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Sonic Boom Question  
User currently offlineas739x From United States of America, joined Apr 2003, 6097 posts, RR: 23
Posted (2 years 9 months 3 weeks 19 hours ago) and read 7804 times:

So this past Sunday my wife and I met some friends on the Hornblower at SF Fleetweek. After the UA 747 finished it's show we knew the F-15 was coming. And moments later there he was hitting the deck on a high speed pass and it formed the beautiful cone. But as he started a right bank, literally 200 feet from us the cone got smaller and as it past when the sound got to us there was an incredible "Clap" as it went past. Now on deck I heard one Clap, but those below said they heard a double Clap. If this was not a sonic boom, what is the Clapping sound?

Also, is a sonic boom different at low altitude over the water vs. at higher altitudes?


Thanks...


"Some pilots avoid storm cells and some play connect the dots!"
26 replies: All unread, showing first 25:
 
User currently offlineHaveBlue From United States of America, joined Jan 2004, 2098 posts, RR: 1
Reply 1, posted (2 years 9 months 2 weeks 6 days 15 hours ago) and read 7554 times:

Its like someone asking if their elbow is broken... if it was broken, you wouldn't have to ask.   If you heard a sonic boom, there would be no question as to what you heard.. its that loud. That being said, a fighter on the deck doing close to the speed of sound, when he gets right near you the sound hasn't reached you yet so you finally hear it all at once and it is loud.. it doesn't have the gradually increasing intensity of a fighter approaching at a more moderate speed. I've heard this many many times during sneak passes and one F-14 guy who pushed it a little too close and lost his wings for it, but that's another story.

The shape, size and duration of the 'cone' of condensation varies widely. It is dependent largely on humidity and there can be little to no cone or very large and well defined ones.. and as the fighter moves thru varying pockets of air that cloud often appears and disappears flickering on and off at varying levels depending on the local air. Luckily in Florida where I live and being on the coast most of the airshows provide nice cones.

Hope that helps.



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User currently onlinebikerthai From United States of America, joined Apr 2010, 2069 posts, RR: 4
Reply 2, posted (2 years 9 months 2 weeks 5 days 22 hours ago) and read 7442 times:

Understanding that a plane going near M1 can have a shock wave over the wing. Can a by-stander hear anything with respect to that shock over the wing?

bikerthai



Intelligent seeks knowledge. Enlightened seeks wisdom.
User currently offlineSemaex From Germany, joined Nov 2009, 823 posts, RR: 2
Reply 3, posted (2 years 9 months 2 weeks 4 days 17 hours ago) and read 7226 times:

Completely by accident I just found this article, which may explain what you heard or for that matter did not hear:

http://www.space.com/2992-shushing-s...nging-shape-supersonic-planes.html

I haven't read through it all, but a key sentence is this one:
"Researchers drastically reduced the sonic booms produced a U.S. Navy jet by giving it a nose job."


Regards



// You know you're an aviation enthusiast when you look at your neighbour's cars and think about fleet commonality.
User currently offlineKDTWflyer From United States of America, joined Jun 2004, 828 posts, RR: 1
Reply 4, posted (2 years 9 months 6 days 12 hours ago) and read 6804 times:

Listen to some of the sonic booms in this video...

http://youtu.be/4Z4zuOb2JWM

Those are the sonic booms from an SR-71 Blackbird. The clap or double-clap sound is dependent largely upon how long the aircraft is as far as I know. This is because one shock wave forms at the leading edge of the aircraft and another forms at the trailing edge.



NW B744 B742 B753 B752 A333 A332 A320 A319 DC10 DC9 ARJ CRJ S340
User currently offlinesovietjet From Bulgaria, joined Mar 2003, 2577 posts, RR: 17
Reply 5, posted (2 years 9 months 6 days 11 hours ago) and read 6794 times:
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Even IF an aircraft broke the sound barrier at an airshow, you will not hear two distinct booms (or a "double boom" as it is often called). You have to be much farther away from the aircraft for that to happen. This is why all "double boom" videos on youtube feature aircraft flying very high.

User currently offlineconnies4ever From Canada, joined Feb 2006, 4066 posts, RR: 13
Reply 6, posted (2 years 9 months 6 days 4 hours ago) and read 6746 times:

Quoting KDTWflyer (Reply 4):
Those are the sonic booms from an SR-71 Blackbird. The clap or double-clap sound is dependent largely upon how long the aircraft is as far as I know. This is because one shock wave forms at the leading edge of the aircraft and another forms at the trailing edge.

