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NASA Wants to Take the Blast Out of Sonic Booms
Posted by
ScuttleMonkey
on Fri May 09, 2008 04:20 PM
from the softer-side-of-soar dept.
from the softer-side-of-soar dept.
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."
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The Right Stuff (Score:5, Insightful)
Re:The Right Stuff (Score:5, Insightful)
sunborbital ballistic passenger flights... now that would rock(et).
Parent
Re:The Right Stuff (Score:4, Funny)
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Re:The Right Stuff (Score:4, Funny)
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Re:The Right Stuff (Score:5, Insightful)
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Insightful, but look at this and tell us with a straight face that it isn't vaporware. Hasn't somebody heard of these designs before?
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Re:The Right Stuff (Score:5, Funny)
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Re: (Score:3, Insightful)
Silent or not, supercruise is never going to become a viable mode of mass travel.
I'm sure it'll show up in the smaller private/charter turbojets, but that's about it.
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Re:The Right Stuff (Score:5, Insightful)
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Carefully (Score:4, Interesting)
I think the answer involves less airplane and more engine. Theoretically a J-58 engine [wikimedia.org] by itself could operate supersonically with minimal shock waves since it is designed to reflect the shock waves into the engine in a way that they are subsonic before touching moving parts. The tricky part is adding the parts of the airplane the give lift and space for pilots to sit.
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Re:Carefully (Score:5, Interesting)
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!
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Re:Carefully (Score:5, Informative)
Jet turbines and ramjets share the same problem - they are only capable of subsonic combustion and must slow the supersonic airflow before they can burn fuel in it and reaccelerate it. Thus the recent experiments with scramjets (supersonic combustion ramjets). They aren't ready for use yet.
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Re:Carefully (Score:5, Informative)
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 [utoronto.ca], 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-
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Now we know why... (Score:2, Funny)
Re: (Score:2)
Why NASA? (Score:2, Interesting)
Re:Why NASA? (Score:5, Funny)
But it certainly sounds like mission creep for JAXA, which is supposed to be more focused on Gundam-style robots.
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Re:Why NASA? (Score:4, Insightful)
The big advantage would be to allow supersonic or hypersonic flights over continental landmasses. While it doesn't help the main issue of economics, it opens the business possibilities for cross country high-speed flights. Where I see this really opening up possibilities is hypersonic flight (M > 4~5) since the drag drops back down to subsonic levels, making fuel economy on par with the current crop of jet liners. Of course all the hypersonic combustion (scramjet) issues and the heating issues are still uhh, very non-trivial. I hate to know what a fleet of jets with titanium tipped, actively-cooled wings would cost.
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Re: (Score:3, Funny)
Re:Why NASA? (Score:5, Insightful)
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Geez, that takes all the fun out of it (Score:4, Funny)
Yeah, there goes my 20 million dollar plane.
I mean I never get to see them drop bombs, but at least I get to see them tag and make some booms every once and awhile.
Or... (Score:2)
And yes, I am bitter that aviation has been sanitized to the point where its magic and glory are consigned to a Golden Age decades ago.
The hell you can't hear the double boom! (Score:5, Interesting)
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
Re:The hell you can't hear the double boom! (Score:5, Funny)
You're only hearing one boom from the fighter jet. The second boom is caused by the experimental invisible flying saucer made from area 51 technology that is following all of the "conventional" planes. They do it that way so that all you observant but non-clearanced folks on the base won't be suspicious.
Also, while everyone knows that UFOs don't create sonic booms, they haven't figured out that part of the technology yet. That's why NASA is pre-announcing this technology, so that when they finish it people won't be alarmed that suddenly all the super-sonic jets are silent.
Duh.
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Shh, better not tell Capcom! (Score:4, Interesting)
ajax? (Score:2)
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this is not quite new (Score:4, Informative)
Would be nice if they got the facts right (Score:5, Insightful)
And supersonic air travel did not pay when oil was $20 a barrel, how can it ever pay at $120 ?
And there seems to be some insurmountable obstacles in softening up a sonic boom-- you've already exhausted all options by traveling faster than the air can move out of the way....there's no t much wiggle room or time left.
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I think that rocket planes are the way to go (Score:5, Interesting)
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.
Re:I think that rocket planes are the way to go (Score:5, Funny)
Fine for sturdy cargo, but your common slob (such as myself) could NOT withstand that kind of acceleration. You'd have to make people pass physical fitness tests for insurance purposes... plus you'd have to distribute protective codpieces so that your male passengers wouldn't be scraping their balls off their shoes.
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Re:I think that rocket planes are the way to go (Score:4, Informative)
In orbital dynamics, it's often called an impulse, as you are not powered most of the time, compared to powered flight, which requires constant thrust.
One thing that might be a problem is that you probably wouldn't be able to leave your seat the whole time. Maybe they would put depends in with the barf bags.
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Does a bullet make a sonic boom? (Score:3, Interesting)
Re:Does a bullet make a sonic boom? (Score:5, Informative)
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Re:Does a bullet make a sonic boom? (Score:4, Informative)
Also, how are you sure that the aircraft you claim to have seen were indeed supersonic? I've heard a real one (and many recreated F-18 and Concorde ones in Gulfstream's sonic boom demo trailer), you definitely notice it.
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Re: (Score:3, Informative)
Supersonic bullets (for there are subsonic ones too) make shock waves, just like anything else going supersonic. They do produce a little sonic boom, too. From most accounts that I've read, it sounds like a small "crack!" as said bullet travels by. In order to observe this, I expect that you need to be a nontrivial distance from the gun that fired it, so tha
Where's the kaboom? (Score:4, Funny)
Re: (Score:2, Interesting)
rimshot (Score:5, Funny)
It goes "ba-boom". The two booms are far enough to be perceived as distinct but still close enough together to be one event.
Now if it knocks over something metallic it goes "ba-boom, CHING!"
(Thank you, thank you. I'll be here all week...)
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Re: (Score:3, Funny)
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It sounds like moose and squirrel were thwarted. Unfortunately for the Russians Comrade Badenov developed capitalistic streak and did not deliver formula on to glorious Air Force
Re:Go home and be a family man. (Score:5, Funny)
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Re: (Score:3, Interesting)
Then if you consider the drop in efficiency due to the serious amount of drag that would add, and the increase in fuel consumption, it wouldn't be viable to have a rounded craft in atmosphere.
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