Talk:Sound barrier

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[edit] Issue with condensation cloud photo use here?

U.S. Navy F/A-18 at transonic speed. The cloud is due to the Prandtl-Glauert singularity.
U.S. Navy F/A-18 at transonic speed. The cloud is due to the Prandtl-Glauert singularity.

Since the Prandtl-Glauert singularity condensation clouds are so commonly misunderstood as being some sort of magical breaking through the sound barrier, or 'breaking the speed of sound,' when they commonly happen at lower speeds, is it appropriate to use this photo for the main one on this page? Or does that just continue to reinforce this confusion/misunderstanding? (even with the photo caption link to PGS)

Admittedly, according to the description written by the photographer, (copy available here), this particular condensation cloud did happen as he heard the sonic boom.

If this one is deemed misleading, what better photo might we use on this page? Perhaps a historical one from Chuck Yeager info?

Should this page at least have a mention in the content area of the common misunderstanding about the PG clouds, and linking over to Prandtl-Glauert singularity?

Any opinions on this? jwilkinson 00:40, 7 January 2007 (UTC)

Yes, although the image description try to explain it, the first thought that may cross one's mind is that that's what happens when you break the sound barrier, and that's that. It's a good photo though, and maybe the image description is good enough. *shrug* — Northgrove 16:46, 21 August 2007 (UTC)

[edit] Compressible? could that be right?

I changed the statement that air behaves as a compressible fluid at transonic speeds with a little trepidation. It seems clear to be that air behaves as a compressible fluid at subsonic speeds, so the change wouldn't seem to make sense otherwise. DJ Clayworth 21:20, 20 Apr 2004 (UTC)

[edit] used in an odd way in this context

But for purposes of aerodynamic at subsonic speed, air behaves as an incompressible fluid. With appropriate adjustments, the same analysis used in aerodynamics may be applied to submersible (underwater) craft. This is what is meant by incompressible. It does not mean that the air cannot be compressed (by appropriate means), only that compression is irrelevant for the analysis. Leonard G. 21:43, 20 Apr 2004 (UTC)

My friendly fluid dynamicist down the corridor said the same. Sorry. DJ Clayworth 21:56, 20 Apr 2004 (UTC)

[edit] problem with F-18 photo?

Some of you aero folk might be able to clear up a problem. The photo is spectacular and really neat and ... But is it actually what is claimed? I've seen similar 'mist nimbus' trailing from assorted edges on a Tomcat doing airshow evolutions (high rate coordinated short radius turns at low altitude and of course low speed) and was told (by an aero grad student standing right next me and following the pointing finger) that it was a compression/expansion effect made visible by water vapor condensation, and was not a local instance of supersonic flow. This appears to be quite an outstanding example of the same thing. Is it?

I can offer only one additional bit of speculation in support of my qualm. The history of the photo suggests that it was taken manually (albeit, given the object motion I suspect a tripod was used), but otherwise manually. Manual tracking and shutter release for an aircraft moving at 770mph+ seems beyond me. I'm sure Gay is in much better shape than I and he surely has better reflexes (no one ever mentioned my flying jets into controlled crashes on aircraft carriers), but ... What have I missed? If anything. ww 20:01, 4 Aug 2004 (UTC)

