quote:

Originally posted by Sluosforelaets:

quote:

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 concede that my original statement about frequency being more important is wrong. i do still believe that this is a factor given that glass has multiple chemical make-ups from sample to sample and while they may break at the same ammount of pressure there would be sound wave frequency differences between the samples. This factor is a possible suspect in situations where one peice of glass is broken whle others are not.

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No they are not. The b00m is created when the projectile breaks the trans-sonic boundry. Once the barrier is broken that's it...

...I will stake my ammunition business on this information.

Can we expect your letter of resignation?

Just to note, different aircraft create different intensities of sonic booms. The Hornet is relatively benign compared to some of the older aircraft like the Phantom, or as mentioned earlier, the Shuttle.

If you really wanted to knock out those windows, try a B-1 at 200 feet.

NASA has a research F-5 where they are (were) trying different forward fuselage shapes to minimize the intensity of the sonic boom in an effort to find the sweet spot that would eventually allow the construction of aircraft that could fly supersonic over populated areas without the annoying boom.

I'd like to see the fellows re-test the myth using B-1B's this time. Four F-16 engines (GE F101) in full burner is quite a sight. Even subsonic, a low altitude pass by a B-1B sets off car alarms and shakes windows.

I grew up in Tampa within a mile or two of MacDill AFB and we had a back porch that was glassed in with jalousies that was blown out twice in 2 years by booms. It was from this earlier time that the myth grew. I think a couple of things are being ignored in the Myth test.

no fly zones are pretty recent

• pilot and mechanical error can send a jet into a no fly zone or a low flight path
  
• modern aircraft have been designed to lower or control the boom impact- testing with an F-4 or B-57 would bring different results
  

Enjoyed the show but I find the premise puzzling. Am I the only one who has NEVER heard of the myth "ALL sonic booms ALWAYS break glass"? There is simply no such myth.

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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

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Once the barrier is broken that's it.

I see it time and time again, when someone claims to be an expert, most often they are not....

You owe someone an ammunition business.

Pay up.

The sonic boom is first reached in the muzzle after the gun is fired. If you watch the high-speed camera when they replay the firing, you'll see the wave come out of the front where there are the slits on the front of the barrel. This is caled the detachable muzzle brake. This helps the recoil, since you are firing a 50 caliber bullet. You can see the shock wave come out of there and then the shockwave is not as powerful when it does reach the glass.
M107 information

Captain Random is quite correct about the continuous nature of the sonic boom. Recalling from Ben Rich's memoir about running Lockheed's Skunworks, they interviewed SR-71 pilots. One of whom mentioned a cross country flight from LA to New York that (I paraphrase) 'created the first continuous sonic boom across the country'.

Therefore, in any fixed point in the country (in Phoenix, St. Louis, etc) you'll only hear the boom once as it rolls across country.

Great episode though - great opportunity, Adam, to fly with the Blues!

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Originally posted by Ballistic Expert:
You guys have to know that the bullet breaks the sound barrier immediately out of the muzzel. As the bullet passes the glass you had up it is already supersonic. So the test is bunk.

You are wrong. If this was truly the case then the tests with the blue angels would have been much harder to do. But if you noticed, the blue angels were already flying at Mach 1 for a good few seconds before they reached the site, the split second they reached the site, and a few seconds after they passed the site. And of course you heard the loud pressure wave.

Simply put, if you had 10 people spaced 1 mile apart in a line and had a jet fly at Mach 1 over them, they would all hear and experience a sonic boom (of course at different times when the jet was over them).

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Originally posted by f-22_raptor:
The sonic boom is first reached in the muzzle after the gun is fired. If you watch the high-speed camera when they replay the firing, you'll see the wave come out of the front where there are the slits on the front of the barrel.

Those slits are there to allow for the expanding gasses to escape from the explosion that happens when you pull the trigger.

I just watch this episode ( sonic boom ) today off my DVR.

for what its worth, the Air & Water show in chicago which was flown by the Blue Angels 4 years ago and they blew out close to 100 windows on buildings in downtown by doing a sonic pass 1 mile out.

You should have used a B-1 bomber at 500 feet i think that would do all the damage you would need.

Adam, Jamie

Guys - excellent show. The reason the window pane breaks and the wineglasses (and Jamie's glasses) don't is that you need a strong pressure differential. The window on a sealed building experiences an overpressure. The open wineglasses don't. Depending on the overpressure, surface area, and type of glass (and lots of other variables), the windows will break but your glass of Lafitte Rothschild will be safe.

cheers

David Voss
Editor
Physics

I live in an area that is close to a base that has daily flights where aircraft break the sound barrier. I have a few concerns and questions.

Would constant daily sonic booms weaken glass and make it more supceptible to breaking?

Would pressure differences between a enclosed house make a difference in the reaction of the glass?

I would also note, different aircraft make different intensities of sonic booms. i.e. the F-22 is by far the most intense. For example a T-38 flying below 18000 and breaking the sound barrier doesnt make a very audible boom. Perhaps this is due to the speed at which the aircraft reaches mach 1?

I spent my childhood in besieged Sarajevo, Bosnia&Herzegovina, Wikipedia: Siege of Sarajevo , and I've seen and heard of quite a lot of glass-shattering in the city during the war.

I can't believe the JNA-planes were flying over us at just a couple hundreed feet - the city's surrounded by mountains so it would probably have been too dangerous. Since I'm not an aero-anything expert I don't know whether it would've made a difference, but I think they mostly had MIGs back then...

Tarik

All you have to do is research the Halifax Explosion to learn about sonic booms. when the ships blew up, the sonic boom that was created, shook and broke windows in Truro, some 50 miles away.

In the case of sonic booms, size counts.

Next time flatten the Head of the Bullet so it's pushing Air and not cutting through it!

To what end? The myth was that ANY sonic boom will break glass. The bullet they fired on the show went supersonic, and it did not break glass. Myth busted.

Sorry. The myth is not busted! Do any Google search with the following key words (Israeli Army uses sonic boom to break windows) And you will hit multiple reliable new sites and eye witness reports of Sonic Booms being used against civilian targets for the sole purpose of doing damage!

Myth is not busted! You'd think the research department would have known this.. Maybe you should give the IDF a call and see what their strategy was?