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NASA Space Technology

NASA Wants to Take the Blast Out of Sonic Booms 187

Posted by ScuttleMonkey 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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NASA Wants to Take the Blast Out of Sonic Booms More

NASA Wants to Take the Blast Out of Sonic Booms

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  • The Right Stuff (Score:5, Insightful)

    by Ethanol-fueled ( 1125189 ) * on Friday May 09, 2008 @04:22PM (#23355488) Homepage Journal
    Hmmph. I recommend reading Tom Wolfe's The Right Stuff [wikipedia.org], which contains much factual(and entertaining) data about test-flying in the era of the original space-race, to include much first-hand data about supersonic flying in the upper atmosphere(hint: it's much more dangerous than it sounds). Come on, Nasa & JAXA: find some folks with the right stuff and concentrate on long-term space station and moon missions. Don't piss away our taxpayer dollars exploring something that's already well-known! Who gives a fuck if China has stealth and who gives a fuck of ours is better than theirs! Should we all go to war, we'll be fucked by nukes anyway. Can't we just have a healthy space-race(V 2.0) pissing contest?

    • Re:The Right Stuff (Score:5, Insightful)

      by WinPimp2K ( 301497 ) on Friday May 09, 2008 @04:29PM (#23355566)
      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).

    • Re:The Right Stuff (Score:5, Insightful)

      by geekoid ( 135745 ) <{moc.oohay} {ta} {dnaltropnidad}> on Friday May 09, 2008 @04:30PM (#23355580) Homepage Journal
      um, being able to take the 'Boom' out of the sonic boom would mean supersonic transport will be a reasonable option.

      • http://www.apg.jaxa.jp/res/stt/0a01.html [apg.jaxa.jp]

        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?

        • Re: (Score:2, Funny)

          by Anonymous Coward
          ...says the advocate of Ethanol.

        • Re: (Score:2)

          by geekoid ( 135745 )
          There is a difference between in R&D and Vapourware. There not saying it's built, there saying there going to research it. Maybe it will get built, but it is an interesting design.

          Of the thing was built, you wouldn't need a joint JAXA/NASA program for this vehical.

      • Re: (Score:3, Insightful)

        by TubeSteak ( 669689 )

        um, being able to take the 'Boom' out of the sonic boom would mean supersonic transport will be a reasonable option.
        You let me know when they resolve that fuel efficiency problem.

        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.
        • The real costs is not speed, but speed in atmosphere. Simply move up to about 70-80K' i.e. same area as SR-71. That sounds hard, but realistically, it is not only possible, but the only way to do it.

          • Re: (Score:2)

            by Nimey ( 114278 )
            That would require the passengers to wear pressure suits, not so?

      • Re: (Score:2)

        by Nimey ( 114278 )
        Except for the increased fuel usage. Bit of a concern these days.

    • Re: (Score:2)

      by AK Marc ( 707885 )
      Someday I'll have to read some accounts and see if my uncle's stories are true. Apparently, he is the first American to survive traveling over the speed of sound. The story goes that in a test flight, there was a fatal malfunction. The aircraft was out of control and diving, passing the speed of sound. The pilot and navigator ejected. The navigator and tail became one, with dire effects on both, the pilot survived, and lives to tell the tale. That Chuck guy gets credit because he intended to break the

  • Carefully (Score:4, Interesting)

    by Anonymous Coward on Friday May 09, 2008 @04:23PM (#23355496)
    How do you make an engine where the supersonic airflow doesn't damage the compressor parts? Carefully.

    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.

