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NASA Wants to Take the Blast Out of Sonic Booms
coondoggie writes to tell us that NASA and JAXA (the Japan Aerospace Exploration Agency) have announced a partnership to study the sonic boom. Hoping to find the key to the next generation of supersonic aircraft, the research will include a look at JAXA's "Silent Supersonic Technology Demonstration Program." "The change in air pressure associated with a sonic boom is only a few pounds per square foot -- about the same pressure change experienced riding an elevator down two or three floors. It is the rate of change, the sudden onset of the pressure change, that makes the sonic boom audible, NASA said. All aircraft generate two cones, at the nose and at the tail. They are usually of similar strength and the time interval between the two as they reach the ground is primarily dependent on the size of the aircraft and its altitude. Most people on the ground cannot distinguish between the two and they are usually heard as a single sonic boom. Sonic booms created by vehicles the size and mass of the space shuttle are very distinguishable and two distinct booms are easily heard."
Someone forgot what NASA is an acronym for. Second letter stands for "Aeronautics". So even non-space travel is well within NASA's authority. And the more they (NASA/JAXA) get distracted with that, the more likely it is that a private company will come up with a proper replacement for long distance air travel.
sunborbital ballistic passenger flights... now that would rock(et).
You either believe in rational thought or you don't
um, being able to take the 'Boom' out of the sonic boom would mean supersonic transport will be a reasonable option.
The Kruger Dunning explains most post on
Well, there are *civilian* uses for not having a loud sonic boom, like, being able to fly one of those things over populated areas.
But it certainly sounds like mission creep for JAXA, which is supposed to be more focused on Gundam-style robots.
Information theory is life. The rest is just the KL divergence.
Actually, at supersonic speeds you wouldn't hear it coming anyway because it would arrive before the sound anyway.
I live in the Edwards Air Force Base restricted air space, so we here many sonic booms in any given week, mostly from small fighter jets. In every instance the double boom is clearly audible, unless it's a tail-less spacecraft like SpaceShipOne. Whenever we hear a single boom, it is blasting going on at the nearby CalPortland Cement Plant limestone quarry or the gold mine.
Sometimes the booms are so loud the windows shake and things rattle around. We all love it because that's why we're here. But reducing the boom signature is an important area of research, so 'normal' folks can have supersonic airliners going overhead without disturbing their chiuahua's sleep patterns. That's why the concord only flew ocean routes. It would be nice to have supersonic transport between LA and New York.
--Mike
But Guile didn't really yell "Sonic Boom". At that sample rate it sounded more like "Phonic Poo". You'll have to wait for an article about phonic poo to repost your comment.
The state you are in while your HEAD is detached... - wait, what?
I remember when the SR-71 set the transcontinental speed record in the late 1970's. (They have since improved on it a little.) The boom was quite loud and clearly double, and I was impressed at how much energy was wasted by it, given that I was 30-40 km away, and that it made the same boom across the entire country. That flight was a little under a km / sec average velocity.
That's why, unless there is some real drag breakthrough, I think that rocket planes are the way to truly fast passenger travel. One ballistic impulse of 7 km / sec or so to get up above the atmosphere and on your way is 50 times the energy requirement of the SR-71 to get to maximum speed, but that would get you across the Pacific in 30 - 40 minutes and use less energy than a Mach-3 aircraft, which would take 2 or 3 hours for the same trip. Plus, except at re-entry, a rocket plane has no sonic booms.
Were you making some type of joke about vaporware and the low boiling point of alchohol, or are you saying booze is vaporware? Because belive me, it's made it to production. Like thousands of years ago. I'm drunk off my ass rright now.
The SR-71 blackbird pilots used to have a way to tell when the cones on the engine did not make the right decision and let in a bit of supersonic airflow before it got it right. The short but massive increase in thrust would throw their head into the side window on the side that had the malfunction. They hit pretty hard too!
When I was a young teen we used to manage an apartment complex where about six SR-71 pilots lived. They were all good friends and they had some great stories!
Couple of problems with this.. First, the internal surfaces of a divergent (subsonic) duct experience adverse pressure gradients. This means you need to very gradually increase the duct area in order to prevent flow separation. Subsequently, you would need an extremely long duct to achieve an appreciable reduction in flow velocity, all of which is subject to friction and viscous drag. All in all, not good.
The second major problem with this is that a divergent duct in supersonic flow actually increases the flow velocity. You may notice in engines that possess a throat (i.e. the exhaust stream is supersonic), the duct area increases, accelerating the flow (take rocket engines for example). In order to slow down supersonic flow, you need a converging duct.
Aside from that, a couple other points.. shockwaves don't make flow turbulent. In fact, nearly all flow through a jet engine is turbulent, as opposed to laminar. This is actually desirable in most cases, because although turbulent flow causes an increase in skin friction drag, it is highly beneficial in delaying flow separation, which is very bad in most cases.
Finally, with respect to the ramjet, there are some serious issues still to overcome, especially for slower speeds. First and foremost, it can generate no static thrust, meaning you need an alternative means for propulsion to get your bird off the ground. This adds weight and takes up volume, both of which are very bad things.
And as for how fast it goes.. The faster a ramjet travels, the higher the increase in stagnation temperature of the flow. This affects how combustion occurs, and it actually reaches a point that by adding fuel and combustion it, you are cooling off the flow, which is the opposite effect that you desire. This upper limit on speed depends a great deal on the inlet design and the materials used, but in general it is sub-hypersonic (as in hypersonic speeds are too high).
Work is being done to develop a scramjet (supersonic combusition ramjet), which is essentially the same as a ramjet except that the combustion occurs while the flow is travelling at supersonic velocities (meaning less of an increase in stagnation temperature, less pressure loss, etc.), as well as schramjets, which again are similar, however use detonation waves to ignite the fuel/air, reducing profile drag due to burners and flameholders etc.
I hope this at least answered parts of your questions..
Aikon-
Removing the "Boom" dramatically alters the economics because you can fly it over dense population centers that were banned to Concorde. Happy?