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."

Comments

It must be asked

[Anonymous Coward]

So the shuttle goes boom boom?

Re:It must be asked

[dwiget001]

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.

Re:It must be asked

[rspress]

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.

Re:It must be asked

[9Nails]

Yes. Followed by a chorus of "honk, honk, honk" and "errr, EEEE, errr, EEEE, pew, pew, pew, whooOOP, whooOOP, anh, anh, anh, anh." Its noting that you can dance to, but exciting all the same.

Re:It must be asked

[rubeng]

Really? it went supersonic during drop tests? I'm skeptical, but if someone knows more, I'd be interested to hear about it.

Re:It must be asked

[rts008]

Have you been playing Fallout2 and got the CyberDog and Brainbot for your NPC's?

If not, then WTF?!?!? are you talking about?

Re:It must be asked

[SpinningCone]

perhaps he lives next to Michael Winslow?

The Right Stuff

[Ethanol-fueled]

Hmmph. I recommend reading Tom Wolfe's The Right Stuff, 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

[WinPimp2K]

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

[geekoid]

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

[Red Flayer]

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

[Ethanol-fueled]

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

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

[Anonymous Coward]

...says the advocate of Ethanol.

Re:The Right Stuff

[TubeSteak]

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.

Re:The Right Stuff

[moderatorrater]

It's better than dealing with the airlines.

Re:The Right Stuff

[MightyYar]

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

[philspear]

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

[geekoid]

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

[Anonymous Coward]

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

Re:The Right Stuff

[Anonymous Coward]

AerionCorp 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

[Henry V .009]

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

Re:The Right Stuff

[Kalriath]

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

[CodeBuster]

Where are my mod points when I need them? I am falling out of my chair laughing....hahaha MOD THE PARENT UP

Re:The Right Stuff

[The Master Control P]

Unfortunately, that doesn't mean much since being raped in the ass and mouth by your gyro-car's controls is also (slightly) less painful than dealing with the airlines.

/South park FTW

Re:The Right Stuff

[AK Marc]

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 sound barrier and managed to do so and not spend a month in the hospital after. But I give the family disclaimer, this was told by one family member to another, so this could be just as true as my other uncle who would pull his thumb off his hand, or steal my nose repeatedly.

Re:The Right Stuff

[Nimey]

Except for the increased fuel usage. Bit of a concern these days.

Re:The Right Stuff

[rbanffy]

Well... I am not sure where you intend to go, but I have been using ethanol in cars for the past two decades. Of my last, say, 10 cars, 9 ran on ethanol.

Re:The Right Stuff

[Foolicious]

I do, for one. Just to answer your question. I care about stealth.

The reason stealth is handy and needs to be, well, the stealthiest, is so you won't end up going to war in the first place. But anyways, where'd all the "Right Stuff" test pilots (Yeager,Crossfield,etc) come from? Where'd the Mercury Seven come from? They were all military pilots. If you want to send people to space and the moon, that's fine. But it's foolish and obtuse to act like arms/weapons/military development and space development are somehow mutually exclusive. Maybe, just maybe, they've a symbiotic relationship and they benefit each other.

Re:The Right Stuff

[drsquare]

Having the Concorde being made by America would have solved the 'problem' just as easily. Had Boing come up with a super-sonic plain, you bet your arse it would have been allowed to fly over American corn fields.

Re:The Right Stuff

[Jeff DeMaagd]

The cost of fuel and the cost of developing a new transport is still a concern. Air travel is very price sensitive. Would you pay an extra $1000 for a transatantic flight, to save a few hours? Concorde flyers spent $10,000 a trip and I think the airline still lost money on occasion. These are the same airliners that bought half their Concordes for $1 a piece because no one else wanted them, so even with the cost of the plane cut in half, they still had a hard time making money. The 9/11 tragedy is what killed Concorde, because enough of the Concorde's customer base died that day, or the business collapsed.

Re:The Right Stuff

[Anonymous Coward]

Well, the Bell X-1 exceeded the sound barrier on October 14th, 1947. At this time only Swedish or German production aircraft had ejection seats.

Re:The Right Stuff

[Steve Max]

We've been using ethanol without problems here in Brazil for decades. Almost all new cars sold here can use either ethanol or gas. Every gas station has a 50-50 split on gas/ethanol pumps. Ethanol is way cheaper than gas (at least while the sugar cane production is not at its low point), cheap enough to compensate for the lower energy density; and that is without any government subsidies. The US program may be a failure due to the use of corn, but ethanol as a fuel source is very far from vapourware.

Re:The Right Stuff

[c6gunner]

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.

Sorry to break it to you, but unless your uncle's name is George Welch, he's probably full of shit.

Carefully

[Anonymous Coward]

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 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

[WinPimp2K]

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

[mbone]

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

[smellsofbikes]

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

[rspress]

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:Carefully

[rcw-work]

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

[Anonymous Coward]

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

Re:Carefully

[AikonMGB]

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-

Re:Carefully

[splashbot]

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?

