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Sonic Boom - Really An Issue?  
User currently offlineKeta From Germany, joined Mar 2005, 448 posts, RR: 0
Posted (8 years 3 months 4 weeks 1 day 6 hours ago) and read 3113 times:

One of the big problems of supersonic commercial airplanes is that the supersonic flight is limited to over the sea. It seems like the boom is very strong and can cause problems to people.

My question is, how strong is the sonic boom? Are there any effects other than loudness? The restrictions imposed to the Concorde were only political? I don't think so, because fighter aircraft have restricted supersonic flight too.

I have never heard a sonic boom, only a video (you can see it here on YouTube) and it doesn't seem to be very loud. Maybe hearing it everytime an airplane passes above would be a different thing, though. Have you ever heard one? Is it really that bad? Will planes have to fly supersonically over non-populated zones only?


Where there's a will, there's a way
18 replies: All unread, jump to last
 
User currently offlineSimtim From United States of America, joined Mar 2006, 46 posts, RR: 0
Reply 1, posted (8 years 3 months 4 weeks 1 day 6 hours ago) and read 3106 times:

Hi Keta,

Sonic booms are indeed quite loud. Of course, it depends on the altitude of the aircraft in question. In the USA the regulation for supersonic flight is 30 miles from the nearest land and 30,000 feet or higher. Of course, provisions are made for military defense.

- Tim



Radar service terminated, squawk and maintain VFR, frequency change approved!
User currently offlineStarlionblue From Greenland, joined Feb 2004, 17003 posts, RR: 67
Reply 2, posted (8 years 3 months 4 weeks 1 day 5 hours ago) and read 3103 times:

Having heard fighter aircraft breaking the sound barrier, I can confirm that booms are VERY LOUD. And consider that a fighter plane is quite small compared to Concorde.

I have also lived in West London. You could always tell that it was around 1730-1740 from a low rumbling that would start. Concorde would pass about 5 minutes later (I am not making this up) and was of course not even supersonic at this point.

I normally have little sympathy for NIMBYs, but even I would draw the line at frequent sonic booms.

EDIT: Just to clarify, I am not making up the fact that noise would precede subsonic Concorde by at least 5 minutes. The fact that I was not making up Concorde itself should be clear. Big grin

[Edited 2006-04-06 01:46:28]


"There are no stupid questions, but there are a lot of inquisitive idiots."
User currently offlineCorey07850 From United States of America, joined Feb 2004, 2525 posts, RR: 5
Reply 3, posted (8 years 3 months 4 weeks 1 day 5 hours ago) and read 3101 times:

I believe in my aero class, the figure was something like 140 pounds per square foot of force

User currently offlineArmitageShanks From UK - England, joined Dec 2003, 3611 posts, RR: 15
Reply 4, posted (8 years 3 months 4 weeks 1 day 2 hours ago) and read 3041 times:

It is increadibly loud. It's like one of those professional fireworks on the 4th of July.

I would be really pissed if I had one of those over my house every day.


User currently offlineLehpron From United States of America, joined Jul 2001, 7028 posts, RR: 21
Reply 5, posted (8 years 3 months 4 weeks 1 day 1 hour ago) and read 3034 times:

Quoting Keta (Thread starter):
My question is, how strong is the sonic boom? Are there any effects other than loudness?



Quoting Corey07850 (Reply 3):
I believe in my aero class, the figure was something like 140 pounds per square foot of force

Careful, sonic booms are not constants. They are sound, so in essence, they vary with the weight of the plane, speed it travels, altitude (distance from source) and most of all: it's own shape.

Standard audio speakers are shaped to project sound to a target, whether your eardrums in headphones or thousands in a concert. An aircraft's shape can do damage and until recently, it was assumed the sonic boom could not be changed by shape. That is why SSBJ's are proposed as practical. Keeping them smaller and slower allows for the cheapest if not easiest ways of reducing the sonic boom's impact. Changing the shape of the plane to allow for heavier and faster aircraft would require massive investment.

The most visible (future) supersonic market has most routes over water; investing in sonic boom mitigation might be out of the way. Even as a regional, it might not be worth the cost of total mitigation, maybe slightly.

Giving an SST's wing a positive dihedral helps. Instead of having most of the wave reflect down, it goes somewhat outwards and down, spreading out the 'boom carpet', being what the audible path a shockwave makes on the ground. This alone has a dramatic effect. A +15-degree dihedral on Concorde could have cut her sonic boom by a factor of 4, for example, to a half pound per square foot. The one major disadvantage is the plane's stability and control.