What is seen is fundamentally different in cause from that seen in high lift conditions in air near the dew point, although the fog appears due to the same fundamental effect of rapid condensation due to rapid decrease in pressure (yes, decrease).
It is commonly known that air compressed adiabatically (without loss or gain of heat) will become warmer, and conversely when expanded becomes cooler. Warm air has a greater capacity for carrying water vapor (water in its invisible form) and conversely, when cooled has less capacity. The dew point is the temperature at which the air is saturated - if a surface is cooled below this temperature, dew will form upon it, and if that temperature is below freezing, frost. If a free body of air is cooled below its dew point and that is above freezing, microscopic droplets of water will form - fog or cloud. If cooled below freezing and no nucleation sites are available then supercooled droplets are formed, otherwise ice crystals and eventually snowflakes, as is seen in the formation of cumulonimbus clouds due to rising air.
As the expansion is adiabatic, it is possible to very rapidly enter and leave the saturated condition, so clear air flowing over the upper surface of a wing may be seen to flash into fog somewhere past the leading edge and then re-evaporate in the vicinity of the trailing edge. This is commonly seen when seated near the wing in an airliner that is about to penetrate a stratus layer after takeoff. The fog will be seen just before penetrating the lower limits of the stratus layer.
The cone shaped effect seen in the image is due to the rarefication portion of the N shockwave that follows the compression portion. Recall that a stationary observing instrument over which passes a shock wave from a passing supersonic aircraft will first record a pressure increase above ambient, a decent to below ambient, and a return to ambient. It is the second part of the N wave that causes a pressure sufficiently low that under appropriate conditions of relative humidity will bring the temperature briefly below the dew point, creating the visible fog. As the strength of the wave diminishes rapidly away from the source (think of an elastic ring being expanded - it becomes thinner) there will be a radius from the aircraft at which the pressure change is insufficient to create the visual effect, hence the approximate circularity of the margin of the disk. -- Leonard G. 03:29, 17 Sep 2004 (UTC)
Where's the photo ww is talking about? Moriori 03:44, Sep 17, 2004 (UTC)
Belay that. Went to F-18 page in error. Sheepish grin. Moriori 03:46, Sep 17, 2004 (UTC)

[edit] Reliable technical information and photographic sources for the sound barrier, sonic boom, and the stunning Prandtl-Glauert condensation clouds

Collection of "Sound Barrier" tutorials by Dr. Mark S. Cramer. Covers the sonic boom, the sound barrier, and the Prandtl-Glauert condensation clouds. An authoritative site. Site URL: http://FluidMech.net

http://FluidMech.net/tutorials/sonic/sonicboom-intro.htm

"Prandtl-Glauert Condensation Clouds" tutorial by Dr. Mark S. Cramer. Part of the "Sound Barrier" collection of tutorials. The site is authoritative. Site URL: http://FluidMech.net

http://FluidMech.net/tutorials/sonic/prandtl-glauert-clouds.htm

"Gallery of Fluid Mechanics - Condensation due to the Prandtl-Glauert Singularity" by Dr. Mark S. Cramer. One of the best authenticated and documented photo collections of Prandtl-Glauert condensation clouds (alternatively, Prandtl-Glauert Singularity or Prandtl-Glauert clouds). The site really is an authority on the subject. Site URL: http://GalleryOfFluidMechanics.com

http://GalleryOfFluidMechanics.com/conden/pg_sing.htm


ChamorroBible.org, Tenjos (Agosto) 17, 2004, "Manguaeyayon na Palabran Si Yuus - God's Precious Words, with the Photograph of the Day". One of the best authenticated and documented photo collections of Prandtl-Glauert condensation clouds (alternatively, Prandtl-Glauert Singularity clouds or Prandtl-Glauert clouds). Eight photographs are included in Part 1 of 2 (August 17, 2004). All public domain. Site URL: http://ChamorroBible.org (generally referenced as "ChamorroBible.org" or the "Chamorro Bible" WWW site).

http://ChamorroBible.org/gpw/gpw-20040817.htm


ChamorroBible.org, Tenjos (Agosto) 18, 2004, "Manguaeyayon na Palabran Si Yuus - God's Precious Words, with The Photograph of the Day". One of the best authenticated and documented photo collections of Prandtl-Glauert condensation clouds (alternatively, Prandtl-Glauert Singularity or Prandtl-Glauert clouds). Eight additional photos in Part 2 of 2 (August 18, 2004). Included in this collection is a remarkable NASA photo of a Prandtl-Glauert cloud around the Apollo 11 Saturn V rocket at launchtime. All public domain. Site URL: http://ChamorroBible.org (generally referenced as "ChamorroBible.org" or the "Chamorro Bible" WWW site).

http://ChamorroBible.org/gpw/gpw-20040818.htm

[edit] Yeager first to break sound barrier in level flight

Discovery Wings recently aired a biography of Chuck Yeager. In that biography they showed an excerpt from a period USAF documentary about the X-1 (XS-1 in the documentary). That documentary said the XS-1 and Yeager were the first to break the sound barrier "in level flight". This leaves the door open for claims by George Welch to have previously broken the sound barrier by diving an F-86.

