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."

The Right Stuff

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

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

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

It's better than dealing with the airlines.

Re:The Right Stuff

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

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

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

Carefully

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

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

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

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-

The hell you can't hear the double boom!

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!

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!

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

this is not quite new

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

Would be nice if they got the facts right

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.

I think that rocket planes are the way to go

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

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

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:Why NASA?

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?

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?

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

Re:Go home and be a family man.

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.

rimshot

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:Does a bullet make a sonic boom?

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.