The meaning of life is curiosity; we were put on this planet to explore opportunities.
User currently offlineHaveBlue From United States of America, joined Jan 2004, 2098 posts, RR: 1
Reply 6, posted (8 years 3 months 4 weeks 22 hours ago) and read 2995 times:

I've heard the sonic boom of the Space Shuttle, and it is LOUD. I live in Daytona Beach and a couple of times we were in the flight path home to KSC. I was a teenager the first time I heard this incredibly loud BAH BOOM! and was like wtf? until I found out the shuttle had just passed over. It has a double boom actually, and Lephron is correct size, weight, speed and atmospheric conditions all determine how loud that boom is.


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User currently offlineCorey07850 From United States of America, joined Feb 2004, 2525 posts, RR: 5
Reply 7, posted (8 years 3 months 4 weeks 16 hours ago) and read 2948 times:

Quoting HaveBlue (Reply 6):
It has a double boom actually

Yep... Interesting fact is that the shuttle is so long that there is enough space between the tail and wing sonic booms that they don't run together and allow you to hear them both

Quoting Lehpron (Reply 5):
Careful, sonic booms are not constants. They are sound, so in essence, they vary with the weight of the plane, speed it travels, altitude (distance from source) and most of all: it's own shape.

I should have stated that the most powerful sonic boom was from an F-4, measured around 140 pounds of force per square foot.... Just to give the original poster an idea of how strong they are


User currently offlineJush From Germany, joined Apr 2005, 1636 posts, RR: 3
Reply 8, posted (8 years 3 months 4 weeks 15 hours ago) and read 2940 times:

Quoting Corey07850 (Reply 7):
Yep... Interesting fact is that the shuttle is so long that there is enough space between the tail and wing sonic booms that they don't run together and allow you to hear them both

Is that the same reason for Concorde??
Cause you can hear a double-boom from Concorde as well.

Regards
jush



There is one problem with airbus. Though their products are engineering marvels they lack passion, completely.
User currently offlineEGTESkyGod From United Kingdom, joined Jun 2005, 1712 posts, RR: 12
Reply 9, posted (8 years 3 months 4 weeks 15 hours ago) and read 2937 times:
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Quoting Starlionblue (Reply 2):
You could always tell that it was around 1730-1740 from a low rumbling that would start

Its interesting you should say that. I live in Devon, SW England, and at about 5 pm (BA002), and again at 10pm(BA004 until the later years), there was a short sharp rumble from the North, that sometimes made the house creak. That, in itself, is not annoying, in fact being a Concorde nut, I used to listen out for it. Sometimes we even had an extra rumble from the South as the Air France Concordes came in over the English Channel.

However, the video in the link was first played to me in a room full of 100 people at Fly! The London Air Show 2005 at Earls Court by Concorde Captain Les Brodie, and he played it on Big Surround Sound Speakers, and it was very very loud indeed. It is the only time I've ever seen 100 people simultaneously crap themselves!!

It would be much louder in real life, so I dont think it is tolerable for this to be heard over populated area until the boom carpet is sufficiently changed, as Lehpron has stated.



I came, I saw, I Concorde! RIP Michael Jackson
User currently offlineOkie From United States of America, joined Jul 2003, 2989 posts, RR: 3
Reply 10, posted (8 years 3 months 4 weeks 15 hours ago) and read 2931 times:

They did test over flights in my area in the 60's, 3 months in the fall and 3 months in the spring, twice a day at exact times so as to not be confused with other events. I always looked forward to the 1:30 pm sonic boom as it signaled the end of my Latin class.

The sound varied in intensity from day to day, whether atmospheric or relationship to altitude of the aircraft but there was never any doubt it was a sonic boom. The results obviously helped lead to the decision not to fly super sonically over land.

What it did accomplish was to smoke every screwball out of the woodwork. Children were born naked, 15 year old cows quit producing milk, foundations settled and cracked, windows had baseball size holes broken in them, the list went on and on.

Okie


User currently offlineVc10 From United Kingdom, joined Nov 2001, 1407 posts, RR: 16
Reply 11, posted (8 years 3 months 4 weeks 13 hours ago) and read 2896 times:

Lehpron,
Just a point I always thought that the shock wave from a supersonic object takes up the shape of a cone reflecting equally in all directions, so I fail to understand how a dihedral on the wing would affect it.  Sad

little vc10


User currently offlineKeta From Germany, joined Mar 2005, 448 posts, RR: 0
Reply 12, posted (8 years 3 months 4 weeks 12 hours ago) and read 2869 times:

Thanks for your info guys. It's really a shame that it works that way, I hope someday the effects will be reduced enough to be permissible.