[edit] Vandalism

This page seems to be undergoing vandalism ("poop barrier", "Air X1", etc)

70.66.108.79

[edit] Wayne Shorter

Just thought people might like to know that this article is used on the back of the CD insert for Wayne Shorter's new live album, Beyond the Sound Barrier. Unfortunately it's used as part of the artwork, so it's not very legible, and clipped on the right hand side, but it's definitely the Wikipedia article. --Andrew Norman 06:01, 21 Jun 2005 (UTC)

[edit] Merge proposal

This article, Sonic boom and supersonic appear to cover similar material and have considerable overlap. Rsduhamel 01:47, 22 December 2005 (UTC)

[edit] Modestly in favor of a merge

My inclination would be to make "sound barrier" a short paragraph as a historic note under "supersonic", or better yet "transonic". It's a relic of the time when there was concern that Mach 1 might be a true barrier with an insurmountable pressure buildup that would prevent passing it.

I haven't checked yet to see if there are already separate pages for subsonic, transonic, and supersonic. Transonic is the most challenging regime to describe.

Another example that really got my attention was supersonic parachutes. One of Neil Armstrong's little-known achievements was an engineering study that proved Apollo's drogue chute would open at supersonic speed and be stable. Thinking about a flexible airfoil with shroud lines attached conjures up thoughts of chaotically interacting shock waves and a distinct possibility that the darn thing might simply never deploy as a working parachute.

--Paul Raveling 08:04, 12 January 2006 (UTC)

If you read the two articles, you will actually find very little overlap in their content. The graphic content of the two articles duplicates, but the text content does not. I propose keeping these two articles separate. Denni ☯ 02:33, 18 January 2006 (UTC)

Merging the Supersonic and Sound Barrier articles might be a good idea since the Sound barrier article is short and a Breaking the Sound Barrier section is included in the Supersonic article. Furthermore, the Breaking the Sound Barrier section in the Supersonic article contains a lot of the same information that is covered in the Sound Barrier article.

--Hoku 12:38, 12 March 2006 (HST)

[edit] merge good?

Yeah, a merge def. makes sense here with all three articles. Tkevin1 06:14, 24 January 2006 (UTC)

Strongly disagree: these three categories will each expand to interesting articles at differing levels of observers' sophistication. Separation will allow unsophisticated readers a gentle introduction to the concepts, brfore being sucked into arkane arguments of gaseous ethics. Gnu?

I disagree completely with merging these three articles. Sonic boom at least should remain seperate from the other two. It a specific phenomena of its own that I think deserves its own article. Millueradfa 01:04, 19 February 2006 (UTC)

merging seems like a sensible ideaAnlace 04:00, 5 March 2006 (UTC)
Merge bad!WolfKeeper 22:19, 7 August 2006 (UTC)


i think the four categories (subsonic, transonic, supersonic, and hypersonic) should remain seperate, but instead each receive a list showing the progression and linking to each page respectively. these are independant concepts in aerodynamics and have enough information in each category (though they all need expanded) to justify their own pages. Sonic Boom should be included in this list as well. this should not be merged due to the fact that it is related to transonic, supersonic, and hypersonic.

[edit] I'm inclined to favor consolidation, BUT...

I will also note that the terms "sound barrier" and "sonic boom" have an important and interesting historical context - I reference the opening lines to the movie The Right Stuff: "A demon lived in the air...it lived at Mach 1 on the meter..." I also refer to Paul Raveling's previous statement that, " It's a relic of the time [emphasis mine] when there was concern that Mach 1 might be a true barrier with an insurmountable pressure buildup that would prevent passing it..." So, while sonic boom, sound barrier, and supersonic all belong together, in terms of physical process (along with certain other terms), there should be a link to an article treating "sound barrier" and "sonic boom" and "supersonic" in their appropriate historical context - perhaps an article on the Bell X-1, since it was the craft that resolved the historical debate about the "sound barrier."--Bhruic 09:11, 28 February 2006 (UTC)

[edit] Sonic boom as a phenomenon of supersonic flight

As noted in several contributions above, the sonic boom is simply a phenomenon created as a result of supersonic flight, and so, from a purely scientific point of view, might suggest that sonic boom be merged with Supersonic. However, I think the term "Sound Barrier" should still be distinct. The term "barrier" is significant since it reflects well-estabished 19th Century theories of classical physics (at a time when the Director of the US Patent Office resigned since he felt there was nothing left to invent), which suggested the physical impossibility of an object passing through a fluid faster than the speed of sound through the fluid. Therefore, achieving velocities greater than the speed of sound became a goal for aviators, and so has significance as a milestone in aviation.

