Talk:Pratt & Whitney J58/Archive 1

Engine explanation
Why was there so much detail in explaining basic turbojet and ramjet operation? Those topics have their own articles. The only significant parts about the J58 design are its movable spike inlet and the union of two propulsion techniques. Everything else is standard turbojet/ramjet tech. — Preceding unsigned comment added by 69.209.168.59 (talk • contribs) 11 November 2005 (UTC)
 * The moveable spike inlets are not part of the J-58 design. They were created by Ben Rich as part of the Oxcart project.  I will strike mention of them from the article unless anyone objects. — Preceding unsigned comment added by 24.4.28.58 (talk • contribs) 3 August 2006 (UTC)
 * I object. The inlet design of a jet engine is very highly coupled with the engine, and this engine probably more so.WolfKeeper 18:10, 2 January 2007 (UTC)
 * Still, doesn't change the fact that the inlet is not actually part of the engine. I think it would be best to just cover the engine in this article and to bring the inlet/engine/nozzle dynamic in the A-12/YF-12/SR-71 pages 68.192.204.19 (talk) 01:06, 18 March 2009 (UTC)
 * I agree. Johnson makes it clear in his bio that the inlet design is The Big Deal. &mdash;Joseph/N328KF (Talk) 18:52, 2 January 2007 (UTC)
 * The inlet design is a big deal in *all* supersonic-aircraft design. Granted the A-12/YF-12/SR-71/M-21 inlet/engine integration was far more intricate but nonetheless the engine and aircraft inlets were seperate.  After all they can run the engine in a test-cell or in a test-stand 68.192.204.19 (talk) 01:06, 18 March 2009 (UTC)

Are you sure that you have the Fore and Aft directions correct on the velocity vs. spike position? I am not an expert on this engine, but I would think the spike would have moved fore as mach number increases. If I remember my compressible flow the goal is to both ensure subsonic flow at the inlet of the engine and to force the shock to terminate at the outside edge of the engine. As Mach Number increases the shock angle decreases. Therefore shouldn't the spike move forward not aft in order to maintain the shock termination at the same point? Could someone please confirm or deny? —Preceding unsigned comment added by 174.54.97.45 (talk) 00:49, 12 May 2010 (UTC)

Suggest Including Term "Variable Cycle" and Additional Details
I think the amount of descriptive info on turbojet/ramjet operation is appropriate as written, at least of this date.

It's important to include the descriptive term "variable cycle" when referring to the J-58. Also explain what that term means. While the J58 is an example, it doesn't just mean turbo/ramjet. E.g, the GE F120 used to power the F/A-22 is a variable cycle turbofan/turbojet.

Here's some more info on how the J-58 works: Joema 13:15, 20 December 2005 (UTC)


 * I incorporated some of the above. Joema 11:43, 29 March 2006 (UTC)

Should the Early J-58 be mentioned?
Keep in mind, the J-58 was originally developed as an 80% scale version of the J-91 which was a large turbojet with a low-pressure ratio designed for the purpose of powering the WS-110 series of aircraft which would ultimately become the North American XB-70 Valkyrie. It was a competitor to the X-275 and X-279E (The X-279E was the YJ-93). The US Navy required a high performance engine to power an attack plane which to my knowledge was either an advanced derivative of the North American A3J/A-5 Vigilante. Chance-Vought also wanted to develop a high-speed interceptor derivative based on the F8U design, which were internally designated V-418 and V-419, and along with the J-75 powered V-401 (which while slower than the J-58 powered V-418/V-419, the V-401 actually did fly), would have flown as the XF8U-3/F8U-3. While the advanced J-58 powered North American A3J/A-5 derivative, and the V-418 and V-419 designs never actually flew, but the J-58 was developed in it's original form and a couple hundred hours of testing were performed on the engine.

When the A-12 design came along that's when the design fully morphed into the design that we know as the J-58. The compressor was enlarged, the metallurgy was altered substantially, the air-cooling to the turbine dramatically increased, the bleed-bypass system fitted, the nozzles were taken off the engine and were attached to the airframe instead (which was to reduce weight and possibly improve engine/airframe integration), a system to lower the fuel/air ratio at high mach-numbers, and so on. The engine also used a different engine-lubrication, a different fuel - JP-7, and a chemical-ignition system using TEB. AVKent882 (talk) 01:11, 19 March 2009 (UTC)


 * I'm currently writing an article on the J91, and when I've finished that, I may start to add some info on the earlier versions of the J58 (the JT11; the SR-71's engines were the JT11D). - BilCat (talk) 10:28, 5 February 2011 (UTC)

Bad math?
The TEB tank held 600 cc of TEB, which the article claims is enough for "at least 16" starts. It then goes on to describe the start cycle as requiring 50 cc of TEB each time. 600/50 is not 16; it's 12. Bad math, or bad numbers? Something doesn't make sense here.70.226.84.245 (talk) 18:14, 2 September 2009 (UTC)

SST Engine competition
According to the Lockheed L-2000 article, there was an engine competition, between a derivative of this engine, the General Electric GE4, and the Pratt & Whitney JTF-17A. There should be some information here on that. 65.94.47.63 (talk) 06:19, 23 June 2011 (UTC)

Changes to bring information in line with credible engineering sources
I propose deleting all ramjet references, including the section 'Turbo-ramjet design',since the information is incorrect. Where it has been derived from named references they are also, unfortunately, incorrect or the information has been incorrectly transposed.