That is100% correct. For a point moving at M=1 (if you could arrange that) you'd only get a single shock. But for something extended in space there's a forebody shock and an afterbody shock. There is a sort of grey area for something relatively short -- if you could ever nudge a Folland Gnat past M=1 I'd bet there would only be one discernible shock as the two waves would likely merge. Shape also plays into the number of shock waves heard.



Nostalgia isn't what it used to be.
User currently onlineSpacepope From Vatican City, joined Dec 1999, 2900 posts, RR: 1
Reply 7, posted (2 years 9 months 6 days ago) and read 6707 times:

The F-15s I hear in Montana can be several miles away when going supersonic, and you just get one sharp "crack". Farther away you get a duller "thud" and the individual booms tend to blend together.


The last of the famous international playboys
User currently offlineflipdewaf From United Kingdom, joined Jul 2006, 1562 posts, RR: 1
Reply 8, posted (2 years 9 months 1 day 21 hours ago) and read 6392 times:
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Quoting KDTWflyer (Reply 4):
Those are the sonic booms from an SR-71 Blackbird. The clap or double-clap sound is dependent largely upon how long the aircraft is as far as I know. This is because one shock wave forms at the leading edge of the aircraft and another forms at the trailing edge.

I was under the impression that the boom only occured when the component of the aircrafts velocity toward the listener was greater than mach 1. If the realtive velocity goes over M1 then the boom will occur on the way up through M1 and once on the way back down through M1.

If the aircraft was 30,000 feet above you and went supersonic for just one mile before you and one mile after nthen you wouldn't hear a boom at all as the component of velocity towards you would be very low.

Fred


User currently offlineHaveBlue From United States of America, joined Jan 2004, 2098 posts, RR: 1
Reply 9, posted (2 years 9 months 12 hours ago) and read 6195 times:

Quoting flipdewaf (Reply 8):
If the realtive velocity goes over M1 then the boom will occur on the way up through M1 and once on the way back down through M1

I may be reading your statement wrong, but I'm fairly certain the aircraft creates a sonic boom the entire time that is supersonic.. not just as it goes thru Mach 1 and then again as it decelerates back thru it. As long as the aircraft is supersonic its creating the overpressure and thus the audible sonic boom (whether the observer is near enough to hear it is another matter).



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User currently offline474218 From United States of America, joined Oct 2005, 6340 posts, RR: 9
Reply 10, posted (2 years 9 months 12 hours ago) and read 6192 times:

Quoting flipdewaf (Reply 8):
I was under the impression that the boom only occured when the component of the aircrafts velocity toward the listener was greater than mach 1.
Quoting HaveBlue (Reply 9):
I may be reading your statement wrong, but I'm fairly certain the aircraft creates a sonic boom the entire time that is supersonic.

Have blue is correct.


User currently offlinerolfen From Germany, joined Jan 2006, 1803 posts, RR: 2
Reply 11, posted (2 years 8 months 4 weeks 1 day 21 hours ago) and read 6087 times:

When approaching the speed of sound, a wave of pressure builds up in front of the aircraft. Maybe this sound was this wave hitting the deck as the aircraft passed by.


rolf
User currently offlineflipdewaf From United Kingdom, joined Jul 2006, 1562 posts, RR: 1
Reply 12, posted (2 years 8 months 4 weeks 2 hours ago) and read 5961 times:
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Quoting HaveBlue (Reply 9):
Quoting flipdewaf (Reply 8):
If the realtive velocity goes over M1 then the boom will occur on the way up through M1 and once on the way back down through M1

I may be reading your statement wrong, but I'm fairly certain the aircraft creates a sonic boom the entire time that is supersonic.. not just as it goes thru Mach 1 and then again as it decelerates back thru it. As long as the aircraft is supersonic its creating the overpressure and thus the audible sonic boom (whether the observer is near enough to hear it is another matter).

It is always creating the sonic boom but only relative to the point at which the aircraft is moving towards at Mach 1. An aircraft directly above you flying level will have a relative velocity of 0, if an aircraft flies in an arc around you then you shouldn't hear the boom.

Fred

Edit:sorry, thinking of rotating sonic effects.

