
On Jun. 10, 2011, I attended the Thunderbirds’s rehearsal at Jesolo for the Air Extreme 2011 airshow. Pictures I’ve taken show plenty of condesation clouds being generated by the USAF demo team’s F-16s. Even spectators usually think that such clouds surrounding the aircraft represent a visual manifestation of a “sonic boom”, they are the effect of the quick depression on the flight surfaces that brings the water vapour contained in the air at the condensation temperature.
It is a common phenomenon in high-G maneuvers, when the depression on the upper side of the wing increases (as the lift does); it can be observed even at sea level, when the amount of moisture is significant and air temperature is quite hot.
Something quite different are the conic-shape clouds that are generated around aircraft flying at speeds next to the sound’s speed (they are not particularly evident in the pictures taken at Jesolo, though, but you can find many examples here). They are not visual effects of the so called “sonic booms”: more simply, when an aircraft flies at transonic speeds (around Mach 1.0), any of its convess parts (canopy, intakes, etc.) causes a rapid decrease of temperature and pressure with subsequent creation of the cloud.
The variation in temperature caused by the perturbation of the airflows is called Prandtl-Glauert Singularity. The particular shape of the cloud associated to the singularity is caused by the perturbation: at that point the airflow can reach supersonic speed and generate a shock wave (that appears when the fluid decelerates and the temperature suddenly raises).
I hope you have learned why the aircraft fly, David!
You can forget all you learned about Bernoulli and longer airflow path over wing!
All flights take place due to airspeed and Angle of Attack (AOA)!
UsAirForce Museeum in Dayton Ohio still show the false Lift Explantion with Bernoulli and “longer aiflow path over wing”!
I ask them once ,how an F-16 could fly inverted, and they anwered that then the aircraft used “more AOA” to keep flying!
They should however not change there “false” Bernoulli explanation, until Smithsonian Museeum changed their Liftexplantion!
http://www.nasm.si.edu/education/pubs/howthingsfly.pdf
But NASA Glenn Reseach knows better:
http://www.grc.nasa.gov/WWW/k-12/airplane/bernnew.html
http://www.grc.nasa.gov/WWW/k-12/airplane/lift1.html
I once sent NASA Glenn this “downwash grave ” picture:
http://www.grc.nasa.gov/WWW/k-12/airplane/downwash.html
Have you seen the wing of the new B747-8 with flat upperside?
http://www.malaysianwings.net/forum/index.php?showtopic=15600&st=40
Using Navier-Stokes calculation, AOA is simple to be shown, but in potential theory calculation you don´t se AOA.
Best Regards
Jan-Olov Newborg