Re:Carefully

[Wonko the Sane]

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!

Re:Carefully

[smellsofbikes]

That answered a *lot* of my questions, actually. Thanks.

Re:Carefully

[the_other_chewey]

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?

IANAAE ;-) - but I just recently read Ben Rich's book about his time at Lokheed's Skunk Works
(he ended up managing the place) - you are basically right, the affected engine's thrust decreased dramatically.

This issue was internally called an "unstart" of the engine. It wasn't however a simple "accidental thrust
vectoring": The pilots would be thrown all over the cockpit, often unable to tell which engine was affected.
During test flights, the pilot would sometimes guess wrong and switch off the good engine, getting himself in
some pretty uncomfortable situations.

The problem was never solved for good. A workaround was implemented as a firmware upgrade (seriously!) and did
do the trick: If an engine was detected to have "unstarted", the electronics would do the same to the other engine -
thereby retaining thrust symmetry - and then ramping both engines up again together.

Pilots mostly didn't even notice an unstart had happened from there on.

Now we know why...

[Anonymous Coward]

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

Re:Now we know why...

[Chris Burke]

*whispers* sonic boom...

Re:Now we know why...

[Spy der Mann]

Meanwhile, in a wind tunnel in a NASA facility...

- But Sir, this is the 24,723th time, I can't do it any more!
- JUST KEEP FIRING, SOLDIER!
- *gasp* Sonic Boom!

Go home and be a family man.

[CrazyJim1]

Especially to Chun Li.

Re:Go home and be a family man.

[pablomme]

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.

[Chris Burke]

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.

[Anonymous Coward]

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

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

Why NASA?

[VeNoM0619]

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

Re:Why NASA?

[jsnipy]

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

Re:Why NASA?

[DriedClexler]

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?

[Beer_Smurf]

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

Re:Why NASA?

[Anonymous Coward]

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?

[DanWS6]

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?

[Nyeerrmm]

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?

[Anonymous Coward]

is there a boom?

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

Re:Why NASA?

[pilgrim23]

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

Re:Why NASA?

[silentcoder]

So if the pilot takes his girlfriend up in this thing... is that a babyboom ?

Re:Why NASA?

[statemachine]

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

$72 million for 3 such jets in 1993.

Re:Why NASA?

[AikonMGB]

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?

[Chris Burke]

Didn't you hear? JAXA is not in charge of Gundam.

Re:Why NASA?

[AikonMGB]

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
2. Shock-induced Combustion Ramjet (schramjet)

Aikon-

Re:Why NASA?

[icebrain]

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?

[Technician]

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

Having lived under a flight path before they banned supersonic flights in the US, I remember the double boom from military flights. It is true. You don't hear them comming. A loud sudden Boom Boom like a double thunderclap folowed by the jet roar is the norm. 3 years ago while hiking, I got to experiance it again as a low flying military jet flew over the backwoods. I don't think he was supposed to be supersonic, but it was definately a sonic boom that announced his arrival. I think some pilots just need to check out the craft in unpopulated areas, but often fail the know there are hikers in the area. From low flying aircraft, it's really loud. At least in the 1960's they limited supersonid overland flight to high altitude which softened the bang into a more muffled boom like distant thunder.

Re:Why NASA?

[Nyeerrmm]

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:Why NASA?

[AGMW]

... but it was definately a sonic boom that announced his arrival

... but it was definately a sonic boom that announced his departure.

Re:Why NASA?

[Technician]

... but it was definately a sonic boom that announced his departure.

You haven't been arround sonic booms much have you?

Re:Why NASA?

[hr raattgift]

3000nm flight paths are in the limit of short haul hypersonics mainly because of accelerations, even assuming straight-out/(nearly)straight-up and (nearly)straight-down/straight-in terminal flight profiles to avoid lingering in high drag conditions.

The critical problem is accelerations versus passenger tolerance; reaching TASes in the range of 1.3-1.7e03 m/s and back again at comfortable accelerations (say, < 0.4 m/s^2) will take considerable time (an hour), even assuming a constant acceleration is feasible (it's not, without lots of work on propulsion economics). In flight "kicks" are plausible within limits (people strap in when turbulence is predicted, but swivelling chairs have posed serious interior design -- not decoration! -- problems).

Aggressive acceleration that keeps passengers seatbound throughout a 2 hour flight is unlikely to be very popular unless it's also much cheaper than a traditional transonic flight at about five hours (averaging the jetstream, which is also not really present at economic altitudes for hypersonic transport).

For passenger transport, it is the longest haul flights that are the most attractive, since the biggest gains against subsonic flight are made when the time spent in hypercruise is longest.

