Talk:Scramjet

message: :: I note to Gbleem that i reversed a small part of your introduction edit about the upper limit of scramjet operation. This is because a scramjet without oxidiser input is like a jet engine without an afterburner. So you need to clarify, when you're talking about the upper limit, under which circumstances you're talking about. After all, for a long time there were no jet engines which could go supersonic without an afterburner (see some of the discussion in the previous section), but people had no problem about talking about supersonic jet engines. The last paragraph in the theory section is intended to capture some of the flavour of this line of thinking.
::: I was assuming a turbojet with an afterburner is still a jet because the oxidizer is air. A scramjet with oxidizer injection should be a scramjet-rocket hybrid. --Gbleem 15:00, 19 Nov 2004 (UTC)
thread_title: introduction

message: Two of the links in the "references" section are now broken:
* HyShot -University Of Queensland (leads to a generic domain registrar holding page); and
* NASA website for National Hypersonics Plan (404 Not Found)
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)
thread_title:  Broken links 

message: 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)
thread_title:  Metric 

message: 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)
thread_title: Separation of advantages and disadvantages

message: 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)
thread_title:  Half an engine 

message: 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)
thread_title: Unreferenced

message: 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)
replies: text: The edit did not miss the point. There are some chemical reactions that are faster, but *typically* the times will be microseconds. I took away again the sentence which claimed the typical times are of the order of E-19 seconds. This is not only misleading, it is erroneous. Cypoet (talk) 02:37, 27 June 2008 (UTC)

text: I see your point thus -- A few sentences explaining this could be added if you so wish, but I don't think this belongs in this article. This is specific to chemical modeling and CFD, not scramjets.  —Preceding unsigned comment added by Cypoet (talk • contribs) 02:40, 27 June 2008 (UTC)
thread_title: Reaction times

message: 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)
thread_title: Supersonic combustion - Is it still deflagration?

message: 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)
replies: text: You might be right, but it's unreferenced, and the Mach 7-8 is referenced. Verifiability over truth right?- (User) Wolfkeeper (Talk) 15:11, 16 March 2009 (UTC)
replies: text: Did you miss the two references which I just gave right there in the text? In my opinion a reference in the scientific literature beats one in a popular science forum any day. AKAF (talk) 15:50, 16 March 2009 (UTC)
replies: text: Because they're in different circumstances, not really, and note the guy making the statement is a real expert that has actually flown stuff. You should probably add yours as well to the article. Referencing improves, the crowd roars.- (User) Wolfkeeper (Talk) 16:27, 16 March 2009 (UTC)
replies: text: I have not understood that statement at all. AKAF (talk) 18:28, 16 March 2009 (UTC)
replies: text: If there are multiple POVs on a particular thing, like minimum mach, then the wikipedia way is to add all of them or at least representative examples, with references.- (User) Wolfkeeper (Talk) 18:46, 16 March 2009 (UTC)
thread_title:  Minimum Mach number 

message: 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)
thread_title:  Advantages and disadvantages for orbital vehicles 

message: 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.
:Began with the intro.  GreyTrafalgar (talk) 21:58, 30 June 2010 (UTC)
replies: text: Added design principles and basic principles GreyTrafalgar (talk) 14:25, 1 July 2010 (UTC)
thread_title:  June/July 2010 Overhaul 

message: 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)
thread_title:  Tags removed 

message: I removed the phrase from the intro which said the top speed "is near orbital velocity". There are multiple things wrong with this:
*The notion that a Mach number represents an absolute speed is a layman's misunderstanding. Mach number is defined as the ratio of a speed to the speed of sound; the speed of sound varies with air temperature, and temperature varies with altitude, therefore "Mach (anything)" without the altitude can't be meaningfully related to any speed.
*Orbital speed is similarly ambiguous; it depends on altitude and eccentricity. So trying to equate a Mach number to a fraction of an orbital speed is pretty meaningless without being more specific.
*The wikilink to orbital velocity needed to be disambiguated; the article is titled orbital speed. Speed is the appropriate term to use, because velocity means "a speed in a certain direction." (Another layman's error to assume they are synonymous.)
*The assertion that it's near orbital speed is uncited in the body (as is the top Mach number value.) So this really makes it original research. (If it's somebody else's (reliable source) "OR", it should be cited.)
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)
thread_title:  Comparison to orbital velocity 

message: 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)
thread_title:  Thrust-to-weight ratio 

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thread_title:  External links modified 

message: 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)
thread_title:  Basic principles: Incorrect statement regarding Mach flow 

message: 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)
replies: text: Ajax. Nesshunter (talk) 21:25, 10 December 2023 (UTC)
thread_title:  Zircon anyone? 

message: 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)
thread_title:  Multiple stage to orbit