    • Re: (Score:2, Interesting)

      by WinPimp2K ( 301497 )
      Actually, there was an old sci-fi parody story about how to build a supersonic aircraft that was able to cancel out it's own shockwave. Naturally there were certain engineering hurdles to overcome - most notably that the airframe design had to produce zero lift. Brownie points to anyone who can name the stpry and the author

    • Re: (Score:2)

      by mbone ( 558574 )
      There was an old series of drawings of "the airplane as seen by [various engineers]." The aircraft as seen by the propulsion engineers was of course entirely one big engine.
    • I've always been curious about this.
      If you must have a compressor, why not have a big, divergent duct, that slows the air down to subsonic speeds before it hits the compressor? Does the shockwave in the intake make the airflow too turbulent for the compressor blades to handle? Is there a huge drag?
      But if you can go that fast, why bother with a compressor, aside from using it to accelerate for takeoff? Just use a ramjet, no moving parts, who cares how fast it goes (as long as you can still get the fuel mi

      • Re:Carefully (Score:5, Informative)

        by rcw-work ( 30090 ) on Friday May 09, 2008 @06:08PM (#23356464)

        But if you can go that fast, why bother with a compressor, aside from using it to accelerate for takeoff? Just use a ramjet, no moving parts, who cares how fast it goes (as long as you can still get the fuel mixed into the air before it's out the back.)

        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.

      • Re:Carefully (Score:5, Informative)

        by AikonMGB ( 1013995 ) on Friday May 09, 2008 @06:33PM (#23356698) Homepage

        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-

    • Re:Carefully (Score:5, Interesting)

      by rspress ( 623984 ) on Friday May 09, 2008 @05:44PM (#23356244) Homepage
      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!

      • Re: (Score:2, Interesting)

        by splashbot ( 1179993 )
        I think that the engine that experienced a brief exposure to supersonic flow got a sudden 'decrease' in engine thrust, and the pilots threw their heads onto the side that was opposite to the malfunctioning engine. Can an actual areo engineer confirm my theory?

    • The tricky part is adding the parts of the airplane the give lift and space for pilots to sit.
      This is basically what they did with the SR-71.
      What do you see when you look at an SR-71? Two enormous engines, and a little bit of stuff in between. That's the Tim "the Tool Man" Taylor school of engineering: More Power!

  • Now we know why... (Score:2, Funny)

    by Anonymous Coward
    Guile was dropped from Street Fighter II sequels. There's just no more blast in his sonic boom.

  • Why NASA? (Score:2, Interesting)

    by VeNoM0619 ( 1058216 )
    Why NASA...? Why not the DOD, this sounds more suited for a stealth plane.

    • Re:Why NASA? (Score:5, Funny)

      by DriedClexler ( 814907 ) on Friday May 09, 2008 @04:31PM (#23355594)
      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.

    • Re:Why NASA? (Score:4, Insightful)

      by Nyeerrmm ( 940927 ) on Friday May 09, 2008 @04:42PM (#23355714)
      A supersonic plane is already pretty stealthy sound-wise until its already gone over you. The Mach cone extends behind the vehicle so that you'll only hear it after its passed you, at which point if you care that its there its probably too late.

      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.
      • hate to know what a fleet of jets with titanium tipped, actively-cooled wings would cost.

        $72 million for 3 such jets in 1993 [wikipedia.org].

      • Since you seem to know what you're talking about, thought you'd be interested in some research being done at UTIAS:

        1. High-Speed Vehicle Propulsion Systems [utoronto.ca]
        2. Shock-induced Combustion Ramjet (schramjet) [utoronto.ca]

        Aikon-

      • Re: (Score:2, Informative)

        by icebrain ( 944107 )

        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.

        I think you're confusing drag with the drag coefficient. The Cd may go down, but total drag is still much higher (since drag is proportional to the square of airspeed.

        Thus the simplified example: assuming constant Cd and TSFC, doubling speed results in four times the drag --> four times the thrust --> four times the fuel consumption (per time unit). Now, you're going twice as far, but burning four times the fuel, and so your effective "MPG" is half that of the slower speed.

        Assuming that Cd does in

        • Fair enough, I was just going off graphs I remember seeing a few years ago in my aerodynamics courses. I'm more focused on spacecraft dynamics and those kind of things now, so I'm going to guess you know more than me.