It is possible that specific travellers (business people? politicians? 'puter nerds?) might put up with sustained uncomfortable accelerations for marginally faster trans-USA flights, of course, but intercontinental flight seems more attractive.

The big advantage would be to allow supersonic or hypersonic flights over continental landmasses

Like Eurasia and the various populated islands on the "Kangaroo Run", certainly.

However, even considering strictly over-water routes, not leaving a boom carpet across the ocean is going to make for happier environmentalists (and ocean ship crews, especially if numbers of flights start climbing to those experienced on NATs/PACOTs).

the drag drops

Assuming that having to fly at all in the trans-sonic regime (even for short periods) does not add a ridiculous mass penalty (fuel, propulsion system), and that L/D is reasonable enough in subsonic that terminal phases aren't hugely consumptive of fuel, and that great circle routing is straightforward, hypersonic transport should be competitive with foreseeable developments in transonic, ultra-long-haul commercial air transport except in the area of fatter, fuller planes. There is considerable scope for efficiency gain in post-A380 superjumbos, with respect to kg fuel per revenue passenger mile.

(On the other hand, the vast array of "in-flight entertainment" available on steamships did not save the passenger liner industry from the discomforts of early intercontinental passenger aviation, despite the cost, discomfort (noise! yikes!), technical stops, unsurvivable catastrophic accidents, and so forth).

the heating issues are still uhh, very non-trivial

Materials science is one of the critical paths in aviation in all flight regimes. :-)

Probably the biggest problem with hypersonic engineering is that replicating hypersonic flight conditions is, uh, extremely challenging.

There are lots of ideas about metal alloy foams and aerogels, many of which are increasingly cheap and easy to make, but predicting their in-flight behaviours becomes harder and more expensive with increasing Mach number.

Development costs will dwarf manufacturing costs, or it simply won't happen. If the full development costs are rolled into the final products then you would hate to know what a fleet of such jets would cost. That is unlikely to happen though, mainly since it has never happened before. :-) :-) With the hardest development costs paid for through funded academic research and to some degree military application, hypersonic aircraft may (in all likelihood, must) not cost much more than subsonic aircraft, in present value terms of the full capital and running costs.

Re:Why NASA?

[AGMW]

LOL: Yer, sorry! I was under the impression that a sonic boom was caused by something travelling faster than sound, so by the time you heard the boom, whatever caused it had gone ... my bad!

Re:Why NASA?

[Technician]

I was under the impression that a sonic boom was caused by something travelling faster than sound, so by the time you heard the boom, whatever caused it had gone

An object traveling at the speed of sound produces a shockwave that travels from the object at the speed of sound. (may need to read it twice)

As the plane passes overhead, the shockwave reaches the ground at the same time the plane has moved forward the same distance as the distance from the plane to the ground. The plane isn't gone. Look off 45 degrees in the direction of the sound and you will see the plane leaving. It is still high in the sky and not gone. I watched them go lots of times. Sometimes I would see them arriving and wait for the boom.

Re:Why NASA?

[AGMW]

... shockwave that travels from the object at the speed of sound. (may need to read it twice)

Riiiight. So, in essence, you are saying that the shockwave, which takes the form of a sound travels at (and I guess this must be the difficult bit?) the speed of sound. Yep ... a tricky concept indeed.

... Look off 45 degrees in the direction of the sound and you will see the plane leaving ...

LOL ... see the plane leaving kinda suggests its passed? As in No Longer Approaching ? No?

As the plane passes overhead, the shockwave reaches the ground at the same time the plane has moved forward the same distance as the distance from the plane to the ground.

I guess if the plane is travelling at the speed of sound - yes indeedy, and as you say, the sound is travelling down so you can hear it, and, traditionally, planes travel more, well, across. So, and you may want to read this a couple of times, the plane causes a boom whilst above you, and you hear it after the plane has moved the same distance as the distance from the plane to the ground. You will indeed ... see the plane leaving .... So it's gone passed then?

Of course, if the plane is indeed travelling faster than the speed of sound then the departure may be more pronounced, but either way, this is much as I suggested, the sonic boom heralding the departure of the craft that caused it.

Sometimes I would see them arriving and wait for the boom.

OK ... and when would that "boom" be heard? Before they were overhead, or sometime after ... somewhat heralding the departure maybe?

Come on ... admit it ... you don't hear the boom until after the plane has passed (ie is no longer travelling towards) you - unless it is flying at (or V. near) ground level! ... OK ... You could be very tall, or standing on something very tall?

Geez, that takes all the fun out of it

[baggins2001]

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

[Anonymous Coward]

RTFA because no one's posted yet?!?

Now here's something you'll really like!

[Chess Piece Face]

Hush-a-boom

Re:Now here's something you'll really like!

[WinPimp2K]

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...

[Shadow Wrought]

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...

[Vectronic]

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!

[PhantomHarlock]

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!

