First of all, someone here stated that in the 1960's we could do Mach 2 with comfort, and Mach 3 in space-suits. That is not entirely correct. Lockheed did build a SST-contender that was to fly at Mach 3.0 at a cruising altitude between 71,500 feet and 76,500 feet using ordinary Jet-A. In many ways it was more advanced than the Boeing contender in various technical points, including the fact that it didn't require variable geometry inlets to achieve a self-starting high-pressure recovery inlet. It's wings naturally due to it's elaborately tested and constructed conical camber and twist caused the forward delta to take over the bulk of the lift production supersonically countering the nose-down tendency with a nose up one using no variable geometry wings (something Boeing required). It's design was also significantly lighter than Boeing's design. Boeing effectively won the countract because they "bought" the contract: meaning they effectively used their monetary means and political connections to bribe the countract. Technically Boeing's design did theoretically have a lower take off velocity and a slightly higher L/D ratio which some have questioned it's accuracy. Even despite buying the contract, their design had a number of short-comings. The complex wing-pivots, and aeroelasticity problems all added weight to the design. The wing-pivot's weight may have been honestly underestimated, or deliberately fudged to make it look acceeptable figuring they could lower the weight with various machining techniques when it really counted. But in either case, the plane ended up going through various modifications to the tail, flaps and wings, and a fuselage widening that would have made it nearly as wide as a 767, and lengthening that would have probably made the airplane nearly 320-feet long. Canards were also added to the design as well. The plane ended up fully loaded before a single person stepped aboard. They tried to lower the weight-- they failed, and even tried simpler swing-wing configurations before just giving up and using a more conventional looking tailed double-delta wing. The plane still probably would have flown had environmentalists, and various congressmen opposing the amount of taxpayer's funding on it would have bit the bullet. The plane was physically constructable in other words.
Had the L-2000 won the competition, they probably could have got the plane into the air before environmentalists were able to make a sufficient stink to endanger the program. It also was a simpler design that was constructed by people that probably had far more experience with titanium alloys and machining said alloys to save weight. The program called for a first prototype flight in 1970 continuing on to 1972. The production prototypes would have first flown in 1972, and would have been certified and entering airline service in 1974. As most people know, 1973 was the OPEC Oil Crisis: The Arab nations got together and decided to place an embargo on all nations that defended Israel during the Yom Kippur War (1973) as a vindictive punishment. I don't think any SST would have entered service as a result of that-- but such a plane was physically build-able.
The Aurora most people discuss about is often envisioned as a 75-degree delta winged plane capable of flying at Mach 6 at 100,000-something feet. Even if such a real aircraft was to exist, nobody knows if Aurora was it's name. Aurora was a name listed on an appropriations bill that was listed by accident because a censor slipped. It could have been anything, a high-altitude drone, the B-2 bomber, some other aircraft.
In 1989, a man named Chris Gibson while working on a rig off the North Sea noticed an aircraft with a 75-degree sweep next to two F-111's with their wings in a low-sweep configuration (all the way out) off of the plane's port side. The 75-degree delta appeared to be refuelling with a KC
-135 tanker. Chris Gibson was a member of the Royal Observer Corps who also competed in competitions where they would flash a picture of a plane in a far-off, unusual attitude position and they would have to get the right answer: Allegedly he excelled at this. Sure it could have been an F-111 with it's wings stuck in the fully swept position trying to take on fuel before it crashed into the ocean, or it could have been what Chris Gibson claimed. Gibson could not talk about it for about a year or two because of the Official Secrets Act he was still subject to.
Many believe Aurora was a replacement for the SR
-71 Blackbird, a plane retired in 1990, then reactivated in the mid 1990's, and retired again. Some people believe because the "Aurora" wasn't good enough. They were almost right.The Blackstar if I recall it's name right was an aircraft powered by some type of rocket, and carried up to altitude by a mothership aircraft-- another plane that many people have claimed to see. It was around 100-200 feet long with a fighter like canopy, delta wings with two rectangular boxes under the wings with two engines per box, with up-turned wingtips. Some reports said it had canards, others said it didn't. Some say it had chines, others said it didn't... but the basic plane, around 150 feet long, two engine boxes with two engines per pod, white, with up-turned wing tips has been sighted enough times to make one wonder. Hypothetically at Mach 3.0 at 70,000 feet, if you launched a rocketplane like vehicle you could get the aircraft into low earth orbit. You could also scream along the upper atmosphere for a bit even if just on momentum.
