If you already have a couple of these, then I can concentrate on the remaining. I'll look at it in the next couple of days. AKAF 07:25, 26 April 2006 (UTC)
would the person that wrote this section use proper scientific language instead of the ambiguous tripe that is currently in that section,
i am assuming you are refering to the use of a converging - diverging pasage. and anothere thing the working fluid dose not 'become even hotter and more compressed' due to combustion, it may get hotter and expand, unless of course you are talking about some sort of detination of the fuel then there may be some sort of pressure rise any way sorry to bitch, will try and carm down and start a more civilised edit ric
Does anyone else think it would be more logical to have the advantages separated some the disadvantages for clarity? For the most part it is fairly easy to tell which is an advantage or disadvantage, but there are a few places where this could be confusing for some readers. Johnwwatson 12:57, 5 August 2006 (UTC)
This section read "The shockwave of the vehicle itself compresses the expanding gasses..." I don't know much about scramjets, but I went ahead and changed that to "The shockwave of the vehicle itself compresses the inlet gasses..." I reasoned that earlier in the article, at "Simple description" is was discussed that the underside of the vehicle forms the intake and nozzle for the engine. I suspect that both of these versions are true, as the shape of the bottom of the X-43A would seem to indicate that. The engine is not placed on the back of the vehicle, but in the middle. It seems to use the front to compress the inlet gasses into the engine, and then the shockwave and the back may be used to direct the exhaust gasses. That should produce lift from deflection at both stages, and get pretty high efficiency by minimizing the size of the engine. I changed it because in the "History" portion it was noted that the pressure inside the engine must be fairly high in order to have combustion before the gasses leave the nozzle. This seems to indicate that a scramjet has a nozzle, but would probably need the front of the aircraft to produce the necessary compression, hence, it's the front half (the compressing of gases) that wouldn't be performed by the engine. However, it could probably be reasoned either way, so if you know a lot about scramjets, I'd appreciate it if you could expand upon that section. - NorsemanII 07:41, 2 October 2006 (UTC)
I've add the Unreferenced, which may be a bit unkind to some of the article, but not to some key sections. Erich ( talk) 11:02, 19 June 2008 (UTC)
I've reverted the edit to reaction times, because it missed the point. Although the full reaction takes microseconds, modeling the reaction requires that all partial reactions are also modeled. The chain branching reactions are particularly sensitive to small amounts of H and O, and these are self-catalysing reactions, meaning that a very small timestep is required for direct modeling. Exactly what timestep is required, will depend on the modeling scheme, but I think that 10e-19 is a good reference number for simple reactions. Consider for example the H+H+M and O+O+M reactions (NASP 10+12), which are exponential for small quantities of mixed fuel. In this case a good fit or small timestep is required for direct modeling, making the chemical reactions "stiff". AKAF ( talk) 08:36, 26 June 2008 (UTC)
When scramjets burn the air-fuel mixture at supersonic speeds, is it still a deflagration process or is it now a detonation process? -- Pavithran( talk) 06:32, 06 January 2009 (UTC) —Preceding unsigned comment added by 202.169.31.178 ( talk)
Deflagration. GreyTrafalgar ( talk) 22:00, 30 June 2010 (UTC)
I've reverted the minimum Mach number comment for several reasons. Firstly, there have been several successful experiments of both net thrust producing scramjets and supersonic combustion at Mach 6 (for fully aerodynamic engines). See the NASA/CIAM tests (eg AIAA 2002-4128) and the tests using Borane-based fuels by Billig et al (AIAA 93-2329). So Mach 7 is obviously too high for an absolute minimum, and since there are no production engines of this type, its also probably unfounded to say Mach 7 is some kind of functional minimum. The minimum Mach number is very much a function of the fuel and engine design. It may be that Dr Paull's caveats for the Mach 7 number were not fully explained. As far as I know he's only looking at "green" engine designs (= Hydrocarbon or hydrogen). I think this is a far too complex problem to be fully referenced by a single popular science show. AKAF ( talk) 08:07, 16 March 2009 (UTC)
Under this section and subcategory "Propellant" one could read the following.
"An advantage of a hypersonic airbreathing (typically scramjet) vehicle like the X-30 is avoiding or at least reducing the need for carrying oxidizer. For example the space shuttle external tank holds 616,432 kg of liquid oxygen (LOX) and 103,000 kg of liquid hydrogen (LH2). The shuttle orbiter itself weighs about 104,000 kg (max landing weight). Therefore 75% of the entire assembly weight is liquid oxygen."
It is very wrong to say that the oxygen makes up 75% of the space shuttle since nothing is said about the normal takeoff weight of the orbiter (only maximum landing), nothing is said about the weight of the Solid Rocket Boosters that are needed to get the assembly of the launch pad and not even the weight of the external tank that holds the liquid oxygen and liquid hydrogen is taken into consideration.
Of the true "entire assembly" at takeoff the liquid oxygen is much less than 75% of the weight. The external tank weight is either 26,500 kg, 30,000 kg or 35,000 kg depending on tank version used. Each of the two Solid Rocket Boosters weight is 590,000 kg and the orbiter weight with payload is at maximum 109,000 kg with a maximum payload of about 25,000 kg depending on the specific orbiter used.
