Lets talk about the sound barrier

[cycloneman]

YOu can see by the pic the condensation cloud caused by breaking the sound barrier.

Question. Once you break the sound barrier, does it continue to make the crack noise as the aircraft is moving supersonic. Here it is another way.
An aircraft, or object is approaching the sound barrier, once it hits the barrier there is a sonic boom. Does this boom still exist 30 miles down the road if the object is still supersonic? What i am getting at is this. Once you achieve the sonic boom and continue to move supersonic are you still boomin or is it over? I kinda have the idea that this is like a door your crossing into. I have a reason for asking this but I want to see if my thought holds water first.

[jack404]

no as it is now faster than sound .. if you keep going up and down through the sound barrier yes..

the footage i took that ended up on mythbusters shows that

they did a follow up to the supersonic blast show and showed the footage i took here of f-111's overflying at super sonic speeds and busting windows but no sonic boom other than the air getting outta the way at sea level

higher up and you'd never know they went by

http://www.youtube.com/watch?v=rCzChbmJ4w4

warning language of soldiers used ..

[geds]

Glad you answered that Jack - I've always wondered about it too....

And who knew you were Hollywood film maker!

[hjsmith00843]

I think the boom occurs with the sound actually reaches the location. I remember hearing sonic booms in Iraq many times. i would be at one camp and a friend of mine would be at another camp miles away and he would hear it after me by a min or 2.

[jack404]

could be the same boom but heard in another area

sound travels

[geds]

Originally Posted by jack404

could be the same boom but heard in another area

sound travels at the speed of sound

fixed for ya Jack

[cycloneman]

OK

lets talk typ rifles now.

cal does not matter for this discussion.

typ 20" bbl and a bullet leaves the muzzel at 3000 fps

somewhere inside that barrel probably in the first 6" the bullet is supersonic. Why is it that a rifle cant be suppressed if the bullet has broken the sound barrier within the first half of the bbl?

Or am i wrong, can rifles be supressed?

[jack404]

the round on a super sonic rifle will break the sound barrier

but you can suppress ( not silence) the exhaust gasses which are a large part of the report

and why folks who load for silencer hunting use a custom load for sub sonic

my old mac 10 had the sionic kit on it but if you did not use sub sonic ammo it would make noise TAK TAK TAK and be audible but way less than non suppressed

try it yourself if you can . .22 can's are easy to get or make , ( do it legit and pay the fee ) use both sub sonic ammo and regular , you'll notice it soon enough ..

[cycloneman]

Well i am just courious, here is why?

First off i dont need to supress anything. I actually just ordered a pellet rifle for what i want to do.

But I have been courious as to why i see military rifles with supressors on them if they cant stop the crack noise? I do understand that supressors will take away the pop of the primer and some of the other noise. But why would anyone be interested in shooting supersonic ammo and putting a supressor on the rifle? Distance maybe? When shooting far distance in New Mexico in the wind sound does not travel well. I guess this would camo you. So maybe i just answered my own question

[cycloneman]

OK

Follow me here.

I know that if you shoot a rifle in the wind the wind will take some of that sound away.

Facts. There are 3 sound that are being produced when firing a rifle. The sound of the primer, the sound of the bullet crossing the sound barrier and the sound of the bullet again crossing the sound barrier when it slows down back to sub sonic speed.

It seems to me that there is nothing you can do with the bullet slowing back down to sub sonic.

But i think there is a way to stop the first crossing of the sound barrier. I dont think the modern way of using baffels will accomplish this. It seems to me that you would have to use some type of matieral to slow down the vibrations caused by the crossing of the sound barrier. I guess no one has thought outside the box yet to figure it out.

[jack404]

take a look at the altsonic work done by metal storm , contrasting and diaopposed sound offset by a few milliseconds and you dont hear the round being fired , but when it costs as much as a nuke reactor to make a quiet gun that way its beyond balance to produce , even if it works well

[Charles Christensen]

Any object that is traveling faster than sound creates highly compressed shock waves that radiate around it in a cone shape with the apex at the object and the cone trailing behind. This shock wave exists as long as the object continues at supersonic speeds. As the shock wave gets dragged across the ground the sudden change in air pressure results in a sonic boom. As the intensity of the boom relies on speed (higher speed equals greater intensity), altitude (lower altitude means thicker air and greater intensity) and object mass (aircraft equals greater intensity and a bullet much less) a bullet will have a "crack" sound and an aircraft a "boom".

Supersonic air travel failed because of the problem of dragging shock waves across populated areas. That is why the Concorde only did over-water flights.

The cloud you see in the photo is the result of lower air pressure in the forming shock wave as moisture in the air condenses. This effect is easy to see along the tops of wings in videos of navel aircraft operations and does not require supersonic flight.

