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Originally posted by WhackyPlague:

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Originally posted by Ballistic Expert:

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Originally posted by WhackyPlague:
Ballistic Expert: Sonic booms are produced continuously for the entire period of time a projectile is supersonic. It doesn't matter where they put the glass, because a .50BMG projectile is going to be supersonic for a very long distance.

And to be perfectly accurate, the bullet becomes supersonic within the barrel.

No they are not. The boom is created when the projectile breaks the trans-sonic boundry. Once the barrier is broken that's it. After that all you see is the bullet disrupting the air ahead and behind it.

Yes technically the bullet transcends the barrier in the bore. But it is when the projo exits the muzzle is where you get the boom.

I will stake my ammunition business on this information

Sorry, you're wrong.

I hate to use Wikipedia, but it's easy, so:
http://en.wikipedia.org/wiki/Sonic_boom
"Since the boom is being generated continually as long as the aircraft is supersonic, it fills out a narrow path on the ground following the aircraft's flight path, a bit like an unrolling celebrity carpet and hence known as the boom carpet. Its width depends on the altitude of the aircraft. [2] The distance from the point on the ground where the boom is heard to the aircraft depends on its altitude and the angle α."

Sonic booms are not a single event. They are produced continuously.

Sir I stand corected on the fact that an object that is supersonic continually generates a sonic boom.

The pressure wave is still highest at the trans-sonic boundry. So the test is still flawed.

when I was a kid airforce jets from a nearby airforce base trained near our house. Sometimes they would get frisky and fly at treetop level.On day they buzzed our neighborhood and made a sonic boom. At the same time we were building a new house(50'x 100') out of 8" blocks(foundation) and 6" blocks (walls). Thefoundation was aprox. 8' at highest point. We had all the blocks complete, after the flyover 90% of the blocks had been knocked over. My dad called the airforce, they investigated for about one year, and paid for the damage.
They took statements from all neighbors and some jumped in floor thinking it was some sort of bomb.Documented true story Vernon,al.

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Originally posted by DCFanMod:
Broken Glass or Broken Myth? Talk about it here!

DCFM

Congratulations Adam for getting to fly with the Blue Angels!

I have been on a carrier when f14s and f18s broke the sound barrier and when they did supersonic passes. There is a more intense boom upon the original breaking of the sound barrier. The supersonic pass doesn't even compare, which is why it is illegal to break the sound barrier at an airshow on land but not illegal to do a supersonic flyby. The test was flawed.

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Originally posted by Seraphinedreams:
I have been on a carrier when f14s and f18s broke the sound barrier and when they did supersonic passes. There is a more intense boom upon the original breaking of the sound barrier. The supersonic pass doesn't even compare, which is why it is illegal to break the sound barrier at an airshow on land but not illegal to do a supersonic flyby. The test was flawed.

this just reminded me of when i was a kid at an air show at Ellington Air Base in Clear Lake, Tx. i was probably 8-9 yrs old. we were in a hanger looking at helicopters when a canadian dual engine jet went vertical at the mid point of the runway and broke the sound barrier. i swear the floor of the hanged dropped 2 feet and everything shook. i ran outside and looked up to see the twin exhuasts disappearing straight up. so perhaps they needed to break the sound barrier at the moment they were over the glasses and car. this does not change my earlier statement on why i feel the glass did not break. possibly the pressure wave had already dimenished when they passed by the test site. thus just flowing around the objects. but the initial breaking of the sound barrier is definitely much more concussive.

I was pretty satisfied with their testing. I would have liked to see a little more explanation about the mechanics of a sonic boom, but it looked like they pretty definitely showed that while a sonic boom can cause glass to shatter, it takes more than a sonic boom at a certain altitude; it also depends on the glass and its surroundings.

Oddly enough NASA Dryden Flight Research Center, Edwards AFB CA is gearing up for a new set of sonic boom experiments tomorrow (with more flights in August and September) booming large buildings, a follow-on to booming old and new homes on base housing.

