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Post by Cougar on Jul 2, 2007 23:09:55 GMT 9
It is safe to assume that if titanium melts at 3000 degrees its structural stability at temperatures higher than 3000 degrees is that of very heavy water; having nothing at all to do with national security. Therefore, should the SR-71 be propelled to speeds great enough to result in skin temperatures of 3000 degrees, the aerodynamic stresses, that which is responsible for the heat buildup, would result in the disintegration of the aircraft. Ramjet vs Scramjet: both rely on an outside power source to bring them up to their efficient operational speed. The difference in operating parameters is that the airflow through a ramjet is subsonic, while the airflow through a scramjet is supersonic. The difference in thrust is substantial, the SR-71 (ramjet) topped out at Mach 3.3, while the latest flight of the X-43A (scramjet) produced a Mach number of 9.7 - a Los Angeles to Washington flight in less than 20 minutes.
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delta2477a
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Post by delta2477a on Jul 3, 2007 10:51:46 GMT 9
Cougar, Should it not be in violation of national security, why did you say "is believed" to be rapidly approaching a liquid at 3,000 F? I'm just wondering because it sounded like you have doubts. Mr. M.O. Williams, Should this not be in breach of national security: How the hell could a gas turbine engine, even with 65% bypass have unlimited speed? Because as I crunch the numbers, here's what I get Okay, first let's look at the engine the J-58 came from... the J-91, which was a competitor to the J-79-X-279E aka the J-93, the J-93 was rated for performance as high as Mach 4, with the J-91 being capable of the same but with a lower pressure-ratio, compensating by being able to handle greater airflow. As the J-91 lost it's ability to compete with the J-93, which was a smaller, lighter engine with a better pressure ratio and better turbine-cooling, Pratt and Whitney developed the J-58 to answer a Navy contract for a high-performance interceptor which, to the best of my knowledge was a North American contract, which was based on the J-91 but given an even-number since it was for a navy contract and was 80% the size of the J-91. Allegedly the engine could produce 26,500 lbf dry and 45,000 lbf with afterburner, and to compensate for it's smaller size, it would appear that a variable geometry inlet-guide-vane was added that allowed a higher pressure ratio for take-off (Axial) and a lower one (cambered mode) for cruise. Whether the engine had an afterburner that was either on or off, or had multiple stages for the USN design, I'm not really all that sure, but it would appear that the J-58 somewhere along the way was being considered as a J-93 competitor, so I assume it would feature at least multiple afterburner settings. I'm guessing the axial-IGV mode combined with AB would yield the same takeoff and climb performance as the J-93, and at higher altitudes the nozzle-design of the J-58, and perhaps the fact that it's afterburner might produce proportionately more thrust, I ... but it was considered a competitor-- so there couldn't be much difference. Even after the J-93 was selected as a winner the J-58 was kept on just in case the J-93 didn't come through... but it did. During the time the Convair Kingfish (I think that was it's name) and the Lockheed A-12 were being developed, the J-58 to the best of my knowledge incorporated the bypass for it's first time, which eventually was settled with six 9" tubes that bypass off the fourth stage compressor and feed just aft of the turbine to produce a pseudo-ramjet effect. The turbine cooling was improved, various metallurgy changes were made to the compressor, turbine, and even the external engine construction... allegedly the turbine featured a casing that could expand to some extent with the turbines also able to expand safely within the expanding turbine-casing (allegedly being the word-- I heard it mentioned once)... the internal and external nozzle were now placed on the airframe itself with auxiliary suck-in-doors. The blades geometry and compressor diameter changed as well along the way. To improve efficiency, the afterburner was now designed with vernier control just like the compressor. The engine also featured an "engine-trim" system which reduced the fuel/air ratio while maintaining desired engine RPM, helping keep the turbine temp within check. There was also a de-rich system which reduced the fuel/air ratio of the afterburner at high-speed cruise as well which might be to preserve the integrity of the afterburner and it's nozzles. The engine was also modified to use JP-7 for both fuel and engine lubrication. All these modifications, the bleed-bypass, the metallurgy changes to the compressor blades, the turbine, the increased air-cooling, the turbine casing metallurgy and afterburner metallurgy, the engine-trim and de-rich capability, fitted to an engine that was already capable of Mach 4 performance, would logically provide incredible performance increases... but I have doubts that they would have truly unlimited performance-- to my knowledge everything has a limit, and I'm not talking about the pilot or the plane's structural integrity. Now you might be thinking that ramjet's (which the engine sort of works like a ramjet) have no speed limitations, and while theoretically it might sound true, but it's not. Eventually the pressure increase from slowing hypersonic air down to subsonic speed is massive and requires a stronger structure for the ramjet. Active cooling could help at first, but even that would only work to a point, and additionally you'd have other problems... O2 would start to dissociate into single O's... the N and O in the air would start to react, and you'd also have ionized flow. Using magnetohydrodynamics could manipulate the flow and deal with many or all of these problems, but in 1963 when this engine first was tested... that, if it even existed, it was just some scientists wet dream. A scramjet would compensate by not slowing it all the way down to subsonic speed, but keeping it supersonic... to work at lower speeds though it would require a variable geometry capability to allow it to work as a ramjet and even scramjets have limitations. BTW To the best of my knowledge what I wrote is accurate. And was obtained using non-classified data. Regarding the accuracy of the data, I could be wrong, I'm not perfect.