In other words the oxygen weight is only 30% of the entire space shuttle stack at liftoff.
JasonCW - 15:49, 14 November 2009 (CET) —Preceding
unsigned comment added by
JasonCW (
talk •
contribs)
Someone try to work this in. Scramjets can't achieve orbit alone because the final orbital insertion maneuver must occur beyond the atmosphere. Suborbital flight is obtainable and theoretically interplanetary flight but not orbital insertion. Any closed orbit (elliptical or circular) will always return the vehicle to the altitude of the last maneuver. If the final maneuver was in the atmosphere then you will reenter the atmosphere. Unless you reach escape velocity you won't be able to stay in space. Circuitboardsushi ( talk) 08:57, 29 June 2019 (UTC)
Beginning to reorganize, clarify, cite, update, etc.... entire article. If it seems that I'm removing relevant info or links, it's likely they're just temporarily removed as I go from section to section.
Please leave comments, suggestions, criticisms, etc.
The tags have been on the page for over a year in some cases, without the taggers actually bothering to explain on the talk page what they consider the problem. I think that there is some basic minimum assumption that all pages can/should be edited, so the tags are not useful as a general warning. Moreover, the page ratings of >4.0 show that those rating do not feel that the tags are justified. AKAF ( talk) 16:34, 20 September 2011 (UTC)
I removed the phrase from the intro which said the top speed "is near orbital velocity". There are multiple things wrong with this:
There's also the issue that a scramjet must have a maximum altitude limit, because it's air-breathing. And a stable orbit is inversely limited: it won't do any good to reach "orbit" at too low an altitude, because air drag will quickly kill it.
Bottom line is, there are so many variables involved, that any meaningful statement comparing the scramjet's top capability to orbit would involve original research, unless some reliable source makes it. JustinTime55 ( talk) 16:34, 16 January 2012 (UTC)
In the article is assumed thrust-to-weight ration about ~2.0 I don't believe that it is really so low. If I compare with current turbojet engines ( 4.0-7.0 ) and ramjets according to this page ( http://airindustriesresearch.com/siram/ramstats.htm ) could have thrust-to-weight ratio about 30.0 While ramjet/scramjet are both in principle just a specially shaped shock-wave-forming tube with no moving parts the thrust-to-weight of scramjet should be for sure higher than in turbojet and similar to ramjet at its peak of optimal working conditions. While there is no citation of "thrust-to-weight ration about ~2.0" reference, I suspect that this number is misinterpreted - for example it could be thrust-to-weight ratio of the whole airplane ( not just the engine ), or thrust-to-weight ratio at not optimal conditions ( too high or too low velocity ).
As can be seen from the page ( http://airindustriesresearch.com/siram/ramstats.htm ) the thrust-to-weight ratio of this type of engines very much depend on velocity. It could be as low as 7.0 at 0.5 Mach and as high as 30.0 at 3.0 Mach — Preceding unsigned comment added by ProkopHapala ( talk • contribs) 15:03, 8 May 2013 (UTC)
Hello fellow Wikipedians,
I have just modified one external link on Scramjet. Please take a moment to review my edit. If you have any questions, or need the bot to ignore the links, or the page altogether, please visit this simple FaQ for additional information. I made the following changes:
When you have finished reviewing my changes, please set the checked parameter below to true or failed to let others know (documentation at {{
Sourcecheck}}
).
This message was posted before February 2018.
After February 2018, "External links modified" talk page sections are no longer generated or monitored by InternetArchiveBot. No special action is required regarding these talk page notices, other than
regular verification using the archive tool instructions below. Editors
have permission to delete these "External links modified" talk page sections if they want to de-clutter talk pages, but see the
RfC before doing mass systematic removals. This message is updated dynamically through the template {{
source check}}
(last update: 18 January 2022).
Cheers.— cyberbot II Talk to my owner:Online 01:39, 1 April 2016 (UTC)
Under "basic principles", the article states that scremjets slow the incoming air down, before speeding it back up through combustion heat transfer and a diverging nozzle.
Scramjets do slow the air down before the inlet, but Mach numbers converge towards unity, ie M=1, whenever heat is added. See Rayleigh flow. This is important, as that's what the diverging nozzle at the end is for, to speed the flow back up relative to the new speed of sound.
In other words, the flow does indeed accelerate through the combustor and the nozzle, but the Mach number does not continue to increase. The temperature will increase, so the speed of sound will increase, but Mach number also relies on total velocity.
The textbook Mechanics and Thermodynamics of Propulsion by Hill & Peterson (1992) has a lot of detail explaining these mechanisms, but I suggest that explanation be edited to be accurate. 128.227.158.246 ( talk) 00:51, 29 April 2020 (UTC)
Why there is no mentions Russia in this article? Russia has plethora of different missiles, in operation today. Calimero ( talk) 07:35, 10 July 2022 (UTC)
Chemists and physicists predominate but the biological effects of technology makes frequent news. Reusable can of course be multiple or single STO. Electric flight including the atmosphere breathing variety has no mention but examples of both are in service and operate in regimes where rockets are wasteful. Increase in the use equals small scram, small rocket. Operators in a listicle needs linked. Nesshunter ( talk) 21:23, 10 December 2023 (UTC)