[Bobitis]

Excellent response Charles.

A few years ago, Obie was stumping in Seattle for money (as he does every time he comes here). A couple from Eastern WA were flying back to Seattle in their float plane and landed in Lake Washington. Apparently this violated AF1's air space, even though it had been on the ground for hours, and fighters were scrambled.

Mchord AFB is 40 miles south of me. Whidby Island Naval Airbase is 40 miles north. Where did the fighters come from? Portland Oregon. So in order to get here in a timely manner, they went supersonic. The problem is, the couple had half their gear in their car before the support arrived.

The ensuing 'boom' had people freaked out and actually shut down all 911 service in Pierce County (Tacoma). I work about 5 miles from Boeing Field (where AF1 stays) and I heard two booms as well (there were 2 fighters). It's obviously a rolling boom as Tacoma is 20 miles south.

My question is, when does the booming stop?

If these fighters were still supersonic while on top of AF1, they overshot their target by 50 miles.

If yer a pilot and ya break the barrier, then slam on the brakes, does the wave wash back over you?

[gunslinger69]

I would have assumed that if an object sustained exactly the speed of sound it would be as if it was pushing a continuous boom along its path of travel.

[millwright]

Originally Posted by cycloneman

YOu can see by the pic the condensation cloud caused by breaking the sound barrier.

Question. Once you break the sound barrier, does it continue to make the crack noise as the aircraft is moving supersonic. Here it is another way.
An aircraft, or object is approaching the sound barrier, once it hits the barrier there is a sonic boom. Does this boom still exist 30 miles down the road if the object is still supersonic? What i am getting at is this. Once you achieve the sonic boom and continue to move supersonic are you still boomin or is it over? I kinda have the idea that this is like a door your crossing into. I have a reason for asking this but I want to see if my thought holds water first.

Depends upon the POV of the observer. A "sonic boom" is a propagating wave front. A series of observers along the flight path would hear the "boom" in sequence just as a series of observers would hear the same from a supersonic bullet passing. >MW

[Charles Christensen]

As long as the object remains supersonic it is dragging that shock wave behind it. The boom is heard by anyone it passes. As the object slows down the energy of the shock wave drops. Actually, anything moving through the air or any fluid medium compresses that fluid in front of it and sets up a wave form. It starts becoming a matter of energy input that determines the effect of that wave. A sonic shock wave by something low, fast and heavy can produce enough energy to do actual damage like breaking glass thus the restriction on Mach number travel over populations.

[CJ_56]

I grew up in the days when sonic booms were an everyday thing. In fact there were usually at least half a dozen per day where I lived. I lived right along a training route coming out of Wright Patterson and wow did we get some air show.

A couple of things. You will hear the sonic boom of a plane flying high. I couldn't say if the boom continues sounding as it passes by others but every boom I heard was about the same loudness. That might tend to indicate that the boom does travel along as a wave and hit all along the path of the plane. But then it seems if the plane was off to the side it wouldn't be as loud. Maybe it's because they always flew right over our house but one boom was as loud as another. I'm really not sure what that proves but I'm guessing it does have a bearing on this question in some way.

My second point is that low flying planes didn't seem to have sonic booms even when they were clearly breaking the speed of sound. I know they were supersonic because by the time I heard them they were already past me. If you heard one coming the only chance you had to see it was to look the opposite direction from where it sounded like it was coming. I saw maybe a third of the planes that flew over my house at tree top level clearly in excess of 800 mph and likely in excess of 1000 mph. They were F4 Phantoms which is still among the fastest ever low flying planes. I tell you what those babies would make you jump right out of your skin. I was a very young kid at the time and dang I hated those things especially until I figured out how to see them. It would make me mad as a hornet to hear that sound and to never see the plane because the plane got to me before the sound did. We had probably a dozen of those flyovers and we never had a broken window or even a picture shook off a wall. But it was terrible living when you didn't know when the next one of those monsters would fly by. I loved seeing them actually but I got so frustrated that I couldn't see them after getting scared so bad that I got to hate them flying over even after I learned to actually see them. I saw one right over my head. The rest were already way past me before I saw them. But the one I saw over our house was amazing. I could have hit it with a rock if I had known when to throw it up in the air. We had a tree in our yard and it wasn't clearing that tree by more than 5 feet at most. Man that was way too much of a rush for a 6 year old kid. They did right when they banned those training missions over US civilian property. Top speed on the F4's was actually about 1600 knots. But they never flew that fast over US land and not at that speed at tree top level. They were incredibly fast even when flying low though. I heard they did some runs at around 1400 knots at tree top level. That's insane.

[wolfdog]

Main reason for supression of supersonic rifle ammo it is difficult to tell the direction from which fired.