You don't need to be flying to get a sonic boom. Bullets, meteorites, whips all give sonic booms. I don't at all favour a merge. I agree that sound barrier and supersonic flight should be distinct also. These are related, but logically distinct phenomena, putting them in one article would be a bad idea.WolfKeeper 22:17, 7 August 2006 (UTC)

[edit] Introductory sentence needs clarification

The article states that "the sound barrier is the apparent physical boundary stopping large objects from becoming supersonic." Obviously it was understood that bullets were supersonic, but planes experienced all kinds of problems when they tried to do the same thing. However, if it was believed that it was a physical barrier then what was believed to be the maximum size of an object that could break it? It would seem to me that people of the time would have realized that breaking the sound barrier had more to do with shape than size. Or was it simply believed that at or past this boundary, objects could no longer produce lift and went ballistic?

Does this make sense? Essentially what I'm trying to say is the introductory sentence needs some qualification. TomTheHand 20:48, 10 May 2006 (UTC)

[edit] Separate may be best

While the "sound barrier" may be mentioned and often used interchangeably with going the speed of sound or the sonic boom, they are not the same things. They are in fact different aspects of transonic flight. For that reason I believe they should be kept separate. Both the sonic boom and the "sonic barrier" occur only at mach one, speeds above that are supersonic, or if much greater hypersonic. The "sonic barrier" is a result of two mathematical drag models that come together behaving similar to a Dirac delta functional at the point (typically drawn along the x axis) where the velocity is M=1. The two functions are results of experimental and theoretical curve fittings above and below sonic speed for compressible and incompressible flows respectively. With the development of these curves and the knowledge of problems with aircraft traveling these speeds, it became assumed that a "sonic barrier" existed. Contrary to popular belief, this situation was not compared to bullets. The reason is that bullets are pushed through this barrier, aircraft, however, must pull themselves through it. And with the increased rarefaction of the air in front of the intakes, it was in question weather an aircraft could pull itself past this point into the compressible flow area. In reality we generate an artificial "hump" which joins these two drag curves much lower than infinity, but still the drag is certainly the highest and M=1. The drag here is highest, in part due to the alignment of the sound waves transmitted forward of the aircraft. As the aircraft approaches the sonic limit the sound waves it generates in front of itself begin to merge, constructively into an extremely high magnitude sound wave. Thus the sonic boom is a result of a sonic transition, but still a different topic than Supersonic flight. If these were to be grouped the should be under transonic flight, as they are all different aspects of such.-- just my opinion --Gyrfalcon007 09:32, 11 May 2006 (UTC)User:gyrfalcon007

