Technically correct, thank you. Approaching Mach speed the aerodynamic center of lift [the balance point of the flying aircraft] shifts forward. Almost all executive jets are speed limited to 0.89 Mach because of this. As ACL shifts forward the tail surfaces must respond to that change in center of lift balance point. At some speed point the aircraft will go in to what is known as a "Mach tuck" where the center of lift is so far ahead of the wing the elevator surface can not counter balance the aircraft and it goes into a 700 MPH forward tumble and as you may guess airplanes are not stressed to do that, so it breaks up in flight.
Your days work has just been canceled as a pilot when that happens.. Your next appointment is ... well.... permanent.. I believe the 3 aircraft in the video are likely approaching Mach speed in the passes because of the halo effect around the AC , not the lift surfaces. Mach speed isn't a set speed, since it changes with air density and humidity, so it's possible that actual "Mach" for those conditions could have been say 400 kts.. and the pass was done at 340 or so [not all that fast for a fighter]. I'll have to look at the video again and see if afterburners were lit, I don't think they were. Grant... On Thu, Feb 16, 2012 at 9:29 AM, Rich Thomas < richthomas79td...@constructivity.net> wrote: > Technically not "shockwaves" as the airplane is nowhere close to the speed > of sound. Compression and decompression of the air around the surfaces > will cause water vapor to condense, which shows up as the fog cloud (or > ripples as the case might be). You see that a lot in the summer on > commercial planes when landing in humid air, a lot of fog will appear on > the tops of the wings (esp when the flaps drop), and off the tips in the > vortices, and people get all upset, "the plane is on fire!" > > At Mach 1+/- shockwaves will start to appear and then you can really see > the compression in the humid air. The shockwave CANNOT go way forward of > the aircraft as it cannot travel faster than the speed of sound (which is > why shock waves appear -- the disturbance caused by the airplane can only > cause the air to compress where it is forced to become [super]sonic, which > is a local phenomenon) -- they will start on the wings (usually on top > where the air is forced to go faster over the upper surface) and nose of > the plane, and depending on various factors will have various angles off > these surfaces. Before that was fully understood I believe some WW2 > fighters (P-38?) crashed because of loss of lift/control when the airflow > over the wings went supersonic and caused all sorts of problems with lack > of lift, control surfaces, etc. > > The air in that vid is deflected down due to the circulation induced by > the wings and that is what is then pushing on the water to make the ripples > (which brings up a whole 'nuther discussion on what actually causes lift on > an airplane...). You get a little boost from flying in ground effect, and > it can also affect aircraft handling a bit. > > I believe the vid you refer to shows a big shock wave forming a big "ring" > at the front of the fighter, almost vertical since it is just barely sonic, > and others off other surfaces too, and it is very cool. I have also seen > still pics of the same thing, quite beautiful. > > --R (who remembers a little bit from all those years spent in aero/astro > school) > > On 2/16/12 10:40 AM, G Mann wrote: > >> Notice the vapor shock wave building just forward of the tail surfaces? >> That shock wave in ground effect is roughly 3 times the diameter of the >> wing span, so at that low level pass it is just kissing the water surface. >> The size of the shock wave increases with speed and air density as well as >> the intensity of the wave. As speed approaches Mach [speed of sound at sea >> level] the center of the leading edge of the shock wave will shift >> forward. >> At Mach 1 it would be several feet ahead of the aircraft. >> >> Very interesting to watch. Somewhere on Utube there is a video of a jet at >> Mach 1, on the deck over water... it's been a long time since I've seen >> it, >> but the shockwave is opening up a trough across the water surface that is >> huge, with attendant rollers coming off that. >> >> Amazing what you can do with a fighter jock ego and a $15 million jet and >> free fuel, isn't it... ;)) >> >> Grant... >> >> On Thu, Feb 16, 2012 at 6:54 AM, Mitch Haley<m...@voyager.net> wrote: >> >> Interesting surface disruptions when you fly in ground effect over water: >>> http://www.youtube.com/watch?****v=K7rAUu8djZ4<http://www.youtube.com/watch?**v=K7rAUu8djZ4> >>> <http://www.**youtube.com/watch?v=**K7rAUu8djZ4<http://www.youtube.com/watch?v=K7rAUu8djZ4> >>> > >>> >>> ______________________________****_________ >>> http://www.okiebenz.com >>> For new and used parts go to www.okiebenz.com >>> To search list archives >>> http://www.okiebenz.com/****archive/<http://www.okiebenz.com/**archive/> >>> <http://www.okiebenz.**com/archive/ <http://www.okiebenz.com/archive/>> >>> >>> To Unsubscribe or change delivery options go to: >>> http://mail.okiebenz.com/****mailman/listinfo/mercedes_****okiebenz.com<http://mail.okiebenz.com/**mailman/listinfo/mercedes_**okiebenz.com> >>> <http://mail.**okiebenz.com/mailman/listinfo/**mercedes_okiebenz.com<http://mail.okiebenz.com/mailman/listinfo/mercedes_okiebenz.com> >>> > >>> >>> ______________________________**_________ >> http://www.okiebenz.com >> For new and used parts go to www.okiebenz.com >> To search list archives >> http://www.okiebenz.com/**archive/<http://www.okiebenz.com/archive/> >> >> To Unsubscribe or change delivery options go to: >> http://mail.okiebenz.com/**mailman/listinfo/mercedes_**okiebenz.com<http://mail.okiebenz.com/mailman/listinfo/mercedes_okiebenz.com> >> >> > ______________________________**_________ > http://www.okiebenz.com > For new and used parts go to www.okiebenz.com > To search list archives > http://www.okiebenz.com/**archive/<http://www.okiebenz.com/archive/> > > To Unsubscribe or change delivery options go to: > http://mail.okiebenz.com/**mailman/listinfo/mercedes_**okiebenz.com<http://mail.okiebenz.com/mailman/listinfo/mercedes_okiebenz.com> > _______________________________________ http://www.okiebenz.com For new and used parts go to www.okiebenz.com To search list archives http://www.okiebenz.com/archive/ To Unsubscribe or change delivery options go to: http://mail.okiebenz.com/mailman/listinfo/mercedes_okiebenz.com
