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NASA Wants to Take the Blast Out of Sonic Booms

ScuttleMonkey posted more than 5 years ago | from the softer-side-of-soar dept.

NASA 187

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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187 comments

It must be asked (1, Funny)

Anonymous Coward | more than 5 years ago | (#23355486)

So the shuttle goes boom boom?

Re:It must be asked (2, Interesting)

dwiget001 (1073738) | more than 5 years ago | (#23355630)

I lived in Bakersfield, CA, in the 1970's when the shuttle was being tested. It's glide path many times took it right over head, enroute to Edwards. And yes, it has two very distinct sonic booms. Loud ones, at least at that range and altitude.

rimshot (4, Funny)

Ungrounded Lightning (62228) | more than 5 years ago | (#23356108)

So the shuttle goes boom boom?

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...)

Re:It must be asked (2, Interesting)

rspress (623984) | more than 5 years ago | (#23356190)

So does the SR-71 or at least it used to. I live in the flight pattern for beale air force base and have for many years. Back in the 70's SR-71's and their T-38 chase planes and U-2's filled the air. Even being 25 miles away the SR-71 doing an engine run up would make the air rumble. Sonic Booms were part and parcel as well. Now we only get the booms of the Beale EOD and the Explosions from the gold fields mining near the base. Still the U-2's and T-38's, KC-135's and C-5A's fly by.

The Right Stuff (4, Insightful)

Ethanol-fueled (1125189) | more than 5 years ago | (#23355488)

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 (5, Insightful)

WinPimp2K (301497) | more than 5 years ago | (#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 (3, Funny)

Red Flayer (890720) | more than 5 years ago | (#23355686)

sunborbital ballistic passenger flights... now that would rock(et).
Sunborbital? Is that some new kind of horse tranquilizer? I'm intrigued, and look forward to being tranqued every time I fly.

Re:The Right Stuff (1)

MightyYar (622222) | more than 5 years ago | (#23355922)

look forward to being tranqued every time I fly.
I, too, would prefer a flight that still takes 14 hours but you get stoned out of your gourd.

Take THAT, 3 hour flight to Japan.

Re:The Right Stuff (0)

Anonymous Coward | more than 5 years ago | (#23356246)

Might as well be: Burt Rutan knows more than NASA does.

Re:The Right Stuff (0)

Anonymous Coward | more than 5 years ago | (#23356716)

AerionCorp [aerioncorp.com] is working on a Supersonic business jet with some sort of new laminar flow technology at supersonic speeds that give equal range in both subsonic and supersonic flow fields. I'm not too sure about sonic booms, but it has a speed limit of Mach 0.98 over the US.

Re:The Right Stuff (5, Insightful)

geekoid (135745) | more than 5 years ago | (#23355580)

um, being able to take the 'Boom' out of the sonic boom would mean supersonic transport will be a reasonable option.

Re:The Right Stuff (1)

Ethanol-fueled (1125189) | more than 5 years ago | (#23355726)

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:The Right Stuff (2, Funny)

Anonymous Coward | more than 5 years ago | (#23355756)

...says the advocate of Ethanol.

Re:The Right Stuff (5, Funny)

philspear (1142299) | more than 5 years ago | (#23355998)

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.

Re:The Right Stuff (1)

Kalriath (849904) | more than 5 years ago | (#23356880)

I think he's referring to the fact that GGP is called "Ethanol-fueled" when Ethanol as a fuel source is the biggest vapourware in existence.

Of course the joke isn't funny if it needs explaining. Shame on you.

Re:The Right Stuff (1)

geekoid (135745) | more than 5 years ago | (#23356076)

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:The Right Stuff (2, Insightful)

TubeSteak (669689) | more than 5 years ago | (#23355792)

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.

Lot easier than it sounds (1)

WindBourne (631190) | more than 5 years ago | (#23355928)

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:The Right Stuff (-1)

Anonymous Coward | more than 5 years ago | (#23356264)

The Concorde produced a boom, and it provided supersonic transport.

Unless you're suggesting that somehow removing the "Boom" is going to dramatically alter the economics, which, you know, you have not established.

Re:The Right Stuff (5, Insightful)

Henry V .009 (518000) | more than 5 years ago | (#23356746)

Removing the "Boom" dramatically alters the economics because you can fly it over dense population centers that were banned to Concorde. Happy?

