Talk:Sonic boom

Propellers?

The text currently reads: A sonic boom can also be heard on prop planes, even though they do not travel at the speed of sound. The high rotation speed of its rotors is usually faster than sound, creating the "beating, humming" noise of a prop plane.

This does not sound right to me, although my specialty is the history of aviation, not the physics of flight, so I am not quite confident enough to delete or edit it. It was my understanding that as propellers (or at least their tips) approach Mach 1, their aerodynamic performance is degraded considerably. The "beating, humming sound" of a piston-engined aircraft is a just a combination of engine noise and the propeller rotating--not a sonic boom. There are special supersonic propellers but these have never been mounted on any regular production airplane. 165.91.64.240 (talk) 13:46, 20 September 2008 (UTC)RKH

• • No doubt you are right. Take the Viscount 800 (yes, I know this is going back a bit but I have the data). The Dart 510, according to Jane's 1956-7 reached maximum revs or 14500 rpm. It was geared down by 1:0.093 so the prop ran at 1350 rpm or 22.5 rps. The prop diameter was 3.05 m, so the tip speed (how far in 1 sec) 3.05x pi x 22.5 = 215 m/s. That is about M 0.65 at sea level, which is roughly where you are when using max revs, at take off. The gearing ratio is chosen to keep the prop tip at a speed where compressibility effects are not too serious. So the more powerful the engine and hence the bigger the prop, the more rearing down one needs. Of course we have to add the speed of the aircraft (vectorily) to the tip speed on a fast aircraft, leading to interesting prop designs, such as those on the Airbus 400M. The beating effect, by the way is normally due to the props on a twin running at slightly different speed/frequencies; under these conditions you may hear the difference frequency and is nothing to do with compressibility. I think I'll take the comment out.TSRL (talk) 22:38, 8 November 2008 (UTC)

Google

When finding this page from google it says "A sonic boom produced by an aircraft moving at twice the speed of sound." in the text. This seems to be very confusing as sonic booms occur when the aircraft passes the speed of sound. ddd

Waqas

I would like to know what is the exact frequency of sonic boom? How much frequency can a normal human ear bare?

Any pulse of sound contains a range of frequencies, and an infinitesimally short one will produce "white noise", with a flat spectrum from 0 Hz to infinity Hz. Roughly, a pulse 1 ms long will have a top frequency of 1000 Hz about 3 octaves up from middle C, but remember the continuous range of freqencies below this. If you want to get technical, you might want to argue for a somewhat (1/6) lower frequency max, but we are talking principles here. I've heard a lot of sonic bangs and they sound a bit like heavy gunfire (no I haven't heard this first hand), a sort of crump, often double.

If you are young you will be able to hear from about 10 Hz to 20 kHz. Any or all of these at moderate powers are completely acceptable and harmless; it's high power that might do you damage, be unbearable. TSRL (talk) 22:35, 8 November 2008 (UTC)

Sample

Can we get a sample? It's all well & good describing what it sounds like, but sample would be nice. 210.50.248.143 (talk) 12:40, 14 November 2008 (UTC)

• • It's there already. Go to "audible boom one or two" and run the Concorde piece. The aircraft is high enough for the "far field" N-type double shock, the classic sonic boom to be well developed. We are not told what frequency response their kit has, but it sounds plausible. Nearby, at low altitude things are messier, with shocks from all sorts of places where the local airspeed is high.TSRL (talk) 22:58, 14 November 2008 (UTC)

merge

I think the two should merge because When a plane breaks the sound barrier, a sonic boom is the result

Felix1624 (talk) 20:33, 7 May 2008 (UTC)

Please be informed: a sonic boom is NOT resulted when the plane "breaks the sound barrier", it exists throughout the supersonic range.

I've not checked, but presumably the cone angle is that for M=2.0. TSRL (talk) 22:51, 8 November 2008 (UTC) I have checked now: the angle is 20 deg so M=2.92TSRL (talk) 21:29, 11 November 2008 (UTC)

Drawings

Somebody please provide better drawings.