Where there's a will, there's a way
User currently offlineStarlionblue From Greenland, joined Feb 2004, 17003 posts, RR: 67
Reply 13, posted (8 years 3 months 4 weeks 10 hours ago) and read 2845 times:

Quoting Okie (Reply 10):
Children were born naked,

Very impressive feat. Big grin

Quoting Vc10 (Reply 11):
Lehpron,
Just a point I always thought that the shock wave from a supersonic object takes up the shape of a cone reflecting equally in all directions, so I fail to understand how a dihedral on the wing would affect it. Sad

little vc10

As I understand it, if the surface is angled outwards, the cone will move out from a point on that surface perpendicular to the surface. So when you get to the ground, the cone will be larger than if it moved straight down (flat wing). Since the sound is more spread out, the perceived sound at any point on the target is less intense.

But I may be waaaay off base  Wink



"There are no stupid questions, but there are a lot of inquisitive idiots."
User currently offlineJetlagged From United Kingdom, joined Jan 2005, 2543 posts, RR: 24
Reply 14, posted (8 years 3 months 3 weeks 6 days 9 hours ago) and read 2720 times:

Quoting Okie (Reply 10):
The sound varied in intensity from day to day, whether atmospheric or relationship to altitude of the aircraft but there was never any doubt it was a sonic boom. The results obviously helped lead to the decision not to fly super sonically over land.

I remember this too. But the booms were so muffled that you only noticed them if you listened. A supersonic aircraft at 50,000 feet should be no nuisance to people on the ground at all, especially if it were a regular occurence.

Quoting Starlionblue (Reply 13):
As I understand it, if the surface is angled outwards, the cone will move out from a point on that surface perpendicular to the surface. So when you get to the ground, the cone will be larger than if it moved straight down (flat wing). Since the sound is more spread out, the perceived sound at any point on the target is less intense.

You forget these are pressure waves and obey the inverse square law. Whether they are focussed or diffused by wing shape is largely irrelevant.



The glass isn't half empty, or half full, it's twice as big as it needs to be.
User currently offlineLehpron From United States of America, joined Jul 2001, 7028 posts, RR: 21
Reply 15, posted (8 years 3 months 3 weeks 6 days 4 hours ago) and read 2678 times:

Quoting Vc10 (Reply 11):
Just a point I always thought that the shock wave from a supersonic object takes up the shape of a cone reflecting equally in all directions, so I fail to understand how a dihedral on the wing would affect it.

The bow and tail waves are not the only ones. There are many waves spawning off of every point on the plane.

Quoting Starlionblue (Reply 13):
As I understand it, if the surface is angled outwards, the cone will move out from a point on that surface perpendicular to the surface. So when you get to the ground, the cone will be larger than if it moved straight down (flat wing). Since the sound is more spread out, the perceived sound at any point on the target is less intense

I'll be honest, I didn't get what you typed. As far as I know, the main bow wave is shaped from the first volume (cross section integrated over length) that penetrates it. A nose cone renders a cone shock-wave. While a sharp wedge like X-43 renders a wedge shock-wave with two half-cones on either side. Either way, the bow waves are not affected by the shape or orientation of the wing. But like I told Vc10, the bow and tail are not the only ones. We hear two 'booms', but one would have to have real sensitive ears to hear the others.

Quoting Jetlagged (Reply 14):
You forget these are pressure waves and obey the inverse square law. Whether they are focused or diffused by wing shape is largely irrelevant.

That is true but I feel it is a bit over simplified. In my personal research, shape is extremely relevant. Sound from a moving object comes from the fact that it is disturbing that air to move. The object then becomes the source of the sound, I'll go into that right now.

A lot of the following is self taught, forgive the wording, please ask if you are at all confused. I will need you to have the ability to think/imagine in 3D.  Wink

A basic source of sound is point (or a tiny ball in non-scientific terms) and the sound waves propagate (expand) outwards in spheres. When a point moves faster than sound, the spheres collect as a cone.

Imagine a series of points close together, I'll call this a "line source" of sound. Sound waves appear propagate out as cylinders with spheres expanding from both ends. An aircraft fuselage can be approximated as a line source. So can a leading edge of a wing or fin or engine inlet lip.

Now imagine an area of source points (tightly packed in a grid). I'll call this a "plate source" of sound (like an audio speaker). In this case, when sound leaves an area or surface of points, it does so perpendicular to the surface. The edges of the plate can be considered as lines sources and the corners can be point sources. In real life, the intensity of the waves that leave the edges and corners are weak compared to the major surfaces.