In its place I propose adding a new section titled 'Bypass bleed design'. This section will mainly make reference to U.S. Patent 3,344,606 and the F-12/SR-71 Flight Manuals, the 2 definitive engineering documents available on-line which describe how the original J-58 was modified to enable operation at Mach3 and which,incidentally, make no mention of ramjet operation.

The new section will not use terms like variable cycle, variable bypass turbofan, fan-assisted ramjet,etc because these terms are not self-explanatory and require extra explanation to justify their use. Instead, I think it is better just to say how it works, based on its inventors own words, without trying to 'pigeon-hole' it. In addition, it will not have details of the inlet since the inlet did not address the shortcomings of the J58 compressor. The inlet, together with the nacelle airflow and final nozzle, were airframe systems and should be the subject of a separate article. Pieter1963 (talk) 17:03, 28 December 2012 (UTC)

Edit completed. Pieter1963 (talk) 23:49, 1 January 2013 (UTC)


 * Unfortunately this edit has introduced problems, the biggest is that the sources have not been cited using inline citations per WP:CITE and WP:VERIFY, strictly the whole entry could be removed. No wikilinks have been provided, these help readers understand a subject. There is also apparent editor commentary and opinion (WP:NPOV). The explanation of how this engine works at high airspeeds is now too technical for most readers with terms not being explained (what is an IGV?). The entry implies that the exhaust nozzle is an airframe component, images of the engine (including the ground test in the article) appear to show that the nozzle is part of the engine? Removal of the air inlet cone system image is also a retrograde step, I don't see it described elsewhere as the entry suggests. Nimbus (Cumulus nimbus floats by)    09:44, 2 January 2013 (UTC)

Firstly, thank you for your comments. Let me see what I can do to improve this edit as it's my first and I have some learning to do. I can qualify any editor commentary and opinion with suitable references if you can point them out since I thought everything I covered was in the patent and Manual.

I was hoping to improve the article by editing using descriptions from definitive engineering sources whereas previous descriptions were, unfortunately, based on popular misconceptions, hardly worthy of a wikipedia article. Hence, what is basically, my attempt at a self-study guide to the patent. It is 'the' explanation and cannot really be watered down. How the engine works at high airspeeds, or works at all at any speed for that matter, is technical. There are no short cuts. The very title "J58" means " technical". If someone wants to learn about the J58 and Wikipedia is to be their first stop then it should have authoritative value.

To answer your specific points: I will address the IGV entry more clearly.

The nozzle: The edit does not state that the exhaust nozzle is an airframe component. It states that "the final propelling nozzle" is an airframe component. The engine has its own nozzle, which I referred to as "the a/b exit nozzle", apologises for slipping in a/b unexplained, specifically to identify that there were two separate nozzles. It may appear to be getting technical again but that's the way it is. There were two nozzles, an engine one and an airframe one, which did separate jobs. If I were to say "the nozzle" I would be doing the reader, who wants to learn, a disservice.

Why I removed the inlet image: The air inlet cone system image was titled "operation of the air inlets and airflow patterns through the J58 .." This statement is incorrect since it doesn't show airflow through the J58. Since the Wikipedia article is titled "J58" then it should show the engine airflow correctly which I have done by referring to the chart from the Manual.

The air inlet cone system image specifically shows airframe flows and, as such, does not explain anything about the engine so does not qualify to be in an article titled "J58". The image appears more correctly in the wikipedia article on the SR-71 aircraft, although, even there, it still incorrectly claims to show flow through the J58.Pieter1963 (talk) 05:06, 4 January 2013 (UTC)


 * I realise it is your first edit, here are another couple of shortcut links that may help, WP:BETTER and WP:AUDIENCE. Imagine a person (perhaps a teenage boy) sees one of these engines in a museum, they come to the Wikipedia article to learn all about it. They are unlikely to have a full knowledge of turbojet theory. If we ask 'what terms might a reader not understand?' then that is an obvious place for a wikilink. It is convention to write out an abbreviated term in full followed by the abbreviation, from that point on in the article the abbreviation can be used (as it has been explained). There is a wikilinking trick called 'anchoring' which can take the reader to a specific section of an article and another called 'piping' which allows the text within a link to be changed. Here are some links that could be used, compressor (piped link), bleed (piped), stage, rotor and stator (anchored) and compressor stall (plain link). If you look at this post in 'edit' mode you will see how the link coding works. I can not find a good link for Inlet Guide Vane (IGV), in this case a cited footnote can be added in the reference section briefly explaining what this component is.


