Talk:Sound barrier
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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)
used in an odd way in this context
But for purposes of aerodynamic analysis 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)
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 othewise 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)
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
"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
"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
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).
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).
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.
Vandalism
This page seems to be undergoing vandalism ("poop barrier", "Air X1", etc)
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)