[Chris Burke]

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!

[r_jensen11]

The last thing NASA needs is the USAF's Guile to come after them.

ajax?

[pak9rabid]

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?

Re:ajax?

[MightyYar]

Yes, tub I'm lysdexic.

Re:ajax?

[Concerned Onlooker]

Yes, but then the second shock wave hit and straightened things around.

this is not quite new

[emagery]

They've been working on this for a while, actually: See - http://www.nasa.gov/vision/earth/improvingflight/supersonic_jousting.html That particular project was wrapped up.. but maybe the plan to expound upon it =)

Re:this is not quite new

[icebrain]

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

[Ancient_Hacker]

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

[Anonymous Coward]

The OP said pounds per square foot, not PSI.

Re:Would be nice if they got the facts right

[Anonymous Coward]

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.

Re:Would be nice if they got the facts right

[Skeptical1]

Blurb said pounds/square FOOT. About a factor of 144.

Re:Would be nice if they got the facts right

[Anonymous Coward]

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.

Re:Would be nice if they got the facts right

[Nimey]

Why are we using those ridiculous units, anyhow? Nothing wrong with kilopascals.

Re:Would be nice if they got the facts right

[ceoyoyo]

NASA likes to use weird units. They find it makes collaborating with the rest of the world more exciting.

Re:Would be nice if they got the facts right

[Anonymous Coward]

No, it doesn't change the PSI, it changes the PSF

FTA: "The change in air pressure associated with a sonic boom is only a few pounds per square foot"

Square foot, not square inch.

1 square foot = 144 square inches?

Re:Would be nice if they got the facts right

[dkf]

And supersonic air travel did not pay when oil was $20 a barrel, how can it ever pay at $120 ? The problem was that nobody ever built large supersonic planes that can fly supersonic on any route. Get the size and flexibility up, and you can make it pay (fuel costs aren't the only factor in running a plane, not by a long stretch). Getting rid of the sonic boom would help that a lot.

Re:Would be nice if they got the facts right

[Anonymous Coward]

No, NASA uses standard metric units. However, when reports call you haven't to convert everything to English units, because that's what American voters demand. Seems also that some NASA contractors believe in English units as well, but NASA itself is entirely metric. I recently heard a story of someone as part of the "better cheaper faster" program buying an off-the-shelf sensor for a satellite and having to adapt it because it was threaded for American screws.

Re:Would be nice if they got the facts right

[swillden]

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.

By a factor of 144, actually. Notice anything interesting about that number?

Re:Would be nice if they got the facts right

[moosesocks]

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 ?

Actually, the Concorde was profitable.

The profits were, however, not great enough for British Airways to feel that it was worth their while to maintain the fleet.

Richard Branson made several offers to resume Concorde service under the Virgin name, although in the end, BA were unwilling to sell the aircraft.

I think that rocket planes are the way to go

[mbone]

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

[Chris Burke]

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

[Red Flayer]

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

[mbone]

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

[rahvin112]

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

[Chris Burke]

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

[4D6963]

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

[4D6963]

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.

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

[r_jensen11]

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

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

[Anonymous Coward]

The X-15 could just make it across Nevada.

http://www.sierrafoot.org/x-15/mission_large.html

The X-30 continued with this research but never had a manned flight.

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

[Anonymous Coward]

you don't need Depends for a 30-40 minutes flight. Commuter flights that take that long are already 20 minutes going upward and then 20 minutes going downward. There's no time when the seatbelt sign goes off.

Unless you mean the "oh shit!" factor of 2g's... then the Depends would have to be put on before getting on the vehicle

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

[thogard]

1.14G? Maybe at liftoff. 7,648,000 lb of force on a 6,699,000 lb (and decreasing) object.
Or after 150 seconds its 42 miles up and 73 nm downrange at 1st stage separation.
Even Wikipedia claims 4G.

Do Saucer shapes make sonic booms?

[NetNinja]

Seriously,

Do circular objects make sonic booms?

Re:Do Saucer shapes make sonic booms?

[mog007]

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.

Lot easier than it sounds

[WindBourne]

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:Lot easier than it sounds

[Nimey]

That would require the passengers to wear pressure suits, not so?

Re:Lot easier than it sounds

[ppanon]

No, it just requires a pressurized cabin. You would need something that can take a little more pressure than your average airliner but not much. Unlike military aircraft, you shouldn't need to worry too much about someone trying to use a cannon to fire rounds into your cabin, leading to explosive decompression.

Re:Lot easier than it sounds

[Jim Starx]

It's got nothing to do with military vs. civilian. Airliners depressurize occasionally. But they fly low enough that simple airmasks can suffice while the pilots do an emergency descent into the range of breathable atmosphere. You fly high enough and an airmask isn't gonna do the trick anymore.

Re:Lot easier than it sounds

[hr raattgift]

That's one of several procedural problems.