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Post by Cougar on Jul 4, 2007 13:38:25 GMT 9
Cougar, Should it not be in violation of national security, why did you say "is believed" to be rapidly approaching a liquid at 3,000 F? I'm just wondering because it sounded like you have doubts. I had to get clearance from the bureau before responding, but now I can reveal that my saying "is believed" or "widely believed" was part of a trick answer, designed to elicit visions of doubt in the sharpest of minds. Unlike Scooter Libby, who was very sloppy, I try to be extremely careful when dealing with national security issues, especially when the potential exists that the other party may be working for Peter Hunglow, the one-eyed master sleuth.
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delta2477a
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Post by delta2477a on Jul 5, 2007 2:24:20 GMT 9
Okay, I think I got your point. I'll lay off this thread unless any responses are directed towards me and I'll try to be careful to avoid saying anything un-kosher.
In either case, since it was all but said, I assume it would be logically acceptable to guess that it's melting point would be something above 3,000 F
Delta2477A
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Post by Black Bart on Jul 5, 2007 4:27:05 GMT 9
A metallic element, titanium is recognized for its high strength-to-weight ratio.[6] It is a light, strong metal with low density that, when pure, is quite ductile (especially in an oxygen-free environment),[18] lustrous, and metallic-white in color. The relatively high melting point (over 1,649 °C or 3,000 °F) makes it useful as a refractory metal. Commercial (99.2% pure) grades of titanium have ultimate tensile strengths of about 63,000 psi, equal to that of steels alloys, but are 45% lighter.[5] Titanium is 60% heavier than aluminum, but more than twice as strong[5] as the most commonly used 6061-T6 aluminum alloy. Certain titanium alloys (e.g., Beta C) achieve tensile strengths of over 200,000 psi (1.4 GPa).[19] However, titanium loses strength when heated above 430 °C (800 °F)[5] It is fairly hard (although by no means as hard as some grades of heat-treated steel) and can be tricky to machine due to the fact that it will gall if sharp tools and proper cooling methods are not used. Like those made from steel, titanium structures have a fatigue limit which guarantees longevity in some applications.[20] The metal is a dimorphic allotrope with the hexagonal alpha form changing into the body-centered cubic (lattice) beta form at 882 °C (1,619 °F).[5] The heat capacity of the alpha form increases dramatically as it is heated to this transition temperature but then falls and remains fairly constant for the beta form regardless of temperature.[ From this Public Reference, I do not think that Titanium would be good for anything except chemistry at 3,000 degrees F. Happy Independence Day, I,m on Vacation any thus a guest while using someone else's computer. Black Bart
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Post by Cougar on Jul 5, 2007 14:30:11 GMT 9
Okay, I think I got your point. I'll lay off this thread unless any responses are directed towards me and I'll try to be careful to avoid saying anything un-kosher. In either case, since it was all but said, I assume it would be logically acceptable to guess that it's melting point would be something above 3,000 F Delta2477A No need to lay off the thread Delta, just a need to exercise more care in reading. The melting point of Titanium is a matter of public record, ranging between 3002 and 3038 degrees depending upon the source. It can be checked out on-line by googling "Titanium properties". You may then draw your own conclusions, maybe even accepting that Titanium would be rapidly approaching a liquid state at 3000 degrees.