1. The red engine drawing is very unclear and confusing. Which end is at the front? It can be figured out, but why should the reader have to think about that? Objects usually move across a page from left to right, but this aircraft seems to be going from right to left. The two versions ("inefficient" and "unstable") appear to be making a comparison, but to what? Certainly not to each other because the engines are of a different design. Or, is the lower drawing an enlargement of the upper drawing? Where is the "spike" referenced in the caption? Maybe that pointy thing on the right? Okay, but how does it work? Overall, the drawing provides no information value. The caption contains the only useful information.

2. The next drawing (with "fuselage" and "area rule") makes no sense at all. What is it? Is there a wing there, as implied by the caption? Are we looking down or to the side? The "fuselage" looks more like a butterfly -- I fail to see an aircraft there. The captions says something about reusing some air displacement -- is the drawing trying to show this?

Jeff

• • Agree entirely. These pics appear on many web pages. The top one has something to do with shock waves and engine intakes, I think; nothing to do with sonic booms. The lower one, I guess connects to the "area rule". As you suggest, any meaning is deeply hidden and in any case a connection between area rule and booms would need making. I know they have been in the article since Sept 2005, but my view is they should go.TSRL (talk) 17:19, 17 November 2008 (UTC)

• • • Boom boom: they have gone! If the original inserters wish to bring them back, fine; but please explain and argue for their relevance. Enough folk (Jeff, Maury and so on have been unable to make sense of them, and this is supposed to be the easy intro article to compressible aerodynamics.TSRL (talk) 23:11, 17 November 2008 (UTC)

Used as weapon

I heard that during the Vietnam war, F-4 phantoms were flown supersonic close to ground to produce loud sonic booms to kill or seriously injure soldiers on the ground. Was it just a urban legend? Any retired pilot to confirm this? Kowloonese 22:43, 1 May 2006 (UTC)

Correct me if I'm wrong, but I say urban legend. A sonic boom would certainly harrass the enemy, but could an airplane generate a deadly sonic boom? I don't think so. Loss of hearing and psychological impacts are definitely possible though. 69.181.75.37 22:10, 22 November 2006 (UTC)

• There were reports of combat aircraft during Gulf War 2 using their sonic booms to give the entrenched enemy the impression that they were being bombed, causing them to flee their positions. But sonic booms as a killing weapon? I think urban legend. (Me thinks that the Vietnamese jungle would absorb much of the boom) -- Htra0497 (talk) 08:37, 16 January 2008 (UTC)

• • Don't forget that in the early days of supersonic fight, it was standard at airshows to generate a few booms at low altitude over the crowd, which never harmed any one. TSRL (talk) 22:58, 8 November 2008 (UTC)

Megawatt!?

From my limited physics education I find it difficult to believe that a sonic boom can deliver 167 MW (megawatts - 1,000,000 Watts) per square meter. Although I can believe it delivers mW (milliwatts - 1/1,000 Watt) per square meter. Is this just a bad prefix? I think sound pressures are typically given in dBmW (decibell milliwatts.)

Videos at the bottom

I find it very hard to believe that this: # F-14 Tomcat sonic boom flyby (with audio) (file info)

• F-14 Tomcat flies at Mach 1 over the water, creating a sonic boom as it passes.

is an accurate description of a sonic boom.

1) There IS no sonic boom in this video. 2) Just because the water below the aircraft is a whiteish hue it's caused by the altitude the F-14 is flying.. NOT a sonic boom it's unrelated phenomenon. 3) Those people in my mind would be very, very deaf if it really was a sonic boom that close to them. I kind of doubt they'd be cheering in jubilation. 4) I've seen this video on YouTube.. Same kind of dicussion ensues.

The shock would be generated around the aircraft, not on the water. not a sonic boom. 69.181.75.37 22:10, 22 November 2006 (UTC)

Street Fighter....