Whether true or not, I don't know.
In regards to the "Mach 3 in space suits" referring to the Blackbird, you are likely wrong. The Blackbird's speed is still officially classified. The "Official" Manuel for the Blackbird seems to be heavily sanitized. First of all, there is not that much of a temperature rise from Mach 3.0 to 3.2. Mach 3.0 would net you around 500 something degrees (derived from the SST figures) generally speaking. The bulk of kinetic heating increases will occur usually once past Mach 5 when in hypersonic flight. The X-15 for example reached Mach 6, and was designed to withstand 1,200 F. The bulk of that increase in temperature from 500-1200 occured probably from Mach 4.25 to 6.
You folks probably all heard of the XB-70 Valkyrie. It was a beautiful bomber, looked something out of a Sci-Fi movie actually. The X-279E engine that was to power it and it's competitor (the Boeing 804-4) before it was selected as the champion was rated at Mach 4. That's right, a turbojet rated for Mach 4-- by the way the X-279E was the J-93. I'm not making this up either-- in fact I have a book ( a very highly detailed book ) on the XB-70 which confirms this fact.
The Boeing 804-4 was even stated to have Mach 4 performance as well. Allegedly the book states that the XB-70 won because of it having a better L/D ratio. I could understand them picking the slower one if the difference was Mach 0.3 different, not a whole Mach number, even if the slower one's got a humungus lift/drag ratio. To make it interesting I did a search and found a rather interesting NASA document talking about an inlet desgn for the XB-70 that was capable of providing 90-percent efficiency (which is the commonly listed efficiency of the inlets) at Mach 3.8. Now that is more logical... XB was slightly slower but far more aerodynamically efficient, the other jet was a little bit faster, but poor aerodynamics... That makes more sense-- the difference in speed between the two was only around 65 to 67 miles an hour. Big difference if you're in a cessna-- not much for a high-speed bomber. Especially when this slightly slower bomber has twice the bomb-load (50,000 pounds vs 25,000 pounds). Since the XB-70 was capable of Mach 3.8, it was probably also able to fly at higher altitudes as well, probably getting close to 100,000 feet.
Back to the Blackbird, another thing even more interesting about the Blackbird is it's engines. The J-58. It was originally derived from the J-91, one of the other engines in the XB-70 competition. It had a pressure ratio of only 7:1 to allow it to fly at such high speeds. The Navy needed a high-speed interceptor capable of blazing speed, and Pratt n Whitney scaled the J-91 down to 80% and increased it's pressure ratio to get more thrust out of the engine, and used a Inlet Guide Vane to lower the AOA on the compressor, producing around the same pressure ratio as the larger engine, yet allowing nearly all the thrust of the larger engine at lower speeds and altitudes -- around 26,500 (J91 = 28,000), and up to 45,000 on afterburner (J91 Normal = 44,000 / J91-w-HEF-3 in Afterburn = 48,000). The J-58 was even considered as an alternate XB-70 engine powerplant periodically as the XB-70 was built. In some ways it was a far simpler design than the J-93. The J-93 ultimately was used to power the XB-70 throughout all it's flights to my knowledge. The J-93 and J-58 were considered pretty much equivalents in terms of their maximum operating Mach number and thrust levels probably.
The A-12 to fly at Mach 3.2 would not have required such extensive changes to the engine. It would have flown at Mach 3.2 at 85,000 feet just fine with an unmodified J-58-- I don't even think it would have needed the afterburner (could be wrong here!). In fact, the A-12 could have flown up to Mach 4.0 with those engines using continuous afterburn.
As for the exact speed of the A-12/SR-71, I don't know: It's classified. However I can speculate. It's faster than the XB-70 Valkyrie obviously since it's engines have so many modifications to fly faster. How much faster I'm not really sure. It does use a different fuel (JP-7, which can sustain higher temperatures) than the XB-70 (JP-6), and the SR
-71's fuel allegedly can take nearly 1,200 degrees without lighting off.