People survive for quite some time in cold hypoxic or anoxic environments, but time of useful consciousness is on the order of single-digit seconds, and time to recover useful consciousness is proportional to time and degree of exposure, but is at least on the order of several minutes. Pilots likely would have to be masked, and possibly suited, for operations at that altitude, since an emergency descent is limited by structural considerations (how quickly you can decelerate without snapping -- or melting -- flying surfaces) and can take many minutes from that altitude.

Outright onboard fatalities from exposures of several minutes during an emergency descent would be unlikely in healthy adults, and don't seem exceptionally risky in healthy walking children. However, a few minutes of near anoxia and several more minutes of hypoxia will not do anyone much good -- there will be a hell of a hangover at the very least, and a substantial risk of fatal complications of HAPE and HACE arising later.

Another important consideration is fuel loading -- at tolerable altitudes (below 4000m AMSL) the aircraft will not be able to sustain a high subsonic Mach number without huge fuel burn, and is unlikely to carry sufficient fuel for longer, slower flight. The emergency travel distance is therefore a factor. This raises another key problem: inertia.

Turning times are limited by acceleration forces ("gees") both for passenger comfort and structural integrity. The radius of a turn increases with the square of velocity for a given "gee", which implies either a much more straight-line flight pattern than is usual even under ETOPS rules, or higher accelerations in turns (felt by passengers and by structure). A reasonable ultra-long-haul hypersonic flight pattern would be nearly a great circle, which means an emergency descent over an ocean may require a water ditching simply because a suitable airstrip cannot be reached after descending below 4000m.

Accelerations are also important in the climb and descent phase in normal operations, since passengers will not enjoy long periods of noticeable (> 0.1 gee) longitudinal (front-to-back/back-to-front aircraftwise) acceleration, or even short periods of noticeable lateral accelerations, since both will keep passengers seatbound. Accelerations of greater than 1 g have serious structural implications and will preclude a variety of travellers. Accelerations of greater than 2 g are infeasible for commercial travel.

Operations research in this area uses flight simulators a lot (Laminar Research's X-Plane is a popular engine/front-end because it produces acceptable approximations of real physical conditions in almost aribtrary situations, and lets plug-ins do a better job as necessary). Simulated fast supercruise and hypercruise routinely runs into the descent planning problem -- gentle acceleration accumulates a great deal of kinetic energy which has to be gently ditched, and timing problems of merely a few seconds in hypersonic travel (M > 4.0) routinely lead to overshoots or underruns of hundreds of kilometres. These are unavoidable without compromising passenger comfort, structural integrity, or fuel budget. Reentry test vehicles generally trade away human comfort and fuel budgeting (many are almost entirely unfuelled) for structural integrity in order to hit a target area on the ground. This is not a reasonable tradeoff for commercial passenger travel. Fuel is expensive, and backtracking can be just as expensive (and much slower) as powering through a descent started too early. Passengers won't fly if it hurts, even if they are willing to put up with the discomforts of long haul subsonic travel in cramped conditions.

The biggest problem in hypersonic commercial transport is going to be that it intersects with subsonic commercial transport in the terminal phases of flight (ascent, descent, and probably ground operations) but the regulatory regime above FL

Re:Lot easier than it sounds

[Abcd1234]

Airliners depressurize occasionally.

They do?? Jebus, what airlines do you fly on? Because I think I might want to avoid them...

rimshot

[Ungrounded Lightning]

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:rimshot

[Wonko the Sane]

Two drums and a cymbal fall off a cliff

why the altitude-dependance?

[bcrowell]

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?

Re:why the altitude-dependance?

[greyhueofdoubt]

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

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

Re:why the altitude-dependance?

[bcrowell]

The wikipedia article doesn't address the point I was asking about, though.

Re:why the altitude-dependance?

[greyhueofdoubt]

I think it does. Your assumption that the first and second cones share an identical angle is incorrect. The waves take the form of an N (in 2 dimensional depiction). In order for the leading edge V part of the N to not be a negative angle, the trailing I part of the N must compensate. This is easier to visualize in terms of boat wakes. Anyone who has ridden in a boat going at a moderate to high speed can tell you that the bow shockwave and the stern shockwave do not share the same angle of incidence.

Here is the best picture I can find right now:
http://www.iboatnyharbor.com/Vee-wake.jpg

You can see (barely, sorry) that the bow and stern wakes are not congruent. Also of interest is the constructive/destructive interference.

Another way to think about it is this: The shockwave at the bow of a craft can sharpen only slightly with increased speed, while the shockwave at the rear is not constrained by the body of the aircraft itself (avoiding negative angles again). In theory, both shockwaves could approach zero degrees, but in practice the bow shockwave cannot touch aft structures such as leading edges of wings without causing damage. This necessitates the swept wing configuration common to all superconic aircraft (the markedness of the sweep depends on the operational speeds of the aircraft). I guess what I'm saying is that much like a boat's bow wake, a supersonic (bow) pressure wave cannot form an angle that is smaller than the space that the craft itself occupies. Sorry, but I've been tearing down plaster and lathe all day and I'm tired and inarticulate.