Guile's..... Sonic Boom.... Thats what I always think of when I hear sonic boom

---

You're not the only one, dude. SONIC BOOM! (83.151.131.116 23:10, 5 December 2006 (UTC))

PENIS POWERS?

The drawing says "Match One" can we fix it to say "Mach" one? M@$+@ Ju ~ ♠ 19:06, 19 March 2007 (UTC)

Image

Would this image be useful? 81.63.184.84 01:03, 19 April 2007 (UTC)

Units

Richard Seebass and his colleague Albert George at Cornell University studied the problem extensively and eventually defined a "figure of merit" (FM) to characterize the sonic boom levels of different aircraft. FM is proportional to the aircraft weight divided by three-halves of the aircraft length, FM = W/(3/2·L) = 2W/3L. The lower this value, the less boom the aircraft generates, with figures of about 1 or lower being considered acceptable.

Umm, using which units? Dividing a weight by a length doesn't give a dimensionless constant. The 2/3 factor suggests calibration of desirable values against some kind of unit (so the bound can be placed at a nice round 1 rather than 1.5), so which one? -- Milo

Good question. In ever reference I have found to date, there are no dimensions given. Seebass has a recent paper on this that would likely solve the mystery, but it is only available for money. Maury 20:54, 1 May 2007 (UTC)

I tried to work out the correct units by taking the statistics of a Concorde and changing the units around until the result was 1.4, but then I noticed that the article doesn't state if the weight used should be the unfueled weight, the fueled weight or the maximum flying weight (which should be listed anyway) --Genejoker 08:45, 4 September 2007 (UTC)

Sound file?

It would be nice to have a sound file. Could someone supply one pretty please?

Supersonic behind shock wave

Folks, I edited the article to remove the notion that the flow over a supersonic aircraft is subsonic behind the leading shock wave. While a bow shock (normal shock) does drop the gas behind it to subsonic (in the shock-fixed frame), an oblique shock does not (i.e. the gas is supersonic on both sides of the shock in the shock-fixed frame). Supersonic vehicles (as opposed to hypersonic vehicles) are designed to have a leading oblique shock, rather than a bow shock, and so the gas remains supersonic over the vehicle, outside of the boundary layer. The additional shocks produced by wings, tail, etc, are from the supersonic gas being turned to different angles, which requires additional oblique shocks. Blazotron 22:11, 25 June 2007 (UTC)

1991-1992 Sonic Boom in Western Washington

I remember during this time period, there was a really loud boom heard all over Western Washington. I cannot remember what the news media reported was the source, but does anyone have any leads? 209.91.38.50 00:54, 4 August 2007 (UTC)

A meteor? --Una Smith (talk) 21:17, 6 December 2007 (UTC)

Figure of Merit reloaded

Recently, somebody has reverted the FM to the most probably wrong power-law formula FM = W/L^3/2 without any comment. We already had this discussion and found that the formula is at least useless in its current form since no units of weight and length are given. Weight and length of the Concorde are 186 tons (metrical; maximum weight) and 61.66 metres. In SI units (kilograms and metres) we get FM = 186,000 kg / (61.66 m)^1.5 = 384 kg m^-3/2. With tons and metres it is FM = 0.384 t m^-3/2 and with lbs and feet FM = 143 lbs ft^-3/2. All these values are far from the value given in the article (1.4). For the empty weight (79 t) it is even worse. I therefore recommend to remove the formula entirely unless someone fixes it (maybe it is wrongly cited from the original source or it uses some arbitrary units).--SiriusB 08:45, 16 October 2007 (UTC)

FoM is proportional to W/L^3/2, not equal to it. I think you can find the formula here Seebass, R., and George, A. R., “Sonic Boom Minimization,” Proceedings, Second Sonic Boom Symposium, J. Acoustical Society of America, Vol. 51, No. 2 (Part 3), pp. 686-694, 1972. Ydorb (talk) 21:16, 14 March 2009 (UTC)

WikiProject class rating

This article was automatically assessed because at least one WikiProject had rated the article as start, and the rating on other projects was brought up to start class. BetacommandBot 10:03, 10 November 2007 (UTC)

Audible boom one or two?