These are being done using one of Drydens 5 F/A-18 fighters converted to research use.

http://www.edwards.af.mil/news/story.asp?id=123153338

NASA has done many many flights at the Dryden Flight Research Center, and I'm amazed that MB didn't end up there.

Other recent past projects include Lancets and Quiet Spike and were conducted to research how individual components of aircraft contribute to sonic booms:
http://www.nasa.gov/centers/dr...ases/2009/09-04.html

http://www.nasa.gov/centers/dr...ases/2006/06-39.html

Well I was told a story by a buddy who went to Iraq, and he said he took a guys head off with just the shockwave of a .50 cal machine gun.I want to believe him so maybe it was the muzzle break or the muzzle velocity or maybe they should try it with a .50 cal machine gun.

Wouldn't the strongest sonic boom be caused by a bullet travelling very close to the speed of sound? It seems as though that would cause a larger amount of compression directly behind the bullet. With a 50 caliber gun, the bullet is flying so fast it would make sense if the boom was being spread out over a longer duration.

I am happy with the testing but have an example the elimiantes the whole mess with the 50 cal test. When a bullwhip cracks the end of the whip breaks the sound barrier and that I guarantee would not shatter glass...

OK, they totally didn't know how to focus the boom right to get high intensity. You don't get the dramatic film but you get the bigger boom we all expected.

This one needs to be revisited and/or super sized and Dryden's the place to do it!

For the folks that believe they heard sonic booms at air shows, it's almost certain what they heard was lighting of the afterburners, not a sonic boom. Lighting them consists of spraying raw fuel into the hot exhaust where it virtually explodes. Afterburners give greatly increased thrust at the expense of greatly increased fuel consumption and is usually reserved for maneuvers like takeoffs or transitioning into a vertical climb.

Just a concern of safety--If they are trying to use a sonic boom to break glass, then why is Jamie wearing sunglasses???? If the sonic boom were to have broken the sunglasses that he was wearing on his face he would have been seriously injured.

There has been one instance where this has been documented to happen and it was under more severe conditions than the MBs could legally use. In 1977, Daryl Greenamyer broke the low altitude speed record for aircraft in his home built F-104 Starfighter. He achieved just under Mach 1.25 (998 mph) at an altitude of 80 feet. As he flew through the measured mile, the shock blue out the windows of a couple of the observers cars. The pressure wave increases with both proximity, speed, and weight. The F-104 may have also produce sharper shock transients due to it's more straight edge wings and less blended body. I was surprised the MB's didn't push the speed up a little higher since the FA-18 should have had a little more left in her. That could have made the difference. Of course, modern auto glass is somewhat more shatter resistant than the glass in the 70's.

You are right about size mattering in how large a sonic boom an object makes. That is why a relatively small object like the .50 caliber bullet they shot did no damage to the glass with its sonic boom. And to all of you who have heard stories about just the passage of a .50 caliber bullet whether from a machine gun or not you should now know that it is all BS, you have seen it for yourselves.

Some people are close so I'll put it all on one post. Sonic booms are continuously created. You only hear it once because it only passes by you once. If you followed at the same speed as the object creating the boom at the exact same speed and were in the shock wave, you would continuously hear it. If you absolutely need proof of this concept go watch videos on youtube of planes doing passes over water very very low. The pressure wave of the plane disturbs the water as it passes by. 50 cal. bullets, in fact any bullet traveling supersonic, will continue to create a shock wave as long as it is still traveling beyond the speed of sound. The difference between a plane and a bullet is that a jet fighter disturbs a whole lot more air when making a sonic boom, meaning it will have a much stronger pressure wave. A bullet may pop your eardrums as it passes by your head, but it may not break glass. Also about people living near airbases and airshows: Your most likely mistaking the afterburners for a sonic boom. When afterburners are lite, the exhaust gas can exceed the speed of sounds making those awesome looking rings.

