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How We Might Have Scramjets Sooner than Expected
loralai writes "Recent breakthroughs in scramjet engines could mean two-hour flights from New York to Tokyo. This technology, decades in the making, could redefine our understanding of air travel and military encounters. 'To put things in context, the world's fastest jet, the Air Force's SR-71 Blackbird spy plane, set a speed record of Mach 3.3 in 1990 when it flew from Los Angeles to Washington, D.C., in just over an hour. That's about the limit for jet engines; the fastest fighter planes barely crack Mach 1.6. Scramjets, on the other hand, can theoretically fly as fast as Mach 15--nearly 10,000 mph.'"
I feel compelled to point out that's the unclassified speed record. Its actual top speed is still speculative.
Scramjets have the potential to do their high-speed cruise at 100,000 feet. Until we get birds that can go that high, don't be too worried.
rj
1) Mach 3.3 speed record by SR-71 -> official speed record. NASA's X-15 set an unofficial one of Mach 6.7.
2) So.. 3.3 is NOWHERE NEAR the limit for jet engines.
Neither the SR-71 or the X-15 have conventional jet engines- the X-15 had a rocket and the SR-71 has ramjets
You pretty much need forcefields to protect you from air particles at that speed. The SR-71 expanded so much during flight due to frictional heating that even the fuel tanks needed to be built with expansion joints (so the fuel would leak out until it reached operating temperature at altitude). The fuselage would be about 300 degrees Celsius by the time it landed. Getting out of the plane was apparently a bit of a challenge.
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I'll agree for the most part..though I'll respectfully point out that the X-15 was rocket powered, not jet-powered ;)
:) Although getting upwards of Mach 4 is a practical limit for turbojets due to the drag issues of slowing down the stream to subsonic via a "tuned" shockwave ala the SR-71 "cones". That's where SCRAMjets come in...they can sustain combustion with a supersonic stream flowing through the engine from inlet to outlet, thus they don't have the same "upper" limit.
Everything else is spot-on for the most part...even the venerable F-15 has a "public" top-speed of Mach 2.5
Fact-checking is YOUR friend, too, buddy. The X-15 was rocket powered, not jet powered.
Huh?
MiG 29 - Mach 2.3
F-14 - Mach 2.5+
Kfir - Mach 2.3
JAS 39 Gripen - Mach 2.0
The MiG based of the F-15 with larger engines can reach Mach 3
What are you talking about? There's a MiG based on the F-15?
If you're talking about the MiG-25 Foxbat, it was flying well ahead of the F-15 (which itself was a response to the development of the MiG-25), and was designed to intercept bombers like the XB-70, which were never made operational.
Yes, infact I knew someone who use to fly those things and they weren't allowed to fully throttle up. He also said that during normal missions the plane would damage itself when going the faster speeds. Now of course this is all at someones word, so I have no written proof.
I heard the same thing from an SR-71 pilot, the damage was melting the nose and other leading edges. So advances in materials, not necessarily thrust, would presumably allow for greater speeds.
http://en.wikipedia.org/wiki/MiG-31
these are interceptors though, not fighters.
X-15 Hypersonic Research Program (from http://www.nasa.gov/centers/dryden/news/FactSheets/FS-052-DFRC.html)
In the joint X-15 hypersonic research program that NASA conducted with the Air Force, the Navy, and North American Aviation, Inc., the aircraft flew over a period of nearly 10 years and set the world's unofficial speed and altitude records of 4,520 mph (Mach 6.7--on Oct. 3, 1967, with Air Force pilot Pete Knight at the controls) and 354,200 feet (on Aug. 22, 1963, with NASA pilot Joseph Walker in the cockpit) in a program to investigate all aspects of piloted hypersonic flight.
Early flights of the aircraft initially flew with two XLR-11 engines, producing a thrust of 16,380 lb. Once the XLR-99 was installed, the thrust became 57,000 lb.
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ACtually, the concord didnt need the afterburner to reach supercruise.
But it happened that using is was far more efficient (with out afterburner, it spend quite a few minutes in the transition region of the speed of sound which used up way more fuel than a quick boost past the barrier)
HI O WISE PRINCE. WHT TOOK U SO DAM LONG?
No one said we were. So what?
The increase in the price of oil may contribute to making alternatives feasible, but what that really means is that the number of hours of human labor that need to be exchanged for energy in any form will increase, which increases the cost of, pretty much, everything compared to labor.
No, it will be in lockstep with production; there aren't substantial stockpiles to draw down, and there isn't substantial use of stockpiled fuel, so consumption is pretty tightly chained to production.
Unlikely. The only reason demand (not consumption which is "quantity demand", a different thing from the demand curve) changes lag behind supply (not production, which is "quantity supplied") changes is that there are transition costs and barriers on the demand side. And that's what drives the price increases. Even as those are overcome, its more likely that demand approximately catches up to supply, dropping prices back from their peak to something like the prior levels with ongoing gradual increase than that things switch over and demand radically plummets.
The mother of a friend of mine was a top executive at Dow Chemical, at the time the company's highest-paid woman. She always flew Concorde when she could because the company was paying her salary during her flight.
Being able to get across the ocean with time left in the work day meant that Dow actually saved money paying for a Concorde ticket.
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Aerodynamic heating at super/hypersonic speeds is not due to friction (at least as most people think of it), but rather compressibility effects. Air gets hotter as you slow it down(highly simplified explanation--kinetic energy turns into thermal); the change is dramatic across a shockwave.
I don't think the materials are sufficiently developed to allow a non-ablative shield at Mach 12, say; but I think lower speeds around Mach 6 should be possible in a few years. And around those speeds, you don't necessarily need scramjets; a standard ramjet would work fine, assuming your engine can take the static pressure and temperature inside it (my memory from a design project back in school seems to tell me that Mach 6 gives you a pressure ratio of about 50:1, and temperatures approaching modern limits).
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