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Post by Diamondback on Jul 6, 2007 11:39:10 GMT 9
So, for a hypersonic SR, we're looking at a major up-engine, and a ceramic shell (which'll offset some of the power gain). Essentially, we'd be able to reuse the structural member designs and most of the internal systems, but we're still going to be designing a new airframe (albeit at most an F-18A/B/C/D vs. "Super"*snort* Hornet comparison). Can theoretically be done, but it's gonna be a darn expensive project... Could an F135/F136 core design, modified similarly to the J58's J57 roots, be used as the guts of a "J58 redux"? No matter what, you're not gonna be able to just haul one out and rebuild it, this would have to be purpose-built from wheels-up, even with the possibility of leveraging existing parts, aerodynamics and some engineering...
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delta2477a
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Post by delta2477a on Jul 10, 2007 1:49:02 GMT 9
The J-58 isn't related at all to the J-57... it's number is out of sequence and even numbered because it was initially assigned to a Navy contract. It was an 80% scaled version of the J-91 (which was proposed as a nuclear powered aircraft engine, and a conventional/HEF-3 powered rival to the YJ-93 for the XB-70) with a higher pressure ratio with a cambered guide-vane setting to allow lower pressure ratios at high-speeds. It was a single spool engine with a 47" intake diameter, with an alleged thrust of 26,500 dry and 45,000 wet
This is prior to any modifications made for the Lockheed A-12 program
Delta2477A
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Post by Jim on Jul 10, 2007 13:47:25 GMT 9
HYPOTHETICALLY, TAKE THE VARIOUS VERSIONS OF THE SR71 to their max altitude nose it over til its attitude is at 90 degrees to the horizon ( artificial or otherwise) slowly advance the throttles to their max and light the afterburners, maintain contact with the crew on board so they can give a popping rivet by popping rivet account as the aircraft begins to structurally fail- (it will disintegrate long before it melts). I believe that falling objects accelerate at the rate of 32 feet per second per second, but now it (the SR 71) is being drastically accelerated by power assist...... What will the terminal velocity be of the largest piece to strike the surface of planet EARTH? The Old Sarge
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Black Bart
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Post by Black Bart on Jul 11, 2007 0:27:21 GMT 9
At what altitude does break-up occur? 32 ft per second/per second is correct. Black Bart
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Post by lindel on Jul 11, 2007 6:14:21 GMT 9
If the breakup doesn't occur sooner, it will when the bird reaches terminal velocity or in other words, the quick stop at the end of the dive.
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Post by Cougar on Jul 11, 2007 8:39:25 GMT 9
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Post by Jim on Jul 11, 2007 14:05:17 GMT 9
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Post by Cougar on Jul 11, 2007 15:52:56 GMT 9
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Post by Diamondback on Jul 12, 2007 12:09:12 GMT 9
Well, to my thinking, the challenge isn't getting to Mach 6--it's getting there AND having the plane and crew be able to fly again afterward!
Hence, newer, more powerful engines (J58=32.5Klbs, F135/F136=40Klbs) coupled with a redesign to accommodate a new ceramic outer skin over a titanium substrate.
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Post by Cougar on Jul 12, 2007 13:47:20 GMT 9
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Post by Diamondback on Jul 12, 2007 14:45:33 GMT 9
Actually, I couldn't remember the formula, but I was thinking the new stuff talked about just after Columbia, or that Starlite stuff, if either pans out. I can be a little paranoid, so I like to have multiple layers of protection when possible...
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Post by Cougar on Jul 13, 2007 22:30:08 GMT 9
Starlite is an interesting concept, with one major drawback – it is not available. The product was announced in April 93, and a short time later its heat dissipating properties were demonstrated to the public. That demonstration involved heating an egg with a blowtorch for several minutes, the egg having been previously treated with the product. When the egg was cracked open there was no evidence of cooking. Since that time there are no records of the product ever being developed for commercial usage. What happened to Starlite? Who knows, but if the military recognized its strategic value, as well as its value to adversaries, one could entertain thoughts of the military having secured the formula and having it promptly classified.
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delta2477a
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Post by delta2477a on Jul 23, 2007 6:03:46 GMT 9
Makes sense about them classifying it...
So you're saying they considered taking an SR-71, painting it with Starlite, a type of thermal-coat/heat-reflector, or some substance like it, and considered launching it into space in lieu of a shuttle? (confused)
Delta2477A
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Post by Cougar on Jul 23, 2007 8:15:04 GMT 9
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