I hope this helps.

-b

Re:why the altitude-dependance?

[bcrowell]

Hmm...sorry, but I don't follow your argument. I don't understand what you're referring to when you talk about the N shape. I don't understand how the opening angle of either cone can be anything but sin-1(c/v) (I goofed in my previous post by saying tan-1.) I don't see how the shape of the airplane can matter at all.

Re:why the altitude-dependance?

[greyhueofdoubt]

Ok I'm about to go to bed, but here. Take your equation to the limit where the angle is very small- let's say 3 or 4 degrees. The area described by this cone would fit inside the area of the aircraft. You would be saying that there was a shockwave inside the aircraft. That doesn't make sense. The shockwave must follow a line from origination to a point outside of the aircraft. As I mentioned before, operational restrictions are in place to keep the shockwave from hitting the wings. Physics keeps the shockwave from existing solely inside the airplane (not that the airplane would exist long enough for that to happen).

Your equations assume a _point_ traveling at speed and causing a shockwave. Aircraft are not points, and this needs to be taken into account in your equations. Two points, traveling at identical speeds in the same direction would cause the results you are finding. Two points traveling in water in the same direction would create congruent wakes if their respective wakes did not interfere with each other. This is obviously not the case in practice. Hopefully someone who is more awake than me can weigh in here and make sense of all this to us both.

-b

Re:why the altitude-dependance?

[bcrowell]

I don't see how the shape of the airplane can make any difference in the propagation of the wave once it's gotten far away from the airplane. I'm still guessing it's some kind of nonlinearity in the propagation of sound waves. E.g., maybe an extreme decompression propagates at a smaller velocity than an extreme compression.

While discussing SF2 jokes..

[Artuir]

If you haven't seen it already, it'd be worth your time to check out "Street Fighter: The Later Years" on youtube. So far I think they have 9 episodes done.

http://www.youtube.com/watch?v=kLrWgVPeCzI - it's absolutely hilarious.

Re:While discussing SF2 jokes..

[Spy der Mann]

I've seen 'em all, the 9th is the last episode.

SST's: Damn Noisy Things

[reallocate]

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.

Does a bullet make a sonic boom?

[Brad1138]

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?

[427_ci_505]

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?

[onkelonkel]

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?

[Chris Burke]

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?

[Anpheus]

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

Re:Does a bullet make a sonic boom?

[Brad1138]

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?

[Brad1138]

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?

[Brad1138]

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?

[Cosmic AC]

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?

[Anonymous Coward]

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?

[Anpheus]

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?

[onkelonkel]

http://en.wikipedia.org/wiki/Sonic_boom 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?

[thatskinnyguy]

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

Re:Does a bullet make a sonic boom?

[Mopatop]

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?

[rmm4pi8]

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:Does a bullet make a sonic boom?

[Anonymous Coward]

Go search on YouTube for videos of people using silencers or (properly) suppressors on firearms. Subsonic ammo makes the gun almost silent. Supersonic ammo makes a loud crack when fired due to the sonic boom of the bullet.

Re:Does a bullet make a sonic boom?

[Anonymous Coward]

What? "Time for the sound to build up?" Sound doesn't "build up" on a subsonic object. A sonic boom is produced by an object going *faster* then the speed of sound, not by breaking the sound barrier. As such, an aircraft in flight faster then mach 1 produces a boom audible over its entire flight path, not just at the start and end of flight. Also as such, acceleration has nothing to do with how large the boom is. It's all shape, and the medium (air).

So.. yes, a supersonic bullet produces a sonic boom. Its is much smaller then an aircraft's, but that's because the flight profile of a bullet is much smaller then an aircraft, not because it accelerates faster. Of course, the bullet isn't miles above the ground. This all combines to making a supersonic sniper rifle futile to silence. Or well, more futile then a subsonic one... you can still get rid of the initial explosion that marks out the origin.

Re:Does a bullet make a sonic boom?

[Anonymous Coward]

38 special, 44 special, 44-40, 38-40, and 45 Long Colt have standard velocities from a revolver below the speed of sound. The same revolver can fire a 38 special at subsonic velocity and a 357 magnum at supersonic.

People shooting muzzle loading rifles long before modern chronographs noticed a change in sound when their powder loads crossed some threshhold.

Re:Does a bullet make a sonic boom?

[icebrain]

The sound when you fire the gun is from the expansion of the heated gasses after the bullet leaves the barrel. It has nothing to do with the bullet.

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 that the bullet could pass over and leave its boom before the sound from the firing reaches you.