Here's a YouTube video that has one boom and two booms; why don't you always hear two booms? --Una Smith (talk) 19:22, 5 December 2007 (UTC)

There are two shock waves, one at the nose cone, the other at the tail. Kowloonese (talk) 00:21, 23 October 2008 (UTC)

You don't always here them if they're close together in time due to the way the human ear works; so they're nearly always double booms with long aircraft like Concorde, and single with short aircraft. It also depends a bit on how fast the aircraft is going because of the wake angle, but that's a smaller effect.- (User) Wolfkeeper (Talk) 01:03, 23 October 2008 (UTC)

In principle this is right but in practice wrong, in that small aircraft can readily produce double booms. In the 1950s in Eastern England both the RAF and USAF pilots were playing with their Hunters and Sabres etc. They produced a very well defined double boom, which made you jump the first time or two, but rapidly became the norm. We were also under the RAE Bedford to Wash high speed run for prototype Lightnings, F.D 2 etc. They were usually to high to recognise, a con-trail job but there were no Concordes nor Valkyries around then and there. B-36s, though they closed off the light a little did not go bang. Actually, one can do some numbers: a 10 m long aircraft travelling at say 300 m/s (the speed of sound not all that high up)will produce two shocks separated by 1/3 secs if the two shock waves are parallel. These will be heard as a double boom so long as the individual booms are over in, say 0.1 s. Memory (OK, distant) says it was perhaps more like 0.5 s, so maybe they were higher where M 1 is slower. One ought to have been able to work out their height ... TSRL (talk) 22:46, 8 November 2008 (UTC)

• • This calculation would not work well, since the two shocks in the far field (aircraft a long way away) are almost but not quite parallel. If the plane is nearby, then you may hear shocks from wing leading edges, canopy etc. Also note the shocks first form well below M=1, perhaps M=0.8 at the thickest (roughly) part of the wing as soon as the local air speed is M=1. This is on the top, low pressure wing surface. BTW, Dayton did a nice series of measurements with a SR71 plus F15 chase plane, fully instrumented, and also have published so excellent N wave pressure plots. I don't know if these are under copyright or not: careful use of one or two would help the article. The ground level shock from SR71 at M=1.5 at 48000 ft has a pulse separation of about 0.18 s. TSRL (talk) 17:19, 17 November 2008 (UTC)

Firearms

Firearms bullets do produce sonic booms, don't they? Bullets with higher velocities go faster than the speed of sound. Someone could mention this. -- 81.230.2.47 (talk) 21:36, 1 February 2008 (UTC)

• • They do, and there are many nice Schlieren photon displaying the density variation (qualitatively at least ) from the time of no less than Ernst Mach.TSRL (talk) 21:29, 11 November 2008 (UTC)

Display format help, please

For some reason the Category area overlays the References area for this article. Assuming it's not a recently-introduced flaw in the default wikibook skin, I have no idea how to correct it. Perhaps somebody with a little more MediaWiki knowledge could handle this? --Joe Sewell (talk) 15:33, 6 June 2008 (UTC)

Mach Cutoff

The Sonic Boom entry, Abatement and Perceptions sections, merit some discussion of "Mach cutoff", an alleged phenomena occurring under certain high transonic speeds (~1.15 mach), altitudes, and atmospheric conditions, where no sonic boom reaches the ground. The FAA currently prohibits supersonic (>1.0 mach) flight over the United State by civilian aircraft due to the adverse effects of the sonic booms on population centers. At least one business jet developer is attempting to have the prohibition modified if the "Mach cutoff" effects can be reliably exploited. -- —Preceding unsigned comment added by Andy Perhach (talk • contribs) 22:56, 30 June 2008 (UTC)