I agree that separate would be best. Sound barrier can deal with the historical aspect, sonic boom with the noise, and supersonic with... supersonic flight. It might be best to move the "breaking the sound barrier" section of supersonic to here and provide a link instead of providing the history there.
I was under the impression, though, that a sonic boom occurs continuously for an aircraft travelling supersonic, not just when the aircraft crosses mach one. Of course one only hears it once, as the aircraft passes, but people further down the supersonic aircraft's path will hear it as the aircraft passes them.
On the subject of bullets vs. aircraft, I believe I understand better now. Is it related to how air in a turbojet must be slowed down to subsonic? Perhaps during WWII it wasn't realized that an aircraft could travel at supersonic speeds but slow the engine intake air down to subsonic and have the engine produce thrust? What was believed would happen if an aircraft was accelerated through the barrier by rockets?
Would it be best to rephrase the first sentence to refer to self-propelled objects rather than large objects? TomTheHand 12:07, 11 May 2006 (UTC)
You are right... sonic boom is continuous. I'm not, however sure if the cause is the same (not that it matters much). During transonic flight the boom is a result of the coinciding sound waves, while in supersonic flight it is a result of attached or detached shocks forming because the air molecules behave more like individual particles and less like a fluid (perhaps a different manifestation of the combining sound waves?). The effect, as far as I know, is identical, and I know of no different name for the two, so I have to agree that the boom should be treated in supersonic as well.
As for the planes, partly yes, but I'm not sure that the were aware that they would have to shock the incoming air to slow it down. Of course today, we're trying to find ways around that. The main concern they had was that the wind tunnel data, and analytical analysis showed the drag going to infinity. Also remember though that most of the planes at the time were props, and I'm not positive, but I don't believe that even a modern day turbo prop can go sonic. There were a lot of unanswered questions, and it just rubs me when people say "planes can obviously go the speed of sound" or some other such. Back then it wasn't obvious, it's just that hindsight is 20/20. As far as rocket acceleration... the bell x-1 is a good example. The bell proved that drag could be overcome, with rockets at least. I'm not sure if you could correctly extrapolate from the use of rockets that a jet would be capable of over powering the drag just the same. Rockets are governed by momentum the same as a jet, but with a jet the output is dependant upon the air its pushing through, a rocket provides its own exhaust. The model curve of drag that was presumed to continue to infinity was a result of the Prandtl Glauert rule which has a square root of (1-M^2) in the denominator so as mach goes to 1, to quote my professor "you divide by zero, and you go to hell." On a side note, other effects came into play as they were transitioning from supersonic rockets to supersonic jets. Swept wings made a big difference, and the area rule also had a dramatic effect. (The area rule states that for supersonic drag resistance its best to have a constant cross-sectional area. So, as the wings grown in span, the fuselage must be narrowed to maintain a constant area)
As far as first sentence... I'm not sure I have a strong feeling either way. Large takes care of bullets, as they knew bullets were supersonic. Self propelled more accurately realizes the problem of a plane pulling itself through the air, but neglects the drag aspect. I suppose I find neither fully satisfying, but I dislike large objects more, just because it addresses the drag issue, but neglects to say how it was satisfied it for small objects.-gyrfalcon --70.32.196.132 09:52, 17 May 2006 (UTC)
Shells from heavy artillery were supersonic and huge. Schwerer Gustav fired shells that were 3.6m long. Not nearly as large a fighter, sure, but probably bigger than many of the wind tunnel models that were used at the time to see what happened to drag at the sound barrier. That suggests to me that it was known that it was not the size of the object that was the issue, but rather the shape and/or propulsion. That makes me very unsatisfied with the "large objects" first sentence. I'm not trying to say "planes can obviously go the speed of sound," but I do believe it must have been known that it was not a simple matter of size, and saying "large objects" seems like an oversimplification. TomTheHand 12:12, 17 May 2006 (UTC)

[edit] Supersonic train?

Does anyone have a reference for the supersonic train? Article states, "The sound barrier was first broken on land in 1948 by a rocket train in California. It was powered by 50,000 pounds of thrust, reaching 1,019 mph." Peter Harriman 18:41, 27 July 2006 (UTC)

Here is a possible reference: [1]. It doesn't state that it was a land vehicle, though the date and speed match up. Note that the vehicle would only be a train in the sense that it ran on rails; it was likely just a cart with a rocket attached that sat on rails to make sure it went straight, not a method of transport. The US Navy maintains a facility for doing that sort of thing called the Supersonic Naval Ordnance Research Track, or SNORT. TomTheHand 18:57, 27 July 2006 (UTC)

Thanks for that. I've searched for other references to it but all I can find is the same Northrop announcement that "rocket-powered test vehicles" had attained that speed. I'll change the reference to "train" in the article. Peter Harriman 16:41, 4 August 2006 (UTC)

Actually, there's a bit about it here: Edwards_afb#On_the_ground. Peter Harriman 16:55, 4 August 2006 (UTC)

[edit] Broken link

This article has a broken link to "in-flight upset". Does anyone know if this should link to a different article, or should the link be removed?

Benjam47 09:55, 28 November 2006 (UTC)

[edit] Are we forgetting something?