Carefully (4, Interesting)

Anonymous Coward | more than 5 years ago | (#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:Carefully (2, Interesting)

WinPimp2K (301497) | more than 5 years ago | (#23355620)

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:Carefully (1, Interesting)

Anonymous Coward | more than 5 years ago | (#23356534)

Actually that is called the Buseman principle, and it's not fiction. I wonder if the author was aware of it.

Re:Carefully (1)

mbone (558574) | more than 5 years ago | (#23355970)

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.

Re:Carefully (1)

smellsofbikes (890263) | more than 5 years ago | (#23356158)

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 mixed into the air before it's out the back.)

Re:Carefully (4, Informative)

rcw-work (30090) | more than 5 years ago | (#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 (5, Informative)

AikonMGB (1013995) | more than 5 years ago | (#23356698)

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 (5, Interesting)

rspress (623984) | more than 5 years ago | (#23356244)

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!

Now we know why... (2, Funny)

Anonymous Coward | more than 5 years ago | (#23355508)

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

Go home and be a family man. (0)

CrazyJim1 (809850) | more than 5 years ago | (#23355510)

Especially to Chun Li.

Re:Go home and be a family man. (5, Funny)

pablomme (1270790) | more than 5 years ago | (#23355794)

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.

Re:Go home and be a family man. (1)

Chris Burke (6130) | more than 5 years ago | (#23355924)

Hehe, ain't it the truth.
"Phonic poo!"
"Ding-dong kick!"
"Sow dookie!"
"High girl uppercut!"
"Testsoshreaouprhoeu!"

Re:Go home and be a family man. (0)

Anonymous Coward | more than 5 years ago | (#23356150)

You'll have to wait for an article about phonic poo to repost your comment.

Apparently, ask and ye shall receive! [slashdot.org]. Just remember that you must defeat Sheng Long to stand a chance.

Why NASA? (2, Interesting)

VeNoM0619 (1058216) | more than 5 years ago | (#23355516)

Why NASA...? Why not the DOD, this sounds more suited for a stealth plane.

Re:Why NASA? (1)

jsnipy (913480) | more than 5 years ago | (#23355556)

True, then not can you "not see it coming", you won't be able to hear it either :)

Re:Why NASA? (5, Insightful)

Beer_Smurf (700116) | more than 5 years ago | (#23355626)

Actually, at supersonic speeds you wouldn't hear it coming anyway because it would arrive before the sound anyway.

Re:Why NASA? (1)

AikonMGB (1013995) | more than 5 years ago | (#23356730)

Sure, but if you could cancel the shock in such a way that it wasn't heard on the ground, then they wouldn't hear you going either. Sometimes it's good to not be noticed at all, not just on your approach.

Aikon-

Re:Why NASA? (0)

Anonymous Coward | more than 5 years ago | (#23355680)

True, then not can you "not see it coming", you won't be able to hear it either :)

If there's a shock wave and nobody is there to hear it, is there a boom?

Re:Why NASA? (1)

Anonymous Coward | more than 5 years ago | (#23355768)

is there a boom?

No boom today. Boom tomorrow. There's always a boom tomorrow.

Re:Why NASA? (5, Funny)

DriedClexler (814907) | more than 5 years ago | (#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? (1)

DanWS6 (1248650) | more than 5 years ago | (#23355702)

The DOD is a bit preoccupied right now saving the world from the only things worse than sonic booms - terrorists. I'm sure if you could find a feasible threat they'd jump right on this.

Re:Why NASA? (3, Insightful)

Nyeerrmm (940927) | more than 5 years ago | (#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.

Re:Why NASA? (2, Informative)

icebrain (944107) | more than 5 years ago | (#23356906)

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 indeed drop back to subsonic levels, we'd need to see incredible TSFC numbers to be viable. I really don't think that'll happen.

Re:Why NASA? (2, Funny)

pilgrim23 (716938) | more than 5 years ago | (#23355786)

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 (4, Funny)

baggins2001 (697667) | more than 5 years ago | (#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.

What, I have to (0)

Anonymous Coward | more than 5 years ago | (#23355590)

RTFA because no one's posted yet?!?

Now here's something you'll really like! (1)

Chess Piece Face (247847) | more than 5 years ago | (#23355640)

Hush-a-boom

Re:Now here's something you'll really like! (3, Funny)

WinPimp2K (301497) | more than 5 years ago | (#23355718)

Uh oh...

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

Or... (1)

Shadow Wrought (586631) | more than 5 years ago | (#23355660)

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.

Re:Or... (1)

Vectronic (1221470) | more than 5 years ago | (#23355862)

Agreed... to a point...