The X-15 achieved Mach 6 and skin temperatures equalling 1,200 degrees. It featured a blunt-chined fuselage with a slightly blunted nose, and tapered, highly sharp wings. During some of the Mach 6 flights the plane was burned to a crisp in some areas. However, there were derivatives of the WWII V-2 rocket which featured fins that were extended like chines all the way to the nose and were capable of achieving 3,500 nm range. They were probably even faster than the regular V-2's Mach 5 capability, and would have had to have held a high speed for at least some time without falling apart. And that was with 1940's metallurgy. Metallurgy of the late '50's were considerably improved-- stronger and probably lighter, and by the late '50's there were certain titanium alloys are almost as temperature resistant as stainless steel. Combined with a black coating to re-radiate some heat back, and a broad-chined design, even without a blunted nose, some very heat-absorbant fuel, and the right engine, an aircraft could at least in theory achieve or slightly exceed Mach 5 for dashes, and achieve mid/upper Mach 4, to Mach 5 for sustained cruise.
The modified J-58 featured extensive modifications over the original engine. It featured a bypass on the fourth-stage, forming into six bypass tubes which feed just downstream of the turbines, the exact degree of bypass is dicated by compressor inlet temp. The compressor geometry was changed, the turbine casing was designed to allow the blades to expand a little bit, probably better turbine cooling, various metallurgical changes, a more efficient afterburner with vernier control, a engine-trim to lean the fuel/air ratio and a de-rich setting to lower the fuel/air ratio in the afterburner. All these various changes were to increase the maximum speed the engine can fly at, and to increase efficiency. The nozzles were attached as part of the airframe instead of on the engine as originally to save weight and possibly for greater efficiency. The J-58 variant that powered the A-12 was vastly faster than the original design, and probably was capable of hypersonic speed with the correct inlet and airframe.
The Blackbird's inlets are quite an impressive design. They did inordinate amounts of tests on them, probably in various scale models and various speed wind-tunnels. Generally speaking, variable geometry inlets are usually shorter for the same efficiency at a given mach number than fixed inlets-- even despite the variable geometry configuration the inlets take up a large portion of the length of the overall nacelle's length which indicate a very high operating speed. The most notable characteristic about the airplane's inlets are it's centerbodies-- football shaped spikes which are turned in at lower speed and less turned out at higher speeds exposing the centerbody's flared shape which forms a series of oblique shockwaves to produce a higher pressure recovery. While the spikes aren't as flared as you would think, the throat is flared considerably more so the bulk of the shockwaves are most likely formed on the walls of the inlet. The thickest area of the spike feature a series of holes which is used to skim off turbulent airflow. Struts connect the spikes to the walls of the ducts. The strut which connects the front of the engine to the inlet spike features a powerful motor that can extend or retract the inlet through it's full range of travel. The inlet-duct walls feature a series of bypass-door vents, which at low speed act like blow-in doors to add extra airflow to the engine, and close as the speed increases until a certain airflow temperature or a certain mach number is achieved, where they then open to dump some air overboard and relieve the inlet pressure. As the speed increases past a certain point the drag levels become too extreme, so an aft set of bypass doors located just in front of the engine begin opening-- the airflow goes around the engine and feeds into the afterburner plume. The forward and aft bypass door arrangements generally work opposite of each other (ie One opens more, the other closes more). Eventually the forward bypass is kept minimally open or closed, the aft bypass doors in the A position or closed. The engines bleed-bypass system would be operating at this point and would increase as necessary the bypass level. The engine-trim would probably be used around this point to lower the turbine inlet temp by leaning the fuel/air ratio, and eventually using the afterburner de-rich to increase fuel efficiency and possibly to avoid overheating the burner.
The J-58 due to the fact that the turbine-casing was designed to expand a little and allow the blades to expand as well to allow a higher operating temperature. The problem was that they didn't expand at exactly the same rate requiring a climb schedule.
There were observational reports of a plane that was waverider like in appearance with a comrpession ramp on the underside and a couple of engines wrapped along the underside of the ramp with the back part flared up. They said from the front it looked like an evil grin (the intakes). It allegedly made a noise that sounded like the sky ripping open. A rocket-based combined cycle boosted ramjet engine could produce acoustical characteristics described. Such an engine would be able to produce thrust levels equivalent to the fully loaded weight of the airplane, and efficiencies at 25,000 feet subsonic speeds equal to a 1960's military turbofan. The engine could probably run on the ramjet/RBCC together up to Mach 6, with a ramjet only mode of Mach 8 to 9.
If these reports are indeed correct, I'm not sure Lockheed built it. I think McDonnel Douglas did it: they made lots of highly swept-back, compression ramped waverider designs which resembles the aircraft allegedly spotted over the north sea and in at least one potential other sighting. Their NASP contender also looked very similar.
Goodnight. Hope I said everything right. I started typing this post in the morning, and then added more later, and finished up now