I see a lot of excess debatable info on this page. this is more like a history report rather than a page explaining about the speed of sound. In fact how about displaying the speed of sound in large letters at the top of the page or something as i don't see it. It might be a good idea to have pages like this written by someone qualified in the subject rather than someone who just reads other peoples books then we might end up with some hard data for a change.

Check out speed of sound to get the information you want. It's not a constant, though, being dependent on the density of the medium, so it's a set of equations, not a number.
See Wikipedia's policies on verifiability and original research for information on why our articles are not just written off the top of the head of someone who knows about the topic. TomTheHand 15:19, 26 January 2007 (UTC)

A minor clarification to the above entry: the speed of sound in air is dependent on the TEMPERATURE of the air, not the density. The classical formula is [(gamma)(G)(R)(T)]^.5, where gamma is the ratio of the specific heat of air at constant pressure to the specific heat of air at constant volume - it is 1.4 for air, and this value stays relatively constant regardless of density and temperature; G is the acceleration due to gravity (to get the units right when the common value of R is used) - it is 32.17 in British engineering units; R is the constant from the gas equation (pv = RT) - it is 53.34 for air, using British engineering units; and T is the absolute temperature (using Rankine values if the calculation is in British engineering units) - it is 530 degrees for air of 70 degrees F. Thus the speed of sound in 70 degree air is 1128 feet per second, or 769 miles per hour. By the way, Mr. Isaac Newton gave some thought to how to derive the speed of sound (back in 1672, by the way), and he came up with this formula - except that, since the science of thermodynamics didn't exist then, he didn't realize that he needed the GAMMA function. Thus the speed which he calculated was about 20% too low, and even with the primitive experimental apparatus available back then, it could be demonstrated that his calculated value was too low. So he put this project on the back burner and apparently never addressed it again. Too bad - the man was a genius in so many ways.Raymondwinn 03:26, 8 November 2007 (UTC)

[edit] Removed tags

I have removed both tags from this article. The first was a mergeto/from, but considering that the topics are not even really related (sound barrier >> sonic boom) and the length of the articles in question, I'm not sure what such a merge would look like or what topics it would cover. Certainly control reversibility and aeroelastic problems don't belong in an article on sonic boom. The second tag appears to be a drive-by refs. Although I agree the article is underrefed it does contain one. I'd be happy to add more if people would be willing to point out what claims they consider questionable. Maury 21:52, 26 February 2007 (UTC)

[edit] Question: Both Technical and Historical with Possible Application to This Article

I think it is unclear in lay minds (certainly mine) what the actual term "sound barrier" meant to technical experts of the time. From the article there is this sentence "All of these effects, although unrelated in most ways, led to the concept of a "sound barrier" that would make it difficult, perhaps impossible, for an aircraft to break the speed of sound." but still gives no actual concept of consensus upon which experts agreed if any. It would be speculation, but it must seem the consensus was aircraft controllability at or near sonic speed was the problem and (nearly) insoluble since that was what was lacking? "Sound Barrier" has become such a popular term, and the fact that experts of the time surely knew of ballistic missiles, bullets, artillery shells etc. with transonic speed, then the term still needs definition as to how it was actually considered, and how popular culture uses (or misuses it) now. 75.70.76.166 06:49, 20 July 2007 (UTC)

[edit] What / When was the first supersonic bullet or shell ?

It would be notable to identify the first gun whose shell or bullet was supersonic. Does anybody know? Charles 20:08, 22 September 2007 (UTC)

[edit] Conflict?

>The sound barrier was first broken in a vehicle in a sustained way on land in 1948 by a rocket-powered test vehicle at Muroc Air Force Base (now Edwards AFB) in California, United States. It was powered by 6000 pounds (27 kN) of thrust, reaching 1,019 mph (1,640 km/h).[5]

>On October 15, 1997, in a vehicle designed and built by a team led by Richard Noble, driver Andy Green became the first person to break the sound barrier in a land vehicle. The vehicle called the ThrustSSC ("Super Sonic Car"), captured the record almost exactly 50 years after Yeager's flight.


Is the first vehicle mentioned an unmanned test? If so, Was it seriously 50 years from the first test land vehicle before someone actually got into one? TheHYPO (talk) 20:12, 15 December 2007 (UTC)