Fred

[Edited 2011-11-04 03:35:24]

User currently offlineprebennorholm From Denmark, joined Mar 2000, 6387 posts, RR: 54
Reply 13, posted (2 years 8 months 3 weeks 6 days 9 hours ago) and read 5875 times:

Quoting flipdewaf (Reply 12):
It is always creating the sonic boom but only relative to the point at which the aircraft is moving towards at Mach 1. An aircraft directly above you flying level will have a relative velocity of 0, if an aircraft flies in an arc around you then you shouldn't hear the boom.

Wrong.

An aircraft flying at supersonic speed creates a sonic boom all the time - that part is correct. That boom spreads in the shape of a cone with the plane at the tip of the cone. And it spreads at sonic speed relative to the atmosphere.

If it flies in a perfect circle around you in totally calm weather (no wind at all), then you will hear a constant boom. (That phenomenon will be very hard to produce in practise).

If you fly in a plane at Mach 0.9, and you are overtaken by a plane flying at Mach 1.1, then you will certainly hear the boom, even if the relative speed between you and the supersonic plane is only Mach 0.2. But the pitch of the sound will be very much changed, just like the pitch of the sound of a car changes when passing you a high speed, only much more changed.

In popular words, any object moving through the atmosphere sends a warning to the air ahead telling "I am coming, please make preparations to get out of the way". That warning moves at sonic speed. A supersonic plane overtakes that warning. The lack of warning totally changes the pressure gradients around aerodynamic shapes. In very much layman's terms, the air is moved by the wing leading edge hitting it like a hammer, instead of by pressure changes escalating ahead of the plane at subsonic speed.



Always keep your number of landings equal to your number of take-offs, Preben Norholm
User currently offlinechrisco1204 From United States of America, joined Dec 2011, 28 posts, RR: 0
Reply 14, posted (2 years 7 months 3 weeks 1 day 22 hours ago) and read 4928 times:

Quoting as739x (Thread starter):
Also, is a sonic boom different at low altitude over the water vs. at higher altitudes?

A sonic boom might sound slightly different over different surfaces like water, dirt, rock, etc. simply due to how it might echo, and interact with those surfaces.

Concerning altitude, the speed of sound is affected by temperature, so if you go higher in altitude (and the temperature subsequently drops) the local speed of sound will decrease. As such, the speed that the aircraft must travel to break the sound barrier will be relatively lower.

I hope that helps.


User currently offlineWingscrubber From UK - England, joined Sep 2001, 845 posts, RR: 0
Reply 15, posted (2 years 7 months 2 weeks 5 days 18 hours ago) and read 4649 times:

Possible explanation for the 'double clap' below deck, and 'single clap' above; sound travels faster through water than air, because the airplane was flying 'on the deck', it was probably creating an audible 'boom' under the water's surface as well as above, the passengers below deck therefore heard this 'water boom' as well as the 'air boom', or possibly the internal acoustics of the boat caused the 'air boom' to echo.


Resident TechOps Troll
User currently offlinespudh From Ireland, joined Jul 2009, 300 posts, RR: 1
Reply 16, posted (2 years 7 months 2 weeks 5 days 16 hours ago) and read 4620 times:

Quoting KDTWflyer (Reply 4):
The clap or double-clap sound is dependent largely upon how long the aircraft is as far as I know. This is because one shock wave forms at the leading edge of the aircraft and another forms at the trailing edge.

As far as I know this is the explanation for a double clap although I thought that there was one caused by the nose and the second was caused by the leading edge of the wing. Fighters are too short to produce a discernable double clap but Concorde, B1 and SR71 should all produce a double with Concordes being the easiest to make out.

I don't actaully remember it myself but I have friends who sail a lot off the west coast of Ireland and they all reckoned you could set your watch from the Concorde double boom back in the early glory days of supersonic passenger flight.


User currently offlineHaveBlue From United States of America, joined Jan 2004, 2098 posts, RR: 1
Reply 17, posted (2 years 7 months 2 weeks 5 days 9 hours ago) and read 4584 times:

Quoting spudh (Reply 16):
Fighters are too short to produce a discernable double clap but Concorde, B1 and SR71 should all produce a double with Concordes being the easiest to make out.

You are correct, but you left out the one double boom generating 'plane' that thousands of people are familiar with... the Space Shutttle! Living in the Daytona Beach area since I was kid to presently we heard many a double booms as the Shuttle made its way back to Kennedy.  

The XB-70 should have made a good one too....