    • Re: (Score:3, Funny)

      by pilgrim23 ( 716938 )
      NASA is where the budget was available. Oh you mean you thought NASA did SPACE exploration? the first A stands for Aeronautics..... and the last A stands for committee meetings

  • Geez, that takes all the fun out of it (Score:4, Funny)

    by baggins2001 ( 697667 ) on Friday May 09, 2008 @04:28PM (#23355554)
    Where is the fun in that. I kind of like hearing one of those guys step on it a little to hard over New Mexico and Texas.
    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.
  • If we weren't such a nation of whiners we could just enjoy the majesty that comes with sonic booms, and remember that there is more to aviation than riding the cattle-car from Duluth to Sioux Falls.

    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)

    by PhantomHarlock ( 189617 ) on Friday May 09, 2008 @04:38PM (#23355662)
    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

    • Re:The hell you can't hear the double boom! (Score:5, Funny)

      by Chris Burke ( 6130 ) on Friday May 09, 2008 @05:16PM (#23356022) Homepage
      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.

      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.

  • Shh, better not tell Capcom! (Score:4, Interesting)

    by r_jensen11 ( 598210 ) on Friday May 09, 2008 @04:44PM (#23355730)
    The last thing NASA needs is the USAF's Guile [wikipedia.org] to come after them.

  • coondoggie writes to tell us that NASA and JAXA (the Japan Aerospace Exploration Agency)
    Did anybody else read that as AJAX on the first pass?

  • this is not quite new (Score:4, Informative)

    by emagery ( 914122 ) on Friday May 09, 2008 @04:57PM (#23355846)
    They've been working on this for a while, actually: See - http://www.nasa.gov/vision/earth/improvingflight/supersonic_jousting.html [nasa.gov] That particular project was wrapped up.. but maybe the plan to expound upon it =)

  • Would be nice if they got the facts right (Score:5, Insightful)

    by Ancient_Hacker ( 751168 ) on Friday May 09, 2008 @04:58PM (#23355854)
    Going up a few floors does not change the air pressure by a few PSI. They got that wrong, by a factor of nearly 100.

    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.

    • Re: (Score:3, Insightful)

      by Anonymous Coward
      The OP said pounds per square foot, not PSI.

      • Re: (Score:2)

        by Nimey ( 114278 )
        Why are we using those ridiculous units, anyhow? Nothing wrong with kilopascals.

        • Re: (Score:3, Funny)

          by ceoyoyo ( 59147 )
          NASA likes to use weird units. They find it makes collaborating with the rest of the world more exciting.

    • Re: (Score:2, Informative)

      by Skeptical1 ( 823232 )
      Blurb said pounds/square FOOT. About a factor of 144.

  • I think that rocket planes are the way to go (Score:5, Interesting)

    by mbone ( 558574 ) on Friday May 09, 2008 @05:00PM (#23355876)
    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.

    • 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.

      The SR-71 is also huge. Though a poster above says they live on Edwards Air Force Base and it's not true that you can only hear one boom most of the time.

      But yeah, sound is a form of wasted energy. Pretty inconsequential though in comparison to everything else going on in that amazing flight I would imagine.

      That's why,

    • Re:I think that rocket planes are the way to go (Score:5, Funny)

      by Red Flayer ( 890720 ) on Friday May 09, 2008 @05:23PM (#23356082) Journal

      One ballistic impulse of 7 km / sec or so to get up above the atmosphere and on your way is...
      a great way to make your jaw come out your ass?

      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.

      • Re:I think that rocket planes are the way to go (Score:4, Informative)

        by mbone ( 558574 ) on Friday May 09, 2008 @05:35PM (#23356192)
        I was being sloppy. An acceleration of 2 g's for 10 minutes or so would suffice. It's just, once you get going, the engine turns off.

        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.

      • Re: (Score:2)

        by 4D6963 ( 933028 )

        a great way to make your jaw come out your ass?

        Do you know that in the initial stage of Saturn V's flights the acceleration didn't exceed 1.14 G? And I know from making a pretty basic solar system/space rocket simulator that using such and acceleration you can easily reach the required 10.8 km/s required to go to the Moon while hovering over Earth's atmosphere. My point being, you undoubtedly can go into orbit without even coming close to 1.2 Gs.