Public safety announcement: Please, kids, don't try this at home. Intentionally standing anywhere in front of the business end of a gun being fired is a bad idea and makes you a moron at best. Being the idiot on the other end, pointing and firing said gun while a person is there is downright criminal (except in very specific circumstances, like legitimate self-defense). If you must, set a cheap camera or microphone up. I'm all for the private ownership and (responsible) use of firearms... but please don't do something stupid.

Now you know... and knowing is half the battle.

Re:Does a bullet make a sonic boom?

[icebrain]

Yeah... lots of handgun rounds fall out in the transonic range. There's only so much speed you can get out of a short barrel before the pressures (and recoil) get too high.

Common .22LR (rimfire) rounds are generally supersonic from a rifle; you can buy subsonic ones or higher-velocity "stinger" type rounds too. Interestingly, the subsonic ones tend to be more accurate... the supersonic-to-subsonic transition is unstable and tends to disturb the bullet.

What I really want is a .17HMR...

Re:Does a bullet make a sonic boom?

[mbone]

Yes, if it is supersonic.

Re:Does a bullet make a sonic boom?

[icebrain]

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:Does a bullet make a sonic boom?

[mortonda]

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.

Re:Does a bullet make a sonic boom?

[Anonymous Coward]

super sonic ammunition has a sonic boom, sub sonic does not. So the answer is... depends on the ammunition.

Re:Does a bullet make a sonic boom?

[Nimey]

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.

Re:Does a bullet make a sonic boom?

[Anonymous Coward]

I read somewhere that a rifle with a very well designed silencer (aka suppressor) can be made to be very quiet (the muzzle blast, that is); but if it's firing supersonic ammunition, the bullet would create a sonic boom that couldn't be muffled by the silencer. That's why it's unrealistic when a sniper in the movies shoots someone from a few hundred yards with a high powered assault rifle with a silencer and it only makes a little peep.

I've also heard that the "crack!" that you hear when you crack a leather whip is the result of a sonic boom when the tip of the whip momentarily moves faster than the speed of sound. Can anyone confirm that this is true?

Re:Does a bullet make a sonic boom?

[BigAssRat]

Sonic Booms are VERY LOUD, occur across the flight path and are not singular events. When I lived in Gainesville, FL while attending the University of Florida, the Space Shuttle landing route was over Gainesville. At the time it is traveling overhead it is indeed supersonic.
I can remember several mornings where I was unaware that the space shuttle was landing, say 6am, and as it passed by it would wake me suddenly from a dead sleep as I thought something in the house had exploded. Finally after a couple of times of that I would make sure to pay attention to when the shuttle was planning to land...and I definitely know why they don't allow supersonic flights over land on a regular basis, unless you know it is coming, it is not that enjoyable to experience. However, I am pretty sure that Depends would love the idea since I am sure their sales would increase exponentially among the general population.

Re:Does a bullet make a sonic boom?

[YoungHack]

In fact they do. This is precisely why it is difficult (despite what you may see in movies) to create a very effective silencer for a fast bullet like 9mm. You'll get the best results with subsonic ammunition. It's just hard to do anything about that hypersonic "crack."

Re:Does a bullet make a sonic boom?

[Agripa]

Spring piston air rifles in .20 and .177 caliber can be supersonic and make a noticeable crack.

Re:Does a bullet make a sonic boom?

[BootNinja]

By the time you are far enough away from the gun to be able to hear the boom of the bullet over the crack of the gun, I would imagine that drag will have decelerated the bullet enough that it will no longer be traveling at supersonic speeds.

Re:Does a bullet make a sonic boom?

[Anonymous Coward]

You would be wrong. Many accounts of military combat talk about the crack noise a near miss makes.

It is even in the book and movie Black Hawk Down.

And of course you are forgetting that if the bullet is travelling supersonic, you will hear the bullet crack before the sound of the gun anyway. The bullet crack doesn't need to be louder, you just need to be a sufficient distance from the gun to tell the two events apart. Which isn't that far, we did a speed of sound vs light experiment in high school by utilising a cricket bat and ball.

Re:Does a bullet make a sonic boom?

[TheLink]

"they also use special subsonic ammunition"

Or supersonic ammunition that don't make very audible sonic booms.

http://en.wikipedia.org/wiki/Busemann's_Biplane

Re:Does a bullet make a sonic boom?

[icebrain]

Some quick googling:

M855 ammunition is a 62-grain 5.56mm NATO round. Standard ballistic tables show a muzzle velocity of 3100 ft/sec, or about Mach 2.7. It drops to Mach 1 at around 700 meters, so maybe if you were around 500-600 meters or so?

M118 (a 7.62mm NATO round) stays supersonic out to 1000 meters, or over half a mile. Certainly long enough to be able to hear it.

Re:Does a bullet make a sonic boom?