IMO: The bullet test was perfectly fine. The plane test could have been done much faster. At mach 1.0x there just isn't that big of a pressure wave made. Fighters do passes at mach .9x all the time and nothing happens because the pressure wave made isn't strong enough to do any damage but still has that kick to it that just feels so cool. Also I think that the smaller glass objects didn't break because the boom wasn't enough to vibrate them to a breaking point. Remember the breaking crystal with your voice myth? On the slow-mo's you can easily see the glasses violently shaking. The glasses in the test were not large enough to vibrate to a breaking point. The small window was just barely big enough, but imagine a window the size of one on an office building or store front. Windows in populated areas are huge compared to a 1x1 foot port hole and would have a lot more surface area to absorb the wave and would also flex more to a point where they would break. The same test with larger more realistically sized windows would be no problem to break.

The bullet test was destined to fail because the bullet generates very low ("almost zero") sound due to the friction with the air. The sound one hears is from the explosion in the gun. This means that the wave amplitude is so tiny and it will not generate a sonic boom as one would expect. Unless the bullet has tiny speakers within it. Now, if you compare it to the jet. Then yes the jet has a significant sound source "the jet engines", so if the plane travel faster than sound as it emits a high amplitude sound, this generates a "traditional" sonic boom.

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Originally posted by LdMacfrankist:
The bullet test was destined to fail because the bullet generates very low ("almost zero") sound due to the friction with the air. The sound one hears is from the explosion in the gun. This means that the wave amplitude is so tiny and it will not generate a sonic boom as one would expect. Unless the bullet has tiny speakers within it. Now, if you compare it to the jet. Then yes the jet has a significant sound source "the jet engines", so if the plane travel faster than sound as it emits a high amplitude sound, this generates a "traditional" sonic boom.

The gun is built to contain the gases, to push the bullet out the barrel of the gun. The sound you hear isn't from inside the gun, but from the gases excaping from the barrel after the bullet leaves. Can't remember who was saying this, but if you put the gun closer to the glass, it will be more of the excaping gases that would shatter the glass.

CaptRandom is right, the bigger the glass, the more likely a sonic-boom will break it, because the glass can flex more. I live near a military base, so I hear sonic-booms everytime the military is training in my area. We had to replace the glass in our windows, maybe twice already. There was a couple of times where the fighters would fly just 500 feet off the ground, in which shattered the glass. I don't see anything wrong with the test the Mythbusters did, since they did shatter the window on the small house. However, they need to use bigger planes of glass.

Also, the altitude in which the glass is at does have an effect on the glass. The high-rise building, aka sky-scrapers, were designed to sway in the wind, so it is much more flexible at higher altitude. But a sudden shock from a sonic-boom, will have a higher chance of shattering the glass, near 100%, lets say 90%, so there is that 10% chance it won't shatter, just incase.

I'm tired so I don't know who said this, but if you were to fly as close to the surface of the water, at super-sonic, the force from the engines will be the more likely cause of the wake, because of how much thrust it is producing to push the aircraft super-sonic, so that test is flawed before it even begun.

i think that some of the glass breaking "issues" also come from the resonate frequency of the glass tested (as shown in previous episodes). The volume/intensity was not as important as that as that of the frequency. I think that this factor might have a role in what types of glass could be broken with a sonic boom.

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Originally posted by Mhowick:
i think that some of the glass breaking "issues" also come from the resonate frequency of the glass tested (as shown in previous episodes). The volume/intensity was not as important as that as that of the frequency. I think that this factor might have a role in what types of glass could be broken with a sonic boom.

It has nothing to do with resonate frequancy of the glass. It's a sudden shock of preasure that would cause the glass to break. A sudden shock of anything preasure can break anything. It just depends on how strong the preasure is, and how sudden the shock is. The lager the glass pane is, the less sudden preasure shock it will take to break it.

I wanted to post a couple illustrations that are relevant. These are Schlieren Photos that illustrate the true nature of sonic booms. The first one is a photo of a supersonic bullet's shockwave.

Bullet Sonic Boom

The second photo is an interesting illustration of the different shockwaves of a muzzle blast and a bullet sonic boom.

Gun Shot

The last one is a freakish photo of an FA-18 just like the one Adam flew in in the transonic regime.

FA-18 Shockwave