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."

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 [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.

Why NASA?

[VeNoM0619]

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

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: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.

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

Shh, better not tell Capcom!

[r_jensen11]

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

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: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.

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: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!

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: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

[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?