      • One ballistic impulse of 7 km / sec or so to get up above the atmosphere and on your way is...

        a great way to make your jaw come out your ass?

        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....

        You make it sound like that's such a bad thing. If more people were in good enough of shape to be astronauts (not that they'd have to actually be an astronaut), health-care costs would plummet. On the other hand, it would make going out with fit birds a hell of a lot harder, what, with all the competition

  • The slashdot summary repeats a statement that I've heard elsewhere, which is that the delay between the leading and trailing booms is altitude-dependant, i.e., the opening angle of the trailing cone is smaller than the opening angle of the leading cone. Does anyone have a good explanation of why this is true? Naively I'd expect the opening angle for both cones to be the same, and given by tan-1(c/v). If that was the case, then the delay between the leading and trailing booms would always be extremely short
    • I don't want to karma-whore by pasting the wikipedia article in here, but it is actually very informative.

      http://en.wikipedia.org/wiki/Sonic_boom [wikipedia.org]

      One thing that never occurred to me is that at high enough speed/altitude, the shock wave won't intersect with earth's surface: Voila, no sonic boom (on the ground, anyways).

      Maybe that is where NASA is headed with this research.

      -b
  • I'd love to see somene figure out how to take the noise out of exceeding the speed of sound. Maybe then we'd be able to fly a palatable SST.

    But, please, not with engines like the Concorde. I lived for a while west of London, down the road a bit from Heathrow. The Concorde flew over my house a lot, just after takeoff. It was probably only doing about 300 mph or so, but, holy moly, was it loud! Can't-talk-on-the-telephone loud. I'll take a sonic boom or two any day in preference to that racket.

    • Re: (Score:2)

      by rcw-work ( 30090 )

      But, please, not with engines like the Concorde.

      Sorry, but there are (likely insurmountable) technical problems with using modern jetliner turbofan engines at supersonic speeds.

      Those turbofans are sort of like a Concorde's turbojet but with a much larger ducted fan bolted onto the front. Some air from this fan is compressed, combusted, and exhausted, but most is simply blown backwards. The ratio of blow to burn is called the bypass ratio [wikipedia.org]. The exhaust stream is big, slow, and cool instead of small, fas

  • Does a bullet make a sonic boom? (Score:3, Interesting)

    by Brad1138 ( 590148 ) * <brad1138@yahoo.com> on Friday May 09, 2008 @06:03PM (#23356420)
    Just a couple days ago my son asked me if a bullet makes a sonic boom? (for the record I don't own a gun) I thought about it for a sec. and came to the conclusion that it probably doesn't or it makes a VERY small one. A bullet is traveling at faster then the speed of sound almost instantaneously. There would be no time for sound to build up in front of it, That was my thought anyway. I don't see a way to help NASA with that info but was an interesting question.

    • Re:Does a bullet make a sonic boom? (Score:5, Informative)

      by onkelonkel ( 560274 ) on Friday May 09, 2008 @06:15PM (#23356518)
      You seem to be labouring under the common misconception that a sonic boom is caused when an object "breaks the sound barrier". As long as an object is moving through the air at greater than the speed of sound it will create a shock wave (cone shaped, think of a boat wake rotated in 3-d) behind it. As the object flies by you, the shock wave passes you and you hear the "sonic boom" So the answer is yes, bullets have a sonic boom.
      • You may be correct but I have always heard/believed that the sonic boom was a single event happening as an object passes the speed of sound (and I am a bit of a Discovery chan junky). I have seen planes fly by at greater than the speed of sound and heard no sonic boom, they are loud but not that loud.
        • http://en.wikipedia.org/wiki/Sonic_boom [wikipedia.org] The shockwave follows the supersonic object. As it passes you, you hear the boom.