A nice "boom" (boom) here and there is quite nice, much like a train whistle, further, I even enjoy a Semi air horn, or the Jake Break as it comes down a large hill...

But, considering an airport like J.F.K. has some 800 flights a day (excluding ocean/international ones)... it would become very annoying, this is of course assuming that all public flights had adopted super-sonic methods...

The hell you can't hear the double boom! (5, Interesting)

PhantomHarlock (189617) | more than 5 years ago | (#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! (4, Funny)

Chris Burke (6130) | more than 5 years ago | (#23356022)

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.

this is not quite new (4, Informative)

emagery (914122) | more than 5 years ago | (#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 =)

Re:this is not quite new (1)

icebrain (944107) | more than 5 years ago | (#23356930)

I worked on that--helped build it, actually. Can't comment on where things might be headed from this point, though.

Would be nice if they got the facts right (4, Insightful)

Ancient_Hacker (751168) | more than 5 years ago | (#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:Would be nice if they got the facts right (3, Insightful)

Anonymous Coward | more than 5 years ago | (#23355870)

The OP said pounds per square foot, not PSI.

Re:Would be nice if they got the facts right (0)

Anonymous Coward | more than 5 years ago | (#23356024)

just for reference... it was found the faster the SR-71 flew, the more fuel efficient it actually became. If they used the same principal ramjet technology (which requires high speeds.. just like the SR-71 was "rated" to mach 3 but had been reported to hit 3.3 or faster), you'd be able to obtain good fuel efficiency due to the thrust of the incoming air charge its self along with quick travel times. The sonic boom becomes the limiting factor. Fix that, and bang, fast, fuel efficient air travel.

They have been doing this at area 51 for years (0)

Anonymous Coward | more than 5 years ago | (#23356516)

NASA, like usual, is just a front for slowly introducing technologies to the mainstream that the military has had for 30+ years.. no news here.

Re:Would be nice if they got the facts right (0)

Anonymous Coward | more than 5 years ago | (#23356694)

I think they're talking about the Bernoulli principle or the air pressure change caused by the not-particularly-streamlined elevator moving through through the elevator shaft.

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

mbone (558574) | more than 5 years ago | (#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.

Re:I think that rocket planes are the way to go (1)

Chris Burke (6130) | more than 5 years ago | (#23355978)

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, unless there is some real drag breakthrough, I think that rocket planes are the way to truly fast passenger travel.

Agree. That's the real promise of "space planes" like Space Ship 1-2. Who cares if they can't get to orbit, if they can get to Tokyo from London in a couple hours that'll be good enough.

Re:I think that rocket planes are the way to go (0, Troll)

rahvin112 (446269) | more than 5 years ago | (#23356216)

The SR-71 is also huge.

Clearly you and I have different views of HUGE. The B-52 is HUGE, a 747 is HUGE. The SR-71 is about the width of a 1-1/2 F-16's and the length of about two F-16's tail to nose. It's a remarkably small plane, not even close to the size of your average 737, I'd wager the dimensions are about the same as a 12 seater regional jet. So either you've never seen an SR-71 in person and are full of shit or you have a very very different understanding of "huge" than the rest of the population. I'd recommend you stop by one of the many air force museums around the country that contain SR-71's and inspect their real size because they aren't a HUGE plane.

Re:I think that rocket planes are the way to go (1)

Chris Burke (6130) | more than 5 years ago | (#23356436)

Clearly you and I have different views of HUGE. he B-52 is HUGE, a 747 is HUGE.

Yes. Mine is with respect to supersonic air craft, the thing under discussion, you know with regard to whether or not you will hear one or two sonic booms? A B-52 is tiny compared to an oil tanker, and neither will break the sound barrier, and thus are about equally relevant to the discussion. A B-52 is only 50% longer than an SR-71 anyway; which would make some people, normal people, say that the SR-71 is huge for a supersonic plane.

So either you've never seen an SR-71 in person and are full of shit or you have a very very different understanding of "huge" than the rest of the population. I'd recommend you stop by one of the many air force museums around the country that contain SR-71's and inspect their real size because they aren't a HUGE plane.

I've seen a SR-71 in person, fuck you very much, the museum in my home town acquired one. It dwarfed the F-14 sitting right next to it, which non-dipshits think is pretty damn big for a supersonic plane. Which makes the SR-71 huge.

"The rest of the population" knows that words like "huge" are relative. And when you're talking about something that does Mach 3, most people don't put that in the same category as a 747. So I recommend you remove the stick from your ass.