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User currently offlinevikkyvik From United States of America, joined Jul 2003, 9780 posts, RR: 26
Reply 18, posted (2 years 7 months 2 weeks 4 days 7 hours ago) and read 4491 times:
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Correct me if I'm wrong, as it's been awhile since I learned this stuff:

Quoting bikerthai (Reply 2):
Understanding that a plane going near M1 can have a shock wave over the wing. Can a by-stander hear anything with respect to that shock over the wing?

If you happen to be standing in the path of that shockwave, then yes.

But the shockwave is only in the area of supersonic flow. For a subsonic aircraft traveling just under Mach 1, the shockwave won't propogate to infinity - it'll end where the supersonic flow ends, as you move away from the aircraft.

Quoting prebennorholm (Reply 13):
If it flies in a perfect circle around you in totally calm weather (no wind at all), then you will hear a constant boom. (That phenomenon will be very hard to produce in practise).

Wouldn't you actually never hear the boom from an aircraft flying in a circle around you? The aircraft's path is at all times perpendicular to the vector between you and it (the radius of the circle), but the boom is angled backwards, so wouldn't it never actually hit you?

Quoting spudh (Reply 16):

As far as I know this is the explanation for a double clap although I thought that there was one caused by the nose and the second was caused by the leading edge of the wing.

Any surface that turns the air away from freestream will cause a shockwave. See all the shocks in this photo:


View Large View Medium
Click here for bigger photo!

Photo © Ismael Jorda



However, in practice, all the shocks tend to coalesce into the forward and aft shocks at sufficient distance from the airplane.

Quoting HaveBlue (Reply 17):

You are correct, but you left out the one double boom generating 'plane' that thousands of people are familiar with... the Space Shutttle! Living in the Daytona Beach area since I was kid to presently we heard many a double booms as the Shuttle made its way back to Kennedy.

Interestingly, of the two times I've heard Space Shuttle sonic booms (three times really, but I was too young to remember the first), one was a mild double-boom, and the other was an extremely powerful single boom. Of course, given how loud it was, it may have just sounded like a single boom.



"Two and a Half Men" was filmed in front of a live ostrich.
User currently offlineprebennorholm From Denmark, joined Mar 2000, 6387 posts, RR: 54
Reply 19, posted (2 years 7 months 2 weeks 3 days 9 hours ago) and read 4426 times:

Quoting vikkyvik (Reply 18):
Quoting prebennorholm (Reply 13):
If it flies in a perfect circle around you in totally calm weather (no wind at all), then you will hear a constant boom. (That phenomenon will be very hard to produce in practise).

Wouldn't you actually never hear the boom from an aircraft flying in a circle around you? The aircraft's path is at all times perpendicular to the vector between you and it (the radius of the circle), but the boom is angled backwards, so wouldn't it never actually hit you?

No, you would still hear it.

I think I know what you mean. A straight cone with the plane at the tip would never touch you. But when flying in a circle, the cone isn't straight, but bent similar to the flight path, or somewhat similar to a snail's house.

The boom is generated at all times from the supersonic plane, and it travels in all directions at the speed of sound.

One funny thing, if we imagine the earlier mentioned "perfect circle" flown around you in the center, and the plane flies with Mach number = Pi (3.1415...etc), then the sound will travel exactly one diameter for each circle the plane makes. Since you are one radius - or half a diameter away, then you will hear the boom continuously, but hear it coming from exactly the opposite direction of where you see the plane.

In that scenario, if we define your position as the trailing end of the cone, then the cone has been bent 180 degrees.



Always keep your number of landings equal to your number of take-offs, Preben Norholm
User currently offlineHaveBlue From United States of America, joined Jan 2004, 2098 posts, RR: 1
Reply 20, posted (2 years 7 months 2 weeks 3 days 8 hours ago) and read 4417 times:

vikkyvik that picture you posted is just sick! I know you didn't take it but the detail is amazing. Nice.

Quoting vikkyvik (Reply 18):
Interestingly, of the two times I've heard Space Shuttle sonic booms (three times really, but I was too young to remember the first), one was a mild double-boom, and the other was an extremely powerful single boom. Of course, given how loud it was, it may have just sounded like a single boom.

I was a teenager the first time I heard it, I wasn't expecting it and it scared the sh*t out of me lol, but it was definitely a double boom.. as were the other times I heard it. Miss that sound..