          Not really wanting to be all argumentative, but if you saw planes fly by at greater than the speed of sound you would most definitely hear the boom. It is apparently loud enough to rattle windows and sometimes break them. Odds are the aircraft you saw were not flying faster than the speed of sound. They don't do it very often over inhabited places.

        • Re:Does a bullet make a sonic boom? (Score:4, Informative)

          by icebrain ( 944107 ) on Friday May 09, 2008 @07:21PM (#23357080)

          You may be correct but I have always heard/believed that the sonic boom was a single event happening as an object passes the speed of sound (and I am a bit of a Discovery chan junky). I have seen planes fly by at greater than the speed of sound and heard no sonic boom, they are loud but not that loud.
          You might watch the Discovery channel, or even stay at the Holiday Inn Express... but I'm an aerospace engineer. GP is right; the boom is not a singular event, but rather it's the perceived sound when the "wake" of the shockwaves passes by the observer.

          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.

      • Re: (Score:2)

        by mbone ( 558574 )
        Yes, if it is supersonic.

      • Re: (Score:2)

        by mortonda ( 5175 )

        So the answer is yes, bullets have a sonic boom.
        Well, it depends on the bullet. They make "subsonic" rounds, which implies that supersonic rounds are the norm.

        Subsonic rounds are somewhat more stealthy, useful for silenced (suppressed) weapons. That "zing" you here on tv when a silenced weapon is used? Totally fake.
    • Yes, bullets make sonic booms, they're just not very loud because a bullet is such a small object.

    • Re: (Score:2)

      by Anpheus ( 908711 )
      The difference between supersonic rounds and non-supersonic rounds is audible.
      • I looked up bullet speed online and everyone I found was multiple times the speed of sound, I think only a BB or pellet gun is subsonic.

        • Re: (Score:2)

          by Anpheus ( 908711 )
          Not true, most small arms, non rifles, I think are very close to subsonic or in the "transonic" area of mach 1, give or take a dozen m/s. I just looked up one counter example, and some .45 ACP cartridges, according to Wikipedia, are at around 270m/s. That's 30m/s below the speed of sound, depending on other factors.

    • There would be no time for sound to build up in front of it
      I didn't know sound had mass.

    • Re: (Score:2)

      by rmm4pi8 ( 680224 )
      Oh, bullets definitely have a sonic boom. That's the "crack" noise you hear. A lot of people think that's the explosion of the powder, but that's false--modern white powder just burns very rapidly, it does not explode. This is why "silenced" weapons not only have "silencers" on the end of the barrel to diffuse the gases so they don't expand into the air so rapidly, they also use special subsonic ammunition.

    • Re: (Score:2)

      by Nimey ( 114278 )
      Yes, but only with higher-powered ones that are supersonic. Most pistol rounds are subsonic.

      With a high-powered rifle like my K31, you get a bang from the burning gunpowder, and another from the bullet. A silencer (more accurately a suppressor) can only help with the gunpowder bang.
  • Unless I'm really confused here, this doesn't make a lot of sense. What is this fella trying to say?

    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.

    Atmospheric pressure at sea level is only 15 PSI. If you experience a "few" PSI pressure change going from ground floor to the 3rd floor, either you're underwater or your floors are thousands of feet high.

    • Re: (Score:3, Informative)

      by td ( 46763 )
      A few pounds per square foot is a few hundredths of a pound per square inch. 14 psi + 1 lb/sq ft is 14.007 psi.
  • 1. Get some HUGE speakers and subwoofers, extremely powerful electromagnet driven ones that can mimic a sonic boom. 2. Get a mic or sound pickup that can pickup every audible frequency crystal clear, even at high volumes. 3. Engineer a FAST device/chip that can take input with crystal clear mic pickups and quickly phase shift the picked up sound 180 degrees. Have it IMMEDIATELY play this phase shifted sound in the direction of the oncoming sound. 4. Profit.
  • http://www.gulfstream.com/news/releases/2005/051108d.htm [gulfstream.com] Gulfstream is working on reducing sonic booms. If the decibel level is brought low enough, it could pave the way for supersonic domestic/private flights over US soil.

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