When we hear a sonic boom, we are hearing the wing's leading edge and trailing edge wave, not the main bow and tail waves of the plane. The wing is experiencing both a supersonic pressure due to motion and wing loading. This causes it to expand into the bow and tail waves, they coalesce as they reach the ground. This is why we hear a double-bang. If the plane flew closer to the ground, we would hear multiple bangs, like a machine gun. But the wing would still be the loudest (and longest period as the length of the chord to length of the plane is biggest). That said, whichever altitude, where you are on the ground matters as well.

This is one of the reasons why supersonic aircraft wings matter so much, at least in my own sonic boom analyses. The area, sweep, and dihedral will affect the way the wing's shockwave (not the main bow or tail cones) expands away from it as it propagates to the ground. Wing area and sweep can vary the intensity of the pressure wave (sound is just air pressure, i.e. air in motion) and the dihedral changes the direction the propagating waves instead of just straight down like a flat wing.

The waves that come off of the airplane that go initially down end up refracting within the atmosphere. Below are pictures which came from a NASA web page but it was a while back. (I couldn't find the original, I have a good idea from where but it wont link here, if any o'ya'll can find the link I'd love it) Both pictures show how the shock-waves move away from the plane before they reach the ground.

This first one shows the waves coalescing from a side view. As you can see the wing had the highest pressure differencial, but then the model shown has an angle of attack...


The picture below shows a forward view. The distance between where the boom hits the ground is known as a "boom carpet", for Concorde it was 80 miles wide -- compare this to flying at 11 miles up. An increase in dihedral would widen the carpet while distributing the same load, the boom pressure would drop.


Again, I didn't draw these, but I'd like the original link. NASA's search gives me links and I think this is it but it wont open for me: http://trc.dfrc.nasa.gov/Newsroom/FactSheets/FS-016-DFRC.html



The meaning of life is curiosity; we were put on this planet to explore opportunities.
User currently onlineTheSonntag From Germany, joined Jun 2005, 3526 posts, RR: 29
Reply 16, posted (8 years 3 months 3 weeks 5 days 14 hours ago) and read 2618 times:

Until maybe 10 years ago, I heard sonic booms quite often in Germany, mostly from fighter planes. I think it has become very seldom today, also because the cold war is over so there are much less fighter planes here today.

I only can say, sonic booms can be extremely loud. I don't know how loud it is when they are at 50000feet, but only recently, a Phantom which intercepted a plane which didn't answer to the communications set off a lot of car alerts in Hamburg.


User currently offlineGDB From United Kingdom, joined May 2001, 13170 posts, RR: 77
Reply 17, posted (8 years 3 months 3 weeks 5 days 11 hours ago) and read 2599 times:

One evening, in 1998 or 1999, on a quiet backshift in the control centre of Concorde Service Delivery hangar, I foolishly perhaps picked up a ringing phone as I passed by.

It was external, from outside BA, (so the BA switchboard had screwed up sending the call, even it was was about Concorde, to our hangar).

It was a quite irate lady calling from the West Country, she wanted to know 'why Concorde had gone supersonic over her house', since she had heard a 'bang' and the place had rattled.

I assured her that Concorde did not ever go supersonic over the UK, that it would be breaking all sorts of rules, but she was adamant it had.
So then I asked if her area ever had low flying military aircraft at all.

This did not go down too well either, worse, I was checking the computer for the inbound evening JFK-LHR BA004, the times she gave corresponded with it.

(I really wanted to say 'yeah it's sounds great doesn't it, I live right near LHR too', but that would have been a silly thing to do, she also sounded like the sort who would take things further as well).

So I gave her the number the dozy switchboard should have put her through to, the BA Press Office, and thanked her for telling us.

I heard no more of it, until a tabloid paper reported a few weeks later, that BA Concordes had started their decelleration a little sooner, going subsonic inbound to the UK a few miles sooner.

What had happened was a 'refracted boom'.
Sometimes conditions at around 150,000 feet caused the upward travelling part of the mach cone to be refracted down again, well forward of of the regular boom, but also much weaker, of much less intensity than the normal boom.
It was caused by high level winds at 150,000 ft.

It was known about, first being recorded in 1976/7, but was an infrequent weather condition.


User currently offlineEGTESkyGod From United Kingdom, joined Jun 2005, 1712 posts, RR: 12
Reply 18, posted (8 years 3 months 3 weeks 4 days 20 hours ago) and read 2532 times:
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Quoting GDB (Reply 17):
a quite irate lady calling from the West Country, she wanted to know 'why Concorde had gone supersonic over her house', since she had heard a 'bang' and the place had rattled.

I know she was slightly closer to the boom carpet than me, cos she was in Cornwall, but it really wasn't that bad. I remember being quite pissed off that she had moaned about it, and the newspaper article said Concorde would now start decelerating 40 seconds earlier.



I came, I saw, I Concorde! RIP Michael Jackson
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