Re:I think that rocket planes are the way to go (1)

4D6963 (933028) | more than 5 years ago | (#23356572)

words like "huge" are relative

Huge is a very relative word indeed! I learnt that when I spent a few weeks in Japan (what's the appropriate onomatopoeia here? Zing?).

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

Red Flayer (890720) | more than 5 years ago | (#23356082)

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 (3, Informative)

mbone (558574) | more than 5 years ago | (#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:I think that rocket planes are the way to go (1)

4D6963 (933028) | more than 5 years ago | (#23356738)

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.

Do Saucer shapes make sonic booms? (1)

NetNinja (469346) | more than 5 years ago | (#23355918)

Seriously,

Do circular objects make sonic booms?

Re:Do Saucer shapes make sonic booms? (2, Interesting)

mog007 (677810) | more than 5 years ago | (#23355968)

Considering it's the aerodynamics that cause sonic booms in the first place, I would think a rounded craft would make a louder boom.

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.

why the altitude-dependance? (1)

bcrowell (177657) | more than 5 years ago | (#23356148)

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 (tens of milliseconds). That's not the case, so what's the more complicated effect that's going on here? Something to do with nonlinearity of sound waves?

SST's: Damn Noisy Things (1)

reallocate (142797) | more than 5 years ago | (#23356316)

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:SST's: Damn Noisy Things (1)

rcw-work (30090) | more than 5 years ago | (#23356682)

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, fast, and hot - that's why they are so much quieter.

High bypass-ratio turbofans can't go supersonic because the tip speed of the fan blades must stay subsonic for the fan to work. Also, the incoming air must be subsonic before it hits the fan blades - this requires long inlet ducts, not the short ring you see around a jetliner's fan.

Does a bullet make a sonic boom? (2, Interesting)

Brad1138 (590148) | more than 5 years ago | (#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? (1)

427_ci_505 (1009677) | more than 5 years ago | (#23356456)

That bang you hear from a rifle, is a bullet passing the sound barrier, is it not?

Re:Does a bullet make a sonic boom? (1)

Brad1138 (590148) | more than 5 years ago | (#23356580)

That bang you hear from a rifle, is a bullet passing the sound barrier, is it not


It could be but I kinda figured it was the explosion of the gun powder

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

onkelonkel (560274) | more than 5 years ago | (#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.

Re:Does a bullet make a sonic boom? (1)

Brad1138 (590148) | more than 5 years ago | (#23356706)

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.

Re:Does a bullet make a sonic boom? (1)

onkelonkel (560274) | more than 5 years ago | (#23356824)

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? (1)

Chris Burke (6130) | more than 5 years ago | (#23356560)

Yes, bullets make sonic booms, they're just not very loud because a bullet is such a small object.

Re:Does a bullet make a sonic boom? (1)

Anpheus (908711) | more than 5 years ago | (#23356578)

The difference between supersonic rounds and non-supersonic rounds is audible.

Re:Does a bullet make a sonic boom? (1)

Brad1138 (590148) | more than 5 years ago | (#23356612)

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:Does a bullet make a sonic boom? (0)

Anonymous Coward | more than 5 years ago | (#23356770)

http://www.google.com/search?q=subsonic+ammo

Most ammo will be supersonic, but they do make some ammo to specifically stay subsonic. And if you're using a gun with a suppresor it's even quieter when paired up with the subsonic ammo.

Re:Does a bullet make a sonic boom? (1)

Anpheus (908711) | more than 5 years ago | (#23356802)

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.

Re:Does a bullet make a sonic boom? (1)

Cosmic AC (1094985) | more than 5 years ago | (#23356766)

A bullet traveling faster than the speed of sound most certainly does have a sonic boom, or "crack" as it's called.

Re:Does a bullet make a sonic boom? (1)

Mopatop (690958) | more than 5 years ago | (#23356924)

Your son is a smart cookie - it is a sonic boom. This is why most silencers on rifles depicted in films/games are completely wrong. Suppressors only soften the sound of the gunpowder explosion, however most rifles shoot bullets which travel at supersonic speeds. The sound of the sonic boom is what most people associate with a gunshot. That's why it sounds like a crack.

You cannot silence supersonic bullets (yet).

Re:Does a bullet make a sonic boom? (1)

rmm4pi8 (680224) | more than 5 years ago | (#23356934)

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.

Underwater maybe? (1)

argent (18001) | more than 5 years ago | (#23356872)

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.
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