ThunderDrums

There is no sense in which sonic booms are like thunder, except that they are (like any another audible effect) the result of setting up a pressure wave, or wave group in air. Banging a drum produces a similar result (a bang) but by an entirely different mechanism. There is no fast moving object in thunder but the locally expanding air itself. Not helpful, it seems to me. TSRL (talk) 23:14, 8 November 2008 (UTC) A little reflection makes me think this comment is slightly (but only slightly) harsh. It may well be that the speed of sound in the hot, ionised air around the discharge is faster than in the surrounding atmosphere, in which case a shock wave will develop. Since the temperature is higher, so should the speed be. Seems quite likely, though I've not checked the details. Even so, IMHO it's not a helpful example for developing the idea of shock waves generated by a solid moving object in a gas, which we're trying to do here.TSRL (talk) 17:46, 11 November 2008 (UTC)

Agreed. A sonic boom is the sound pressure wave caused by the supersonic passage of an object. The crack of a high-powered rifle bullet flying overhead qualifies. Lightening, however, is a linear explosion resulting from superheated air, and is a distinctly different physical phenomenon. Verdict: reference removed. 23:02, 2 May 2010 (UTC) —Preceding unsigned comment added by 75.70.218.190 (talk)

Sonic Laser

Does anyone know why this redirects here, there's no info on it here. 77.102.173.23 (talk) 18:50, 3 January 2009 (UTC)

question of sound dynamic

IF one could accelerate past the speed of sound, does the accelerated individual experience a sonic boom the instant the barrier is broken? And does sound cease beyond that point until the speed is reduced to subsonic?

This is in reference to the way some games like XGRA portray sonic booms, by breaking the sound barrier, you are met with a boom followed by silence, I'm just wondering if there's any truth to it. Murakumo-Elite (talk) 02:47, 18 June 2009 (UTC)

• • I believe this is now answered in "Perception and Noise".

Preroll (talk) 19:54, 23 October 2010 (UTC)

Perception and Noise

Added the fact that nothing is heard from people in the airplane itself and that the boom is continuous. It is a common misconception that only one bang is heard on the plane and some even believe that only one place on the ground receives the boom. Preroll (talk) 04:37, 15 October 2010 (UTC)

Suggestion for: Mach cone.svg

Regarding the diagram: Mach cone.svg. At mach 1, the mach cone exists, but it isn't shown in the image. At mach 1, the mach angle is pi/2, and the mach cone is actually a plane. Is it possible to add a red vertical line to the second image? See: http://img219.imageshack.us/img219/255/sonicfrontsqz7.jpg NOrbeck (talk) 10:01, 23 November 2010 (UTC)

International System of Units

It would be a good idea to use the International System of Units (meter, kilogram) instead of pounds and feet (which might still be put in brackets) — Preceding unsigned comment added by 82.231.224.218 (talk) 16:41, 20 June 2011 (UTC)

Can we rephrase this?

From Measurement and examples: "The pressure from sonic booms caused by aircraft often are a few pounds per square foot."

I do not know if it is just me but the wording seems a little off (not in the sense that the material is wrong, just that it doesn't seem to flow the most smoothly)... Ham Radio 01:59, 8 November 2011 (UTC) — Preceding unsigned comment added by Ke5skw (talk • contribs)

2012 Sonic Boom

This event has attracted coverage in the mainstream British media but is it really worthy of being mentioned in an encyclopedia? The only other specific event mentioned in the article is a notable series of tests which were carried out by the US government which have their own article. I'm going to see what others think but I have taken the liberty to remove some needless exposition about 'a surreal mystery' and something which appeared to insinuate some kind of conspiracy was at play (sigh). Thank you, PamukSoundystem (talk) 21:30, 12 April 2012 (UTC)

I took it out, Wikipedia is not about news, and sonic booms are far too common to mention here more than the very most important ones. This doesn't seem to have been a very major event at all, although sonic booms always seem very dramatic I'm sure.Teapeat (talk) 22:45, 12 April 2012 (UTC)

You're right. This is just a transient event which isn't of any long lasting significance. Thanks for sorting it out! PamukSoundystem (talk) 23:01, 12 April 2012 (UTC)