 * I disagree that the shock cone system is not mentioned, at the moment the reader has to assume that the engine receives air at the compressor face at Mach 3. As this engine was only used in the SR-71/A-12 family it would be better to explain it, the Rolls-Royce/Snecma Olympus 593 is a similar case, the importance of the intake ramp system of Concorde is described. Nimbus (Cumulus nimbus floats by)    10:07, 4 January 2013 (UTC)

I see your point about the intake. Pieter1963 (talk) 21:30, 4 January 2013 (UTC)


 * Getting better, have a read of the WP:OVERLINK guideline. Can not say 'described at Lockheed SR-71' as the description there can be deleted or adjusted to nonsense by anyone, or (unlikely) the whole article can be deleted. Not easy I know. Nimbus (Cumulus nimbus floats by)    22:45, 7 January 2013 (UTC)

In this particular instance using the guideline that concorde is a "good article" and olympus 593 has 2 B's shouldn't I delete the workings of the intake from SR-71 and rewrite it in J58? Then no link required?Pieter1963 (talk) 02:13, 8 January 2013 (UTC)


 * Each article (engine or aircraft) should be able to stand alone with the balance of the text biased toward the subject of the article so this article (J58) should concentrate on the engine with sufficient mention of the inlet system for it to be understood where the SR-71 article would describe the inlet system in more detail with a brief mention of the engine, probably with some duplication between the two. There is a guideline WP:OTHERSTUFFEXISTS which is sometimes used to say 'this is how it should be done', the guideline basically says to ignore other articles.


 * Wikipedia articles are available in PDF format (left sidebar, 'Download as PDF'), these PDF versions have no wikilinks, it's a good exercise to view articles in this format as it becomes obvious that important context might be missing. Wikipedia's Featured articles are generally written so that they can be understood without wikilinks. Cheers Nimbus (Cumulus nimbus floats by)    11:11, 8 January 2013 (UTC)


 * We do have an inlet cone article, not sure if that has been used yet here? Nimbus (Cumulus nimbus floats by)    12:29, 8 January 2013 (UTC)

Looking at the inlet cone. In the meantime please see talk SR71 J58 Engine Airflow Patterns.svg?Pieter1963 (talk) 01:04, 10 January 2013 (UTC)


 * What is being asked for there is a 'file move', the image is hosted on Wikimedia Commons (a duplicate is held on Wikipedia to allow project categorization etc). The process to rename a file on Commons is here, reading through it the file would most likely not be renamed as its description is close enough. They also don't like to move files for link stability reasons. Image file names are sometimes arbitrarily chosen by the uploader and can be completely wrong but in the case of File:SR71 J58 Engine Airflow Patterns.svg the uploader has been thoughtful and included 'SR71' and 'J58' which allows the image to be found through the search box using either term. This engine image, File:ABCDragonfly.jpg, is not what the object actually is, instead of having the file moved I added a note to the description. File naming and description mistakes like this are one reason why images can not be used as a reliable source on Wikipedia. Nimbus (Cumulus nimbus floats by)    11:21, 10 January 2013 (UTC)

Don't want to refer to inlet cone article yet as some fundamentally incorrect statements need correcting first.

I don't agree that the diagram description is close enough. Whilst the uploader may have been thoughtful in leading the inquisitive to 'J58' the reader goes round in a circle since the image and article mutually support each other with the same mistake.

I will show the ramifications of this seemingly innocuous wording. We can find it in an otherwise authoritative AIAA paper.'Design and Development of the Blackbird' Peter Merlin. It has the same diagrams with a similar misleading title '..shows engine operation from 0 to cruise speed'. The author concludes from looking at this diagram with its, I repeat, misleading title-

"The complex airbleed bypass system allowed air to bypass the turbine section and go directly to the afterburner thus working as a turbo-ramjet". (All air that bypasses the turbine section, and I assume he means the engine, goes directly to the ejector nozzle, ie downstream of the afterburner). and "A significant percentage of the air entering the inlet bypassed the engine through ducts and travelled directly to the afterburner".(No air entering the inlet bypassed the engine and travelled directly to the afterburner. The only air that was burned in the afterburner and which had bypassed anything,in this case 5 compressor stages,the engine combustor and turbine, was some of the 20% compressor bleed).

File images are no different from word statements copied verbatim from sources. They can only be reliable if the uploader/writer is familiar with the subject matter. Since this is not always realistic corrections have to be encouraged even if it means in accompanying text. If this contravenes wiki good writing/editing guidelines then it has to be weighed against having incorrect wording which in itself is a wiki no-no.

— Preceding unsigned comment added by 74.14.46.18 (talk) 20:34, 13 January 2013 (UTC) Forgot to sign abovePieter1963 (talk) 16:17, 15 January 2013 (UTC)


 * I am continuing to look at improvements to this article which are based on verifiable engineering documents. One proposal is to replace File:SR71 J58 Engine Airflow Patterns.svg with File:SR71J58.png. I understand that it is not as presentable as the vector image but feel it is less misleading without the vector image title. To go with it I will add a description of the inlet.Pieter1963 (talk) 15:17, 20 January 2013 (UTC)