[Anonymous Coward]

Do not touch the operational end of the device. Do not look directly at the operational end of the device. Do not submerge the device in liquid, even partially. Most importantly, under no circumstances should you-

They have been doing this at area 51 for years

[Anonymous Coward]

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:SST's: Damn Noisy Things

[rcw-work]

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. 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.

Underwater maybe?

[argent]

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:Underwater maybe?

[td]

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.

Re:Underwater maybe?

[argent]

Ah, doh, thanks for clearing that up.

Where do people use "pounds per square foot" as a common unit? I've never run into that one before, so mentally read it as PSI. Is this some NASA-only usage that they use when they're need to lose a Mars orbiter to a translation error or something?

Simple Solution: High Voltage Electricity

[adius]

If you use a voltage that is high enough it will create an enveloping shield. This shield is capable of dealing with mediums such as gas and liquids. Liquids will turn to gas and gas turns to plasma. It works wonders for underwater crafts capable of traveling at high speeds.. or should I say ..UFO/USO crafts. ;)

Re:Simple Solution: High Voltage Electricity

[greyhueofdoubt]

I don't see how changing air to plasma would help- surely the phase change would require tremendous energy, and it would not get rid of the compression wave at the nose and stabilizers of the aircraft. In fact, I'm almost certain that it would make it worse. Right now, you have only the speed of the aircraft compressing the air and causing the boom; with a plasma layer, you'd have the additional speed of the air expanding to form a plasma. At least in my mind, this is almost what happens with lightning. I realize that the boom is caused by the movement of heated air, but the air is heated and moved by the plasma, right?

-b

Easy solution

[insertwackynamehere]

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.

Gulfstream's "Quiet Spike"

[jthegreat]

http://www.gulfstream.com/news/releases/2005/051108d.htm 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.

Where's the kaboom?

[blixel]

There was supposed to be an earth shattering kaboom!

Dumb Idea #109800043

[Anonymous Coward]

Put a military grade subwoofer on the plane's exterior, to disrupt/cancel out its sonic boom. A military grade subwoofer is an explosive, or maybe an electrical device that approximates thunder.

Dumb Idea #109800044
Build a special texture into the exterior of the plane; like golf balls have dimples. Maybe add some wacky looking fins lining the plane, to direct the sonic boom (up?).

Dumb Idea #109800045
Create a plane with 100% thrust and no surface friction or wind resistance. (no lift)

Doesn't have to be as big as a space shuttle

[melted]

I grew up in a town near a military airbase, so I remember sonic booms pretty well, because I heard them at least a few times a week. Sonic booms always came in pairs. They kind of sound like if someone strikes a giant drum with those thick Japanese drumsticks. It made the glass in our windows rattle a bit.

Re:SST's: Damn Noisy Things

[MtViewGuy]

Actually, there is a solution to the issue of developing a jet engine that can meet even the stringent ICAO Stage IV noise emission rules and still be able to fly supersonically: a variable-cycle engine.

GE Aero Engines developed this idea as one of the possible engines for the Advanced Tactical Fighter (ATF) project (the project that became today's F-22A Raptor). By scaling up this technology, you can have an engine that runs in high-bypass mode at low speeds and lower-bypass mode at higher-speeds. Also, thanks to modern engine design and better noise-reduction technology for the engine nacelles, a future SST with such an engine would burn far less fuel and make much less noise, especially if they limit the top speed to around Mach 1.6 to 1.7 (which means much less usage of running the engine in fuel-wasting and noisy afterburner or reheat mode).

Lockheed's been working on this.

[jcr]

The Lockheed Skunk Works (where Stealth technology was invented), has been working on the sonic boom problem for many years, and they have a project in progress to develop a business jet with a minimal sonic boom.

The intention is to make it quiet enough to get it licensed for supersonic travel over land.

-jcr

Aerion Corp claims a boomless SST design

[ah.clem]

Along with Gulfstream and the Skunkworks (mentioned elsewhere in the comments) there is this company - Aerion Corp., who claim to have a boomless SST design.

ah.clem

So Whoooosh?

[the_other_chewey]

So instead of a boom we'll have a Sonic Whoosh now?

Imagine the opportunities for Slashdot commenters!

Is it just me..

[lilfields]

Is it just me or had NASA had a lot of announcements lately, it's like they watched Iron Man or something and thought to themselves..."no, no, fuck that guy, I have an idea!..."

This sounds like...

[Anonymous Coward]

..an American attempt to re-introduce supersonic passenger aircraft after they managed to suppress Concorde (on the grounds that it wasn't invented here).

On a similar topic, how many times do you hear anything about the Thrust SSC land speed record on the net? Thought not. That wasn't American, either....

lb/sq ft

[td]

Yeah. It's a common unit for describing floor load or similar solid mass pushing on solid surface situations (stiletto heels on linoleum is a popular (?) situation), but for air pressure I've never seen it before.