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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.
Don't worry, between the security line, customs, delays, and waiting on the tarmac, you'll still be garunteed at least 10 hours at the airport for any trip.
I still have more fans than freaks. WTF is wrong with you people?
F-16 top speed at altitude: Mach 2+
F-22 top speed at altitude: Mach 2.42 (officially...it's reported it can exceed Mach 4)
F-18 top speed at altitude: Mach 1.8+
I actually couldn't find a modern jet fighter that COULDN'T exceed 1.6 (at least within my aforementioned 2 seconds of research)
Of course, that doesn't diminish the insanity of Mach-15, but still.
Oh yeah, if you turn, your heart will forcibly exit your body via your anus before exploding. Have fun.
Birds aren't usually a problem @ 100,000 feet ;-)
"False hope is why we'll never run out of natural resources!" - Lewis Black
Well, I said fact-checking was *your* friend. Not mine. :P
I like basketball!!1!
The original poster is grossly incorrect regarding the max speeds of current fighters. The venerable F-15 has a very achievable basic airframe limit of mach 2.5. It is rarely flown at that speeds for various reasons, however the engines and basic aircraft are quite capable of reaching that speed. One of the biggest limiting factors, as with all high speed aircraft, is heat buildup. Stuff simply starts melting when you get going that fast and sustain it.
Keep in mind that the mach 1.6 speed quoted is generally tied to the F-16, not the F-15, even though both aircraft use essentially the same engines. The difference is that the F-15 uses a complex variable geometry inlet design while the F-16 uses a fixed inlet. There are very good reasons why each aircraft uses one design or the other, but it has nothing to do with the available technology. It has to do mostly with how much cost we are willing to put up with in order to get the plane to perform up to requirements. The F-15, as our primary air superiority fighter, needed to be able to go very fast yet retain good performance at all speeds and altitudes. So the cost and weight penalty of a complex inlet design was warranted. The F-16 on the other hand, was designed from the start to be a lower cost multi-role fighter, and the cost and weight associated with a variable inlet was not justified by the performance requirements for that aircraft's role.
A similar tradeoff was made with the B-1 design. One of the big differences between the original B-1A design and the production B-1B design was the elimination of the costly and complex engine inlets that were needed to make the B-1 a high supersonic design. The B-1B has much simpler inlets and is therefore speed restricted below the original design specs.
Again, this has nothing to do with the available technology. Rather, it's the result of the basic truism that any speed freak knows, even in automotive racing, that going faster costs more. Almost any design can be pushed to a higher speed, but it's going to cost you and at some point you're throwing a whole lot of money to get marginal speed increases.
The original post's point that we haven't seen a breakthrough in this area in a long time is valid, but anyone following hypersonic technology research knows that in the last few years there have been multiple programs flying actual demonstration hardware with some success. The progress is fairly slow in part because this is considered low priority research since there simply isn't much firm demand for faster air-breathing vehicles (expecially ones that burn petrochemicals and therefore create more pollution than slower, more mature, and more efficient designs) however the research continues in the face of the harsh fact that speed is expensive.
- A need to go that fast.
- An economic way to pay for it.
- A structure that can tolerate the heat.
- Engines that can run for a long time.
- A structure that can hold all the required fuel, and still have low drag.
As far as I know, if you want to go above Mach 2.X, you have to switch to titanium alloys as aluminum softens at about that amount of friction. Mucho $$$ and much bother in construction and maintenance.Also scramjet engines tend to burn out really quickly-- the temperatures you need in there are beyond the ability of most metals, at least for longevity.
There's a heck of a safety issue too-- scramjets can flame-out and are not easily restarted.
It's also a challenge to stuff as much fuel as you need into a low-drag airframe. You need long range as there's no point in short hops when it's going to take many kilomiles to get up to speed and altitude. But people don't like cramped cabins, so you need more fuel to allow a bigger fuselage.
Also it's going to be hard to find people willing to pay maybe 15 times the usual amount to get there a few hours faster.
Airships for non-time-critical journeys? That's a very intriguing idea. It reminds me of a paradigm shift I experienced recently.
My wife and I bought our first robot, a roomba naturally. We watched it intensely as it cleaned for the first hour. When it finished it docked itself to recharge. My wife then noted that there was still some fuzzies on the carpet and that it didn't seem to pick everything up. I told her that it would probably pick it up on its next run.
After a couple days of running the roomba when we would leave the house, the carpets suddenly are cleaner than they have ever been. So clean in fact that our allergies seem to have improved (probably placebo, but that roomba does pick up the dust).
I realized that our house cleaning robots don't work like the Jetsons led us to believe they would, where they clean the house 10 times faster; they in fact take 10 times as long. They are, however, 100 times more meticulous and therefore they clean the house 10 times as well. I think this is a paradigm shift.
Perhaps there is indeed similar benefits to be reaped from a similar shift in the transportation/aerospace sector.
Very thought-provoking.
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There might be very short-duration reasons why the pilot might want to push the limits of the aircraft (testing and/or outrunning missiles). If you can trust the competency of your highly-trained pilot, then you can give them a little more flexibility than if you are trying to "idiotproof" a commercial solution.