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User currently offlinesprout5199 From United States of America, joined Feb 2005, 1852 posts, RR: 2
Reply 21, posted (2 years 7 months 2 weeks 2 days 23 hours ago) and read 4388 times:

Quoting HaveBlue (Reply 20):
I wasn't expecting it and it scared the sh*t out of me lol, but it was definitely a double boom.. as were the other times I heard it. Miss that sound..

My ex actually woke me up one night saying there was an "explosion" outside. Turned out the Shuttle's path came over South Florida for that landing. news said over 1000 calls to 911 saying there was "explosions" right at the time it flew over. I will miss the sound also and going out side to watch every launch.

Dan in Jupiter


User currently offline474218 From United States of America, joined Oct 2005, 6340 posts, RR: 9
Reply 22, posted (2 years 7 months 2 weeks 2 days 23 hours ago) and read 4384 times:

Quoting spudh (Reply 16):
Fighters are too short to produce a discernable double clap but Concorde, B1 and SR71 should all produce a double with Concordes being the easiest to make out.

I grew up in Palmdale California and in the 1950's and 60's I heard thousands of sonic booms. The vast majority were of the double clap type.


User currently offlinevikkyvik From United States of America, joined Jul 2003, 9780 posts, RR: 26
Reply 23, posted (2 years 7 months 2 weeks 2 days 13 hours ago) and read 4345 times:
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Quoting prebennorholm (Reply 19):

No, you would still hear it.

I think I know what you mean. A straight cone with the plane at the tip would never touch you. But when flying in a circle, the cone isn't straight, but bent similar to the flight path, or somewhat similar to a snail's house.

The boom is generated at all times from the supersonic plane, and it travels in all directions at the speed of sound.

One funny thing, if we imagine the earlier mentioned "perfect circle" flown around you in the center, and the plane flies with Mach number = Pi (3.1415...etc), then the sound will travel exactly one diameter for each circle the plane makes. Since you are one radius - or half a diameter away, then you will hear the boom continuously, but hear it coming from exactly the opposite direction of where you see the plane.

In that scenario, if we define your position as the trailing end of the cone, then the cone has been bent 180 degrees.

Gotcha, yeah I didn't really think that one through properly.  

Thanks.

Quoting HaveBlue (Reply 20):
vikkyvik that picture you posted is just sick! I know you didn't take it but the detail is amazing. Nice.

Seriously. One of the best I've seen.

Quoting HaveBlue (Reply 20):
I was a teenager the first time I heard it, I wasn't expecting it and it scared the sh*t out of me lol, but it was definitely a double boom.. as were the other times I heard it. Miss that sound..

Yeah, I've heard two since I moved back to LA in 2007. The first was the mild double-boom, and I knew that one was coming - I was following it on SpaceFlightNow, and walked outside right when it said the shuttle had crossed the coastline.

The 2nd one, in '09 or '10, scared the living crap outta me, cause I wasn't expecting it, and it was really loud.



"Two and a Half Men" was filmed in front of a live ostrich.
User currently offlinespudh From Ireland, joined Jul 2009, 300 posts, RR: 1
Reply 24, posted (2 years 7 months 2 weeks 2 days 2 hours ago) and read 4307 times:

Quoting spudh (Reply 16):
As far as I know this is the explanation for a double clap although I thought that there was one caused by the nose and the second was caused by the leading edge of the wing.
Quoting KDTWflyer (Reply 4):
This is because one shock wave forms at the leading edge of the aircraft and another forms at the trailing edge.

I did a bit of digging last night, KDTWflyer is right but I'm not completely wrong. Vikkyvik is closest to the answer. Here's a link with some good photos using Schlieren photography.
http://library.thinkquest.org/12228/Page4.html
Doesn't linger on why a double or single boom. I think it'll have a lot to do with wave propogation / interference and the relative angle and altitude of the flight path relative to the listener.

In the picture of the T-38 Talon at M1.1 it is obvious that the nose and tail shock cones are at different angles. As these travel away they will be further apart and maybe more discenable as double boom. I can only assume that if the intake and wing etc shock waves are parallel they will merge in terms of sound.

Thats my guess but I'm open to education by any passing wisdom  


25 vikkyvik : Good link, thanks. If you go to the 2nd page of that link (click the bottom where it says "Now that we know what sonic booms are, click here to take
26 geezer : At the time WW 2 started, my sister and her husband moved about 40 miles north to Dayton, Ohio, where he took a job at what was then known as Wright F
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